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Home , Ammonia production, Carbonyl sulfide, Haber process

STAINLESS STEELS IN PRODUCTION

A DESIGNERS’ HANDBOOK SERIES NO 9013

Produced by Distributed by AMERICAN NICKEL AND STEEL INSTITUTE INSTITUTE STAINLESS STEELS IN

A DESIGNERS’ HANDBOOK SERIES NO 9013

Originally, this handbook was published in 1978 by the Committee of Stainless Steel Producers, American Iron and Steel Institute. 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.

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CONTENTS

INTRODUCTION ...... 4 PROCESS DESCRIPTION ...... 5 CORROSIVES IN AMMONIA PROCESSES ...... 5 CONSIDERATIONS FOR SELECTING STAINLESS STEELS ...... 6 Desulfurization of Natural ...... 6 Catalytic of ...... 6 Monoxide Shift ...... 8 Removal of . 10 Methanation ...... 11 Synthesis of Ammonia ...... 11 Turbine-Driven Centrifugal Compression Trains ...... 14 STAINLESS STEELS ...... 15 Metallurgical Structure ...... 16 High-Temperature Mechanical Properties ...... 16 Thermal Conductivity ...... 20 Oxidation Resistance ...... 21 Sulfidation Resistance ...... 22 REFERENCES ...... 22

The material presented in this booklet has been prepared for the general information of the reader. It should not be used without first securing competent advice with respect to its suitability for any given application. While the material is believed to be technically correct, neither the Committee of Stainless Steel Pro- ducers nor the companies represented on the The Committee of Stainless Steel Producers acknowledges the help Committee warrant its suitability for any gen- by Gregory Kobrin, Senior Consultant, Materials Engineering, E.I. eral or particular use. DuPont de Nemours & Company in assembling data for this booklet. single-train plants came increasing demands on materials of construc- INTRODUCTION tion. The process for making am- monia is considered to be only Approximately 12 elements are es- moderately corrosive, so considera- sential to plant growth. Of these, nit- ble use is made of carbon and low- rogen is the main nutrient and is re- alloy steels for vessels and piping. quired in much larger amounts than However, numerous applications any other element. Ammonia is the have been found for the AISI 300 and principal source of , 400 Series stainless steels because and most of the ammonia production of their superior performance under a in the world is applied directly to the wide variety of process conditions, soil or used in the manufacture of not only for original fabrication but for and other important nitrogen- replacement equipment and piping as base . (1)* Because of am- well. monia's importance to human needs, For example, stainless steels are it is considered to be one of the most used in valuable and most widely produced Catalytic steam reforming because chemicals in the world. of resistance to oxidation, carburi- The ammonia production industry zation and nitriding at elevated has grown by leaps and bounds since temperatures; 1964, with U.S. production in 1977 an estimated 17 million to 18 million short Carbon dioxide removal systems tons per year, about four tirnes that of where piping and vessels are sub- 1960 (4.8 million short tons). (2) jected to hot, aqueous solutions Up until 1963, plant capacities containing carbon dioxide at ranged between 50 and 400 short moderate to high velocities; tons per day, many using a multiplicity Ammonia synthesis for superior of parallel process systems, called performance in hot nitriding , multiple trains. In 1963, the first 600- resistance to embrittle- short-tons-per-day single-train am- ment and hydrogen attack, and ex- monia plant came on stream. This cellent toughness at low tempera- represented the beginning of large- tures; capacity, single-train plants and was the first to use centrifugal compres- Centrifugal turbomachinery where sors driven by steam turbines to com- rotating and stationary components press synthesis gas to elevated pres- are subjected to erosion by high- sures. (2) velocity steam and corrosion by Between 1965 and 1970, many , CO and single-train ammonia plants with CO2; capacities of 600 to 1000 short tons Coolers and condensers for resis- per day were built throughout the tance to corrosion and fouling by world. In recent years, larger plants natural . have been commissioned, several with 1500 short tons per day capacity The purpose of this booklet is to and one of 1700 short tons per day, identify the many applications of ranked the largest in the world at pre- stainless steels in a typical process sent. (2) for manufacturing anhydrous am- With the advent of high-capacity monia.

*Numbers in ( ) indicate reference.

4 Partial oxidation of heavy hydro- 1. Desulfurization of natural gas (oils, distillates); 2. Catalytic steam reforming of PROCESS Cryogenic recovery from petroleum natural gas refinery gases or other cracking 3. shift DESCRIPTION operations; 4. Removal of carbon dioxide 5. Methanation Anhydrous ammonia is manufac- Gasification of or coke. 6. Synthesis of ammonia. tured by combining hydrogen and The first, third, fourth and fifth Currently, a high percentage of nitrogen in a molar ratio of 3:1, com- steps are designed to remove im- world ammonia production (an esti- pressing the gas and then cooling it purities such as , carbon mated 70 to 80%) uses hydrogen to about –27ºF (–33ºC). monoxide, carbon dioxide and produced by catalytic steam reform- Nitrogen is obtained from air. Hy- from the feed, hydrogen and syn- ing operations, with natural gas drogen is produced from a feedstock thesis gas streams. In the second () as the primary feedstock. by one of the following processes; step, hydrogen is manufactured and As a result, the following process de- nitrogen is introduced into the pro- scription is limited to ammonia pro- Catalytic steam reforming of natu- cess. The sixth step produces duction by catalytic steam reforming ral gas or naphtha; anhydrous ammonia from synthesis of natural gas, using six basic gas. All ammonia plants use this basic process, although process condltions such as temperatures, and flow rates vary from plant to plant. Approximately 65 to 75% of the natural gas is used as feedstock for the primary reformer; and 25 to 35% is used as fuel for the reformer radiant section and for steam pro- duction. As natural gas reserves continue to dwindle, feedstocks based on heavier and coal gasification processes (3) will undoubtedly be used increasingly in ammonia plants in years to come. A process flow schematic of a typi- cal ammonia plant which uses catalytic steam reforming of natural gas is shown in Figure 1. The six process steps are described in detail in the following sections.

CORROSIVES FOUND IN MANY AMMONIA PROCESSES

Sulfur– present in natural gas feedstock, it causes high- temperature sulfidation of metals,

5 and it combines with other ele- poisoning the nickel catalyst in the Applications for Stainless Steels ments to form aggressive com- primary reformer and depositing The system for removing sulfur from pounds, such as hydrogen , carbon on the catalyst. Sulfur can be the feedstock natural gas consists of , and carbonyl sulfide. present as , mer- two vessels, each containing captans, carbonyl sulfide and organic Chlorides–may be present, either by for removal of sulfur compounds. Carbon beds are entrainment in natural gas, as mercaptan sulfur and hydrogen usually used when the sulfur content carryover from boiler feedwater, or sulfide. Each vessel is designed to is less than 10 grains/per standard in cooling waters. They may cause handle all the sulfur expected in the cubic foot (SCF), whereas hot iron localized attack of some stainless feed gas. As soon as the activated or (4) beds are used steels. carbon in the first vessel becomes for gas with higher sulfur content. saturated with sulfur, the feed gas Carbon Dioxide–occurs in steam Most modern ammonia plants use stream is diverted to the second reforming of natural gas. It com- activated carbon for feedstock vessel to allow steam regeneration of bines with moisture to form car- desuIfurization. the carbon bed in the first vessel. bonic . Natural gas at several hundred For the most part, operation takes psig and ambient temperature is Ammonia–at high temperature has place above the dew point and carbon passed through the activated carbon high potential for nitriding metals. steel is a satisfactory material of con- bed. Sulfur compounds are absorbed At high pressure, corrosive am- struction for the vessels and related on the carbon or reacted with the monium carbamate may be piping. However, AISI Types 304, 321, metallic oxide in the carbon to form a formed. Condensed ammonia is a or 316 stainless steels are specified metallic sulfide by this equation: corrodent, and in anhydrous state for the wire mesh screens and grating CuO + H S → CuS + H O it can cause stress-corrosion 2 2 which support the activated carbon When the carbon bed becomes cracking of stressed carbon steels beds in the desulfurizers. For this loaded with sulfur, it is regenerated or high-strength, low-alloy steels. application, corrosion rates must be with steam or a mixture of steam and virtually nil, otherwise a corroded Hydrogen–in itself not corrosive but air at 300 to 555ºF (149 to 290ºC) for screen could result in carbon can lead to blistering and embrit- several hours. The free reacts breakthrough and carryover into the tlement of steel. Also, it readily with the metal sulfide to form the cor- primary remormer with potentially combines with other elements to responding metal oxide and free sul- severe effect on reforming catalyst produce corrosive compounds. fur, which remains trapped in the car- and radiant tubes. bon bed pores. Much of the sulfur is Oxygen–in high-temperature envi- Types 304 and 316 are also used vented to the atmosphere along with ronments can cause oxidation in other applications where freedom the steam. scaling of metal surfaces of under- from corrosion and corrosion products alloyed material. is essential, such as on-stream Nature of Corrosion instrumentation and valve trim. Corrosion in the natural gas desul-

furization step of the ammonia process CONSIDERATIONS is a function of purity of the natural gas feedstock and steam used for Catalytic Steam FOR SELECTING regenerating the activated carbon beds. Small quantities of sulfur are Reforming of present at all times, either as H2S, SO2 STAINLESS or carbonyl sulfide. Traces of chlorides may also be present, either by Natural Gas

STEELS entrainment in the natural gas or as carryover from boiler feedwater used Process Description Desulfurization for steam manufacture. Thus, In this step (Figure 2), sweetened condensates highly corrosive to steel natural gas which leaves the desul- of Natural Gas may be formed at the beginning of a furizers at ambient temperature is carbon bed regeneration cycle. How- preheated and mixed with steam and ever, serious corrosion is avoided by further preheated to 930 to 1020ºF Process Description addition of a small amount of am- (500 to 550ºC) in a waste heat recov- The sulfur content of the natural monia to the steam to keep the con- ery coil usually located in the primary gas feedstock must be reduced to as densate at a neutral or slightly al- reformer convection sections. The low a level as possible to prevent kaline pH. steam-to-gas ratio is maintained in

6 the range of 3 to 4 moles of steam The virtually completely reformed phenomena in addition to simple oxi- per mole of gas. synthesis gas leaves the secondary dation. Sulfur entrainment and boiler The preheated steam/gas mixture reformer at 1740 to 1830ºF (950 to feedwater salts carryover in the natu- enters the primary reformer tubes 1000ºC) and is cooled in a waste ral gas/steam reformer feed can which are filled with a nickel-base heat boiler to about 680ºF (360ºC). cause sulfidation and molten salt at- catalyst. The reaction, The boiler produces steam at tack respectively of reformer catalyst tubes, outlet manifolds and transfer CH4 + H2O → CO + 3H2, approximately 1500 psig (10.3 MPa) is endothermic. Heat is supplied from which is used to drive lines. Methane and higher hydrocar- external burners which use natural turbomachinery. bons in feedstocks will carburize most gas or oil as fuel. Heat in the flue gas which leaves metals rapidly at these temperatures About 70% of the methane is con- the primary reformer radiant section if the proper steam-to-methane ratio verted to hydrogen in the primary re- at about 1760ºF (960ºC) is recovered is not maintained. Fluctuations in former. The partially reformed gas in several preheat coils in the convec- steam/methane ratios subject alloys leaves the primary reformer at 1345 tion section. The flue gas exits to a highly destructive cyclic to 1510ºF (730 to 820ºC) and enters through the reformer stack at 390 to carburization/oxidation phenomenon the secondary reformer where it is 480ºF (200 to 250ºC). similar to metal dusting. Trace mixed with air to produce a synthesis Nature of Corrosion amounts of impurities such as lead in gas with a hydrogen-to-nitrogen ratio Catalyic steam reforming of natu- reformer tube alloys will promote cat- of 3:1. Heat required to complete the ral gas occurs at elevated tempera- astrophic oxidation of these alloys. reforming reaction is obtained by tures – 1290 to 1830ºF (700 to Bunter fuels are also a source of combustion of the air/gas mixture 1000ºC) – so materials of construc- high-temperature corrodents. For over a bed of nickel-base catalyst tion may be subjected to a number of example, fuel oil ash deposits (on similar to primary reformer catalyst. high-temperature metal wastage outer tube surfaces) which contain

7 sodium, vanadium and sulfur com- Other satisfactory experience with reforming steps contains about 12%

pounds can cause severe molten salt stainless steels in steam/natural gas CO and 8% CO2 which are unwanted attack of reformer alloys. reforming includes Types 304, 321 products of reforming. The gas is and 310 inside the primary reformer passed over a bed of chromium Applications for Stainless Steels firebox for heat shields around riser oxide-promoted iron oxide catalyst in Virtually all ammonia plants use welds; jacketing around outlet man- the high-temperature shift converter centrifugally cast high-alloy tubes to ifold insulation; thermocouple sheaths; (Figure 3) which operates at 625 to contain the nickel-base catalyst in the thermal/mechanical protection tubes 1020ºF (330 to 550ºC). CO is con-

primary reformer furnace. The most around thermowells; manifold drain verted to CO2 and more hydrogen by commonly used tube alloy is similar in and sample nozzles; and flue gas the following exothermic reaction;

composition to Type 310 – nominally sample tubing. CO + H2O → CO2 + H2. 25% chromium and 20% nickel, Types 304 and 321 are used for tie Gas leaving the high-temperature balance iron – but with a carbon rods and tube supports on the pro- shifter at 800ºF (425ºC) is cooled to content in the range 0.35 to 0.45% for cess gas side of primary waste heat about 390ºF (200ºC) in a heat ex- improved high-temperature creep and boiler tube bundles. changer and is then passed over a stress rupture strength. The Alloy Virtually all piping and equipment bed of copper oxide/zinc oxide Casting Institute has designated this throughout this system requires ex- catalyst in the low-temperature shift alloy as Grade HK-40. ternal thermal insulation to conserve converter. This step reduces the CO Linings of castable and fired brick heat. Sheet metal jacketing of Types content of the synthesis gas to about refractories are used for thermal pro- 430 or 304 provide outstanding pro- 0.4%. The gas is cooled to 195 to tection of piping and equipment be- tection against weather and mechan- 250ºF (90 to 120ºC) and enters the cause of the high temperatures – 1290 ical damage for all types of insulation carbon dioxide removal system. Un- to 1830ºF (700 to 1000ºC) – en- – preformed, blanket or block. reacted steam is condensed and countered throughout this system. In- High-pressure steam, which is separated from the synthesis gas in cluded are the process effluent transfer generated in the primary waste heat a knockout drum. This steam line from the primary to the secondary boilers and, where utilized, auxiliary condensate may be reused in the reformer; and secondary reformer; power boilers, requires boiler feedwa- process or discarded. crossover lines between the secondary ter of exceptional purity to avoid foul- reformer and primary waste heat ing of heat transfer surfaces and tur- Nature of Corrosion boilers; and the primary waste heat bine components by boiler salts. Most Principal corrodents in the carbon large, modern ammonia plants have monoxide shift step are CO, CO , H , boilers themselves. To prevent 2 2 facilities for demineralizing water with refractory erosion by the hot, high- and steam condensate. CO2 is not velocity gas streams, refractory ion exchange resins. Water quality of particularly corrosive as a hot, dry gas surfaces are frequently lined with metal less than 5 parts per billion total im- but forms corrosive shrouds (1/16 to 1/4 inch thick) (1.58 to purities is common. To maintain this when dissolved in steam condensate 6.35 mm) of Types 304, 321 or 310. purity and for good, all-around corro- However, ammonia additions to con- Types 304 and 321 have sion resistance in this aggressive densate are effective in keeping rates demonstrated satisfactory oxidation medium, Type 304 is frequently of attack at an acceptable level. Hy- resistance in piping and equipment specified for demineralized water drogen is not corrosive as such, but operating at 1290 to 1650ºF (700 to storage tanks and piping, and trim in can diffuse into carbon and low-alloy 900ºC) (e.g. transfer lines), whereas valves and pumps. Type 316 finds steels and cause embriftlement of Type 310 has provided good protec- applications in the ion exchange resin hardened regions (e.g. weld heat- tion at temperatures between 1650 system because of good resistance to affected zones) at low to moderate and 1830ºF (900 and 1000ºC). cold, dilute caustic and temperatures and severe reductions Oxidation resistance is not the only solutions which are used for re- in strength and ductility at elevated criterion for using austenitic stainless generating the resin beds. temperatures by chemical attack of

steel shrouds in this system. The pro- the unalloyed iron in steel to cess gas stream has high potential for form methane. nitriding and, on occasion, carburizIng Carbon Monoxide metals and alloys. The austenitics Applications for Stainless Steels provide reasonable at low cost Shift Major equipment in the carbon

when compared with the more resis- monoxide shift system (Figure 3) in- tant and more expensive high-nickel Process Description cludes pressure vessels for the pri- alloys in this service. The cooled synthesis gas from the mary and secondary catalytic con-

8 version of CO to CO2 in the synthesis cause of excellent resistance to at- Type 304 for fittings such as tees and gas, heat exchangers which cool the tack by CO, CO2, H2 and steam. ells where impingement erosion- catalytic converter effluents and re- In some plants, the secondary corrosion by the wet gas stream is cover waste heat in the process, and shifter effluent is cooled to its dew cause for failure. After several years' a separator for removing steam con- point by direct contact with a fine service and especially with increased densate for reuse as process water. spray of recycle process water process throughput, many plants Generally, the carbon and low-alloy (steam condensate) in a section of have replaced all original carbon steel steels such as carbon-0.5% Mo and piping. The spray quench piping sec- sections with Type 304 stainless steel 1¼Cr-½Mo are specified for vessels tions at and immediately downstream for greatly prolonged life. and piping exposed to the hot CO- of the internal spray nozzle are The carbon steel separator is sub-

CO2-H2 gas streams. specified as Type 304 for resistance jected to corrosion by CO2 dissolved However, Types 304 and 410 are to impingement erosion-corrosion by in water (carbonic acid) and thus has employed for the wire mesh screens water droplets in the high-velocity gas a finite life. Type 304 stainless steel and grating that support the catalyst stream. linings are frequently installed after beds in the primary and secondary After additional cooling of shifter original corrosion allowances are shift converters, as well as for grid effluent to 150 to 160ºF (65 to 70ºC) used up, as an economical alternative sections installed on top of the beds to in a , most of the to vessel replacement. One method keep the catalyst from shifting and for water vapor condenses and is consists of welding strips of stainless more uniform gas distribution through removed in a separator or knock-out steel sheet to the steel shell. Another the beds. Thermocouple sheaths, drum. Piping to the separator was consists of surface preparation by grit thermowells and thermowell guide frequently specified as all plain blasting followed by flame spray tubes are frequently of Type 304 be- carbon steel, or carbon steel for metallizing with stainless steel pow-

9 der or wire. This porous lining, usually The regenerated MEA is cooled in a aqueous solutions containing CO2. 0006 to 0.010 inch (0.1524 to heat exchanger and solution cooler Most of the equipment in CO2 re- 0.254mm) thick, is then sealed with a and returned to the absorption tower. moval systems consists of large, ver-

catalyzed epoxy or epoxy-phenolic This process permits CO2 removal at tical scrubbing and distillation-type coating. atmospheric pressure with con- vessels, and heat exchangers. The sequent reduction in compression re- CO2 absorber, where CO2 in shifter quirements. effluent gas is absorbed in an aque- ous solution of MEA, generally con- Removal of Nature of Corrosion sists of a carbon steel shell with sub- Process conditions in CO2 removal stantial corrosion allowance, filled with systems can result in moderate to se- Type 304 ring packing or fitted with Carbon Dioxide special Type 304 trays. vere corrosion of materials of con-

struction by contact with hot, aqueous The "rich" (With CO2) solution iron

Process Description solutions of CO2 in the presence of the bottom of the absorber is heated Following shift conversion, carbon MEA, or other and then fed near the top of the CO2 dioxide must be removed from the absorbants. Solution temperatures stripper where CO2 is released from the mixture of hydrogen and nitrogen range from 105 to 300ºF (40 to 150ºC). solution, after which it is called “lean” (Figure 3). About 1.2 metric tons of Corrosion of steel is accelerated by because of low CO2 content.

CO2 are produced for every metric ton increased process stream velocities Many plants require an upper shell of ammonia manufactured. (5) which occur, for example, in pumps, section of Type 304, either solid or clad on carbon steel, and Type 304 The removal of CO2 depends on its pressure let-down valves, at piping acidic character. It tends to form car- tees and ells, etc. Heat transfer condi- sieve trays in the stripper. The stripper bonic acid in water by this reaction: tions which cause hot wall effects, as in overhead piping, condenser and ac- CO + H O → H CO . reboilers and other heat exchangers, cumulator, which handle the wet CO2 2 2 2 3 Carbonic acid undergoes reversible also accelerate corrosion. Other stripped from the MEA solution, are reactions in solutions of amines by corrodents in these systems include frequently Type 304 also. chemical absorption as follows: products of degradation of MEA. The heat required to operate the 2NH CH CH OH + H CO → CO stripper is supplied by exchang- 2 2 2 2 3 However, accumulation of these 2 complex organic compounds may be ing rich solution with steam or hot (NH2CH2CH2)2CO3 + 2H2O. controlled by side-stream solution re- process gas (i.e. shifter effluent) in The carbonate thus formed decom- claiming operations. Also, corrosion shell-and-tube reboilers. The corro- poses on heating into CO2 and the inhibitors such as filming amines and sion accelerating effects of heated amine. This drives off the CO2 and regenerates the absorption solution. certain proprietary additives (6) have surfaces are maximized in these ves- The classical method for removing been used effectively to reduce cor- sels. Here too, however, Type 304 has given good service for tubing and CO2 is absorption in monoethano- rosion in process piping and equip- larnine (MEA). Approximately 80% of ment. tube supports. On occasion, corrosion all ammonia plants use this solution. of Type 304 may be excessive e.g. The remaining plants use hot potas- Applications for Stainless Steel operation at higher temperatures or sium carbonate or proprietary so- For efficient conversion to ammonia, with excessive amounts of MEA lutions based either on amines or the hydrogen/nitrogen synthesis gas degradation products. Under these . must contain no more than 10 parts conditions, Type 316 generally pro- In the MEA system, synthesis gas per million CO plus CO. Thus vides somewhat better service. 2 Hot, lean solution from the bottom containing CO is passed up through ammonia plants require heavy 2 of the stripper is cooled by heat ex- an absorption tower countercurrent to investment in equipment and piping change with the cool, rich solution in a 15-20% solution of MEA in water. specifically for the removal of CO2 The amine solution which is rich in (Figure 3). Its acidic nature makes CO the shell-and-tube solution exchang- 2 ers. Both Types 304 and 316 have CO2 is preheated and then regener- the most corrosive constituent in the been specified for original vessels– ated in a reactivating tower. CO2 is ammonia manufacturing process. first removed by steam stripping and However, effective and economical tubes, tube supports and solid or clad then heating. CO2 of about 98-99% use is made of austenitic stainless tube sheets and shells–or for units purity is either vented to the atmo- steels, primarily Types 304 and 316, in which replaced original carbon steel sphere or used as feedstock for other both wrought and cast form, equipment where the superior processes such as and throughout this system because of erosion-corrosion resistance justified urea. demonstrated resistance to hot the higher cost of stainless steel. Type 304 has also found wide

10 spread application for both rich and atmospheres according to these for the synthesis of lean solution piping, pumps, valves reactions: ammonia are now used commercially. and on-stream instruments. Cast ver- All are fundamentally the same, i.e. CO + 3H2 → CH4 + H2O nitrogen is fixed with hydrogen as sions of this alloy, designated as CO2 + H2 → CO + H2O

Grade CF8 by the Alloy Casting Insti- CO2 + 4H2 → CH4 + 2H2O ammonia in the presence of a tute, are used far pump casings and This reaction is the reverse of that catalyst. However, they vary with re- impellers and valve bodies. Neither involved in steam reforming of gard to flow arrangement and con- intergranular corrosion nor stress methane. Reversal is accomplished struction of equipment, composition of corrosion cracking by process through use of lower temperatures catalysts, temperatures and pres- streams appear to be problems with and absence of excess water, both of sures. application of austenitic stainless which favor the formation of methane. The first step in ammonia steels throughout this system. The methanator exit gas is cooled synthesis is compression of the synthesis gas from the methanator Many CO2 removal systems re- to 100ºF (38ºC) and contains less quire reclaimers which purge degra- than 20 ppm carbon . (Figure 4). Within the last 15 years, a dation products from rich solution. Condensate is removed in a process revolution has occurred in the Austenitic stainless steels are nearly condensate drum. The final synthesis ammonia industry through the always specified for these vessels gas at 100ºF (38ºC) and about 370 application of centrifugal driven by steam turbines for handling because of superior resistance to cor- psig (2.55 MPa) contains hydrogen synthesis gas at pressures between rosive complex organic compounds. and nitrogen in a ratio of 3:1, and less 2000 psig (13.8 MPa) and 10,000 psig Nearly all ammonia plant operators than 1.5% methane. use corrosion inhibitors in their CO (69 MPa). These require 2 removal systems to minimize corro- lower investment, maintenance and Nature of Corrosion sion of carbon steel portions of piping requirements per ton of Corrodents in the methanation and equipment. One of the most ef- ammonia than reciprocating machines. step are similar to those in the carbon fective appears to be a proprietary Synthesis gas is compressed in monoxide shift–CO, CO , H and inhibitor labeled "Amine Guard" by its several stages to 2000-5000 psig 2 2 developer, Union . They re- condensed water. Although methana- (13.8-34.5 MPa) and mixed with re- port significant reductions in corro- tion reaction pressures are lower and cycled synthesis gas from the reac- sion rates of both mild steel and temperatures are somewhat higher, tors. The combined gas stream is Type 304 after addition of this this process is no more aggressive to cooled to -10 to 32ºF (-23 to 0ºC) in a inhibitor to MEA systems serving two materials of construction than is the refrigeration cooler. Condensed am- ammonia plants. (6) CO shift process. monia is separated from the uncon- verted gas in a liquid-vapor separator Applications for Stainless Steels and a pressure let-down separator. Applications of stainless steels – The gas is preheated to about 360ºF mostly Type 304–in the methanator (180ºC) before entering the converter. Methanation are limited to wire mesh screens At this point, the synthesis gas con-

and grating, which support the cata- tains hydrogen and nitrogen in the Process Description lyst bed in the methanator, ther- proper 3:1 ratio, along with 12-14% mocouple sheaths, thermowells and All CO2 absorption systems leave a inerts and about 4% ammonia. small amount, i.e. less than 1%, of other on-stream instruments and In the converter, synthesis gas is residual carbon oxides in the gas. valve trim. Otherwise, plain carbon dispersed through a promoted iron and low alloy steels dominate the ma- Both CO2 and residual carbon oxide (Fe3O4) catalyst (an iron oxide monoxide must be removed, other- terials of construction in the methana- catalyst whose activity is increased or wise they will poison most ammonia tion step. promoted by the addition of oxides of synthesis catalysts. Removal is ac- aluminum or potassium). The gas complished by a catalytic methanation which exits the catalyst beds in the process (Figure 3). Heat of reaction is converter is about 700ºF (370ºC) and recovered from the methanator Synthesis of contains approximately 15% ammonia effluent by exchange with boiler and 14% inerts. This hot gas is used feedwater. Ammonia to preheat boiler feedwater for the

The synthesis gas is passed over a steam system and is then inter- nickel-containing catalyst (NiO on changed with feed gas to the conver- Process Description alumina) at 600 to 1110ºF (316 to ter. The ammonia-rich gas is recycled 600ºC) and pressures up to 600 Many variations of the original through the synthesis be-

11 low-alloy steels. (8) Other process considerations for materials selection include hydrogen at elevated tem- peratures and pressures: steam at pressures up to 1500 psig (10.3 MPa) used for driving high-performance turbines; and maintenance of product purity. Applications for Stainless Steels Although carbon steel exhibits a low corrosion rate in this system, carbon steel tubes in the water-cooled exchangers have failed prematurely in service because of fouling and cor- rosion by aggressive natural waters used for cooling. Type 430 stainless steel replacement tubes have pro-

vided many years of leak-free service at some plants, especially in units where water is circulated through the tubes. This alloy is also immune to chloride stress-corrosion cracking by chloride-bearing waters. In some waters, pitting of Type 430 under deposits could be a problem, especially where the water is circulated on the shell side of the exchanger with more opportunity for accumulation of deposits at baffles and tube sheets. In these cases, the new ferritic stainless steels which contain 26% Cr and 1% Mo may find application because of superior pitting fore being cooled to condense the separator to low-temperature resistance as compared to Type 430 ammonia. A small portion of the over- atmospheric pressure storage. stainless steel and similar immunity to head gas is purged to prevent ac- chloride cracking. Two grades are cumulation of inerts in the circulating Nature of Corrosion specified in ASTM A-268: Gracie XM- gas system. The purge gas is cooled Ammonia is synthesized in the 27 (UNS S44625) which is furnished to 10ºF (-23ºC) to minimize loss of converter at temperatures between with very low carbon and nitrogen ammonia, and burned as fuel in the 840 and 930ºF (450 and 500ºC), and contents, and Grade XM-33 (UNS primary reformer. Some plants use a the synthesis gas has high potential S44626): Both alloys are stabilized. recently developed cryogenic system for nitriding metals at these tempera- Another grade of ferritic stainless steel to recover hydrogen from the purge tures. Another requirement for am- that may be considered is ASTM A- gas which is then used as feedstock monia synthesis is fairly high pres- 268, Grade UNS S44400, which to produce additional ammonia. (7) sure (2000 to 5000 psig) (13.8 to 34.5 contains 18% chromium and 2% Liquid ammonia from the primary, MPa). Corrosive ammonium carba- molybdenum and is stabilized with secondary and purge separators col- mate may be formed during the sev- titanium and niobium. lects in the let-down separator where eral stages of compression of synth- Synthesis converters are pressure the ammonia is flashed to atmos- esis gas prior to introduction into the vessels consisting of heavy wall car- pheric pressure at -27F (-33C) to converter. Condensed ammonia is bon or low alloy steel shells, which remove additional impurities such as also a corrodent, and in the anhydr- contain a removable cartridge filled . The flash vapors are con- ous state, can cause stress-corrosion with the promoted iron oxide catalyst densed in a pressure let-down chiller. cracking of stressed carbon steels required for conversion of synthesis Anhydrous liquid ammonia of high and heat-treated, high-strength, gas to ammonia. The cartridge con- purity is transferred from the let-down

12 tains an integral tubular heat ex- 3. The austenitic stainless steels as Grade 688 in ASTM-A-638, has changer that preheats fresh inlet gas showed good resistance. given excellent service. For compari- with hot reacted gas from the last 4. Increased nickel contents resulted son, the precipitation hardening S17400 catalyst bed. The combination of both in increased resistance to nitriding. stainless steel in Condition H950 has reacted and unreacted gases at Thus, it follows that the newer failed prematurely by hydrogen 2000+ psig (13.8+ MPa) and tem- modified Haber process converters embrittlement under identical peratures approaching 930ºF (500ºC) which operate at lower temperatures conditions. can be quite destructive to carbon and pressures are affected to a lesser The ammonia synthesis system and low alloy steels and other metals extent by the process stream. contains a large investment in refrig- with regard to hydrogen embrittlement Much of the piping and equipment, eration facilities and equipment for and attack, and nitriding. Therefore, e.g. heat exchangers, around the handling process streams at low tem- Type 304 is nearly always specified converter are fabricated from low peratures. These facilities are required as the optimum material of alloy steels such as carbon-½% Mo for ammonia condensation in the construction for the catalyst cartridge and 1¼%Cr-½% Mo for resistance to synthesis loop, recovery of ammonia and integral heat exchanger. In gen- hydrogen attack. At certain combina- from vented gases, synthesis gas eral, the austenitic stainless steels are tions of temperature and hydrogen compressor inter-stage chilling, plus resistant to nitriding and hydrogen , nascent hydrogen refrigeration and storage of the ernbrittlement and immune to hydro- will diffuse into plain carbon steels anhydrous liquid ammonia product. gen attack. Over a period of several and combine with carbon to form Plain carbon steels have satisfactory years' operation, shallow–up to methane. The results are loss of corrosion resistance in the process about 0.005 inch (0.127mm)– strength by decarburization plus loss streams. However, all equipment nitriding will occur in the hottest re- of ductility by microfissuring. Hydro- components–vessel plates, forgings, gions, resulting in a hard, brittle skin gen attack has caused catastrophic tubing, pipe, etc.–generally require on the stainless steel surface. How- failures of piping and vessels. The Charpy V-notch impact testing or drop ever, this appears to have little or no American Petroleum Institute Publi- weight testing to insure good fracture effect on the structural integrity of cation 941, "Steels For Hydrogen toughness at temperatures between 32 this equipment. Service at Elevated Temperatures and -27ºF (0 and -33ºC). Procurement In the early 1960's, investigators and Pressures in Petroleum Re- of certified components is not much of a from the International Nickel Com- fineries and Plants", problem for large, new investments in pany, Inc. published results of about 3 Second Edition (June 1977), is an facilities, but could pose a problem years exposure of corrosion coupons update of a compilation of data from when components are required on short of austenitic and ferritic stainless steel plant experience and laboratory tests notice, i.e., during major shutdowns for and nickel-base alloys in Haber- which G.A. Nelson of the Shell De- modifications or repairs. Under these Bosch (9) and Casale process (10) velopment Corporation initiated in the circumstances, plants frequently ammonia converters. The operating 1940's. Curves showing safe limits for substitute austenitic stainless steel conditions were as follows: plain carbon and low alloy steels are components because of availability Haber-Bosch–915 to 1020ºF (490 plotted vs. temperature and hydrogen from stock and excellent fracture to 550ºC); 5200 partial pressure. toughness down to -328ºF (-200ºC) and psig (35.9 MPa) Curves for the austenitic stainless beyond, generally without an impact Casale– Nominal 1005ºF steels are not included because these test requirement. Welds are readily (540ºC); 11,000 materials are virtually immune to this made between the stainless steel psig (75.8 MPa) phenomenon under all combinations components, usually Types 304 and The following conclusions were of temperature and hydrogen partial 316, and the existing carbon steel parts, drawn from these tests; pressure. Thus, critical on-stream in- by gas tungsten arc and/or shielded 1. Nickel and nickel-base alloys struments, control valves and valve metal arc processes with Type 309 or exhibited the best nitriding resis- trim in the converter loop are fre- 310 weld filler metal. tance in both exposures. quently specified in austenitic stain- In general, anhydrous liquid am- 2. Depth of nitriding is a function of less steels, primarily Types 304 and monia is considered to be noncorrosive operating pressure; coupons 316. Where higher mechanical to a variety of metals and alloys exposed in the higher pressure strengths are required, such as for including carbon steel and all classes of Casale converter were pene- valve stems subjected to heavy cyclic stainless steels. Recent work (11) has trated to greater depths than loads, the precipitation hardening shown many metals and alloys– those exposed in the Haber- stainless steel A-286 (15Cr– including the aforementioned carbon Bosch converter. 26Ni–1 ¼Mo–2.15Ti), designated steel and stainless

13 steels, along with titanium, zinc, water to the ammonia. It is noteworthy plants, with similarities in materials of Monel and aluminum alloys– that the austenitic stainless steels construction. Plants require com- exhibiting either very low weight los- have shown no cracking tendencies in pression trains for the following ser- ses or slight weight gains in anhy- ammonia under any conditions. vices: drous liquid ammonia after one to 1. Compress natural gas feed to eight month's exposure at room tem- the primary reformer operating perature. Turbine-Driven at pressures of 440 to 550 psig The intergranular stress-corrosion (3 to 3.8 MPa). cracking, or "season" cracking as it is Centrifugal 2. Provide air to the secondary commonly known, of some copper al- reformer. loys, most notably the brasses, by Compression 3. Compress synthesis gas to the moist ammonia has been well converter operating at pressure: documented. So has the more recent Trains of 2000 to 5000 psig (13.8 to disclosure of stress-corrosion crack- 34.5 MPa). ing of stressed carbon steels and 4. Provide refrigeration for several high-strength low alloy steels by air- Turbine-driven centrifugal com- key steps in the synthesis of contaminated liquid anhydrous am- pression trains are listed as a seventh ammonia. monia (8), and inhibition of this crack- heading, because there are four such Virtually all of the 1500 psig (10.3 ing by addition of a minimum of 0.2% trains in most modern-day ammonia MPa) steam generated in waste heat

TABLE 1 Chemical Analysis, % (Maximum unless noted otherwise) (12) AISI Type (UNS) C Mn P S Si Cr Ni Mo Other

405 0.08 1.00 0.040 0.030 1.00 11.50/14.50 Al 0.10/0.30 (S40500)

410 0.15 1.00 0.040 0.030 1.00 11.50/13.50 (S41000)

422 0.20/0.25 1.00 0.025 0.025 0.75 11.00/13.00 0.50/100 0.75/1.25 V 0.15/0.30 (S42200) W 0.75/1.25

430 0.12 1.00 0.040 0.030 1.00 16.00/18.00 (S43000)

304 0.08 2.00 0.045 0.030 1.00 18.00/20.00 8.00/10.50 (S30400)

304L 0.030 2.00 0.045 0.030 1.00 18.00/20.00 8.00/12.00 (S30403)

309 0.20 2.00 0.045 0.030 1.00 22.00/24.00 12.00/15.00 (S30900)

309S 0.08 2.00 0.045 0.030 1.00 22.00/24.00 12.00/15.00 (S30908)

310 0.25 2.00 0.045 0.030 1.50 24.00/26.00 19.00/22.00 (S31000)

310S 0.08 2.00 0.045 0.030 1.50 24.00/26.00 19.00/22.00 (S31008)

316 0.08 2.00 0.045 0.030 1.00 16.00/18.00 10.00/14.00 2.00/3.00 (S31600)

316L 0.030 2.00 0.045 0.030 1.00 16.00/18.00 10.00/14.00 2.00/3.00 (S31603)

321 0.08 2.00 0.045 0.030 1.00 17.00/19.00 9.00/12.00 Ti 5 x C (Min.) (S32100)

14 recovery and auxiliary boilers is used surfaces for added wear resistance nominal 26% Cr and 1 % Mo may find to drive the turbines in these trains. are also industry standards. application in condensers that operate Each turbine is capable of generating Austenitic stainless steels have at higher steam temperatures or in thousands of horsepower at speeds been applied to some extent in shell- more-aggressive cooling waters. between 6000 and 10,000 rpm. Type and-tube surface condensers that use Alternately, several highly alloyed au- 403 is an industry standard for buc- cooling water to condense the large stenitic stainless steels may be con- kets and shrouds on rotors where quantities of turbine exhaust steam sidered. stress levels are low-to-moderate. At for reuse as process condensate. The multi-stage centrifugal com- higher stress levels, heat treated However, steam temperature must pressors are heavy users of stainless Type 422 has provided excellent ser- not be excessive or chloride stress- steels also. Type 410 is in common use vice. Type 405 is frequently specified corrosion cracking may occur in some for rotor impellers because of good for stationary components such as chloride-bearing cooling waters. One corrosion and erosion resistance, diaphragms and nozzle blocks, espe- major chemical company maintains strength and fabricability. In cases cially where welding is required. the steam temperature at or below where stress levels are high and Steam admission and throttle valve 140ºF (60ºC) to avoid stress-corrosion particularly where impellers are seats and plugs of Type 410 with a cracking problems. The ferritic fabricated by welding, Type 410 with hard surface weld overlay on seating stainless steels which contain a addition of niobium in the range of 0.15 TABLE 2 to 0.25% has been specified for Nominal Mechanical Properties improved fracture toughness in the heat (Annealed sheet unless noted otherwise) (12) treated condition and good weldability Yield Elongation Tensile in the annealed condition. Stationary Strength In 2" Strength parts such as inlet guide vanes are AISI Type (0.2% offset) (50.80 mm) Hardness (UNS) ksi MPa ksi MPa % Rockwell frequently fabricated in austenitic or

ferritic stainless steels. 405 65 448 40 276 25 B75 (S40500) Other applications in compression

410 70 483 45 310 25 B80 trains and related equipment include (S41000) Type 304 for interstage separator 422* 145 1000 125 862 18 320 demister pads, valve trim and on (S42200) (Brinnell) stream instrument components. The 430 75 517 50 345 25 B85 new ferritics may find application in (S43000) interstage coolers of shell-and-tube 304 84 579 42 290 55 B80 design and cooled with natural waters. (S30400) 304L 81 558 39 269 55 B79 (S30403) STAINLESS 309 90 621 45 310 45 B85 (S30900) STEELS

309S 90 621 45 310 45 B85

(S30908) There are a total of 57 separate

310 95 655 45 310 45 B85 and distinct compositions that are (S31000) recognized by American Iron and 310S 95 655 45 310 45 B85 Steel Institute as standard AISI- (S31008) numbered stainless steels. Of these 316 84 579 42 290 50 B79 57 types, nine are regularly used in (S31600) ammonia production equipment. The 316L 81 558 42 290 50 B79 chemical compositions of these types (S31603) (plus their low-carbon counterparts)* 321 90 621 35 241 45 B80 are shown in Table 1, and their (S32100) mechanical properties are shown in Table 2.

*Hardened and Tempered Bar *Note: Intergranular corrosion does not appear to be a problem in ammonia production. However, the low-carbon grades are readily available for chemical plant construction so they are identified for the information of the reader.

15 fairly good ductility, and some can be Type 410 with about 12% chromium heat treated to tensile strengths ex- is the general-purpose stainless steel Metallurgical ceeding 200,000 psi (1379 M Pa). of the martensitic group. Structure

Stainless steels in the Austenitic High-Temperature Mechanical Properties group, containing chromium and nickel, are identified as AISI 300 Se- Stainless steels are used routinely vated temperature applications and ries types. (Those containing up to temperatures of 1500ºF (816ºC) the added advantage of nickel plus chromium, nickel, and manganese are because they possess good high- chromium. identified as 200 Series types.) temperature strength, ductility, and The stresses that will cause Although the austenitic grades resistance to high-temperature oxida- rupture of several austenitic stainless have different compositions, they tion and sulfidation. Types 309 and steels in 10,000 and 100,000 hours have common characteristics. They 310 are quite frequently used in are shown in Figures 6 and 7 as a can be hardened by cold working, but oxidizing environments at tempera- function of temperature. Stresses that not by heat treatment. Annealed, all tures as high as 1800ºF (982ºC). will cause creep at the rates of 0.0001 are nonmagnetic; however, some may Figure 5 shows the Allowable De- and 0.00001 per cent per hour are become slightly magnetic on cold sign Stresses from the ASME Unfired shown in Figures 8 and 9. Interpola- working. They have excellent Pressure Vessel Code, Section VIll tion to other rupture times, creep corrosion resistance, mechanical Division 1 versus temperature for rates, and stresses can be made by properties (at ambient as well as low several austenitic stainless steels, using Figures 10 to 16, which show or elevated temperatures), and form- ferritic stainless steels, chromium- the effects of applied stresses on the ability. molybdenum steels, and carbon rupture times and creep rates for the Type 304 (frequently referred to as steel. This graph portrays the value of same stainless steels at different 18-8) is the general-purpose stainless chromium additions to steel for ele- temperatures. steel of the austenitic group with a nominal composition of 18% chromium and 8% nickel. In the Ferritic group are the straight-chromium, 400 Series types that cannot be hardened by beat treatment, and are only moderately hardened by cold working. They are magnetic and have good ductility and resistance to corrosion and oxidation. Type 430, nominally 17% chromium, is the general-purpose stainless steel of the ferritic group. In addition to the AISI types, some proprietary ferritic stainless steels are also candidate materials for ammonia production applications. Several of these are listed in Table 3. These stainless steels represent improve- ments in refining practices, particularly with respect to carbon and nitrogen removal, achieved commercially only in the last five years. In the Martensitic group are the straight-chromium 400 Series types that can be hardened by heat treat- ment. They are magnetic. They resist corrosion in mild environments, have

16 TABLE 3 Alloy ASTM UNS

18Cr-Ti (Alloy 439) XM-8 S43035

18Cr-2Mo-Ti/Nb (Alloy 444) * S44400

18Cr-2Mo-S XM-34 S18200

26Cr-1 Mo (E-Brite 26-1) XM-27 S44625

26Cr-1 Mo-Ti XM-33 S44626

*This steel is covered in ASTM Specifications, e.g. A 176 and A 268, but ASTM no longer gives "XM" designations, relying instead on the UNS (Unified Numbering System) designation.

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18

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Thermal Conductivity

Curves showing the average effect of temperature on the thermal con- ductivity of seven austenitic stainless steels are shown in Figure 17. Heat transfer efficiency is a subject of in- creasing importance among plant engineers because of the need to achieve closer to optimum perform- ance in heat exchangers and thus economize on heat investment and energy utilization. The thermal con- ductivity of the ferritic stainless steels is somewhat higher than that of the austenitics.

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Oxidation Resistance

The most important alloying ele- ment for increasing scaling resis- tance above 1000ºF (538ºC) is chromium. This element appears to oxidize preferentially to iron. It forms a tightly adherent layer of chromium- rich oxide on the surface of the metal, retarding the inward diffusion of oxygen and inhibiting further oxidation. Other elements such as silicon and aluminum also increase scaling resistance, particularly when added to a steel containing chromium. Nickel imparts high temperature strength, it stabilizes the austenitic structure, and it adds a small measure of high-temperature corrosion resistance. Figure 18 provides an indication of the relative scaling resistance of commonly used high-temperature alloy steels. Stainless steels containing less than 18% chromium are limited to temperatures below 1500ºF (816ºC). Those containing 18-20% chromium TABLE 4 are useful to temperatures of 1800ºF Maximum Service Temperatures for Satisfactory Use Under (982ºC), while adequate resistance to Oxidizing Conditions Without Excessive Scaling (18)* scaling at temperatures up to 2000ºF

AISI Continuous Service Intermittent Service (1093ºC) requires a chromium content Type* C F C F of at least 25%, such as Types 309

304 925 1700 870 1600 and 310. The maximum service tem- perature, based on an oxidation rate of 925 308 980 1800 1700 10 mg per sq cm in 1000 hours, is 309 1095 2000 980 1800 given for several stainless steels in 310 1150 2100 1035 1900 Table 4. Steam will increase the oxi- dation rate. 870 316 925 1700 1600 For conditions in which tempera- 317 925 1700 870 1600 tures vary, temperature limits also

321 925 1700 870 1600 shown in Table 4 in the column "In- termittent Service." 1035 330 1150 2100 1900 Additions of silicon also increase 347 925 1700 870 1600 resistance to oxidation, such as in

405 705 1300 815 1500 Type 314, but silicon tends to de- crease high-temperature strength. 410 705 1300 815 1500

430 815 1500 870 1600

*The temperature limits shown may have to be revised downward fn the presence of combus- tion products or gases high in sulfur compounds and if vanadium–containing ash is present.

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As with oxidation, resistance to sulfidation relates to chromium Sulfidation content. Unalloyed iron will be converted rather rapidly to iron sulfide Resistance scale, but when alloyed with

chromium and nickel, sulfidation Sulfur attack is second only to air resistance is enhanced. Silicon also oxidation in frequency of occurrence affords some protection to sulfidation. and is of even greater consequence In addition to the usual factors of because deterioration is likely to be time, temperature, and concentration, more severe. sulfidation depends upon the form in Like oxidation, sulfidation proceeds which the sulfur exists. An alloy by converting metal to scale, which possessing useful resistance to sulfur may be protective, except that sulfide in one form may actually experience scales are friable and tend to exfoliate, accelerated corrosion when the sulfur exposing bare metal to further is present in another form. sulfidation.

CO REFERENCES 2 Removal Systems," Chem- less and Heat Resisting Steels ical Engineering Progress, V. American Iron and Steel Inst- 69, No. 2, February 1973. tute, December 1974. 1. Kelloggram,1977 Series, Issue 7. "Ammonia Plants Seek Routes To 13. ASME Boiler and Pressure Ves- 2, published by Pullman-Kellogg, Better Gas Mileage," Chemical sel Code, Section VIII, Division Division of Pullman, Inc., Hous- Week, 116 (8):29, February 1974. ton. 19,1975. 14. Simmons and Van Echo, "Report 2. Quartulli, O.J. and Buividas, L.F, 8. Loginow, A.W. and Phelps, E.H., on the Elevated-Temperature "Some Current and Future "Stress-Corrosion Cracking of Properties of Stainless Steels Trends In Ammonia Production Steels in Agricultural Ammonia," ASTM Data Series Publication ," Nitrogen, March/ Corrosion, V. 18, August 1962. DS-5-Si (formerly Special Tech- April 1976. 9. Moran, J.J., Mihalisin, J.R. and nical Publication No. 124). 3. Partridge, L.J., "Coal-Based Skinner, E.N., "Behavior of Stain- 15. Simmons and Cross, "Report on Ammonia Plant Operation," less Steels and Other Engineer- the Elevated-Temperature Prop- Chemical Engineering Pro- ing Alloys in Hot Ammonia Atmo- erties of Chromium Steels, 12 to gress, August 1976. spheres," Corrosion, V.17, April 27 Percent," ASTM Special 4. Finneran, J.A., Buividas, L.J. and 1961. Technical Publication 228. Walen, N., "Advanced Ammonia 10. McDowell, D.W., "Alloy Behavior 16. "Mechanical and Physical Prop- Technology," in Casale Ammonia Converter," erties of the Austenitic Chro- Processing, April 1972. Materials Protection, July 1962. mium-Nickel Stainless Steels at 5. Streizoff, S., "Choosing the Op- 11. Jones, D.A. and Wilde, B.E., Elevated Temperature." The In- timum CO2-Removal System," "Corrosion Performance of Some ternational Nickel Company, Inc Chemical Engineering, Sep- Metals and Alloys in Liquid New York, 1968. tember 15,1975. Ammonia," Corrosion V. 33, No. 17. Smith, G.V. "Properties of Metal 6. Butwell, K.F., Hawkes, E.N. and 2 (February 1977). at Elevated Temperatures, Mago, B.F., "Corrosion Control In 12. Steel Products Manual, "Stain- McGraw-Hill Book Company 1950. 18. Stainless Steel Industry Data.

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Quality from American Labor

Committee of Stainless Steel Producers American Iron and Steel Institute 1000 16th Street, N. W. Washington, D.C. 20036

Permission is granted to accredited trade journals to reproduce any of the material published in this issue. Additional copies are available.

The following companies are represented on the Committee of Stainless Steel Producers:

Allegheny Ludlum Steel Corporation Armco, Inc. Atlas Steels, A Division of Rio Algom Ltd. Carpenter Technology Corporation ITT Harper Jessop Steel Company Jones & Laughlin Steel Corporation Joslyn Stainless Steels Republic Steel Corporation United States Steel Corporation Universal-Cyclops Specialty Steel Division, Cyclops Corporation Washington Steel Corporation

The following alloy suppliers are also represented on the Committee:

Climax Molybdenum Company Falconbridge International Ltd. Foote Mineral Company The Hanna Mining Company The International Nickel Company, Inc. Union Carbide Corporation, Metals Division

November 1978

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