Performance of Austenitic Stainless Steel in Wet Sour Gas Part 2

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t i l s P r o r mance SEPTEM BER 2 004 h t t p mp . nace . o r g

P £ fass ive ox ide fi lm by sy nerg is tic acdo n

be tween c h lo rides a nd H 1S. At rh is w riting, no well- p rm ·en gu ideli nes ex isr forer 0 rmance 0 apply ing ss in wet so ur gas-co nraini ng

ustenitic Stainless

Steels in Wet SourGas Part 2

V IRENDRA S INGH GASC O

This article discusses seven failures on austeniticsteels in a sour gas processing plant. It presents

data compilation, analysis and conclusions from these

failures and those covered in Part 1 August 2004 MP fromthree other plants . The plants were built over a period oftime with changing material selection criteria . Thefailures have all occurred in similar process units of thecondensate recovery and vapor compression sections where different plant designers used austenitic stainlesssteels types 304 and 316L [UN8 830400 an d UN8 831603]).Chloride-assisted stress corrosion cracking caused thef i l u ~ e s

46 MATE RI ALS PERFOR MANCE SrptrmLa 2 4

mi l rece nrl y i t was wi dely beli e,·ed rhat rh e cracking of austen it ic sra in lesss tee l (SS ) in w e t sourgas-conrni ni ng ch lorid eswa s cau sed by chlor id eassis te d sr r css co r rosio n

c rack ing CSCC) at f.wo rabl c rcmp craru r cs . A rccc nr srud y on co rros io n- r es isranr a lloys. howeve r, shows rh at CSCC

l i l u rc ty pe of en \ iro nm enr a lly assisted c rac king (E AC) - is dri ven eith erby e nhan ced 1 1 ad so rpti o n or h ydroge nsul fi de (1 1

5) -enh anced br en kdow n of h e

ch lorides .

ase StudiesA tota l of 13 fa ilu res at fo ur gas pla n ts

have been ide ntified as cases of EAC o nauste ni t ic SS. S urpri sing ly, a ll o f th e f a ilur es occ ur r ed o n types 30 4, 404L, and3 16 L SS UNS 53 0400 , UNS 53 04 03,

and UNS 53 1603 , respecd ,·cly) an d a refro m rhe co nd ensa t e sw b ilizarion a nd

vapo r co m p ress io n secri o n of he so ur gaspla n es. ll1 e faci li ties a re s how n o n sim p lifie d p rocess Row d iagr a ms a lo ng w it ho pera ting para m ere rs and analyt ical data .l n\ es ci ga rive fi ndi n gs are gh·c n case-bycase a long w irh appli ca ble cla ra.

Par r I of t his a rric le, w h ich a ppeare din th e A ugust 2004 issue of MP (p. 52),

disc ussed Cases I th r oug h 4 ar Pl ant Ia nd Cases 5 a nd 6 at Plant s 2 a nd 3 . P a rt

2 co\ e rs Cases 7 t hro ugh 13 a r Plant 4. It

a lso includ es clara co mp ilati o n , ana lysis ,a nd co nclu s io ns fo r a ll 13 milu res.

C ASE ST UDIES FROM PLANT 4Fig ur e I illustrates a simp lified process

A w diagra m of rhe co nd e nsare srab ilizario n and va po r co mp ressio n se cri on o fPlanr 4. Th e pla nr ·was buil r ro p rocessso u r asso cia ted gas. l11c cri tical eq u ipmenr was ma d e from clad or so lid a lloy825 ( UNS N088 2 5) . So lid or clad rype3 16 L SS was used fo r the ,·a po r comp ressor suc rion a nd inre r-scage drums , airco o lers , a nd pi ping.

CttseA leak was no ticed on rh c I0 - in. (25.4 -

cm ) N PS ry pe 3 16 L SS a ir coo ler o url erpipin g co the inr er-stage kn oc k-o ur (KO)d rum , as show n in the pr ocess Row di agram (F ig ur e I ). l11e gas i n rhe pipe wasladen wirh condensed wcr liqu id f ro m theair c oo ler. l l 1c leak was clam ped. Radiogra phi c ins pec tion o f nea rby weld jo imsshowe d fi ne crac ks tr ans,·er se ro rh e girr hweld s. A few days la rer, an ot her lea k wasobser\ e d on the next we ld a nd ir was a lsoclamped pendin g ins pectio n and p rope r



~ t e r i l sPerformance SEPTEMB ER 2004 h t t p : / /m p n a c e o r g

proper repairs. Both of t he leaks wereconfined £O rhe roe of rhe weld. Periodicmonitoring a nal ys is from th e suctio nsc rubb ers and int er-stage drum showedth e presence of chl orides (Fig ure l).

A m et allographic smdy on th e fa iled

pipe spool was rh en conducted (F igure 2),whic h revea led t h e prese nce of multiplecracks that w ere transverse (perpendicular) ro rhe weld in various locat ions of he

circ um f erenria l bur r weld. A shorr section,remo,·ed t rans,·erse £O the weld area , re

vealed rhe presence of more than si:< visib le macro cracks , bra nchi ng in nature ,rhat emanated from rhc inside surfuce ofrhe joinr. 1l1e micro-examination , ar lowa nd hi gh m agnifi cation , revea led rhe presence of multiple classical branched CSCCema nati ng from the inside sur fuce of rhejoinr in rhe area of the weld. A hardn ess

FIGUR

lAgend Alloy 825 ·0\V = Oily wntor - - Alloy 825 dod CB = bJIJ:(g),C: (; SS 316Q · =Chlorides - - SS 316 clod CS

check showed <2 00 Hardn ess, Vicke rs Process flow diagram showing items that failed from EAC in Plant 4HV 10 . 1l 1e m em l co mposition of th e

pipe and wcld-meml was confirm ed £O be

FIGURE

r ~

~ - - ~ h d; . ' • t c a con ttton

As polished

Microg raph s howing the cla ssica l s tr e sscorros ion cracks observed in the weld metal

a t low and high magnification

micro· sections howing cracksin w e ld metal(s hown by arrows)

EAC on the type 316L SS piping from air cooler to KO drum in Plant 4

FIGURE3

Photograph of compressor suction strainers showing EAC of type 316ss

S r p t n n l ~ t r2 4 MA RIALS PERFORMANCE 47

~



• t e r i l sPe r formance SEPTEMBER 2004 h t t p : mp . n a c e . o r g

Mater·alsSelectio esignFIGURE4

-

Cases 1 11nnd 12

1he compressorsuct ion and inrersrage vess el s weremade of ca r bonsteels (CS) clad with

0 '") 'l .• - \ l ~

.

type 316L SS imernally . A ll the nozzleweld con n ec ti onsw irh she ll and

Cracks in type 316L SS weld ove rlay in Stage 1 suction scrubber.

do m es were inter

nally weld o,·erlaidwi rh rype 316L SS.These vessel s h adund e rgone post-

type 316L SS. Corros ion deposits onthe in side surface of th e elbow wereana lyzed quantitat ively, revea lin g a significant amount of su lfide (12.1 o/o andch lorides (2 .0%).

Cnscs 8 nud 91 h e st rainers from Stages l and 2 on

the compressor inlet p ipi ng we re fou ndrobe bad ly dama ged (Figure 1). Materia lidentification co nfirmed rhar bm h straine rs were mad e of type 3 16L SS. Damageon the Srage 2 strai ner was mor e ex tensivethan on the Stage J strainer (Figure 3).The cracking resembled th at of Cases 2and 3 in Plant 1 (sec Aug us t 2004 MP .

FIGURE5

100,000

~C

10,000 C

co;0 ( )00

1,000

100

10

weld heat treatmentas per rhe d esig n and f.1bricarion code forth e shel l thi ckness .

1h e fluid in the vessels was wet sourgas, and anr co nd e nsable liqu id wasknocked down from rhe gas after co mpr ess ion. A ,·isual inspec tion of the surmc esshowed so me o ily spots rhat were clea nedand checked wit h dye penetrant . It re

vealed numer ous cracks in the weld overlaid sections (Fig ure 4). 1l1ese were considered the cases of EAC, and no furtherilwestigario n was ca rried out.

Case 131he first-sta ge a ir cooler{Figure 1) was

made of ype 3 16L SS seam less tubes an d

g...

0C0

0

000010

0gg

MR017 5-2003 ,

Cl < 50

MR017 5- IS -1515 6-3 IS -15 156-3, NORSOK· NORSOKM001,Cl < 5

NORSOK·M001 ,Cl < 5

2003, Temp Temp M001,Temp < so < so•c Cl < 1

< so•c

Environment limits for type 316 SS as recommended by international standards.

48 MATERIALS PERFORMANCE 5i·pumba 2004

type 316L SS header boxes. 1he fluid wasthe same wet gas as in the prev ious case.1 h e gas was coo led down by exch;mginghear wit h air and any condensable liqui dwas dropped our. H ydrostatic resting w ithdemineralized water showed profuse leaksfrom the tube ro the tub e sheer weld joilu .C lose inspectio n revea led leaks from 27rubes in the bottom row. No furt her investigat ion was carr ied our as the natureof rhe cracking sugges ted it was a caseofEAC.

Reviewo p ~ l i c a t i o noAustenitic SS in Sour Gas

It was established lon g ago that theprese nce of ch lorides in wet gas can causeCSCC on SS under f.,,·orab le temperature co nditions. It was esta blished mu chlater that rhe pr esenc e ofH 2S cou ld assistin SCC. T hese cases of cracking arcgrouped as EAC. EAC is driven either byH -enhanced H absorption or H:Senhan ced breakdown of he passive oxidefilm by syne rgistic act ion betw een ch lo

rides and H S.1

No well-proven guideline

is yet available for

material selection o

corrosion-resistant alloys

in sour gas-containing

chlorides .

EAC f.1ilures ge ne ra lly a re catastrophic and difficult to reproduce in la boratorysmdies. Hence no well -proven guidelineis yer a\'ailable fo r mater ial selection ofcor rosion-res istant alloys (CRAs) in so urgas-co ntaining chlor ides. Anothe r im porranr cons idera t ion has bee n the nona va ilability of realistic wa t er c h emistry ofvarious strea ms ar the plant design stage.Th e estimated chloride conte nt is seldomco rrect beca use c hloride co ntent may \'ar yconsiderab ly based on dynamic downholeconditions. Fur ther more, material s selection depe nd s on the experience and con -



a t e r i l s P e r f o rm a n c e S EPTE MBER 20 04 h t t p : mp.n a c e . o r g

fiden ce le vel of che cor r os io n e ngin ee rassoci at ed w ith plant d esign.

Fo ur do cum en ts a re freq uentl y citedin re ference to C R.A applicati o ns in so ur

env ir on m e nt s:• NA C E St an dar d MRO 75J lim t hech em ica l compo si tion s of m ateri a ls(UN S numb ers ) a nd reco mm e nd sha rd ness (streng th ) limi ta ti o ns a long

with environm ent al limit s.• Eur opean Federa tio n of Co rrosio nPub lic ation- 17J o ff ers gui da nce o n

evalua tin g EAC suscep tib ilit y.• ISO 15 156-3 4 pr ov id e s requ irements and reco mmend ations for m arcrial qu alifi cati on and selectio n .

FIGURE6

Failures at Chlorid e s < 50 mg/L10,000

'i 'a ~~ C E / 1 5 0lim it of f .H,S < 3,500 mbor i

,..-

1,000 · - · - · - · - -- - · - · r: .- .- · - · - -- -- . - -- ·NORSOK Umlt ofpH,S < 100 mbor

'~ .., 6

. - . ;:. y ;:.100 · - · · - · ~ · . - . - · · ~ . - · - ·-

rE..

fi fi r- ... ~ r- ~~

.a ~ ~ n op

~~

~--

10 ll ppH,s, mbarialDTemp. •ca Chloride, ~

1 I ICa se 1 Case 2 Case 3 Case4 Case 7 Case 8 Case 9 Case11 Ca se 12 Case 13

• No rwegian speci fica tio n N 0 RSO K Operating parameters of the failed equipment <50 mg/l of chlorides .M-OOP pr o \ ides etwir o n m ent al re-stri c tions fo r use o f C RAs.Figu re 5 co mp ares reco mm end ed lim

iting emir o nm em s fo r type 3 16 SS (UNSS3 1600 ) in a s our em ·ironm enr .

Review of nalytical ata

of FailuresA practica l ap p roac h was m ade ro co l

Ieee and ve ri fY o peratin g da t a for th e opera tin g pl ant s. Res ul t s fro m res t ru ns,sub sequ ent 1-year plan t o pera tion d ata,a nd rhe pe riod ic sa mpl e an alysis resul ts(laboratory ) were co llected an d \ erifi ed.Typ ica l d ata are list ed o n rhe respecr iveprocess Row di agra ms. 1l1e press ur e a nd

tem pera tu r e ,·alu es a re rhe ty pi cal averageva lues. 1l1c listed mo niro rin g resul t s forpH arc rhc low est laboratory resul t s and

arc not in situ va lues. 1l1crc has bee nmu ch , ·ariacio n in chlo r ide content, a nd

the ma ximum va lues a re listed o n rhedi ag ram s. 1l1e liste d part ial pr essu re of1-1JS was the ca lcubr ed value fro m p er iodi c labo ra to r y a na lyses of gas o n rheneares t t est poi m in th e str eam . 1l 1c result s were g ro up ed to ge t he r in th e respective co rros io n cir cu its to revi ew r he e nviron m ent fo r in d ividu al eq ui pm ent and

pip in g.1l1e clara in Figur es 6 th ro ugh 8 are

plorrc d grap hica lly in respect to H S pa rtial p ressu re, c hlo ride cont ent , and remperamr c r he th r ee most cri tica l em ·ironm enml co ndit io ns fo r EAC. Co mm ent s

FIGURE7

Fallllnt l a t Tamp. < 80"C10 ,000 - - - -

JNACE/I SO limit ofpH,S < 3,500 mbar C> C>... ...wh e n Cl · < 50 mg/L ... ...

~ ~ ~ ~ ~ ~ t = ~~ ~ sJ · · · · r ·...- ;;g

C>

. - . ;:. . - . . - .< 10 000 mg,000

.... "' ~. . .,:::..

...."' "'- ;:..

·..=. · · · . · · · . · - ·... i; "' Q

~.....

"' i;' ' "' In- r - - ... - ....

"'..

100

~ N N ~.... -·N N r -- n n I0

0 ppH,S , mbarlal I[J Temp. •c0 Chlorid e , mg/L I

II _l l_ _l j _ j _Case 1 Case 2 Case 3 Case 4 Case 8 Case 9 Case 10 Case 12

Operating parameters of the failed equipment<60"C.

arc ad d ed ro com pare th e cla ra with rh climitin g va lu es fro m NACE. ISO, o rNORSO K specifica tio ns. 1l1e fi nd ings arcdiscussed as fo llows.

FAILURES BELOW 50 MG/ L OFCHLORIDES IN THE STREAM

Figur e 6 displa ys a ro ral of I 0 cases outof 13 cha t showe d fi1ilu rc whe re chl or ide

co m cnt wa s belo w 5 0 m g/L in rhe fluid

s tr eam , w ith rhe fo llowin g findin gs :• 1 lu ee fa ilur es -Cases 7. II , a nd13 c o u ld be am ib w cd ro a high erop e ratin g rcm pcmr u re abm·e t he 60 C

lim it as pe r NACE/ ISO. Bur o ne ofth em Case 13 - w a s also h igher rha nrh e 120"C l imir as pe r NO RSOK.

• Fo ur fa ilur es-Cases 2, 3, 8, and9 c ould b e at t r ib uted to co ldwor king.

ptrmlur 2004 MATERIAlS PERFORMANCE 49



(

~ e ~ i l sPerformance SEPTEMBER 2004 h t t p : / /m p n a c e o r g

aterialsSelectionesignFIGURES

Fa ilures a t Temp . < 60 'C, pH2S < 1000 mbar and Chloride < 50 mg / L1,000 - - - - 1

~ ~ A C E I S Olimit of

, ..pH,S < 3,500 mbar

_ NORSOK limit ofpH,S < 100 mb a r

,::....100 - -- -- ----· - · - · · · - · - -- ·- ·- -- - . . .

' ' 1r :I

rl-- "' I

10 - -- - - --- · j

0 ppH ,S , mbarlal

[]Temp. •c0 Chloride, mg/ L I

I I

1Ca se 1 Ca se 2 Case 3 Case 4

Operating parametersof equipment that failed >60•C.

The remaining rhree cases fuiled within th e 3,500 -mbar limit of H 2S as perNACE/ISO bur abo ,·e the 100-mbarlimit as per NORSOK specificatio ns.

FAILURESAT TEMPERATURESBELOW60 °C

Figure 7 disp lays a coral of eight casesour of 13 that failed below 6o•c wich rhefollowing findings:

• Four of the failures-Cases 2, 3, 8,and 9- co uld be amibured t o coldforming.• All of the remaining four cases havefa iled ac H 25 le,·els higher chan rherecommended H 2S limit of 100 mbar(for chloride s< 1%) as per NORSOKspecificat ion s.• Case I 0 cou ld be :mribuced copp H 2S abo\'e I ,000 mbar as perNACEIJSO in the sour gas hav in gch lorides abO\·e rhe limit of 50 mg/L.

FAILURES AT TEMPERATURESBELOW 60 °C, H 2S < 1,000 MBAR,

AND CHLORIDE < 50 MG/LFigure 8 displays che four cases our of

13 rim f.1i led wi thin che lim rs ofNACE/ISO in respect to temperature, H 25,and chloride co nt ent with the followingfindings:

• Two fi1i lures, Cases 2 and 3 . couldbe amibucable co cold working.

50 MATERIALS PERFORMANCE Srptrm rr 1 4

• The remainin g rwo cases had H 2Slevels much above che I00-mbar limit sof NORSOK specificat ions for chloride levels of< Io/o.

Conclusions• Th e findings presented in chis anide establ ish that the see min gly insignificant amounc o f ch lorides in wetsou r gas is definitely sufficient co causeEAC of austeni t ic SS when then: is arisk of co nden sing water. Such is rhccase in the co nd ensate scabilizarionand vapor compression section of condensate reco \'ery uni ts in a so ur gasprocessing plane .• 1he author's analysis suggests charsy nergis tic action be twee n chlorid eand H 2S may exist. 1l1e act ion mayh a,·c c.1 uscd f.1ilures co occur belowche reco mm ended le\'els of h l o r i d ~ ~ s

and H S.

• The prese n t environment li mitslisred in NACEIISO specifica tions coprotect rype 3 16 SS materia l fromEAC in sour gas -conc ai nin g chlorideswere found co be inadequat e. Surprisingly, all cases off.1ilures conform ed coNORSOK specifica tions , except Case13 be ing above che 12o•c limit.

• Us ing austenit ic SS inwee

so urgas

sen·ices as listed above is nor recomm t:ndcd. Alloys 825, C-4 (UNS

N06455), or C-276 (UNS N10276)are preferable as they showed satisfacto ry p lant performance in rh e casesdescribed in this art icle.• Th e aucho r suggests that NACEre\'iew the en viron menc limits for austenitic SS in view of che planr failuresdiscussed.

cknowledgmentsThe author would l ike t o thank

GASCO management for giving permis

sion m pub lish chis article a nd his co lleagues in Inspection, Process, and Maintenance, who extended their support inadding pertinent informacion co this article. The views expressed in this article arepersonal op inions of che author and haveno bea ring o r respo nsibi liry of any natureshould chey pro\'e to be erro neous.

References1. P. R. Rho de>. "EJI\•iron ni CJH - A>.<isccd C r-J ck

ing of C orr os ion -Rcsis canc Allor s in Oil and Ga sPro du ction En\'ironm cncs: A R c•·icw, " C orr os io n

57, 11 (2001 ).1 NA C E S1a nd :trd MR01 75 -20 0 3 . " Me•al s

for Sulphide Snc ss Crn cking and S1ress C orrosionC r.•cking Rc.i >lan cc in Sour Oilfield En•·iro111ncm (Houscon , TX: NA C E. 1003).

3. European Federmion of C orro sion Publica·do n - 17, "Corro s ion Rcsisc:t nc Allors for Oil and

Ga.• l'rodu c1ion: G uidance on G enernl Requirem entsand Tcs1 lvlc1hods for H S Sc n ·icc" (l o ndon. U.K.:EFC ).

4. ISO 15156-3, ''l'erro leum and Na1 u rnl G:tSlndu snic 1\·l :t crial for Usc in H ,S Comai ning E n·•·ironmcm in O il and G:ts Produ c1ion - P:m 3: Cm cking Rcsis1am C Rt\s (Corro sion·R cs imm Allo )'S) and

01 h cr Alloys (Genc\ :1 , Switt crland: I SO) .5 . Norwcgklll Te chnolog y Centre Petrole um

S1andardi s:uion. NO R SOK M-OOI: Mat erials sclc.:lio n. Rc •· . (N on var : No•·. 2002 ).

VIRENDRASINGH is Senior Metallurgical Engineerwith GASCO, Projects Engineering. POBox 665, Abu·Dhabi, U.A.E. He has more than33 years of experience in the oil and gas indus·tries in plant integrity, inspection, maintenance,corrosion, and engineeringdisciplines fromwellhead to oil and gas production, oil refiner·ies, gas processing, and petrochemical plantsin India. l'raq, Kuwait, Qatar. and the U.A.E. Heholds a B.S. in metallurgical engineering. Heis a NACE Corrosion Specialist, CP Specialist,and board member of the NACE U.A.EChapter. lVP

Documents

Performance of Austenitic Stainless Steel in Wet Sour Gas Part 2