Corrosion Resistance of Nickel-Containing Alloys in Organic

Corrosion Resistance of Table of Contents PART I. INTRODUCTION Nickel-Containing Alloys A. The Organic Acids 4 B. Scope 4 C. Corrosion Testing in Organic Acid Media 4 in Organic Acids PART II. ACETIC ACID A. General 5 B. Austenitic Stainless Steels 5 and Related Compounds 1. General 5 2. Effect of Alloy Composition 6 3. Effect of Contaminants 10 4. Effect of Temperature 12 5. Effect of Microstructure 14 6. Quality Control 15 C. Martensitic & Ferritic Stainless Steels 15 D. Duplex Austenitic-Ferritic and Precipitation Hardening Stainless Steels 15 E. Iron-Base Nickel-Chromium-Copper Molybdenum Alloys 16 F. Nickel-Base Chromium-Iron-Molybdenum- Copper Alloys 17 G. Iron-Base Nickel-Chromium-Molybdenum Alloys18 H. Nickel-Base Molybdenum-Chromium-Iron Alloys 18 I. Nickel-Copper Alloys 20 J. Copper-Nickel Alloys 21 K. Nickel-Chromium Alloys 23 L. Iron-Nickel-Chromium Alloys 23 M. Nickel-Base Molybdenum Alloys 24 N. Nickel 24 O. Process and Plant Corrosion Data 25 l. Acetic Acid Production 25 a. Oxidation of Acetaldehyde 25 b. Liquid Phase Oxidation of Straight-Chain Hydrocarbons 26 c. Methanol-Carbon Monoxide Synthesis 28 2. Acetic Acid Storage and Shipping 28 3. Vinegar Production and Storage 29 P. Acetic Anhydride 29 PART III. OTHER ORGANIC ACIDS A. Formic Acid 31 B. Acrylic Acid 36

C. C3 Through C8 Acids 38 (Propionic, Butyric and Higher Acids) D. Fatty Acids 44 (Lauric, Oleic, Linoleic, Stearic, Tall Oil Acids) E. Di and Tricarboxylic Acids 46 (Oxalic, Maleic, Phthalic, Terephthalic, Adipic, Glutaric and Pimelic Acids) F. Naphthenic Acids 52 G. Organic Acids with Other Functional Groups 53 1. Glycolic Acid 53 2. Lactic Acid 53 3. Tartaric Acid 54 4. Citric Acid 54 5. Chloroacetic Acids 56 6. Amino Acids 57 7. Sulfoacetic Acid 57 PART IV ESTER PREPARATIONS A. Acetic Esters 58 B. Phthalate Esters 60 C. Esterification of Fatty Acids 60 D. Acrylate Esters 60

References 64 Trademarks Inside Back Cover

Page 1 Nominal Composition of Nickel-Containing Alloys in Use or Corrosion Tested in Organic Acids and Related Compounds

Composition, % Alloys Ni Fe Cr Mo Cu C Si Mn Other

WROUGHT ALLOYS Stainless Steels—Austenitic AISI Type 201 4.5 Balance 17.0 – – 0.15 Max 1.0 Max 6.5 N 0.25 Max AISI Type 202 5.0 Balance 18.0 – – 0.15 Max 1.0 Max 8.0 N 0.25 Max AISI Type 204 5.0 Balance 18.0 – – 0.08 Max 1.0 Max 8.0 N 0.25 Max AISI Type 204L 6.0 Balance 18.0 – 0.03 Max 1.0 Max 8.0 N 0.25 Max AISI Type 216 6.0 Balance 19.5 – – 0.08 Max 1.0 Max 8.0 N 0.25-0.50 AISI Type 216L 6.0 Balance 19.5 – – 0.03 Max 1.0 Max 8.0 N 0.25-0.50 AISI Type 304 9.5 Balance 18.5 – – 0.08 Max 1.0 Max 1.5 AISI Type 304L 10.0 Balance 18.5 – – 0.03 Max 1.0 Max 1.3 AISI Type 309 13.5 Balance 23.0 – – 0.20 Max 1.0 Max 2.0 Max AISI Type 310 20.0 Balance 25.0 – – 0.25 Max 1.0 Max 2.0 Max AISI Type 316 13.0 Balance 17.0 2.25 – 0.08 Max 1.0 Max 1.7 AISI Type 316L 13.0 Balance 17.0 2.25 – 0.03 Max 1.0 Max 1.8 AISI Type 317 14.0 Balance 19.0 3.25 – 0.08 Max 1.0 Max 2.0 Max AISI Type 317L 14.0 Balance 19.0 3.25 – 0.03 Max 1.0 Max 2.0 Max AISI Type 318 14.0 Balance 18.0 3.25 – 0.08 Max 1.0 Max 2.5 Max Cb + Ta 10XC Min AISI Type 321 11.0 Balance 18.0 – – 0.08 Max 1.0 Max 2.0 Max Ti 5XC Min AISI Type 330 35.0 Balance 15.0 – – 0.25 Max 1.0 Max 2.0 Max AISI Type 347 11.0 Balance 18.0 – – 0.08 Max 1.0 Max 2.0 Max Cb + Ta 10XC Min NITRONIC alloy 50 12.5 Balance 22.0 1.5–3.0 – 0.06 Max 1.0 Max 5.0 N 0.2-0.4, Cb 0.1-0.3 Stainless Steels—Duplex and

Precipitation Hardening AISI Type 326 6.5 Balance 26.0 – – 0.06 Max 0.40 0.40 AISI Type 329 4.5 Balance 27.5 1.0–2.0 – 0.10 Max 1.0 Max 2.0 Max CRUCIBLE alloy 223 - Balance 16.0 0.4 1.0 0.03 Max 1.0 Max 12.0 N 0.3 17-4PH 4.0 Balance 16.5 – 4.0 0.07 Max 1.0 Max 1.0 Max Cb + Ta 0.3 17-7PH 7.0 Balance 17.0 – – 0.09 Max 1.0 Max 1.0 Max Al 1.1 PH15-7Mo 7.0 Balance 15.0 2.5 – 0.09 Max 1.0 Max 1.0 Max Al 1.1 Iron-Base Nickel-Chromium Copper-Molybdenum Alloys CARPENTER alloy 20(1) 29.0 43.0 20.0 2.0 Min 3.0 Min 0.07 Max 1.0 0.8 CARPENTER alloy 20Cb-3 34.0 39.0 20.0 2.5 3.3 0.07 Max 0.6 0.8 Cb + Ta 0.6 Nickel-Base Chromium-Iron Molybdenum-Copper Alloys INCOLOY alloy 825 41.8 30.0 21.5 3.0 1.8 0.03 0.35 0.65 AI 0.15, Ti 0.9 HASTELLOY alloy G 45.0 19.5 22.2 6.5 2.0 0.03 0.35 1.3 W 0.5. Cb + Ta 2.12 Iron-Base Nickel-Chromium Molybdenum Alloys ALLEGHENY alloy AL-6X 24.0 46.0 20.0 6.5 – 0.025 Max 0.5 Max 1.5 Max HAYNES alloy 20 Mod 26.0 42.0 22.0 5.0 – 0.05 Max 1.0 Max 2.5 Max Ti 4XC Min JESSOP alloy JS-700 25.0 46.0 21.0 4.5 – 0.03 0.5 1.7 Cb 0.30 MULTIMET alloy 20.0 29.0 21.0 3.0 – 0.12 1.0 Max 1.5 Co 20.0, W 2.5, N 0.15,Cb + Ta1.0 Nickel-Base Molybdenum Chromium-Iron Alloys HASTELLOY alloy C(2) 54.0 5.0 15.5 16.0 – 0.08 Max 1.0 Max 1.0 Max Co2.5Max,W4.0, V 0.4 Ma) HASTELLOY alloy C-276 54.0 5.0 15.5 16.0 – 0.02 Max 0.05 Max 1.0 Max Co2.5Max,W4.0, V 0.4 Ma) HASTELLOY alloy C-4 61 ..0 3.0 Max 16.0 15.5 – 0.015 Max 0.08 Max 1.0 Max Co 2.0 Max, Ti 0.7 Max HASTELLOY alloy N 69.0 5.0 7.0 16.5 – 0.06 0.3 0.3 AI 0.5 INCONEL alloy 625 60.0 5.0 Max 21.5 9.0 – 0.1 Max 0.5 Max 0.5 Max Cb + Ta 3.65 Nickel-Copper Alloys MONEL alloy 4OO 66.0 1.35 – – 31.5 0.12 0.15 0.9 MONEL alloy K-500 65.0 1.0 – – 29.5 0.15 0.15 0.6 AI 2.8, Ti 0.5 Copper-Nickel Alloys Copper-Nickel alloy C70600 10.0 1.25 – – 88.0 – – 0.3 Pb 0.05 Max, Zn 1.0 Max Copper-Nickel alloy C71000 20.0 0.75 – – 78.0 – – 0.4 Pb 0.05 Max, Zn 1.0 Max Copper-Nickel alloy C71500 30.0 0.55 – – 67.0 – – 0.5 Pb 0.05 Max, Zn 1.0 Max Nickel-Chromium Alloys INCONEL alloy 600 76.0 7.2 15.8 – 0.1 0.04 0.2 0.2 NICHROME V 80.0 – 20.0 – – – – –

Page 2 Nominal Composition of Nickel-Containing Alloys in Use or Corrosion Tested in Organic Acids and Related Compounds

Composition, % Alloys Ni Fe Cr Mo Cu C Si Mn Other WROUGHT ALLOYS Iron-Nickel-Chromium Alloys INCOLOV alloy 800 32.0 46.0 20.5 – 0.3 0.04 0.35 0.75 INCOLOY alloy 804 41.0 25.4 29.5 – 0.25 0.05 0,38 0,75 AI 0.3, Ti 0.6 Nickel-Base Molybdenum Alloys HASTELLOY alloy B* 61.0 5.0 1.0 Max 28.0 – 0.05 Max 1.0 Max 1.0 Max Co 2.5 Max, V 0.3, P 0.025 Max, S 0.03 Max HASTELLOY alloy B-2 67.0 2.0 Max 1.0 Max 28.0 – 0.02 Max 0.1 Max 1.0 Max Co 1.0 Max, P 0.04 Max, S 0.03 Max Other Nickel and Cobalt-Base

Alloys IN-102 68.0 7.0 15.0 3.0 – 0.06 – – Ti 0.5, Cb 2.9. A1 0.5, W 3.0 MP-35N 35.0 – 20,0 10.0 – – – – Co 35.0 ELGILOY 15.0 15.0 20A 7.0 – 0.15 – 2.0 Co 40.0, Be 0.05 HAYNES alloy No. 25 10.0 3.0 Max 20.0 – – 0.10 1.0 Max 1.5 Co. 49.0, W 15.0 CAST ALLOYS Stainless Steels ACI CD-4MCu 5.5 61.0 26.0 2.0 3.0 0.04 Max 1.0 Max 1.0 Max ACI CF-3 10.0 66.0 19.0 – – 0.03 Max 2.0 Max 1.5 Max ACI CF-3M 11.0 63.0 19.0 2.5 – 0.03 Max 1.5 Max 1.5 Max ACI CF-8 9.0 67.0 19.0 – – 0.08 Max 2.0 Max 1.5 Max ACI CF-8M 10.0 64.0 19.0 2.5 – 0.08 Max 2.0 Max 1.5 Max ACI CG-8M 11.0 62.0 19.0 3.5 – 0.08 Max 1.5 Max 1.5 Max ACI HK 20.0 49.0 26.0 – – 0.4 2.0 Max 2.0 Max Iron-Base Nickel-Chromium-

Copper-Molybdenum Alloys ACI CN-7M3) 29.0 44.0 20.0 2.0 Min 3.0 Min 0.07 Max 1.0 1.5 Max WORTHITE 24.0 48.0 20.0 3.0 1.75 0.07 Max3.3 0.6 Iron-Base Chromium-Nickel-

Copper-Molybdenum Alloy ILLIUM alloy P 8.0 58.0 28.0 2.0 3.0 0.20 0.75 0.75 Iron-Base Nickel-Chromium-

Molybdenum Alloys IN-862 24.0 44.0 21.0 5.0 – 0.07 Max0.8 0.5 KROMARC 55 20.0 50.0 16.0 2.0 – 0.04 2.0 Max9.5 Iron-Base Chromium-Nickel-

Iron Alloy ILLIUM alloy PD 5.0 57.0 26.0 2.0 0.5 Max 0.08 1.0 Max 1.0 Max Co 7.0 Nickel-Base Chromium-

Molybdenum-Copper-Iron Alloy ILLIUM alloy G 58.0 5.0 22.0 6.0 6.0 0.2 0.2 1.25 Max Nickel-Base Molybdenum-

Chromium-Iron Alloys ACI CW-12M-1(4) 58.0 6.0 16.5 17.0 – 0.12 Max 1.0 Max 1.0 Max ACI CW-12M-2(5) 57.0 3.0 Max 18.5 18.5 – 0.07 Max 1.0 Max 1.0 Max Nickel-Base Molybdenum Alloys ACI N-12M-1(6) 60.0 5.0 1.0 Max28.0 – 0.12 Max 1.0 Max 1.0 Max V 0.2–0.6, Co 2.5 Max ACI N-12M-2(7) 62.0 3.0 Max 1.0 Max 31.5 – 0.07 Max 1.0 Max 1.0 Max Other Nickel and Cobalt-Base

Alloys WAUKESHA alloy 23 80.0 – – – – – – – Sn 8.0, Zn 7.5, Pb 4.0 WAUKESHA alloy 54 75.0 0.4 – – – – – 2.5 Sn 8.0, Zn 7.0, Ag 6.0 WAUKESHA alloy 88 70.0 5.0 12.5 3.0 – 0.05 Max – – Sn 4.0, Bi 3.75 ILLIUM alloy 98 55.0 1.0 28.0 8.0 5.0 0.05 0.7 Max1.25 Max ILLIUM alloy B 49.0 3.0 28.0 8.0 5.0 0.05 4.5 1.25 Max B 0.05-0.55 STELLITE alloy No. 3(8) 3.0 Max 3.0 Max 31.0 – – 2.35 1.0 Max 1.0 Max W 12.5, Others 1.0 Max, Bal Co STELLITE alloy No. 4(8) 3.0 Max 3.0 Max 30.0 1.5 Max – 1.0 Max 1.5 Max 1.0 Max W 14.0, Bal Co STELLITE alloy No. 6 3.0 Max 3.0 Max 29.0 1.5 Max – 1.1 1.5 Max 1.0 Max W 4.5, Bal Co Nickel Alloyed Cast Irons Ni-Resist Type 2 20.0 70.0 2.2 – 0.5 Max 3.0 Max 1.9 1.2 Ni-Resist Type 4 30.5 55.0 5.0 – 0.5 Max 2.6 Max 5.5 0.6

(1) An improved version of this alloy, CARPENTER alloy 20 Cb-3, has replaced (5) Includes alloys such as CHLORIMET alloy 3, ILLIUM alloy W2, etc. CARPENTER alloy 20. (6) Includes alloys such as cast HASTELLOY alloy B, ILLIUM alloy M1,etc. (2) Improved versions of this alloy, HASTELLOY alloys C-276 or C-4, have (7) Includes alloys such as CHLORIMET alloy 2, ILLIUM alloy M2, etc. replaced HASTELLO alloy C. (8) STELLITE alloys 3 and 4 are cast wear resistant alloys that are no longer (3) Cast “type20” alloys such as DURIMET alloy 20, ALOYCO alloy 20, etc. produced by Cabot Corporation. (4) Includes alloys such as cast HASTELLOY alloy C, ALOYCO alloy N-3, ILLIUM alloy W1, etc. * An improved version of this alloy, HASTELLOY alloy B-2 has replaced HASTELLOY B.

Page 3 PART I. INTRODUCTION B. Scope This bulletin attempts to characterize the corrosion resistance of alloys in the wide range of exposure conditions employed today in the production and handling of the A. The Organic Acids organic acids. Space does not allow the complete coverage of alloy use in all organic acid processes, or even full The organic acids constitute a group of the most important treatment of such a large subject as acetic acid production. reactive chemicals of industry today. Billions of pounds of However, once the basic properties of the alloys in such acetic acid are produced in the United States every year to media are established, along with adequate warning of provide the precursor for numerous products from aspirin to problems to be avoided, the judicious choice of an alloy for the recovery of zaratite minerals. Acetic acid is best known a similar application can usually be made. The major pitfall as the astringent compound in vinegar, but the acid and its in such use of data is assurance that the recorded conditions anhydride are used in the manufacture of cellulosic fibers, of exposure are indeed the same as those existing in the commercial plastics, agricultural chemicals, dyes, plas- proposed application. Only parts per million of certain ticizers, certain explosives, ester solvents, metal salts; contaminants in an organic acid process stream can have a pharmaceuticals such as aspirin, sulfa drugs, vitamins, and profound effect on the corrosion rate of an alloy. Thus, it is as a precursor for a host of other organic compounds used in critical to learn the details of proposed operating conditions, the preparation of drugs. as well as the possibilities for inadvertent changes in stream Other organic acids are produced in much smaller composition. volume, but constitute important chemicals for the prepara- Corrosion data reported throughout this bulletin must be tion of compounds used daily in our lives. The reactive acid interpreted as providing valuable information regarding the (carboxyl) group present in these organic molecules is relative corrosion resistance of the various alloys in specific responsible for their wide use as ready building blocks for environments and modes of testing. Retesting of the alloys, many commercial compounds. particularly those containing chromium, under the same Research efforts to provide these chemicals in greater apparent conditions may provide variations in corrosion quantity at less cost has paralleled their increasing impor- rates of two to three times. However. the relative resistance tance. A multitude of processes have been commercialized of the various alloys normally remains the same. for the production of acetic, acrylic, adipic, lactic and the Corrosion data for alloys in all of the many organic acids higher acids. The volume and use of corrosive by-product are reported when they are available. Extensive data for the formic acid has continually increased. In all of these more common acids encountered are reported. In addition, processes, nickel-containing alloys are standard materials of data for representative homologues of the various types of construction to withstand the corrosive environment and organic acids are reported. With this information as a guide, maintain product purity. the interested party should be able to select candidate materials for an organic acid exposure of any type. The nominal composition of alloys cited in the tables and text are shown in the table on pages 2 and 3. An attempt has been made to provide as comprehensive a listing of alloys as possible to achieve the maximum utility from these data. Some of the proprietary alloys have been improved by compositional modifications. Where data exist for the newer modification they are included; however, some data on the obsolete alloys are included. Corrosion rates on the newer, improved alloys may be assumed to be approximately equivalent. Trademarks of proprietary alloys have been used in the text and are listed on the inside back cover. All materials are assumed to be in the mill annealed condition unless notations to the contrary are shown.

C. Corrosion Testing in Organic Acid Media Some of the techniques used for determining corrosion rates and changes in environment in aqueous systems are difficult to apply in organic acid media. The specific conduc- tance of the higher acid concentrations is low for electrochemical studies and the low dissociation constant of the Type 316L stainless steel tanks and piping and cast ACI CF-8M pumps and valves are utilized in this plant handling organic acids. Courtesy common organic acids requires major dilution of the com- Walworth Company-Aloyco Valves. pounds before reliable electrochemical data can be obtained.

Page 4 Attempts to make potentiometric measurements are most in the second period little if any air will be present in boiling successful in the dilute solutions; ten per cent acetic acid is solutions and a loss of oxygen will occur in solutions held at often used as an investigative medium. Also, the addition of the lower temperatures. Thus, short test periods can provide sodium salts or chloride salts is reported to allow measure- results totally different from those obtained by longer ment of potential changes with current variations.1 How- exposure times. Unless specifically stated to the contrary in ever, many electrochemical investigators have reported data the tests reported, it must be assumed that air was present, at obtained in strong acetic acid, acetic acid-anhydride and least initially, in a laboratory test and was probably absent in formic acid solutions. These tests showed an active-passive a field test. behavior for most alloys, which is consistent with field In addition, corrosion products form in the test medium experience. and can exert a controlling influence on the corrosion rates The influence of even tenths of a per cent of water in an in long-term laboratory tests. Aggressive, highly-ionic organic acid can have considerable influence on corrosion. media, such as the mineral acids, may attack a metal surface Anomalous results obtained in “glacial” acetic acid are almost immediately on contact, and even on those metals often attributable to small differences in water content in the and alloys having protective oxide films the passive period two different media. In any event, proper testing of alloys in may be very short. However, when evaluating materials in anhydrous organic acid environments is restricted to grav- acids such as acetic, a considerable variation in rate of imetric techniques, mechanical measurements or by the use corrosion can be obtained depending on the length of the of changes in electrical resistance of metal cross sections as test period and the incubation period required to initiate corrosion occurs. corrosion. With these and other factors operative, it is not Data are often obtained by immersion testing in the surprising that considerable discrepancy in corrosion data laboratory. Such tests must be assumed to be without exists for the exposure of alloys in organic acids. control of the atmosphere unless aeration, nitrogen sparg- All percentages expressed in the data are in weight per ing, or other gaseous injections are identified. Without cent unless another basis is specifically stated. Corrosion control of the atmosphere, a test environment above rates are reported in millimeters per year (mm/y) followed ambient temperature will have two periods of differing by the corrosion rate in mils per year (mpy) (one mil = exposures. Initially the solution will be air-saturated, while 0.001 inch.)

PART II. ACETIC ACID

A. General B. Austenitic Stainless Steels Acetic acid and its derivatives are produced in large quan- 1. General tities as commercial products. Perhaps of even greater The wrought and cast austenitic stainless steels serve as the interest from a corrosion standpoint is the fact that in workhorse of industries handling acetic acid. The addition industries processing many other organic chemicals, acetic of sufficient nickel to iron-base alloys containing chromium acid is a common impurity in process streams as a result of is necessary to provide the optimum alloy for ease of the oxidation of lower compounds or the degradation of fabrication and adequate resistance to attack by the acid. larger molecules. Consequently, a knowledge of the corro- In a typical acetic acid production facility, such as exempli- sive potential of the acid is necessary to assure the fied by the direct oxidation of hydrocarbons to the acid, the economic life of equipment or to prevent contamination of reactors, distillation columns, heat exchangers, separators, process streams with metallic corrosion products. decanters and much of the tankage are constructed of Although acetic acid has a low ionization constant compared with many other acids, the effective acidity of TABLE I aqueous streams contaminated with the acid increases Concentration of Acetic Acid Versus rapidly with concentration. Table I shows change of pH pH in Aqueous Solution with concentration of acetic acid. A wide range of alloys can be used in acetic acid Concentration pH exposures. Those alloys renowned for resistance to oxidiz- g/I ing conditions are often a first choice for a specific exposure 0.0006 5.2 while in a remarkably similar application the wisest choice 0.006 4.4 will be alloys used to combat reducing conditions. In some 0.06 3.9 process areas, both can be equally resistant and an economic 0.6 3.4 comparison is necessary before making a choice. However, 6.0 2.7 60.0 (6%) 2.4 a thorough appraisal of each exposure must be made to identify the optimum material of construction. Reference 43

Page 5 In the vast majority of exposures, there is no difference in corrosion resistance between the wrought and cast alloys of similar analysis provided that both are in proper metallurgical condition (annealed). The presence of small amounts of delta ferrite (2-10%) normally found in the austenitic matrix of the cast alloys does not lessen the corrosion resistance of the metal as illustrated by Table II. Even greater amounts of ferrite will show no deleterious effects in most pure acid media. Flowers, et al.2 investigated ferrite contents in the CF-8 and CF-BM alloys up to 38 per cent and claim anodic polarization of the ferrite in such a dual phase alloy reduces overall attack on the metal. However, such passivity is not to be expected under all conditions of organic acid exposure and thorough testing of specific alloy compositions is advised. Cast ACI CF-8M valves and pumps in finished acetic acid storage Other comparative data for the cast alloys may be found service. Piping and tanks are constructed of Type 316L stainless steel. in Table XXVII and Figure 1. Courtesy Walworth Company-Aloyco Valves. 2. Effect of Alloy Composition The addition of proper chromium-nickel ratios in a ferrous base to provide an austenitic stainless steel affords a limited resistance to organic acid exposures. Lower concentrations wrought Type 316 stainless steel, or Type 316L stainless of pure acetic acid may be handled to the boiling point or steel if weld fabrication is to be employed. Forgings of the higher concentrations may be used to some 90 ºC (194 ºF) these alloys are found as valve parts, perhaps as heat with Fe-Cr-Ni alloys such as Type 304 stainless steel. exchanger tube sheets, and for certain other structural parts. Adding greater amounts of chromium and nickel (Types The pumps and many valves are constructed of the cast 309 and 310 stainless steels) does not change the corrosion counterpart of the Type 316L stainless steel analysis known resistance of the alloys basically (see Table III). Using as ACI CF-3M. The ACI CF-8M (0.08 max carbon) is graphical multiple correlation techniques, Dillon has shown equally acceptable if in the solution annealed condition but that chromium and nickel variations of the commercial has the disadvantage that weld repairs have to be followed alloys have little effect on the resistance to acetic acid.3 by solution annealing to restore corrosion resistance. At this time, there is no reason to believe that obtaining an austenitic matrix by the use of combinations of nickel, manganese and nitrogen imparts any change in the organic acid resistance of the alloy.4 That is, a Type 204 stainless steel is equivalent to a Type 304 stainless steel and Type 216 is as resistant to acid attack as Type 316. See data in Tables III through V for the corrosion of the high manganese and nitrogen-containing stainless steels.

FIG 2– Effect of Molybdenum Content on Corrosion of Austenitic Stainless Steels in Condensate from Boiling Acetic Acid FIG 1– Corrosion of Cast Stainless Steels in Glacial Acetic Acid Solutions

Page 6 TABLE II Comparison of Cast Stainless Steels with Wrought Type 316 Stainless Steel in Organic Acid Media Test Conditions: All tests at boiling temperature for approximately 150 hours in laboratory. Each result shown represents duplicate specimens.

Corrosion Rate

ACI CF-8M Wrought Type 316 Annealed Sensitized Stainless ACI Type 329 Steel ALLOYCO Stainless 5%* 10%* 5%* 10%* Temperature Annealed CD-4MCu WORTHITE** 20*** Steel Solution ºC ºF mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy Glacial Acetic Acid 117 242 .05 2 .05 2 .03 1 .03 1 .05 2 Nil Nil 03 1 <.03 <1 <.03 <1 50% Acetic Acid 102 216 .03 1 .03 1 .03 1 03 1 Nil Nil Nil Nil Nil Nil .03 1 <.03 <1 10% Acetic Acid 100.5 213 <.03 <1 <.03 <1 .03 1 01 0.5 Nil Nil Nil Nil Nil Nil <.03 <1 – – 85% Acetic-15% Formic 109 228 .15 6 .18 7 .13 5 .15 6 .08 3 <.03 <1 <.03 <1 <.03 <1 – – 50% Acetic-15% Formic 106.5 224 .30 1 2 33 13 .18 7 .20 8 .25 10 08 3 <.03 <1 <.03 <1 .64 25 85% Formic-15% Acetic 104.5 220 .84 33 .89 35 .23 9 .25 10 .13 5 15 6 03 1 .03 1 1.35 53 88% Formic Acid 104.5 220 48 19 43 17 .28 11 .28 11 .33 13 18 7 05 2 .03 1 1.65 65 50% Formic Acid 102 216 .64 25 76 30 .61 24 .66 26 .51 20 .15 6 .15 6 .10 4 8.38 330 10% Formic Acid 100 212 .38 1 5 36 14 .46 18 .46 18 .43 17 <.03 <1 08 3 .10 4 – – *% Ferrite in alloy **Trademark of Worthington Corp. ***Trademark of Aloyco, Inc.

TABLE III Field Tests in Acetic Acid Distillation Columns

Location in Column Top Top Mid Bottom Bottom Test Duration (Days) 11 40 375 62 30 Temperature ºC (ºF) 120 (248) 106 (223) 100 (212) 121 (250) 119 (246)

Per Cent Acetic Acid 99.5+ 99.9+ 20 99.9+ 90 Corrosion Rate Alloy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy Type 316 stainless steel <.03 <1 < .03 <1 .05 2 < .03 <1 .15 6 Type 304 stainless steel .30 12 .05 2 Type 309 stainless steel .89 35 Type 329 stainless steel .03 1 Type 216 stainless steel <.03 <1 Type 410 stainless steel >12.7 >500 Type 430 stainless steel >12.7 >500 CARPENTER1 alloy 20Cb-3 <.03 <1 <.03 <1 JESSOP2 alloy JS-700 <.03 <1 INCOLOY3 alloy 825 <.03 <1 .13 5 <.03 <1 .05 2 HASTELLOY4 alloy C* <.03 <1 .03 1 <.03 <1 CHLORIMET5 alloy 2 .05 2 HASTELLOY alloy B .13 5 INCONEL3 alloy 600 .15 6 .25 10 MONEL3 alloy 400 .08 3 28 11 C 10300 (Copper) .15 6 Nickel 200 .08 3 .08 3 41 16

(1) Trademark of Carpenter Technology Corporation (2) Trademark of Jessop Steel Company (3) Trademark of the Inco family of companies (4) Trademark of Cabot Corporation (5) Trademark of The Duriron Company, Inc.

*An improved version of this alloy, HASTELLOY alloy C-276, has replaced HASTELLOY alloy C.

Page 7 TABLE IV Comparison of Nickel and Manganese Austenitic Steels in Organic Acid Exposures Conditions: Duplicate specimens tested in the boiling solution (temperatures shown) for 48 hours or longer. Air not excluded or added.

Corrosion Rate Type 304 CRUCIBLE* Type 316 Temperature Stainless Steel alloy 223 Stainless Steel

Test Medium ºC ºF mm/y mpy mm/y mpy mm/y mpy Acetic acid, 100% 117 242 .46 .18 .18 7 .01 0.4 Acetic acid, 75% 104 219 4.06 160 .05 2 .01 0.3 Acetic acid, 50% 102 216 6.98 275 Nil <0.1 .08 3 Acetic acid, 25% 100 212 7.11 280 <.008 0.3 Nil Nil Acetic acid 99%; Acetic anhydride 1% 117 242 .33 13 2.26 89 .22 8.5 Acetic acid 90%; Formic acid 10% 109 228 .23 9 .08 3.1 .17 6.5 Formic acid, 20% 102 216 1.75 69 4.75 187 .56 22 2-Ethyl butyric acid, 100% 185 365 .53 21 .04 1.5 .04 1.4 Esterification mixture1 86 187 .41 16 2.79 110 .02 0.7

(1) Synthetic mixture of 75% butyl acetate, 11% butanol,10% acetic acid, 4% water, 0.3% sulfuric acid.

*Trademark of Colt Industries, Inc.

When molybdenum is added to produce such alloys as TABLE V Types 316 and 317 stainless steels, and other alloys, a Corrosion of Alloys in Acetic-Hydroxy Acid Solution remarkable increase in resistance to hot organic acids occurs. The startling efficacy of molybdenum is best shown Conditions: Exposure of approximately 50 days in stripping of acetic acid at temperatures shown by curves from Uhlig (Figure 2). Note that in the two ex- from a 70% acetic acid containing ca. 8% posures defined for these curves, the effect of molybdenum β -hydroxy acids, 20% manganese salts and is fully realized at approximately 2.2 per cent. In the vast residues. Nitrogen blanket on system. majority of organic acid environments, this approximate amount of molybdenum provides satisfactory corrosion Corrosion Rate resistance. For this reason, Types 316 and 316L stainless steels are utilized for the overwhelming majority of hot 124 ºC (255 ºF) 140 ºC (284 ºF) organic acid applications. Alloy mm/y mpy mm/y mpy Relative values of corrosion resistance for three common Type 304 Stainless Steel .01 0.4 1.12 44 alloys in hot process acid are shown in Table IV to Type 316 Stainless Steel supplement the data for the Type 316 stainless steel shown (annealed) Nil <0.1 .09 3.7 in Table II. Data generated by all major acetic acid Type 316 Stainless Steel producers confirm that for a pure, uncontaminated acetic (sensitized) .01 0.3 .11 4.2 acid of any concentration, Type 316 stainless steel or its low Type 216 Stainless Steel Nil <0.1 .05 2.0 Type 317 Stainless Steel Nil <0.1 .08 3.2 carbon counterpart Type 316L is usable as a material of Type 326 Stainless construction to temperatures beyond the boiling point. (See Steel (IN-744) Nil <0.1 2.84 112 Effect of Temperature.) These alloys are used extensively in CARPENTER alloy 20Cb-3 .00 0.1 .05 1.8 the fabrication of distillation columns, heat exchangers, INCOLOY alloy 825 .01 0.2 .03 1.2 decanters, piping and other apparatus employed in the JESSOP alloy JS-700 Nil <0.1 .01 0.3 production or processing of acetic acid. HASTELLOY alloy G Nil <0.1 .01 0.4 Under certain conditions of exposure, it has been found that additional amounts of molybdenum in the alloy are beneficial. Types 317 and 317L stainless steels are available for such applications when required. Tables V through VIII show process corrosion data where the superiority of the The effect of further alloying on the corrosion resistance Type 317 stainless steel can be observed. of commercial alloys is indicated in succeeding sections.

Page 8 TABLE VI Effect of Thermal Treatments on Molybdenum-Containing Stainless Steels

Corrosive medium: Acetic acid 35%, formic acid 1.0%, water 64%. Conditions : Process liquid at 131 ºC (268 ºF) (boiling) for 84 days, air free.

Corrosion Rate Alloy Condition of Specimen mm/y mpy

Type 316L Stainless Steel Annealed .06 2.5 1 hr 677 ºC (1250 ºF) AC .06 2.5 4 hr 871 ºC (1600 ºF) AC, 1 hr 677 ºC (1250 ºF) AC .04* 1.4* As-welded (316L rod) .08 3.2 Welded, 1 hr 704 ºC (1300 ºF) AC .08 3.0 Welded, 1 hr 871 ºC (1600 ºF) AC .07 2.6 As-welded (310 Mo rod) .06 2.3 Welded (310 rod) 1 hr 871 ºC (1600 ºF) AC .06 2.4 Type 316 Stainless Steel Annealed .39 15.5 2 hr 621 ºC (1150 ºF) AC .39 15.3 1 hr 677 ºC (1250 ºF) AC .65 25.5 As-welded (316 rod) .40 15.9

Welded, 1 hr 871 ºC (1600 ºF) AC .71 27.7 Type 317 Stainless Steel Annealed .05 2.0 4 hr 593 ºC (1100 ºF) AC .16* 6.3* 1 hr 677 ºC (1250 ºF) AC .68* 26.9* As-welded (317 rod) .04 1.73 Welded, 1 hr 704 ºC (1300 ºF) AC .55* 21.5* Type 318 Stainless Steel Annealed .07 2.6 1 hr 677 ºC (1250 ºF) AC .07 2.6 1 hr 1316 ºC (2400 ºF) AC + 1 hr 677 ºC (1250 ºF) AC .64* 25.1* As-welded (318 rod) .06 2.4 Welded + 1 hr 704 ºC (1300 ºF) AC .07 2.6 Welded + 1 hr 871 ºC (1600 ºF) AC .30 12.0

* Intergranular attack noted Reference 11 NOTE: AC = Air-Cooled

TABLE VII Corrosion of Alloys in Acetic-Formic Acid Process Mixtures

Corrosion Rate

Type 316 Type 317 Stream Test Stainless Stainless CARPENTER INCOLOY HASTELLOY HASTELLOY INCONEL Nickel MONEL Arsenical EVERDUR* Composition Temperature Period Steel Steel alloy 20 alloy 825 alloy C alloy B alloy 600 200 alloy 400 Admiralty 1010

C F days mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy 17% Acetic Acid 1 % Formic Acid 100 212 452 03 1 .03 1 – – – – – – 05 2 .61 24 .25 10 – – 08 3 .05 2 82% Water 18% Acetic Acid 40% Formic Acid 91 196 55 .08 3 .05 2 .05 2 .03 1 <.03 <1 – – – – – – – – .10 4 – – 2% Water 40% Organics 6% Acetic Acid 10% Formic Acid 81 178 55 15 6 .13 5 .08 3 .08 3 <.03 <1 – – – – – – – – .10 4 – – 3% Water 81% Organics 12% Acetic Acid 3% Formic Acid 121 250 355 05 2 – – – – – – – – <.03 <1 – – – – .05 2 .08 3 .03 1 85% Water

40% Acetic Acid 6% Formic Acid 106 223 99 .51 20 .28 11 38 15 – – .18 7 – – – – – – .51 20 .03 1 – – 5% Water 49% Organics

*Trademark of Anaconda American Brass Co.

Page 9 3. Effect of Contaminants sufficient oxidation capacity in the system to maintain a Although pure acetic acid can be handled readily in many passive oxide film on the stainless steels. Similar data alloys, the presence of only parts per million of other obtained in a mixed acid column were presented in chemical agents can render an alloy useless as a material of reference 7. Field experience with the equipment confirmed construction. the validity of the laboratory data. The effect on other types Acetic anhydride is produced as a co-product in the of alloys of adding oxygen to an acetic acid medium can be older acetaldehyde oxidation process for acetic acid, and seen in Tables XXII, XXIII and XXV. the anhydride can often be found in other acetic acid process streams. When small quantities of the anhydride exist in a glacial acid, a greatly accelerated attack on the stainless steels can be anticipated. Tables IV, IX and X TABLE VIII incorporate data substantiating the adverse effect of anhydride in acetic acid as reported by Elder5 and others. Corrosion of Metals in Acetic Acid Residue Still The difference in the two commercial, glacial acids shown Test Conditions: Test assembly installed in liquid and in in Table XI can probably be attributed to the presence of vapor space of still at temperatures of anhydride in the product of Plant B. As the amount of 80 to 100 ºC (176 to 212 ºF) for 2000 anhydride in the acid is increased, the rate of attack rapidly hours. Residues contain acetic acid, drops to an acceptable level, and high concentrations of anhydride, acetates, tar. anhydride are innocuous. (See section on Acetic Anhydride.) However, the presence of small amounts of Corrosion Rate anhydride sufficient to dehydrate the acid produces in- Liquid Vapor 6 creased attack on all alloys. Alloy mm/y mpy mm/y mpy Oxygen may influence corrosion rates in acetic acid, and other organic acids as well. Even though process streams Cast iron 2.13 84 1.32 52 Ni-Resist Type 11 have been stripped of gaseous components in distillation .97 38 .30 12 Mild steel 2.01 79 2.51 99 systems, the possibility of oxygen pickup from air leaks Type 501 chrome steel 2.01 79 1.47 58 into the system is present. The use of stainless steels as Type 430 stainless steel 1.22 48 .36 14 materials of construction assures that no accelerated attack INCONEL alloy 600 .18 7 .13 5 will occur under such circumstances. Indeed, when corro- HASTELLOY alloy C Nil Nil Nil Nil sion of the stainless steels in a process system is higher than DURIMET* 20 .05 2 .13 5 desired, the rate of attack can often be reduced by Type 329 stainless steel .18 7 .30 12 introducing oxygen into the system. Table XLIII shows Type 304 stainless steel .76 30 .36 14 Type 316 stainless steel .03 1 .18 7 the effect of adding oxygen to a distillation column during .03 1 .05 2 the processing of propionic acid. A hundred-fold reduc- Type 317 stainless steel tion in the corrosion rate is evident as the oxygen provided *Trademark of The Duriron Company, Inc.

TABLE IX Corrosion of Type 316 Stainless Steel in Acetic Acid Solutions Containing Chlorides Conditions: Duplicate 48-hour tests conducted at the boiling temperature in glacial acetic acid with additions made as shown.

Corrosion Rate Chloride Ion Added, ppm* Diluent addition 0 18 36 61 to acid mm/y mpy mm/y mpy mm/y mpy mm/y mpy None – – .05 2 .43 17 2.10 81 0.2% Acetic Anhydride 1.98 78 1.27** 50** 1.22** 48** 1.19** 75* 0.1 % Water .03 1 – – – – – – 0.3% Water .03 1 – – – – – – 0.33% Water – – .08 3 .33 13 .71 28 0.50% Water .03 1 – – – – – – 0.67% Water – – .03 1 .66 26 .38 15 1.0% Water – – .18 7 .41 16 .36 14

* Added as sodium chloride ** Minute, profuse pitting

Page 10 Peracids or other per compounds are often formed in TABLE X the reaction step of most oxidation processes designed to Corrosion of Alloys in Contaminated Acetic Acid produce acetic acid. Peracetic acid is the common, strongly oxidizing compound formed although various Condition: Duplicate tests of 120 hours conducted at other per compounds can be produced. The per compounds the boiling temperature with additions made act similarly to oxygen in the system. Thus, the stainless as shown. steels again provide good stability in such media and can Corrosion Rate often be stabilized by the addition of such compounds. Test Type 316 CARPENTER HASTELLOY The effect of adding a peroxide to acetic acid can be noted No. Test Medium Stainless Steel alloy 20Cb-3 alloy C in Tables XII and XLIII. mm/y mpy mm/y mpymm/y mpy Iron, copper, manganese and similar salts present in an 1 Glacial acetic acid .08 3 <.03 <1 Nil Nil 2 (1) + 0.1 % Acetic .94 37 .84 33 .03 1 operating system can serve as powerful oxidizing agents if Anhydride in the higher valence state. Such salts quite often ac- 3 (2) + 0.1% Sodium 1.32 52 1.07 42 .03 1 cumulate in portions of a system from corrosion products Chloride or as carry-over from the reaction catalyst system. As long 4 (1) + 0.1% Sodium 1.73 68 1.47 58 .03 1 as the anion of the salt is an acetate, such as in ferric Chloride acetate, the presence of these compounds is normally 5 (4) +1% Water .03 1 .03 1 .03 1 beneficial to the stainless steels. However, the data of TABLE XI Table XII would suggest that a thorough investigation should be made if ferric ion is present at high tempera- Corrosion of Type 316 Stainless Steel in tures. The presence of the ion in these tests actually Acetic Acid Solutions accelerated the attack. Cupric ion is particularly effective Conditions: Coupons exposed in hot wall tester to as an oxidizing ion, and occasions arise in the processing glacial acetic acid from Plant A and Plant B of acetic acid solutions in stainless steel equipment where with the additions shown. the addition of cupric acetate is advantageous in reducing Specimen Acid Exposure Corrosion Addition Wall attack on the stainless steel and maintaining passivity of Tested Period Rate the surface. Rabald cites the efficacy of mercuric salts in Temperature eliminating attack on a Type 304 stainless steel in glacial hr ºC ºF mm/y mpy acid.8 Plant A (None) 48 136 277 .23 9 The presence of the reduced (ous) state of these cations 96 146 295 .10 4 Plant A 1%water 68 132 270 .03 1 shows no effect on the corrosion rate of the stainless steels 92 131 268 .03 1 or other metals and alloys. Plant A 0.5% formic 48 137 278 .03 1 Chlorides can be considered as the major hazard when Plant A 1.0% formic 48 141 286 <.03 <1 processing acetic acid in stainless steels. Acid contami- Plant B (None) 68 149 300 7.80 307 nated with chlorides can produce pitting and rapid stress- 96 152 306 12.55 494 corrosion cracking of the 300 series stainless steels in Plant B 1 % water 48 140 284 .03 1 specific areas of the equipment. Greatly accelerated, Note: All coupons pitted to some extent under all conditions. general corrosion can also ensue if the chloride content is TABLE XII sufficiently high. Tables IX and X reveal the effect of chloride ion added as sodium chloride. It will be seen that Corrosion of Type 316 Stainless Steel in Acetic Acid with a concentration of less than 20 ppm can be allowed before Additives at Higher Temperatures the rate of attack on Type 316 stainless steel is intolerable. Conditions: Laboratory tests in glacial acetic acid con- These data correlate well with the data of reference 7 that tained in pressure autoclaves at temperature no more than 25 ppm of chloride is permissible before shown for multiple runs of 48 hours each. Data excessive attack occurs at the boiling temperature. It is averaged. Additions to the acetic acid made as assumed that increasing amounts of hydrochloric acid are shown. formed as the weak acid is heated over prolonged periods Corrosion Rate with the strong acid salt. Where small quantities of Temperature Annealed Sensitized* chloride salt in a process steam are allowed to accumulate Additive ºC ºF mm/y mpy mm/y mpy and concentrate in process equipment, the effect can be None 190 374 .20 8 – – 1500 ppm disastrous for the stainless steels. Both pitting and exces- hydrogen peroxide 190 374 .23 9 – – sive overall attack on the stainless steels may occur. The 3000 ppm last line of data of Table X is suspect in that the Type 316 hydrogen peroxide 190 374 .08 3 – – stainless steel maintained passivity throughout the test 3000 ppm H2O2 + period. This result is in conflict with the data of the last 1500 ppm line in Table IX. It is believed that Table IX provides a Fe+++ (a) 190 374 .69 27 – – 1500 ppm Fe+++ (a) 190 374 .56 22 – – more accurate description of the effect of chlorides in the 1500 ppm presence of water. Pitting of the stainless steel would hydrogen peroxide 240 464 .61 24 .89 35 ensue also if the test period were extended. *650 ºC ( 1202 ºF) for one hour

a = Added as FeOH(C2H3O2)2

Page 11 Processes employing halide catalysts in the reaction until excessive rates of attack are obtained. However, CF- system to produce acetic acid must be assessed thoroughly 8M resists the effect of increased temperature quite well to determine where the less costly stainless steels can be and has potential for use at the 200 ºC (392 ºF) temperature. used in the process train. Type 316 stainless steel usually Field applications utilizing CF-8M pumps in acid near this cannot be used in the reaction area or in the first separation temperature confirm the utility of the alloy for handling hot steps. More highly alloyed materials are required. Once the acid when oxidizing conditions exist. halide ion is removed, the overhead acid stream from the Table XII shows other data obtained in the upper distillation train can be processed safely in stainless steel. temperature region of Figure 1. Note the lower corrosion (See section on Process and Plant Corrosion Data.) rate for a Type 316 stainless steel at 190 ºC (374 ºF), Stress-corrosion cracking of the 300 series stainless steels although the test period is longer. Sufficient peroxide may occur readily in aqueous acidic media containing appears to be effective in reducing corrosion, even at these chlorides. Presumably the cracking will not occur in a high temperatures. The presence of ferric ion was detri- completely anhydrous medium, but such a water-free sys- mental at these temperatures as opposed to the beneficial tem is obtained rarely and some water must be assumed to effect noted at lower temperatures. be present. Where the chloride-containing acid solution Vapors of the acid at higher temperatures are not can concentrate on the surface of stainless steel under aggressive in the absence of condensation (Tables VIII and stress, cracking of the metal can occur. Such areas as XIV). However, condensation or drippage of liquid on a hot gasket joints, crevices and liquid-vapor interfaces in the metal surface can produce excessive attack. In addition, equipment are examples of zones where such cracking pitting of the austenitic stainless steels in acetic acid (and pitting) often occurs in chloride-containing acetic exposures at the higher temperatures is possible. acid. Cracking may also occur beneath deposits or at the It is obvious that careful assessment of the stability of the base of pits on the surface of the stainless steels. Where 300 series stainless steels in an acetic acid environment the metal surface is washed continually with fresh liquid, must be made before discounting their use at even the there is little likelihood of stress-corrosion cracking. If the higher temperatures. process temperature is less than 80-90 ºC (176-194 ºF) the cracking process may be sufficiently slow to allow a respectable service life for the equipment before failure TABLE XIII occurs. At temperatures below 50-60 ºC (122-140 ºF), stress-corrosion cracking usually does not occur. Stress- Corrosion of Nickel-Containing Alloys in Buffered corrosion cracking may be avoided by the use of higher Acetic Acid at High Temperature nickel alloys or duplex stainless steels. Test Conditions: Specimens exposed in a high pressure With the exception of formic acid, (see Section on autoclave at temperature of 200 ºC Formic Acid), other contaminants found in the usual acetic (392 ºF) for 8 days to the following acid process stream only serve to dilute the acid and reduce solution without aeration or agitation: the rate of attack. Aldehydes, ketones, esters and higher 15% acetic acid plus 19% ammonium acids are in this category. acetate aqueous solution at 250 psi. Corrosion Rate

Alloy mm/y mpy 4. Effect of Temperature HASTELLOY alloy C-276 02 0.6 It has been shown that Types 316 and 316L stainless INCONEL alloy, 625 02 0.7 steels are satisfactorily resistant to attack by all INCOLOY alloy 825 02 0.8 concentrations of acetic acid to the boiling point and that HASTELLOY alloy G 03 1.0 Type 304 stainless steel is acceptable for use in all Nickel 200 04 1.5 IN-862 Cast Alloy 05 1.8 concentrations of acid less than approximately 90 per cent Type 315 Stainless Steel (sensitized) 13* 5.2* to the boiling point. As the temperature is increased Type 316 Stainless Steel (annealed) 04* 1.5* beyond these points, the rate of attack on the stainless steels in the liquid acid increases, but certainly not as *Incipient pitting rapidly as the Arrhenius equation would indicate. Laboratory and field data presented in Tables V and XI TABLE XIV through XIII show that for both wrought and cast alloys Corrosion of Stainless Steels in Vapors Over 52 Per the stainless steels remain useful at temperatures well Cent Aqueous Acetic Acid at High Temperature above the atmospheric boiling point. Various techniques of testing can produce significantly different results and System Corrosion Temperature ingenuity is required to establish stable conditions for the Pressure Rate desired test environment. Alloy ºC ºF psig mm/y mpy Figure 1 condenses considerable data generated by Type 304 Stainless Steel 142 288 35 .03 1 Ohio State University personnel when exploring the Type 304 Stainless Steel 153 308 55 .10 4 corrosion resistance of the cast alloys in acetic acid up to Type 316 Stainless Steel 142 288 35 <.03 < 1 9 200 ºC (392 ºF). The cast CF-8 alloy corrodes at in- Type 316 Stainless Steel 153 306 55 .05 2 creasingly greater rates as the temperature is increased Each datum is average of eight tests conducted in closed pressure vessel.

Page 12 Previous comments regarding temperature were in Decomposition products of organic compounds can form reference to the bulk temperature of a liquid or vapor in on the hot surface. Lastly, any corrosive heavy ends in the contact with a metal surface at essentially the same liquid can concentrate at the surface to attack the metal, or temperature. These conditions do not exist in heat ex- tars can form over the metal to produce crevice corrosion in changers, calandrias and interchangers of an acetic acid a random configuration. For these reasons, an actual heat process. When a metal surface at a higher temperature is exchange test should be conducted in any questionable used to evaporate the acid, higher corrosion rates occur mixture. than obtained isothermally. One explanation is that the Groves, et al.10 have described a simple apparatus for constant heating and cooling of a heat exchanger surface conducting heat exchange “hot wall” tests. Their data are cracks the protective oxide film on a stainless steel to reproduced in Table XV and illustrate the significant expose active metal. Also, ebulition of the liquid at the increase in attack which occurs on an alloy when using the surface supplies a mechanical force to dislodge the film. surface as a heat exchange medium. Further use of this

TABLE XV Corrosion by Acetic Acid Under Heat Transfer Conditions

Temperature Corrosion Rate

Type 304 Type 316 Without With Heat* Stainless Stainless CARPENTER HASTELLOY INCONEL MONEL Heat Transfer Transfer Steel Steel alloy 20 Cb-3 alloy B alloy 600 alloy 400 ºC ºF ºC ºF mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy Test Medium Acetic10% Acid 101 214 – – <.03 <1 <.03 <1 <.03 <1 .08 3 .51 20 1.30 51 – – 110 230 <.03 <1 <.03 <1 <.03 <1 .18 7 .71 28 14.73 580 – – 125 257 <.03 <1 <.03 <1 <.03 <1 .15 6 .69 27 >25.40 >1000 – – 140 284 <.03 <1 <.03 <1 <.03 <1 .10 4 .20 8 >25.40 >1000 50% 102 216 – – 3.30 130 <.03 <1 <.03 <1 .13 5 1.24 49 1.93 76 – – 110 230 5.33 210 <.03 <1 .05 2 .13 5 1.12 44 3.05 120 – – 125 257 5.59 220 <.03 <1 .08 3 .05 2 .79 31 3.68 145 – – 140 284 6.35 250 <.03 <1 <.03 <1 .05 2 36 14 3.30 130 99.6% 118 244 – – 1.75 69 <.03 <1 .18 7 <.03 <1 .56 22 .03 1 – – 110 230 6.60 260 <.03 <1 .13 5 .18 7 .91 36 3.05 120 – – 125 257 8.64 340 33 13 .05 2 .18 7 1.14 45 1.73 68 – – 140 284 51 20 .25 10 2.54 100 .08 3 .36 14 5.59 220

*Metal temperature Reference 10. See that publication for apparatus and technique used.

TABLE XVI Corrosion with Heat Exchange in Aqueous Acetic Acid Containing Additives Test Conditions: Apparatus and procedure same as described in Reference 10. Metal temperature 110 ºC (230 ºF) with bulk liquid temperature of 100 ºC (212 ºF). Test periods of 4 to 96 hours used. All results represent duplicate specimens.

Corrosion Rate Type 304 Type 310 Type 316 Type 329 CARPENTER HASTELLOY AMBRALOY* MONEL Stainless Stainless Stainless Stainless Test Medium alloy 20 Cb-3 alloy C-276 901 alloy 400 Acetic Steel Steel Steel Steel Acid Additive mm/y mpy mm/y mpy mm/ympy mm/ympy mm/y mpy mm/y mpy mm/y mpy mm/y mpy

56% 1% H2SO4 36.07 1420 Nil Nil 5.84- 230- Nil- Nil- 64 25 – – – – .23 9 15.24 600 80 30

56% 5% H2SO4 22.35 880 Nil- Nil- 76.63 3017 5.72 225 17.93 706 – – 36.58 1440 .91 36 61.57 24 24 25% 4% Formic 28.83 1135 50.8 200 .71 28 Nil Nil Nil Nil Nil Nil – – 1.17 46 Acid

*Trademark of Anaconda American Brass Co. Reference 43

Page 13 same technique provided the data of Tables XI and XVI. Persons evaluating the possible effects of sensitization Table XI illustrates the important point that all glacial of an alloy in a specific environment should be aware that acetic acid is not necessarily the same. This fact is a comparison of weight loss measurements between sensi- particularly noticeable when comparing two different tized and annealed specimens of the metal are not always acids by means of the “hot wall” test. Also note that again an adequate procedure after organic acid exposures. Little a small amount of water in the acid is most helpful in difference in weight loss may be noted between the two. In reducing attack on the stainless steels. The water is most fact, many data indicate that the mass of the austenite effective in this respect regardless of the mode of testing, grain in a sensitized metal becomes cathodic to the grain and field work verifies this inhibitory effect. The effect of boundary which results in a tower overall loss in weight adding sulfuric or formic acid to the acetic acid is shown than for the annealed structure (Table XVII is typical). in Table XVI. Notice the accelerating effect of only a Unless obvious “sugaring” or the dropping of grains from small amount of formic acid added to the acetic. Such an the metal has occurred, the welded or sensitized corrosion addition would produce no increase in corrosion of Type test specimen should be evaluated by bending to open and 316 stainless steel in an immersion test conducted at expose the attack, by “ringing” to determine if the metal 110 ºC (230 ºF). The effect of adding the even more has lost the characteristic metallic tone, by conducting aggressive, higher boiling sulfuric acid, such as used in an magnetic permeability tests, or preferably by a metal- esterification reaction, may be catastrophic as can be lographic examination of a cross section of the metal to observed from the data. observe the type and extent of any selective attack on the structure. Susceptibility of the austenitic stainless steels to this 5. Effect of Microstructure type of attack may be avoided by utilizing a low carbon The austenitic stainless steels are subject to specific types grade (.03 C max) or restricting the use of regular carbon of attack when exposed to hot organic acids in the same grades (.08 C max) to the annealed condition, without any manner as that observed in the mineral acids. Adverse subsequent heating into the sensitizing temperature range. mill treatments, fabrication heating cycles, post-fabrica- With low carbon grades, there is little likelihood of tion heat treatment and welding can produce changes in sensitization developing in the alloy during welding or the alloy structure which greatly reduce the corrosion heat treatments. A stabilized counterpart to Type 316 resistance in hot acetic acid. stainless steel known as Type 318 stainless steel is now Chromium depletion associated with carbide precipita- obsolete because present melting technology can readily tion along the grain boundaries (sensitization) on heating attain low carbon levels on a routine basis. an unstabilized, regular carbon (0.08 C max) stainless The exposure of the chromium-nickel-molybdenum steel within the range of 425-760 ºC (800-1400 ºF) gives stainless steels after various thermal treatments to a rise to intergranular attack when the alloy is exposed to process stream containing acetic acid has been reported by hot, concentrated acetic acid. Severe intergranular attack the Welding Research Council.11 (Table VI.) The corrosion can result in the phenomenon known as “sugaring” or rates obtained were high for such an exposure for reasons “grain dropping.” The attacked, heat-affected surfaces are not detailed in the stream analysis. Also, the higher left in a very rough condition with a bright, (sugary) corrosion rates exhibited by the Type 316 stainless steel faceted surface. If the alloy is sensitized throughout its are in conflict with the usual data obtained when thickness, such attack may proceed until the entire thick- comparing the alloy with the Type 316L alloy. However, ness of the metal is penetrated. the data are emphatic in pointing out the effect of adverse heat treatments on susceptible materials. Note particularly the adverse effect of solution annealing followed by a sensitization treatment on the columbium-stabilized Type 318 alloy. This type of treatment can occur during multi- TABLE XVII ple-pass welding and may result in “knife-line attack” on Corrosion in Acetic Acid Vaporizer stabilized alloys. Although carbide precipitation is the best known and Field Test: 312 hr, 140 C (284 F) mass temperature. most common cause of intergranular attack on the stain- Chlorides present less steels, certain other metallurgical phenomena must be Corrosion Rate recognized as presenting potential problems as a result of fabrication procedures. The formation of sigma phase or Alloy mm/y mpy chi phase in the alloy can be as devastating as carbide Type 316 stainless steel, annealed 8.13 320 sensitized 6.86 270 precipitation under certain conditions of acetic acid ex- Type 304 stainless steel 33.02 min* 1300 min* posure. Welding alloys such as Types 316L and 317L CARPENTER alloy 20Cb-3 6.35 250 stainless steels presents no problems when using solid INCONEL alloy 600 6.60 260 construction. However, as the process pressure increases Titanium .08** 3** and the use of clad construction is indicated to be HASTELLOY alloy C-276 .08 3 economically desirable, problems can be encountered if *Dissolved adequate precautions in the fabrication of the vessel are **Pitting

Page 14 not observed. Type 316L stainless steel, when heated for stainless steel has been supplied. The molybdenum spot prolonged periods in certain temperature regions above test is most often utilized in this regard. The cost of such a 500 ºC (932 ºF), can produce sigma or chi phase in the procedure is appreciable, but becomes insignificant in alloy. Type 317L stainless steel with higher molybdenum comparison with the failure of a piece of equipment once con-tent is slightly more prone to formation of these the unit is in operation. Simple items such as the drain plug phases. These phases are rich in chromium (chromium and in a pump, a welding elbow in a hot acid line, a few molybdenum in the case of chi phase) and can have much incorrect tubes in the heat exchanger and many other small items can create disastrous problems if an inadvertent the same effect as the more commonly known M23C6 and substitution of a lower grade of stainless steel has been M6C carbide precipitation in the alloy. Such a metallurgical phase change can occur in the fabrication of the clad made for the Types 316 or 316L analysis identified for the vessel when it becomes necessary to stress relieve the steel use. A materials identification procedure on the site to backing. At the 500-650 ºC (932-1202 ºF) stress relief provide assurance of proper alloy installation is very easily desired, sigma or chi phase can be produced to create justified economically. Kits are commercially available severe corrosion of the clad material on the interior during with complete instructions for doing such work on the site process operations. Lower stress relieving temperatures are very quickly and easily. One person assigned to this work required to avoid such an undesirable metallurgical throughout the life of a project may pay for the services condition if these grades of stainless steel are to be used. many times over.

6. Quality Control Qualification tests are often used to assure that the initial C. Martensitic and Ferritic Stainless Steels material is of proper quality and that any heat treatment of The standard AISI grades of martensitic and ferritic the equipment has not produced undesirable effects. stainless steels generally do not possess sufficient corro- Clippings from sheet and plate, small sections of tubes sion resistance for use in acetic acid service, except and other small sections removed from pieces of equip- possibly at low concentrations and temperatures. Table ment are sent to the laboratory for validation of the XVIII shows typical corrosion data for the martensitic existing condition of the material and its ability to maintain Type 410 stainless steel. Included for comparison are steel, appropriate corrosion resistance. These qualification tests cast iron and a nickel alloyed cast iron. When evaluating have been standardized by the American Society for these materials for an application, it is important to assure Testing and Materials (ASTM) and are divided into that the service conditions are reproduced as closely as practices A through E of Recommended Practice A 262. possible. Laboratory tests can show a considerable Each of these is designed to detect specific types of phase disparity in results because of the possibility of forming a formation in the alloy. Of these, Practice A, the electrolytic fragile protective film on the alloy in a short time. After a oxalic acid etch (EOAE) test, is the most sensitive. high initial rate of attack, the rate will subside to a low Normally, if a heat of stainless steel fails to pass the EOAE value if the film is undisturbed by flow or other test, samples are tested in accordance with one of the other mechanical effects. practices before rejection of the heat is allowed. However, because of the sensitivity of the EOAE test, some workers have advocated that acceptance or rejection be based upon D. Duplex Austenitic-Ferritic and Precipitation this test alone to assure maximum corrosion resistance in Hardening Stainless Steels the alloy. Major losses in equipment and even more expensive, extended periods of downtime may be avoided Duplex structured austenitic-ferritic stainless steels and by these simple procedures. certain precipitation hardening stainless steels can show Castings to be used for pumps, valves and other critical remarkable resistance to organic acids depending on the parts of the equipment can be tested in the same manner. ratio of nickel to chromium and other minor alloying Solution annealing of castings is mandatory to assure the constituents. Table XIX illustrates the resistance of several optimum corrosion resistance desired. Small amounts of precipitation hardening stainless steels in acetic acid at ferrite provided in the matrix to assure crack-free castings various temperatures. It is important to understand that the of the best strength and quality are not harmful. However, selection of such alloys for a specific application is more carbides and other constituents which might be isolated critical than when appraising an austenitic stainless steel. along the dendrites of a casting should be in solution to Prior processing of the alloy can have a significant effect prevent selective attack of such areas. on the corrosion resistance. The influence of heat The quality control program for assuring that the treatment on the corrosion resistance of three precipitation stainless steels used in acetic acid manufacture meet hardening stainless steels in acetic acid is shown in Table specification requirements is sometimes extended to XIX. It is obvious that the metallurgical condition of the qualitative chemical analysis by means of spot testing of alloy must be known when considering these alloys for all material received by the fabricator of the equipment and acid service. Certain treatments of the alloys can greatly by those in the field responsible for installing piping, reduce their corrosion resistance. The data also reveal the heat exchangers, vessels and all other equipment to be borderline passivity of these alloys in such service, par- exposed to the hot acid to help assure the proper grade of ticularly in the intermediate concentration of acid. The effect of heat treatment on the molybdenum-containing

Page 15 TABLE XVIII Corrosion of Alloys in Acetic Acid

Corrosion Rate Per Cent Temperature Type 410 Type 430 Ni-Resist Acetic Acid ºC ºF Cast Iron Carbon Steel Stainless Steel Stainless Steel Type 2 mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy 5 25 77 – – .25* 10* – – <.03 < 1 .91 36 5 99 210 254 10,000 57.15 2250 – – – – – – 10 25 77 – – – – – – <.03 < 1 .53 21 20 25 77 – – .20* 8* – – <.03 < 1 – – 20 100 212 – – – – – – 3.05 120 – – 20 116 241 – – – – – – 4.27 168 – – 25 25 77 – – – – – – – – .58 23 25 104 219 – – – – – – .38 15 – – 25 116 241 – – – – – – .25 10 – – 30 116 241 – – 127 5000 – – <.03 < 1 – – 40 116 241 – – – – – – <.03 < 1 – – 50 25 77 – – .20* 8* – – <.03 < 1 1.96 77 50 116 241 – – – – – – 1.02–7.62 40–300 – – 60 110 230 27.69 1,090 – – – – – – – – 75 25 77 – – – – – – – – 1.68 66 75 65 149 – – 7.62 300 – – 1.02 40 – – 75 116 241 – – – – – – 1.27 50 – – 95 25 77 – – 1.02 40 – – – – – – 95 116 241 – – 16.51 650 – – – – – – 99.9 25 77 – – .76 30 – – – – .53 21 99.9 116 241 – – 12.7 500 1.27–4.86 50–585 6.86 270 – – 99.9 90 194 – – 6.86 270 – – – – – – 100 25 77 – – 1.65 65 – – Nil Nil – – 100 35 95 2.03 80 1.70 67 – – – – – – 100 50 122 – – 1.78–11.18 70–440 .01 0.3 – – – – 100 100 212 – – – – – – 1.27 50 – – 100 116 241 20.07 790 – – – – .64–5.08 25–200 – –

Data combined from various published articles and private communications. *Rates obtained under quiescent conditions. Removal of the corrosion film will greatly increase the rate of attack.

alloy is particularly critical and must be thoroughly under- are some rare cases where the corrosion resistance of these stood when appraising the alloy for acid services. alloys is no better than Type 316 stainless steel, but usually Duplex stainless steels can also exhibit good corrosion they provide a higher plateau of corrosion resistance to hot resistance in acetic and other organic acid environments. organic acids. The higher cost of these materials requires Type 329 stainless steel and cast ACI CD-4MCu are that their area of use in a process be pinpointed and examples. Tables II, III, VIII, XVI and XXVIII show the justified by longer service life. excellent corrosion resistance evidenced by these alloys in The cast and wrought alloys of this category are essen- certain specific exposures. These alloys are also more tially the same in chemical resistance although some small sensitive to changes in environment than are the aus- difference may be noticed in a specific environment. The tenitic stainless steels. However, in the proper application, cast alloys are exemplified by ACI CN-7M. There are the alloy can exhibit good stability while providing resis- many proprietary alloys of this general type which bear tance to stress-corrosion cracking. It is for this latter trade names. Quite often the designation ends with the reason that the duplex alloys are sometimes appraised for number “20,” and indeed this group of alloys is known to organic acid use. many as the “type 20” alloys. Alloys included in this category are: wrought CARPENTER* alloy 20Cb-3 and cast DURIMET** 20, ALLOYCO*** 20, WORTH- E. Iron-Base Nickel-Chromium-Copper- ITE**** and others. Molybdenum Alloys When an acetic acid environment is too corrosive for utilization of Types 316 or Type 317 stainless steels, the next group of materials usually considered are the iron- * Trademark of Carpenter Technology Corporation ** Trademark of The Duriron Company, Inc. based alloys containing higher percentages of nickel and *** Trademark of Aloyco Inc. chromium with molybdenum and copper added. There **** Trademark of Worthington Corporation

Page 16 The superiority of this class of alloy may be noted by reference to Tables II, V, XXVII and XXIX. Particularly when the acid is contaminated with agents inimical to the use of Type 316 stainless steel, these alloys usually provide significant improvement in resistance. For hot acid pumps, the CN-7M composition shows greater resistance to erosion-corrosion than CF-8M castings and is often used in installations that are otherwise entirely of Type 316L stainless steel construction. The higher nickel content of the “type 20” alloys provides a fully austenitic structure, imparts good strength with ductility, is in optimum ratio with the chromium for maximum corrosion resistance in the iron-base alloys and increases the resistance of the alloy to chloride stress- corrosion cracking considerably. The wrought or cast “type 20” alloys will not crack in many environments which produce stress-corrosion cracking in Type 316 stainless steel. The “type 20” alloys are susceptible to sensitization as described for the 300 series stainless steels unless stabilized or solution annealed. Low carbon contents or the addition of columbium is used to combat the Black, Sivalls and Bryson Inc. utilize a number of different alloys to problem. “Knife-line attack” may sometimes occur along resist various corrosives in its extensive line of rupture disks. Included beads of multiple-pass welds in the metal-stabilized are Alloys 400, 600, and HASTELLOY alloy C-276 as well as Type 316 alloys. Castings should be used in the solution annealed stainless steel and other high nickel alloys to insure reliability. condition.

environments and far superior to Type 316L stainless steel F. Nickel-Base Chromium-Iron- in the hotter, more aggressive organic acid environments. Molybdenum-Copper Alloys This is shown in Tables V, VII, XII1, XXVII, XXVII and The nickel-base Cr-Fe-Mo-Cu alloys such as HASTEL- XXX. Their superiority is also indicated in later sections of LOY* alloy G and INCOLOY** alloy 825 are generally this bulletin. (See Tables LI, LVIII, LXVII, LXXIV and equivalent to 316L stainless steel in “mild” acetic acid LXXVIII.)

*Trademark of Cabot Corporation ** Trademark of the Inco family of companies TABLE XIX Averagea Corrosion Rates of Precipitation Hardening Stainless Steels in Acetic Acid

Acetic Acid Concentration 100% 75% 50% 25%

Corrosion Rate Alloy mm/y mpy mm/y mpy mm/y mpy mm/y mpy Type 430 4.90 193 1.32 52 7.67 302 4.27 168 Type 304 .43 17 2.21 87 <.03 < 1 <.03 <1 PH15-7Mo (as received)b <.03 < 1 .05 2 03 1 <.03 <1 PH15-7Mo (Al 750) 08 3 <.03 < 1 <.03 < 1 <.03 <1 PH15-7Mo (TH1050) 08 3 30 1 2 71 28 76 30 PH15-7Mo (RH950) 08 3 18 7 56 22 51 20 17-7PH* (as received) 30 12 46 18 28 11 <.03 <1 17-7PH (A1750) 38 15 10 4 28 11 <.03 <1 17-7PH (TH1050) 28 11 03 1 <.03 <1 <.03 <1 17-7PH (RH950) 25 10 05 2 08 3 .05 2 17-4PH* (as received) 25 10 15 6 <.03 <1 <.03 <1 17-4PH (H900) 28 11 03 1 <.03 <1 <.03 <1 17-4PH (H1025) 33 13 25 10 <.03 <1 <.03 <1 17-4PH (H1150) 23 9 05 2 <.03 <1 <.03 <1

a. Average of duplicate specimens for three 48-hour exposure periods in boiling acid. b. Heat Treatment– A = Annealed T = Transformation near 760 ºC (1400 ºF) H = Hardening between 482-593 ºC (900-1100 ºF) of T or R material R = Refrigerate treated to –73 ºC (–100 ºF) *Trademark of Armco Steel Corporation

Page 17 TABLE XX  Corrosion of the HASTELLOY and Associated Alloys in Acetic Acid

Tests of 120 hours’ duration at the temperature shown.

Corrosion Rate 25 ºC (77 ºF) 66 ºC (151 ºF) Boiling Medium mm/y mpy mm/y mpy mm/y mpy 10% Acetic Acid HASTELLoy alloy B .01 0.5 .15 6 .02 0.7 HASTELLoy alloy C .01 0.2 .01 0.2 .01 0.4 HASTELLoy alloy D .02 0.6 .23 9 .05 2 HASTELLoy alloy N .03 1 .07 2.7 .03 1.2 HAYNES* alloy No. 25 Nil Nil Nil Nil .00 0.1 MULTIMET* alloy Nil Nil Nil Nil .00 0.1 50% Acetic Acid HASTELLOY alloy B .03 1 .10 4 .01 0.4 HASTELLOY alloy C .00 0.1 .00 0.1 .00 0.1 HASTELLOY alloy D .08 3 .46 18 .08 3 HASTELLOY alloy N .03 1 .06 2.5 .04 1.7 HAYNES alloy No. 25 Nil Nil Nil Nil .00 0.1 MULTIMET alloy Nil Nil Nil Nil .00 0.1 99% Acetic Acid (Glacial) HASTELLOY alloy B .00 0.1 .01 0.5 .01 0.2 HASTELLOY alloy C .01 0.2 .00 0.1 .00 0.1 HASTELLOY alloy D .01 0.5 .13 5 .02 0.9 HASTELLOY alloy N 02 0.7 .02 0.7 .02 0.8 HAYNES alloy No. 25 Nil Nil Nil Nil Nil Nil MULTIMET alloy Nil Nil Nil Nil .00 0.1

*Trademark of Cabot Corporation Reference 45

G. Iron-Base Nickel-Chromium- H. Nickel-Base Molybdenum- Molybdenum Alloys Chromium Iron Alloys There are several proprietary alloys of approximately Increases in temperature, increases in pressure and a more 25Ni-21Cr and 4 to 6.5 per cent molybdenum that were complex chemistry in the acetic acid process stream are developed mainly for resistance to localized attack such as characteristics of the more modern processes for produc- pitting and crevice corrosion in chloride environments. ing the acid. In many of these process streams, the Included among these alloys are wrought JESSOP* alloy presence of formic acid, higher acids, or halides requires JS-700, HAYNES** alloy 20 Mod, ALLEGHENY- that the ultimate material of construction in acid resis- LUDLUM*** alloy AL-6X and cast IN-862. Judging by tance, resistance to pitting and resistance to chloride their composition, their corrosion resistance in acetic acid stress-corrosion cracking be used. The nickel-base alloys and organic acids generally should be superior to Type containing molybdenum, iron and chromium are those 316 stainless steel in many halide contaminated environ- materials. The alloys are exemplified by wrought ments. Unfortunately, data on these alloys are sparse HASTELLOY alloys C-276 and C-4, INCONEL* alloy although some data exist as shown in Tables III, V, XIII, 625, cast CHLORIMET** alloy 3 and ILLIUM*** alloys LXXII and LXXVIII. Note the superiority of alloy JS-700 W1 and W2, among others. in the acetic-hydroxy acid solution in Table V and the The data in Tables III, VII, VIII, XIII, XV1, XVII, XX, freedom from pitting exhibited by cast IN-862 in the XXI, XXVII and XXVIII through XXX show the excel- buffered acetic acid solution at 200 C (392 F) shown in lent resistance of these alloys to corrosion by hot acetic Table XIII. This type of alloy should certainly be acids. In pure aqueous acid streams, or in uncontaminated evaluated for aggressive acetic acid environments. glacial acids, the use of these alloys in preference to Type Welded samples of comparable thickness to the equipment 316 stainless steel is usually not economically justifiable. under consideration are suggested for test evaluations However, when impurities are present, they often offer the because of the possible formation of sigma or chi phases. most economical choice.

* Trademark of Jessop Steel Company * Trademark of the Inco family of companies ** Trademark of Cabot Corporation ** Trademark of The Duriron Company, Inc. *** Trademark of Allegheny Ludlum Steel Corporation *** Trademark of Stainless Foundry & Engineering, Inc.

Page 18 As shown previously, the presence of anhydride in the contaminate an acetic acid stream with halide ions, the use acetic acid can render the use of Type 316 stainless steel of the nickel-base, high alloy materials offers the greatest unsuitable. Titanium is also attacked by the acid- certainty of economical operation. As discussed under the anhydride mixtures (Table XXI). These nickel-base effects of contaminants, the presence of chlorides in an higher alloys retain immunity to attack in all mixtures of acetic acid stream may produce disastrous results with the the acid and anhydride. For this reason, parts of the stainless steels. Titanium is also severely attacked when distillation columns of the acetaldehyde-to-acetic acid sufficient chloride ion is present. The copper alloys may process were constructed of these high alloy wrought be useful depending on the corrosion allowable in the materials and many of the required pumps were of the system and depending on what other contaminants are in cast counterparts. the stream (e.g., oxygen, heavy metal cations, peroxides, When formic acid is a co-product of the oxidation etc.). The nickel-base alloys containing molybdenum, reaction to produce acetic acid, the process stream can chromium and iron are essentially unaffected by such again be overly aggressive to Type 316 stainless steel contaminants. As an example, the data of Table XVII and more highly alloyed corrosion resistant alloys must show the results of a test conducted in an acetic acid be considered for use. If air or other contaminants are vaporizer using acid contaminated with a small amount of present, the nickel-base molybdenum-chromium-iron al- chloride. The effect on other alloys was severe while the loys are prime candidates as materials of construction. HASTELLOY alloy C-276 material maintained adequate When the process conditions or operating problems stability.

TABLE XXI Comparison of Corrosion of Various Proprietary Alloys in Acetic Acid Solutions Conditions: Duplicate specimens tested in the boiling solution for 48 hours or longer. Air not excluded or added.

Corrosion Rate

50% 10% 99% 90% 90% Acetic 30% Esterifi- Acetic Acid Acetic Acid Acetic Acid Acetic Acid Acetic Acid Acetic Acid Acid, Aqueous cation 50% Acetic 2% 1 1% Acetic 10% 70% 10% Acetic glacial Acetic Acid Mixture Anhydride Formic Acid Anhydride Formic Acid Anhydride

mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy Alloy Type 316 .01 0.4 1.07 42 .03 1 <.03 < 1 9.12 359 .23 9 .17 6.5 – – – – Stainless Steel INCOLOY alloy 825 1.70 67 20.24 797 – – .36 14 3.66 144 – – – – – – – – IN alloy 102 (A)2 <.03 < 1 .69 27 – – .15 6 .18 7 – – – – – – – – IN alloy 102 (HT)3 .03 1.1 .71 28 – – .10 4 .18 7 – – – – – – – – INCONEL <.03 < 1 .08 3 – – .03 1 .28 11 – – – – – – – – alloy 625 (A)2 INCONEL <.03 < 1 .08 3 – – .03 1 .28 11 – – – – – – – – alloy 625 (HT)3 HASTELLOY <.03 < 1 .38 15 – – .04 1.5 .28 11 – – – – – – – – alloy C-276 Titanium <.03 < 1 1.83 72 – – – – 6.12 241 <.03 < 1 <.03 < 1 – – – – HASTELLOY alloy D <.03 < 1 – – – – – – – – – – – – .05 2 – – WAUKESHA* No. 23 .76 30 .69 27 – – – – .71 28 – – .15 6 – – 1.45 57 WAUKESHA No. 54 .64 25 1.19 47 – – – – 1.14 45 – – .76 30 – – .61 24 WAUKESHA No. 88 1.12 44 .91 36 – – – – .05 2 – – .28 11 – – .56 22 KROMARC** 55 .18 7 2.46 97 – – – – 4.09 161 .41 1 6 .08 3 – – – – JESSOP JS-700 – – .03 1 – – – – .66 26 – – – – – – – – CARPENTER alloy 204 – – .03 1 – – – – .36 14 – – – – – – – – Multiphase .05 2 <.03 < 1 – – – – – – – – – – – – – – MP35N*** CROLOY***** 16-1 1.47 58 .43 17 5.84 230 – – 10.67 420 – – – – – – – – Chromium Carbide – – .69 27 – – – – 1.50 59 – – – – – – – – with 12% nickel binder

1. Synthetic mixture of 75% butyl acetate, 11% butanol, 10% acetic acid, 4% water, 0.3% sulfuric acid 2. Annealed 3. 840 ºC (1544 ºF) for one-half hour and furnace cooled 4. CARPENTER alloy 20 has been superseded by an improved alloy CARPENTER alloy 20Cb-3

* Trademark of Waukesha Foundry Company ** Trademark of Westinghouse Electric Corporation *** Trademark of Standard Pressed Steel Co. ***** Trademark of Babcock & Wilcox Co.

Page 19 TABLE XXII Corrosion of High Nickel Alloys in Acetic Acid

Corrosion Rate

% Temperature MONEL alloy Nickel INCONEL alloy Acetic Acid ºC ºF 400 200 600 mm/y mpy mm/y mpy mm/y mpy 2 30 86 .03B 1B .05 2 2 70 158 .10 4 2 116 241 .01 0.2 5 116 241 .03 1 .28 11 .08 3 6 26-30 79-86 .30A,.05B 12A,2B 1.19A,.10B 47A, 4B 10 26-30 79-86 .33A,.08B 13A,3B .10B 4B .02 0.8 10 70 158 1.37A 54A 10 116 241 .33 13 20 70 158 1.30A 51A 25 26-30 79-86 .41A,.08B 16A,3B 30 26-30 79-86 3.30A 130A 30 60 140 .46B 18B 50 26-30 79-86 .74A,.10B 29A,4B 4.32A,.25B 170A, 10B 50 80 176 1.68B 66B 50 116 241 .05 2 .48 19 70 116 241 .36 14 75 26-30 76-86 .36A,.05B 14A,2B 99.9 26-30 79-86 .23A,.08B 9A,3B .13B 5B 99.9 80 176 .61B 24B 99.9 116 241 .15 6 .36 14 100 26-30 79-86 .10 4 100 116 241 .30 12 .99 39 3.05 120

A = Aerated Reference 46 primarily. B = Unaerated

There are process conditions which require that essen- conditions are such that general attack or pitting of this type tially no corrosion of the material of construction occur. of alloys is excessive, the use of tantalum, zirconium, Critical items of equipment required to operate with close graphite and brick-lined construction may be explored. tolerances such as orifice plates or control valve trim are examples. Another possibility is that the catalyst system I. Nickel-Copper Alloys used in the reactor of the process will not tolerate contamination with foreign metallic ions. In these cases, the Alloy 400 and other nickel-copper alloys have very good maximum in corrosion resistance is demanded of an alloy, resistance to pure acetic acid solutions in the absence of air and only the nickel-base Mo-Cr-Fe, the nickel-base or other oxidants. Tables XXII and XXV, among others, molybdenum, zirconium, titanium and tantalum alloys are show the low rate of corrosion of MONEL* alloy 400 when potential candidates as solid or clad materials of the exposure is free of oxidants. As with other alloys, the construction. maximum corrosion appears to occur in the 50-70 per cent Although the organic acids are less aggressive than acid range. The data agree well with the curve (Figure 3) mineral acids in detecting sensitization of this class of alloy, published by Uhlig for corrosion of the alloy in acetic acid at prolonged exposure of the sensitized alloy in hot acetic acid 30 ºC (86 ºF). can produce intergranular attack. The newer wrought MONEL alloy 400 withstands the effects of oxidants materials, such as HASTELLOY alloys C-276,12 C-4 and added to acetic acid better than do either nickel or copper INCONEL alloy 625 are stabilized to forestall such attack alone, as shown by Table XXIII. However, the presence of on fabricated items of equipment. Castings of this type of air or an oxidizing agent such as ferric or cupric ion in alloy should be purchased in the fully solution-annealed solution is cause for concern and may lead to excessive condition. A test for susceptibility to intergranular attack is attack. Corrosion tests should be run to ascertain the defined in reference 13. behavior of these alloys under operating conditions if These alloys usually provide the ultimate in corrosion oxidants are suspected to be present. resistance to hot organic acid streams. If the environmental * Trademark of the INCO family of companies

Page 20 The presence of oxidizing agents in an organic acid stream completely changes the corrosive characteristics of the medium. Parts per million of oxygen, cupric or ferric salts, or peracid compounds in the stream will react stoi- chiometrically with alloys which do not produce protective oxide films. For instance, copper is essentially immune to attack by pure, uncontaminated acetic acid. Yet a small ingress of air at a circulating pump can drive the corrosion rate in a copper column to > 2.5 mm/y (hundreds of mils per year). Indeed, copper can be used as a scavenger of oxidizing species in an organic acid medium and has been so used. FIG 3—Corrosion of MONEL alloy 400 in Acetic Acid The addition of nickel to the copper moderates the effect of oxidants. In general, the greater the amount of nickel in the alloy, the less the effect of oxygen on the corrosion rate. This is illustrated by the data of Table XXV. The addition of nickel to copper appears to have little influence The effect of liquid velocity on the corrosion of on the rate of attack in acid contaminated with heavy MONEL alloy 400 is shown in Table XXIV. No metal ions. The accelerating effect of these ions produces acceleration of the corrosion rate occurred up to 12.5 higher rates of attack which remain excessive regardless of ft/sec velocity at a temperature of 30 ºC (86 ºF). It is the alloy composition. It is interesting to note the effect of believed that velocities of this magnitude would not dilution on the corrosive properties of the various increase the attack on MONEL alloy 400 up to mixtures. As would be anticipated, the corrosion rate is temperatures of 100 ºC (212 ºF). greatly accelerated when adding water to an air Alloy 400 and the cast counterpart of Alloy 400, ACI sparged solution or one containing ferric ions. However, M-35 alloy, have found useful service for many years in some dilute acetic acid solutions handled in the food industry at the lower temperatures. Alloy 400 is attractive because contamination of the food products with ferric or cupric ions is undesirable. Small amounts of iron can contaminate the products if ferrous alloys are TABLE XXIII used and excessive copper pickup can be experienced if Effect of Aeration on Corrosion of Nickel, Copper and the copper content of the alloy is higher than that of Their Alloys in Acetic Acid Alloy 400. Corrosion rates for MONEL alloy 400 in a typical dilute acetic acid solution of this type are shown Conditions: Laboratory tests in 6% acetic acid at 30 ºC in Table XXII. Mason has covered the subject of the (86 ºF) alloy’s use in food products very well.14 Corrosion Rate

Without Aeration With Aeration J. Copper-Nickel Alloys Alloy mm/y mpy mm/y mpy All of the copper alloys excepting those with high (> 15%) Nickel 200 .08 3 .28 11 zinc are resistant to acetic acid in the absence of air and MONEL alloy 400 .05 2 .20 8 other oxidants. Until the advent of the stainless steels, C 71500 (70-30 Cupro-nickel) .08 3 .81 32 copper was used almost exclusively for the handling of Copper C 10300 .08 3 .48 19 acetic acid. Reference 47

TABLE XXIV Effect of Velocity on Corrosion of MONEL Alloy 400 in Acetic Acid

Temperature Corrosion Rate Test Velocity Medium ºC ºF Period, hr Aeration ft/sec mm/y mpy 50% aqueous Acetic Acid 30 86 48 100 cc/min 0 .38 15 1.8 .41 16 3.8 .43 17 8.7 .41 16 12.5 .46 18

Page 21 dilution markedly decreases the attack in a solution could still be used as materials of construction without a containing cupric acetate. This is probably attributable to practical limitation. Increasing nickel content in the alloy the formation of a protective film on the surface, such as a provided no change in the corrosion resistance. Data for basic cupric acetate. Type 316 stainless steel are provided in this table for Note that the addition of ferric ion as the chloride comparison. produced significantly higher corrosion rates than when The excellent corrosion resistance of the cupro-nickel ferric acetate was used as an additive in glacial acetic acid. alloys in hot acetic acid and the retention of that resistance A comparison of the effect of the same additives in the 50 in chloride-contaminated acid has significant commercial per cent acid suggests that the chloride was not mainly implications. The chemical industry around the world has responsible for the greater attack in the 100 per cent acid, constructed seashore installations predominantly during the but that the small amount of water added as the ferric past 20 years. For such plants, the least costly cooling water chloride hydrate produced the greater corrosion. system is the direct use of filtered seawater. The cupro- Further evidence that chloride ion does not greatly nickel alloys are essentially a standard for handling clean affect the corrosion of copper-nickel alloys in organic acids saline cooling water in condensers and other heat exchange is shown in Table XXVI. Adding 0.05 to 2.0 per cent surfaces if compatible with the process stream. sodium chloride to a synthetic mixture of various organic Consequently, in organic acid plants using unpolluted salt- acids produced a ten-fold change in the corrosion rate on water cooling of condensers, the C70600 alloy (90-10 copper and the cupro-nickel alloys. However, the rates cupro-nickel) is widely used, and C71500 alloy (70-30 remained low enough that copper and copper-nickel alloys cupro-nickel) and Alloy 400 are used for certain special

TABLE XXV Corrosion of Copper-Nickel Alloys in Acetic Acid Solutions Conditions: Quadruplicate specimens exposed in pure aqueous acid solutions for 120 hours at the boiling temperature except tests without air sparging were extended to 336 hours. Additives added as shown.

Corrosion Rate 3200 ppm 2900 ppm 2100 ppm Cu++ Fe+++ Fe+++ Per Cent Per Cent No Air Added as Added as Added as Acetic Acid Nickel in Alloy Air Sparge Sparged Cu(OAc) Fe(OH)(OAc) 2 2 FeCl3•6H20 mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy 100 0 .01 0.4 .08 3 51 20 .25 10 .76 30 10 .02 0.7 .08 3 1.32 52 .30 12 .76 30 20 .01 0.3 .08 3 2.87 113 .28 11 .74 29 30 .01 0.2 .08 3 6.15 242 .25 10 .74 29 67 Nil 0.1 .05 2 2.97 117 .18 7 1.30 51 100 .04 1.4 .03 1 81 32 .13 5 5.21 205

75 0 .03 1 10 .03 1 20 .03 1 30 .03 1 67 .05 2 100 .01 0.4

50 0 .03 1 7.87 310 .48 19 3.28 129 3.00 118 10 .03 1 5.41 213 .79 31 2.64 104 2.59 102 20 .03 1 4.95 195 .86 34 2.69 106 2.06 81 30 .03 1 4.78 188 .84 33 2.36 93 2.46 97 67 .03 1 2.13 84 .91 36 1.83 72 2.82 111 100 .08 3 1.60 63 .71 28 1.98 78 4.39 173

25 0 .05 2 10 .03 1 20 .03 1 30 .03 1 67 .03 1 100 .15 6

Portion of Data from Reference 48

Page 22 exposures. For a complete description of the excellent properties of these alloys in seawater, see “Guidelines for Selection of Marine Materials.”15 In addition, if mechanical problems arise which allow seawater contamination of the process stream, such as a leaking condenser tube, the cupro-nickels and Alloy 400 are not excessively corroded by the contaminated acid.

K. Nickel-Chromium Alloys The nickel-chromium alloys represented by Alloy 600 and ACI CY-40 are little used in the production and handling of acetic acid. In general, the iron-base alloys with chromium, nickel and molybdenum exhibit superior corrosion resistance in the acid streams and economic considerations dictate no better choice. For certain specific appurtenances on the major equipment, INCONEL alloy 600 has been used when required because of availability or to take This 15,000 pound capacity reactor kettle of INCONEL alloy 600 was used advantage of certain mechanical properties of the alloy. for over 27 years for the dehydration or polymerization of castor, linseed However, these uses have been minimal. The more and soybean oils. Alloy 600 was chosen to withstand the corrosive effects of vegetable oil acids and C fatty acids at a temperature of 600 ºF. corrosion-resistant iron-base nickel-chromium-molyb- 18 denum-copper alloys are used to combat stress-corrosion cracking when the stainless steels are not useful and forestall any consideration of the nickel-chromium alloys L. Iron-Nickel-Chromium Alloys for the new construction of major items of equipment. When existing equipment of the versatile nickel-chromium Alloy 800 has fair resistance to hot acetic acid solutions. alloy is available, the processing of various acetic acid The iron and chromium of the alloy dictate that conditions mixtures is permissible if the corrosion characteristics of should be slightly oxidizing to realize the best resistance the medium have been properly defined. In general, the from the alloy. However, the alloy cannot compete with lower concentrations of acetic acid (< 60%) in aqueous Alloy 825 or other metals containing molybdenum as a solution can be handled without excessive corrosion. If prime candidate for process use. oxygen is present in the solution, the nickel-chromium The good chloride stress-corrosion cracking resistance alloy is superior to the nickel-copper or cupro-nickel alloys of the alloy makes use of the material attractive for small, in corrosion resistance. specialty applications, but the corrosion rate must be Data showing the resistance of the basic nickel-chro- determined closely to assure that adequate life will be mium alloys to corrosion by acetic acid are presented in obtained. As a general statement, the better solution to a Tables VII, VIII, XV XVII, XXII, XXVII, XXVIII and problem involving acetic acid corrosion and chloride stress- XXX. corrosion cracking is the use of the “type 20” alloys, or the nickel-base iron-chromium-molybdenum-copper alloys.

TABLE XXVI Effect of Sodium Chloride in a Mixed Acid Medium on the Corrosion of Copper-Nickel Alloys Conditions: Duplicate specimens immersed in a boiling 116 ºC (241 ºF) solution of 60% acetic acid, 10% formic acid, 10% heavy organic acids and 20% water for 100 hours.

Corrosion Rate

C70600 C71500

Per Cent NaCI (90-10 (70-30 Type 316 Added to Acid Copper Cupro-Nickel) Cupro-Nickel) Stainless Steel

mm/y mpy mm/y mpy mm/y mpy mm/y mpy

0.05 .01 0.4 .01 0.3 .01 0.3 .38 15 0.10 .01 0.3 .01 0.3 .01 0.5 .56 22 1.0 .08 3 .05 2 .08 3 12.27 483 2.0 .10 4 .08 3 .10 4 22.66 892

Page 23 M. Nickel-Base Molybdenum Alloys Corrosion data for this type of alloy are given in Tables Greater attention has been given to this class of alloy for III, VII, XV, XX, XXVII and XXVIII through XXX. acetic acid exposures in recent years. For most acetic acid applications, the nickel-base iron-chromium-molybdenum- N. Nickel copper alloys are superior to the nickel-base molybdenum alloys without chromium. However, HASTELLOY alloys Commercial nickel is less resistant to attack by acetic acid B and B-2 have good organic acid resistance and have at any temperature than are the nickel-copper alloys, the sometimes been used for the distillation of acetic acid cupro-nickel alloys, or the austenitic stainless steels. mixtures. The cast alloys in this family of alloys include Consequently, nickel as a basic material of construction is ASTM A 494 grades N-12M-1 and N-12M-2. Trade not generally used. The material is used as the underbead names associated with these cast grades include in the welding of copper-clad steel, being compatible with CHLORIMET alloy 2 and ILLIUM alloys M1 and M2. both the copper and the steel backing. These alloys offer excellent corrosion resistance in Data showing the resistance of wrought Nickel 200 to certain of the newer acetic acid processes utilizing acetic acid under varying conditions are contained in chloride catalysts under reducing conditions at high Tables III, VII, XIII, XXII, XXIIL XXV, XXVII, XXIX temperatures. Under these conditions, only zirconium, and XXX. titanium, and the nickel-base molybdenum alloys appear The presence of air accentuates the corrosion of nickel. to be attractive.16, 17, 18 For the high pressures employed for For example, Uhlig reports a rate of attack of .02 mm/y the reaction area, the use of clad construction is very (0.9 mpy) for nickel in a 6% acetic acid solution charged attractive. with nitrogen at room temperature, but a rate of .28 mm/y (11 mpy) when air is introduced.19

TABLE XXVII Corrosion of Metals and Alloys in Acetaldehyde Oxidation Process for Acetic Acid

Corrosion Rate

Exposure* 1 2 3 4 5 6 7 8 9 10 Alloy mm/y mpy mm/y mpy mm/y mpy mm/ympy mm/ympy mm/y mpy mm/y mpy mm/y mpy mm/y mpymm/y mpy

ACI CF-8 – – – – – – – – – – – – – – 0.38 15 – – – – ACI CF-8M – – – – – – – – – – – – – – .03 1 – – – – ACI CN-7M Nil 0.1 – – – – – – .13 5 Nil 0.1 .02 0.6 .01 0.4 .01 0.5 – – Type 446 Stainless Steel .19 7.5 – – – – – – – – – – – – – – – – – – Type 204 Stainless Steel .06 2.5 – – 2.54 100 1.70 67 – – – – – – – – – – – – Type 304 Stainless Steel .09 3.5 – – 1.78 70 1.22 48 2.16 85 .18 7 .13 5 .08 3 .03 1 .25 10 Type 316 Stainless Steel .06 2.4 2.34 92 .33 13 .43 17 .05 2 .03 1 .03 1 Nil Nil Nil Nil .01 0.4 Type 317 Stainless Steel .02 0.7 – – .01 0.5 .01 0.5 .03 1 – – – – Nil Nil Nil Nil Nil 0.2 CARPENTER alloy 20 .01 0.5 .89 35 .18 7 .20 8 .05 2 Nil Nil Nil Nil Nil Nil Nil Nil Nil Nil INCOLOY alloy 825 – – – – – – – – – – .03 1 Nil Nil Nil Nil Nil Nil Nil Nil HASTELLOY alloy C Nil Nil .03 1 .03 1 .03 1 .03 1 Nil Nil Nil Nil Nil Nil Nil Nil Nil Nil HASTELLOY alloy B 01 0.5 .28 11 – – – – .23 9 .03 1 .05 2 .18 7 .25 10 – – HASTELLOY alloy D – – .1 5 6 – – – – – – – – – – – – – – – – INCONEL alloy 600 .12 4.6 – – .36 14 .23 9 – – – – – – – – – – – – Nickel 200 .10 4.1 – – .86 34 .81 32 – – – – – – – – – – – – MONEL alloy 400 .11 4.4 – – 1.12 44 1.07 42 .94 37 .01 0.3 .03 1 Nil Nil Nil Nil – – EVERDUR 1010 Silicon Bronze .10 3.9 – – – – – – – – – – – – – – – – – – Copper .28 11 – – – – – – – – – – – DURIRON** – – <.03 < 1 – – – – – – – – – – – – – – – –

*Exposure 1-Product flash kettle base liquid at 95-100 ºC (203-212 ºF) for 737 days. Approx. 58% acetic acid, 40% anhydride, 2% residue with peroxides present. 2-Stripping still kettle liquid at 148-150 ºC (298-302 ºF) for 56 days. Approx. 65% acetic acid, 36% anhydride, residues, peroxides and catalyst salts. 3-Liquid of stripping still base section at 120 ºC (248 ºF). 4-Vapor of stripping still base section at 120 ºC (248 ºF). 5-Liquid of stripping still mid-section. 6-Anhydride still kettle liquid at 145 ºC (293 ºF). Essentially anhydride. 7-Anhydride still kettle vapor at 145 ºC (293 ºF). 8-Acetic acid refining still base liquid at 145 ºC (293 ºF). Mostly anhydride. 9-Acetic acid refining still base vapor at 145 ºC (293 ºF). 10-Acetic acid refining still overhead at 120 ºC (248 ºF).

**Trademark of The Duriron Company, Inc.

Page 24 Nickel plating appears to have essentially the same tion. Such a situation demands more detailed testing and corrosion resistance in acetic acid solutions as the economic evaluation of alloys, taking into account not only wrought metal. An increase in corrosion resistance is first cost but maintenance costs and reliability as well. reported for electroless nickel which is properly heat a. Oxidation of Acetaldehyde treated. Volokhova, et al. report rates of .10 and .05 mm/y The oldest of the current processes used for any (4 and 2 mpy) for untreated electroless nickel plate in 5% significant production of acetic acid is the oxidation of and glacial acid, respectively, at room temperature while acetaldehyde. In this process, acetaldehyde is air-blown in a specimens of heat-treated plating showed only .01 and nil small tubular converter with distillation of the product and mm/y (0.3 and 0.09 mpy) in the same acids.20 recycling of unreacted acetaldehyde to the reactor.21,22 The primary converter product contains, in addition to acetic acid and unreacted acetaldehyde, varying quantities O. Process and Plant Corrosion Data of acetic anhydride, ester, peracetic acid and catalyst salts 1. Acetic Acid Production from the converter. As pointed out previously, the pre- The modern industrial chemical plant has changed radi- sence of the anhydride increases the corrosive nature of the cally during the past few decades. Efficient, economical stream. (See Tables IV, IX and X.) Until the anhydride and production requires large single-train units that put greater catalyst salts are separated from the acid, a close evaluation emphasis on the reliability of components. If a failure does of the corrosion to be expected in all sections of the occur, it causes a shutdown of the entire process. When equipment is necessary. For instance, the still used this happens, production losses will often far overshadow to separate the acid and anhydride may require a nickel- any differences in cost between alloys of marginal corro- base molybdenum-chromium-iron alloy for the base ket- sion resistance and more durable materials of construc- tle, the calandria and a few lower sections of the column.

TABLE XXVIII Corrosion of Alloys in a Hydrocarbon Oxidation Unit for Acetic Acid

Corrosion Rate

Location * 1 2 3 4 5 6 7 8 9 Alloy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy Type 304 Stainless Steel – – – – – – – – – – – – – – – – 28 11 Type 202 Stainless Steel – – – – – – – – – – – – – – – – .30 12 Type 316 Stainless Steel .05 2 .05 2 .05 2 .03 1 .25 10 .03 1 .03 1 .05 2 <.03 <1 Type 317 Stainless Steel – – – – – – – – – – – – – – .03 1 Type 329 Stainless Steel .05 2 <.03 <1 .05 2 – – – – – – – – – – – – CARPENTER alloy 20Cb-3 <.03 <1 <.03 < 1 <.03 <1 <.03 < 1 .05 2 <.03 <1 <.03 <1 – – – – HASTELLOY alloy G – – – – – – <.03 <1 – – – – – – – – – – HASTELLOY alloy C .10 4 <.03 < 1 .10 4 .05 2 <.03 < 1 – – Nil Nil Nil Nil <.03 < 1 HASTELLOY alloy B – – – – – – – – – – – – – – – – 5.59 220 INCONEL alloy 600 .13 5 – – – – – – – – – – – – – – – – IN alloy 102 .05 2 – – – – – – – – – – – – – – – – MONEL alloy 400 – – – – – – – – <.03 <1 – – – – – – 3.56 140 STELLITE alloy No. 3** – – – – – – .10 4 – – – – – – – – – – STELLITE alloy No. 4 – – – – – – .18 7 – – – – – – – – – – STELLITE alloy No. 6 – – – – – – .46 18 – – – – – – – – – – HAYNES alloy No. 93** – – – – – – >2.54 >100 – – – – – – – – – – HAYNES alloy 25 – – – – – – .03 1 – – – – – – – – – – ILLIUM B*** – – – – – – <.03 < 1 – – – – – – – – – – ILLIUM P – – – – – – <.03 <1 – – – – – – – – – ILLIUM PD – – – – – – <.03 <1 – – – – – – – – – ILLIUM 98 – – – – – – .10 4 – – – – – – – – – – DURICHLOR**** – – .08 3 – – – – – – – – – – – – – – Titanium <.03 <1 Nil Nil Nil Nil – – .56 22 – – .69 27 – – – – Zirconium – – Nil Nil – – – – – – – – – – – – – – Copper – – – – – – – – – – .05 2 .10 4 .08 3 – – C70600 (90-10Cupro-Nickel) – – – – – – – – .05 2 .05 2 – – .10 4 – – * See process diagram Figure 4. ** Trademarks of Cabot Corporation *** Trademark or Stainless Foundry & Engineering, Inc. ****Trademark of The Duriron Company, Inc.

Page 25 The middle column sections may require somewhat less b. Liquid Phase Oxidation of Straight- highly alloyed materials, such as the iron-base nickel- Chain Hydrocarbons chromium-copper-molybdenum alloys, while the top por- Among the important processes of today for acetic acid tion of the column, the condenser and all associated piping production are those based on the direct oxidation of may be made of Type 316L stainless steel. Returning to straight-chain hydrocarbons, such as propane, propylene, the higher temperatures of the base area, the calandria butane, butene and higher aliphatics. The oxidation can be circulating pump and other cast appurtenances must be of achieved using air or oxygen. Reaction conditions are a Type CN-7M casting as a minimum, and the use of more much more severe than for the simple oxidation of an corrosion-resistant alloys or graphite may be necessary. aldehyde with temperatures near 200 ºC (392 ºF) at The remainder of all operating facilities of an pressures of more than 700 psi. Breaking up a hydrocarbon acetaldehyde-based acetic acid unit can normally be con- by such a severe oxidation obviously produces many by- structed of Type 316L stainless steel with Types CF-8M products in addition to acetic acid. Among these are or CF-3M cast valves and pumps. The anhydride refining formic, propionic, butyric and higher acids, ketones, esters still normally presents no exceptional corrosion problems and peroxide compounds. The reaction conditions of the for Type 316L stainless steel. Copper, cupro-nickel alloys converter can be varied to increase or decrease the ratio of and Alloy 400 nickel-copper alloy can be used for any the by-products. This mix of products and by-products required applications once the peracetic acid is destroyed creates two problems not present in an aldehyde oxidation in the system by high temperatures in holding tanks or process: (1) much more separation equipment is required column bases and the equipment is sealed from the ingress to recover the products and (2) the corrosion medium is of air. Corrosion data obtained in an acetaldehyde more complex. Added to this is the large size of the oxidation process unit are tabulated in Table XXVII. equipment required for the large volume output of a Additional data for a wide range of allays exposed in an modern single-train unit. acetic acid residue still of the same process are given in A simplified flow diagram for a typical hydrocarbon Table VIII. oxidation unit is shown in Figure 4. Essentially the entire

TABLE XXIX Corrosion of Allays in Laboratory Equivalents of the Methanol-Carbon Monoxide Reaction Medium

Conditions: Small autoclave tests for 48 hours using 50% hydrate and 7 grams potassium iodide per acetic acid at autogenous pressure without 100 grams of acetic acid). Carbon monoxide and with catalyst (7 grams cobalt acetate atmosphere.

Corrosion Rate Without With

Temperature Catalyst Catalyst Alloy ºC ºF mm/y mpy mm/y mpy Type 304 Stainless Steel 250 482 – – 2.03 80 Type 310 Stainless Steel 300 572 >25.4* >1000* – – Type 321 Stainless Steel 250 482 – – 10.16 400 Type 347 Stainless Steel 300 572 >25.4 > 1000 – – Type 316 Stainless Steel 300 572 9.14* 360* – – 250 482 5.08 200 – – 260 500 – – 22.35 880 CARPENTER alloy 20 300 572 1.63 64 – – 250 482 3.81 150 – – INCOLOY alloy 825 260 500 – – 5.08 200

HASTELLOY alloy C 280 536 .36 14 – – 260 500 – – 1.78 70 230 446 – – 5.08 200 HASTELLOY alloy B 280 536 <.03 <1 – – 260 500 – – .36 14 230 446 – – 71 28 Nickel 200 260 500 – – 5.84 230 Silver 230 446 – – 3.05 120 DURIRON 260 500 – – 2.67 105 Titanium 260 500 – – <.03 < 1 Zirconium 260 500 – – <.03 < 1 Tantalum 260 500 – – <.03 < 1

*Pitting Reference 17

Page 26 facility can be constructed of Type 316L stainless steel. TABLE XXX There are certain precautions, however: •The high temperature of the reactor requires that the Corrosion of Alloys in Synthetic Reactor Product from Methanol-Carbon Monoxide Process for Acetic Acid Type 316L stainless steel be fully qualified and in its most corrosion-resistant condition. (See Effect of Microstruc- Conditions: Aqueous 70% acetic acid at the boiling tem- ture.) Type 316L stainless steel clad construction over a perature 107 ºC (243 ºF) without and with steel substrate offers the most economy for the high catalyst (ca. 6% cobalt acetate hydrate and pressure reactor but the fabrication techniques must assure 6% potassium iodide). Purged with CO. that the maximum corrosion resistance of the stainless steel is retained. Corrosion Rate •Proper operation of the plant is essential. Although Type Without With

316L stainless steel is resistant to the normal conditions of Catalyst Catalyst operation existing in the reactor, if the temperature reaches Alloy mm/y mpy mm/y mpy much more than the nominal 185 ºC (365 ºF), the corrosion , rate for the alloy increases rapidly. Type 304 Stainless Steel 41 16 15* 6* Type 321 Stainless Steel .51 20 .25* 10* •There have been instances in which weld deposits have Type 347 Stainless Steel 1.91 75 .33* 13* been less corrosion resistant than the base metal, perhaps Type 316 Stainless Steel .15 6 .08* 3* because of compositional differences. For this reason, many 24Cr-20Ni-Mo-Cu** <.03 <1 .03* 1* welds are made using a more highly alloyed weld rod or CARPENTER alloy 20 – – .23* 9* filter wire. INCOLOY alloy 825 – – .05 2 •Circulating pumps for the hot process liquid are usually INCOLOY alloy 800 – – .13* 5* of a solution treated CN-7M alloy casting. If temperatures HASTELLOY alloy C – – .10* 4* are maintained at lower levels for the reaction, the CF-8M HASTELLOY alloy B – – .20 8 or CF-3M alloy castings will exhibit a satisfactory service INCONEL alloy 600 – – .38 15 Nickel 200 15 6 .33 13 life. MONEL alloy 400 <.03 <1 .41 16 The acids longer than acetic (propionic, butyric, etc.) C71500 (70-30 Cupro-Nickel) .48 19 .94 37 produced in the reaction add little if any to the corrosivity C70600 (90-10 Cupro-Nickel) .53 21 1.14 45 of the stream, because temperatures of the process Aluminum Bronze .18 7 2.34 92 following the reaction are lower than those required to Titanium Nil Nil Nil Nil promote corrosion of the stainless steels by these acids. (See DURIRON Nil Nil Nil Nil section on Higher Organic Acids.) * Pitting occurred. Authors correctly reported only observations and weight loss of coupons. For comparison, the weight loss was convert- ed to corrosion rate on basis of data given. ** Contained 2.3% Mo and 2.0%Cu Reference 18

Page 27 By-product formic acid adds acidity to the system, but Certain other interesting observations can be found in does not greatly increase corrosion of the stainless steels. references 17 and 18. The catalyst system requires very Table VII shows corrosion rates of various alloys in acetic- high concentrations of catalyst. When half of the catalyst formic acid mixtures typical of those existing in a hydro- is a halide salt, the potential for corrosion is greatly carbon oxidation unit, but without peroxides present. As in increased. (See Effect of Contaminants.) By comparison other processes for acetic acid production, the peroxides with various other tests, particularly when appraising the react with other components of the stream or are decom- austenitic stainless steels, it is apparent that the iodide ion posed with sufficient time at the higher temperatures. Thus, is not as aggressive as is the chloride ion. the cupro-nickels and Alloy 400 can be used after the The authors found no adverse effect of carbon monox- process stream passes the separation column of such a ide on the nickel-base alloys at the temperatures and system, if desired. pressures explored. Indeed, the presence of CO was Actual corrosion data obtained in the various parts of a reported to reduce corrosion, particularly pitting of iron- hydrocarbon oxidation unit are shown in Table XXVIII. base alloys. Contamination of the process stream with chlorides, metal salts, or other inorganic materials introduced in the feed streams or by leakage into the system can have disastrous 2. Acetic Acid Storage and Shipping effects as noted under the discussion on the effect of Stainless steels are used for the construction of storage contaminants. vessels for acetic acid to maintain the highest quality of the acid. Vessels of the dished-head type, API variety, or external support construction have been used for this c. Methanol-Carbon Monoxide Synthesis purpose. The latter has been used extensively in the wine The methanol-carbon monoxide process is one of the fields for the storage of wine in the past and provides the newer and economically attractive routes for the produc- most economical method of fabricating field tanks for acetic tion of acetic acid. In this process, all factors contributing acid storage if the size is not excessive. to higher corrosion rates are encountered—a 50-75% acid When choosing the stainless steel grade, consideration concentration, higher temperatures, higher pressures and should be given to the temperature of storage proposed and the use of halide salts as catalysts. The use of boron to the grade of acid required. In the northern latitudes, trifluoride as a catalyst did not become popular because of it will be necessary to provide a heating coil to assure fluid the exceedingly high pressures involved, but the use of iodides in combination with other metallic salts has increased in popularity throughout the world. No data directly derived from the field exposure of alloys in operating equipment of the methanol-carbon monoxide process are available. However, Togano and others have delineated the problem facing the corrosion engineer when materials selection must be made for these processes.16-18 The reaction vessel must be made of the most resistant alloys available. In all probability, the process stream must be carried through the first two still columns before the halogen is reduced to a level sufficient to allow the use of the austenitic stainless steels. Even at this point, care must be exercised in selecting a stainless steel because the acid is not derived from an oxygenated reaction. Thus, no peroxides or oxidizing gases from their decomposition will be available to aid in passivity of the stainless steel. Certain of the higher nickel alloys do appear to have promise in this process. Tables XXIX and XXX taken from the Tagano reports show HASTELLOY alloys B and B-2 to be worthy of thorough testing along with titanium, zirconium and tantalum for the high pressure, high temperature reaction area. Once the temperature is reduced to the normal recovery conditions, the use of nickel-molybdenum and nickel-copper alloys appears attractive even with the catalyst salts present. It also appears that INCOLOY alloy 825 should be evaluated with close attention to make sure that the resistance to pitting shown in Table XXX is consistent. As indicated, once the halide salts are removed, the conventional materials used for the Of the 15 miles of pipe used in this storage terminal for handling separation and recovery of the acid can be employed. organics, 3 miles are of Type 316 stainless steel. This material protects the purity of formaldehyde, acetic acid and propionic acid.

Page 28 conditions for the acid (m.p. 16 ºC or 61 ºF). For this service, the coil is usually constructed of Type 316L stainless steel. Heat transfer on the surface of Type 304 stainless steel can produce excessive corrosion at normal steam temperatures. The vessel proper can be constructed of Types 304, 304L, 321, 347, 316, or 316L stainless steels. If a truly meticulous grade of acetic acid is required, such as USP grade, it will be necessary to use the molybdenum- containing grade of stainless steel if temperatures are to exceed 50-60 ºC (122-140 ºF). In this range, a minute amount of metallic contamination of acetic acid can occur in contact with the Type 304 analysis or other grades not containing molybdenum. The use of a molybdenum- containing stainless steel moves this point of initial The forward tanks in this double-skinned barge are clad with Type 316 contamination to some 70-80 ºC (158-176 ºF) before any stainless steel, capable of transporting organic acids as well as other detectable metallic ion is picked up by the acids.5 liquid cargo. When using the stainless steels for tankage equipment in a meticulous service, it is advisable to clean (pickle, passivate) the interior of the vessel to remove all traces of iron contamination that might have been embedded in the 3. Vinegar Production and Storage stainless steel at the mill. Sulfamic acid, nitric acid, oxalic All vinegars contain acetic acid in addition to variable acid, or other acids as suggested by ASTM A 380 can re- amounts of nonvolatile organic acids such as malic and move the embedded iron and at the same time provide a citric acids and smaller amounts of succinic and lactic uniform clean surface for the stainless steel. Since the acids. The term “grain strength” is used to express the more aggressive acids can cause intergranular corrosion of acetic acid concentration, which is ten times the acetic sensitized stainless steels, it appears prudent to utilize a acid content. Protection of the vinegar from metal low carbon or stabilized grade if fabrication by welding is contamination, particularly iron and copper, has led to the anticipated. use of the austenitic stainless steels for both production Shipping containers constructed of stainless steel and storage. Table XXXI shows that both Types 304 and provide the greatest durability combined with the best 316 stainless steels are unaffected in 40-320 grain vinegar preservation of the refined acetic acid of all materials at the -17 to 35 ºC (2 to 95 ºF) process temperatures available today. Tankers have stainless steel-lined com- involved. Because of the low temperatures, intergranular partments for shipment of the organic acids and other corrosion of sensitized stainless steel is not a problem. corrosive products. If entire compartments are not justified Although 120 grain (12 per cent acetic acid) is a common on tankers for conveying the acetic acid, deck tanks can be strength, the particular plant at which this test was run added which are durable and free of harmful corrosion in produces up to 300 grain vinegar in Type 304 stainless the severe exposures of marine transportation. Complete steel equipment and piping without corrosion problems or barges have been constructed using stainless steel for product contamination. meticulous care of the product during shipment. Tank cars constructed of stainless steel have been used for 40 years on the rails for acid shipments as well as to provide the P. Acetic Anhydride versatility required for the shipments of other aggressive Acetic anhydride has long been made as a co-product in commodities. the “dual” oxidation of acetaldehyde to acetic acid. With In the smaller containers, the austenitic stainless steels the many streams in this process containing both acetic remain unparalleled as the material of construction for acid and the anhydride, it is important to understand the drums, cans and other items used for the shipment of effect of small amounts of anhydride residual in hot acid acetic acid. With the higher area-to-volume ratios existing streams. However, the anhydride itself is only mildly in the small containers, it is imperative that no corrosion corrosive. In the absence of acetic acid, distillation in occur on the container walls to contaminate the acid. For Type 304 stainless steel equipment is acceptable. this reason, the stainless steels constitute standard con- In the newer process where acetic acid or acetone is struction identified as ES and ESM (DOT designation for cracked to ketene, which is then reacted with acetic acid to Types 304 and 316 stainless steels) drums and cans for form the anhydride, it is reported that Type 316 stainless acetic acid shipments. These not only provide good steel is fully satisfactory for the construction of distillation protection of the acid during long periods of shipment and columns and other process equipment. However, Type storage, but are durable and reusable for many years 316L stainless steel is often selected so that the equipment because of the good strength and external corrosion is more versatile and can be used for other organic acid resistance of the stainless steel container. Stainless steel services where more stringent conditions might exist. containers are readily cleaned on the inside to provide a In the process utilizing acetic acid as the starting spotless, uncontaminated surface for reuse. material, the cracking tubes are of prime interest.23 Once

Page 29 TABLE XXXI Corrosion of Stainless Steels in Vinegar Production

Corrosion Rate

Test 1 Test 2 Test 3 Test 4 Alloy mm/y mpy mm/y mpy mm/y mpy mm/y mpy

Type 304 Stainless Steel Nil* Nil Nil Nil Nil Nil Nil Nil Type 316 Stainless Steel Nil Nil Nil Nil Nil Nil Nil Nil Type 304 Stainless Steel Nil Nil Nil Nil Nil Nil Nil Nil sensitized for 1 hour at 677 ºC (1250 ºF)

*No detectable attack in the form of general corrosion, pitting or crevice corrosion.

Test 1 Test 2 Test 3 Test 4 Storage Storage Location Tank Accumulator Freezer Tank Vinegar Concentration 40-66 80-122 50-300 80-320 (Grain) Temperature Range ºC 21-35 27-34 –17 to –2 0-16 ºF 70-95 80-93 2-28 32-60 Test Duration all tests 150 days

the acetic acid is fully vaporized, the stream is essentially TABLE XXXII innocuous from a corrosion standpoint. However, proper- Deterioration of Alloys in Glacial Acetic Acid Vapors at ties of the cracking tube alloy are significant. The catalytic 750 C (1382 F) properties of nickel can cause breakdown of hydrocarbons at high temperatures. For this reason, various nickel-free Average Penetration Initial Exposure Second Exposure alloys have been developed (Fe-Cr, Fe-Cr-Al, Fe-Cr-Al-Si) 200 hours 100 hours for use in such services. However, the operating temperatures of 700-750 ºC (1292-1382 ºF) can develop Metal mm/y mpy mm/y mpy sigma and other adverse metallurgical conditions in the Type 430 Stainless Steel .48 19 1.22 48 iron-chromium alloys. To make furnace operations less Type 446 Stainless Steel – – .91 36 critical and to obtain improved fabricability, the use of cast ACI HK Alloy .18 7 .41 16 austenitic alloys was explored. It was found that the inner surface of the tubing was rapidly coated with a deposit of carbon which sealed the process stream from catalytic effects conferred by the metal surface. Thus, advantage can be taken of the better ductility and fabricability of the austenitic alloys for such service. Rates of degradation of the various alloys caused by the oxidation reactions that occur in the environment are shown in Table XXXII. Handling of the acetic anhydride and its dilution with acetic acid presents no problem other than that described under the processing of acetic acid. Type 304 stainless steel is eminently satisfactory for the distillation, storage, or shipment of the anhydride. Nickel plating showed a nil rate of attack in acetic anhydride at ambient temperature during a 121-day test.

Type 304L stainless steel equipment and piping and ACI CF-8M valves for metering acetic anhydride to process kettles. Courtesy Walworth Company-Aloyco Valves.

Page 30 PART III. OTHER ORGANIC ACIDS

A. Formic Acid drippage of a formic acid-water azeotrope impinges on the metal surface. As with other one-carbon homologues of an organic Table XXXIV compares the corrosion of Type 316 family, formic acid exhibits unique properties. The acid is stainless steel with a number of other alloys in a closely more highly ionized than are most other members of the controlled laboratory test. Some anomalies are apparent, group and reacts readily with many oxidizing and reducing but in general the data reflect corrosion rates to be compounds. This potent reactivity is apparent also in the expected in equipment handling boiling formic acid of the reaction with metals. Formic acid is the most aggressive of concentrations shown. As in the case of acetic acid, copper all organic acids containing only one carboxyl group. This and the cupro-nickel alloys are useful for such service in fact and the singular properties of the molecule require the absence of oxygen or other oxidants. The addition of that thorough testing of materials be conducted in any nickel to the copper makes the resulting alloy somewhat medium known to contain the acid. less sensitive to the presence of oxidants. Comments regarding corrosion by formic acid were Data for a much wider range of alloys in aerated and introduced in the section on acetic acid, inasmuch as many unaerated acid are provided in Table XXXV The presence commerical processes today for producing acetic acid also of air in the test medium has the effect anticipated by contain formic acid. A review of Tables 11, IV and XXI, decreasing the rate of attack on those alloys forming among others, will show the more aggressive character of protective oxide films and increasing the corrosion of process streams containing formic acid. In general, the copper alloys, nickel and MONEL alloy 400. Note that same materials of construction suitable for handling acetic alloying a stainless steel with higher amounts of chromium acid can be used for the higher concentrations of formic and nickel does not improve the resistance of the alloy acid. The corrosion of a specific alloy will be slightly (Type 310 vs. Type 304 stainless steels), but the addition greater when exposed to formic acid at the same tempera- of molybdenum produces a much more corrosion resistant ture. alloy (Types 316 and 317 stainless steels). The major area for concern relates to concentrations of The data of Table XXXV also provide an interesting aqueous formic acid between 50 and 90 per cent. In this illustration of the importance of testing techniques in zone, the corrosion rate for Type 316 stainless steel varies providing meaningful information. For example, the ma- greatly and can be higher than desirable for commercial jority of corrosion rates for specimens of Types 316 and applications. The variable test data reported probably 317 stainless steels and CARPENTER alloy 20 show relate to the period of passivity of the stainless steel during greater attack in the vapor exposure than when the the test, because the presence of the water would tend to specimens were fully immersed. This phenomenon would extend the life of passive films on the alloy surface. Some be unrecognized if only the usual immersion test were of the more consistent laboratory data, which agree well used. Yet a distillation column will have both liquid and with field experience, are shown in Table XXXIII. Note vapor exposures which must be analyzed before selecting the aggressive attack on the Type 316 stainless steel until a material of construction, and the data obtained from the formic acid concentrations of about 90 per cent are vapor exposures in these tests suggest further avenues of encountered. High rates of attack are experienced where exploration before making a final decision.

TABLE XXXIII Corrosion of Type 316 Stainless Steel in Boiling Formic Acid Solutions Test Conditions: Specimens exposed in liquid of boiling, aqueous formic acid solutions under an- aerobic conditions for 72 hours.

Corrosion Rate Liquid Vapor Condensate* Concentration of Formic Acid, % mm/y mpy mm/y mpy mm/y mpy 50 .38 15 .41 16 .46 18 70 .33 13 .48 19 .89 35 78 .36 14 .51 20 .38 15 90 .15 6 .46 18 .61 24 97 .15 6 .13 5 .25 10 100 .11 4 .08 3 .25 10

*Condesate falling on one side of vapor area specimen.

Page 31 TABLE XXXIV Corrosion of Five Alloys in Boiling Aqueous Formic Acid Solutions Test Conditions: Average rate of duplicate specimens exposed in boiling 100-107 ºC (212-223 ºF) solutions for 96 hours except as noted. No aeration or deaeration.

Corrosion Rate

Type 304 Type 316 C70600 Stainless Steel Stainless Steel (90-10 Formic Acid Test A Test B* Test A Test B* Copper Cupro-Nickel) Titanium mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy

1 .18 7 .36 14 .08 3 <.03 < 1 .03 1 .03 1 – – 5 .79 31 1.07 42 .05 2 .20 8 .03 1 03 1 – – 10 1.34 53 1.52 60 25 10 .20 8 .03 1 .03 1 13 5 20 1.93 76 1.75 69 .28 11 .20 8 .20 8 41 16 2.41 95 40 3.45 136 2.39 94 .10 4 .25 10 .12 5 .33 13 – – 50 4.24** 167** 2.11 83 .51** 20** .28 11 .25 10 .53 21 3.05 120 60 3.45** 136** 2.11 83 .46** 18** .23 9 .05 2 .03 1 – – 70 4.04** 159** 2.31 91 .48** 19** .25 10 .76 30 .71 28 – – 80 4.29** 169** 2.13 84 .48** 19** .25 10 .20 8 13 5 – – 90 3.28** 129** 2.11 83 .28** 11** .28 11 .23 9 .18 7 <.03 <1

*Test solution changed each 24 hours of the 96-hour test. **Test discontinued after 48 hours because of concentration of corrosion salts in solution.

TABLE XXXV Corrosion of Alloys in Boiling Formic Acid Solutions Test Conditions: Laboratory test results averaged from three separate 48-hour test periods in most cases. Tests conducted with and without aeration in acid concentrations noted.

Corrosion Rate

10% 50% 90% 99%

Unaerated* Unaerated* Aerated Unaerated* Aerated Unaerated Liquid Vapor Liquid Vapor Liquid Vapor Liquid Vapor Liquid Vapor Liquid Vapor Alloy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy

Mild steel – – – – – – – – – – – – 24.13 950 – – – – – – – – – – Type 430 – – – – – – – – – – – – 11.26 444 .89 35 – – – – – – – – stainless steel Type 304 – – – – – – – – – – – – 10.41 410 1.52 60 – – – – – – – – stainless steel Type 310 – – – – – – – – – – – – 10.21 402 .61 24 – – – – – – – – stainless steel Type 316 .18 7 .23 9 .23 9 .53 21 <.03 <1 74 29 .36 14 .18 7 < 03 < 1 .79 31 .13 5 .10 4 stainless steel Type 317 – – – – – – – – – – – – .13 5 .13 – – – – – – – – – stainless steel CARPENTER – – – – – – – – <.03 <1 30 12 .05 2 – – 03 <1 .66 26 – – – – alloy 20 HASTELLOY – – – – – – – – .10 4 03 1 .05 2 – – 10 4 <.03 <1 – – – – alloy C HASTELLOY – – – – – – – – .51 20 10 4 .08 3 – – 08 3 .03 1 – – – – alloy B INCONEL – – – – – – – – – – – – .76 30 .64 25 1.24 45 .20 8 – – – – alloy 600 MONEL <.03 <.1 .08 3 .23 9 .08 3 – – – – .03 1 .03 1 7.62 300 .23 9 – – – – alloy 400 Nickel 200 .15 6 .15 6 .36 14 .43 17 .84 33 2.24 88 .61 24 .28 11 69 27 .41 16 – – – – Copper .08 3 .18 7 .13 5 .28 11 – – – – .25 10 .15 6 14.30 563 37.80 93 – – – – EVERDUR 1010 – – – – – – – – – – – – .18 7 .23 9 3.30 130 .69 27 – – – – Aluminum 3003 31.09 1224 21.89 862 – – – – 31.70 1248 10.16 400 7.62 300 – – 10 4 <.03 <1 – – – – Titanium .13 5 – – 2.92 115 – – – – – – <.03 <1 – – – – – – – – – – Chromium .51 20 – – – – – – – – – – – – – – – – – – – – – – carbide with 12%

nickel binder

*Boiling solution without sparging of any gas.

Page 32 Table XXXVI demonstrates the excellent corrosion alloys at temperatures above those obtained at one at- resistance of HASTELLOY alloy C-276 in formic acid mosphere of pressure. Consequently, the effect of solutions. Throughout the entire range of temperatures increasing the temperature on the corrosion rate of the and concentrations of formic acid, the nickel-base molyb- common alloys must be determined. Table XXXVIII denum-chromium-iron alloy exhibits good stability. presents a composite of the data contained in the report However, in formic acid exposures, more than in acetic of Miller and Wachter on corrosion by acids at high acid exposures, the HASTELLOY alloys B and B-2 temperatures.24 Of greatest interest is the information for materials must be given consideration as materials of the Type 316 stainless steel. The rates are higher for this construction. Other nickel and cobalt-base alloys can be alloy than would be expected for a test of longer useful for specific field applications when the metallurgi- duration. The important inference to be made is that the cal properties of these alloys are required. rate of attack approximately doubles for each 15°C Applications involving heating are more demanding (27°F) increase in temperature. (It should be recognized than isothermal exposures for an alloy. (See comments in that this is a very rough approximation that does not the section on Acetic Acid—Effect of Temperature.) always hold true.) Corrosion tests in many other media Calandria or vaporizer tubes require construction with a show a similar relationship rather than one conforming to corrosion-resistant alloy. Table XXXVII provides data the ideal Arrhenius equation. for six alloys tested under heat transfer conditions. The Figure 5 and isocorrosion charts (Figures 6 through rate of attack on the austenitic stainless steel alloys 11), originally published by the NACE,25 indicate the increases sharply with a higher metal temperature under corrosion behavior of several alloys in formic acid. heat transfer conditions. CARPENTER alloy 20Cb-3 and Isocorrosion charts are intended only as guides; there are HASTELLOY alloy B show rates of attack sufficiently conditions where higher or lower rates can prevail. In low to warrant their selection under most of these fact, Figure 5 shows much lower rates for Type 316 conditions. Unfortunately, data for HASTELLOY alloy stainless steel in boiling formic acid than is shown in the C-276 and INCONEL alloy 625 are not included, but isocorrosion chart, Figure 6. It is believed that Figure 5 is they would be expected to be as good or better than that more representative of pure formic acid and that the shown for the “B” alloy. higher rates shown by the isocorrosion chart must reflect Many commercial applications require the use of the the presence of unidentified impurities.

TABLE XXXVI Corrosion of HASTELLOYS and Related Alloys in Formic Acid Solutions Laboratory data obtained without aeration or deaeration using five 24-hour test periods. (Courtesy of the Cabot Corporation, Stellite Division.)

Corrosion Rate % Temperature HASTELLOY HASTELLOY HAYNES MULTIMET Formic Acid ºC ºF alloy B alloy C-276 alloy No. 25 alloy mm/y mpy mm/y mpy mm/y mpy mm/y mpy 10 26 78.8 .03 1 <.03 <1 Nil Nil Nil Nil 66 150 .23 9 <.03 <1 Nil Nil Nil Nil Boiling .08 3 .13 5 .20 8 .10 4 20 26 78.8 .05 2 < .03 <1 <.03 <1 <.03 <1 66 150 .25 10 <.03 <1 <.03 <1 <.03 <1 Boiling .10 4 .18 7 .25 10 .15 6 30 26 78.8 08 3 <.03 <1 – – – – 66 150 .30 1 2 <.03 <1 – – – – Boiling .08 3 .20 8 – – – – 40 26 78.8 .08 3 <.03 <1 <.03 <1 <.03 <1 66 150 .28 11 <.03 <1 Nil Nil Nil Nil Boiling .05 2 .13 5 .38 15 .20 8 60 26 78.8 .05 2 < .03 <1 <.03 <1 <.03 <1 66 150 .25 10 <.03 <1 Nil Nil <.03 <1 Boiling .03 1 .18 7 .51 20 .15 6 90 26 78.8 <.03 <1 <.03 <1 <.03 <1 Nil Nil 66 150 .03 1 <.03 <1 <.03 <1 Nil Nil Boiling <.03 <1 .05 2 .15 6 .08 3

Page 33 Process facilities for handling formic acid are normally contaminants present in the acid, the temperature of the constructed of Type 316L stainless steel, copper, or the system and the type of cooling water used, it is not unique cupro-nickels. Data obtained by the exposure of alloys in a to find a distillation column and accessories to be con- formic acid distillation column are shown in Table XXVIII. structed of a combination of Type 316L stainless steel, Other data generated by the testing of alloys in a 90% C70600 (90-10 cupro-nickel), ACI CN-7M castings and formic acid still are contained in the reference NACE HASTELLOY alloy C-276. Other materials combinations 25 report. Depending on the acid concentration, the type of are obviously possible from a perusual of the data, but

TABLE XXXVII Corrosion by Formic Acid Under Heat Transfer Conditions

Temperature Corrosion Rate Formic Acid Without With Heat Type 304 Type 316 CARPENTER HASTELLOY INCONEL MONEL Test Medium Heat Transfer Transfer* Stainless Steel Stainless Steel alloy 20Cb-3 alloy B alloy 600 alloy 400 ºC ºF ºC ºF mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy 10% aqueous 101 214 – – 18.85 742 .25 10 <.03 <1 .25 10 .89 35 3.38 133 – – 110 230 >25.4 >1000 .41 16 .05 2 1.27 50 1.85 73 16.26 640 – – 125 257 14.48 570 1.57 62 .20 8 1.42 56 1.68 66 >25.4 >1000 – – 140 284 14.48 570 1.85 73 .69 27 2.03 80 1.52 60 >25.4 >1000 50% aqueous 103 217 – – >25.4 >1000 .99 39 .15 6 .28 11 1.55 61 2.21 87 – – 110 230 >25.4 >1000 1.47 58 .23 9 .23 9 1.93 76 1.93 76 – – 125 257 >25.4 >1000 1.52 60 .33 13 .13 5 3.30 130 1.22 48 – – 140 284 >25.4 >1000 2.13 84 .31 12 113 5 2.92 115 2.54 100 89% aqueous 103 217 – – 18.19 716 .25 10 .13 5 <.03 <1 1.02 40 .03 1 – – 110 230 13.72 540 1.22 48 .10 4 .13 5 1.27 50 .56 22 – – 125 257 12.7 500 1.02 40 .15 6 .08 3 1.93 76 .84 33 – – 140 284 13.21 520 1.22 48 .25 10 .18 7 1.42 56 1.27 50

*Metal temperature. Reference 10. See that publication for apparatus and technique used

TABLE XXXVIII Corrosion of Alloys in Formic Acid at High Temperatures (Tests conducted in sealed pressure tubes) % Formic Acid 1 2* 4.6 24

Test Period, days 1 27 1 1

Test Temperature Corrosion Rate Alloy ºC ºF mm/y mpy mm/y mpy mm/y mpy mm/y mpy Type 410 stainless steel 170 338 – – – – 16.26 640 – – Type 430 stainless steel 170 338 – – – – 10.41 410 – – Type 446 stainless steel 170 338 – – – – .66 26 – – Type 304 stainless steel 150 302 – – .46 18 – – – – 170 338 – – – – 3.56 140 – – Type 310 stainless steel 170 338 – – – – 2.36 93 – – Type 316 stainless steel 100 212 – – – – .58 23 1.04 41 150 302 .13 5 .10 4 1.52 60 3.05 120 170 338 .20 8 – – 1.83 72 – – 200 392 .89 35 – – 1.68 66 3.30 130 Type 317 stainless steel 150 302 – – .05 2 – – – – 170 338 – – – – 1.60 63 – – HASTELLOY alloy C 170 338 – – – – .10 4 – – HASTELLOY alloy B 170 338 – – – – .23 9 – – INCONEL alloy 600 150 302 – – .08 3 – – – – 170 338 – – – – 3.30 130 – – Nickel 200 150 302 – – .03 1 – – – – 170 338 – – – – 2.34 92 – – MONEL alloy 400 150 302 – – .03 1 – – – – 170 338 – – – – .89 35 – – C71500 (70-30 Cupro-nickel) 150 302 – – .03 1 – – – – Copper 150 302 – – .03 1 – – – – 170 338 – – – – .20 8 – – Silver 170 338 – – – – .15 6 – – Aluminum 1100 170 338 – – – – 10.16 400 – – DURIRON 170 338 – – – – 7.37 290 – –

*Also contained 1.5% formaldehyde. Reference 24

Page 34 extensive testing of the candidate alloys must be conducted beforehand to assure an adequate economic life of the equipment. When appraising stream compositions for corrosion testing or the designation of materials of construction, it is important to understand the unstable nature of the one- carbon compounds. Formaldehyde reacts readily with oxygen to produce the acid, and it is difficult to handle and store the aldehyde without generating sufficient formic acid to make a corrosive agent out of what would otherwise be a rather innocuous compound. It is for this reason that Type 304 stainless steel is often selected as the material of construction for formaldehyde storage tanks. Not only does the use of the stainless steel provide a trouble-free material of construction, but the lack of contamination of the FIG 7–Isocorrosion Chart for Type 304 Stainless Steel in Formic Acid aldehyde maintains good color in the solution and reduces the rate of oxidation of the product to additional acid. A brief summary of proper formaldehyde storage is provided by Teeple in reference 26. Formate esters are also most unstable. The methyl ester is often encountered in process streams, and, when any water is present, must be considered as contributing to a significant acidity in the medium.

FIG 8–Isocorrosion Chart for Wrought “20 Type” Alloy in Formic Acid

FIG 5–Comparison of Types 304 and 316 Stainless Steels in Various Concentrations of Boiling Formic Acid FIG 9–Isocorrosion Chart for HASTELLOY alloy B in Formic Acid

FIG 10–Isocorrosion Chart for HASTELLOY alloy C (C-276) in Formic FIG 6–Isocorrosion Chart for Type 316 Stainless Steel in Formic Acid Acid

Page 35 acetic acid streams and the contaminant may control the corrosion rate. Acrylic acid per se is not required as an end product in large quantities as is the ester. Consequently, many of the commercial processes are designed to prepare the ester from a basic organic molecule without isolating the acrylic acid. Regardless of the route to the final product, however, all processes produce the acid as an intermediate with subsequent esterification. Acrylic aid, or the acid-ester in one sequence, has been produced by at least nine different processes. Three basic reactions have been used predominantly.27 These are the acetylene-carbon monoxide, the nitrile and the propylene oxidation processes. Today, the direct oxidation of pro- FIG 11–Isocorrosion Chart for MONEL alloy 400 in Formic Acid pylene to acrolein and finally to the acid in a one or two- step process is the most popular. B. Acrylic Acid The acetylene-carbon monoxide process relies on the catalytic activity of nickel carbonyl in the presence of a Acrylic acid is the most common 3-carbon acid encoun- strong acid (hydrochloric) to prepare the acid. Obviously, tered in industry. The great reactivity of this unsaturated the presence of the HCl controls the corrosive conditions acid makes the material and its esters useful in the existing in the process. Even at the low reaction tempera- preparation of a wide variety of resinous products used in tures, 30-52 ºC (86-126 ºF), the reaction step is most manufacturing plastics, paints, textiles, paper and pol- corrosive and is conducted in glass, ceramics and ishes. There are probably some one billion pounds of the TEFLON* equipment. Following this step, the nickel- esters produced in the USA today, of which 75% is ethyl base molybdenum alloys can be used, and as the mineral acrylate. acid is removed, the alloy content of the materials of The significant fact about handling acrylic acid is that construction can be reduced until Type 316 stainless steel temperatures are maintained as low as possible to prevent is acceptable to handle the acrylic acid. homopolymerization of the acid. Distillation in vacuum The nitrile procedure for production of the acid suffers stills, dilution with innocuous solvents, storage of the the same drawback from a materials standpoint with product at the lowest convenient temperatures and reaction sulfuric acid used to produce an organic sulfate which can of the acid in polymerization processes at low temperatures be released to the acid or directly reacted to form the ester. are common process conditions. Consequently, exposure Ammonium acid sulfate is formed as a by-product, and conditions in most acrylic acid applications are less severe the higher process temperatures, 150 ºC (300 ºF) region, than in the saturated acid processes. generate SO2 and SO3 which must be contended with in As with propionic acid, the acrylic acid can be consid- equipment design. The problems encountered are essen- ered as equivalent to acetic acid in aggressiveness at a tially the same whether using acrylonitrile or ethylene given temperature. However, the contaminants in acrylic oxide and hydrogen cyanide as the starting materials. acid process streams can be different from those found in Table XXXIX provides typical corrosion data for a nitrile type process operation through the distillation of the crude acid. Sets of data are given for two exposures in the same equipment (top head of reactor condenser) to show the wide variation in corrosion rates experienced during different periods of operation. Such large changes in the corrosive environment may be found wherever a mineral acid is mixed with an organic acid. When using metallic materials of construction in such processes, the operation must be conducted with particular care to maintain favorable conditions for a maximum life of the equipment. A few hours of adverse operating conditions can severely damage equipment under such circumstances. Monitoring of the corrosion by continuous or sequential testing is also advised to detect periods of unusual corrosion. This process is obviously most corrosive until the decomposition products of the inorganic acid and salts are removed. The usual materials, primarily This HASTELLOY alloy C-276 tube bundle is used in the reboiler in the the austenitic stainless steels, are then used to process the manufacture of acrylic monomers. It was found to be the most economical material of construction for this severely corrosive service. acrylic acid. Courtesy Stellite Division, Cabot Corporation.

*Trademark of E.I. duPont de Nemours & Co.

Page 36 TABLE XXXIX Corrosion of Alloys in a Nitrile-Type Acrylic Acid Process

Corrosion Rate

Exposure* 1 2 3A 38 4 5 6 7 8

Alloy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy

Type 304 >7.62 >300 2.24 88 10.16 > 400 – – .03 1 <.03 <1 08 3 03 1 <.03 <1 Stainless Steel Type 316 >7.62 >300 2.11 83 10.16 400 – – Nil Nil <.03 <1 <.03 <1 <.03 <1 <.03 <1 Stainless Steel Type 201 – – 3.00 118 – – – – Nil Nil Nil Nil 13 5 – – <.03 <1 Stainless Steel CARPENTER >7.62 >300 64 25 4.98 196 – – Nil Nil <.03 <1 Nil Nil – – <.03 <1 alloy 20 INCONEL >7.62 > 300 – – 4.57 180 – – – – 03 1 20 8 <.03 <1 – – alloy 600 INCONEL – – – – – – .89 35 – – – – – – <.03 <1 – – alloy 625 HASTELLOY 7.11 280 – – 2.95 116 74 29 – – – – – – <.03 <1 – – alloy C HASTELLOY 1.35 53 – – 74 29 25 10 – – – – – – – – – – alloy B MONEL >7.62 >300 2.54 100 2.64 104 – – .05 2 03 1 15 6 .20 8 > 7.62> 300 alloy 400 C70600 (90-10 – – – – – – 1.14 45 – – – – – – – – – – Cupro-nickel) Copper 6.09 240 6.35 250 2.95 116 1.17 46 .05 2 05 2 23 9 76 30 >7.62 > 300 Lead, >7.62 >300 – – 5.28 208 – – – – 25 1 0 30 12 > 5.08 > 200 – – chemical Aluminum 3003 >7.62 >300 – – 10. 16 > 400 – – – – 38 1 5 33 13 > 7.62 > 300 – – Titanium .86 34 – – 1.35 53 13 5 .03 1 – – <.03 <1 – – <.03 <1 Zirconium .03 1 – – <.03 <1 <.03 <1 – – – – – – – – – – Tantalum – – – – – – <.03 <1 – – – – – – – – – – *1 –Reactor liquid for 1600 hours at ca. 125 ºC (257 ºF). 2 –Reactor vapor line to condenser for 190 hours at ca. 130 ºC (266 ºF). 3A –Reactor vapor condenser top head for 1200 hours at ca. 130 ºC (266 ºF). 3B –Same as 3A during different period for 2600 hours. 4 –Condensate from exposure No. 3 at ca. 30 ºC (86 ºF) for 190 hours. 5 –Bottom of extractor for 1600 hours at ca. 30 ºC (86 ºF). 6 –Top of extractor for 1600 hours at ca. 30 ºC (86 ºF). 7 –Base of crude acid stripping still for 4000 hours at 110 ºC (230 ºF). 8 –Overhead liquid-vapor from exposure No. 7 (feed to acrylic acid refining still) for 3 days at 88 ºC (190 ºF) (air present).

TABLE XL Corrosion of Alloys in Propylene Oxidation Process for Acrylic Acid

Corrosion Rate Exposure* 1 2 3 4 5 6 7 8 9 10 11 12 Alloy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy Type 304 <.03 <1 <.03 <1 <.03 <1 <.03 <1 <.03 <1 <.03 <1 <.03 <1 <.03 <1 <.03 <1 <.03 <1 <.03 <1 <.03 <1 Stainless Steel Type 316 <.03 <1 <.03 <1 <.03 <1 <.03 <1 <.03 <1 <.03 <1 <.03 <1 <.03 <1 <.03 <1 <.03 <1 <.03 <1 <.03 <1 Stainless Steel CARPENTER <.03 <1 – – – – – – – – <.03 <1 <.03 <1 <.03 <1 <.03 <1 <.03 <1 <.03 <1 <.03 <1 alloy 20 HASTELLOY – – – – – <.03 <1 – – <.03 <1 – – – – <.03 <1 <.03 <1 alloy C INCONEL – – – – – – – – – – <.03 <1 – – <.03 <1 – – – – <.03 <1 – – alloy 625 INCONEL – – <.03 <1 <.03 <1 <.03 <1 – – <.03 <1 – – <.03 <1 – – – – <.03 <1 – – alloy 600 MONEL – – .25 10 .25 10 .03 1 – – – – – – – – – – – – .13 5 .48 19 alloy 400 Copper – – .97 38 .81 32 .20 8 .05 2 – – – – – – .13 5 .08 3 .53 21 .91 36 Nickel 200 – – .28 11 <.03 <1 .03 1 .05 2 – – – – – – – – – – – – – –

*1–Propylene oxidation converter at 400 ºC (752 ºF) for 180 days. 7–Acrolein oxidation converter at 220 ºC (428 ºF) for 220 days. 2–Quench line from converter at 110 ºC (230 ºF) for 300 days. 8–Oxidation reactor quench line at 80 ºC (175 ºF) for 220 days. 3–Scrubber circulating line at 85 ºC (185 ºF) for 31 days. 9–Solvent extraction column overhead at 42 ºC (108 ºF) for 8 days. 4–Acrolein stripper base at 140 ºC (284 ºF) for 300 days. 10–Water layer from solvent column separator at 35 ºC (95 ºF) for 330 days. 5–Crude acrolein separator pot at 25 ºC (77 ºF) for 180 days. 11–Solvent recovery column base at 105 ºC (221 ºF) for 110 days. 6–Acrolein refining still base at 105 ºC (221 ºF) for 20 days. 12–Recovery column for No. 10 above at 95 ºC (203 ºF) for 360 days.

Page 37 TABLE XLI Corrosion of Stainless Steels During the Preparation of β-Methacrylic Acid

Corrosion Rate Type 304 Type 316 CARPENTER HASTELLOY HASTELLOY Silicon Aluminum Exposure DURIRON Stainless Steel Stainless Steel alloy 20 alloy C alloy B Bronze 3003 mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy Oxidation of the acid by .03 1 .03 1 <.03 <1 <.03 < 1 – – – – – – – – air blowing of the aldehyde at 40 ºC (104 ºF) Distillation of the crude <.03 <1 <.03 <1 <.03 <1 <.03 < 1 .03 1 .05 2 Nil Nil .51 20 oxidation product at ca. 55 ºC (131 ºF) (liquid exposure) As above (vapor exposure) <.03 <1 <.03 <1 <.03 <1 <.03 <1 .38 15 1.88 74 <.03 <1 .23 9

TABLE XLII pylene-acrolein process. The oxidation product of the ß - Corrosion of Alloys in Dimethyl Acrylic methacrylic aldehyde would contain some oxidized de- (Seneceoic) Acid composition compounds such as formic and acetic acids. However, the reasonable low temperatures at which the Field test obtained by exposure of alloys in the overhead stream of a refining column at 145ºC (293ºF) product must be handled, combined with the low con- for three days. centration of such contaminants, does not produce an aggressive medium for the stainless steels. The data of Table XLI show results obtained in oxidation and primary Corrosion Rate distillation steps of the process. Alloy mm/y mpy Further information relating to the acrylic acids is Type 304 Stainless Steel 1.83 72 contained in Table XLII. In processing the more stable Type 316 Stainless Steel (annealed) .18 7 dimethyl acrylic acid at the higher temperatures, it is Type 316 Stainless Steel (sensitized) .18 7 apparent that a Type 316 stainless steel is required. The HASTELLOY alloy C <.03 < 1 temperature of the operation exceeds the point where the HASTELLOY alloy B .05 2 Type 304 stainless steel is adequately resistant. MONEL alloy 400 .46 18 Copper 1.45 57

C. C3 Through C8 Acids The first of the remaining higher acids, the 3-carbon The major commercial approach to acrylic acid produc- propionic acid, is produced in considerable quantity. The tion today is the direct oxidation of propylene to acrolein acid and its unsaturated counterpart, acrylic acid, are very with subsequent oxidation to acrylic acid or a one-step similar to acetic acid in reactivity with metals. The oxidation with only the acid recovered. One advantage of corrosion rate of the common materials of construction is the process is the milder corrosive conditions existing essentially the same in propionic and acrylic acid as in throughout the unit. Steel and the austenitic stainless acetic acid at the same temperature. Certainly, all factors steels may be used for all equipment except where described as influencing the corrosion of alloys in acetic chloride stress-corrosion cracking of the stainless steels acid are applicable to corrosion mechanisms in the 3- requires the use of Alloy 600, Alloy 400, or other crack- carbon acids. resistant alloys. Table XL provides data regarding the Corrosion rates of various alloys in boiling propionic corrosion of a number of alloys in significant portions of a acid solutions are shown in Figure 12.5 Elder points out propylene oxidation process. Although the austenitic the anomalous results that can result from the short test stainless steels are resistant to the primary corrosive period used for these tests and the effect of dissolved agents throughout the process, the use of INCONEL alloy oxygen on the results. The beneficial effect of added 600 and other high alloys have been used in the process oxygen on austenitic stainless steels is not restricted to for the reason cited. laboratory tests but was also attained in the field as shown Similar data were obtained by the exposure of alloys in in Table XLIII. It is interesting to note that a maximum a plant preparing ß-methyl acrylic (crotonic, 2-buteneoic) rate of attack on the stainless steels appears to occur at acid. Types 304L and 316L stainless steels and CARPEN- approximately the same concentrations (60-80 per cent) as TER alloy 20Cb-3 were unattacked in process handling of found for acetic acid in boiling solutions. For welded the acid up to 90 ºC (194 ºF) in a process similar to that construction, the low carbon stainless steel grades should described for the production of acrylic acid by the pro- be employed unless it has been definitely established that

Page 38 welded regular carbon grades are free from intergranular corrosion in the heat-affected zones of welds. To supplement the curves of Figure 12, the data of Table XLIV summarize the resistance of several alloys to propionic acid solutions below the boiling point. When the temperature is raised appreciably and propionic anhydride is added to the acid, the stainless steels, including the iron-base nickel-chromium-copper-molybdenum alloys, are no longer useful as a material of construction. Table XLV shows data derived from a test conducted at 260 ºC (500 ºF). For all alloys considered for a specific service involving propionic acid, the data presented for acetic acid may be used as a general guide. It is important to use data acquired at the proper temperature, keeping in mind that the boiling point of propionic acid is much higher than HASTELLOY alloy C-276 replaced silver in this primary cooler for propionic that of acetic acid and that tests conducted below the acid. The alloy was found to have better resistance to thermal cycling than the boiling point are not the same as those made in a boiling precious metal. Courtesy of Stellite Division, Cabot Corporation. solution. Organic acids of greater chain length than the 3-carbon acids are produced in smaller quantity, but constitute an important group of products, primarily as intermediates in the preparation of pharmaceuticals, agricultural chemicals, food products, plasticizers and other end-use chemicals. creasingly stable with increasing chain length. Numerous The chemical characteristics of the longer monocarbox- tests conducted in butyric and higher acids indicate that ylic acids are important in interpreting the corrosive the exposure is innocuous until some specific temperature potential of the products. Complete miscibility in water of is reached, at which point sufficient dissociation is the two three-carbon acids (propionic and acrylic) is achieved to initiate and sustain corrosion. This critical achieved, but the solubility of the remaining acids de- temperature is higher for each succeeding higher homo- creases rapidly with increasing chain length. The extent of logue in the series. Thus, for a specific acid, a temperature dissociation of the dissolved acid remains essentially the of 190 ºC (374 ºF) may produce essentially no corrosion same as acetic acid. However, in the pure form, or in on a Type 304 stainless steel, but a temperature of 210 ºC organic dilutions of the acids, the higher acids are in- (410 ºF) may produce exceedingly high corrosion rates.

FIG 12—Corrosion of Alloys in Propionic Acid at the Boiling Temperature

Page 39 TABLE XLIII Effect of Oxygen on Corrosion of Stainless Steel in Propionic Acid Conditions: 95% propionic acid containing 2% water, alcohol, ketone and higher acids used in laboratory tests and processed in field.

Corrosion Rate Type 316 Type 304 Type 202 Type of Test Additive Temperature Exposure Stainless Steel Stainless Steel Stainless Steel ºC ºF mm/y mpy mm/y mpy mm/y mpy Laboratory None 122 252Liquid .15 6 .30 12 – – to to Vapor .20 8 .28 11 – – 135 275 Condensate .05 2 .36 14 – –

Laboratory Air Sparged 122 252 Liquid Nil Nil 1.63 64 – – to to Vapor Nil Nil .15 6 – – 135 275 Condensate Nil Nil Nil 01 – –

Laboratory 9 ppm H202 122 252 Liquid 01 0.3 .04 1.5 – – to to Vapor 01 0.2 .02 0.6 – – 135 275 Condensate Nil 0.1 Nil 0.1 – –

Laboratory 1 ppm H2O2+ 122 252 Liquid Nil Nil Nil Nil – – air sparged to to Vapor Nil Nil Nil Nil – – 135 275 Condensate Nil Nil Nil Nil – –

Laboratory 200 PPM CuSO4 122 252 Liquid Nil <0.1 Nil <0.1 – – to to Vapor Nil <0.1 Nil <0.1 – – 135 275 Condensate Nil <0.1 Nil <0.1 – –

Field Column Air and H2O2 110 230 Kettle Nil <0.1 Nil <0.1 Nil <0.1 processing the acid* injected to to Based on column Nil <0.1-0.1 Nil-.03 <0.1-1 Nil <0.1-0.1 in feed stream 137 279 Feed line Nil 0.1 Nil 0.1 Nil 0.1 Middle of column Nil 0.1 Nil 0.1 Nii <0.1 Top of column Nil <0.1 01 0.3 Nil <0.1

*Three separate field exposures made of 168-254 hours.

Table XLVI shows data generated by the laboratory whether the acid is refined or contaminated with the lower immersion test of five alloys in C2 through C10 acids. The acids (crude). The higher iron or nickel-base alloys difficulty with such laboratory tests relates to the exposure containing chromium and molybdenum exhibit the same of the copper alloys and the stainless steels. Organic acids excellent stability in the higher acids as noted in the one are excellent retainers of air in solution. Heating of the and two-carbon compounds. acid at temperatures below the boiling point does not Corrosion to be anticipated in a more modern process expel all the oxygen, and corrosion rates on the copper for the preparation of the longer acids is indicated in Table alloys will be higher than would be experienced in a closed XLIX. Here, the catalyzed oxidation of a straight-chain system devoid of oxygen. On the other hand, the stainless hydrocarbon to an eight-carbon acid produced no signifi- steels retain passivity for a longer time in such media cant corrosion of the stainless steels. Although only .13 before corrosion is initiated. Longer test periods, dynamic mm/y (5 mpy) corrosion of Type 304 stainless steel was test apparatus and a close control of the entire environ- obtained in this instance, the choice of Types 316 or 316L ment are important when attempting to identify specific stainless steels for such a reactor would be advisable to materials of construction for a proposed application. assure adequate resistance to variations in process condi- However, the data of this table are consistent with field tions that might occur. experience. As indicated by the laboratory tests, Types When working with the higher organic acids, it is 316 and 316L stainless steels have excellent resistance to difficult to provide test conditions and a length of ex- the acids to temperatures approaching the boiling point at posure sufficient to produce intergranular attack on sen- atmospheric pressure. For this reason, the approximate sitized stainless steel. The higher acids will produce boiling point temperature of each acid is listed in the table. selective attack on a structure containing carbide pre- The more extensive listing of alloys exposed in four, six cipitation, however, and the use of the L-grade or sta- and eight-carbon acids is given in Tables XLVII and bilized stainless steels at temperatures above 100 ºC XLVIII. The essential resistance of Type 316 stainless (212 ºF) is suggested as a safeguard, regardless of the test steel in organic acids is maintained in these higher acids data obtained.

Page 40 Combinations of sulfuric acid and the organic acids are passivity of the stainless steels in this medium. As often found in the process industry. The mineral acid is discussed in the section on acetic acid, the use of a heating added to catalyze certain reactions with the organic acid or coil in such an environment would pose a different to react with unwanted impurities in the acid. The effect of problem. Under heat-flux conditions, it is unlikely that adding one or two per cent of strong sulfuric acid to an the 300 series stainless steels would show adequate eight-carbon organic acid is shown in Table L. Under these resistance to such a mixture. Also, if a water wash of the conditions, Type 304 stainless steel was as resistant as the organic acid is to be made to remove the sulfuric acid, the Type 316 alloy in the temperature regions explored. The aqueous phase containing a dilute mineral acid could be anamolous data of test 4 suggest that the stability of the extremely aggressive to the 300 series alloys. Higher alloys stainless steels may be borderline under these conditions, of the “20” type for wrought materials or the CN-7M although even higher temperatures failed to destroy the castings would be minimal for resistance to the diluted passivity of the alloys. The strong oxidizing capacity of the mineral acid in the presence of the organic acid. concentrated sulfuric acid probably aids in maintaining

TABLE XLIV Corrosion of Stainless Steels in Propionic Acid Below the Boiling Temperature Conditions: Duplicate tests in various concentrations of propionic acid at 75 and 50 ºC (167 and 122 ºF) without aeration or deaeration.

Corrosion Rate

% Propionic Type 420 Type 304 Type 316 Acid Stainless Steel Stainless Steel Stainless Steel 75 ºC (167 ºF) 50 ºC (122 ºF) 75 ºC (167 ºF) 50 ºC (122 ºF) 75 ºC (167 ºF) 50 ºC (122 ºF)

mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy 99 2.54 100 .03 1 Nil Nil Nil Nil Nil Nil Nil Nil 80 52.32 2060 6.09 240 .05 2 .05 2 <.03 <1 .03 1 67 90.93 3580 9.27 365 .03 1 .05 2 Nil Nil Nil Nil 50 79.76 3140 1.65 65 <.03 <1 <.03 < 1 Nil Nil <.03 <1 33 39.88 1570 4.83 190 <.03 <1 Nil Nil <.03 < 1 <.03 <1 20 42.67 1680 1.57 62 <.03 <1 Nil Nil <.03 < 1 Nil Nil

Corrosion Rate

% Proponic Type 318 HASTELLOY HASTELLOY Acid Stainless Steel alloy C alloy B 75 ºC (167 ºF) 50 ºC (122 ºF) 75 ºC (167 ºF) 50 ºC (122 ºF) 75 ºC (167 ºF) 50 ºC (122 ºF) mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy 99 <.03 <1 Nil Nil Nil Nil Nil Nil .64 25 .15 6 80 <.03 <1 .03 1 Nil Nil Nil Nil .30 12 .61 24 67 Nil Nil Nil Nil .03 1 Nil Nil .28 11 .30 12 50 Nil Nil Nil Nil <.03 <1 Nil Nil .10 4 .38 15 33 <.03 <1 Nil Nil Nil Nil Nil Nil .08 3 .20 8 20 <.03 <1 Nil Nil Nil Nil Nil Nil .05 2 <.03 < 1

Corrosion Rate

% Propionic INCONEL MONEL Acid alloy 600 alloy 400 Copper 75 ºC (167 ºF) 50 ºC (122 ºF) 75 ºC (167 ºF) 50 ºC (122 ºF) 75 ºC (167 ºF) 50 ºC (122 ºF)

mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy

99 .38 1 5 <.03 <1 1.19 47 .48 19 >1.27 >50 1.02 40 80 .48 19 .41 16 .15 6 .41 16 .23 9 1.09 43 67 .18 7 .36 14 .13 5 .23 9 .28 11 .41 16 50 .10 4 .20 8 .13 5 .28 11 .25 10 .38 15 33 .10 4 .18 7 .10 4 .05 2 .28 11 <.03 <1 20 .13 5 .13 5 .13 5 .18 7 .05 2 .13 5

Page 41 TABLE XLV TABLE XLVII Corrosion of Stainless Steel in a Propionic Corrosion of Proprietary Alloys in 2-Ethyl Butyric Acid Acid-Anhydride Mixture Duplicate specimens exposed for 48 hours or longer in Conditions: Specimens exposed in pressure equipment refined boiling acid without aeration or deaeration. at 260 ºC (500 ºF) and 300 atmospheres pressure from 4 to 7-hour periods in a 65% propionic acid/35%propionic anhydride mixture with continuous feed of two liters/ Corrosion Rate hour. Alloy mm/y mpy

Corrosion Rate Type 316 Stainless Steel .03 1 Alloy Liquid Vapor CRUCIBLE alloy 223 .05 2 mm/y mpy mm/y mpy Titanium <.03 <1 Type 430 Stainless Steel 129.41 5095 80,01 3150 WAUKESHA 23 .89 35 Type 304 Stainless Steel 141.86 5585 78.10 3075 WAUKESHA 54 .18 7 Type 347 Stainless Steel 3.63 143 116.84 4600 WAUKESHA 88 .28 11 Type 316 Stainless Steel 9.91 390 7,09 279 KROMARC 55 .03 1 Type 316 Stainless Steel (Sen.) 12.01 475 4.01 158 E-BRITE 26-1 <.03 <1 Type 317 Stainless Steel 4.55 179 2.44 96 CRUCIBLE 26-1 .03 1 Type 318 Stainless Steel 7.95 313 7.65 301 CROLOY 16-1 5.33 210 CARPENTER alloy 20 7.26 286 8.36 329 CARPENTER alloy 20Cb-3 <.03 <1

TABLE XLVI Corrosion of Alloys in Higher Organic Acids Conditions: Laboratory tests for 48 hours at temperatures shown in refined (99.9+) acids.

Corrosion Rate

Acid (Approximate Test Silicon Type 304 Type 316 Carbon Steel Copper boiling point) Temperature Bronze Stainless Steel Stainless Steel ºC ºF mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy Acetic (116 ºC or 240 ºF) 26 78.8 2.79 110 .28 11 .41 16 <.03 <1 <.03 <1 116 240 5.33 210 .08 3 .08 3 .25 10 .08 3 Propionic (140 ºC or 284 ºF) 26 78.8 .71 28 .05 3 .15 6 <.03 <1 <.03 <1 110 240 1.98 78 2.13 84 3.40 134 .13 5 <.03 <1 Butyric (163 ºC or 325 ºF) 26 78.8 .15 6 Nil Nil .05 2 <.03 <1 <.03 <1 163 325 – – – – – – 1.14 45 .10 4 Valeric (185 ºC or 365 ºF) 26 78.8 .05 2 .05 2 .05 2 <.03 <1 <.03 <1 140 284 1.37 54 2.06 27 .13 5 <.03 <1 <.03 <1 2-Ethylbutyric (190 ºC or 374 ºF) 26 78.8 .18 7 .03 1 .03 1 <.03 <1 <.03 <1 150 302 .86 34 .41 16 .23 9 .53 21 <.03 <1 2-Methylpentanoic (195 ºC or 383 ºF) 26 78.8 .03 1 .08 3 .10 4 <.03 <1 <.03 <1 150 302 .53 21 .30 12 .08 3 <.03 <1 <.03 <1 2-Ethylhexanoic (220 ºC or 428 ºF) 26 78.8 .03 1 <.03 <1 <.03 <1 <.03 <1 <.03 <1 190 374 1.27 50 <.03 <1 <.03 <1 .20 8 <.03 <1 Iso-octanoic (240 ºC or 464 ºF) 26 78.8 .03 1 05 2 .03 1 <.03 <1 <.03 <1 190 374 .89 35 <.03 <1 <.03 <1 .43 17 <.03 <1 Iso-decanoic (265 ºC or 509 ºF) 26 78.8 .03 <1 <.03 <1 <.03 <1 <.03 <1 <.03 <1 190 374 .84 33 <.03 <1 <.03 <1 .20 8 <.03 <1

Reference 5

Page 42 TABLE XLVIII Corrosion of Alloys in Higher Organic Acids (Laboratory Tests)

Corrosion Rate

Type 304 Type 316 Stainless Stainless CARPENTER INCOLOY HASTELLOY Temp. Time Steel Steel alloy 20 alloy 825 alloy C Copper Steel

Acid ºC ºF days mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy 2- Ethyl butyric acid Crude acid (60%) 26 78.8 10 Nil Nil Nil Nil – – – – – – – – – – Crude acid 115 239 10 .08 3 .08 3 – – – – – – – – – – Refined acid 125 257 1 Nil Nil Nil Nil – – – – – – – – – – 2- Ethyl hexanoic acid Refined acid 125 257 1 Nil Nil – – – – – – – – – – – – Refined acid 150 302 5 61 24 <.03 <1 – – – – – – <.03 <1 .89 35 n- Butyric acid 130 266 60 – – 05 2 .03 1 .03 1 .01 0.3 1.52 60 – – +5% Acetic Acid agitated

TABLE XLIX Corrosion of Alloys During Preparation of n-Octanoic Acid

Corrosion Rate Type 304 Type 316 Stainless Stainless CARPENTER HASTELLOY Temp. Time Steel Steel alloy 20 alloy C Exposure ºC ºF days mm/y mpy mm/y mpy mm/y mpy mm/y mpy Preparation of the acid by carbonylation of the appropriate olefin 175 347 7 13 5 <.03 <1 <.03 < 1 <.03 < 1 Distillation of the octanoic acid from above preparation 230 446 5 2.54 100 <.03 < 1 <.03 < 1 <.03 < 1

TABLE L Corrosion of Alloys in 2-Ethyl Hexanoic Acid

Corrosion Rate

Test No.a 1 2 3 4 5 6

Alloy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy Type 304 Stainless Steel 08 3 05 2 08 3 36 14 05 2 .08 3 Type 316 Stainless Steel .15 6 13 5 08 3 46 18 15 6 13 5 CARPENTER alloy 20 .10 4 .05 2 – – .08 3 .08 3 – – HASTELLOY alloy C .03 1 <.03 <1 – – .05 2 .03 1 – – HASTELLOY alloy B <.03 <1 <.03 <1 – – <.03 <1 .03 1 – – Silicon Bronze 05 2 05 2 .20 8 .18 7 08 3 56 22 Copper 15 6 .15 6 1.12 44 .18 7 .23 9 .66 26

a Test 1–1% of 98% H2SO4 added to commercial grade 2-ethyl hexanoic acid. Solution at 90 ºC (194 ºF) at atmospheric pressure for 7 days with agitation.

Test 2–1% of 98% H2SO4 added as before. Solution at 120 ºC (248 ºF) at atmospheric pressure for 7 days with agitation.

Test 3–1% of 98% H2SO4 added as before. Solution averaged 143 ºC (290 ºF) at 200 mm pressure for 3 days with agitation.

Test 4–Same as Test 1 except 2% H2SO4 added.

Test 5–Same as Test 2 except 2% H2SO4 added.

Test 6–2% H2SO4 added; average temperature of 142 ºC (288 ºF) at 300 mm pressure for 3 days.

Page 43 D. Fatty Acids The fatty acids comprise those organic acids exceeding Data reported for the corrosion of metals in the fatty four carbons in length according to some chemical text acids are not explicit regarding stream compositons. As a definitions. However, the term as used industrially and in consequence, a comparison of the results obtained in a this text refers to the higher acids of six or more carbons. number of industrial exposures at various temperatures is These are characterized by lauric, oleic, linoleic, stearic, necessary to gain a proper view of corrosion to be tall oil and rosin acids as produced for commerical use expected in these media. A number of factors can from products of the meat, agricultural and paper industry. influence the corrosion rates observed: The large volume product of industry is not a pure • Light ends (lower acids), if allowed to remain in the compound, but a mixture of two or more of the com- mixed fatty acids, can result in a more aggressive pounds meeting certain chemical specifications. environment. At the lower temperatures, the acids may be considered • The ratio of fatty to rosin acids affects the corrosion rate. as harmless polar “oils.” However, when the products are • The presence or absence of water will have an effect, heated to the high temperatures necessary for processing particularly on the corrosion of the stainless steels. and production, significant corrosion of steel can result. • Decomposition products generated by overheating the Fortunately, there is a wide variety of alloys which have acids will add to the corrosiveness of the solution. excellent resistance to the conditions of production and • Pretreatment of the acids may leave traces of ions in the subsequent use of the acids. A proper economic analysis acids that increase corrosivity. of the use of the alternative materials is necessary to • The temperature of the processing operation is a major achieve an optimum selection. variable of concern.

TABLE LI Corrosion of Alloys in Tall Oil Fractions

Corrosion Rate Conditionsa 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Temperature ºC (ºF) 100(212) 275(527) 260(500) 300(572) 25(77) 265(509) 265(509) 265(509) 220(128) 250(482) 240(464) 265(509) 247(477) 247(477) 220(428) 260(500) Time, days 30 195 3 19 54 134 100 242 66 50 73 66 66 66 63 Exposure Vapor Liquid Vapor Liquid Liquid Liquid Liquid Liquid Vapor Liq–Vap. Liq–Vap. Liquid Vapor Liq–Vap. Vapor Vapor Alloy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy Steel .09 3.4 Consumed Consumed – – – – Consumed Consumed – – – – – – – – – – – – – – – – – – Cast Iron .06 2.5 >6.35 >250 >6.35 >250 11.1 440 – – – – – – – – – – – – – – – – – – – – – – – – Ni–Resist Type 2 .02 0.9 .77 30 .25 10 – – – – – – – – – – – – – – – – – – – – – – – – – – Nickel 200 .02 07 .38 15 .08 31 .13 5 0.9 3.5 MONEL alloy 400 .03 1 .20 8 .09 3.6 .20 8 0.1 0.5 .17 6.6 .23 9 – – .15 6 – – – – .91 36 – – – – – – – – INCONEL alloy 600 Nil 0.1 .25 10 .09 3.7 .05 2 0.1 0.2 – – – – .43 17 .28 11 .43 17 .79 31 1.60 83 .43* 17 .61* 24* .15 6 .79 31 Type 304 Stainless Steel Nil* 01 >.76 >30 >7.6 >30 1.57 62 Nil 0.1 4.70 185 Consumed – – – – – – – – – – – – – – – – – – Type 316 Stainless Steel Nil 0.1 .36 14 <.03 <1 .05 2 – – Nil 0.1 .86 34 .84 33 .20 8 .08 3I .05 2 1.78* 70 08* 3* .03* 1 .10 4 Nil Nil Type 31 7 Stainless Steel – – – – – – – – – – Nil NII .23 9 .08 3 – – Nil Nil Nil 0.1 .99* 39 Nil Nil Nil Nil .02 0.8 Nil Nil CG–8M Casting – – – – – – – – – – – – – – .10 4 .03 1 Nil 0.1 – – – – – – – – – – – – Type 310 Stainless Steel Nil 0.1 >.76 >30 >7.6 >30 .15 6 – – – – – – – – – – – – – – – – – – – – – – – – Type 330 Stainless Steel Nil 0.1 >.76 >30 .46 18 – – – – – – – – – – – – – – – – – – – – – – – – – – INCOLOY alloy 825 – – – – – – – – – – – – – – – – .05 2 Nil NII .02 0.7 .61* 24* Nil NII – – – – – – INCOLOY alloy 800 – – – – – – – – – – – – – – – – – – – – 2.67 105 >2.13 >84 – – – – – – – – INCOLOY alloy 804 – – – – – – – – – – – – – – – – – – – – 86 34 >2.29 >90 – – – – – – – – HASTELLOY alloy C Nil 0.1 <.03 <1 <.03 < 1 .03 1 – – – – – – Nil Nil Nil Nil Nil Nil .01 .05 Nil Nil – – Nil Nil Nil Nil Nil Nil HASTELLOY alloy B – – – – – – – – – – – – – – Nil Nil – – – – – – .01 0.3 – – – – – – – – Copper .08 3 >7.6 >30 >7.6 > 30 .25 10 _ CN–7M Casting – – – – – – – – – – Nil Nil .71 28 – – .03 1 Nil Nil .02 .06 1.04 41 Nil Nil Nil* NII .08 3 Nil Nil Titanium – – – – – – – – – – – – – – – – Nil Nil Nil Nil – – – – Nil Nil – – – – – – *Pitted References 30, 31, 49. 52 aConditions of the exposures: 1– Field test in vapor of light-odor tall oil fraction during distillation in vacuum column. Water present. 2– Field test in bottom and top of tall oil vacuum distillation column. Oil (presumably crude) from southern kraft pulp mill. 3– Laboratory test in crude tall oil acids from kraft pulp mill distilled under vacuum with agitation of 300 rpm in kettle.52 4– Laboratory test in crude and semi-refined oil with velocity of 0.3 fps provided in liquid. 5– Field test in base of tall oil distillation column (20% oleic acids, 60% rosin acids and 20% pitch).30 6– Field test in base of tall oil distillation column (65% fatty acids and 35% rosin acids).30 7– Field distillation of 65% fatty acid–35 % rosin acids. 31 8– Field distillation of 93% fatty acids–5% rosin acids.31 9– Field distillation of 90-93% oleic acids with <1% rosin acids with steam injected. Velocity of 62 fps.31 10– Field test six inches above the outlet of a reboiler on 97% fatty acids,1.5% rosin acids and 1.7% residues with high velocity.31 11– Field test in heat exchanger head handling 85% fatty acids and 15% rosin acids with steam present. 12– Field test in reboiler nozzle at base of distillation column handling 90-93% oleic acids and 1% rosin acids with steam injected. 13– Field test on distillation column tray near bottom while processing 90% oleic acids, 2% stearic acid, 0.4% rosin acids, 0.5 light ends and 6.4% higher acids with steam present. 14– Field test in top of distillation column handling analysis of No. 13 above. 15– Field test near bottom of distillation column handling 30-32% rosin acids, 8-20% oleic acids and 62-48% higher boiling acids with steam present.

Page 44 Pitting and crevice corrosion can occur on essentially Note that Types 316 and 316L stainless steels are useful all alloys in these environments and must be appraised for many tall oil processing requirements but, in some before a material is selected. Extensive comments on the instances, either an excess of light ends or an excep- processing of the fatty acids and the selection of materials tionally high temperature causes high rates with this alloy. of construction are contained in references 28-34. In these cases, the use of Types 317 or 317L stainless One of the most important sources of fatty acids today steels or alloys with a higher molybdenum content should is the pulp and paper industry where tall oil fractions are be investigated in the search for an economical material of recovered and refined. These are composed of the construction. If these alloys are inadequate, the use of straight-chain fatty acids and mixed rosin acids. Table LI more highly alloyed materials can be considered. The shows results compiled from various sources. Whenever nickel-base molybdenum-chromium-iron alloys show es- possible, the stream compositions have been defined. sentially a nil corrosion rate in all such exposures. Alloy 600 is a contender for use in a number of applications and should not be overlooked. The use of nickel- TABLE LII copper alloys or copper-nickel alloys varies depending on the oxidizing capacity of the solution, as would be Effect of Temperature on Corrosion in Refined Tall Oil expected. In the absence of oxidants, the rate of attack on Conditions: Laboratory tests conducted in liquid of these alloys is acceptably low. same oil at various temperatures. It has been stated that streams containing a higher proportion of the straight chain fatty acid produced more Corrosion Rate corrosion than those containing a higher ratio of rosin 285 ºC (545 ºF) 300 ºC (572 ºF) 315 ºC (599 ºF) 330 ºC (626 ºF) (cyclic) acids. This does not appear to be invariably true.

Material mm/y mpy mm/y mpy mm/y mpy mm/y mpy The presence or absence of steam has a significant effect on the corrosion to be expected, particularly as Type 302 4.57 180 12.7 500 20.32 800 – – observed for the stainless steels. The oxidizing capacity of Stainless Steel Type 316 .10 4 .10 4 1.35 53 12.7 500 the water reduces corrosion rates on the stainless steels Stainless Steel appreciably while accentuating attack on the nickel-copper Type 317 .03 1 .03 1 .53 21 – – and/or copper-base alloys. Stainless Steel As with any other corrosive environment, the effect of HASTELLOY alloy C .10 4 .13 5 .10 4 – – temperature must be carefully defined. Table LII shows INCONEL alloy 600 .25 10 .25 1 0 .33 13 .28 11 data for five alloys exposed to the same refined tall oil

TABLE Llll Corrosion of Metals in Vegetable Fatty Acids

Conditionsa 1 2 3 4 5 6 7 Temp. ºC (ºF) 370 (698) 370 (698) 190 (374) 190 (374) 277 (530) 116(240) 255(491) Time, days 45 3 30 23 50 32 42 Exposure Liq-vap. Vapor Liquid Liq-vap. Vapor Vapor Vapor Corrosion Rate Alloy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy Carbon Steel – – – – 38 1 5 1.04 41 3.05 120 25 10 – – Cast Iron – – – – 48 19 – – 10.92 430 – – 12.45 49 Ni-Resist Type 2 – – – 03 1 20 8 43 17 01 05 86 340 Type 304 Stainless Steel 01 0.2 – – Nil Nil Nil 0.1 97 38 Nil 0.1 25 10 Type 309 Stainless Steel – – – – Nil Nil – – – – – – 05 2 Type 316 Stainless Steel Nil 0.1 – – Nil Nil Nil 0.1 Nil 0.1 Nil 0.1 Nil Nil Type 317 Stainless Steel – – – – Nil Nil – – – – – – – – INCONEL alloy 600 Nil 0.1 Nil 0.1 Nil Nil Nil 0.1 0.3 1 Nil 0.1 Nil 0.1 Nickel 200 08 3 25 10 10 4 10 4 30 12 03 1 20 8 MONEL alloy 400 .08 3 .18 7 .05 2 .13 5 .25 10 .02 0.9 .20 8 C71500 (70-30 Cupro-nickel) – – – – 01 0.4 – – – – – – – –

HASTELLOY alloy C – – – – – – – – – – – – Nil Nil_

aConditions:

1–Field test in closed autoclave converting castor oil to drying oil. 2–Field test in top of kettle while refining high purity linseed oil. 3–Field test in receiving tank for dirty palm used in tin-plate line. 4–Field test in distillation column handling crude vegetable oils plus palmitic and stearic acid (acid value of 85-95). 5–Field test in distillation column for cottonseed oil acids. 6–Field test in top of distillation column handling palmitic and stearic acids. 7–Field test in top of distillation column deodorizing crude cottonseed fatty acids by steam distillation.

Page 45 TABLE LIV Corrosion of Alloys in Animal Fatty Acids Conditionsa 1 2 3 4 Temp. ºC (ºF) 100 (212) 250 (482) 250 (482) 250 (482)

Time, days 130 147 210 84 Exposure Liquid Liquid Vapor Vapor Corrosion Rate Alloy mm/y mpy mm/y mpy mm/y mpy mm/y mpy Mild Steel .18 7 – – Consumed Consumed – – Cast Iron 1.63 64 – – >3.46 >140 Consumed Consumed Ni-Resist Type 2 .23 9 – – .33 13 .79 31 Type 304 Stainless Steel Nil Nil .36* 14* .05* 2* .20 8 Type 316 Stainless Steel Nil Nil Nil 0.1 .01* 0.2* Nil Nil INCONEL alloy 600 Nil Nil .01 0.3 .01 0.3 .05 2 Nickel 200 .08 3 .41 16 .13 5 .08 3 MONEL alloy 400 .05 2 .58 23 .15 6 .10 4 Copper – – – – – – .13 5 *Pitted References 28,49 aConditions: 1–Field test in storage tank for mixed acids from fish oils. 2–Field test in outlet of preheater to distillation column processing animal tatty acids. 3–Field test in overhead vapor of column distilling acids from fish oils. 4–Field test on feed tray of distillation column handling crude fatty acids from tallow.

fraction at various temperatures. It is obvious that at some The lower acids of this series are more aggressive in place above 300 ºC (572 ºF) the use of the 300 series aqueous solution than are the monobasic acids at the same stainless steels is questionable in such a mixture. At this temperature and concentration. Dissociation of these point, the use of the more highly alloyed materials should acids in water is greater than for acetic or formic acid. In be investigated. addition, the multiple acid grouping has the capacity to The vegetable oils, characterized by stearic and palmitic solubilize cations by chelation. Thus, protective, insoluble acids among others, appear to have somewhat less aggres- corrosion products are normally not found on the surface sive characteristics than the tall oil acids. Table LIII shows of a metal attacked by this group of acids. This allows data for the exposure of alloys in a diverse group of field continuous attack on the clean metal surface. Since the exposures. It will be noted that INCONEL alloy 600 and rate of attack is not as severe as when using mineral acids, Type 316 stainless steel are resistant to all of the processing oxalic, citric and certain other of the dibasic acids are used conditions. Indeed, INCONEL alloy 600 vessels have to clean metal surfaces. been used for over 30 years with good success in the The elemental dibasic acid is oxalic (ethanedioic) acid; processing of vegetable oil acids. Other aspects of the sublimes at 150 ºC (302 ºF). As with other first handling of these vegetable oil fatty acids would be the homologues of a series, oxalic acid is extremely same as described for the tall oil acids. aggressive in its attack on most metals. Rates of corrosion Those acids derived from animal fats appear to be are significantly higher on alloys than with acetic acid at somewhat more aggressive. Table LIV shows data ob- the same concentration and temperature (Table LV). tained while processing acids derived from fish oils and However, the relative corrosion resistance of the alloys beef tallow. Again, the INCONEL alloy 600 and Type 316 remains essentially the same. Higher alloying is required stainless steel appear to be the most attractive materials to provide an alloy with useful resistance to attack. For for construction of such equipment. instance, Type 304 stainless steel is attacked excessively in most concentrations of the acid at temperatures above ambient, and Type 316 stainless steel, although E. Di and Tricarboxylic Acids significantly more resistant, has severe limitations of use. Although the di and tricarboxylic acids are produced in Table LVI shows the corrosion to be expected by less quantity than the monobasic acids, the products exposure of a variety of alloys to oxalic acid. More constitute a most important industrial commodity. Many corrosion data are available for the 10 per cent concentra- of the acids and corresponding anhydrides are used in the tion of the acid at the boiling temperature than far other synthesis of drugs, food products, plasticizers and resins. combinations, because: (a) 10 percent represents satura- Citric, oxalic and certain other of the acids are used tion in cold, 25 ºC (77 ºF), water, (b) the mixture is an extensively as metal cleaning agents. However, the most aggressive cleaning solution for metals and (c) the mix- important of the products are maleic and phthalic ture is often used as a corrosion test medium for the anhydrides used to produce alkyd and polyester resins, evaluation of alloys. the para-phthalic acid used in the preparation of polyester It is obvious that higher amounts of nickel in an fibers and adipic acid required for nylon synthesis. austenitic base are beneficial in combatting attack by

Page 46 TABLE LV Corrosion of Annealed and Heat Treated Alloys in Dicarboxylic Acids Laboratory test in 10% boiling dibasic acid stated for 5 days without aeration or deaeration. Acetic acid added for comparison.

Corrosion Rate

Oxalic Maleic Phthalic Acetic Acid Acid Acid Acid Alloy mm/y mpy mm/y mpy mm/y mpy mm/y mpy Type 316L Stainless Steel (annealed) .94 37 .01 0.2 .01 0.2 .01 0.3 Type 316L Stainless Steel .66 26 .01 0.2 .01 0.3 Nil <0.1 (Heat treated)* CARPENTER alloy 20Cb-3 (annealed) .58 23 .01 0.2 Nil <0.1 Nil <0.1 CARPENTER alloy 20Cb-3 .23 9 Nil <0.1 Nil 0.1 Nil 0.1 (Heat treated)* INCOLOY alloy 825 (annealed) .51 20 Nil 0.1 Nil <0.1 Nil <0.1 INCOLOY alloy 825 .38 15 .02 0.7 Nil 0.1 .05 1.8 (Heat treated)

*650 ºC (1200 ºF) for one hour, water-quenched. oxalic acid. As with corrosion in the monobasic acids, the steel can be reduced essentially to zero in even boiling 10 addition of molybdenum is very beneficial. Nickel-base per cent acid by the addition of approximately 50 ppm of alloys containing molybdenum exhibit the best resistance iron as ferric oxalate.35 of all alloys in hot, aqueous oxalic acid (Table LVI). Less As noted in Table LV, the dibasic acids above oxalic in costly alloys, such as Type 316 stainless steel, can be used the series are much less corrosive. Maleic acid, m.p. 130 ºC for specific applications at temperatures somewhat higher (266 ºF), can be considered as the next homologue, and than ambient in aqueous solutions of the acid. Streicher the acid is innocuous in aqueous solution when compared to has shown that the rate of attack on Type 304 stainless oxalic acid.

TABLE LVI Corrosion of Alloys by Oxalic Acid Laboratory tests without aeration or deaeration except as noted

% Oxalic Acid 1 10 10 10 10 10 30 Temp. ºC Boiling 25 35 50 80 Boiling 60 ºF Boiling 77 95 122 176 Boiling 140 Test Period (days) 1.5 7 6 6 0.1-10 2-10 11 Corrosion Rate Alloy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy Type 430 stainless steel – – – – – – – – – – 63.5 2500 – – Type 304 stainless steel .81 32 .03(1) 1(1) – – .81(1) 32(1) 1.52(1) 60(1) 2–16–14.48(1) 85–570(1) – – Type 316 stainless steel – – – – – – – – – – .18– 2.44 7–96 – – Type 216 stainless steel – – – – – – – – – – 1.52 60 – – ALLEGHENY alloy AL-6X* – – – – – – – – – – .28 11 – – Act CN-7M – – – – – – – – – – .18 7 – – HASTELLOY alloy C-276 – – – – – – – – – – .25 10 – – HASTELLOY alloy B – – – – – – – – – – .13 5 – – ELGILOY** – – – – – – – – – – .10 4 – – Titanium – – .03 1 .03 1 11.68 460 – – 24.1–73.7 950– – – Vanadium – – – – .41(2) 4(2) .25(2) 10(2) – – 5.46(2) 215(2) – – C71500 (70-30 Cupro-nickel) – – – – – – – – – – – – .20 8 WAUKESHA No. 23 – – – – – – – – – – .63 25 – – WAUKESHA No. 54 – – – – – – – – – – .48 19 – – WAUKESHA No. 88 – – – – – – – – – – .05 2 – – KROMARC 55 – – – – – – – – – – .23 9 – – Multiphase MP35N – – – – – – – – – – .10 4 – –

(1) Type 304L material heat treated at 675 ºC (1250 ºF) for 1 hour *Trademark of Allegheny Ludlum Steel Corporation. (2) Aerated. **Trademark of Elgiloy Co.

Page 47 TABLE LVII Corrosion of Alloys in Aqueous Maleic Acid Solutions

Corrosion Rate

2%* 5%* 10%* 30%** 40%* 59%**

Alloy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy Type 304 Stainless Steel .03 1 .03 1 4.06 160 4.06 160 3.71 146 5.33 210 Type 316 Stainless Steel Nil Nil Nil Nil Nil Nil <.03 <1 Nil Nil <.03 <1 CARPENTER alloy 20 – – – – – – <.03 <1 – – <.03 <1 HASTELLOY alloy C – – – – – – – – – – <.03 <1 HASTELLOY alloy B – – – – – – .08 3 – – – – Nickel 200 – – – – – – – – – – .91 36 Copper (C10200) – – – – – – .10 4 – – .03 2 Silver (fine) – – – – – – – – – – Nil Nil

*At 50 ºC (122 ºF) for 4 days with agitation by aeration. **Boiling for 6 days without aeration or deaeration.

Actually, there is little industry interest in maleic acid. tion of paper sizing and other resinous products as well The acid is a contaminant in processes used to produce as the synthesis of food additives. maleic anhydride and phthalic anhydride. These The presence of maleic acid in process streams of anhydrides are important basic building blocks for the the anhydrides does create corrosion problems. The preparation of polyester and alkyd resins, plasticizers and anhydrides are essentially innocuous, but the presence of agricultural chemicals. The isomer of maleic acid, termed malefic acid at the high temperatures used in the various fumaric acid, has commercial applications in the prepara- processes means attack on lower alloys by streams con-

TABLE LVllI Field Exposure of Alloys in a Phthalic Anhydride Plant

Corrosion Rate

Exposurea 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Alloy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy

1 2 – – – Mild Steel .03 .05 1.22 48 .01* 0.4* – – – – – – – – – 1.93 76 >7.62 >300 3.10 122 – – 2 2 – – – Cast lron (gray) .05 .05 .56 22 .01 0.3 – – – – – – – – – – – – – 3.02 119 – – 1 1 – – – Ni-Resist Type IV .03 .03 .10 4 .01 0.2 – – – – – – – – – – – – – .97 38 – – <0. 0.2 39 39 Nil Type 304 Stainless Steel Nil .01 .03 1 Nil <0.1 .99 .41 16 .99 .56 22 5.08 200 <0.1 .01 0.2 – – .28 11 Nil 0.1 1 0.4 19 48 – Type 309 Stainless Steel Nil .01 .03 1 Nil <0.1 .48 – – 1.22 – – – – – – – 2.21 87 – – – – <0. 0.2 0.3 0.7 Nil Type 316 Stainless Steel Nil .01 .03 1 Nil <0.1 .01 .02 0.6 .02 .01 3.3 Nil 0.1 <0.1 .01 0.2 .99 39 .02 0.6 Nil <0.1 1 <0. 0.1 0.1 – Type311 Stainless Steel – Nil – – – – Nil – – Nil – – – – – Nil 0.1 .28 11 Nil <0.1 Nil <0.1 <0. 1 <0. – – CARPENTER alloy 20 – Nil – – – – Nil – – – Nil Nil .02 0.7 – Nil 0.1 .86 34 – – .01 0.2 1 <0. 1 <0. Nil ACI CN-7M – – – – – – – – – Nil Nil Nil Nil 0.1 <0.1 – – – – – – – – – 1 – 1 – INCOLOY alloy 825 – Nil – – – – Nil – – – – – – – – .01 0.2 .51 20 – – Nil 0.1 – – <0. – 01 HASTELLOY alloy C – – – – – – – – – Nil – – – – 0.2 Nil Nil Nil <0.1 – – – – – <0. 1 0.1 >5.0 HASTELLOY alloy B – – – – – – – – – .02 – – – – >200 .01 0.3 – – – – – – – 1 – 0.8 8 INCONEL alloy 600 Nil .01 .03 1 Nil <0.1 .84 – – .56 – – – – 0.4 Nil 0.1 1.22 48 .15 6 0.1 0.3 – – – 22 01 Nickel 200 Nil Nil .08 3 Nil <0.1 1.88 – – 1.55 – – – – >200 .01 3 – – .69 27 .18 7 – – 33 51 >5.0 MONEL alloy 400 .05 .01 .08 3 Nil <0.1 1.12 – – .56 – – – – 160 .01 2 51 20 .13 5 .20 8 <0. 0.4 74 22 8 Copper .18 .13 1.14 45 .69 27 – – – – – – – – – – – – – .46 18 – – 1 0.1 44 – 4.06 Titanium – – – – – – – – – – – – – – < 0.1 – – – – – – – – 0.1 0.2 – – – Aluminum 3003 Mel .02 .03 1 .05* 2 – – – – – – – – – – – – – .56 22 – – 0.2 5 – – Nil 7

*Pitting FIXED BED NAPHTHALENE OXIDATION UNIT a1- Mixture of phthalic and malefic anhydride vapors near exit throat of a converter at 200-380ºC (329-716ºF) for 71 days. High temperature excursion to cause melting of 3003 aluminum. 2- Vapors of phthalic and maleic anhydride near bottom of distillation column at 204ºC (396ºF) for 16 days. 3- Same column as No. 2, but exposed at top at temperature of 195ºC (383ºF). 4- Liquid and vapor of phthalic anhydride in the lights heater at 177ºC (351ºF) for 157 days. 5- Overhead of distillation column for phthalic acid dehydration to phthalic anhydride and resulting distillation at 107-143ºC (225-289ºF) for 14 days. 6- Near top of batch still column with phthalic and malefic acids present. Distillation Involved 1 :10 ratio of total reflux versus distillation at 100-143ºC (212-289ºF) for 95 days. 7- On top tray of phthalic anhydride purification still with small amount of malefic acid and water present at 96-140ºC (205-284ºF) for 45 days. Vapor velocity of 7 ft per sec. 8- Top of distillation column for phthalic and maleic acids at 70ºC (158ºF) for 22 days. 9- Vapor space of column distilling 7% phthalic acid in water at 180ºC (356ºF) for 40 days. 10- Immersed in maleic acid recovery holding tank (10-18% maleic acid plus little phthalic acid and a-naphthoquinine) at 35ºC (95ºF) for 27 days. 11- Crude phthalic anhydride vapor in treater tank at 160-285ºC (320-545ºF) for 59 days. Liquid and vapor exposures essentially the same. 12- On reflux distributor plate of batch still handling crude phthalic anhydride containing phthalic acid, malefic acid, benzoic acid and maleic anhydride at 165-260ºC (329-500ºF) for 56 days. 13- Same as No. 12, but in another plant using temperatures of 225-290ºC (437-554ºF) for 85 days. 14- Same as No. 11, but in plant of No. 12. Essentially same temperatures for 25 days.

Page 48 taining the molten acid or in scrubber waters rich with the TABLE LIX water-soluble acid. As an example, the majority of equip- Corrosion of Alloys in ment used in the butane oxidation process for maleic Phthalic Acid and Phthalic Anhydride anhydride was originally of Type 304L stainless steel construction. However, unforeseen accumulations of mal- Conditions: Laboratory test of duplicate specimens at eic acid in portions of the equipment dictated a shift to the 150 ºC (302 ºF) for 13 days without aeration use of the more resistant Type 316L stainless steel. The ordeaeration. benzene process to produce the anhydride is even more corrosive, and Type 316L stainless steel is used exten- Corrosion Rate sively throughout the process chain. 1:1 Phthalic Phthalic Anhydride: Phthalic Corrosion to be expected from exposure of alloys in Anhydride Phthalic Acid Acid various aqueous concentrations of maleic acid at the Mixture boiling point is summarized in Table LVIL These data Alloy mm/y mpy mm/y mpy mm/y mpy relate to the corrosion found in process scrubber systems Mild Steel <.03 <1 <.03 <1 .03 1 where water is used as the scrubbing medium. Note the Type 304 loss of Type 304 stainless steel as a usable material of Stainless Steel <.03 <1 <.03 <1 <.03 <1 construction at concentrations of 10 per cent or more acid. Type 316 Higher iron-base stainless steel alloys, such as Type 316L Stainless Steel <.03 <1 <.03 <1 <.03 <1 and above, show acceptable resistance in all aqueous concentrations. The determination of corrosion rates for the stainless steels in both aqueous and molten maleic acid compositions is difficult. The maleic acid in the absence of more aggressive anions is slow in penetrating the oxide film on the stainless steels to initiate corrosion. Consequently, Phthalic acid, decomp. ca. 200 ºC (392 ºF), is found in multiple tests of sufficient duration must be conducted to many of the same process streams containing the maleic provide meaningful “rate” data for the corrosion process. acid. However, the contribution of phthalic acid to corro- Also, during the test period, a conversion of a portion of sion of the equipment is minimal. Table LIX shows the maleic acid to insoluble fumaric acid will occur, which corrosion data for steel and Types 304 and 316 stainless must be taken into account if the data are to be precise. steels exposed to hot phthalic acid, phthalic anhydride and Pure maleic acid in the molten form is not encountered a mixture of the two. These chemicals are not aggressive. normally in industry, but does exist in certain of the However, the austenitic stainless steels are often used to anhydride process streams. See Table LVIII for field process these chemicals to prevent contamination of the corrosion data obtained in streams containing the molten product and to provide a surface that can be cleaned acid as a contaminant. readily.

TABLE LX Corrosion of Alloys in Terephthalic Acid Media Laboratory Test Laboratory Test Field Test Field Test 6% Terephthalic 6% Terephthalic Acid TPA Leach Feed Leach Crystallizer Acid in Water 84.6% Acetic Acid Slurry (TPA + Liquid (14.1 % TPA, 9.4% Water Acetic Acid) 82.7% Acetic Acid, 2.7 % water) Temperature, ºC 232 232 260 177 Temperature, ºF 450 450 500 351 Test Period, days 24 24 14 523

Corrosion Rate

Alloy mm/y mpy mm/y mpy mm/y mpy mm/y mpy Type 304 Stainless Steel .01 0.4 .06 2.4 – – – – Type 316 Stainless Steel .01 0.3 .02 0.8 – – .03 1.0 Type 216 Stainless Steel – – – – .19 7.3 – – Type 317 Stainless Steel – – – – – – .01 0.2 CARPENTER alloy 20Cb-3 – – – – – – .02 0.7 INCOLOY alloy 800 – – – – – – .35 13.8 HASTELLOY alloy C- 276 Nil 0.1 Nil 0.1 .04 1.5 .03 1.1 Titanium Nil <0.1 Nil 0.1 Nil 0.1 Nil <0.1

Page 49 TABLE LXI Corrosion of Alloys in Adipic Acid Process Low temperature, 100 ºC (212 ºF), reaction with ammonium vanadate and cupric ion, process involved oxidation of cyclohexanone and cyclohexanol (KA oil) in strong nitric acid. In addition to the desired adipic acid, succinic, glutaric and lighter acids were formed in the process.

Corrosion Rate Product Lower Washing Separation Reactor Scrubber Absorber Crystallizer Acids Crystallizer Centrifuge and Still Stripper Drying Equip. Alloy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy Type 304 .23 9 .30 12 .23 9 .91 36 .18* 7* .41 16 .03 1 .13 5 Nil Nil Stainless Steel Type 316 .36 14 .05 2 .05 2 .30 12 .08* 3* .05 2 .03 1 .05 2 Nil Nil Stainless Steel CARPENTER .10 4 .05 2 .03 1 .13 5 Nil Nil .03 1 Nil Nil .03 1 Nil Nil alloy 20Cb-3 HASTELLOY Nil Nil Nil Nil Nil Nil Nil Nil Nil Nil Nil Nil Nil Nil Nil Nil Nil Nil alloy C-276 Titanium Nil Nil Nil Nil Nil Nil Nil Nil Nil* Nil* Nil Nil Nil Nil Nil Nil Nil Nil

*Pitting indicated

Data derived from corrosion tests in a large phthalic With the research interest to produce a simpler and anhydride plant are presented in Table LVIII. These show more economical mode of preparation, a number of new that, in addition to the higher stainless steels, the use of methods have evolved. One of the more common pro- Alloys 400, 600 and other nickel-base alloys is permissible cedures is the use of oxygen along with a cobaltic ion in many areas of the process. For equipment handling the catalyst to effect the reaction. Again, acetic acid is used as brominated anhydride, the use of HASTELLOY alloy C- the medium for the reaction. Thus, acetic acid is the 276 has proven to be attractive. primary corrosive to be considered. Contamination of the Terephthalic acid (para-phthalic acid) is produced in acetic acid by the terephthalic acid (TPA) adds little to the large quantity, primarily for the preparation of polyester corrosion produced. The major problem is one of han- resins used in the textile industry. A number of processes dling an acetic acid medium at high temperatures. There have been investigated to produce the acid in as pure form are a number of steps in the process where the tempera- as economically as possible. tures are well above those required for producing acetic Initially, the process required the oxidation of xylene acid itself. In these areas, the use of materials suitable for using a bromide catalyst. Inasmuch as acetic acid is used as exposure in acetic acid at high temperatures under oxidiz- a dilulent in the process, the reaction mixture of a halogen ing conditions are acceptable. (See discussion of acetic and acetic acid was extremely corrosive. HASTELLOY acid.) alloy C-276 was the only contender for use in these areas. Table LX shows data generated by both laboratory and Once the bromide ion was removed, Type 316 stainless field tests designed to explore corrosion within the area of steel was found to be useful for the vast majority of the the leaching step of the process. At this point, the acetic remainder of the equipment. acid medium is taken to a very high temperature to allow the rather insoluble TPA to precipitate from solution before taking the material to a crystallizer. It will be noted that Type 316 stainless steel is a borderline material for this specific area because contamination of this stream is undesirable. Titanium is favored for this most aggressive TABLE LXII area in the process. For all of the remainder of the process, Laboratory Tests for Corrosion of Alloys the use of Type 316 stainless steel has been found to be in Molten Adipic Acid at 170 ºC (338 ºF) most satisfactory. It is necessary to avoid the presence of crevices or other areas where differential corrosion cells Corrosion Rate can be created in either titanium or the Type 316 stainless Alloy mm/y mpy steel equipment. Type 304 Stainless Steel 1.30 51 Type 321 Stainless Steel .43 17

Page 50 Adipic acid is an essential ingredient in the production Pure molten adipic acid is corrosive to an austenitic of nylon resin. The process to produce this dibasic acid is stainless steel without molybdenum. Table LXII shows quite lengthy and corrosive in the latter stages. rates of .43 mm/y or more (17 mils per year or more) in a Cyclohexane, produced as a hydrogenated benzene, is molten adipic acid at 170 ºC (338 ºF). Type 316 stainless oxidized to cyclohexanone and cyclohexanol in a conven- steel should show adequate resistance to such an ex- tional oxidation process. The conditions of this prepara- posure. tion of the “KA oil” are not exceptionally corrosive, and The higher dibasic acids present unique problems when steel is used for large portions of the process equipment appraising the potential for corrosion of the common with Type 304 stainless steel used where moisture, alloys. In general, aqueous solutions of the acids are only organic acids, or other corrosive agents tend to accumul- mildly corrosive up to 100 ºC (212 ºF). For instance, water ate. The KA oil is then oxidized with strong nitric acid at saturated wth succinic (butanedioic) acid at 95 ºC (203 ºF) approximately 100 ºC (212 ºF) to produce adipic acid and produced no corrosion of Type 304 stainless steel during a other degradation products from the oxidation step. These test period of one week. include succinic acid, glutaric acid and all of the lower The molten acids can vary in aggressiveness depending monobasic organic acids. The ammonium vanadate and on the residual contaminants from the process. These cupric ion catalyst contributes little to the corrosion contaminants may be lower organic acids or inorganic afforded by the strong nitric acid. Inasmuch as problems compounds which control to a great extent the rate of relating to this portion of the process are engendered by penetration of passive films on the stainless steels and the the nitric acid, Type 304L stainless steel is used exten- subsequent corrosion rate observed. Corrosion data re- sively in the equipment. Where dilution occurs or corro- ported for these higher acids seldom if ever identify the sion by the organic acids becomes predominant, Type purity of the acid tested. 316L stainless steel is used. This is particularly true in the Table LXIII provides information regarding the corro- scrubber, absorber and the first centrifuge of the latter sion of alloys during the synthesis of a glutaric (pen- process. The temperatures are maintained as low as tanedioic) acid-anhydride mixture. The oxidation step, possible by vacuum equipment for economy and to conducted at relatively low temperatures, was not corro- reduce corrosion throughout the process. Table LXI sive to the stainless steels, as would be expected. How- shows typical data for common alloys in the latter steps of ever, when the reaction mixture was heated to higher the adipic process operation. Note the excellent resistance temperatures with the attendant loss of the oxidizing of the more highly alloyed stainless steels to conditions species, corrosion of the stainless steels became much existing through the unit. Care must be exercised in the more pronounced. The more highly alloyed materials choice of Type 304 or Type 316 stainless steels for specific retained good resistance to the more rigorous conditions uses. However, with a judicious choice of material, the of the high temperature distillation. stainless steels can be used extensively throughout the Similar data representing the distillation of pimelic process.

TABLE LXIII Corrosion of Alloys in Glutaric Acid— Glutaric Anhydride Mixtures

Conditions: Temperature, ºC 40-90 210 2602 2103 Temperature, ºF 104-194 410 500 410 Exposure, days (oxidation)1 (distillation)1 7 9 2 13.5 Corrosion Rate Alloy mm/y mpy mm/y mpy mm/y mpy mm/y mpy Type 304 Stainless Steel <.03 <1 1.58 62 .94 37 .69 27 Type 316 Stainless Steel Nil Nil .28 11 .20 8 41 16 CARPENTER alloy 20 – – .15 6 – – – – Type 201 Stainless Steel 03 1 .56 22 .86 34 – – Type 202 Stainless Steel – – 66 26 – – – – HASTELLOY alloy B – – <.03 <1 <.03 <1 – – HASTELLOY alloy C – – Nil Nil Nil Nil – – INCONEL alloy 600 – – – – – – 23 9 Copper 3.56 140 30 12 Nil 1 18 7 MONEL alloy 400 – – – – – – .20 8 (1) Pilot unit operations. Acetic acid present in mixture. (2) Laboratory kettle test designed to represent mixture for field distillation (no acetic acid present); 3 parts acid: 1 part anhydride. (3) Actual field distillation.

Page 51 TABLE LXIV F. Naphthenic Acids Corrosion of Stainless Steels in Molten The naphthenic acids have received much attention during Pimelic (Heptanedioic) Acid the past 20 years as a corrosive in process streams of the Conditions: Metal specimens completely immersed in oil refineries. A considerable volume of data has been generated relating to the operation of equipment handling molten acid under quiescent conditions at 29, 36-40 225 ºC (437 ºF). Unreported contaminant streams contaminated with these acids. suspected to be present. Results shown The term “naphthenic acids” describes a group of aro- are averages of duplicate tests. matic compounds containing one or more carboxyl groups and does not refer to a specific structure. The term em- Corrosion Rate braces acids from benzoic through those of the true naph- Initial 117 hr Second 73 hr thenic structure, all of which can contribute to corrosion at the very high temperatures of oil refining. The corrosive Alloy mm/y mpy mm/y mpy potential for streams containing these acids is defined by Type 304 Stainless Steel 9.36 369 12.89 508 “neutralization number” rather than acid content. Thus, Type 347 Stainless Steel 5.89 232 7.26 286 all acidic materials in the stream are categorized by the Type 316 Stainless Steel 1.65 65 2.77 109 term naphthenic acid. Providing materials of construction to resist naphthenic acid corrosion is not difficult, although the economics of (heptanediocic) acid are summarized in Table LXIV The selection are critical. When the neutralization number greater corrosive activity of the acid in these tests is exceeds 0.5, the streams are considered to be corrosive to probably attributable to a process contaminant. Although steel. The use of an austenitic stainless steel will provide the higher iron-base and nickel-base alloys were not resistance to corrosion during processing of the streams. tested, it is probable that these alloys would be satisfac- However, the economics of providing materials of con- torily resistant under such conditions, particularly the struction for such large process equipment requires that nickel-base molybdenum-chromium-iron alloys. the optimum material be found. Thus, the various alloy The tricarboxylic acids without other functional groups materials between steel and the 300 series austenitic are found in nature (e.g., tricarballylic acid in beets), but are produced by industry only as a development chemical. No corrosion data are known to have been published concerning those compounds. It is possible that such a structure would generate corrosion comparable to that observed for citric acid. (See Section G-4, Part III.)

A vacuum distillation column at a major petroleum company. This photo shows the crossover piping loops in foreground and 1,500 mm (60-inch) transfer line entering column tangentially. The transfer line and the Fig 13– Corrosion Isotherms for Various Steels and MONEL alloy 400 in column are lined with Type 316 stainless steel to resist naphthenic acid White Oil/Naphthenic Acid Blends at 235 ºC (455 ºF) Tempera- and sulfidic corrosion. ture

Page 52 stainless steels are explored as potential candidates. The normal carboxylic acid terminus to the molecule, and, in ease of fabrication of the Type 304 stainless steel, com- addition, the incorporation of a halogen, an amino, a bined with its more than satisfactory corrosion resistance, hydroxy addition, or other active ion added to the mole- makes the material a prime candidate for such service. cule which brings unique characteristics to the product. No corrosion of Type 304 stainless steel in the most 1. Glycolic Acid basic of the aromatic acids (benzoic) is apparent. Tests The simplest of the organic acids in this category is using a two per cent aqueous solution at 100 ºC (212 ºF) or glycolic (hydroxyacetic) acid. As an acid in aqueous of 10 per cent in an anhydrous octanol solution at 130 ºC solution, the material does not appear to be excessively (266 ºF) produced no attack on the alloy. corrosive at the lower temperatures. For instance, Type In many instances, the corrosion attributable to organic 304 stainless steel will show only .003 mm/y (0.1 mpy) acids in such systems is compounded by the presence of corrosion rate or less in a 6% solution of glycolic acid at sulfur compounds, the lower aliphatic acids, chlorides and ambient temperature. At 50 ºC (122 ºF) during tests of other contaminants. Thus, in making a choice of materials eight days, both Types 304 and 316 stainless steels for such service, the possible effect of chloride ion, sulfur showed no attack in a 50% aqueous solution. Thus, the ions, or other contaminants that may accumulate at times in acid could not be described as exceedingly corrosive at the equipment must be considered. Stress-corrosion conditions normally encountered. However, it has been cracking of the austenitic stainless steels can be experi- found to be corrosive when heated to higher temperatures enced under certain circumstances and must be evaluated when contained in process streams as a contaminant. thoroughly before the choice of such an alloy is made. Again, the stainless steels resist attack at the high Gutzeit has pointed out that the corrosion in such temperatures, but areas where steel would normally be systems is directly related to the neutralization number. acceptable become impractical with contamination of the Curves showing the corrosion rate for various alloys as streams by glycolic acid. Type 304 stainless steel is then related to the neutralization number are provided in his required. paper.40 One of those is reproduced here as Figure 13. 2. Lactic Acid Corrosion occurs in the liquid phase with only mild Lactic acid (hydroxypropionic acid) is familiar to most corrosion experienced in the vapor areas. Thus, hot persons as the corrosive agent in milk. To maintain the condensate is always a potential corrosive in such a purity of the milk, tanks and tank trucks of Types 302 and system. The use of Alloys 400 or 600 and 800 in such 304 stainless steels have been constructed for many years systems has merit. If stress-corrosion cracking of the for the handling of this precious commodity. stainless steels are experienced, the use of these alloys As indicated by Tables LXV and LXVI, Type 304 should be considered. stainless steel and its cast counterpart CF-8 is most G. Organic Acids with Other satisfactory for the handling of aqueous lactic acid solutions at the lower and intermediate temperatures. At some Functional Groups point between 2 and 10%, aqueous solutions of lactic acid There are a large number of organic acids of complex begin to attack Type 304 and CF-8 stainless steels exces- structure which have found extensive use in industry and sively. One can then use Type 316 stainless steel and its home. The corrosion characteristics of this group of cast counterpart CF-8M which shows good resistance compounds varies widely, as do the organic structures. throughout the range of concentrations and temperatures Organic acids with other functional groups describe the explored (Table LXV11). Thorough testing of Type 316

TABLE LXV Corrosion of Alloys in Various Concentrations of Aqueous Lactic Acid

Conditions: % Lactic Acid 0.5 1 2 5 45 10-50 Temperature, ºC 100 65 100 26 26 54 Temperature, ºF 212 149 212 79 79 129 Test Period, days 1 1 1 21 14 15 Other – – – – Aerated; Field Test agitated in vacuum evap. Corrosion Rate 0.5% 1% 2% 5% 45% 10-50% Alloy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy Type 304 Stainless Steel .03 1 Nil Nil .03 1 – – – – – – INCONEL alloy 600 – – – – – – – – Nil 0.1 .20 8 C71000 (Cupro- nickel 80- 20) – – – – – – .02 0.9 – – – – C71500 (Cupro-nickel 70-30) – – – – – – – – – – 1.4 57

References 19, 49

Page 53 service in specific applications. It will be noted that some The use of Alloy 400 and the copper-nickel alloys is rates exceeding .25 mm/y (10 mpy) have been obtained dependent on the aeration to be encountered in the acid for the Type 316 alloy in lactic acid at boiling temperatures. stream. Nickel-copper alloy 400 has excellent resistance At the higher temperatures, it is considered to be good to all concentrations of the hot lactic acid solutions in the practice to use an L-grade stainless steel if welding is to be absence of air. However, corrosion becomes excessive if performed on the alloy. Table LXVI shows appreciable aeration is provided as a condition of the exposure. differences for annealed and sensitized conditions for cast stainless steels exposed to the acid at elevated temperatures and pressures. This admonition is true for the use of the stainless steels in all of the organic acids when exposed at the higher temperatures.

TABLE LXVI High Temperature Exposure of Cast Stainless Steels in Aqueous 50% Lactic Acid (Laboratory tests in autoclaves for 18-22 hours at temperatures shown)

Corrosion Rate 107 ºC (225 ºF) 151 ºC (304 ºF) 157 ºC (315 ºF) 162 ºC (324 ºF) Alloy mm/y mpy mm/y mpy mm/y mpy mm/y mpy CF-8 Nil Nil – – 27.94 1100 – – CF-8* Nil Nil 44.20 1740 39.88 1570 – – CF-8M Nil Nil Nil Nil – – – – CF-8M* Nil Nil 2.03 80 – – .99 39 Copper 2.29 90 – – – – 1.65 65

*650 ºC (1202 ºF) for one hour, water quenched. Reference 9 4200-Gallon Uniframe Transport Container. One of a fleet of five Uniframe Type 304 stainless steel transport tanks with 6″ of foam in- place insulation being lifted aboard ship at Seattle with a load of milk TABLE LXVII for Alaska. These tanks make the long trip by flatbed truck trailer, ship, Corrosion of Alloys in Boiling Aqueous Lactic Acid and rail flatcar between Seattle and Alaska. Solutions During Five-Day Laboratory Tests

Corrosion Rate 3. Tartaric Acid Alloy mm/y mpy mm/y mpy mm/y mpy Tartaric acid (dihydroxybutanedioic acid) is one of the Type 304 .08–54.61 3–2150 56.64 2230 7.21 284 more innocuous acids produced in large quantity. As Stainless Steel indicated by Table LXVIII, the product is not aggressive in Type 309 3.30 130 – – – – aqueous solution up to the boiling point. Any of the Stainless Steel austenitic stainless steels maintain purity in the product and Type 316 <.03–.38 <1–15 .03 1 .08–.333–13 prevent undesired contamination when storing or Stainless Steel processing the tartaric acid solutions. Higher alloys are not <.03 <1 .03 1 .18 7 CARPENTER indicated to be required for such service. alloy 20Cb-3 INCOLOY <.03 <1 – – – – 4. Citric Acid alloy 825 Citric acid (hydroxypropane tricarboxylic acid) is a more HASTELLOY .05 2 .03 1 .03 1 aggressive compound. This tart-tasting constituent of alloy C-276 HASTELLOY – – .10 4 .05 2 citrus products can be handled well by the austenitic alloy B stainless steels. Data for many of the other alloys are INCONEL – – .43 17 .38 15 shown in Table LXIX. Here it will be noted that Alloy 400 alloy 600 is a candidate for use in many of the food product services. MONEL .13–.33 5–13 .15 6 .15 6 Others have described the use of MONEL alloy 400 and alloy 400 other nickel-base alloys for such use.14, 41, 42 As with the Copper .33 13 .05 2 .08 3 other organic acids, the presence of air will determine the Zirconium Nil Nil Nil Nil Nil Nil rate of corrosion on Alloy 400 in these solutions. Alloy Titanium .03 1 .03 1 <.03 <1 600 and other alloys of chromium and nickel have good Tantalum Nil Nil Nil Nil Nil Nil Columbium <.03 <1 – – <.03 <1 resistance to the acid and can be used when desired.

References 49, 51

Page 54 Chloride is a commonly encountered contaminant in with such solutions. However, the presence of chlorides in citric acid solutions. The effect on the austenitic stainless combination with an acid create potential problems of steels of this contaminant in 20% aqueous citric acid is pitting and stress-corrosion cracking particularly in cre- shown in Table LXX. At levels up to 500 ppm of chloride, vices and other stagnant areas in the equipment. no significant general corrosion occurs on stainless steel

TABLE LXVIII Corrosion of Metals by Aqueous Tartaric Acid Solutions

Conditions: Laboratory tests without aeration or deaeration except as noted.

Corrosion Rate

2 5 10 25 30 50 57 %Tartaric Acid 26 (79) 26(79) 35(95) 60(140) 100(212) 103(217) 35(95) 60(140) 100 (212) 26(79) 60(140) 35(95) 60(140) 100(212) 54(129) Temperature ºC (ºF) 21 21 6 6 6 2 6 6 6 11 11 6 6 6 10 Test Period, days – – Aerated Aerated Aerated – Aerated Aerated Aerated – – Aerated Aerated Aerated Field lead. Other yacuum yap. Alloy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy

Type 304 Stainless Steel – – – – – – – – – – Nil Nil – – – – – – – – – – – – – – – – – – Type 316 Stainless Steel – – – – – – – – – – .03 11 – – – – – – – – – – – – – – – – – – CARPENTER alloy 20 – – – – Nil Nil .01 .4 .01 0.2 – – Nil Nil .01 .02 Nil 0.1 – – – – Nil Nil .01 0.4 .05 2.1 – – INCONEL alloy 600 – – – – – – – – – – – – – – – – – – – – – – – – – – – – .06 2.4 ELGILOY – – – – – – – – – – Nil Nil – – – – – – – – – – – – – – – – – – Titanium – – – – Nil Nil Nil .1 Nil 0.1 – – Nil Nil Nil 0.1 Nil Nil – – – – Nil Nil Nil Nil .01 0.5 – – Zirconium – – – – Nil Nil Nil Nil Nil <0.1 – – Nil Nil Nil Nil Nil <0.1 – – – – Nil Nil Nil Nil Nil Nil – – Vanadium – – – – .01 0.4 .04 1.5 .48 19 – – – – – – – – – – – – – – – – – – – – C71000 (80-20 Cupro- nickel) – – .02 0.8 – – – – – – – – – – – – – – – – – – – – – – – – – – C71500 (70-30 Cupro- nickel) .04 1.6 – – – – – – – – – – – – – – – – .03 1.2 .05 1.8 – – – – – – – – References 19, 46, 50

TABLE LXIX Corrosion of Metals by Citric Acid

Corrosion Rate

% Type 316 Citric Test Stainless INCOLOY INCONEL MONEL C71500 (70-30 CARPENTER Acid Temperature Period Steel alloy 825 alloy 600 Nickel 200 alloy 400 Cupro-nickel) Copper alloy 20Cb-3

ºC ºF Days mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy

1 26 78.8 44 – – – – – – .01 2 Nil Nil – – – – – – 2 26 78.8 7 – – – – – – .06 2.2 – – – – – – – – 26 78.8 21 – – – – – – .16 6.2 – – .06 2.5 .07 2.8 – – 5 16 60.8 30 – – – – – – .02 .9 .03 1.1 – – – – – – 30 86 7 – – – – – – .12 4.9 – – .02 .8 – – – – 60 140 7 – – – – – – .13 5 – – – – – – – – 7 102 216 3 – – – – 09 3.5 – – – – – – – – – – 10 100 212 6 – – – – – – – – – – – – – – .01 .2 15 66 150.8 3 – – – – – – .10 4.1 .07 2.7 – – – – – – 100 212 2 – – – – – – .11 4.2 – – – – – – – – 20 Boiling 45 Nil Nil – – – – – – – – – – – – – – 25 100 212 6 – – – – – – – – – – – – – – Nil .1 30 26 78.8 11 – – – – – – – – .04 1.5 – – – – – – 60 140 11 – – – – – – – – .19 7.4 – – – – – – Boiling 7 – – – – – – .22 8.8 .21 8.4 – – – – – – 50 20 68 1 – – – – – – – – .53 2.1 – – – – – – 100 212 6 – – – – – – – – – – – – – – Nil Nil Boiling 6 – – – – – – – – – – – – – – .14 5.5 58 26 78.8 7 – – – – – – Nil .1 Nil .1 – – – – – – 90 194 2 – – – – 53 21 – – – – – – – – – – Boiling 1 – – – – – – .43 16.8 .16 6.2 – – – – – – 61 60 140 30 – – – – 02 0.6 .01 .5 .02 .9 – – – – – – 60-78* 42-64 37 – – – – 06 2.4 – – – – – – – – – – 107.6- 147.2 65 Boiling 30 .21 8.1 .12 4.8 .79 31 .19 7.3 .11 4.2 – – – – – –

*Field test in evaporator during concentration of the acid. References 19, 49, 51

Page 55 TABLE LXX Corrosion of Stainless Steels by Citric Acid Containing Chlorides

Corrosion Rate

Solution 20 wt. per cent Citric Acid 20 wt. per cent Citric Acid No Chloride 500 ppm NaCl No Chloride 500 ppm Chloride

Temperature, ºC (ºF) 85 (185) 85 (185) 100 (Boiling) (212) 100 (Boiling) (212)

Metal Specimen 1 Specimen 2 Specimen 1 Specimen 2 Specimen 1 Specimen 2 Specimen 1 Specimen 2 Type 304 <.03 <1 <.03 <1 .10 4 .08 3 <.03 <1 <.03 <1 .03 1 .03 1 Stainless Steel Type 316 <.03 <1 <.03 <1 Nil Nil Nil Nil <.03 <1 <.03 <1 <.03 <1 <.03 <1 Stainless Steel

5. Chloroacetic Acids Corrosion data for a wide range of alloys exposed to The chloroacetic acids are a most important product for various monochloroacetic acid solutions are contained in the preparation of drugs, dyes, agricultural chemicals and Table LXXI. It will be noted that Type 316 stainless steel as intermediates for the preparation of other organic appears to be attractive in a number of these exposures. compounds. Monochloroacetic acid and dichloroacetic Such an inducement for use of the austenitic stainless acid are normally produced simultaneously and separated steels should be approached carefully. Pitting and stress- as desired. Trichloroacetic acid may be produced by an corrosion cracking in such a medium could be disastrous. additional process step. A better choice for handling the product in aqueous

TABLE LXXI Corrosion of Alloys in Monochloroacetic Acid (MCA)

Testa 1 2 3 4 5 6 Temperature ºC (ºF) 25 (77) 25 (77) 60 (140) 18 (64) 55 (131) 170 (338) Test Period, days – – 28 1 7 22 Corrosion Rate Alloy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy MONEL alloy 400 .18 7 .28 11 .18 7 .43 17 .05 2 .10 4 Nickel 200 .51 20 .56 22 .18 7 .69 27 .03 1 .08 3 INCONEL alloy 600 – – – – – – .61 24 .03 1 3.56 140 Copper – – – – – – .48 19 .08 3 – – HASTELLOY alloy B .03 1 – – .51 20 .15 6 .03 1 .18 7 HASTELLOY alloy C .10 4 – – .94 37 <.03 <1 <.03 <1 .36 14 HASTELLOY alloy D .03 1 .33 13 .79 31 – – – – – – CARPENTER alloy 20 – – – – – – <.03 <1 .05 2 .70 28 Type 316 Stainless .20 8 .97 38 2.16 85 <.03 <1 .08 3 20.32 800 Type 317 Stainless – – – – – – <.03 <1 .05 2 – – DURICHLOR .66 26 2.03 80 2.21 87 <.03 <1 <.03 <1 1.27 50 Lead – – .94 37 – – – – .33 13 – – Silver – – – – – – .05 2 .03 1 – – 30% Nickel Cast Iron – – – – – – – – – – .53 21 NICHROME V* – – – – – – – – – – 1.50 59

a1–Laboratory test in 60% monochloroacetic acid liquor from a process containing 1.5% acetyl chloride, 0.5% hydrogen chloride and the remainder acetic acid. Light agitation. 2–Same as No. 1 with high agitation. 3–Field test in MCA liquor comparable to that of Test No. 1 4–Field test in tank containing 78% MCA in water with moderate aeration 5–Field test in same solution as Test No. 3, but with no aeration. 6–Field test in refined MCA in storage tank. *Trademark of Driver-Harris Company

Page 56 solution would be nickel-copper Alloy 400 or the nickel- systems at moderate temperatures. based molybdenum-chromium-iron alloy. The use of The decomposition products of such acids at the higher Alloy 400 is contingent again on the removal of oxidizing temperatures can present unique corrosion problems that species from the aqueous systems; residual chlorine, air or should be avoided. This is particularly true when nickel or other oxidants, can greatly increase the rate of attack. copper-containing alloys are used. Discoloration of the For the reaction area in chloroacetic acid production amino acid can occur when using nickel or copper alloys equipment, where chlorine is reacted with acetic acid, at temperatures above ambient temperatures. glass-lined steels, TEFLON-lined, or other fluorocarbon The austenitic stainless steels are most satisfactory for plastic-lined equipment is often used. HASTELLOY alloy handling the amino acids. No problem with their use is C-276 appears to be acceptable for many of these ex- usually anticipated until temperatures above the boiling posures, but the conventional process utilizes lined equip- point of the aqueous systems are encountered. Some of the ment for the reaction area. Other metals such as tantalum acids not normally encountered, such as cyanuric acid, or titanium may also be used if available. can be corrosive in streams and should be identified as a Trichloroacetic acid is perhaps even more corrosive than potential corrodent when choosing materials of construc- monochloroacetic acid. Glass-lined equipment, titanium, tion for applications involving amine solutions. HASTELLOY alloy B-2, DURICHLOR and certain other specific alloys selected after extensive testing may be used 7. Sulfoacetic Acid for handling the material at lower temperatures. None of Sulfoacetic acid characterizes one of those organic acids the chloroacetic acids should be stored or processed in any containing a sulfur atom. The material is not particularly quantity without a thorough understanding of the corrosive corrosive once it is prepared and has the general charac- nature of these materials and the judicious choice of the teristics of acetic acid itself. If the preparation is made by materials of construction for tankage or process the addition of a strong sulfuric acid solution to acetic equipment. Although the nickel-based alloys are prime anhydride, the process conditions are too severe for use of candidates for use in these solutions once the free chlorine the austenitic stainless steels. HASTELLOY alloys B-2 is removed, all alloys may show evidence of pitting or and C-276 are apparently acceptable for this step based crevice corrosion in the halogenated acids, and a thorough upon service experience. Once the product is prepared, the exploration of corrosion resistance of the various alloys in austenitic stainless steels are almost always excellent for a specific stream should be conducted. handling the acid up to 100 ºC (212 ºF). 6. Amino Acids The aminocarboxylic acids are an important group of chemicals used for the preparation of drugs, agricultural chemicals and as precursors for numerous other organic compounds. As a group, the compounds are not excessively corrosive. The basic material glycine (aminoacetic acid) provides essentially the same corrosive characteristics as acetic acid at the lower temperatures and is less corrosive than its counterpart at the higher temperatures. As the molecule is lengthened, the amino acids become less corrosive, and those above approximately four carbons in length can be considered as inhibitors in aqueous

INCOLOY alloy 825 tanks for the storage of monochloracetic acid resin solution. This alloy was required to maintain product purity.

Page 57 PART IV. ESTER PREPARATIONS is continually removed as the process continues. The A. Acetic Esters residual sulfuric acid concentration continually increases One major use of acetic acid is as a precursor of the various and can then create very aggressive conditions toward esters that become important solvents for paints and other latter stages of a batch process run. chemical products. In the production of acetic esters, the The kettle used for this process is of major concern. The acid is combined with other organic compounds contain- heating coils, calandria, or other heating device sustains ing a hydroxyl group. The more common esters are ethyl the major corrosion in the process. On the tubes of such a acetate, butyl acetate, isopropyl acetate and Cellosolve heater, severe pitting, grooving and general attack develop acetate. by concentration of the acid on the hot surface, by the Corrosion to be expected in the preparation of these formation of tars on the metal and, in some instances, by esters can vary greatly depending on the operation. If the accumulation of corrosive salts from the solution. As a acetic acid were the only corrosive contaminant present, consequence, it is exceptionally difficult to provide defini- the data provided previously for acetic acid could be used tive data for the corrosion of a specific alloy in the as a guide. Unfortunately, a catalyst is necessary to preparation of these esters. Only empirical data obtained improve the efficiency of the process, and in most over a lengthy period of time will provide proper guidance instances, the presence of this catalyst determines the for the final selection of the material of construction for corrosion to be expected. Temperatures required for the the coils, kettle, vapor lines, condensers and a primary production of these esters will range from 60 to 150 ºC column for the process. (140-302 ºF), depending on the boiling point of the ester. In Table LXXII, field data obtained by the exposure of Sulfuric acid has long been used as the catalyst for numerous alloys in five different ester preparations are synthesis of the esters. This is added as concentrated provided. It will be seen here that considerable variation sulfuric acid in small quantities of only 0.5 to 2.0% of the exists in the data obtained for any one alloy. Because of total charge. In anhydrous medium, this would not be the great turbulence existing and the factors enumerated excessively corrosive. However, water is produced by the above, the corrosion of an alloy in the same process reaction between the alcohol and acid which can serve as a during two different exposures can be greatly different. temporary diluent for the sulfuric acid. The water formed Although the data would indicate that Type 304 stain-

TABLE LXXII Corrosion of Alloys in Batch Acetic Ester Preparations Conditions: Exposure of racks in same kettle during the preparation of esters using sulfuric acid catalyst. Temperature varies with ester prepared. Cupric ion present. Liquid (L) and vapor (V) exposures. Test 1–Ethyl and isopropyl acetate alternately for 50 days @ 110 ºC (230 ºF). Test 2–Isopropyl acetate for 14 days @ 110 ºC (230 ºF). Test 3–Amyl acetate for 11 days @ 115 ºC (239 ºF). Test 4–Ethyl and isopropyl acetate alternately for 81 days @ 110 ºC (230 ºF). Test 5–Butyl and methyl Cellosolve acetate alternately for 29 days @ 115 º C(239 ºF) and 150 ºC (302 ºF).

Corrosion Rate

1 2 3 4 5

L V L V L V L V L V

Alloy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy mm/y mpy

Type 304 – – – – .05 2 .56 22 .15 6 .28 11 .05 2 .43 17 .05 2 .30 12 Stainless Steel Type 329 – – – – <.03 <1 – – .15 6 – – .28 11 – – .03 1 .03 1 Stainless Steel Type 316 .18 7 .10 4 <.03 <1 .23 9 .18 7 .23 9 .08 3 .10 4 .03 1 <.03 <1 Stainless Steel Type 216 .23 9 .41 16 – – – – – – – – .23 9 .08 3 – – – – Stainless Steel CARPENTER .13 5 .13 5 – – – – – – – – – – – – .03 1 alloy 20 Cb-3 JESSOP – – – – – – – – – – – – – – – – – – .03 1 alloy JS-700 HASTELLOY – – – – .03 1 .03 1 .08 3 .08 3 .05 2 .05 2 – – – – alloy G MONEL .86 34 .15 6 – – .13 5 – – .08 3 – – .03 1 – – – – alloy 400 Copper 1.65 65 .10 4 4.57 180 .05 2 1.42 56 .08 3 2.72 107 .43 17 .13 5 .03 1

Page 58 less steel would be satisfactory for immersion conditions increases rapidly as the sulfuric acid is concentrated in the in an esterification kettle, this is most unlikely. The use of kettle. Also, there can be some small amount of degrada- Types 316 or 316L stainless steels is borderline for these tion of the acid to provide corrosive sulfur compounds in applications. As the alloy content is increased, reduced the vapor. rates of attack are obtained, but the economics of the The severe effect of the acid conditions on a heating selection require detailed analysis before committing one surface is apparent by reviewing the data of Table LXXIV. to a final decision. Laboratory “hot wall” tests of various alloys show the It will be noted that those materials high in nickel have corrosion to be much higher for the materials than would good promise for use in the process. It has been reported be experienced in a simple boiling solution. Certainly, that nickel-copper Alloy 400 has been used extensively for experience in the field has confirmed the severe corrosion pumps, reactors, heating coils, piping and agitators for to be expected on such heating surfaces in the process. For such acetic acid services in unaerated solutions where this reason, graphite calandrias are sometimes used to sulfuric acid is present.22 The data and literature show that assure adequate resistance of the heating element. in numerous instances nickel-chromium Alloy 600 has There are other, less corrosive acids available for cata- exhibited excellent resistance to esterification environ- lyzing the esterification reaction. Toluene sulfonic acid ments. For instance, INCONEL alloy 600 exposed in an (TSA) has often been used for this purpose and, in amyl acetate preparation at 149 ºC (300 ºF) during a 28- day exposure showed corrosion of only .15 mm/y (6 mpy) while MONEL alloy 400 showed a rate of .69 mm/y (27 mpy). Some combinations of Type 316 stainless steel, TABLE LXXIII Alloys 400 and 600 and the copper alloys are indicated to be the basic choices for this service. Effect of Sulfuric Acid Concentration on Corrosion of When using an austenitic stainless steel, such as the Type 316 Stainless Steel in an Esterification Reaction Type 316L, it can be shown that a considerable reduction Conditions: Solution of 25% acetic acid, 59% butyl of the corrosion rate can be achieved by the addition of acetate, 10% water and 6% butanol prepared oxidizing ions to the solution. Cupric and ferric ions are and sulfuric acid added as indicated. Tests both effective for this purpose. One way of providing such conducted at the boiling point. an environment is the use of a copper alloy kettle with stainless steel heating coils. The stainless steel can have an Corrosion Rate adequate life in such service, whereas an all Type 316L % Sulfuric Acid Added (as 95% H SO ) mm/y mpy stainless steel system would not be acceptable. 2 4 The effect of the concentration of sulfuric acid in such a 0.0 Nil Nil batch process can be noted by reference to Table LXXIII. 0.1 .48 19 At the temperatures of the esterification reaction, the 0.5 5.92 233 corrosion rate of Types 316 and 316L stainless steels 1.0 17.53 690

TABLE LXXIV “Hot Wall” Tests of Alloys in a Synthetic Esterification Mixture Conditions: Laboratory tests using “hot wall” apparatus for three days (<3 days for alloys showing

high corrosion rates) in a mixture of 83% acetic acid–9.3% formic acid–3.8% H2S04– 3.9% water. Comparison with conventional immersion test at boiling temperature 112 ºC (234 ºF) provided.

Hot Wall Hot Wall Hot Wall Immersion Solution Specimen Corrosion Test Corrosion Temperature Temperature Rate Rate Alloy ºC ºF ºC ºF mm/y mpy mm/y mpy E-BRITS 26-1 120 248 150 302 3.94 155 1.88 74 HASTELLOY alloy G 112 234 155 311 .99 39 .20 8 HASTELLOY alloy C-276 118 244 140 284 .48 19 – – MONEL alloy 400 118 244 137 277 .41 16 – – Copper (C10200) 118 244 135 275 1.42 56 – – Zirconium 118 244 142 288 .03 1 – – Type 316 Stainless Steel – – – – – – 3.63 143

Page 59 general, affords less corrosion of austenitic stainless steel equipment. The ester itself is innocuous and can be surfaces than does the sulfuric acid. Table LXXV shows processed or handled in steel equipment if contamination data obtained by field exposure of various alloys in a TSA of the product is not objectionable. Thus, the concern catalyzed reaction during two different runs. Other mate- with corrosion in such a process is centered totally in the rials that can be used are benzene sulfonic acid and reaction area of the equipment. acetylsulfoacetic acid (ASA). Of these, the ASA is the least corrosive to the austenitic stainless steels but increases the rate of attack on copper alloys significantly. B. Phthalate Esters Tables IV and XXI show other data relating to the The phthalate esters are prepared directly from the anhy- preparation of these esters. Table XXI particularly lists a dride in a manner analogous to the preparation of the wide range of alloys evaluated in a synthetic butyl acetate acetic esters. The temperatures are higher, but a drier reaction mixture. medium is maintained than during acetic ester prepara- One of the newer catalysts for use under certain tions. Table LXXVII shows typical data generated by circumstances for esterification reactions is boron tri- three exposures of numerous alloys in phthalic ester fluoride. Table LXXVI shows data generated by condi- preparations. The same general statements as provided tions required for such a reaction. Type 316 or Type 316L for the acetic esters relate to this type of exposure. stainless steels appear to be adequate for this reaction. Phthalate esters prepared from octyl, decyl and other However, extensive testing should be conducted before alcohols are important as plasticizers for various plastics. committing an austenitic stainless steel to such a fluoride They also have excellent heat stability and can be used environment. for heating mediums for a number of processes. As indicated, essentially all the corrosion to be experienced in the esterification process occurs in the reaction kettle and appurtenant equipment. Distillation of the C. Esterification of Fatty Acids esters from the kettle is normally conducted in a Type Esterification of the fatty acids to produce soap is not 316L stainless steel still to assure low corrosion rates in 28, 32-34 exceptionally corrosive. Data shown in Table this equipment. However, further refining of the ester, or LXXVIII reveal moderate corrosion of the stainless other techniques required for improving the quality of the steels, and very low corrosion rates of the more highly product, can be conducted in Type 304 stainless steel alloyed materials in three different field exposures. As with other esterifications, once the esterification itself is completed, processing of the product becomes much less difficult; Type 304 stainless steel is satisfactory for such a TABLE LXXV purpose. Corrosion of Alloys in a Typical Acetic Esters Reaction Conditions: Batch reactions producing butyl acetate D. Acrylate Esters with kettle exposure of alloys in 25-45% The acrylate esters comprise one of the newer, more acetic acid, 30% acetates, 20% alcohol, reactive group of chemicals available for the synthesis of a 5-8% water and 0.75% toluene sulfonic acid. Test 1 conducted at 107 ºC (225 ºF) for 34 days and Test 2 at 121 ºC (250 ºF) for 29 days. TABLE LXXVI Comparison of Esterification Catalysts on Corrosion Rate Corrosion of Alloys Test 1 Test 2 Conditions: Preparation of a higher acetic ester in semi- Alloy mm/y mpy mm/y mpy works equipment using 1.5 per cent sulfuric Type 304 Stainless Steel 11.18 440 8.38 330 acid at 75-110 ºC (167-230 ºF) during 32 Type 329 Stainless Steel .25 10 – – days for Test 1 and 0.32 per cent boron trifluoride at 75-85 ºC (167-185 ºF) for 5 Type 316 Stainless Steel .33 13 1.14 45 days in Test 2. Type 317 Stainless Steel .43 17 – – CARPENTER alloy 20 .36 14 – – Corrosion Rate INCOLOY alloy 825 1.27 50 – – Test 1 Test 2 ILLIUM alloy G .58 23 – – Alloy mm/y mpy mm/y mpy HASTELLOY alloy C .20 8 – – Type 304 Stainless Steel .03 1 .43 17 HASTELLOY alloy B .58 23 – – Type 316 Stainless Steel .03 1 .05 2 INCONEL alloy 600 .23 9 – – E-BRITE 26-1 .05 2 2.49 98 MONEL alloy 400 .51 20 .18 7 CARPENTER alloy 20Cb-3 .03 1 .03 1 Nickel 200 .99 39 .43 17 HASTELLOY alloy C-276 Nil Nil Nil Nil Copper .51 20 .18 7 Copper (C10200) .18 7 .30 12

Page 60 wide range of resinous products. The esters are best be used to reduce corrosion in the reaction area. In the data known as the starting material for the preparation of latex shown, conditions in the vapor line from the reactor are paints. even more corrosive than those encountered in the kettle Previous comments given in the sections on acrylic acid liquid. This situation may or may not occur in a similar and the acetic esters are pertinent to the production of the unit, depending on the mode of operation. acrylates. It was pointed out in the discussion of the The coils, or other heating apparatus used on the kettle, acrylic acid that a simultaneous production of the ester will again experience the greatest corrosion. For this can be achieved starting with propylene. If the process reason, a major effort should be made to identify the produces only acrylic acid, the acid is reacted in a manner optimum material of construction for this service. Graph- analogous to that used for the acetic esters.27 ite construction is sometimes used for this specific area. Ethyl acrylate is produced in a continuous system by As for the other ester preparations, Type 304 stainless the addition of sulfuric acid, or a similar catalyst, to the steel is adequate for many of the recovery stages following acid in alcohol. As in the case of the acetic esters, the the reaction. If wash waters are used in the process, the conditions in the reactor are most aggressive. Type 316L possibility of stress-corrosion cracking from chlorides in stainless steel can usually be used for all equipment the water should be considered. Otherwise, the stainless following the reaction step, and Type 304 stainless steel steels will provide product of a good quality at a minimum can be used for many of the recovery areas. On the other cost. Duplex structured stainless steel such as Type 329 or hand, the conditions in the kettle can be so severe that alloys containing higher nickel contents such as Alloys alloy materials higher than the austenitic stainless steels 600 and 800 are resistant to chloride stress-corrosion are required. cracking in this service. Table LXXIX shows typical data from the exposure of The higher acrylate esters (four carbon and higher) are coupons in an ethyl acrylate synthesis. Note the extreme produced in a manner comparable to the ethyl acrylate corrosion of Type 316 stainless steel which occurred. As process. However, the temperatures are higher and the in the case of acetic esters, combinations of nickel-copper attendant corrosion is increased. Here the reaction condi- Alloy 400, nickel-chromium Alloy 600, copper alloys and tions are extremely severe, as noted in Table LXXX. the nickel-base molybdenum-chromium-iron alloys may Extensive corrosion testing should be conducted to identify the desired materials of construction for the reactor

TABLE LXXVII Corrosion Generated in Phthalic Anhydride Esterifications

Exposure 1–Octyl phthalate batch preparation using 0.15% H2SO4 with trace chloride present in some batches. Exposure of 83 days on 84 rpm agitator shaft in kettle liquid at average of 149 ºC (300 ºF). Exposure 2–Higher alcohols and phthalic anhydride plus 0.5% toluene sulfonic acid

and 0.25% H2SO4 at 140 ºC (284 ºF) average for 135 days in kettle liquid. Exposure 3–Toluene sulfonic acid catalyzed reaction of phthalic anhydride and higher alcohols at 174 ºC (345 ºF) for 10 days in glass laboratory kettle.

Corrosion Rate 1 2 3 Alloy mm/y mpy mm/y mpy mm/y mpy Type 304 Stainless Steel .25 10 >1.27 >50 .05 2 Type 202 Stainless Steel .30 12 – – – – Type 316 Stainless Steel .15 6 1.60 63 .05 2 Type 317 Stainless Steel .08 3 1.04 41 – – CARPENTER alloy 20 .03 1 .03 1 – – ACI CN-7M Casting <.03 < 1 – – – – HASTELLOY alloy C .03* 1* – – .03 1 HASTELLLOY alloy B .08* 3* <.03 <1 – – INCOLOY alloy 825 .03 1 .03 1 – – INCONEL alloy 600 .10 4 .33 13 – – MONEL alloy 400 – – .08 3 .13 5 Nickel 200 .18 7 .20 8 – – Ni-Resist Type2 – – .15 6 – – Copper – – – – .18 7 Titanium .08* 3* – – – –

*No Pitting. All other alloys pitted to some extent.

Page 61 and accompanying equipment. In general, the vapor from interest from a corrosion standpoint. The Reppe process the reactor is no worse than that described for the ethyl prepares the ester from acetylene, carbon monoxide and acrylate process. However, the first distillation column in alcohol. This reaction is conducted in an acid medium the recovery chain can experience severe corrosion in the with nickel chloride present. As a consequence, corrosion base, and the use of nickel-base molybdenum-chromium- in the reaction area can be very high. iron alloys and other highly corrosion-resistant materials Table LXXXI shows data obtained in a reaction to should be evaluated for use in this area. prepare ethyl acrylate by this procedure. Note that the As described before, conditions in the recovery system liquid contains over two per cent hydrochloric acid along are not severe. The austenitic stainless steels are used for with free acrylic acid. Among the alloys tested, only the vast majority of the equipment. Again, adequate HASTELLOY alloys B and C-276 appear to offer good attention should be given to the possible detrimental corrosion resistance in this environment. Once the ester is introduction of chlorides or other foreign species into the removed from the reaction medium, the conventional streams. materials of construction for recovery of the ester can be One other method of preparing ethyl acrylate is of employed.

TABLE LXXVIII Field Exposure of Alloys in Fatty Acid Esterifications

Exposure 1–On agitator shaft in liquid of kettle during esterification of C12-C18 fatty acids with

alcohols + 0.25% H2SO4 at 100 ºC (212 ºF) for 33 days. Exposure 2–In liquid of kettle near head during esterification of fatty acids (myristic present) with alcohols (isopropanol present) with sulfuric acid at approximately 110 ºC (230 ºF) for 82 days. Exposure 3–Liquid and vapor phase of a kettle (liquid velocity ca. 16 ft/sec) for 18 days during glyceryl esterification, amidation and sulfurization of tall oil.

Corrosion Rate 1 2 3* Liquid Liquid Liquid Vapor Alloy mm/y mpy mm/y mpy mm/y mpy mm/y mpy Type 304 Stainless Steel .51 20 .16 6.2 .23 9 <.03 <1 Type 216 Stainless Steel – – .03 1.1 – – – – Type 316 Stainless Steel .51 20 .15 5.8 .05 2 <.03 <1 Type 317Stainless Steel – – .08 3.1 – – – – CARPENTER alloy 20Cb-3 .10 4 .01 0.4 – – – – ACI CN-7M Cast Alloy – – – – <.03 <1 <.03 <1 NITRONIC** 50 – – .02 0.9 – – – – INCOLOY alloy 825 – – .01 0.4 – – – – INCONEL alloy 600 .25 10 – – .13 5 <.03 <1 INCONEL alloy 625 – – .02 0.7 – – – – HASTELLOY alloy G – – .01 0.4 – – – – HASTELLOY alloy C-276 – – .01 0.5 <.03 <1 <.03 <1 HASTELLOY alloy B – – .09 3.7 .18 7 .15 6 JESSOP JS-700 – – .05 2.0 – – – – MONEL alloy 400 .10 4 – – .56 22 .30 12 Nickel 200 – – – – .97 38 .36 14 Copper .15 6 – _ – – – – Titanium – – .01 0.3 – – – – 30% Nickel Cast Iron – – – – .33 13 .15 16 Ni-Resist Type 1 – – – – .15 6 .30 12 *Reference 30 **Trademark of Armco Steel Corporation

Page 62 TABLE LXXIX TABLE LXXXI Corrosion of Alloys in Ethyl Acrylate Synthesis Corrosion of Alloys in Ethyl Acrylate Preparation from Acetylene Conditions: Specimens exposed in an ethyl acrylate reactor for 74 days at a temperature of Conditions: Specimens exposed in the reaction kettle 110 ºC (230 ºF) with sulfuric acid catalyst. where acetylene, carbon monoxide, ethanol and nickel chloride were agitated heavily for Corrosion Rate 17 days. Acids formed were approximately Vapor Line 5% acrylic and 2.5% hydrochloric acid.

Base of Reactor from Reactor Alloy mm/y mpy mm/y mpy Type 304 Stainless Steel .89 35 5.08 200 Corrosion Rate Type 316 Stainless Steel .25 10 >10.16 >400 CARPENTER alloy 20 .13 5 .33 13 Alloy mm/y mpy HASTELLOY alloy G .13 5 – – Type 316 Stainless Steel 1.27 50 HASTELLOY alloy C .08 3 .20 8 CARPENTER alloy 20 .33 13 HASTELLOY alloy B .03 1 .51 20 HASTELLOY alloy C-276 .08 3 HASTELLOY alloy D .05 2 – – HASTELLOY alloy B .05 2 INCONEL alloy 600 .08 3 .91 36 Nickel 200 .25 10 MONEL alloy 400 .03 1 .58 23 MONEL alloy 400 2.03 80 Nickel 200 – – .63 25 Copper 3.30 130 Copper .03 1 1.14 45 Titanium .53 21 – – Zirconium <.03 <1 – –

TABLE LXXX Corrosion of Alloys in Higher Acrylate Esters Production Conditions: Exposure in base of reactor processing higher acrylates at 110-160 ºC (230-320 ºF) for times shown. Sulfuric acid catalyst used.

Butyl Octyl Decyl

67 days 11 days 11 days Corrosion Rate

Alloy mm/y mpy mm/y mpy mm/y mpy Type 316 Stainless Steel 3.63-5.49 143-216 10.16 400 >38.1 >1500 CARPENTER alloy 20 .13-.58 5-23 1.78 70 1.27 50 INCOLOY alloy 825 .61 24 – – – – HASTELLOY alloy G .10 4 – – – – HASTELLOY alloy C .08-.61 3-24 1.02 40 .76 30 HASTELLOY alloy B .15-.28 6-11 – – – – HASTELLOY alloy D .08 3 – – – – INCONEL alloy 600 .66-1.24 26-49 2.79 110 1.90 75 MONEL alloy 400 .18-.25 7-10 – – – – DURIRON .03 1 – – – – Titanium .08-.13 3- 5 – – – – Zirconium .03-.05 1- 2 – – <.03 <1

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Page 64

TRADEMARKS PRODUCT OF

ALLEGHENY Allegheny Ludlum Steel Corporation ALOYCO Aloyco Inc. AMBRALOY Anaconda American Brass Co. CARPENTER Carpenter Technology Corporation CHLORIMET The Duriron Company, Inc. CROLOY Babcock & Wilcox Co. CRUCIBLE Colt Industries Inc. DURALOY The Duraloy Co. DURICHLOR The Duriron Company, Inc. DURIMET The Duriron Company, Inc. DURIRON The Duriron Company, Inc. E-BRITE Allegheny Ludlum Steel Corporation ELGILOY Elgiloy Co. EVERDUR Anaconda American Brass Co. HASTELLOY Cabot Corporation HAYNES Cabot Corporation ILLIUM Stainless Foundry & Engineering, Inc. INCOLOY INCO family of companies INCONEL INCO family of companies JESSOP Jessup Steel Company KROMARC Westinghouse Electric Corporation MONEL INCO family of companies MULTIMET Cabot Corporation MP35N Standard Pressed Steel Co. NICHROME Driver-Harris Company NITRONIC Armco Steel Corporation STELLITE Cabot Corporation TEFLON E. I. duPont de Nemours & Co. WAUKESHA Waukesha Foundry Company WORTHITE Worthington Corporation PH 15-7Mo Armco Steel Corporation 17-7PH Armco Steel Corporation 17-4PH Armco Steel Corporation