CA1246902A

CA1246902A - High-strength alloy for industrial vessels

Info

Publication number: CA1246902A
Application number: CA000476603A
Authority: CA
Inventors: Thomas H. Bassford; James R. Crum
Original assignee: Inco Alloys International Inc
Current assignee: Huntington Alloys Corp
Priority date: 1984-03-16
Filing date: 1985-03-15
Publication date: 1988-12-20
Also published as: DE3578673D1; JPH0525944B2; FI851036A0; FI75869C; EP0155011A2; ES541303A0; FI851036L; FI75869B; BR8501127A; KR900001561B1; AU3969885A; KR850007098A; JPS60211053A; EP0155011B1; EP0155011B2; ES8608055A1; AU580758B2; EP0155011A3

Abstract

ABSTRACT OF THE DISCLOSURE

An sustenitic nickel-iron-chromiun alloy exhibiting high-strength, good corrosion resistance and having a low work hardening sate. The economic alloy is particularly useful for tubes and industrial vessels and, more particularly, heat exchangers and chemical and petrochemical equipment. The alloy includes about 24-32% nickel, about 12-19% chromium, about 1-3.5% molybdenum, about 2-5.5% copper, up to about 2.5% titanium, up to about 1.5% manganese, up to about 0.1% cerium, and the balance mostly iron. Depending on the quantity of titanium, both age hardenable and non-age hardenable versions may be produced.

Description

69~

~IG~-STR~GT~ ALLQY FO~ INDUSTRIAL ~ESSELS

TEC~NICAL ~IELD

The inB~ant invention relates to nickel-iron-chr~mium alloy~ in general and more p~rticularly to ~ hi8h strength, oorrosion resistdn~ alloy haYing 8 low work hardenability rate with variable age hardenable ch2racteristics. The nlloy reduces copper pick-up in fluid ~tream BA~GROUND ART

Po~er plant operator~ and boiler manufacturer~ recognized early on that to improve the efficiency of ~team gener&tors (both fossil and nuclear), it ~8~ u~eful to adopt regenerative feed~ater heating, E~sentially, ~team i~ e~tracted from the steam turbines to preheat the boilertreactor feedwater before it ii introduced into the economizer of a boiler or directly into a steam geDerator¦
reactor. The heating of the feed~ater occurs in, naturally enough, f~edwater heaters. Steam i~ used to heat the feed~ater inside the feed~ater heater tubi~g to impart a portion of the Ytea~'~ latent heat to the water. Water ~emperatures from about 100-650F (37.7-343.3C) and pres~ure~ up to 5200 p8i (358.53 MPa) ~re not unrommon. ~oreover, advanced design~ are now contemplating pressure~ up to 7200 p8i (496.42 MPa) and 700F (371.1C).

-2- ~C-1~59 Currentlg, ~teela (carbon ~nd sta;nle~s) and sometimes nickel-copper allo~s (NONEL* ~ickel-copper ~lloy5) are u~ ed in feed~ater heaters. ~lthough ~he feed~ater ia treated to re~ove che~ical~ and oehe~ i~pusitie~, corrosion of the tubing ~ay still oc~ur, Free o~ygen ~ill attsek the ~eel~. Superalloy~ ~re sfte~
difficult to form i~to tube~ due to their high uork hsrdeni~g rstes. High copper-containing material~ are generslly fro~med upon ~ince coppsr and corro~io~ produee~ ~re believed to deposit on boiler tube~ and ma~ be carried over into the ~tes~. These undesirable entrained products ~ay enter into the turbines resuleing - in lower effisiencies~ Indeed, opera~ors wi6h to eli~inate all pos~ble copper pick-up in the ~team becau~e of fouling and the reBU1ting 10~B of efficiency of the turbine blades when the copper plate~ out of the ste~. It iB ~180 believed that tbe copper depo~it6 ~ay ret up local ~alvanic sells with the ferrous alloys thereby ssusing additiosal oorro~io~O Opesa~ors ~i~h ~o ~ay away from nickel-copper alloys which otherwise di6play better chemical and physical properties than the oeher alloya. ~owe~er, ~he ~bstitution of low casbo~ or stainle~8 Bteel~ for the nirkel-ropper alloys currently available are not al~ays satisfactory since the~e material~ do not ha~e the requisite sorrosion resi~tance, stress corrosion cracking resistance or 6trength. Thi~ leads to high maintenance CoBt~. Moreover, in the case of carbon ateels, uDdesirably short lifetime~ of three to eight year6 have been reported. Contrast this atste of affair~ with an expected ~ervice life in e~ceaa of twenty years. Accordingly, power plant operators Bre i~ a qu ndry: steel~ corrode; high alloys are coatly; and the nickel-copper alloys coutain high quantities of copper.
It i8 apparent that there i6 a need for a reasonable co~t alloy that exhibits corro~ion resi~tance, atrength and fJrmability propertie~ ~uitable for feetwater heater~, chemical and petrochemical inst~llation~ and other 6imilar application~.

SUMMARY OF l`HF lNV~NTION

Accordingly, there i~ provided an austenitic alloy having a low work hardening r~ee e3pecially ~uited for, but no~ limited to, *A trademark of the ~nco family of companie~.

_3_ 61790-1573 industrial vessels and par~icularly for heat exchanger tubing for high temperature, high pressure appllcations. The instant alloy combines improved corrosio~ resistance and the requisite high strength in a system that is of lower cost than the more expensive higher alloys. The alloy displays good stress corrosion cracking resistance and good high temperature corroæion resistance.
Due to its low work hardenability rate, (caused in part by the nickel-chromium combinations) the instant alloy easily lends itself $o tube fabrication and other cold working operations. Moreover, by modulating the ti~anium conten~, age hardenable and non-age hardenable characteristics may be developed. Titanium levels below about 0.8% lead to a non-age hardenable alloy whereas titanium le~els above about 0.8% are increasingly a~e hardenable.
The alloy includes about 24-32% nickel, about 12-19~
chromium, up to about 3.5% molybdenum, about 2-5.5% copper, up to about 2.5% titanium, about 1% manganese, up to about 0.2%
aluminum, up to about 0.1% cerium~ up to about 0.2% nitrogen, the balance iron, and other minor impurities and processing aids Isuch as calcium, boron, silicon, etc.).
In accordance with one aspect of the present invention there is provided an austenitic, high strength, corrosion resistant nickel-iron-chromium alloy, the alloy consisting essentially of about 24-32% nickel, about 12-19% chromium, about 1-3.5% molybdenum, about 2-5.5% copper, up to about 2.5% titanium, up to about 1.5% manganese, up to abou~ 1.5% silicon, up to about 1% columbium and tantalum, up to about 0.~% aluminum, up to about ~.

~2~ Z
-3a- 61790-1573 0.1~ cerium, up to ~bout 0.01% boron, up ~o about 0.2~ nitrogPn~
the balance mostly iron, and with trace amounts of impurities.
In accQrdance with another aspect o the present invention there is further provided an industrial vessel comprised of an austenitic alloy exhibiting high strength and corrosion resistance, the alloy consisting essentially of about 24-32%
nickel, about 12-19% chromium, about 1-3.5~ molybdenum, abou~ 2-5.5% copper, up to about 2.5~ titanium, u2 to about 1.5%
manganese, up to about 1.5% silicon, up to about 1% columbium and tantalum, up to about 0.2% aluminum, up to about 0.1% cerium, up to about 0.01% boron, up to about 0.2% nitrogen, the balance mostly iron, and with trace amounts of $mpurities.
In accordance with another aspect of the present invention there is further provided an austenitic, nickel-iron-chromium alloy, the alloy displaying hlgh-strength and corrosion resistance while simultaneously minimizing copper loss in fluid streams, the alloy conststing essentially o~ about 26-29% nlckel, 15-18% chromium, up to about 3% molybdenum, up to about 5~ copper, up to about 2. 5% titanium, up to about 1.5% manganese, up to about 1.5% silicon, up to about 0.~% aluminum, up to about 0.01% boron, up to about 0.2% nitrogen, up to about 0.1% cerium, the balance mostly iron, and with trace amounts of impurities.
In accordance with another aspect o~ the present invention there is further provided a method for producing an austenitic alloy exhibiting high strenyth and corrosion resistance, the alloy comprlsing about 24-32% nickel, about 12-19%
chromium, about 1-3.5% molybdenum, about 2-5.5% copper, up to t~
-3b- 61790-1573 abou~ ~.5% ~itanium, up to about 1.5% manganese, up to about 1.5 siliconr up ~o about 1% columbium and ~antalum, up ~o abou~ 0.2%
aluminum, up to about 0.1% cerium, up to about 0.01% boron, up to about 0.2~ nitrogen, the balancei mostly iron, and wlth trace amounts of impurities wherein the method comprises heat treating the alloy ak a temperature range from a~out 1100 (593~ to about 1400~F (760C) for the appropriate period of time.
In accordance with the present inventlon there is further provlded a method for producing a tube, the tube comprising about 24-32% nickel, about 12-19~ chromium, about 1-

3.5% molybdenum, about 2-5.5~ copper, up to about 2.5% titanium, up to about 1.5% manganese, up to abou~ 1.5% silicon, up to abou~
1~ columbium and tantalum, up to about 0.2% aluminum, up to abou~
0.1% cerium, up to about 0.01% boron, up to ahout 0.2% nitrogen, the balance mostly iron, and with trace amounts o~ impuri~ies wherein the method comprises (a) forming a tube, (b~ sizing to a predetermined size, (c) annealing the tube, ~d) straightening the tube, and (e) h~iat treating the tube at about 1100 (593) ~o 1400E
(760C) for the appropriate period o~ time.
BRIEF DESCRIVTION OF THE DRAWINGS
The Figure plots yield stress vs. percent reduction.
PREFERRED MODE FOR CARRYING OUT THE INVENTION
The addition of a measured quantity of ti~anium imparts an age hardening response of at least 60 ksi (413.7 MPa) yield s~rength and 120 ksi (827.4 MPa) tensile streng~h in the cold worked and annealed conditions. The titanlum raises the work hardening rate of the alloy. Copper, chromium, and molybdenum :' ,.

-3c- 61790-1573 improve ~he corrosion resistance of the alloy. Alumlnum, cerium, boron and calc~um assist in the deoxidatlon of the alloy.
Nitrogen may be added to the low titanlum level alloys as an austenlte former. It also serves to boost the alloy's ability to withstand corrosive attack. The nitrogen raises the strength and increases the work hardening rate of the alloy in the annealed condition. Table I below sets forth a number of heats with the above formulation ranges. Heat 12 is a low titanium non-age hardenable modification of the alloy.
lTABLE 1]

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-5- PC~1259 ~AMPL~ 1 In one ~et of ~e~t~, he~t 12 was evalu~ted for ~tress COrrOYiOD cracking ~"SCC") and high ~e~perature ~ater corro~ion resistance. It war ~est~d in the a~-col~-rolled (CR) and heat treated at 1400F (600C) ~nd compared to ~nnealed MONEL alloy 400 and 304 6tsil~1ess .
Stress corrosion cracking tect re~ulta are given in Table 2 below.
.

l~ABLe 2]

SCC te~ts were csrried oue with u-bend specimens ~t 600F
~315.55C). General corro~ion te~ts were conducted in deaerated ~ater with coupona suspended from inaulased hook~. Weight change in the ~ater tests were determined b~ weighing u~cleaned ~pecimens after 500 hour6 and 1000 hours. The average corrosio~ rnts wa6 determined on cleaned spe~imen~ after 1000 hours.
All tast material W~8 in the for~ of 0.125 inch gauge (0.32 cm) ~ 2~5 inch (6.35 c~) wide strip. Experimental compo~itions were te~ted i~ as CR 50~ ant/or CR ~ 1750F (954C)/one hnlf hour, water quenched ~ 1400F (760C)¦one hour air cooled conditions. Commercial MONEL alloy 400 (nominal composition: 32.56% copper, 2040% iron, 1.04Z
mangaDe~e~ O.lZ silicon, 0.1% carbon9 balance e6sentinlly nickel) and 304 ~tai~lesa (nominal composition: 18.09% chromium, 9.18~ nickel, 1.77%
mangaDese, 0~73Z ailicon, 0.24% molybdenum, balance essentially iron) were compared to heat 12.
In e 600F 1% NaC1 ~olution, only alloy 304 cracked ~ithin the 720 hour te~t. There wa~ no evidence of SCC cracking in heat 12.
In boiling 45~ MgC12, hent 12 had n greater SCC resistance to crack propagation than 304 ~tainles~.

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-8- PC-12~9 In boili~g 50~ NaOEI, he~t 12 crscked sligh~ly ~nd experienced light aurface ~tteck. Alloy 304 ~ subject to severe general corrosioD ~nd cracking ~7hile ~lOMEI. alloy 4no ~aB ~eBi~tane ~0 att~ck under these circu~t~nce~ .
In summary, heat 12 tispl~yed good SCC re~istance and i~
e2pected to re3i~t c8u8tic ~d chloride SCC better than alloy 304. The higher Dickel provide~ this improved 5CC resi~t~nceO
In the high temperELture deaer~ted water te~t ~ho~ T~ble 3 belo~, general corrosion ratec iu the ~lloy lZ ~ere similar to 304 st~inles6 and some~h~t better than MONEI. alloy 400.

GeTleral Corrosion Test Re~ult~
Deaer~ted ~ater~ P~7 a 600 F
Heat 12 as CR ~ Other~ CRA

Wei~ht Chan~e (m~/c~2) 1000 h Corrosion Heat/Alloy 50Q h 1000 h * Rate, mpy . , ~
12 -0.023 ~0.031 0.10 -0.060 -0.105 ~.lO
Monel Alloy 400 -0.102 -0.044 0.23 " -1.579 -1.625 0.73 St~inles6 304 --0.017 -0.025 0.06 ~0.035 -0.018 0~06 ~Rate determined on clesned specimen~.

He~t~ 1-3 and 12 (14 kg ~elt~j were Y~cuum melted ~nd cs3t ~o 4 inch ~10.16 cm) di~me~er ingot0. Forged 9/16 i~ch ~1~43 cm) Bquaren plU8 forged 3l4 ~ 2 x 12 inch (1~91 x 5.08 x 30.48 cm) fl~ts were ~l~de with frequent rehe~ts at 2150F

6~

-9- PC-1~59 tll77C). After o~erhauling ~h~ fl~t~ to a uniform thickne~s, ~bey ~ere hot rolled ~o 1/4 in~h (0.64 ~) at 2150F. The hot rolled 1/4 inch ~trip was ann~aled at lg50F (1066C)/ one hour water q~e~ch and pickled prior to cold rolling. ~Prdne~s and tensile tests were taken at variou~
levels of cold ~ork to e~tablish a ~osk h~rdening recponse. A low work hardening rate i~ very de4irable in the manufacture of relatiYely small diameter thin-walled ~ubing.
Of particul~r importance i~ the yield strength et high le~el~
.. of cold eductio~ ~u~h aa 60 to 30~ redu~tion. Many ~u~e mills protuce ~ large hot-worket tube shell ~hich ~UBt be reduced i~ size during a number of cnld working snd anneali~g 6tage8. Experience h~s ~hown th~t alloys ~hich have lower yield s~rength ~fter high cold reduction~ ~ay be colt worked to a greater degree ~ithout spliteing, requiring le~s nnealing s~ages and lower manufacturing cost~. The Figure ~ho~s heat 16 to have a lower yi~ld ~trength after ~ high cold redu~-tion than heats 14 and 15 ~ith lower nickel co~tent.
After a cold reduction of 60 to 80Z, the yield strength of heat 16 i~ al80 lower than the commercial alloy INCOLOY* alloy 800.
INCOLOY alloy 800 i8 uhown i~ the Figure for co~p~rative purposes only.
A general purpose alloy, it has good ~Drkability characteri~tics and i8 ea~ily processed. ~he i~fitant i~vention ~as developed with the~e sttributea in ~ind.
All he~t~ h~d good mslleability. Tensile data on cold rolled strip using incre~sing amount~ of titanium ~re ~hQwn in Tables 4, 5 and 6.
TABLE_4 Effect of Cold Work on Ten~ile Properties Annealed at 1950F (1066C) ~eatCold ~ork YS T~ El ~ard ~ed* ~ard NoO ~ ksi ksi ~~b/Rc Ra Rb~c Ra 12 0 30.4 74.g 49.5 70b 44.0 19.1 97b 59.5 90 56.5 32.3 107.0 112.7 9.5100b 61.5 51.0 113.3 121.9 7.0 26c 63.5 69.0 122.5 140.7 5.5 29c ~5.
*Aging 1350F/l hour, AC
*~ ~r~dem~rk of the Inco f~milY of compsnie ~L~4L69V;~

-lg- PC-1259 TABL;13 5 ~ffect of Cold l~ork Oll T~n~ile Properti2s 15~20% 65~ 71X
eat/No. AS ANN C~ CW Cl~ C~

YS, k~i 36. 82~1 lOQ.l 134.7 13~.9 : TS, Itsi 80.100.1 113.6 147.1 155.
131, X 45 28.5 13. 5. 3.5 llsrd Rb 76.596 99 Rc 17 . 21. 32 32 .5 2 YS, k~i 34.83.6 112.7 137.3 145.5 ~S, k~i 79.5105.1 124.2 148.8 159.2 El, ~ 46.525.5 B. 5. 4 ~lard ~b 74.596 103 - -Rc 17 26. 32 33.4 3 YS3 ksi 36.585.7 97 139.8 139 TS, kRi 80.5107.7 116 153.1 158.5 El, % 45.25.5 18 5. 3.5 Hard ~b 77 97 99 Rc 19 21 32 33 A~N ~ annealed C~ n ~:old ~orked ~ ~6~
( ~ PC-1259 TABL~ 6 Te~ile Psoperties of Cold ~olled Plu~

A~ 15X 20Z 65~ 7lX
~e~t No~ ~ C~ CW C~ C~

I YS, k~i 110 llD.9 136.6 157.5164.8 TS, ksi 120 142~7 159O5 176~5181~0 E;l, % 22~5 17~0 ~0 ~0 ~rd, ~c 25 30 34 39 40 2 YS, ksi 110 1~6.2 151.6 16~7171.4 TS9 k~i 120 153.4 174.8 185.7189.6 El, ~ 20 11.0 7O08~0 ~rd, Rc ~3.5 32.5 38.0 40.40.

3 YS, ksi 1~4 126.7 147.6 17~.1176.g TS, ksi 134 159.8 175.1 195.8197.8 El, % 21.0 15. 9.07.0 Hard, ~c 27 35. 37. 42.43.5 * All sample~ aged 1350F/l hr, AC

~hen titanium ~aa ~ai~ed to 2.0~, the work hardening rate increa6ed but no chsnge occured aB titanium wa~ raised to 2.3X.
The aged ten~ile test resulta in Table 6 indicate that 50 ksi yield ~tre~gth and 120 k~i tenAile strength can be accomplished with approximately 1.75Z titanium and low level cold wor~ing. Indeed, the co~bination of about 20% cold reduction with a ~lightly lower titaniu~ cootent might be optimum for feedwater heaters.
Table 7 shows the ~trength and ductility charscteri~tics in the annealed and aged c~Dditions.

TABI~ 7 Effect of ~eat Treatment on Age-~arden~ble Allo~
For~ed 9116 in. Sgu ~es ~elt ~eat Treatment YS TS E1 RA
o.F/hr ksi kci Z ~ _ : 11750/113 3907 93-~ b.6 f~5.1 Age(l) 87.3 140.6 27 52.2 " ~ ~ge(2)112.3 157.2 22 34.6 21750/113 ~0.1 ~5.4 43 ~5~7 ~ + ~ge 84,7 151.3 29 47.2 " ~ Ag~( )124.2 169.9 21 38.S

317~0/1/3 40O5 97.5 41 $2.8 Age 86.4 15902 30 48,3 " ~ Age( )134.4 180.4 21 30.9 Age (1~ 1350F¦l hr.
Age (2? 1350F/8 hrs FC 100F/hr to 1150F/8 hrs, ~C

Corro~ion te~ts ~ere conducted on heats 4-12. Corro~ion test environmeDta relavant to feed~ater heater service ~nd other poaaible ~pplicstioDs ~ere examined.
T~ble 8 depict~ the SCC test result~ in sodium ~hloride and sodium hydroxide ~olution~.

lT~BLE S]

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The tests show that the instant alloy is more res-ls~ant ~o SCC (caused by chlorides and sodium hydroxide) than 304 stainless.
The relatively high nickel content of the instant alloys provides the increased chloride and càustic cracking resistance.
The test data also indicates very good resistance of the alloys to polythionic acid cracking. This is a common cause of failure of stainless steels and high nickel alloys in petrochemical service. The influence of high titanium content on carbide precipitatioll is believed to be responsible for good polythionic acid SCC resistance.
Table 9 shows general corrosion test results.

[TABLE 9]

Tables 8 and 9 also demonstrates the resistance of the alloy to environments other than that posed by feedwater heaters.
Molybdenum addition of 2-3% greatly improves resistance to hydrochloric acid. Copper additions of 4% or more improved sulfuric acid resistance. The combinaeion of copper and molybdenum appears to improve resistance to phosphoric acid. The instant alloy lends itself to chemical and petrochemical applications.
The design strength of the alloys destined for tubular applications is usually based on the tensile strength of the alloy comprising the apparatus. In the cold worked plus stress relieved conditions, the instant alloy system will meet the 120 ksi minimum tensile strength usually specified by design engineers. This value compares favorably with such alloys as INCONEL alloy 625 and INCOLOY
alloy 80].
Table 10 compares minimum tubular wall thicknesses between MONEL alloy 400, 304 stainless and the instant alloy for various temperature and pressure conditions. Table 10 was constructed to compare the minimum wall thickness between the listed alloys. The next heavier standard wall thickness was used to calculate the weight per foot.

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-15- P~:-1259 ~q ~o I i ~ t I ~ ~
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In order to produce objects and, more particularly, tubes which may be seamless or welded, the objec~ or tube, made by methods known to those skilled in the art, may be subjected to a stress relieving heat treatment of abo~t 1100 to 1400F (599.3-760C) for an appropriate period of time. The time period is, of course, a function of the temperature selected and the section size.
In particular, the non-age hardenable tubes may be drawn to final siz~, annealed at about 1700-2000F (767-933~C) for a suitable time, straightened, bent into the appropriate shape (if

10 desired), and stress relieved at about 1100-1400F up to about three hours. The age-hardenable tubes may be drawn to final size, annealed at about 1700-2000F for a suitable time, straightened, aged for about an hour at 1100-1400F, bent into the appropriate shape and stress relieved (which also ages the tube) at about 1100-1400F for the appropriate time.

q Feedwater Heater Minimum Tube Wall -(A) 550F - 4,500 psi 3/4 OD Avg. Wall Allowable Min. Std. lbs.
Tube Alloy Stress, psi Wall Ga. per ft.
_ . _ MONEL alloy 400 21,000 .074 .083 0.666 Type 304 SS 11,800 .124 .134 1.10 Type 304 SS (a) 15,900 .0954 .095 0.6~2 Low Carbon Steel 11,800 .124 .134 1.05 25 Instant Alloy (b) 26,000 .0606 .065 0.482 (B) 700F - 5,000 psi 3/4 OD Avg. Wall MONEL alloy 400 20,100 .085 .095 0.748 Type 304 SS 11,000 .143 .148 1.33 Type 304 SS (a) 15,900 .118 .120 0.97 30 Instant Alloy (b) 25,000 .0695 .072 0.530 i~

~6~3~

~17- p~-1259 (C3 700F - S,500 p~i 3/4 OD Avg. Wall ~ONEL alloy 400 20,100 .107 .109 0.840 Type 304 ~S ll,lOO .178 .180 1.48 Type 304 SS ~a) 159900 .~2 .~4 1.10 Instant Alloy (b) 25,000 .0885 .095 0.674 (~) These strec~es may result in permanent strain.
~b) Age hardenable version ~i.e. titanium in e~cess o about 1 o8%) I~ should be noted tha~ due ~o the relatively low chromium content, the pitting resistance of the alloy ia about She same as 8tainle8~ 304 and i~ not recommended for aervice ~here superior resistance to locali~ed attac~ i8 required. The low chromium lo~er~ resist~nce to intergrannular attack and li~it~ ~se in highly o~idizing environment~ such a8 nitric acid.
A preferred composition or overall strength, corro~ion re~istance and economy for feedwster heaters i~ heat 8 (28 Ni -16 Cr -- 4 Cu - 1.8 Ti - 2 ~o - Bal Fe). Thi~ compo~ition sppear6 to hnve the mechanical and corrosion properties nece~ary for a high pressure material. It al~o has e~cellent general CorroBion re~is~ance in hydrochloric, sulfuric ~nd pho~phoric acids~ The good resistance of thi~ compo~tion to polythionic ecid attack al~o indicate0 potential petrochemical applications.
~ hile in nccordauce with the provisions of the ~tatute, here i~ illu~trated and described herein specific embodiment~ of the inventionO Those ~killed in the art will under~tand that changes may be mnde in the for~ of the invention covered by the claim~ and thst cer~sin fe~ture~ of the invention may ~ometimes be u~ed to advantage without a corresponding use of the other feature 8 .

Claims

The embodiment of the invention in which an exclusive property or privilege are defined as follows:

1. An austenitic, high strength, corrosion resistant nickel-iron-chromium alloy, the alloy consisting essentially of about 24-32%
nickel, about 12-19% chromium, about 1-3.5% molybdenum, about 2-5.5%
copper, up to about 2.5% titanium, up to about 1.5% manganese, up to about 1.5% silicon, up to about 1% columbium and tantalum, up to about 0.2% aluminum, up to about 0.1% cerium, up to about 0.01%
boron, up to about 0.2% nitrogen, the balance mostly iron, and with trace amounts of impurities.

2. The alloy according to claim 1 wherein the alloy consists essentially of about 28% nickel, about 16% chromium, about 2%
molybdenum, about 4% copper, about 1.8% titanium, up to about 0.1%
cerium, the balance mostly iron, and with trace amounts of impurities.

3. The alloy according to claim 1 wherein the alloy includes more than about 0.8% titanium and is age hardenable.

4. The alloy according to claim 1 wherein the alloy consists essentially of about 28% nickel, about 16% chromium, about 2%
molybdenum, about 4% copper, up to about 0.8% titanium, about 1%
manganese, about 0.4% silicon, up to about 0.4% columbium and tantalum, up to about 0.2% nitrogen, up to about 0.1% cerium, the balance mostly iron, and with trace amounts of impurities.

5. The alloy according to claim 1 wherein the alloy includes less than about 0.8% titanium and is non-age hardenable.

6. The alloy according to claim 1 wherein the alloy is heat treated at a temperature range from about 1100 (593) to about 1400°F
(760°C) for up to about sixteen hours.

7. The alloy according to claim 1 wherein the alloy is in tubular form.

8. The alloy according to claim 7 wherein the tube is heat treated at a temperature range from about 1100 (593) to 1400°F
(760°C) for up to about sixteen hours.

9. An industrial vessel comprised of an austenitic alloy exhibiting high strength and corrosion resistance, the alloy consis-ting essentially of about 24-32% nickel, about 12-19% chromium, about 1-3.5% molybdenum, about 2-5.5% copper, up to about 2.5% titanium, up to about 1.5% manganese, up to about 1.5% silicon, up to about 1%
columbium and tantalum, up to about 0.2% aluminum, up to about 0.1%
cerium, up to about 0.01% boron, up to about 0.2% nitrogen, the balance mostly iron, and with trace amounts of impurities.

10. The vessel according to claim 9 wherein the alloy consists essentially of about 28% nickel, about 16% chromium, about 2%
molybdenum, about 4% copper, about 1.8% titanium, up to about 0.1%
cerium, the balance mostly iron, and with trace amounts of impurities.

11. The vessel according to claim 9 wherein the alloy consists essentially of about 28% nickel, about 16% chromium, about 2%
molybdenum, about 4% copper, up to about 0.8% titanium, about 1%
manganese, about 0.4% silicon, about 0.4% columbium and tantalum, up to about 0.2% nitrogen, up to about 0.1% cerium, and with trace amount 5 of impurities.

12. The vessel according to claim 9 wherein the alloy includes more than about 0.8% titanium and is age hardenable.

13. The vessel according to claim 9 wherein the alloy includes less than about 0.8% titanium and is non-age hardenable.

14. The vessel according to claim 9 wherein the vessel is a heat exchanger.

15. The vessel according to claim 9 wherein the vessel is a feedwater heater.

16. The vessel according to claim 9 wherein the alloy comprises tubes within the vessel.

17. The vessel according to claim 9 wherein the vessel is used in chemical and petrochemical service.

18. The vessel according to claim 9 wherein the alloy is cold reduced about 20% from its initial size and formed into tubes.

19. The vessel according to claim 9 wherein the alloy is heat treated at a temperature range from about 1100 (593) to about 1400°F
(760°C) for up to about sixteen hours.

20. The vessel according to claim 9 wherein a tube, made from the alloy, is heat treated at a temperature range from about 1100 (593) to about 1400°F (760°C) for up to about sixteen hours.

21. An austenitic, nickel-iron-chromium alloy, the alloy displaying high-strength and corrosion resistance while simultaneously minimizing copper loss in fluid streams, the alloy consisting essentially of about 26-29% nickel, 15-18% chromium, up to about 3%
molybdenum, up to about 5% copper, up to about 2.5% titanium, up to about 1.5% manganese, up to about 1.5% silicon, up to about 0.2%
aluminum, up to about 0.01% boron, up to about 0.2% nitrogen, up to about 0.1% cerium, the balance mostly iron, and with trace amounts of impurities.

22. A method for producing an austenitic alloy exhibiting high strength and corrosion resistance, the alloy comprising about 24-32%
nickel, about 12-19% chromium, about 1-3.5% molybdenum, about 2-5.5%
copper, up to about 2.5% titanium, up to about 1.5% manganese, up to about 1.5% silicon, up to about 1% columbium and tantalum, up to about 0.2% aluminum, up to about 0.1% cerium, up to about 0.01% boron, up to about 0.2% nitrogen, the balance mostly iron, and with trace amounts of impurities wherein the method comprises heat treating the alloy at a temperature range from about 1100 (593) to about 1400°F (760°C) for the appropriate period of time.

23. A method for producing a tube, the tube comprising about 24-32% nickel, about 12-19% chromium, about 1-3.5% molybdenum, about 2-5.5% copper, up to about 2.5% titanium, up to about 1.5% manganese, up to about 1.5% silicon, up to about 1% columbium and tantalum, up to about 0.2% aluminum, up to about 0.1% cerium, up to about 0.01% boron, up to about 0.2% nitrogen, the balance mostly iron, and with trace amounts of impurities wherein the method comprises a) forming a tube, b) sizing to a predetermined size, c) annealing the tube, d) straightening the tube, and e) heat treating the tube at about 1100 (593) to 1400°F (760°C) for the appropriate period of time.

24. The method according to claim 23 wherein the tube is aged.

25. The method according to claim 23 wherein the tube is bent to a predetermined shape.

26. The method according to claim 25 wherein the tube is stress relieved after bending.

27. The method according to claim 23 wherein the annealing step occurs at about 1700-2000°F (926-1093°C) for an appropriate period of time.