The material presented inthis pUblication has beenprepared for the generalinformation of the readerand should not be used orrelied on for specificapplications without firstsecuring competent advice.

The Nickel DevelopmentInstitute, its members, staffand consultants do notrepresent or warrant itssuitability for any general orspecific use and assume noliability or responsibility ofany kind in connection withthe information herein.

G. Sorellis a consultant to the

Nickel Development Institute

PART I

Corrosion-resistant nickel alloysAguide for selection and application

Conlinuing advances in mClallurgicaltechniques and manufacturing tech­nologies have spurTed the develop­

ment of nickel alloys and their broaderutilization in the chemical industry.

Nickel alloys offer a combination ofexcellent corrosion resistance. strength,toughness. metallurgical stability. fabrica­bility and weldability. Many nickel alloysadditionally possess outstanding healresiSllmce. making them ideal choices forapplications requiring chemical resistanceand strength at elevated temperatures.

This survey of wrought nickel-basedalloys (here defined as containing morethan 45% nickel) covers a range ofwrought corrosion-resistant 3110ys com­monly used in chemical plant applications.

Chemical compositions and UnifiedNumbering System (UNS) designationsof these alloys are shown in Table I. Toaid the reader, 3.nd not as an endorsement.some familiar trade names are identifiedin the sidebar.

Properties of alloysNickel alloys are more expensive thanstainless steels. However. economic com­parisons on a first-cost. rather than on alife-cycle basis. can be: deceiving. Forinstance. Ni-Cr-Mo alloys cost roughlyfive times as much as ISCr-8Ni stainlesssteels and about twice as much as super­austenitic stainless steels.

Owing to the exceptional corrosionresistance of nickel alloys. the initial COStpremium can often be recouped throughlong-term savings due to prolongedequipment life. reduced maintenance and

fewer shutdowns.Physical properties of nickel alloys are

quite similar to those of the 300 Seriesaustenitic stainless steels. As a class, nick­el-based alloys have thermal expansionrotes about equal to carbon steel. but sig.

Nickel alloys offer a combina-

tion of excellent corrosion resis-

tance, strength, toughness, met-

allurgicaJ stability, fabricability

and weldabilit)'.

nificantly lowcr than 300 series stainlesssteels.

Though the thermal conductivity ofpure nickel exceeds that of carbon steel.most nickel alloys have markedly lowerconductivities. in some instances evenlower than austenitic stainless steels.

Except for pure nickel. the nickelalloys used in chemical processing areconsiderably stronger than the 300 Seriesstainless steels. Nickel alloys also havevery good ductility (as illustrated by theroom temperature mechanical propertieslisted in Table 2) and toughness.Maximum allowable design Stresses formost of the alloys used in chemical plantequipment are published in Section vmof the ASME Boiler and Pressure VesselCode.

Nickel alloys have fully austeniticmicrostructures. Nearly all of the gradesemployed in the chemical industry aresolid-solution strengthened. They derivetheir enhanced strength properties fromthe addition of effective hankners such asmolybdenum and tungsten. rather thanfrom carbide formation. Like austeniticstainless steels, solid solution nickelalloys cannot be strengthened by heattreatment. only by cold working.

Another broad class of nickel·basedalloys are strengthened by a precipitation­hardening heat treatment, These are

reserved largely for ultrahigh-strengthapplications sllCh as those encountered indeep oiVgas production and extreme high­pressure processes.

Except for selected components invalves and TOtating machinery. precipita­tion-hardened nickel alloys find limitedapplication in chemical plants. Included inthis alloy class are heat-resistant superal­loys employed in gas turbines. combus­tion chambers and aerospace applications,

Corrosion-resistanceNickel alloys represent a step up fromconventional slainless steels and super­austenitic iron-based alloys in resistingcorrosion by a wide spectrum of acids.alkalis and salts. An outstanding attributeof nickel alloys is exceptional resistance10 aqueous solutions containing halideions, In that regard, nickel alloys are farsuperior 10 auslenitic stainless steels.which are notoriously prone to attack bywei chlorides and fluorides.

This superior corrosion behavior ofnickel alloys manifests ilself not only interms of lower metal loss. but in the abili­ty to better withstand localized auack,notably pining/crevice corrosion, inter­granular auack and Stress corrosion crack­ing. These forms of localized allack. moreso than general thinning. account for themajority of corrosion-induced failures inthe chemical industry,

Nickel alloys owe their corrosionresistance partly 10 the inherent lowerreactivity of nickel relative to iron. asmeasured by its more noble oxidationpotential in the EMF Series. Similar tostainless steels. chromium-containingnickel alloys have the capability to passi­vate (i,e.. to spontaneously form an ultra­thin but tenacious surface oxide that func­tions as an effective corrosion barrier).

An added advantage of nickel over iron

Rf!prinlt!dfrom Cllt!mical Pmussing Maga:int!· NO'o,t!m!Hr 1997 ..

HIGH·PERFORMANCE METALS & ALLOYS

Table 1 Nommal composihon 01 corrosion-resIstant nickel allovs (wi %).

Alloy UNS no. Ni Cr M. F. W Cu Other

200 N02200 99.6400 N044QO 66.5 1.0 31.5 1.0 Mn600 N06600 75.0 15.5 8.0625 N06625 62.0 21.5 9.0 2.5 3.8(Nb+Ta)690 N06690 61.0 29.0 9.0825 N08825 42.0 21.5 3.0 29.5 2.3 1.0 TiG-3 N06985 44.0 22.0 7.0 19.5 1.5' 2.0' 2.1 NbG-30 N06030 43.0 29.8 5.0 15.0 2.8 1.7 1.0INb+Ta)C-276 N10276 57.0 15.5 16.0 5_5 3.8C-22 N06022 56.0 22_0 13.0 3.0 3.0C·2QOO Nl0200 59.0 23.0 16.0 1_5 1.6622 N06022 58.0 20.5 14.2 2.3 3_2686 N06686 60.0 21.0 16.0 5.0' 3_759 N06059 60.0 23.0 15.8 1.5'8-2 Nl0665 69.0 1.0' 28_0 2.0'8-3 Nl0675 68.5 1.5 28.5 1.5 3.0'8-4 Nl0629 66.0 1.0 28.0 3.5·Maximum

is the ..bilit)' to accept large fractions ofalloying elements wilhout fonning briulephases. Common alloying additions forenhanced corrosion resistance are chromi­um. molybdenum and copper. Their rolesare addressed in the brief chamcterizationsof nickel alloy syStems thaI follow.

Comparative resistance ratings of nick­el alloys in common chemical planl cov;­ronlTl('nlS are shown in Table 3. These gen­eral guidelines are nOi intended for specifi­calion purposes but only as a starting pointin the materials selection process.

Welding guidelinesThe majority of nickel alloy welds are per­formed by shielded metal arc welding(SMAW). gas tungsten arc welding(GTAW) and gas metal arc welding(GMA W). Nickel alloy weldmcnts arevery ductile. and their low thennal expan­

sion characteristics reduee residual stressesand warpage. Postweld heat treaunent isgenerally required only for precipitation­hardcnablc grades. Specifications issuedby the American Welding Society (AWS)for nickel alloy welding electrodes andfiller metals are liSlOO in Table 4.

Welding procedures for nickel alloysare fairly similar to those used foraustenitic stainless steels. Howevcr. due to

the greater sluggishness of Ni-rich weldpuddles and the lower penetration charac­teristics of nickel alloys. the productionof full penctration welds may requiremodification of joint configurations andwelding techniques. Nickel alloys areless tolerant than ferrous materials to con­tamination that could cause weld embril­tlemenl.

The combinatioo of high ductility, lowthennal expansion and the ability to toler­ate dilution by numerous metallic ele­ments h:ts made nickel-rich welding coo­sumables universally 3CCepied for joiningdissimilar metals. This includes not onlywelds of nickel-based alloys to iron-basedalloys. but also for welds of stainlcsssteels to carbon and alloy steels.Similarly. nickel alloys can be weld­deposited on carbon steel without the riskof crocking.

Types of nickel alloysNickel alloys are commercially availablein a broad variety of product formsincluding plate. sheet. strip. tubes. pipe.fittings and forgings. Selected ASTMspecifications for some of these are notedin Table 5. Some nickel alloys arc alsoproduced as castings. These generallyhave different charactcristics from their

wrought counterparts.Nickel alloys are generally classified

according to their principal alloying con­stilUents. The families of nickel alloysextensively utilized in chemical plantequipment are briefly characterizedbelow;

• Pure nickel. Pure nickel (Alloy 200)has very good resistance to a wide rongeof reducing acids and salts. but is not asuiw.bte choice for strongly oxidizingenvironments such as nitric acid. Themost significant allribute of pure nickel isunexcelled resistance to caustic alkalis,even when molten. Though outstanding inits resistance to dry halogen environ­ments, nickel is not adequately resistantbelow the water dewpoint. For applica­tions m~ than 600"F. a low·carbon vari­ant, designated Nickel 201 (UNSN02201), is the preferred choice.

• Ni·Cu Alloy 400. The corrosionbehavior of nickel-copper Alloy 400. likethat of nickel. is best under reducing con­ditions and can be compromised by aera­tion and oxidizing chemicals. Alloy 400possesses very good resislance to halogenacids and compounds. particUlarly hydro­fluoric acid and hot gases rich in fluorineor hydrogen fluoride.

The alloy is used widely for handling

Ell Rt!prillttdfrom Cl1l.'mjrnl Proussing Maga:jnt!· NOI'emINr 1997

HIGH·PERFORMANCE METALS & ALLOYS

Table 2 MInimum room temperature mechamcal properlies of nickel alloy.

Alloy Ultimale tensile Yield strength ElongationlIeslgnalion slrenglh llesl) 0.2% olfs.l(lesi) (%)

200 55 15 40400 70 28 35600 80 35 30625 110 55 30690 85 35 30825 85 35 30G-3 90 35 45G-30 85 35 30C-276 100 41 40C-22 100 45 45C-2000 100 41 45622 100 45 4559 100 45 45B-2 110 51 40B-3 110 51 40B-4 110 51 40

Table 3. General guidelines lor corrOSion resistance.

Alloy Sulfuric Phosphoric Hydrochloric Hydrofluoric Nitric Organic Strong Reducing Oxidizingacid acid acid acid acid acids alkalis salts salts

200 .. .. .. • • • • • •400 • .. .. • • • • • •600 .. .. • .. .. • • • ..625 • • • • • • • • •690 .. • .. • • • • • •825 • • .. • • • .. • ..G·3 • • .. • • • • • •C·276 • • .. • .. • • • •B·2 • • • • • • • • •• Excellent 10 good;... Good to satisfactory;• Not recommended.

R~prill1~dfrom Chtmical Processing Maga:int. NQI,t'm/)er /997 ..

HIGH·PERFORMANCE METALS & ALLOYS

sulfuric acid solutions. sea water andbrines. For applications requiring higherstrength. such as thaI demanded for valveand pump components, use is made ofAlloy K-500 (N05500), a precipitation­hardenable variant of Alloy 400.

.Ni·Cr·Fe Alloy 600. The addition ofchromium to the nickel matrix extends the

suitability of Alloy 600 imo the oxidizingrange. Though only mediocre for mil'leralacids. Alloy 600 has cltccllcnt resislallCe 10organic acids and is used e:uensively infatty acid processing. It is also employedwidely in the production and handling ofcaustic and alkali chemicals.

Alloy 600 also qualifies as an excellentm:lleriaJ for high-temperature applicationsrequiring a combination of heat and COfTO­

sion resistance. The alloy's excellent perfor­mance in hol halogen environments makesit a favorite choice for organic chlorinationprocesses. Other elevated temperaturedegradation processes against which Alloy600 has demonslrated excellenl resistanceare oltidation. carburizalion and nitridation.

• Ni·Cr·Mo Alloy 625. The addition ofmolybdenum to the Ni-Cr systems broad­ens resistance to mineral acids and salts.both oxidalion and reducing. Molybdenumadditionally confers resistance to pillingand crevice corrosion by wet chlorides.

Alloy 625 is a very strong material withexcellent resistance to fatigue. Alloy625LCF. a bellows.quality version ofAlloy 625. lays claim to exceptionallygood resistance to low.cycle and thermalfatigue.

Like Alloy 600. Alloy 625 serveseffectively both as a corrosion-resislantand heat-resistant material. The combina­tion of eltcellenl high.temperaturestrength and resistance to halogen attack,oxidation and carburization has madeAlloy 625 a favored choice for chemicaland petrochemical process equipmentexposed to hoslile, high-temperalllre envi·ronments.

• Ni-Cr Alloy 690. Alloy 690 has thehighest chromium content among nickelalloys suilable for fabrication of pressureequipment. which confers eltceptionalresistance to oxidizing media. It is effec­tively used for hot concentrated sulfuricacid, nitric acid and nitric,1lydrofluoric acidmixtures, as well as for oxidizing salts.The high chromium content also improvesresislance in hot sulfidizing environments.

• Ni·Cr·Fe Alloy 825. Because of itsnear 30% iron content. Alloy 825 is s0me­

times included in the family of super­austenitic stainless steels. The alloy excelsin sulfuric and phosphoric applicalions

thai. as with Alloy 20, were major devel­opment targets. Though reasonably resis­tantto hydrochloric acid, Alloy 825 is sub­ject to chloride pitting and crevice corro­sion. panicularly in stagnant. unaeratedsolutions. Its high iron content makesAlloy 825 less resistant than higher nickel·containing alloys to alkalis and halogens.

.Ni-Cr-Fe-Mo "G" alloys. Alloy G-3offers improved corrosion resistance overalloys 400, 600 and 825 in a wide range ofapplications. The: alloy is especially resis­tant to sulfuric acid and contaminatedphosphoric acid. and can withstand bothreducing and oltidizing conditions. Themore recently developed Alloy G-30 hasbetter weldability and offers improved a11­round corrosion resistance. TlOtably in weldheat-affected zones.

• Ni-Cr·Mo ''C'' alloys. Alloy C-276is considered [he preeminent alloyemployed in the chemical industry forexceptionally corrosive environments thatare beyond the capability of stainlesssteels. It has outstanding resistance toacids. acid salts and a wide spectrum ofother aggressive substances encountered inchemical processing.

Alloy C·276 is particularly effective insuch punishing environments as wet chlo­rine and hypochlorites. Owing to its

Table 4. AWS specifications for welding materials.

Alloy Welding electrode (AS.ll) Filler metal (A5.l4)

200 ENi-l ERNi-1400 ENiCu-7 ERNiCu-7600 ENiCrFe-3 ERNiCrFe-3625 ENiCrMo-3 ERNiCrMo-3G-3 ENiCrMo-9 ERNiCrMo-9G-30 ENiCrMo-11 ERNiCrMo-l1C-276 ENiCrMo-4 ERNiCrMo-4C-22 ENiCrMo-10 ERNiCrMo-l0622 ENiCrMo-l0 ERNiCrMo-l0686 ENiCrMo-14 ERNiCrMo-1459 ENiCrMo-13 ERNiCrMo-13

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HIGH·PERFORMANCE METALS & ALLOYS

Table 5 ASTM speciflcatlOns lor selected product forms.

Alloy Plato! Seamless Welded Seamless W,ld,dsbeet pip, pip, tubes lubes

200 B162 B161 B725 B161 B730400 B127 B165 B725 B165 B730600 B16B B167 B517 B167 B516625 8443 B444 B705 8444 8704690 8168 8167 B167825 8409 8407 8407 8515G-3 B582 8622 8619 8622 8626G-30 B582 8622 8619 8622 B626C-276 8575 8622 8619 8622 8626C-22 B575 8622 8619 8622 8626C-2000 8575 8622 B619 8622 B626622 8575 8622 8619 8622 8626686 8575 8622 8619 8622 862659 8575 8622 8619 8622 86268-2 8333 8622 8366 8622 86268-3 B333 8622 8366 B622 86268-4 8333 8622 8366 8622 8626

Rt'prinredfrom Chemical Processing Moga:illt. NO\'embn 1997

molybdenum content, Alloy C-276 is high­

ly resislant 10 chloride-induced pitting andcrevice corrosion.

The quest for materials possessing bet­

lcr metallurgical propenies and corrosionresistance than Alloy C-276 has spurred

the development and commercialization ofseveral proprietary (.type alloys. repre­sented by alloys C-22. 622, 59. 686 and C­2000.

All have roughly comparable molybde­

num content but significantly higher

chromium content than Alloy C-276. Somegrades also contain tungsten and copper.

The effect of these minor alloying con­SlilUents on metallurgical propenies andcorrosion resislance is complex andbeyond the scope of this anicte.

• Ni·Mo "B" alloys. Alloy B-2 has

exceptional resistance 10 sulfuric. phos­phoric and hydrochloric acids under reduc­

ing conditions. It is panicularly suited forequipment handling hydrochloric acid atall concentrations and temperatures up to

the boiling point.Oxidizing chemicals adversely affect its

corrosion resistance. notably such strongoxidizers as ferric and cupric salts thai may

be present as contaminants.

Recently introduced alloys 8-3 and 8-4offer improved properties over Alloy B-2.A practical advantage of these new gradesis minimized formation of undesirable

microstructures during fabrication that cancause embritllemenl.

By G. Sorell. president ofG. SorellConsiliting St'rvius. North Calm.,t'll. NJ.Sorell is a mott'rialS/CQrrosion engineer withmore toon 40 years of/lIdlUlrial experience.Preparation oftlJis artielt' ...as sllpported by(ht' Nickel DeI'tlopmt'rtI Institute.

..

HIGH·PERFORMANCE METALS & ALLOYS

Evolution of nickel alloys

Trademartl: holder

Haynes International, Inc.Haynes International, Inc.Haynes International, Inc.Haynes International, Inc.Inca family of companiesInco family of companiesInco family of companiesKrupp VDM GmbHKrupp VDM GmbH

Trade name

HASTEllOV<> 6-3~

HASTEllDY<> C-22"HASTEllOV<> C-2000>HASTEllDV<> G-31l"INCDNEL<> 622INCDNEl<> 625lCfINCONEl<> 666Nicrofere 6629Nicrofe.e 5923hMo

Alloy

6·3C-22C-2000G-306226256666-459

Table A. AlloV trade names.

Uke iron and copper, nickel has been used in alloys since the dawn of civilization. However, in contrast to steels, brasses andbronzes, nickel alloys are recent newcomers to the chemical industry.

The first nickel alloy of signHicant commercial importance was Alloy 400, developed and marketed by the International NickelCo. (now Inco Alloys Interll3lionaJ) in 1905 under the MONEL trademart. The next important milestone was the emergence around1930 of Ni-Mo Alloy Band Ni-Cr·Mo-W Alloy C. Their developer, the Haynes Stellite Co. (now Haynes International Inc.), trade·marKed both of these materials as HASTElLOY. The next important rung in the evolutionary ladder of nickel·based alloys camefrom Inca, with the advent of Ni-Cr-Fe Alloy 600 in 1931 and Ni-Fe·Cr in 1949, respectively named INCONEL and INCOLOY.

capitalizing on the familiari1y and reputation of these original trademarts, Inca and Haynes are now marketing acombined totalof about 50 corrosion- and heat-resistant alloys in the MONEL, INCONEL, lNCOLOY and HASTELLOY families.

The German company Krupp VDM GmbH, amore recent entrant as aprominent developer and producer of abroad line of nick­el-based alloys, uses the trade names Nicrofer, Nimofer and Nicorros.

These three leading companies continue to develop improved and new nickel alloys of interest to the chemical industry. Theirproprietary alloys mentioned in this article are listed in Table A.

All of the early proprietary alloys have long ago lost their patent protection and are now available worldwide from many otherproducers. either under their own tradenames or simply as generic alloys con­forming to recognized standards orspecifications. As with pharmaceuticals,there is an ongoing debate as to theequivalence of generic versus propri­etary products.

Familiar specifications such as ASTMand DIN may have less restrictiverequirements that those self-imposed byprominent alloy developers and produc­ers. Such in-house requirements mayinvolve tighter limits on alloy composi­tion and metallurgical parameters aimed

L ---'at properties enhancement.

Reprintedfrom Chemica! Processing Maga:ine. NO~'tmber 1997

PART II

Picking nickel-base alloysto resist heat and corrosionHere's aguide to selecting and using the alloy that's right for the job

Table 1. Nommal composillOn of wroughl heal-reSistant nickel alloys. wt %

Alloy UNINo. NI Cr Mo Fe W Co Other

600 N06600 7S.0 15.0 8.0601 N06601 60.5 23.0 14.4 1.4 AI617 NIl6617 52.0 22.0 9.0 1.5 12.5 1.2 AI625 NIl6625 61.0 21.5 9.0 2.5 3.8

(Nb +Ta)X NIl6OO2 47.0 21.8 90 18.5 1.5 1.4 AI2141 N07214 75.0 16.0 3.0 4.5 AI230' N1l6230 57.0 22.0 2.0 1.5 14.0 2.52421 65.0 8.0 25.0 2.0' 2.5'333 NIl6333 46.0 25.5 3.30 17.0 3.3 3.3 1.1 Si45TM' N06045 46.0 27.5 23.0 2.8 Si602CA' NIl6025 63.0 25.0 9.5 2.1 AI

"Maximum1. Haynes8 Alloys 214ftl• 230", 242ftl (Haynes international, Inc.)2. Nicrofe,e AllOy 45ftl, Nicrofer 6025tfT·aIIoy 602CA (Krupp VDM GmbH) ..Rrprilltedjrom Chrmicul Processing Maga:ille· October /998

The ability to withstand the combined

onslaught of heat and corrosionmakes nickel-base alloys a good

choice for aggressive high-temperatureenvironments. Nickel alloys find extensiveapplication for chemical plant equipmentc;.;posed 10 corrosive process streams atelevated temperatures. commonly definedas more: than about 1./XllYF.

In many instances, high suength, chem­ical-resistant nickel alloys are the favored.if not the only. practical material for hos­

tile environments beyond the capability ofaustenitic and superaustenitic stainlesssteels. Though more expensive than iron­base alloys. the excellent performancecharacteristics of heal- and corrosion-resis­tant nickel alloys often makes them themost economicallong-tenn choice.

Alloy cDmposltionsThe chemical composi­tion of heal- and-eorro­sion-resistant nickelalloys (here defined ascontaining more than45% nickel) that findextensive application inchemical processing arelisted in Table I. Thealloys are identified bytheir common designa­tion and by the UnifiedNumbering System(UNS). Although Ihelong-established alloyshave lost their patentprotections. lhey're stillcommonly known bytheir original tradenames.

For example. generic

Alloys 600. 601 and 625 are commonlyassociated with the INCQNEL. rrademarkheld by the Inco family of companies.Similarly. Alloy X is best known under the

HASTELLOY. trademark owned byHaynes International Inc. More recentlydeveloped alloys are still proprielaJ)' male­rials available only from their developen,as fOOhloted in Table I.

The types of alloys surveyed arewrought materials, strengthened principal­ly by solid solution hardeners. Not covered

AII,5000F nickel allnys relain

40% to 75% of their room tem-

perature yield strength.

are nickel-base alloys strengthened by pre­cipitation hardening, nor oxide dispersion

strengthened (ODS) alloys produced bypowder metallurgy techniques. Thosesuperalloys. used principally in gas turbineand aerospace applications. are rarely usedin chemical processing. Also excludedfrom this article are cast versions of alloyslisted in Table I.

PhysIcal and mechanical prof)8f1les1be physical properties of nickel alloys aresimilar to those of the 300 Series Cr-Nistainless steels. Depending on the individ­ual alloy. lhermal conductivity and expan­sion characteristics may differ significanllyand need to be considered in equipmentdesign.

The mechanical properties of nickelalloys as a class are excellent. both instrength and ductile properties. Minimumroom temperature strength and duclilityvalues are listed in Table 2. Except for

HIGH-PERFORMANCE METALS & ALLOYS

Alloy 601. minimum yield strengths areconsiderably higher than 30 ksi, which isthe value for the common austenitic stain­

Jesses.The greater strength of nickel-base.

compared with iron-base materials,increases prqgressively with temperature,as shown in Table 3. N()(c thaI at 1,5(l(FF.

the nickel alloys relain 40% to 75% oftheir room temperature yield strength,compared to only 20% to 35% for siain­less steels.

The superiority of nickel alloys extendsto creep rupture. as illustrated in Table 4.While stainless steels essentially lose any

Some nickel alloys, like 600 and

601, show virtual immunity to

age embrittlement.

Table 2. Minimum room temperature mechamcal properties

Alloy UIU..... I...n. Y1.ld ItrInglb, Elongation,.........,al O,2%oftIIl,al %

600 80 35 30601 80 30 30617 95 35 30625 100 40 30X 95 35 35214 110' 65' 25'230 110 45 40242 184' 113' 38'333 80 35 3045TM 90 35 35602CA 94 43 30

'Typical properties

Table 3. Typical hot yield strength, 0.2% olfset, ksi

Alloy Amblotd 1,0lIII'f 1,2OO'f 1,6OO'F 1,BOD'F

30455 42 18 16 1030955 45 26 23 18310 SS 45 25 21 IS600H 29 17 15 13 9600 50 40 37 20 9601 40 32 28 20 7617 45 32 34 35 18625 48 32 35 38 18X 49 33 30 26 18214 82 72 76 81 8230 57 40 39 21242 113 70 76 50 28333 43 25 25 24 1045TM 53 36 34 28602CA 50 38 37 31 13

useful srrengm at temperatures of 2,()()()IlFand above. nickel alloys can still functioneffectively for moderately stressed compo­nents. For example. the I.QOO-hr rupturestrength at 2,ooooF is about 1.0 ksi forAlloys 600. 601. 214. 230 and 333. and 1.4ksi for Alloys 617 and 602CA.

The ASME Boiler and Pressure VesselCode contains allowable stresses for thealloys surveyed. except for Alloys 214,242 aod 45TM.

MetallUfJ1cai stabilityAl10Iher important property in alloy selec­tion for high-temperature applications ismetallurgical stability, which is alsoknown as thennal stability. The tenn refersto the resistance to fonn brinle micr05U\1c­tural phases or precipitates upon aging. i.e.,after prolonged ellposure 8t elevated tem­peratures. That so-called "age embrittle­ment" manifests principally as reducedductility and toughness. and may alsoimpair corrosion resistance.

While some alloys. such as 600 and601. are vinually immune to age embrittle·ment. most undergo varying degrees ofimpairment. Among those adversel)'affected is Alloy 625, which may suffer amarked drop in ductility and impactstrength when exposed in the range of

about 1.2000F to 1,4()(pF. At higher tem­peratures, those properties are partlyrestored because brittle precipitates tend toredissolve. Equipment failures attributableto reduced ductility and toughness areinfrequent. which can be ascribed 10 thevery high starting properlies typical ofunaged nickel alloys.

Chemical resistanceThe most prevalent form of attack in hightemperature chemical processing environ-

ments is gaseous corrosion. principallyoxidation, sulfidation and halogenation(chloridation and fluoridation). Otherfonns of deterioration encountered in hos­tile elevated-temperature environments arecarburization, nitridation and hydrogenattack. Those are not classed as corrosionin the conventional sense of the word.because there is no metal loss or surfacerecession. Rather. damage manifests asmetallurgical/mechanical impairment­most often in the fonn of embrittlemenl... Rl!printedfrom Chl!mica/ PrQussing Maga:inl!· Ocwber /998

HIOH·PERFORMANCE METALS & ALLOYS

Table 4. Typical creep rupture strength. ksi

Table 5. Ellecl 01 alloying additions In nickel alloys on high-tempera lure allack

M.......- MI' F' Cr Ma Ca W Cb 51

Oxidation •Sulfidation •Chloridation '. '. '.Auoridation • •Carburization •Nitndation • ••

6 "Improves resistance;• " Lowers resistance;

6. :: Dependent on specific conditions;• "Effect 01 increased nicksl content.

Stmslo rupture in 1.000 hrAlia, Condition 1,4OO'F 1,60O'F 1,800'F

30455 A 7.4 3.0 1.230955 A 7.2 2.7 1.031055 A 7.4 3.0 1.2800H SA 10.0 4.9 2.0600 5T 8.1 3.5 1.8&01 5T 9.8 4.4 2.2617 SA 22.0 8.4 3.6625 5T 22.0 7.5 2.7X 5T 16.0 6.5 2.1214 SA 24.0 7.8 1.7230 SA 19.0 9.0 2.8242 AA 15.0333 5T 14.0 5.2 2.145TM 5T 6.1 2.9 1.5&02CA 5T 8.0 4.5 2.4

A:: Annealed:All:: Annealed and aged;SA" Solution anoealed;ST '" Solution treated.

.

TiAI

Forms of IIttaekThe common fOMs of high-temperaturechemical attack are brieny characterizedbelow. Hydrogen attack is omitted becausenickel alloys are highly resistant.

Oxidation. Oxidation, the most com­mon fonn of corrosion at elevated temper­atures, is characterized by the formation ofmetal oxide corrosion products. 1lIose se­called scales are usually quite dense andtenacious and thus able to retard furtherattack. However. in severely hostile envi·ronments oxide scales can be penelra!ed orspall off.

Chromium is by far the most importantelement for conferring oxidation resistance.As with stainless steels. small additions ofaluminum. silicon and rare earth elementsfurther enhance oxide stability and tenacity.especially under thermal cycling conditions.Stable oxide scales nO( only retard furtheroxidation bot also act as an effective barrieragainst other fonns of attack.

Sulfidalion. Sulfidation producesscales rich in metal sulfides that offer lit­tle. if any. protection against furtherattack. Reducing-sulfidizing environ­ments are usually more aggressive thanoxidizing-sulfidizing atmospheres. Nickelalloys. as a class. are more susceptible to

sulfidation than stainless steels largelybecause of the formation of low melting­point nickel sulfide. As with oxidation.alloying with chromium progressivelyimproves resistance.

Chloridation. High-temperatureexposure to chlorine and its compounds

rapidly corrodes stainlesssteels. Because iron chlo­rides and oxychlorides arequite volatile, severe chlo­ridation may proceedwithout appreciable scal­ing. Nickel-base alloys arefar more resistant thaniron-base alloys. makingthem the materials-of-choice for environmentscontaining chlorine orchlorides.

Carburization. Inhigh carbon activityatmosphere, carbon tendsto diffuse into the metal

' .

lion modes may occur simullafleOUsly. Forexample. many industrial environments c0n­

tain both oxygen and chlorine. subjectingexposed mcIaIs to ol(ychlorination, a highlyvirulent fonn of corrosion. Exceptionallyse~ COITOSion can also be caused by liquidphases. such as molten salts, ash Of metals.1llose aggressive species are rarely encoun­tered in chemical processing and hence faJ!beyond the scope of this article.

The directional effect of alloying con­SlilUents on either retarding or exacerbatinghigh-tempernture chemical altack of nick­el-base alloys is shown in Table 5.

The effect of Cr. Mo, Co. w. 5i and AImay be either favorable or detrimental,depending on the specific exposure condi­lions. notably lempernture and reducingversus oxidizing atmosphere.

In practice. several material degrada-

r

ReprimMfrom Chemical Proressing Magodne· Oc/obf!r /998

HIGH-PERFORMANCE METAU & ALLOYS

ea versus corrosion-resistani a o'sAkJy pmdUC81S and spec/fication writefs sometimes find it convenient to classify alloys as either heat-resistant or corrosion-resis­tant. ThaI somewhat arbitrary dlstinctioo centers on whether the alloy composition and microstructure is optimized for aqueouscorrosion resistance or for eIeYat8d temperature service. Heat·resistant alloys ca11 be further subdivided according 10 whether they

designed prirrrarily for chemical resistance in hot aggressive environments or for optimum strength and metallurgical stability.In practice, there Is considerable overlap and some versatile nickel alloys are capable of serving effectively in multiple capacities.

ANovember 1997 Chemical Processing article (p.54) discussed corrosion-resistant nickel alloys for applications in aggres­sive aqueous-environments. Complementing that ear1ier article, this one is focused on nickel alloys targeted for corrosion resis­itance in high-temperature gaseous environments. Both stories include Alloys 600 and 625 because of their excellent performanceover abroad temperature SjlOCIrum.

Table 6. AWS speCifications for recommended weldmg materials

1. These consumables are not exact matches to the loose metal composnions and the result­ing weld deposits may not have the same high-lemperature corrosion resistance as the basemetal.2. Matching filler metals are available but are not Included in AWS specifications.

Alloy Welding electrode (AS.11) Filler m.lal (A5.14)

600 ENiCrFe-3 ERNiCrFe·3601 ENiCrFe·3' ERNiCrFe·31,2

617 ENiCrt:oMo-1 ERNiCrt:oMo-1625 ENiCrMo·3 ERNiCrMo·3X ENiCrMo-2 ERNiCrMo-2214 ENiCrMo·2\ ERNiCrMo-2\.2230 ENiCrWMo-1 1 ERNiCrWMo·l 1,2

242 ENiMo-3\ ERNiMo-31,2

602CA ENiCrCoMo-1 1 ERNiCrCoMo·l l ,2

SlImlns tube Welded tube

8167 85168167

B444 87048622 86268622 86268722 87268167 85168167 8516

(GMAW). Nickel alloy weldmenlS typical­ly exhibit excellent duclility. and their lowthermal expansion characteristics tend toreduce residual slresses and diSlortion.

Woldedplp.SUml.. plp.

ly welded by Ihe common weldingprocesses. inclUding shielded metal arcwelding (SMAW). gas tungsten arc weld­ing (GTAW) and gas melal arc welding

8168 8167 85178168 81678168 854li8443 B444 87058435 8622 8619843S 8622 86198718 8722 87238168 8167 85178168 8167 8517

Table 7. ASTM specifications for selected llroducl forms

matrix IlI1d ronn metal carbides. ThaI formof lIt1ack, called carburizlIlion. can causesevere impainnent of me<:hllnical proper­ties. notably duclility and impact strength.Nickel alloys exhibit good carburizationresistance because nickel. unlike iron. isno! a strong carbide fonner.

Nitridation. Nitridation. orten callednilriding. refers to nitrogen diffusion intothe metal lanice to form metal nilrides. Inthe chemical industry. it is encounteredprimarily in high-temperature ammonia­rich atmospheres. As in carburization.damage manifeslS no! as metal loss but asembrittlement. Nickel does not formnitrides. which accounlS for the excellentnilridalion resislance of nickel-rich alloys.

Inlernal attack. Carburizalion andnilridation are by no means the only high­temperature degradation modes character­ized by inlemal damage. Vinually all hightemperature corrosion is diffusion drivenand characterized by substantial subsurfaceattack. predominanlly along grain bound­aries. That applies to oxi-dation. sulfidation. andespecially 10 halogenation.In many instances. internalattack penetrales deeper Alloy PI.......into the metal than surfocemelal loss. Evaluation ofhigh temperature corrosionshould therefore be basednot solely on thickness orweight loss. but additional·lyon metallographicexamination.

BOO601617625X23033345TM

Welding guidelines 602CANickel alloys can be: readi- L. J

Rtprillledfrom Chemical Processing Maga:ine· OCf~r 1998

HIGH.PERFORMANCE METALS & ALLOYS

PostweJd heal treatment is generally notrequired for solution strengthened alloys.

RCl:ommended welding consumablesfor the alloys surveyed. as covered byAmerican Welding Society (AWS) specifi.

cations AS.II and A5.14. are listed inTable 6. Although not included in AW$AS.II and A5.14, matching filler melals

for Alloys 601, 214. 230. 242 and 602CAare commercially available. Matching fillermelals are the preferred choice for weldsexposed to aggressive high-temperalUreenvironments because they provide greaterassurance that the weld metal will have thesame corrosion resistance as the basemetal. Nickel-rich weld materials are wide·Iy used also for dissimilar metal weldjoints between nickel-base and iron-basealloys and for depositing weld overlays onfenuus subslrJles.

Welding procedures for nickel alloys are

broadly similar to those for stainless steels.However. modifications of joint designs and

Welding procedures are broad-

Iy similar for nickel alloys and

stainless steel.

welding techniques may be indicated to

achieve full penetration welds, conditionedby the sluggish flow characteristics of high­

nickel weld puddles. Nickel alloys areinherently more sensitive than iron-basemetals to weld embriulemeOl by contami­

nants. Exercise special care to shield the

wcld zone from foreign substances.Wrought heat- and corrosion-resistant

nickel alloys come in a wide range of prod­

uct forms. including plate/sheet and bothseamless and welded tubular goods.ASTM specifications covering those are

listed in Table 7. Most of the alloys in

Table I can also be produced as castings.albeit with minor chemistry modifications.

Alloy characlerlsticsThis brief rundown highlights the attributes

of each of the alloys discussed that affecttheir suitability for corrosive high tempera­ture environments in chemical plants.

Alloy 600 has excellent resistance to

oxidation. chloridation. carburiz.ation andnitridation, but poor resistance to sulfida­tion. Alloy 600 is widely used for hOI chlo­

rine/hydrogen chloride and for ammonia

atmospheres.

• Alloy 601 has excellent resistance tocarburization and cyclic oxidation. It has

moderate strength but excellent thennalstability. Alloy 601 is widely used in cont­aminated combustion environments.

• Alloy 617 has an exceptional combi­nation of high-temperature strength, ther­

mal stability and resistance to oxidationand carburization. The alloy is used innitric acid and petrochemicals production.

Alloy 625 has the favoroble combina­

tion of high strength and good all-around

corrosion resistance. including aqueousenvironments. II has excellent fatigue

resistance but only moderate thennal sta­bility. Alloy 625 is used extensively inchemicaVpetrochemical plant services.

• Alloy X has an outstanding combina·tion of strength. fabricability and resistance

to oxidizing. carburizing and nitridinggllse~. It is a popular alloy for stressedcomponems in aggressive combustionenvironments.

• Alloy 214 has superb resistance tooxidation (up to 2.2WF), chloridation.

carburiZlition and nitridation. It hasmediocre thermal stability, fllbricability

and welJability. Alloy 214 is a niche alloy

for ex.ceptionally cOfTOsh'e environments.There is limited availability of productfonns and quantity.

• Alloy 230 has the beSt balance ofstrength. thermal stability and fatigue resis­tastce, oxidation resistance and fabricability

among major high-temperature alloys. It isfavored for high-strength components in

punishing combustion environments.

• Alloy 242 is the best among nickelalloys for fluorine and fluoride resistance.It has very high strength and good !hennalstability. Alloy 242 is nOt TC<:ommended

for applications above 1.5WF. It is used in

fluoropolymers production..Alloy 333 has ex.cellent oxidation and

carburization resistance. as well as good

sulfidation resistance and mechanical prop­enies. It is used in diverse chemical/petro­

chemical plant applications.

• Alloy 45TM is the optimum choice

for combined chloridationloxidation,lsulfi·dationjcarburization resistance. The alloy

excels in incineration and gasification

proo=.• Alloy 602CA has ex.ceptional resis­

tance to cyclic oxidation (up to 2.2CJ01'F)and carburization and also provides good

resistance to oxidizinglsulfidizing gases.It offers high creep strength at extremetcmperatures.

Cost fa<torsThe alloys surveyed are about two times tofive times costlier than Type 310 stainlesssteel. The cost differentials are consider­

ably lower on an installed--equipment basis.largely because the cost of fabrication does

not vary greatly between nickel alloys andstainless steels.

Another imponant consideration in ec0­

nomic analysis is the greater capabilities,lower maintenance and looger life of high­

perfomlance materials. On the basis of life­cycle cost. nickel alloys often prove the

best economic choice.

By G. Sorell, prtsidel1l ofG. SorellConslliting Sn-,,·icts. NOrlh Call"'n!!l. NJ.Sorell is a materials/carrosiOrl erlgirleer ....ilhmort Ihan 40 years ofintlllSlrial experimce.Preporo/iOrl of/his Or/ide ....as s/lPporied by/lie Nickel Derefopmem IIlS/i/llte.

Reprimedfrom C/lemical Procusing Maga:irle' October 1998 m