CORROSION RESISTANCE OF NICKEL AND NICKEL- CONTAINING ALLOYS IN CAUSTIC SODA AND OTHER ALKALIES (CEB-2)
A PRACTICAL GUIDE TO THE USE OF NICKEL-CONTAINING ALLOYS NO 281
Distributed by Produced by NICKEL INCO INSTITUTE CORROSION RESISTANCE OF NICKEL AND NICKEL-CONTAINING ALLOYS IN CAUSTIC SODA AND OTHER ALKALIES (CEB-2)
A PRACTICAL GUIDE TO THE USE OF NICKEL-CONTAINING ALLOYS NO 281
Originally, this handbook was published in 1973 by INCO, The International Nickel Company, Inc. Today this company is part of Vale S.A. The Nickel Institute republished the handbook in 2020. Despite the age of this publication the information herein is considered to be generally valid. Material presented in the handbook has been prepared for the general information of the reader and should not be used or relied on for specific applications without first securing competent advice. The Nickel Institute, the American Iron and Steel Institute, their members, staff and consultants do not represent or warrant its suitability for any general or specific use and assume no liability or responsibility of any kind in connection with the information herein.
Nickel Institute [email protected] www.nickelinstitute.org Table of Contents
Page PART I. INTRODUCTION 3
PART II. CORROSION BY CAUSTIC SODA...... 4 A. Nickel ...... _ ...... 4 1. Effect of Concentration, Temperature and Carbon Content ...... _ ...... 4 2. Effect of Velocity ...... _ ... __ ...... _ 6 3. Effect of Aeration .•...... 6 4. Effect of System Thermal Gradients ...... 7 5. Effect of Impurities .,. _...... _ ...... _ ...... 7 6. Effect of Stress ...... 8 7. Effect of Dissimilar Metal Contact .. _ ...... _ ...... _ ...... '. 8 8. Cathodic Protection...... 9 B. Nickel-Chromium Alloys (Alloy 600) .. _ ...... 9 C. Nickel·Copper Alloys (Alloy 400, Alloy K-500) ...... _. 10 D. Copper-Nickel Alloys .... _ ...... _ ...... ___ ...... _ ., 11 Copper-Nickel Alloy CA 706 (90-10) Copper-Nickel Alloy CA 710 (80-20) Copper-Nickel Alloy CA 715 (70-30) E. Iron-Nickel-Chromium Alloys (Alloy BOO) ...... _ ...... _ . .. 13 f. Austenitic Chromium-Nickel Stainless Steels (AISI 300 Series) ...... 13 G. Iron-Base Nickel·Chromium...copper-MoJybdenum AHoys and Nickel-Base Chro- mium...copper-Molybdenum Alloys ...... _ ...... __ ...... , 15 {Alloy 825. CARPENTER 20Cb-3, HASTELlOY alloy G and cast ACt CN-7M alloys} H. Nickel-Base Molybdenum or Molybdenum·Chromium-lron Alloys...... 16 (HASTElLOY alloy C-276, Alloy 625. HASTEllOY alloy B) I. Cast Irons and Ni-Resists .... _ . _ .... __ .. __ . __ ...... 17
PART m. CORROSON BY OTHER ALKAliES...... 19 A. Caustic Potash (KOH) ...... 19 B. Ammonia and Ammonium Hydroxide ...... 20 C. Other Alkaline Solutions of Sodium and Potassium Salts ...... 22
PART IV. INDUSTRIAL APPLICATIONS...... 24 A. Caustic Soda Manufacture ...... 24 B. Caustic Potash Manufacture ...... 28 C. Caustic Soda Storage and Transportation ...... ". 28 D. Soap Manufacture ...... _ ...... _ ...... 30 E. Pulp and Paper Industry ...... __ ...... _ .. _ ...... 32 1_ Digesters _...... 32 2. liquor Heaters ...... 33 3. Black liquor Evaporators ...... _ ...... 34 4. Recausticizing ...... 34 f. Aluminum Industry...... 35 G. Caustic fusions ...... 35 H. Petroleum Refining ...... _ ...... _ . _ ...... 36 I. Caustic DescaJing . _ . _ ...... _ ...... 37 J_ Reclaiming Caustic for Economy and Pollution Control...... 37
PART V. WELDING ...... __ ..... _ ...... 38 A. fabrication of Nickel·Clad Equipment .. _ ...... " 38. B. Repair of Equipment in Caustic Service ...... _ ...... _ ...... 39 References ...... _ ...... ' 40 Trademarks ...... Inside back cover Table I
Nominal Compositions of Nickel Alloys in Use or Corrosion Tested in Caustic Solutions
Composition. %
M;aterial Hi Fe Cr Mo Cu C Si Mn Otber
WROUGHT MATERIALS Nickel Hickel 200 99.5 0.15 - 0.05 0.06 0.05 0.25 - Hickel20t 99.5 0.15 - - 0.05 0.01 0.05 0.20 - DURAH.CKEL· alloy 30t 94.0 0.15 - - 0.15 0.55 0.25 0.25 AI 4.5; Ii 0.5 Nickel-Chromium Alloys .HCOHEL· alloy 600 16.0 7.2 15.8 - 0.10 0.04 0.20 0.20 - H.MONtC· alloy 75 71.4 0.5 20.5 - - 0.10 - - Ii 0.l5; AI 0.15 Nickel-Copper Alloys MONU· alloy 400 66.0 1.35 - - ll.5 0.12 0.15 0.90 - MON£!.,• al'lI1 K.SO!!:. 65.0 leO - - 29.5 0.15 0.15 0.60 AI 2.8: Ti 0.5 Copper-NiCkel Alloys Copper-Nkke:1 allo, CA 706 10.0 1.25 - - 88.0 - - 0.3 Pb 0.05 max; In 1.0 rna. Copper·Nickel alloy CA 710 20.0 0.75 - - 78.0 - - 0.4 Pb 0.05 rna.; Zn 1.0 max Coppef·Nlekel alloy cA 715 30.0 0.55 - - 61.0 - - 0.5 Pb 0.05 max; In 1.0 max Iron·Nickel-Chromium Alloys 'NCOLO"- alloy 800' 32.0 46.0 20.5 - 0.30 O.M 0.35 0.75 - Stainless Steels AISI Type :202 5.0 67.0 18.0 - - 0.15ma. 1.0 max 8.1 N 0.25 max AISI Type 31)2 9.0 70.5 18.0 - - 0.15 max 0.5 1.5 - AI5ITy,•. 304 9.5 70.0 18.0 - - 0J)8 max 0.5 1.5 - AISI TYlle 304l 10.0 69.0 18.0 - - 0.03 max 0.5 1.3 - AISI tYPe 316 13.0 65.0 17.0 2.0mi.. - O.OS max 0.5 1.7 AISI tJllO 316l 13.0 65.0 17.0 2.0 min - 0.03 max 0.5 1.8 - AISI Type 309 13.5 60.5 23.0 - - 0.20 malt 1.0 max 2.0m3X - AISI Type 310 20.0 52.0 25.0 - - 0.25mn 1.0 max 2.0ma. - AISI Type 330 35.0 41.0 1.5.1) - - 0.25 rna. 1.0 rna. 2.0 mal - AISI Type 347 11.0 68.0 18.0 - - 0.08mu 1.0 max 2.0mu Cb;-Ta IOxC min AISI Type. 438 - Bal 17.0 - - 0.12 max - - - Iron Base Nicket·Chromium-Copper-MoIybxlenum Alloys c;"'Rn'n:~- Stainless No. 20 <1' 29.0 43.0 20.0 2.0 min 3.0m;n 0.07 max 1.0 0.8 - CARPEfC-r£R' Sta,"t~$s No. 2OCb-3 34.0 39.0 20.0 2.5 3.3 0.01 max 0.6 08 Cb+Ta 0.6 Nickel Ba';'e l'bn-Chromium·MoIybdenum Anoys 'HCOl.OY- a!Joy 825 41.8 30.0 21.5 3.0 1.8 0.03 0.35 0.65 AI 0.15: Ii 0.9 HAST£LLO.. " alloy G 45.0 19.5 22.2 6.5 2.0 0.03 0.35 1.3 W 0.5; Cn ,. Ta 2.12 HAST£t..~OY· :alloy C ~2) ~.O 5.0 15.5 16.0 - 0.08 max 1.0 rna. 1.0 max Co 2.5ma<; W 4.0: V 0.4 max HASTELLO.. - alloy C·2l6 54.0 5.0 15.5 16.0 - 0.02 max 0.05max 1.0max Co 2.5 rna.; W 4.0: V OA max 'HC_I:L- alloy 625 60.0 5.0ma. 21.5 9.0 - 0.10 max 0.5 max 0.5 max Cb- Ta 3.65 Nickel Base Molybdenum Alioy ..ASULLO'\'- alloy B 61.0 5.0 1.0 max 28.0 - 0.05 max - - Co 2.5 rna.: V 0.2·0A; P 0.025 rna.; S 0.030 max
CAST MATERIALS Nickel America.. Casti"e Institute ACI CZ·l00 95.0 min 1.5 max - - - 1.0 max 2.. 0 1.5 max - Nickel·Ch.romlum·fron Alloy ACI CY·40 70.0 9.5 15.5 - - 0.3 3.0 max 1.5 max - Nickel-Copper Alloys Hickel·Copper alloy 50S 64.0 2.0 - - 29.0 O.OS 4.0 0.80 - ACI "'-35 64.0 3.5 max - - 29.5 (1.35 mall 2:.0 mat 1.5 max - Stainless Steels ACI Cr-8 19.5 66.0 9.5 - - 0.08mllll: 2.0m,n 1.5 mall - ACI Cf·8M 19.5 63.0 10.5 2.5 - OJl8 max 1.5ma. 1.5 max - ACI CA·tS 1.0 max 83.0 12.8 Q.5max - 0.ISm3l 1.5mu 1.0ma. - ACt HA - 87.0 9.0 1.1 - 0,20mu' ).0 rna. O.S - Iron Base Nickel-ChromiUm-CjPper Alloys I wo...... tn:· Stainless 24.0 48.0 20.0 3.0 1.75 0.1)7 max 3.3 0.6 - ACI CN-7M "'0 29.0 44.0 20.0 2.0 mill 3.0 min 0.01 milx 1.0 UiJlnax - Nickel Base 'ron-Chromium·Molybdenum Alloys CHLORIM£T" 3 I 60.0 2.0 18.0 JUt - 0.01ma1l 1.0 1.0 - ILLIUM' alloy to 56.0 6.5 22.5 U $.5 0.20 0.65 1.25 - Nickel Base Molybdenum Alloy .' cHt.o,nMII!T· 2 63.0 3.0ma. - 32.0 - 0.15 IIIa~ 1.0 1 ..0 - Nic,kel Base Sitleon Alloy "AS.TEL~OY· alloy D 82.0 2.0lllllx 1.0 rna. - 3.0 O.l?max 90 0.5·1.25 Co 1.5 max Nickel Alloyed Cast Irons NI·Res)st Type 1 15.5 69.0 2.2 6.5 2.8 2.0 1.2 _.- HI·Ru;st Type 2 20.0 70.0 2.2 - 05ma. 3.0 max 1.9 1.2 - HI-Resist Type 3 30.0 62.0 3.0 - O.Sma. 2.6ma. 1.5 0.6 - Ni·Resist Type 4 30.5 55.0 5.0 - 0.5 rna. 2.6 mal 5.5 06 - Ni·Resist Type D2 20.0 72.0 2.1 - - 3.0 max 2 ..f 0.9 -- HI·Resist Type D3 30.0 61.0 3.0 - - 2.6 max 2.2 O.Sma. -
(1) An improved version of this alloy. CARPENTER'" stainless',No. 20Cb·3. has replaced CARPENJ£R'" ~ta'nie~s No. 20 (2) An improved version of this alloy. HASTEllOY· alloy C·276. has replaced ..ASTUt:OY· alloy C. (3) Cast Alloy 20 alloys such as DUR,MUO alloy 20. ALOYCO" alloy 20. etc• • See ins;de back cover for registered trademarks.
2 Corrosion Resistance of Nickel and Nickel-Containing Alloys in Caustic Soda and Other Alkalies
PART I. INTRODUCTION
Caustic soda (sodium hydroxide) is the most purities in the caustic, the necessity for product widely used and avaBablealkaline material. In the purity. corrosion rate, susceptibility to stress United States almost all of the caustic soda is pro corrosion cracking (caustic embrittlement) and duced as a co-product in the production of chlorine economics. Caustic soda can be handled in cast by the electrolysis of sodium chloride. The elec iron or steel equipment at low· temperatures. if trolytic cells used can be divided into two general iron contamination is not detrimental to end use. types: mercury cells and diapllragm cells. With At elevated temperatures, however, iron and steel mercury cells,high purity SOt;(. caustic is pro are subject to caustic embrittlement and high cor duced directly, whereas with diaphragm cells. the rosionrates. Plant and laboratory tests and oper caustic concentration produced is within the ating experience over many years have demon range of 9 to 15 per cent, and has to be further strated that nickel and nickel alloys are the purified and concentrated before sale. A small preferred materials for handling caustic solu amount of caustic soda is produced by the lime tions in many applications. Nickel can be used for soda proce$S which WaS formerly the prime source practically an concentrations and temperatures. for this chemical. In addition to caustic soda. several other im Caustic soda is generally marketed in concen portant alkalies are discussed in this bulletin. but trations of 50 percent, 73 per cent or anhydrous. no attempt has been made to be all-inclusive. The chemical industry is the largest consumer of Nominal compositions of alloys referred to in caustie soda, followed by the rayon and film in the text are shown in Table L Materials other dustries. the pulp and paper industry and the than nickel-eontaining alloys included in a num aluminum industry. ber of tests are reported for reference purposes. A large number of alloys can be used for han An corrosion rates are reported as mils pene dling caustic soda, and selection is based upon tration per year (mpy). (1 mil = 0.001 inch.) such factors as concentration. temperature, im-
Fig. 1 - These caustic soda evaporator units are a combination of both solid Nickel 200 and steel clad with Nickel 200. Diaphragm cell liquor feeds into the double-effect evaporator: overflow from a settler tank feeds the single'effect evaporator for conc.entration to 50% caustic soda. The system produces 700 tons of salt and delivers 434 tons of NaOH (100%1 per day. Ph%qraDh by courtesy ot the Swenson Division Of Whiting Corporation.
3 PART II. CORROSION BY CAUSTIC SODA
A. Nickel 1. Effect of Concentration, Temperature and Carbon Content Corrosion test results for nickel in commercial caustic soda solutions were obtained by a number of investigators at different times and locations. Typical test data are shown in Table II and these have been incorporated in the isocorrosion chart, Figure 2. Only at high caustic concentration near the boiling point does the corrosion rate exceed one mil per year. This isocorrosion chart is in tended only as a guide; there are specific condi tions under which higher or possibly lower cor rosion rates can prevaiL These conditions are discussed later.
700 r---..,.-----r---r----..,.---"r"> 371
600 316 Fig. 3 - View of caustic transfer piping from marine storage tank area to terminal where rayon grade 50% caustic soeta is loaded into a barge. Several hundred feet of lightweight. welded Nickel 200 piping in 8-inch and 12-inch sizes are 500 ]60 used.
u... 4 oo In caustic concentrations above 75 per cent and ..:; "0 including molten caustic soda. nickel is second Q; Q only to silver in resistance to corrosion. When 100 f-~ nickel is to be used at temperatures above 316 C (600 F). a low-carbon grade, Nickel 201 (0.02% C max). should be employed to preclude the possi 200 '13 bility of graphite precipitation in the grain boun "- 0.1 mpy 4 Table II Typical Corrosion Test Data for Nickel and High Nickel Alloys in Caustic Soda Solutions Corrosion Rate, mils per year Nickel Nickel Copper Chromium HaOH Alloy ;oncen Alloy Temperature Test (MONEL ltNCONEl tration, Period, Hicke! alloy alloy % C F A.e1ation Agitation days Comments 200 40ll) 6nO\ D-1 3{l 86 Nooe Hone 27 Test coupons removed, cleaned and dried each day fOf lOdays 0.01 0.01 nW 4 30 86 Hone None 1&2 Average of tests run at 8 separate laboratories 0.05 0.16 - 4 3{l 86 Air agitated Air agitated 1&2 Average of tests run at 8 separate laboratories 0.05 0.21 - 5-10 21-32 70-90 Extensive due to 124 Storage lank 0.15 O.ll 0.05 filling tank 14 88 190 None None 90 First effect of multiple- effect evaporator 0_02 0.05 0.03 22 50-60 12{)-140 None due to 133 Storage tank coupons filling tank immersed 95% of time nil 0_01 0_01 34 65 150 Extensive Mild 37 Storage tank in which air was bubbled through from bottom 0.03 - 0.03 30"50 81 178 None None 16 Single-effect evaporator_ Rates are average of 3 tests 0.09 0.19 - 49-51 55-75 131-167 None due to 30 Storage tank coupons 31165 av 149 lining tank fully immersed 0.02 0.03 0.02 50 55-61 131-142 None due to 135 Storage tank 0.02 0.02 0.02 31158 a1l 136 filling tank 50 60-70 14~158 Moderate by lOOgpm 393 Transler piping. at pump av65 al/ 149 flow from discharge 0.07 0.10 0.03 pump 50 150 302 None None 14 laboratory test on tubing; average of 4 coupons - - 0.25 72-73 116 273 None due to 183 Storage tank 0.3 0.7 0.4 filling tank 72 121 282 Moderate due to 119 Storage tank OJ 0.3 0_1 filling tank 73 95-100 203-212 None by rocking 111 rest tank_ simulating action of tank of tank car 0.13 0.16 0.14 73 100-120 212-248 None due to 52 Storage tank coupons avll0 a1l230 filling tank immersed 95% of time 0.05 0.04 0.06 13 104-116 244-251 None due to 126 Storage tank coupons av 110 av248 filling tank lully immersed 0.02 0.10 0.0\ 14 130 266 Not specified by movement II trips Coupons in railroad of tank car of 7-9 tank car 0.3 0.4 - days 15 135 271 Not specified due 10 35 Storage tank between filling tank evaporator and finishing pots. Ammonia Soda Process 1.6 1.7 1.3 60 to 15~260 302-500 None None 2 Concentration in caustic nearly evaporator anbydrnus 3.9 13.4 - • Less than 0.005 mils per year. 5 Table llt laboratory Corrosion Tests in Caustic Solutions at Elevated Temperatures NaOH Corrosion Rate, mils per year Concen Temperature Test MONEL WORTHITE sIs Hi tration, Period, Nickel alloy (solution Resist Cast ACI % C F hr 206 400 quenched) Type 2 CN·7M 20 110 262 15 nil 40 110 262 15 nil 60 llO 262 15 nil 80 110 262 15 nil 20 115 272 19 nil 40 115 272 19 nil 60 ll5 272 19 nil 80 US 272 19 nil 20 162 355 19 nil 40 162 355 19 nil 60 162 355 19 nil 80 162 355 19 nil 20 149 332 19 nil 40 149 332 19 3 60 149 332 19 1 20 132 270 ]9 4 40 132 270 19 9 GO 132 270 19 1 80 132 270 19 nil 20 111 340 19(2 tests} 25,69 40 111 340 19 (2 tests) 36.28 60 l7l 340 1912 testsl 2,38 80 17l 340 19 (2 tests) nil. nil 20 156 345 20 14 40 156 345 20 17 GO 15G 345 20 33 86 156 345 20 1 20 127 293 15 94 40 127 293 15 6 GO 127 293 15 17 80 127 293 IS 28 20 150 334 18 10 46 150 334 18 1 GO 152 336 19 12 20 183 394 15 nil GO 183 394 15 151 80 183 394 15 2 2. Effect of Velocity 3. Effect of Aeration Velocity has little effect on the corrosion rate of Aeration has not been observed to accelerate nickel in caustic at temperatures below 500 C corrosion in lower concentration caustic soda (932 F) but at 540 C (1004 F) and above, increas solutions. However, at high concentrations and ing velocity may cause a several-fold increase in temperatures, such as occur when concentrating the rate of attack. Figure 4 shows the results of to anhydrous, precautions should be taken to two-week laboratory experiments by Gregory, minimize aeration. et al., in high temperature molten caustic soda under dynamic conditions. 6 taining atmosphere in the vicinity where corro sion is occurring. Forestieri and Lad found that, M"lten Coust;c Sodo 720 C (1328 Fl 480 as a result of the presence of chromite ion (CrO:I- 1 ), mass transfer and cOITosion were 400 essentially eliminated for 50 hours by one per >- ~ 680 C (1256 Fl cent addition of 325-mesh chromium powder in E 320 a test loop operating at a fluid velocity of 15 fps ~ 0 oc and 816 C (i500 F) with a temperature difference c 240 _Q .------of either 11 C (20 F) or 22 C (40 F) .>1.9 However, E (; 635 C P 175 Fl a small mass transfer deposit was obtained after u • • 250 hours, indicating that a single chromium ad 600 C {I I 12 Fl 400 C ( 752 FI dition would not protect a nickel system in 580 C {1076 Fl 500 C I 952 F) 540 C (l004 F) definitely. 100 200 300 400 500 600 5. Effect of Impurities Rotot;on $peed_ rpm Chlorates in caustic can increase corrosion rates Fig. 4 - Corrosion rate of nickel as a function of rotational speed.' as indicated in the later section on caustic soda manufacture (page 27). Small amounts of so Table IV dium chlorate are produced in electrolytic dia Static Corrosion Rates of Nickel and Nickel Alloys phragm cells. The effect of the chlorate on corro in Molten Caustic Soda sion rate is not critical unless the chlorate is de composed. and thermal decomposition does not Corrosion Rate, mils per year occur below a temperature of 260 to 290 C (500 to Temperature 554 F). If it is intended to operate nickel equip 460e 500e 58fl e 680e ment at or above this temperature range. four Alloy (750 f) (932 f) (1076 f) (1256 f) alternatives are available: Hickel20t 0.9 1.3 2.5 37.8 a. Use "rayon grade" caustic which has a speci HASTELLOY a!toy e 100.5 HASTELt.OY aUoy D 0.7 2.2 9.9 fication of 5 ppm maximum chlorate content. MONEl. alloy 400 1.8 5.1 17.6 b. Use caustic produced by electrolytic mercury INCONEL aUoy 600 U 2.4 5.1 66.4 cells or by the lime-soda process, or, OURANICKEI. alloy 30t 1.7 3.2 10.4 40.7 NIMONIC all01 75 1.1 14.3 20.8 47.6 c. Use anhydrous caustic; there are no chlorates (pitted) in the anhydrous grade. • Gained weight. Swollen outside surface largely oxide-heavily cor· roded. d. Add reducing agents as discussed in the sec tion on caustic soda manufacture (page 27) . 4. Effect of System Thermal Gradients The presence of oxidizable sulfur compounds In molten caustic soda at temperatures above in caustic soda tends to increase the corrosion about 550 C (1022 F), nickel is subject to thermal rate of nickel at elevated temperatures. This is gradient mass transfer.:;· 4;. 7 In this type of at noted particularly with hydrogen sulfide, mer tack, nickel is dissolved in caustic at a high tem captans, or sodium sulfide, and to a much lesser perature surface and is precipitated at a low extent with partially oxidized compounds such as temperature surface in a circulating system. thiosulfates and sulfites. Gregory, et at, concluded that the corrosion rate The effect of the addition of oxidizable sulfur of nickel in molten caustic soda could be ten times compounds to caustic soda on the corrosion rate as great under dynamic conditions as it was of nickel has been studied in the laboratory with under static conditions because of the solubility the results shown in Table V. Test 1 was made temperature relationship.:; during the evaporation of a commercial caustic The mass transfer effect can be inhibited but soda solution under 28 inches of vacuum. Sulfur not prevented by maintaining a hydrogen-con- content of the original caustic. calculated as per 7 Table V (Nickel 201) will circumvent this problem. Applied or residual stresses apparently do not Effect of Oxidizable Sulfur Compounds on Corrosion of Nickel 200 in Caustic Soda significantly affect the genera! corrosion rate of nickeL 11 Temperature: 130 C c::: 5 C (266 F c::: 9 Fl. Corrosion 7. Effect of Dissimilar Metal Contact Test Rate, No. Corrosive mils per year Galvanic corrosion can occur in caustic soda solu Commercial Sodium Hydroxide being concentrated tions if different materials of construction are from 50 to 75% NaOH (Sulfur content at start. electrically connected. Whether this effect is aca calculated as H,S. 0.009%} 1.7 demic or critical depends upon the specific condi 2 75% C.P.· Sodium Hydroxide 0.6 tions that exist in a partiCUlar installation. For 3 75% C.P. Sodium Hydroxide plus 0.75% Sodium Sulfide 22.8 instance, the data in Table VII illustrate that gray cast iron corrodes from about one and one-half 4 75% C.P. Sodium Hydroxide plus 0.75% Sodium Th~wlf~e ~9 Table VI 5 75% C.P. Sodium Hydroxide plus 0.75% Sodium Sulfite 5.2 laboratory Tests in fused Caustic Soda with and 6 75% C.P. Sodium Hydroxide plus 0.75% Sodium without Addition of 5% Sodium Peroxide Su!!ate 0.6 • Chemically pure. Temperature Metal Pickup. grams COHosive C f Nickel Imn Copper cent H;!S in dry caustic, was 0.009 per cent. Test 2 was made in chemically pure caustic soda. Tests 3 Caustic Soda 350 662 .4 through 6 were made in chemically pure caustic 360 680 .01·.02 400 752 Irace·.02 .426 to which the various sulfur compounds had been 450 842 .01·.02 .2·.3 added. 500 932 .005·.015 .2·.3 It has been found that the detrimental effect 550 1022 .4·.43 600 1112 .i3·.3 of oxidizable sulfur compounds in caustic can be counteracted by the addition of sufficient sodium Caustic Soda 350 662 .0024 .024 trace with 5% Sodium 400 752 .0135 .025 .013 peroxide to form sulfates. An excess of peroxide Peroxide 450 842 .OBI .Il .03 does not seem to be detrimental. as shown in • SI rangly attacked Table VI which compares the resistance of nickel, Table VII iron, and copper to fused caustic soda with and without an addition of 5c;. sodium peroxide.lo Galvanic Corrosion of Gray Cast Iron In each test, 5 grams of the substance were fused Conditions: Corrodent: 5% sodium hydroxide. for four hours in a laboratory crucible of the Temperature: 43 C (ll 0 F). given metal and analyzed for metal pickup. Flow: 16 feet per minute. Aeration: Saturated WIth air. 6. Effect of Stress Cathode to anode area ratio 2: 1. Experience has indicated that Nickel 200 is not Corrosion Rate of Corros ion Rate of Gray Cast Iron. Cathodic Material, subject to stress-corrosion cracking in pure mils per year mils per year caustic solutions. However, it is subject to In In stress-corrosion cracking by mercury, and there Cathodic Galvanic Galvanic Material Insulated Couple Insulated Couple have been a few cases of cracking of nickel when "upsets" occur in producing plants that utilize Nickel 200 l.l 1.5 mercury cells. Nickel 200 0.6 ]6 0 <0.1 MONEL alloy 400 0) 2.1 <01 <0.1 In addition, cracking along precipitated grain MONEL alloy 400 0.6 17 0 0 boundary jTraphite in Nickel 200 has occurred 0.75 1.72 after caustic soda exposure above 316 C (600 F). Average Average As indicated previously. a low-carbon grade • Slight welgh1 gain 8 to three times its normal rate when connected to 8. Cathodic Protection Nickel 200 or MONEL alloy 400, under the given In the continuous production of anhydrous caus set of conditions. However, the normal rate for tic, experience has shown that cathodic protection cast it-on in 5~-;' caustic is so low that these higher can be applied successfully to nickel evaporating corrosion rates are usually tolerable. equipment. In one such case, a cathode current At higher caustic concentrations, tempera density of about 1 ampere per square foot of ex tures, and with large cathode to anode r;:ttios. posed nickel surface provided satisfactory pro galvanic corrosion becomes more pronounced. tection. In other less corrosive applications, as in The galvanic current curves shown in Figure 5 storage of 75~(· caustic, current densities as low are from tests made above and close to the upper as 0.01 ampere per square foot have been reported tube sheets of operating caustic evaporators. The effective. Nickel 200 anodes are used in these ap general conclusions to be drawn from these tests plications_ Laboratory tests in 75% caustic soda are that in concentrated caustic soda solutions. at 120 C (250 F) and also in fused anhydrous significant galvanic corrosion may occur on cast caustic soda at 480 C (900 F) have shown that iron or steel when in contact with nickel or cop \",ith equal areas of nickel for anode and c.athode, per. In the construction of caustic evaporators. and with an applied anode current density of it is desirable, if not actuaHy necessary, to use 10 amps per square foot, the corrosion rate of nickel or nickel-clad steel tube sheets in conjunc the nickel anode does not exceed that of uncoupled· tion with nickel tubes. nickel. A pure technical grade of sodium hydrox 70r---~----'----r----.----r----'----r---. ide was u~ed in these tests, which contained less u. q than 0.04 per cent of heavy metal impurities. The GoJvonrc Current Flow Between ~ b.O C05-t 1£on end Copper result.c; are shown in Table VIn. ~ 5.0 A"'?oe: c.,;~ !"on Ar~" . C 3QS -;:: ;:. t C,~d~ode: Ccpoer A~e'1 0.*9"4 ;-:: =. Si 4.0 Table Viti c ~ laboratory Tests of Nickel 200 Anodes and Cathodes {; 3.0 o" in 75 Per Cent and Fused Caustic Soda Temperature: 120C (250F) for 75% caustic. 480 C (900 F) for fused caustic. " ~ 1.0 Duration of Tests: 18·21 hr. .( Volume of Solution Used: 1 liter. JS Anode Current Density: 10 amp per sq ft. Area of Specimens: 0.066-0.087 sq ft. 7.0,-----,..-----,----,..-----.--__-,- ____,-- __-,- __--, Average Corrosion Rate. Golvonic Cv ... enf flow Between mils lIer year Cad Iron ond Niclel 75% Caustic fused Caustic A"\Cd:~: C~S~ h,)~ Af"-e:2 =-.C c.J~a ~ J c. C,+ode: N;d:e~ Are~ ...:. il.24; 5.;)::. Nickel 200 Anode 0.8 11.3 Nickel 200 Cathode 0.2 0.9 NickeI200-Uncollpletl 1.0 11.2 ~ .~ 3.0 0 ?" 2.0 Note that the cathodic nickel surface benefited U from cathodic protection, while the corrosion rate "D" 1.0 .(" of the nickel anode was not increased. 0 Q S Fig. 5 -- Current measurements between cast 9 corrosion resistance in caustic soda, as shown in Tables II, IV and XL. Alloy 600 is commonly used in equipment for the production of anhydrous caustic when sulfur bearing fuels are used for heating because it is more resistant to sulfidation than nickel. There have been a few instances of stress corrosion cracking of Alloy 600 in some strongly alkaline environments. A review of these serviee failures has indicated that they usually occurred in concentrated caustic solutions at high tempera tures, 190 to 450 C (374 to 842 F). In seven-day laboratory tests, caustic concentration, tempera ture, and the presence of air were shown to be important variables, as shown in Tables IX and XIV. No stress-corrosion cracki ng occurred if the Fig. 6 - This barge has eight tanks with a capacity of Alloy 600 U-bend specimens were stress-relieved 34,000 barrels.. The tan~s are used to carry fuel oil or as· at 900 C (1650 F) for one hour or 769 C (1400 F) ph~lt. and a specli;ll 54.00·barret tank fabricated of INCONEl alloy 600-clad steel is used to carry 73010 caustic soda, am· for four hours after bending. monia·basefertilizers, or jet fuels. higher than nickel at temperatures above the Table IX atmospheric boiling point, as shown in Table III. Stress·Corrosion Cracking of INCONEl Alloy 600 However, it should be noted that even in those U-Bend Specimens in Caustic Solutions cases where AHoy 400 is inferior to nickel, the Seven-Day Tests corrosion rates are still quite low. There have been a few reports of stress-corro Temperature Over- Caustic CORcentratiolt, weight % pressure. sion cracking of cold-worked and stressed Alloy C f 150 psi Caustic 10 50 90 400 in caustic soda. However, the eXact conditions 200 390 Air NaOH OK OK under which most of these failures occurred are 250 480 Air NaOH stress-cracked not known. It is known that some of the reported 300 570 Air NaO" OK stress·cracked stress·cracked failures associated with mercury cell caustic were 200 390 Argon NaO" OK OK caused by intergranular attaek by mercury and 250 480 Argon NaOH OK subsequent loss of ductility. 300 570 Argon NaOH OK OK OK Laboratory tests have shown that Alloys 400 200 390 Air KOH OK slight inter· granular and K-500 can be susceptible to stress-corrosion penetration cracking unde.r extreme exposure conditions. that 250 480 Air KOH stress·cracked 300 570 Air KOH OK OK stress-cracked is, high stresses in combination with high tem peratures and concentrated caustic soda can cause Note: Testing performed in autoclaves under static conditions without replenishment of air or argon. cracking. Table X shows the results observed with tensile loaded specimens tested at 300 C (570 F) in condensing steam after being coated with either potassium or sodium hydroxide. C. Nickel-Copper Alloys Under these exposure conditions, Alloy 400, Nickel-copper anoys, such as MONEL alloy 400, which had been cold-worked or cold-worked and are practically as resistant to caustic soda as stress-relieved prior to testing, was susceptible nickel, as shown in Table II. to stress-corrosion cracking~ cold-worked mate The corrosion rate of Alloy 400 is higher than rial that had been annealed at 850 C (1560 F) or nickel at caustic soda concentrations above 75 per 950 C (1740 F) prior to testing was resistant. As cent when concentrating to anhydrous. It is also with Alloy 400. Alloy K-500 cracked when cold- 10 Table X Stress-Corrosion Tests on MONEL Alloy 400 and MONEl Alloy K-500 Type and Degree of Yield Applie II Cracking Strength, Stress, Alloy Heat Treatment ton/ S1l in. tonI sq in. NaO\( KO\( MONEL alloy 4(1(1 None-as cold-drawn 43.8 33.1 IIG 41'11 850 C (1562 fltIti hr/W.O. 12.8 16.3 5 5 MONEL alloy 40(1 Stress relieved 540 C 11004 fl/ ¥z hr 24.0 20.1 OIG OIG MONEL alloy 40(1 Works anneal· 950 C U742 fll Y2 hr 11.4 8.3 5 5 MONEL alloy K·S(I(I None-as COld-drawn 52.5 33.1 3IG+TG 5 870 C U598 f)f5 min/W.O. 21.2 10.3 5 5 580 C (1076 fl/S hf/fC· 65.5 37.2 4TG 5 810 C US98 A/S min/W.O. + 580 C{1016 fl/16 hr/FC· 44.9 37.2 OrG OIG MONEL alloy K·500 None-as cold·drawn 53.2 33.1 4NI 870 C(1598 fl/5 min/W.O. NO 10.3 5 580 C n076 AIS hrl FC· NO 37.2 OIG 870 C (1598 fl/5 min/W.Q. + saocno76 flfl6 hr/fe· NO 37.2 DIG • Fumace-coaled at about 10 C (18 Fl/nr to 480 C 4 = Shallow cracks visible under microscope (896 Fl then "if.-coa!ed to room lef'lperature. 5 = No cracks NO = Not Determined TG = Transgranular cracks o == Specimen fractured IG == Intergranula. cracks 1 == Coarse 'cracks visible to naked eye I'll = Type of cracking nQt jdentified-cracks very 2 == Fine cracks visible to naked eye short. 3 == Deep cracks visible under microscope worked and was resistant in the annealed condi tion. However. the thermal-hardening treatment >- 0- at 580 C (1076 F) rendered the alloy very suscep E tible to cracking. o'" 12 a:: The practical interpretation of these data is .;;;5 8 difficult because threshold values of stress, caustic l? soda concentration, and temperature at which ~ 4 stress-corrosion cracking will occur have not been established. With these limitations in mind, it 20 40 60 100 would appear prudent to stress-relieve AHoy 400 Per Cent Nidel in Copper.Nickel Alloys in the range of 538 to 566 C (1000 to 1050 F) or Fig. 7 - Results of corrosion tests of copper-nickel alloys anneal it ill the range of 760 to 816 C (1400 to in 50% caustic soda evaporator. 1500 F) for one to three hours when it is to be used in higher strength caustic at elevated tem Copper-nickel alloy CA 715 (70% Cu-30% Ni) peratures. possesses excellent resistance to dilute concen trations of caustic soda at low temperatures and appears to have useful resistance to caustic soda solutions of up to 73 per cent at the boiling point. D. Copper-Nickel Alloys However, this resistance does not extend to fused The corrosion resistance of copper-nickel alloys caustic. Alloy CA 715 has been used successfully in can.stic soda solutions is dependent upon the as evaporator tubes for concentrating to 50 per nickel content of the alloy, as illustrated in Fig cent where copper pickup by the caustic could be ure 7. There are a limited amount of additional tolerated. data which are shown in Table XI. Copper-nickel alloys CA 706 (90(~ Cu-lO('~ Ni) 11 Table XI Corrosion of Copper-Nickel Alloys by Caustic Soda Solutions Nominal Alloy HaOM Composition Test Corrosion Concen- Copper- Temperature Dura- Rate, tration, Hickel Wt% Wt% tion, mils per % Alloy Cu Hi C F days year Comments 5 - 60 40 15-20 I 59-68 21 Nil· laboratory test in glass bottle. 11 60 40 Hot-Exact temperature 25 0.5 Diaphragm cell liquor· unknown coupons in distributor box to settlers. 5 70 30 15·20 .1. 59-68 21 Nil laboratory test in glass bottle. 11 70 30 Hot-Exact temperature 25 4.3 Diaphragm cell liquor· unknown coupons in distributor box to settlers. 50 70 30 95 203 67 0.8 Velocity 1.8 ftl sec. Salt saturated. 50 CA 715 70 30 65 149 30 Nil In storage tank. 73 70 30 105 221 118 1.2 60-75 70 30 150-175 302·347 l/Z 4.4 In evaporator concentrating from 60-75%. 60-1Im 70 30 150·260 302·500 2 21 In evaporator concentrating from 60% to anhydrous. 100 70 30 400·410 752·770 1 70 In anhydrous melt. 5 80 20 15·20 59·68 21 Nil laboratory test in glass bottle. 60·75 80 20 150-175 302·347 liz 8.1 In evaporator concentrating CA 710 from 60·75%. 60·100 80 20 150·260 302·500 2 28 In evaporator concentrating from 60% to anhydrous. 100 80 20 400·410 752·770 1 90 In anhydrous melt. 50 90 10 95 203 67 1.8 Velocity 1.8 ft/sec. Salt CA 706 saturated. 73 90 10 105 221 118 2.0 ,. Less than 0.1 mit per year. and CA 710 (80% Cu-20% Ni) have useful resist Table XII ance to caustic soda solutions but their applica Corrosion Rate of Copper-Nickel Alloy CA 715 tion is limited to lower concentrations and tem in Alkaline Solutions Containing Sulfur Compounds peratures than AHoy CA 715. Because of the Corrosion limited data available it is difficult to define limits Duration, Rate, for these two alloys. Conditions of Exposure days mils per year While corrosion of the copper-nickel alloys by 1. In open tank used to boil 18·22 per cent caustic solutions may be aggravated by the pres NaGH to release mercaptans at 80 C (175 fl 30 2. In reboiler of caustic stripper, 1·2 per cent ence of sulfur compounds, Alloy CA 715 is able NaDH.3 per cent Na,S. 10 per cent sodium to resist attack under some conditions, as shown phenolate + 0.7 mg per liter as sodium mercaptides at 124 C (255 Fl 131 25· in Table XII. No data appear to be available on 3. In 10 per cent sodium sulfide in storage the susceptibility of these alloys to stress-corro tank at atmospheric temperature 81 sion cracking in caustic soda solutions. 4. In 60 per cent sodium sulfide in flaker feed tank at 171 C (340 f) 28 14 5. In regenerator reboiler for steam stripping of mercaptans from solutizer solution 25.2 per cent potassium hydroxide 37.8 per cent potassium isobutyrate 5.5 per cent potassium sulfide 1.9 per cent potassium mercaptides 2.1 per cent potassium carbonate at 141 C (286 f) 140 15 6. In vapors from solution in item 5 140 12 ~ Pitting up to 3 mils depth. 12 E. Iron·Nickel·Chromium Alloys Table XIV Based upon data obtained in several test expo Laboratory Tests-Results of U-Bend sures and shown in Tables Xln and XL, it appears Specimens in 90% Caustic Soda at 300 C (572 F) that INCOLOY alloy 800 approaches INCONEL alloy Maximum Depth of Cracks, mils 600 in resistance to caustic soda. However, Alloy Argon 15 psig 50 psig 150 psig 800 is more susceptible to stress-corrosion crack atm. air air air 1 week 1 week 8 weeks 1 week ing than Alloy 600, as shown in Table XIV. Material There has not been sufficient experimental INeOLOY alloy 800 10 7 120lal 1151bl work on the stre.ss-corrosion cracking of Alloy INCONEL alloy 600 0 0 75 115 Type 304 800 to determine if stress-relieving in a tempera Stainless Steel 100 110 11 10 ture range which will cause sensitization (pre (a) Removed at four weeks. cipitation of chromium carbides in a continuous (b) Two·week test. Note: Testing performed in autoclaves under static conditions without network) renders the alloy more susceptible to replenishment of air or argon. this form of attack. Therefore, it would appear prudent to anneal the alloy in the range of 1120 to 1150 C (2050 to 2100 F) or stress-relieve and sta bilize at 870 C (1600 F) for one to two hours when it is to be used in higher strength caustic soda at elevated temperatures. Table XIII Plant Tests-Corrosion Rates in Caustic Production Equipment Using Electrolytic Diaphragm Cell Caustic Exposure times vary from 24 to 29 days (. Conditions Corrosion Rate, mils per year ~ ~ ~ ~ '" '" ~ ~ '" '"= ~ M =~ .,.'" ~ '" :s~ :'§a; :Sa:; ~ ~ !9~ ~~ .e.e ~ Temperature concentrated solutions and at higher tempera F. Austenitic Chromium-Nickel tures. An isocorrosion chart (Figure 8) sum Stainless Steels marizes the corrosion behavior of austenitic Austenitic chromium-nickel stainless steels offer stainless steels in caustic soda. good corrosion resistance to boiling caustic soda Typical corrosion rates for several stainless solutions up to about 10 per cent concentration, steels are shown in Tables XV and XL. Type 316 but from 10 to 50 per cent, the temperature for stainless steel does not appear to offer any ap satisfactory service probably would not exceed preciable improvement in corrosion resistance 93 to 100 C (200 to 212 F). Generally more severe over Type 304 stainless steel in caustic soda solu but inconsistent corrosion rates occur in more tions. 13 700 .-----r------,-----r----r------.-. 3 It Therefore. post-weld heat treatment of regular (0.08 max) carbon grades or the selection of a low-carbon or stabilized grade of stainless steel 600 lib does not appeal' to be required for these exposure conditions. However, intergranular corrosion of sensitized Type 304 stainless steel was observed 500 2&0 by Agrawal and Staehle in boiling solutions of ..o..pF=".Jre~· 5tre~~\·CO(f·Os~O':"I 20 to 80('; NaOH.I:t C'OC';"1 Bou"cio,y Chromium-nickel stainless steels are subject '-'-. 400 to stress-corrosion cracking in caustic soda solu ~ \ .1\ ·:""";)-~oher;.: ~ \ I Bo;';n9 P;i", C~rve tions at elevated temperatures. Nathorst H re \ 0' 30moy "Q. E ported several cases of stress-corrosion cracking ~lOO \. , of austenitic stainless i3teels caused by alkalies. f to ' ...... 50 m py A comparison of the cracking behavior of Type 200 Q) 304 and Alloys 600 and 800 is given in Table XIV. A stress-corrosion cracking zone based upon these .-: 1 ::npv and other known failures reported in the litera AU Grades 100 19 ture is shown in Figure 8. A dashed line was used to indicate the temperature-concentration bound ary because this zone is probably not completely OL-____~--L-~----~L-----~----J 17 S defined. Agrawal and Staehle have shown that o 20 &0 ,,-' 100 sensitized Type 304 stainless steel is more prone than annealed material to stress-corrosion crack fig. 8 - Isocorrosion chart for austenitic chromium· nickel 'stainless steels in sodium hydroxide, ing in boiling caustic sodaP A portion of their data is shown in Figure 9. The cracking obtained J. M. Stone observed that Type 304 stainless was predominantly intergranular in the sensi steel sensitized for one hour at 677 C (1250 F) tized material and predominantly transgranular was not susceptible to intergranular corrosion in the annealed material. during 40-week exposures in: 1:!0 Commercial standard grade 50r;. caustic soda 1. 10% NaOH at room temperature from diaphragm cells can have up to 11.000 ppm 2. 10% NaOH boiling at about 102 C (216 F) chlorides. and commercial 50c; caustic soda from 3. 50% NaOH at room temperature. and mercury cells and reagent grade anhydrous caus 4. 50% NaOH at 60 C (140 F). tic can have up to 50 ppm chlorides. It has been Table XV Corrosion of Stainless Steels by Caustic Soda Solutions HaOH Concel!- Temperature Test Corrosion AISI tration. Duration. Rate. Type % C F days mils per year Comments 302 20 50·60 122·140 134 <0.1 storage tank 309 20 50-60 122·140 134 <0.1 storage tank 310 20 50-60 122·140 134 <0.1 storage tank 304 22 50..60 122·140 133 <0.1 storage tank 309 34 65 149 37 <0.1 storage tank 310 34 65 149 37 <0.1 ;Iorage tank 309 50 21 70 134 <001 storage tank 3to 50 21 70 134 <0.1 storage tank 202 50 50·65 122·149 167 0.5 storage tank 304 50 50..65 122·149 167 <01 storage tank 14 10' L ~ '".} j 10 So;\;"9 So:"·<,~; lcood JOOe "_ ~J Y e':i >'tres," ,O','="O----::l:?O=----=li:-O--..-'=0---SOL----/,L.O---L70---180 Fig. 9 - Stress·corrosion cracking of annealed and sensi· tized Type 304 stainless steel in caustic soda solutions.l3 suggested that unreported chloride impurities Fig. 10 - Piping and certain internal parts of these two KAMYR ¢ digesters used in the pulp and paper industry are are responsible for some of the stress-corrosion Type 316L stainless steel to resist caustic soda and sodium cracking. I;; Whether the reported cracking was sulfide. Insulation sheathing is Type 304 stainless steel to resist alkaline spills. caused by caustic solutions or the chlorides these • See inside back cove 15 140 C (284 F).I' However, the same reference Table XVIII also cites high corrosion rates for alloys of less Corrosion of HASTEllOY Alloys Band C than 70'; nickel, which would include WORTHITE in Caustic Soda Solutions 18 stainless steel, in a storage tank handling 73'"; NaOH Temperature Corrosion Rate. mils per year caustic soda at temperatures ranging from 120 to Concen- tration. HASTEllOY HASTELlOY 171 C (248 to 340 F). Thus, the 140 C (284 F) ap % C F alloy B aUoyC plication may be at the upper limit of usefulness for this aHoy. 5 Room Room Nil Nil 5 66 150 Nil Nil if these alloys are to be used in conjunction 5 102 215 Nil Nil with nickel and high nickel alloy equipment in to Room Room Nil Nil strong caustic soda solutions at elevated tempera 10 103 217 <2 2·20 10 121 250 2·20 tures, consideration should be given to electrical 20 107 225 <2 2·20 insulation between the dissimilar alloys so as to 25 Room Room Nil Nil prevent harmful galvanic effects. 25 66 150 Nil Nil 30 166 240 <2 2·20 40 Room Room Nil Nil 40 128 261 <2 2-20 50 Room Room Nil Nil 50 66 150 Nil Nil H. Nickel-Base Molybdenum or 50 144 291 <2 2·20 Molybdenum-Chromium-Iron Alloys 50 400 750 152 60 165 328 2·20 2·20 Materials such as HASTELLOY alloys Band C-276. 70 191 375 2·20 2-20 INCONEL alloy 625 and cast CHLORIMET alloys 2 Note: I) N.t means no measurable corrosion was observed in five and 3 have not been used to any great extent in 24·hour test periods. 2) 2-20 means corrosion (ate was within this range. caustic soda solutions. Ag a result. corrosion data for them are rather mea~er. Tables IV and XVIII than 50 per cent C.lllnot be determined with the show the results of some iabonltory corrOfiion exi::;ting data. HASTELLOY alloy C and INCONEL tests. From these data. it is evident that HASTEL alloy 625 were both found to be subject to stre::;s LOY alloy B can be u:~ed in concentrations up to 50 corrosion cracking in seven-day tests in aerated per cent at the boiling point and that the tempera 90'; NaOH at 300 C (572 F). but did not crack if ture limit for HASTELLOY alloy C-276 would be ar~on was Sub5tituted for the air in tests at the somewhat less than with Alloy B. Temperature Paul D. Merica Rese~lrch Laboratory of The Inter limitations in caustic soda concentrations ~reater national Xickel Company. Inc. Table XVII Iron Base Nickel-Chromium-Copper-Molybdenum Alloys and Nickel Base Chromium·Copper-Molybdenum Alloys in Caustic Soda Solutions HaOH toncel}- Temperature Test Corrosion tration. Period. Rate. % C F days Comments mils per year 10 24 75 laboratory test. INCOLOY alloy 825 <0.1 10 66 150 laboratory test. INCOlOY alloy 825 <0.1 13 95·100 203·212 111 Test tank simulating action of lank car. WORTHITE stainless steet 0.2 74 130 265 II trips rest iOl tank car. of 7·9 days CARP[NHR alloy 20 0.3·0.9 16 I. Cast Irons and Ni-Resists The beneficial etred of nickel additions 011 the corro:,ioll t'esistance of cast irons in moderately concentrated caustic alkali is shown by data in Tables XIX, XX Hnd XX I. It is evident that nickel contents of 20 to 30 per cent pro\'ide vet'y marked improvement in resistance to corrosion as com pared 'with unalloyed cast iron. It is also apparent that as lo'w as 3 to 5 c ; nickel may improve the corrosion resistance of cast iron in some con centration ranges, Table XIX Effect of Nickel Additions on Corrosion Rates of Cast Irons in 50 to 65% Caustic Soda Temperature: Boiling under 26 in. (mercury) vacuum. Fig. 11 - Moiten sodium hydroxide at an initial tempera· Duration: 81 days. ture of 370 C (700 F) is converted to flake caustic by this flaker and breaker. All surfaces exposed to caustic are nickel Corrosion Rate, except for l'li'Resist Type 3 cooling drum. Nickel, % mils per year Table XXI o 73 o 91 Plant Corrosion Test in 74% o 86 Caustic Soda in Storage Tank 3.5 47 Specimens exposed for total of 32 days (20 days in liquid 5 49 and 12 days in vapor). 15 30 Corrosion rates based on 20 days exposure to liquid. 20 3.3 20 (plus 2% Chromiuml S.O Temperature:. 125 C (260 n. 30 0.4 Corrosion Rate, Material mils per year In practice. the nickel cast irons most widely MONEl. alloy 400 0.9 used with caustic solutions, where minimum con H.i-Resist Type 3 2.5 tamination of the caustic is desired. are the Ni Hi·Resist Ductile rron Type 02 5 Resist alloys and their spheroidHl graphite coun Hi-Resist TYlIe 2 6 Type 304 Stainless Steel 15 terparts. the ductile Ni-Resist alloys, The corro Mild Steel 75 sion rates of these alloys fora number of different Cast Iron 76 exposures are shown in Table XXII. Copper-free Ni-Resist Type 2 may be used in Table XX preference to Xi-Resist Type 1 (6.50:-; copper) Corrosion of Nickel Cast Irons in the where it is desired to keep copper content of the Evaporation of Caustic Soda from 37 to 50 Per Cent solution at a minimum, The 30 r ;. nickel cast iron Average Temperature: 120 C (248 F). (Ni-Resist Type 3), in addition to having some Duration: 51 days. what g-rcater resistance to corrosion by hot caus Corrosion tic solutions than Ni-Resist TypeS 1 and 2, has a Nickel, Chromium, Copper, Silicon. Carbon. Rate. low coefticient of expansion, an advantage for % % % % % mils per year expOSUI"C conditions invo!\'ing sudden changes in 28.60 1.71 1.30 2.87 17 temperature. 28.37 1.50 2.72 18 14.26 2.39 6.08 1.62 3.15 22 Of the fi\'e basic types of ~i-nesist. Type 3 ap 19.40 1.42 3.15 24 pear:' to be the best suited to meet the require 19.02 2.90 1.22 3.18 28 ments for caustic sen"ice. !'\i-l1e::;ist Type 3 or 20.53 1.25 2.91 31 Type D3 can be con::;idered as alternate materials 17 to nickel and the high nickel alloys for caustic chloride aqueous environments. Although these soda concentrations up to 73 per cent, but nickel environments did not include caustic soda, it is preferred for higher concentrations. \\"ollld appear a reasonable precaution to stress There have been occasional stress-corrosion reliew these alloys at 677 C (1250 F) for one cracking failures with the Ni-Resists in high- hour before use in hot caustic soda solutions. Table XXII Corrosion Rates of the Ni-Resists in Caustic Soda Corrosion Rate. mils per year NaOH c C> Concen- '" '" '~("')'" '" Temperature Test "'~ ";:;fN "Vi v ~.~~ tration, "'", "'", "'", "'", .- '" Period, '70.. '70.. '70.. '70.. ~o:: ~ % C F Aeration Agitation days - >- .- >. .- >. .- >. =:Ii • ..!. >.. '" x>- X..- 201- XI- c2O>- c..>'" 8.5-9 82 180 None due to 32 plus 15·15.5% 2.5 0.8 1.5 15 filling tank NaCI in storage tank 10 88 190 Moderate due to 279 plus 12');' NaCl 0.2 4 filling tank in storage tank I 14 88 190 None due loevap. 90 lirst eHect of ! i 8 multiple effect ! evaporator I 23 93 200 Moderate Medium 48 plus 7-8% NaCI 1.2 21 in salt settler 30 85 185 Moderate Moderate 82 plus heavy con- 0.8 0.4 0.1 0.5 6 centratlOn of suspended NaG! in sail settler 35-45 116 240 Moderate Small 24 plus 6-7% NaGI 3.3 49 in salt settler. Intermittent ex- posure to vapor I 49-51 55 149 None due to 30 storage tank II filling tank I 50 55 131 Moderate 1.8 Ips 173 plus heavy con- 0.5 0.2 I, <0.1 0.2 1.2 cen,ration of suspended NaC! in transfer line I I I I 50 71-104 160-220 Moderate 1 Ips llS plus 10·15% NaG! OA 6 in cooling tank 50 95 203 Moderate 1.8 Ips 67 plus heavy con- 1.0 0.6 0.4 11 cent ration of suspended NaGl in transfer line 50 21-127 70-260 None None 10 days laboratory test 4.7 5.0 @250F & 4 days @70r 50-65 Boiling None due to evap. 81 30 3.3 OA 86 50-70 121 250 None due to evap. 10 in evaporator 90 290 72 121 250 Moderate very small 1]9 star age lank 4.7 15 74 127 260 Above & Slight 20 specImens 6 2.5 5.5 Below exposed in storage liquid lank for 32 days level (20 days in liquid and 12 days in vaporl. Corrosion rales based on 20 days exposure in liquid 100 510 950 I None Moderate 14 concentratIOn in 70 87 534 60 141 open pot !60 18 PART III. CORROSION BY OTHER ALKALIES caustic soda of similar concentration and tem A. Caustic Potash (KOH) perature can be used to approximate corrosion Caustic potash is produced by the electrolysis resistance in caustic potash. Iff of muriate (potassium chloride) brine. Several Under extreme conditions, some nickel alloys types and concentrations of KOH are available, are subject to stress-corrosion cracking in caustic but 45 and 50 per cent liquid and 85 and 90 per potash solutions. However, the information pre cent solid are most commonly marketed. Above sented in Tables IX and X suggests that stress about 50 per cent concentration, caustic potash corrosion cracking of Alloy 600, Alloy 400 and has a higher boiling point than caustic soda of Alloy K-500 is not quite as severe with caustic the same concentration. This differential is espe potash as with caustic soda. cially pronounced at high concentrations. For The beneficial effect of nickel in cast iron ex this reason. the commercial product is usually not posed to caustic potash is shown in Table XXIV. concentrated above 90 per cent because of the The reductions in corrosion rates are similar to high temperatures involved. those obtained in caustic soda solutions. In general. those materials which are useful in Table XXV shows the results of laboratory cor caustic soda are also suitable for caustic potash. rosion tests of several Ni-Resist alloys in hot. con Nickel 200 and INCONEL aHoy 600 are both suit centrated caustic potash. Lower corrosion rates able for service in hot caustic potash. as indicated would be expected with a decrease in either tem by the data presented in Table XXIII. Negligible perature or caustic potash concentration. Ni data exist for other nickel alloys in caustic potash. Resist Type 3 appears to have equivalent, and Gegner has suggested that because caustic potash sometimes superior. corrosion resistance in com is so similar to caustic soda. the corrosion data in parigon to Types 1 and 2. Table XXIII Corrosion Tests in Caustic Potash Solutions Corrosion Rate. mils per year KO" COllcen Temperature Test INCONEl. MONEl. tration. Period. Nickel alloy aUoy % C F Aeration Agitation days Comments 200 600 400 13 30 85 None due to 207 storage tank impurities- nil' nil nil filling tank KJeo J 3 gpl. KCf 170 gpl. KClO .. 0.1% 30 113 236 None Boiling 26 laboratory test-saturated l. 0.2 l. 0.1 with KCf. 0.05% KClO, V.0.3 V.O.1 47 139 281 None Boiling 26 laboratory test-saturated l. 0.1 l. 0.4 with KG\. 0.18% KClO, V.O.3 V.O.1 50 28 82 None due to 207 storage tank impurilies- nil nil nil lilting lank K,CO. 0.3%. KGI 0.75%. KGto, 0.10% 50 150 300 None 2\.61pm 7 laboratory test-U·Bend nil 0.5 specimen showed . no cracking 50 150 300 None 3481pm' • 35 laboratory test nil 0.5 10 150 300 None 21.6fpm 7 laboratory test 0.4 0.7 10 150 300 None 3481pm" 35 laboratory test 1.6 5.7 • nil-less than 0.05 mils pel'" year. l-liQuid V-Vapor ." Specimens m~ved at th!s veloc11y fof'" 8 hr each working day and at zero ft per mtn overn1ght and duong weekends. Th,s was equlvatent to ten 24 ·hour days at the high velocity rate. 19 Table XX'V Considerable amounts of Types 316 and 316L Effect of Nickel in Cast Iron stainless steels are used in the ammonia-soda on Corrosion by Caustic Potash process for the production of soda ash (Na2C03 ). Concentration: 950 g KOH per liter. The main reaction involves the carbonation of an Temperature: 400 C (750 F). ammoniated brine to form sodium bicarbonate and ammonium chloride. The ammonia is recov- Nickel Content of Alloy Iron, Corrosion Rate, % mils per year o 21-30 Table XXVI 3 3.0 6.5 2.0 Plant Corrosion Test in Ammonia 12.4 0.4 Surge Vessel of Urea Manufacturing Plant Solution: 22% NH, • 71 % H,O, 7% CO, and trace of NH.NO, . Temperature: 66C (150 F). Table XXV Test Period: 300 days. Aeration: None. Corrosion of Ni-Resists in Caustic Potash Agitation: Moderate. Location: Uquid phase at bottom of aqua ammonia surge Hi-Resist ClIrrosjon Rate, vessel. Type Exposure mils per year Corrosion Rate, 1 68-hour test in 81 % KOlt at 225 C (437 f) 30 Material mUs per year 2 68-hour test in 81% KOH at 225 C (437 f) 20 INCOlOY alloy 825 <0.1 3 68-hour test in 81 % KOH at 225 C (437 f) 10 Type 347 Stainless Steel <0.1 2 36-hour test in 92% KOlt at 268 C 1516 f) 10 Type 316 Stainless Steel <0.1 Type 304 Stainless Steet 0.3 3 3S-hour test in 92% KOlt at 268 C (516 f) 10 Type 316 Stainless Steel mercial solutions, as shown in Table XXVI. • Nil == Less than 0.01 mill><" year. 20 Table XXVIII Table XXX Plant Corrosion Test in Ammonia-Carbon Plant Corrosion Test in Ammonia Recovery Still, Dioxide Gas Stream in a Metal Refining Plant Ammonia-Soda Process for Production of Sodium Carbonate Gas: 26% NHJ • 14% CO,. balance water vapor. Temperatur-e: 66 ro 93 C (150 to 200 F); Average 82 C Middle Section (l80 F). Temperature: 60 to 71 C (140 to 160 F). Test Period: 65 days. Liquor Composition: 2% NHl , 9% NH.CI, Aeration: Moderate. 14% NaCl, 2% CO2 • Agitation; 25 to 40 fps gas flow. Test Period: 220 days. Location: NH1·CO~ stripping still overhead line. Top Section Corrosion Rate. Temperature: 60 to 71 C (140 to 160 F). Material mils per year Liquor Composition: 5% NHl • 9% NH.CI, 14% NaCl, 3.4% CO2 • Type 202 Stainless Steel <0.1 Test Period: 220 days. Type 304 Stainless Steel <0.1 Type 316 Stainless Steel <0.1 Corrosion Rate, mils per year INCOlOY alloy 825 <0.1 Middle lop INCOLOY alloy 800 1.5 Material Section Section INCONEl alloy 600 4.1 Type 410 Stainless Steel 0.1 Type 316 Stainless Steel OJ 0.1 Type 502 Stainless Steel 20 Zirconium 0.1 0.1 Mild Steet 22 Titanium 0.1 0.2 HASTEllOY alloy C 0.1 14' Nickel 200 >33" >32" Mild Steet >73" >71" Table XXIX • Specimen pitted in crevice beneath insulating wasber. Plant Corrosion Test in Contaminated •• Specimens cQrroded away.. Ammonia Vapors in a Coke By-Products Plant Gas: Ammonia vapors plus H,S. CO,. HCN. phenols and Nickel is not attacked by anhydrous ammonia, steam. but is resistant to ammonium hydroxide solutions Temperature: 100 to 110 C (212 to 230 F); Average 105 C (221 F). in concentrations only up to about one per cent. Test Period: 144 days. Aeration may induce passivity in concentrations Aeration: None. under 10 per cent, but even in the presence of air, Agitation: High velocity gas flow. more concentrated solutions are highly corrosive location: Ammonia liquor still vapor outlet. to nickel. The corrosion data shown in Table XXXI Corrosion Rate, were obtained in room-temperature laboratory Material mils per year tests ()f 48-hour duration in one normal ammo Type 304 Stainless Steel KiI nium hydroxide, following a previous 48-hour ex- Type 316 Stainless Steel Nil' I NCONEl alloy 600 0.1 Mild Steel S.O MONEL alloy 400 >40 Table XXXI (corroded away) Nickel 200 >40 Corrosionof Nickel 200 in One Normal (corroded away) Ammonium Hydroxide (1.7% NHa) • Nil "" 1.ess tban 0.04 mils per year. Corrosion Rate,· Test Condition milspllryear ered in this process for reuse. Table XXX shows Total Immersion corrosion rates for metals and alloys in an am Quiet 0.8 monia recovery still in a soda ash plant. The pos Air"'Agitated <0.1 sibility of pitting must be taken into account in Alternate Immersion Conti!luous 2.7 the design of equipment where there are such lntermittent 0.4 high chloride levels, so as to avoid crevices where Spray {4 to 30 Daysl <0.1 chlorides can concentrate to even higher levels • Specimens exposed at room temperature tor 2 days after a previous and promote crevice corrosion. 2-day exposure except for spray expo'Sure. 21 posure. The re~ults of 20-hour tests in highly agitated ammonium hydroxide solutions at room tempel·ature are shown in Table XXXII. Typical corrosion rates for Nickel 200 in several indus trial exposures are also given in Table3 XXVII, XXIX and XXX. Table XXXU Corrosion of Nickel 200 in Ammonium Hydroxide Solutions NH.OH Cancentration, CCIfI"lISion Rate, • % mils per year 1.1 o 12.9 560 Fig. 12 - Sodium carbonate filters use Type 304 stainless 20.2 370 steel or MONEL alloy 400 for the perforated backing sheet or 27.1 180 winding wire. The same materials are also used for back· ing wire cloth and facing cloth. • Tests run to agitated solution at room temperature for 20 hours. salt solutions can be handled in the same materials Nickel-copper alloys. such as Alloy 400, are re suitable for caustic soda. As with caustic soda, sistant to anhydrous ammonia and are slightly dilute solutions at low temperature are not very more resistant than commercially pure nickel in corrosive to carbon steel and may even act as cor ammonium hydroxide solutions. as shown in Table rosion inhibitors, but concentrated solutions at XXXIII. However, their usefulness is restricted high temperatures often require nickel or high to dilute solutions up to about 3<1· ammonium nickel alloys. hydroxide. In solutions of higher concentration. The results of tests within an evaporator han corrosion rates are increased considerably by dling sodium metasilicate are shown in Table aeration and agitation. XXXIV. Another plant test in a kettle during the dis TableXXXm solving of silicates in strong caustic soda gave the laboratory Corrosion Tests of corrosion rates shown in Table XXXV. MONEL alloy 400 in Ammonium Hydroxide The superiority of Alloy 400 and austenitic Temperature: Room. Test Period: 20 hours. stainless steels for a phosphate hydration was Agitation: 371 feet per minute. demonstrated in a short-duration test shown in HH3 Cancentration, Carrosian Rate, Table XXXVI. % mils per year Nickel and high nickel alloys offer good resist 2.7 o ance to corrosion by sodium sulfide solutions. In 3.6 70 5.5 298 Table XXXIV 8.2 317 11.1 327 Corrosion Tests in Sodium Metasilicate 18.3 231 25.8 36 Composition: 50% sodium silicate. 50% sodium hydroxide. Ave~age Temperature: HOC (230 F). Test Period: 6 weeks. Corrosion Rate. Material mils per year C. Other Alkaline Solutions of Nickel 200 <0.1· Sodium and Potassium Salts MONEL alloy 400 <0.1 INCONEL alloy 600 <0.1 Salts su~h as sodium sulfide. sodium carbonate, Hi-Resist Type 1 0.4 sodium silicates, trisodium phosphate and others Mild Steel 13 form alkaline water solutions. These alkaline Cast Iron 18 22 Table XXXV centrate sodium sulfide from 25 to 60 per cent Corrosion Te.sts During Dissolving of are given in Tables XXXVIU and XXXIX. Oper Silicates in Caustic Soda ating experience over a number of years with Location: Test specimens suspended near bottom of kettle. evaporator tubes in sodium sulfide evaporation Temperature: 77 C (170 f). Test Period; 32 days. has shown that Nickel 200 and Alloy 400 are satisfactory for this application. COffoswn Rate, Material mils per year Experience has also demonstrated that Alloy 600 is useful .for direct-tired pans in which sodium Nickel 200 0.1 Ni:Resist Type 3 0.2 sulfide is eoncentrated from 25 per eent to 60 per Ni:Resist Type 2 0.5 cent. Operating temperatures on the order of 150 Nickel Cast Iron (3% Ni) 8 to 177 C (300 to 350 F) prevaiL Under sueh condi Cast Iron 33 Mild Steel 41 tions. Alloy 600 has given a service life of up to eight years. Table XXXVI Table XXXVIlI Conosion Tests in Phosphate Hydrator Plant Corrosion Test in Direct·Fired Open Pot Used Composition: 50% solution of sodit.t1l1 tripolyphosphate and for Concentrating Sodium Sulfide to 60 Per Cent sodit.tm tetrapotyphosphate. Average Temperature: 74 C (165 F}. Test Period: 60 hours. Temperature: 100 to 180C (212 to 356 f). Aeration: Extensive. Agitation: Considerable. Test Period: 81 days. Corroswn Rate, Corrosion Rate. Material mils pet year Material mils per year Type 3114 Stainless Steel 0.1 MONEL altoy 400 8 Type 316 Stainless Steel 0:4 fMCOJltEl.. alloy 600 10 MONEt. alloy 400 0.7 Nickel 200 16 Mild Steel 133 Copper-Nickel alloy CA 715 20 HASTELLOY alloy B 22 ILLiUM G 48 10:t sodium sulfide. the corrosion rates are quite Type 316 Stainless Steel >72* Type 3114 Stainless Steel >73* Jow. as shown in Table XXXVII. The most severe KASrELLOY alloy C >85* service conditions are encountered in hot. concen DURIMEr alloy 20 110 trated solutions. The results of two plant corro ~ Specimens corroded away. sion tests in direct-fired evaporators which con- Table XXXIX Table XXXVII Plant Corrosion Test in Gas-fired Plant Corrosion Test in a Open Tray Used for Concentrating Sodium Sulfide Storage Tank Sodium Sulfide from 25 to 60 Per Cent Solution: 10% Na2S. Aeration: Open tank. Temperature: 125to 175C (257 to 347 f). Temperature: Atmospheric. Agitation: Only due to filling tank. Test Period: 19 days. Test Period: 81 days. Corroswn Rate. Corrosiolt Rate. Material mils per year Matl!rial mils per year MONEL alloy 400 3 . Nickel lO!l 23 PART IV. INDUSTRIAL APPLICATIONS A. Caustic Soda Manufacture equipment such as evaporators, heat exchanger Service records, often dating back for 20 to 30 tubing, pumps, crystallizers, valves, fittings, etc., years, have demonstrated the satisfactory service used in the concentration and handling of caustic of nickel and nickel alloys in caustic soda manu soda. Corrosion test data cited earlier in this bul facture. In one plant, nickel centrifugal pumps letin were obtained largely in caustic soda manu handling 50% caustic soda from mercury cells are facturing processes. 27 years old and are still in operation. In another A comparison of the corrosiveness of caustic plant, nickel evaporators continue to give good soda produced from mercury cells with that pro service after 30 years' use. Nickel 200, low-car duced by diaphragm cells was made by Committee bon Nickel 201, Alloy 600, Alloy 400 and their T5A-3D of the National Association of Corrosion cast counterparts are "standard" materials of Engineers. Data obtained in this survey are construction, either solid or as a cladding for shown in Table XL. It appears that there is not a Fig. 13 - Triple-effect evaporators for the concentration of diaphragm cell liquor to 50% caustic soda_ All threeevapora tors are constructed entirely of Nickel 200 and Nickel 200-clad steel. Photograph courtesy of Blaw-Knox Company_ 24 Table Xl "Round Robin" Test Program by Four Caustic Soda Producers-Comparison of Corrosiveness of Diaphragm Cell vs. Mercury Cell Caustic Conducted by NACE Committee TSA-3D Average Temperature Corrosion Rate. Company mils per year 1 2 3 4 C.Dmpany Material Corredent C f C f C F C F 1 2 3 4 Nickel 200 50% NaOH-Oiaphragm Cell 35 95 29 85 88 190 54 130 <0_1 <0.1 <0.1 Nickel 2IltJ 1.5 260 IHCOHEt. alloy 6flO 2.2 380 moved; the addition of sucrose (U. S. Patent 2,610,105) or dextrin (British Patent 778.226) appear to be the most common. While these ad ditions minimize corrosion and attendant metal contamination of the product,- they do increase the carbonate concentration. Bradbury and Cooper have shown that the addition of sorbitol and subsequent heating will also remove chlo rates but with the formation of less carbonate.21 Liquid-liquid extraction with ammonia is also widely used to remove chlorates and chlorides.22 fig. 14 --Evaporator bodies and vapor piping at a large chlorine-caustic soda plant for concentraticn t.o 730/0 NaOH. In the continuous vacuum concentration and All evaporatcrs are constructed entirely .of Nickel 200 and production of anhydrous caustic soda, low-carbon Nickel 200·clad steel. Nickel 201 and Nickel 201-clad steel equipment Chlorates are removed from diaphragm cell have given excellent service as evaporator tubes. caustic soda when concentrating to anhydrous in tube sheets and shells, and as receiving tanks and nickel or high nickel alloys to minimize corrosion piping. 27 Alloy 600 has also been used extensively for caustic potash at concentratiolls of 90 per cent producing anhydrous caustic soda and is the and above. preferred material of construction where the heating is accomplished with any media in which there is a po:.;sibility of sulfur compounds being C. Caustic Soda Storage and present. Alloy 600 for this service should be Transportation stress-relieved or annealed as indicated in the dis After extreme care has been taken to assure cussion of nickel-chromium alloys in Part II of high purity in the production of caustic. it is this bulletin. important that storage and transportation facili ties provide for continuing product purity. NickeI clad steel tank cars have been used for transport ing iron-free caustic since 1930. Nickel and nickel clad steel barrels are also in use for the transpor tation of smaller quantities. More recently. nickel plated steel tank cars and piping have been employed. The first tank-trailer constructed of INCOLOY alloy 825 was put in service in 1963 to haul 50% caustic soda. This alloy was selected because of its versatility in its ability to transport other corro sive materials induding sulfuric. nitric and phos phoric acids. INCONEL aHoy 600 was selected for barge tanks to carry 73 (-; caustic one way and return with ammonia-base fertilizers or jet fueL Fig. 15 - Tubes fabricated from Nickel 200 afe used in the inclined heat exchanger in front of the Nickel 200-dad evaporator which prodl.l<.:es 50% caustic soda. separator atop the system. which separates sodium chloride and other salts from the caustic solution. is also Nickel 200. B.Caustic Potash Manufacture The production of caustic potash is carried out in nickel and nickel alloy equipment in a similar manner t9 the production of caustic soda. One important difference. however, is the higher boiling point encountered in caustic potash above 50 per cent concentration. Because of the higher temperahx ~~; involved. cathodic protection is often used for low-carbon Nickel 201 or high Fig. 16 - Marine terminal where caustic soda is unloaded from barge. Nickel 200 lined caustic transfer pipe is at right nickel alloy equipment u:=;ed for the production of foreground. 28 Tt'an;;fer of materia! to and from storage tanks usually requires pumps. Table XLIII shovv's the results of a plant test in which Xickel 200, MONEL alloy 400 and INCONEL alloy 600 corrosion coupons wet'e subject to turbulent flow just downstream of a pump handling 50('~ caustic soda. Similar cor rosion resistance would be expected fl'O!1l the cast counterparts of these wrought materials (ACI CZ-IOO, M-35 and CY-40). Pumps cast from ACI CZ-IOOhave given over 25 years service as previ ollsly noted. Table XLIII fig. 17 ~ This barge carries 50%. caustic soda from a field Test in 50% Caustic Soda mercury cell plant to storage facilities'along the Tennessee. Just Downstream of a Pump Ohio and Mi Rivers. Four cylindrical tanks have a total capacit liquid tons. To insure a long sef\lice Temperature: 60 to 70 C (140 to 158 f); life for the ge and to protect product purity. all cargo AI/erage 65 C (149 f). piping is either solid Nickel 200 or Nickel 2oo-clad steel with Test Period: 393 days. Nickel 200 fittings: The cargo fromal! four tanks empties into a Ni,ckeI2oo-clad steel well from which ,it ispl.lmped to Aeration: Moderate. on-shore facilities_' .' . ' flow; 100 gpm in 3·inch pipe. Corrosion Rate. Material mils per year The use of nickel;..cla _.. fig. J,8 -:- INCOLOY aUoy 8,25 ,is used for the inner tank and all internal parts that come into contact with corrosil/e cargoes in these two trailers-inner shell and heads. manhole ring and cover. dip tubes. spill dam and discharge pipe. Although presently used for hauling 50% caustic soda. the corrosion resistance of this material will allow the hauling of a variety of corrosives. tained above the freezing point. Tables XLIV and D. Soap Manufacture XLV give the results of tests in transportation Soaps are made by the reaction, called "saponi and storage facilities. fication,"between alkali and fatty oils (gly_ It is common practice to load and unload cars cerides) and fatty acids of animal or vegetable of 73% caustic through Nickel 200 heat exhang origin, or a mixture of both. The largest produc ers, pumps and piping. tion, and the most familiar, is "hard" soap made with caustic soda as the saponifier. Caustic potash Table XLIV produces a "soft" or liquid soap. Field Test in Tank Car Transporting In certain high grade soaps, it is necessary to 74% Caustic Soda avoid contamination by such metals as iron and Temperature: 130 C (265 F). copper in order to obtain a high quality product. Test Period: 11 trips of 7·9 days. Therefore, pure caustic must be used in combina Aeration: None. Agitation: By movement of tank cars. tion with corrosion-resistant equipment. The Corrosion Rate, matter of iron contamination is particularly sig Material mils per year nificant in soap-boiling kettles because the soap Nit;lle1200 0.3 spends so much time there. particularly in the fuH INCOlOY alloy 825 0.3 boiled process. This is especially significant in the MONEL alloy 400 0.4 upper parts of the kettles where corrosion rates CARPENTER alloy 20 0.9 Type 316 Stainless Steel 8.4 are highest. Table XLVI shows the results of one plant corrosion test in a soap-boiling kettle. Some of the earliest applications of ~orrosion-resistant materials were in the construction of soap kettles. Table XLVI Plant Corrosion Test in Soap·Boiling Kettle Specimens immersed near the top of the settling cone duro ing saponification and graining. Temperature: 70 to 100 C (160 to 212 F). Test Period: 106 days. Corrosion Rate. Material mils per year Hit;ke1200 <0.1 Fig. 19 - 1300 feet of transfer pipe with a rolled and MONEL alloy 400 <0.1 welded internal lining of Nicke1 200 carries 50% caustic .NCOffEl. alley 600 soda from a marine terminal to a Nickel 2oo·c1ad storage <0.1 tank. Nickel 200-clad tank cars are in the background. Hi·Resist Type 1 0.1 Mild Steel 3.2 Cast Iron 11.0 Table XLV Field Test in Storage Tank for 73% Caustic Soda The first step. in most cases, was to line the upper Temperature: 116 C (240 F). portions of existing steel kettles with Nickel 200. Test Period: 183 days. AHoy 400 or either Type 304 or Type 316 stain Aeration: None. Agitation: None except for filling of tank. less steel. Because of occasional difficulties win Corrosion Rate, these lined vessels (usually weld cracks in thE -Material mils per year liner because of differential thermal expansior Nickel 200 0.3 between the steel kettle and the liner) , new vessel: I NCONEl alloy 600 0.4 were sometimes constructed completely from cla( MONEL alloy 400 0.7 Zirconium L4 plate. The same materials are also used for heat Titanium 4.7 ing coils. swing pipe, kettle covers and othe Mild Steel Destroyed during test accessory equipment. 30 Much of the corrosion test work in soap plants ment in four different soap plants are shown in has been concerned with the treatment of spent Table XLVII. soap lye and recovery of glycerine. since these Alloy 400 and Nickel 200 or steel clad with processes represent particularly corrosive condi these materials are used for both acid-treating tions. The pH of the solution during acid treat and caustic-treating tanks because of their resist ment is usually 4 to 4.5 and sometimes as low as ance in both environments. Austenitic chromium 3, due to the presence of hydrochloric or sulfuric nickel stainless steel and Alloy 600 are also used acids. Agitation of the mixture with air, a com but pitting is possible with these alloys under mon practice, tends to increase the corrosion rate certain conditions as shown in Table XLVII. Ni of steel. The results of six tests during acid treat- Resist Type 3 is used instead of Types 1 or 2 for Table XLVII Plant Corrosion Tests in Acid Treatment of Spent Soap lye Test 1: Immersed in acid treating tank in mixture of 13% NaCI and 4.5% glycerine to which is added 150 Ib of 28% HCI and 75 Ib of 17% aluminum sulfate per 30,000 Ib soap lye. Temperature: 1 to 82 C (30 to 180 F). Test Period: 167 days. Plant L Test 2: Immersed half·way down in acid treating tank in mixture of 18% NaCI plus glyce.rine to which is added 0.5% solution of aluminum chloride. Aerated. Average tempera· ture: 74 C (160 F). Test Period: 65 days. Plant 2. Test 3: Immersed in trough of filter in acid treated filtrate from Test 2. Aerated. Average temperature: 71 C (160 F}. Test Period: 65 days. Plant 2. Test 4: Immersed half·way down in acid·treating tank in mixture of 8 to 10% NaCI and 4.5% glycerine made acid to pH 4.5 with HCI and ferric chloride. Air agitation. Temperature: 21 to 71 C (70 to 160 F). Test period: 28 days. Plant 3. Test 5: In acid treating tank in spent soap lye made acid to pH 4.5 with HCI and ferric chlo· ride, and aluminum sulfate. Agitated wiUl1iIir. Temperature: 54 to 79 C (130 to 114 F). Test Period: 45 days. Plant 3. a. Immersed in bottom of tank near air inlet. b. In vapor in top of tank. . Test 6: Immersed half·way down in solution containing 13 to .16% NaCI plus Na2S0. and 10 to 12% glycerine made acid to pH 4.5 with sulfuric acid and ferric chloride. Aerated. Temperature: 32 to 100 C (90 to 212 fl. Average 85 C (180 Fl. Test Period: 105 days. P\ant4. C.onosion llate.lIllJs per year Test 1 Test 2 Test 3 . TesH Test Sa Test Sh TestS Material Plant 1 Plant 2 Plant! Plant 3 Plal1t3 Plant 3 fitaltt4 MOHEL alloy 400 .9 0.3 4.8 2.9 5.6 4.4 16.0 Hickel 200 1.1 0.9 3.7 L8 5.1 4.7 10.0 IHCOHEL aUoy SOO .6 <.1 .7 0.8 .7 Type 302 stainless steel <.1 .7 (a) O.5!d Type 304 stainless steel .5!d LOlh) Type 316 stainless steel <.1 A (b) LO(i) Copper·Nickel alloy CA 715 27.0 Aluminum. Type 1100 4.4 (d) Hi·Resist Type 3 3.0 Hi· Resist Type 2 2.7 1.0 4.0 Hi·Resist Type 1 2.5 0.9 3.4 5.0 Mild Steel 5.3 3.0 17.0 16.0 29.0 (e) 34.0(gl 14.0 Wrought Iron 18.0 24.0 (f) 44.01gl 14.0 Cast Iron 11.0 6.0 16.0 14.0 (a) Perlorated by pitting. original thickness 31 mils. (f) Pitted to maximum depth of 9 milS. (bl Pitted to maximum depth of 11 mils. (gl Pitted to maximum depth of 8 mils. (e) Pitted to maximum depth of 5 mils. (h) Pitted to maximum depth of 6 mils. (d) Pitted to maximum depth of 3 milS. (i) Pitted to maximum depth of 14 mils. (e) Pitted to maximum depth of 20 mils. 31 the construction of soap lye filters and filter plates tered in a lye tank and a centrifuge in one of these to withstand possible therma·' shock when the hot processes. solutions enter a cold filter process. Pumps of iron-base nickel-chromium-copper-molybdenum Table XLIX alloys such as WORTHITE or DURIMET 20 have given Plant Corrosion Test in Third-Stage Centrifuge good performance handling both acid- and Specimens located at soap discharge. Mixture contained alkali-treated soap lye. Austenitic chromium 15% NaOH and 11 % NaC!. Low aeration, flow 350 gallons per hour through 4·inch pipe. . nickel stainless steels, usually Type 304, have been Temperature: 91 to 96 C (195 to 205 F). used to advantage for "finishing and packaging" Test Period: 102 days. equipment. Corrusion Rate, Maximum Depth Although a considerable amount of the world's Material mils pef year of Pitting, mils soap is still produced batch-wise, efforts to reduce Nickel ZOO Nil o None the 4 to 11 days required with the fun-boiled kettle MONEL alloy 400 Nil None method have resulted in a number of continuous I/'ICONE.L alloy 600 Nil None processes for soap manufacture. In one such Type 304 Stainless Steel 0.1 None process, blended fats with zinc oxide catalyst are Type 316 Stainless Steel 0.1 None Type 341 Stainless Steel 0.1 None reacted countercurrently with water in a 65-foot Hi-Resist Type 1 0.4 None high. Type 316 stainless steel hydrolyzing tower Mild Steel 10 Perforated maintained at 282 to 260 C (450 to 5(,)0 F) and Cast Iron 12 55 600-700 psi. Fatty acids are continuously drawn • Less than 0.05 mils per year. off the top and crude glycerol off the bottom of the column. The fatty acids arevacuum-distiUed and then neutraiized in a high-speed mixer· with a caustic soda solution containing salt. thus produc E. Pulp and Paper Industry ing soap in about four hours.24 Over a million tons of caustic soda are used In other continuous processes which usually annually in the pulp and paper industry, prin utilize centrifuges. the corrosives encountered cipally for the extraction of alkali-soluble impuri are much the same and considerable quantities of ties in multistage bleaching and for pH control. austenitic chromium-nickel stainless steel. Alloy Small amounts are used for preimpregnation of 400 and Nickel 200 are utilized. Tables XLVIII wood chips and for the production of soda pulp. and XLIX indicate the corrosion rates eneoun- More than two-thirds of aU paper is pX'Qduced by the Kraft process. Digestion of certain soluble portions of wood chips is accomplished by a hot Table XLVIII alkaline liquor consisting of a mixture of dilute Plant Corrosion Testinfourth·Stage lye Tank caustic soda and sodium sulfide with a total alka Immersed in tank containing soap lye with 2% MaOH and linity of about 3 per cent. The following are prin 11% MaC!.. cipal areas where carbon steel may corrode at Temperature: 88 to 96C (190 to 205 F). an excessive rate and nickel-containing alloys Test Period: 102 days. (usually austenitic chromium-nickel stainless Corrosion Rate, Maximum Depth steels) can be used to advantage. Material mils per year of Pitting, mils Nickel zno Nil o None 1. Digesters Nil None MONEL alloy 400 Batch-type Kraft digesters are commonly built INcolfEl aUoy 600 Nit None Type 316 Stainless Steel Nil None of carbon steel with a corrosion allowance in Type 341 Stainless Steel Nil None excess of one inch. Until recent years this resulted None Type 304 Stainless Steel 0.1 in a service life of about 15 years, but with the Hi·Resist Type 1 0.1 None Mild Steel 1.0 7 increasingly severe conditions imposed. by modern Cast Iron 3.0 22 pulping methods, service life was reduced to about • Less than 0.05 mils pel' year. 7 to 9 years. Weld overlays employing A WS E310, 32 or A WS E310-Mo. have been employed to extend Table LI the service life of corroded steel batch digesters. Plant Corrosion Test in a Digester Utilizing Table L indicates the excellent corrosion resist a Duplex Sulfate Process ance of stainless steel and several other nickel Temperature: 100 to 171 C (212 to 340 f). alloys in one Kraft digester. Cycle: Chips steamed for one hour, temperature rises from 100 C to 118 C (212 to 244 f). Acid liquor removed. Alkaline liquor containing 82 gpl NaOH and 25 gpl Na,S added. Charge brought to 171 C (340 f). cooked Table l for total of 5 hours. Plant Corrosion Test in a Sulfate Process, location: In vapor. Test Period: 731 days. Alkaline, Wood Pulp Digester Corrosion Rate, Material mils per year Temperature: 177 C (350 f). Test Period: 586 days. Type. 316 Stainless Steel 0.1 Aeration: None. Type 341 Stainless Steel 0.1 Agitation: Violent boiling during cook. CARPENTER alloy 20 0.1 Top--Vapors in the top of the digester. Occa· INCj)NELalloy Spo OJ sional splashing of chips, pulp and cooking MONEL alloy 400 23 liquors. Titanium 55 Bottom-Liquid and slurry on bottom screen of Mild Steel 107 digester. Specime(ls: Combination of stress and general COrrosion. Strips were stressed beyond the yield point by bolting down over a fulcrum. Some specimens were welded or contained weld overlays as noted. No stress· corrosion cracking occurred. Corrosion Rate, mils per year Material Condition Top Bottom INCONEL alloy 600 Plate. as·received 0.02 0.21 CARPENT£R alloy 20 Welded 0.03 0.09 INCoNEL alloy 600 Welded 0.03 0.23 INCOlOY alloy 825 Plat.e. as·received 0.03 0.09 INCOlOY alloy 825 Welded 0.03 Type 316 Stainless Steel Plate, as·received 0.04 0.15 Type 316t. StainJess steel Plate. as·received 0.05 Type 31Sl Stainless Steef Welded 0.06 0.17 Type 316 Stainless Steel Welded 0.06 0.15 AViS Eltflllveriay on Steel Weld Overlay 0.05 0.17 Note: A dash indicates no coupon was exposed. There are a few Kraft digesters that utilize a duplex process in which the charge is initially acid (pH 4) and later alkaline. Table LI shows corro sion rates in this process. There are several hundred continuous digesters operating on wood chips in the United States. Fig. 20 ~ This top separator on a KAMYR continuous di· These are constructed primarily from carbon gester separates the chips from the flushing liquor. With the steel with high corrosion rate areas lined or clad exception of the drive mechanism. this separator is can· structed of Type 304 stainless steel. with Type 316L stainless steeL These high corro sion rate areas include the upper section. where fresh, hot alkaline liquor is injected, and the siderably reduced wall thickness and much lower bottom section in the area of the blow valve. maintenance costs. Internal accessories such as scrapers and chip screens are usually fabricated from Type 316L 2. liquor Heaters stainless steeL Construction of digesters with clad Shell and tube heat exchangers are used to heat Type 316L stainless steel would allow for con- the digester liquor prior to its introduction into 33 both batch and continuous digesters., Results of a Table lit corrosion test in such a heater are shown in Table Corrosion Test in Kraft Pulping LII. These data may indicate a lower than actual Exposed 68 Days in Head of liquor Heater corrosion rate for carbon steel, since the heat Flow rate of 2400 gpm at temperature of 173 C (344 F). exchanger tube walls are at a temperature higher Corrosion Rate, than the liquor in which the test specimens were Material mils per year exposed. The liquor contains a large proportion of Type 304 Stainless Steel 0.5 fresh caustic and sulfide in addition to some black Type 316 Stainless Steel 0.8 liquor recovered from a previous digester cook. INCONEL alloy 600 0.9 Experience over many years has proven the ade MONEL alloy 400 38 Nickel 200 57 quacy of annealed Type 304 stainless steel for this Mild Steel 95 service. The use of "as-welded" tubes has some Cast Iron 342 times resulted in failure by intergranular cor rosion immediately adjacent to the weld. This type Vapor domes in the hottest effects are often clad of corrosion has not been observed when tubes with Type 804Lor Type 316L stainless steel, since are used that have been made in compliance with carbon steel in this area may corrode at a rate ASTM A 249. This specification caUs for welded, exceeding 100 mils per year. There are also instal drawn, quench-annealed tubing. Tubes of this lations where sta.inless-elad steel has been used for type have been known to last in excess of.10 years, the entire evaporator body. Advantages of such but service life is dependent on specific operating construction.inelude less carry..over of corrosion conditions. In a few instances, the Type 304 stain products and less fouling of the evaporator tubes less steel tubes have been subject to failure by by these products. chloride stress-corrosion crackng. Alloy 600 and Defiectorpla.tes and auxiliary piping are usu Alloy 20 have been successfully employed to resist any made of solid Type 804L stainless steeL For this type of attack. valves and pumps, Ni-Resist Type 2, CF-8 and CF-8M castings are used. 3. Black liquor Evaporators To permit recovery of chemical values in the 4. Recausticizing digester liquor when chip cooking is complete, it As part of the operation to regenerate chemi is necessary to concentrate the liquor, together cals reclaimed from the recovery furnace, sodium with the chip wash water. This is required to raise carbonate is treated calcium hydroxide the solids content to more than 50 per cent. which (milk of lime) to produce sodium hydroxide. will permit burning in the recovery furnace. Kraft liquor vacuum evaporators are multiple Table lin units usually consisting of one or more sets of six long tube vertical effects connected in series. Corrosion Test in Kraft Pulping Corrosive conditions on the tubes are somewhat Exposed 68 days in green Uquor. 175 to ~5 gpl as Na2 CO, in flow bQx.from recovery furnace to claSSIfiers. less severe than in digester liquor heaters since Temperature: 66 to 99 C.(150to 210 F). the vacuum operation results in lower boiling Some aeration and agitation. temperatures. The first effect operates at the Corrosion Rate, highest temperature of about 135 C (275 F). Tem Material mils per year peratures decrease in each succeeding effect. It tN(:ONEL alloy 600 <0.1 has been customary to use Type 304 stainless Type 302 Stain1ess Steel 0.1 steel for tubes in the first effect and often in the Type 309 Stainless Steel 0.1 second effect. A number of installations have used Type 310 Stainless Steel 0.1 Type 304 stainless steel tubes in all effects, re Type 316 Stainless Steet 0.2 Nickel 200 0.3 sulting in less frequent downtime fer cleaning, MONEL alloy 400 0.5 long service Hfe, and maintenance of high heat Mild Steel 115 transfer rates. Cast Iron 176 34 Carbon steel, with a corrosion allowance. has tively smallam{llwts of nickel and nickel altoys been used for most of the equipment. As shown have been utiJized in these plants. in Table LIII, fairly high rates can occur on car Alloy 400 tubes have been successfully em bon steeL Light gauge Type 304 stainless steel ployed for digester preheaters. and Alloy 400 is an economic selection for troublesome areas. insert ferrules have been used to overcome the inlet end corrosion in other steel preheater tubes. Relatively thick (30 mils minimum) electroplated nickel {lll steel has been used to advantage for Indu~try F. Aluminum piping and digester preheater channels. Nickel Despite extensive use of caustic soda by the weld-overlays haVe proven \Iseful on pump cas aluminum illdustry for the extractioRofhydrated ings, and cast nickel (ACI CZ-IOO) has given good alumina from bauxite in the Bayer process, rela- service as pump impellers. valve bodies and for other instrumentation. However. the present practice with bauxite digesters is to use thick-walled carbon steel at low stress levels. Some cases of stress-corrosion cracking (If steel have occurred in plants handling caustic soda solutions in the Bayer extraction process.z::> The recent trend awaYI;r;om ores high in gibbs ite C{lntent toward the use of Ores relatively high in boehmite c()ntent has necessitated digester operation at higher pressures and temperatures. This increases the pos!;;ibHity of caustic embrittle ment of steeL Thus. nickel or nickel-clad steel should be given consideration for the processing of these higher boehmite bauxites. G. Caustic FuSions Nickel 200 and Nickel 201 are useful as mate rials of construction for vessels for the caustic fusi{ln of·· organic comp{lunds. Where tempera tures exceed 316 C (600 F). the low.-carb{ln Nickel 201 is preferred to preclude grain bound ary precipitation of carbon which greatly reduces duetility. For those reactions where sulfur com pounds are present at temperatures over 250 to 300 C (482 to 572 F). either in the process or the heating medium, nickel may be attacked inter granularly and Alloy 600 is preferred. One process for the production of resorcinol has involved the caustic fusion of benzene meta Fig. 21 - This ll·foot long. 16·inch diameter pipe has been disulfonic acid at 325 C (617 F). Equipment for electmplated with nickel to yield a 30-mil thick deposit on this production has been made of wrought Alloy the inner diameter and about 2 mils on the outer diameter. Sections like this are welded toget:he( to form piping used 600 and ACI CY -40 castings. Both alloys should in bauxite refining in the aluminum industry. Lengths of be stress-relieved as indicated in the section on greater than 11 feet can also be plated. Photo by courtesy of Plating Engineering Company. Milwaukee. Wise. nickel-chromium alloys (Part II B). 35 H. Petroleum Refining In the t'egeneration of caustic solutions, it is common practice to use Alloy 400 in critical por Cau~tic soda or, occasionally, caustic potash or sodium carbonate is used in petroleum refining tions of the system where steel is unsuitable. for acid neutralization and the removal of unde These locations include the regenerator reboiler, sirables such as mercaptans and hydrogen sulfide. preheaters and piping for handling hot caustic Aqueous solutions may range from 2 to 50 solutions and sometimes for the bottom sections of the regenerator towers. These components may per cent. For many of the applications where temper be either solid or clad. ACI CZ-IOO, ACI M-35 ature and concentration are low, the corrosive ductile Ni-Resists and WORTHITE stainless steei conditions are mild enough that steel can be used. have been used for valves and pumps. The results Where the corrosive conditions are more aggres of plant corrosion tests in the reboilers of caustic regenerator units are shown in Table LIV. sive, Nickel 200, AHoy 400 or Alloy 600 are used. Very often Alloy 400 is used because it appears to have a greater tolerance for the impurities Table ltV present in the process. Plant Corrosion Tests in Caustic Regeneration Units Test A-In open tank used to boil 18 to 22% caustic soda plus merca pta ns and cresolates for regeneration of caustic solution. Test specimens were immersed in solution above heating coils. Test Period: 30 days. Temperature 38 to 104 C (100 to 220 F). Average 80 C (175 F). Test a-Just ab~ve reboiler inlet below bottom tray of reo generating tower. Solution 18% caustic soda for· tified with naphthenic acid. cresols and phenols to 22 to 28 ·Be. Solution also contained 0.040/0 mer· captan sulfur. Test Period: 660 days. Temperature: 21 to 116 C (70 to 240 f). Average 107 C (225 F). Test C-At bottom of stripping tower 18 inches above reo boiler tubes. Solution 7 % caustic soda with trace of mercaptans. Test Period: 354 days. Temperature: 121 to 149 C (250 to 300 F). Average 135 C (275 Fl. Test o-In vapor sectj~n of caustic soda regeneration unit. Solution entenng contained' 13.2% caustic soda. 0.37% sulfide sulfur and 0.80% mercaptide sulfur. Test Period: 55 days. Temperature: 150 C (300 F). Corrosion Rate. mils per year Material TestA TestS Test C Test D INCONEl alloy 600· <0.1 <0.1 <0.1 0.3 Type 304 Stainless Steel" • 0.1 0.1 0.1 Nickel 200 0.1 0.2 1.1 2.0 MONEL alloy 400 0.3 0.1 0.9 2.0 Type 316 Stainless Steel"· 0.4 0.2 Copper·Nickel alloy CA 715 1.1 4.5 Fig. 22 - Nickel·copper alloy 400 was used for the walls of Hi·Resist Type 1 3.8 4.0 13.0 the caustic stripper towers. reboiler tube bundles and hot Cast Iron 13.0 10.0 caustic lines in this refinery. After 10 years of service. the Carbon Steel·· 29 12.0 33.0 Alloy 400 components continue to withstand the corrosive mineral acids. sulfur compounds and hot caustic soda in .., Subject to pitting. the fluid hydroformer and caustic regenerating equipment. "') May be 'Subject to stress-corrosion cracking_ 36 In view of its good resistance to caustic alkalies I n one process, the parts to be descaled are immer containing hydrogen sulfide and mercaptans, Al sed in a 370 C (700 F) bath of molten caustic soda loy 600 is also a useful material for evaporator containing 1.5-2% sodium hydride. Other proc tubes or other parts of regenerator systems. Alloy esses operate with molten caustic at 480 C (900 600, rather than Nickel 200 or AHoy 400, should be F) or higher. used in this service where metal temperatures in Carbon steels are often used for the equipment excess of about 250 to 300 C (482 to 572 F) are handling these fused caustic baths up to about encountered, since Nickel 200 and Alloy 400 are 480 C (900 F). In cases where carbon steel has subject to sulfidation at higher temperatures. not proven satisfactory. Nickel 201 and Alloy A caustic stripper, at a major Louisiana refin 600 have been demonstrated to give good per ery, constructed of MONEL alloy 400, exhibited no formance. Nickel 201 is used for sodium hydride detectable metal loss after more than 4 l'2 years' generators in one process. Both Nickel 201 and service handling up to 45<; caustic soda at tem Alloy 600 are used for sheathing on electric heat peratures up to 143 to 149 C (290 to 300 F). It is ing elements in caustic baths. AHoy 600 is used still giving repair-free service after 15 years. for gas-fired heater tubes in some cases. In cases In one Texas refinery, mercaptains are removed where the caustic baths are operated at higher by the Dualayer Process * which utilizes two temperatures than usual, such as 566 to 621 C layers of immiscible solvents. The first solvent (1050 to 1150 F), Nickel 201 is used instead of layer, a water solution of caustic· potash and carbon steel for pickling tanks and associated potassium cresylate, removes the mercaptans. equipment. A plant corrosion test in a commercial The second and lower layer is a water solution molten caustic pickling bath operating at 482 C of caustic potash that maintains the composition (900 F) showed a corrosion rate of one mil per of the upper layer. Water and potassium hydrox year for nickel in a 60-day test. ide migrate between lower and upper levels, sus taining the equilibrium. MONEL alloy 400 was used for the stripper preheater, reboiler. and stripping tower trays and. in a cast form (ACI M-35), for the bottom pump. The tower itself was lined with J. Reclaiming Caustic for Economy MONEL aHoy 400 and stress-relieved. This equip and Pollution Control ment continues in operation after 20 years. In the diverse industries which make use of Nickel-copper alloy 505 has excellent non caustic solutions, numerous companies have galling properties and can be combined with cast found that it is economically attractive to reclaim nickel-copper alloy ACI M-35 in pump assemblies and concentrate the caustic values of their effiu- to avoid seizing. particularly in mixtures contain ents. Even the return on investment for ing gasoline or similar solvent materials where caustic recovery units is not high enough for justi lubrication is practically impossible. fication on this basis alone. pollution control is desirable and may become mandatory as local anti-pollution laws become more stringent. Recovery and concentration plants are commer cially available for some industries. Of the total L Caustic Oescaling caustic soda purchased yeariy by a textile mill Several processes involving molten caustic soda for mercerizing cotton. often as much as 65 per are in commercial use for the descaling of various cent can be recovered from the mercerizingframes metals and-alloys, particularly the stainless steels. and up to 95 per cent at the mercerizer. The con Some of these processes involve addition to the centration of caustic soda is from about 5 per cent caustic of reducing agents to reduce the metallic in contaminated liquor to the de~;jred concentra oxides to metal or lower metal oxides, most of tion for the particular mercerizing operation. which flake off in the subsequent water quench. These plants utilize nickel or high nickel alloys for • Patented Process. Mohil Oil Corp. evaporators and associated equipment . 37 PART V. WELDING A. Fabrication of Table LV Nickel-Clad Equipment Corrosion of Iron·Contaminated Nickel Welds in 73% Caustic Soda at 121 C (250 F) 27 In the welding of nickel-clad equipment, a cer tain amount of iron dilution of the nickel weld Corrosion Rate, mils per year deposit occurs. Special precautions are usually Iron First Second Total taken in order to minimize this dilution. With in Weld, Exposure, Exposure, Exposure, % 30 days 60 days 90 days special precautions, the nick~l welds in a nickel clad tank for a chemical tanker were limited to 0.51 8 5 6 5.56 8 5 6 an iron content of 0.35-3.29%.26 Gegner has sug 11.43 7 5 5 gested that considerably more iron than this can 13.15 7 4 5 be tolerated.27 17.62 7 5 5 22.85 6 4 5 Although iron-contaminated nickel weld metal and nickel-iron alloys are not severely attacked in Table lVI 73% caustic soda at 121 C (250 F). as shown by data in Tables LV and LVI, nickel-iron alloys can Corrosion of Nickel and Nickel·lronAlloys in 73% Caustic Soda at 121 C {250 f)27 be the anode in an electrolytic cell with nickel, as shown in Table LVII. Note that the 20% iron Corrosion Rate, alloy corroded at three to five times the rate it did Iron. % mils per year when it was not coupled to nickel. Even greater . 0 7 increases in rate would be expected in large pieces 0 7 of equipment where the relative ratio of cathodic 5 8 5 8 area (cladding) to anodic areas (weld) is greater 10 6 than the 10:1 ratio of the test. to 8 20 8 20 8 Table LVII Galvanic Corrosion Tests in Caustic Soda of Nickel to Nickel-Iron Alloy Couples Area: Nickel 0.5 sq dm Aeration: None. Nickel·lron Alloy O.05sq dm Test Period: 7 days. Motion: None. Corrosion Rate. mils per year 50% HaOH at Couple Couple 23% NaOH at 105 C (221 Fl 15C (161 Fl 15% NaOH at 126 C (259 Fl No. Materials Coupled Uncoupled Coupled Coupled Uncoupled 5% Fe·Ni 1.6 1.4 2.4 1.0 1.0 Nickel 0.6 0.4 0.8 1.6 1.5 2 10% fe·Ni 2.6 L2 2.0 1.5 1.4 Nickel 0.4 0.4 0.6 LO 1.5 3 20% Fe·Ni 3.6 0] 1.6 1.8 0.6 Nickel 0.6 0.4 0.4 1.1 1.5 Notes: 1. The iron·nicket alloys were in the form of castings. 2. No tests were made, uncoupled. in the 500/0 NaOH solution. 38 fine wheel or a disc grinder, or chemically, by B. Repair of Equipment in pickling, is recommended. After cleaning, the Caustic Service welding procedures outlined for new metal should Before doing any repair or maintenance weld be followed in every detaiL ing of nickel or nickel-containing alloys or dad Flash pickling solutions are effective for clean steel plate that has been in caustic service, it is ing nickel and high nickel alloy surfaces. These necessary to remove products of corrosion, and may be applied with long-handled swabs or any other foreign material, from the vicinity of brushes where equipment is large, or may be held the area to be welded. (The caustic soda and other in glass or ceramic crocks for pieces that are impurities present can cause loss of ductility and easily handled. such as the ends of nickel caustic cracking if present during welding.) Therefore, evaporator tubes that have been removed from great care should be taken to obtain a clean, bright evaporator service and are to be used for pipe metal surface over an area extending 2 to 3 inches lines. The tubes can be dipped vertically and from the site of welding on both sides of the piece. cleaned for a minimum distance of 3 inches from Cleaning mechanicalIy, by grinding with either a the end. AVAILABLE LITERATURE The following Corrosion Engineering Bulletins are available for your use: "Resistance of Nickel and High Nickel Alloys to Corrosion by Sulfuric Acid" "Corrosion Resistance of Nickel and Nickel-Containing Alloys in Caustic Soda and Other Alkalies" "Resistance of Nickel and High Nickel Alloys to Corrosion by Hydro chloric Acid, Hydrogen Chloride and Chlorine" "Corrosion Resistance of Nickel-Containing Alloys In Phosphoric Acid" "Corrosion Resistance of Nickel-Containing Alloys in Hydrofluoric Acid, Hydrogen Fluoride and Fluorine" 39 REFERENCES 1. Swandby, R. K., "Corrosion Charts: Guides to Ma ments", Report No. COO-2018-21 (Q6) for period terials Selection", Chen!. Eng., Vol. 69, No. 11, Nov. April 15, 1970-July 14, 1970, Ohio State University, 12, 1962, p. 197. Columbus, Ohio. 2. Fontana, M. G., "Corrosion at Elevated Temperatures 14. Nathorst, H., "Stress Corrosion Cracking of Stainless and Pressures", The Ohio State University Research Steels-Part I Practical Experiences", Welding Re Foundation, Report No. 10, Project 350, May 1, 1951, search Council Bulletin, No.6, October, 1950, pp. 6-7 p.F2. and 10. 3. Badger, W. L. and Standiford, F. C., "Anhydrous 15. ASM Committee on Stainless Steel in Chemical Corro NaOH: Today's Technology", Chern. Eng., 61, Feb. sion Service,lHetals Handbook, Am. Soc. Metals, 1961, 1954, pp. 183-187. p.566. 4. Gregory, J. N., Hodge, N. and Iredale, J. V. G., "The 16. Beck, F. H. and Fontana, M. G., "Corrosion by Static Corrosion of Nickel and Other Materials in Aqueous Solutions at Elevated Temperatures and Molten Caustic Soda", AERE CIM 272, March, 1958. Pressures", Corrosiun, Vol. 9, No.8, August, 1953. pp. 5. Gregory, J. N., Hodge, Nand Iredale, J. V. G., "The 287-293. Corrosion and Erosion of Nickel by Molten Caustic 17. Pratt. W. E., "Corrosion Resistance of Worthite in Soda and Sodium Uranate Suspensions Under Dy Caustic Soda", Chemical EnginC(!ring, Vol. 56, No. 12, namic Conditions", AERE CIM 273, March, 1956. 1949, pp. 213-214 and VoL 57, No.1, 1950, pp. 213-214. 6. Lad, R. A. and Simon, S. L., "A Study of Corrosion 18. "Hastelloy Corrosion-Resistant Alloys", Union Car and Mass Transfer of Nickel by Molten Sodium bide Corporation, 10th Edition, May, 1957 and private Hydroxide", Corrosion, 10, December. 1954, pp. 435- communication from Haynes Stellite Co. 439. 19. Ge~ner, P. J., "Corrosion in Alkaline Environments", 7. Smith; G. P., Sieidlitz, M' E. and Hoffman, E. E., ProcecdiJlgs of Shm·t Course 0)/ Pl"(lCeSS Industry "Corrosion and Metal Transport in Fused Sodium Corrosio)t, National Association of Corrosion Engi Hydroxide", Co)Tosion. 13, September, October, 1957. l!eers, September 12-16. 1960, p. 1 L pp. 561t-564tand 627t-630t. 20. McCallion, J., et at, "Switch to Continuous Evapora 8. Forestieri, A. F. and Lad, R. A., "The Use of Metallic tion Boosts Capacity But Not Manpower", Chemical Inhibitors for Eliminating Mass Transfer and Corro P"ocessing, August, 1968. pp. 20-21. sion in Nickel and Nickel Alloys by Molten Sodium Hydroxide", Lewis Flight Propulsion Laboratory, 21. U. S. Patent 3,380,806, April 30, 1968. Cleveland, Ohio, February, 1955, NACA RM E54L13. 22. Twiehaus, H. C. and Ehlers, N. J., "Caustic Purifica tion by Liquid-Liquid Extraction", Chemical Indus 9. May, C. E_, "Correlation Between Hydro~en Pressure tries, August, 1948, pp. 230-233. and Protective Action of Additives in the Molten Sodium Hydroxide-Nickel System", Lewis Flight 23. Friend, '.V. Z. and Mason, J. F., "Corrosion Tests in Propulsion Laboratory, Cleveland, Ohio, February, the Processing of Soap and Fatty Acids", Corrosion, 1966. NACA RM E55LOl. Vol. 5, No. 11, 1949, p. 358. 10. Wallace, T. and Fleck, A., "Some Properties of Fused 24. Kirk-Othmer, Ellcyclopl'tiia 40 TRADEMARKS Following is a list of the registered trademarks referred to in this publication together with the names of the trademark owners. • • • • • • • ALOYCO Registered trademark of Aloyco Inc. CARPENTER Registered trademark of Carpenter Technology Corporation. CHLORIMET Registered trademark of The Duriron Company. Inc. DURANICKEL Registered trademark of The International Nickel Company. Inc. DURIMET Registered trademark of The Duriron Company. Inc. HASTELLOY Registered trademark of Cabot Corporation. ILLIUM Registered trademark of Stainless Foundry & Engineering, Inc. I NCOLOY Registered trademark of The International Nickel Company. Inc. INCONEL Registered trademark of The International Nickel Company. Inc. KAMYR Registered trademark of Kamyr Inc. MONEL Registered trademark of The International Nickel Company. Inc. NIMONIC Registered trademark of The International Nickel Company. Inc. WORTHITE Registered trademark of Worthington Corp.