Iron, Mild Steels, and

Iron, Mild Steels, and Low Alloy Steels Carnegie-Illinois Steel Corporation, Pittsburgh, P n .

Y F,kR the highest piopoitioii

oI all types of chemical erigneering equipment is made of low carbon steel. It is -sfi. t o *ay that other materials of con-truction are used only if there ii .t.vidence that steel will not serve the purpose. The reason< arv that steel has a great versatility of properties, is readily fabiicated, arid generally costs less than do the other construction material. ’The following new developments which occurred largely duririg 1 h i paqt decade will be discussed in turn:

1. The use of iron or steel equipinent for new cheiiiicals 01 processes. 2. The use of new protective measures to render older applications of iron or steel equipment more Satisfactory for conventional applications or t o make posqible the use of iron 01 steel equipment for new applications. 3. The use of new or modified compositions of iron or stwl i i i i ronventional or new applications. 4. Modifying the design or construction of conventional type* of equipment to permit the more satisfactory use of iron or steel.

4*onieyears ago Roetheli and Forrest ( 10 1 ) published a coniprehcnqive list of materials of construction used in contact with k a r i oils chemicals. As far as the authors are aware, no such complete list has been prepared more recently, although m w h information is given by McKap and ii70rthington ( 7 1 ) . I n order to have a starting place for the present article, applications of iron, Yteel. and low alloy irons and steel not mentioned by Roetheli and Forrwt (101) will be discussed here. Hon-ever, particular empha-is %-illbe given to applications of the ferrous materialq i s hich Iiwi e been made since about 1940. EQUIPMENT FOR NEW CHEMICALS OR PROCESSES

I t is rather difficult to obtain iiiformation on the use of iroii a d i t erl

equipment for new chemicals or processes from 1iteraturP iurveys. Most authors of articles dealing with such developments have a tendency to omit definite statements about the m:iterial employed for processing equipment unless it is unusual. Presumably, when they state that a n evaporator, a leach tank, a ,:ondrnser, or a n absorption tower \vas used, if the material of con*truetion is not stated, it is carbon steel or cast iron. I n general, -pt.cific mention of unalloyed iron or steel is made only when an riricxpected result is obtained. It n-odd be helpful if more d i h 7:iilcd information on the materials of construction werc giwn. In articles on hydrofluoric acid alkylation, it is nientioiieil wpratedly that carbon steel is the inaterial of construction gcnt.1’ally used. For instance, Holmberg “(‘:irbon steel is the basic material” u :ilh?.lation equipment “and is adequate rtbniperatures of approximately 150” F.” Kriting on thr 5anii’ -utijttct, Skinner (101) states: “Except, for some points in iiirrrunit.ritation and equipment trim, all portions of the plant coining hi contact with HF acid or acid mixtures are constructed of c a r h i l -1t~e1.’’ Skinner points out subsequrntly that running fa( siiia11 moving parts which contact hydrofluoric acid should br i i i d e of nonferrous metals since the ceating of iron fluoride which forms on ferrous articles may intrde1.r with the operat ion of such ; ) u t ? ($9). One of the important tirvc~li,l~rnrnt~ during t h r war UH;. t h t b

IIoudry catalytic, crackiiig process. Aluch of the equipment fur this process is of stecl. Servton and Bhimp ( 8 8 ) mention several LIYS of &eel for such equipment. For example, they indicate that forged steel body gate valves are employed at temperatures in the neighborhood of 850” F. Steel cooling tuhes are used in the catalyst case, since the heat, transfer coefficients between steel and salt (a eutectic mixture of potassium nitrate and sodium nitrit’e iised for cooling) are very good, and the salt is noncorrosive toward carbon steel below 900” F. For higher temperatures calorized or alloy piping is satisfactory. The authors also point out ( 8 9 ) that carbon steel converters are used with catalyst t’rmperatures from about 650’ to 875’ F. Molten mixtures of alkali nitrates, sometimes in conjunctioii with nitrites, are extensively used as conducting media in the heat treatment, of metals. Corrosion of the pots or containers of these molten mixtures is a problem of long standing. However, because of the widespread use of aluminum for aircraft, the selection of equipment for handling molten nitrates became more important during the recent war. Lloyd and Chamberlain (68) investigated the effect of various niolten nitrate mixtures to determine the materials most suitable for use as containers. They concluded that ingot, iron was more resistant than steel and that sprayed aluminum coatings on steel pot’swere not, uniformly va!uablv as protection. Further studies by Box and Middleton ( 1 7 ) confirmed the s u p rior resistance of ingot iron, as compared bo steel, to attack hy molten nitrates. They also point out that rise in alkalinity of t h r nitrates frequently indicates that they are becoming corrosiw. I n the TCC catalytic cracking process ( 8 7 ) the reactor is R “simple cylindrical steel vessel.” In the Isomate process for making high octane fuels, sterl containers, including settlers and tank cars, are used. for handling the catalyst ccimplex which consists of a liquid aluminum chloridewhydroearbon mixture ( 1 1 1 ) : carbon steel is also used for the hydrochloric acid absorbers and strippers. I n the production of high octane mot or fuels by hytlroforming, considerable carbon steel equipment i s employed, ei: hri. bare or brick-lined (%). For the motor-operated valves used i n this process, 4-6 chrome-nirkel 5teels w r e found to be very sat i3factory (53). Iri the production of carbon and pot,ash from molasses! cast iron rxrhonizilig retorts are med for distiller’s stillage (-99). Stwl tubes are employed (93) in heat excharLgers whcre arihy~ I Y J U Shydrogen chloride is present on one side of the tubes and \\-:iter or steam on the other in the Standard Oil procesa for the iv)merization of light hydrocarbons. As long as there is no Icak:ip ( J f moisture into the hydrogm chloride, the s t w l t u b w do not I Y J ~ Y Y appreciably. J ~ ~ Iluring the war a nex procrss was developed for utilizing availailk normal paraffins by catalytically converting them t o tile i,qonirrs which are mor? valuable for high octane aviation fuels. \Ic.lllister and eo-workers (6.9) point out that, steel has 1)ct.n found suitable for all major plant, equipment which does not, norinally contact the catalyst and where the concentration of aluriiinum chloride is low. Steel is ako used for the catalyst scrubber column, since t,he antimony triclilorirle present at t hi-l ~ L T temperatures up to 2009 C. Above 200” c.,centrifugal pump* of the cantilever type with cast steel casings, cast steel impellers. and high alloy steel shafting are employed. For pumping molter lead at 450” C., standard cast iron vertical submerged pumps could not be used because of grain grovth. Pumps having oversize shafts manufactured from high tensile strength stec.1 give exrellent service. For anhydrous hydrogen chloride equipment Maude (7o’j rtports that “iron can be used safely 30” C. above the HCl-HdJ dew point.” Here again condensation of “dew” must be avoided, but, even dryer conditions are required since ferric chloride is very hygroscopic. Steel rings are used as tower packing in the continuous vbeuuni distillation of dipropylene glycol-ethylene glycol solvent and hydrocarbons (108). In preparation of penicillin, the fermentation broth and my(celium we filtered through cast iron plate-and-frame presses (72’Je NEW OR MODIFIED COMPOSITIOXS

Cast iron and steel, particularly plain carbon steels, are the niaterials of construction most widely used in the chemical industry. For many applications such unalloyed irons arid steels are entirely ,atisfacton Tn particular rasps S p w i n l r r q u i i t ~ r n m t sare needed

Vol. 39, No. lC

This has srimulated the developmelit of iruris or steels with specific outstanding characterietics. For instance, to achieve weight saving in mobile equipment, a whole family of high strength steelF has been dcveloped. Generally these have increased resistance to atmospheric corrosion since they are intended for use in lighter mtions. The yield strengths of these new steels are all above 50,000 pounds per square inch as contrast,ed with approximate15 30,000 pounds for mild steels. These steels also generally have enhanced resistance to atmospheric corrosion, as indicated in si recent article (8). Figure 1 gives typical time-corrosion curver(64) for representative high strength steels and ordinary steels They show that the more resistant high strength steels offered t c t’he trade possess, in the main, four to six times the atmJspherir corrosion resistance of ordinary steel. In the development oi high strength steels, particular attention was given to weldabilita and notch toughness. It should be emphasized tha,t, while the resistance to atmospheric corrosion of these steels is excellent, it does not necessarily follow that they will resist chemicals or eveL natural waters better than ordinary steels. In cases where tht surface of the steel dries periodically or where waters in cont,acr with the steel are highly contaminated with industrial wastes, the high strength steels usually show a decided advantage in resisting attack. Applications of the high strength steels in the chemica: industry include gas cylinders, conveyer systems, screens, hoppers, chutes, mine cars, coal cars, gasoline truck tanks and storage tanks, oil barges and small. tankers, material handling equipment. Rater softener tanks, hot water storage tanks, evaporators fon salt processing, various part9 of carbon black plants, and sewage disposal equipment,. I n addition, a vast number of alloy steels were developed t o meet a multitude of specific requirements involving strength ai room or elevated temperatures, fatigue, corrosion fatigue, hardnesP and depth of hardening, toughness, oxidation, and corrosion resistance. Associated with such controlling propwties, these steels must be adapted t,o fabrication by a t least some of the customary methods. Thus, the steels may have to be readily machinable, weldable, suitable for carburizing or nitriding, formable hoi or cold, or susceptible to heat treatment. During the early year? of the war, in order to conserve strategic alloy, considerable deveiopment, was carried out with a view toward reducing the allo! content of such steels. This resulted in t,he NE series of steels a+ an adjunct to t.he older SAE series of alloy steels. Examples o! the wide variety of applications of these steels are found in severa. papers ( I O , 14, 24, 73, 111, 128) published during the war years Most of t,hese NE steels were so well received that they have become established as standard postwar grades. SAE or AIS: Ypecifications have nox been issued on most of these alloys. The manner of select,ing and specifying steels as well as some typica: applications have been given in several papers (-5, 7 , 11, 40, L.4 85, 122) and books ( 2 , 3, 4,22, 81, 130). As an example of t,he use of specific low alloy steels, Pratt tl.nl: I h k c t l (98) point out that, in the handling of chemicals a t loa temperatures, low carbon steels containing 3.5% nickel are superior to unalloyed steels because of their higher impact strengths a: lovi temperatures. The successful use of t,heee steels depend. lioivever, on proper heat treatment. Norre11 and co-workers (85) point out an interesting use 0; steel equipment in connection with the purification of butadiene with cuprous salt solutions even at t,emperaturea as high as 225 F King (6O), in a discussion of hIoriell’s paper, points out tha! the presence of cupric copper in the solutims may be of more importance in preventing attack of the step1 t,han merely high content of cuprous copper. Recent developments in plain carbon steels (26, 27, 70, 185 have been concerned mainly with providing special properties such as minimizing the tendency t o age-hardening, improving t,he notch toughness, improving machinability, obtaining better vitreous enameling characteristics, etc. These advances are 0‘ direr-t or indirect value t o rhemical process equipment.

Ocrobez 1947

I N D U S T R I A L AND E N G I N E E R I N G CHEMISTRY

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additions of chromium from 1 up to B u j , , alone and in combinstion with nickel, manganese, columbium, titanium, and nitrogen Smith gives typical applications of the various cast materials, anc points out that the low (1 to 4%) chromium cast irons and steel. have been used particularly in the oil industry. Vmnerholm (191) discuse6 wi-artime developments in gray anc malleable irons, He refers to the detrimenta effect of hydrogen pickup resulting from moisturb ~- - - .-- . -I -7 present in the cupola during melting, and alsr describes the effect of inoculants added to the stream of metal from furnace LO pouring ladle. A proprietary, IOT alloy, spheroidized iror known as Z-metal is described by Albrecht (1, This material contains small additions of manganese and copper, and is heat-treated to obtair optimuni properties. High strength, wear resist. ance, and increased resistance to corrosion, as cornpared to gray iron or malleable iron, are claimed foZ-metal. Specifications and important propertier of present-day malleable iron castings are d k cussed by Linabury (67). 1_7_-----J j 4 Blaylock (16)summarizes the appropriate speciT I M E . (CARS fications on steels and caSt irons for the varioui Figure 1, Time-Corrosion Curves for Steels Typical of \arious component parts of heat transfer equipment. The Classes, after Exposure to Industrial 4tmospherr special properties required for specific application? in certain parts include oxidation, corrosion o* eiosion resistance, high strength, resistance t o creep. notch Glen (41) studied the effect of various additions to steel OL resistance to creep a t elevated temperatures. He concludes that Goughness, and stability of properties. I n an interesting discussion on pressure vessels, Meigs (781de small additions of molybdenum and certain other elements reduce the creep rate of steel while additives of aluminum c a u ~ eabnorscribes current designs of pressure vessels, gives the advantage? mally high creep rates. end limitations of each design, and mentions materials used fotheir construction, Paramount in these applications are gooc CAST IRONS AND STEELS impact strength at low temperatures or high resistance t o creep 8 i An excellent survey of the effect of various demerits which elevated temperature. might be added to cast iron or steel on the resulting chemical and Fowler and BroFn (351 discuss the relative net costs of t h e physical properties was prepared by Pigott (95); an older article aomponent parts of pressure vessels and pressure fractionating by Merica (80)and a recent one by Foster (34)treat the same subcolumns made of various steels and cast iron. In a general article ject. LaQue (63)gives a comprehensive table listing the average by Bliss (If?), the costs of chemical equipment are summarized corrosion rates for cast iron and austenitic cast iron in contact While the figures cited in these two papers are probably not 81". with a large number of chemicals under various conditions of excurate a t present, the relative costs on similar types of equipmen posure. Vande Bogart (180) rates the usefulness of iron and steel made of different materials are probably still approximately cor. tn contact with various chemicals. rect. The data in these papers emphasize the economic desirabilRecent improvements in cast irons are summarized in a paper ity of employing steel or cast iron in this equipment whentveOY De Longe (SO). He points out four factors that have been possible. mainly responsible for these improvements: ( a ) lowering the carSome years ago Harnsberger ( 4 6 )published a detailed sumrilm bon content, and thereby reducing the amount of graphite present. of the materials used in the construction of pumps for oil refinerfb) ladle treatment of irons to obtain desirable graphite distribuies. More recently Prlellen and Smith (79) presented a more gem tion, ( e ) use of alloys for higher strengths and higher machinable era1 discussion of the materials used for pumps in the entire cheniihardness, ( d ) heat treatment for higher strengths and better wear cal industry. They point out deficiencies of certain materials i~ resistance. specific applications and give examples m-here improved performFor resistance to temperatures up 10 dOO" C., Burgeas and rtnce has been obtained through a better ch&e of material. Bishop (20) conclude that plain or 2% chromium cast irons conaonstruction. taining 3.0 to 4.5% silicon are superior to those containing more Hermann (50) discusses the factursl in centrifugal fan deaigr or less silicon. nyhich are of particular importance hen handling corrosive 0% Chilled cast iron is widely used where resistance to wear and erosive gases. Plain carbon steels are in general use except Rhi.re deformation under high intensities of preseure are the essential excessive corrosion makes their u5e uneconomical. In such i~,. requisites. In the chemical process industry the major use is for stances protective coverings on carbon steel parte are sometime. castings for crushing and grinding equipment. Developments in utilized. the metallurgy of chilled iron are discuesed by Massari (74). Materials for use in oil field refinery equipment have been diWhite cast iron containing boron or nickel and boron also has sussedby Zima (134),Vollmer and Wescott ( l 2 2 ) ,and Hildorf (51 high abrasion resistance (54). I t is widely used for oil well pump Ferrous materials generally used in these Qervices, together wit1 barrels, plungers, slush pump lines, cylinder sleeves, pump shaft the developments of new steels or new applications of existing sleeves, stamping dies, etc. steels are described. The continued need for the developmentf 0: Brown (18) recently discussed alloy cast irons; particular atnew steels was emphasized by all of these authors. tention is given t o the effect of nickel alone or in combination Comstock (26)states that difficulties from hydrogen embrittlewith chromium or molybdenum. The effect of chromium adment a t high temperatures and pressures can lie combated by usditives to iron (109) and steel castings are presented by Smith ing 4 4 % chromium steels with about 0.5%) molybdenum in(110). HI. discusses cast irons and steels containing various S W X of ~ plain carbon steel. Several papers have pointed out (31, 55) thaG incidental elements such w carbon, phosphorus, sulfur, and copper can influa c e the rate of corrosion of mild steels in specific media. This emphasizes the desirability of exercising care in selecting compositions from the mild steel classification for process equipment 1 1 4for handling certain chemicals.

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I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY

13ecause of the advantages of iron and steel equipnlriii, i: is frequently desirable to employ these materials even in contact with chemicals which are corrosive to them. Various protectivch mrasures may be employed in such cases. They includc lining5 ' i f metallic or nonmetallic materials, organic or inorganic coatings, d d i t i o n of corrosion inhibitors t o the products being haiidled r i d the use of cathodic protection. Examples of suvh protc . ! I irasures were described in several recent papers. Larson (66) mentions a phosphoric acid treatment of *I el 1daitt.b for tank construction. It. was perfected by the Roy:tl l h t c ~ h 5hell Oil Company in Europe and is supposed t,o lead t o ~ s c c l l t ~ r L t adherence of subsequent paint coatings. Similar procews UIJ used on tin plate and galvanized coatings. Generators made of steel lined nith stonewire or glabs are u w l for making chlorine dioxide (i3i)in a new process recently developed for making chlorine dioxide for bleaching flour. Rubberiined steel and lead-lined steel equipnient is employed for making citamins (57). A new type of ceramic coating for the protrctiori 1 mild steels in high temperature service was developrrl duririg the war hy the National Bureau of Standards (46). I n a newly developed sulfuric arid process for the proiluvtion of aluminum from clay, steel equipment is protected ti!. ixrious linings from the action of sulfuric acid (127). Extraciion tanks were of steel coated wit,h lead, Pyroflex, or Elaitiguq and then lined with acidproof brick using Xsplit cement niortar. .UI t>hreecoatings were found to be satisfactory. The aluniinuni eulfate solutions formed in this process aere filtered in a rubber-linrd Kelly pressure filter. Lead-lined tanks were used for intermediate storage of the acid solutions and Ceilcote coatings as a lining on steel toviers in t,he iron precipitation equipment. In the silica I,emoval step, lead-lined steel tank pipes were utilized. Evaporators for viscose rayon spin bath now often employ lead-covered steel tube sheets wit11 other parts of rubber-coated steel (32); nickel-clad steel parts are used in evaporators for caus:ic soda. The use of various types of coatings and linings on vquipment for handling the mineral acids is discussed by Seuhaus (86). The metal cladding of steel (42) to obtain material of high resistance to attack by various chemicals is being used on an inw a s i n g scale. Undercoatings of nickel on steel for vitreous enameling have also received considerable attention in recent years (126, 135). The use of heavy deposits of nickel on ferrous materials for chemical processing equipment was introduced during ref lead equipment are employed for making alum and handling d u m solutions as part of the processing. The plant has si:, 42,000-gallon lead-lined steel tanks for alum and acid solutiona In addition, there are thirty-two lead-lined bead-forming toners. These are tile-covered for insulation. This plant uses about 125 Gens of lead pipe and equipment. The following comments on thik Drowse were made by Fettri Y

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(46): Originally, the tank for making alum was lined with inch chemical lead. The tank is heated and cooled two to three times per day, the maximum temperature being 240-260 a F. After only 8 to 10 months of service this lining sagged and failed. Failure appeared attributable t o an insufficiency of lead-covered steel st,rap supports. The second linings were 3/8-inch thick tellurium lead strapped every 2 feet on sides and bottoms. To date, after about 2 years of service, the lining wh3 evidently rntirely satisfactory and showed no signs of deterioration. Recently Wormser (77), in his paper on lead equipment ilsed 111 the chemical industry, listed hhirt,y-one chemicals satisfactorily used with lead. He also discussed lead alloys, including one or more nf the following elements: antimony, tellurium, tin. and silver. Kilkinson (?6), in his study of the use of metals in handling sulfuric acid in petroleum processing, appears to prefer koniogeneous lead linings, wherein the lead is fused to the steel, to brieh iinings which he finds too expensive. On the other hand, Burke and Mantius (37) find brick linings adviaab!e for certain steps in the concentration of sulfuric acid They give a thorough discussion of the equipment used in the vacwum distillation of the acid. For their processing, brick linings me used inside of the lead linings when the acid is over 4OC; strength. Since the inception of this Simonson-Mantius prowsf in 1921, there has been continuous development to date in making the equipment more efficient'. I n addition to using 6% antimoniai lead and chemical lead for heating pipes, they also use Karbate. high silicon iron, and other materials. Recently Dowtherm has been adopted for some purposes, using 575-590' F. at' 20-25 pounds per square inch gage. About 5 years life for the brick linings is obtained lsit,h concentrations of 92-937, acid, with moderate maintenance costs. They find that leakage of acid betweer the bricks does not impair the lead if the seepage is more or lev Ttagnant, but currents of acid on the lead beneath the bricks caus rxeessive corrosion. Fifteen years of service has been reported i r some cases for brick linings. Discussions by American Institu.:G of Chemical Engineers members accompany the article. Potassium metabisulfite is now made in lead-lined equipmeni . ~ 2 ) .Sulfuric acid is now made in improved chambers (MillsPackard towers, 19). Description of a lead lined tank for treating tallow has been given (20). The design is simple and intended to minimize construction and maintenance costs. I n sewage treatment. and disposal, lead equipment is involved. The handling of copper sulfate has been discussed (7), and the use of lead in cbimnej- and condensers a t a disposal plant, is described (8).