Corrosion Mechanism Graphitization
Description
Temp. Range (F)
Change in microstructure after long !00"##00 term oper of CS & 0.Mo steel Loss in strength, ductility & creep Se$ere % #000 in yr resistance Slight ' !0 in 0"0 yr eC decompose into graphite nodules
Softening (Spheroidization)
Change in microstructure of steel !0"#00 after ele$ated temp e*posure. +n CS caride agglomerate from plate li-e to at #00 " fe2 hours spheroidal form, in LS (#"0.Cr) from at !0 " se$eral years /nely dispersed to large agglomerated caride. Loss in strength (up to 0 usually accompanied y increase in ductility) and1 or creep resistance.
3e 3emper 4m 4mrittelment
5eduction in to toughness in in ce certain L LS due to metallurguical change due to long term operation. 3his cause up2ard shift in ductile to rittle transition temp y C67 (May result in 8 during s1u and s1d)
Strain ging (4mrittlement)
Comined e=ect of deformation and +ntermediate temp (2ith aging at intermediate temp in old deformation) $intage CS and C"0.M> steel results increase in hardness, strenght and decrease in ductility and toughness
90"#0:0 (More ;uic-ly at <00, ut more se$ere after L3 at !0)
!!o 4mrittlement 4mrittleme nt
Loss in toughness due to metallurgical 900"#000 change in alloys containing 455+34 (thousands of hrs may e ?@S4 due to high temp e*posure re;d at 900)
Sigma ?hase 4mrittlement 4mrittlem ent
ormation of sigma phase results in loss of fracture toughness in SS due to high temp e*posure
#000"#:00
8rittle racture
Sudden rapid fracture under stress (51) 2ith little or no ductility or plastic deformation
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Creep & Stress 5upture
t high temp metal can slo2ly deform 3hreshold 3hreshold temps under load elo2 yield stress (time dependent) leading to rupture
!!o 4mrittlement 4mrittleme nt
Loss in toughness due to metallurgical 900"#000 change in alloys containing 455+34 (thousands of hrs may e ?@S4 due to high temp e*posure re;d at 900)
Sigma ?hase 4mrittlement 4mrittlem ent
ormation of sigma phase results in loss of fracture toughness in SS due to high temp e*posure
#000"#:00
8rittle racture
Sudden rapid fracture under stress (51) 2ith little or no ductility or plastic deformation
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Creep & Stress 5upture
t high temp metal can slo2ly deform 3hreshold 3hreshold temps under load elo2 yield stress (time dependent) leading to rupture
3hermal atigue
3 is the result of cyclic stresses 7o set limit. s practical caused y $ariations in temp resulting rule crac-s may occur if in crac-ing 2here A4 is constrained temp s2ing e*ceeds B00 (under repeated thermal cycling)
Short 3erm >$erheating Stress ?ermanent deformation occuring at 5upture relati$ely lo2 stress le$els due to localized o$erheating results in ulging & stress rupture
Steam lan-eting
AMF Crac-ing
7ormal heat Do2 results in formation of discrete steam ules (nucleate oiling) on tues +A, 2hen heat Do2 disturs, ules Eoin to form steam lan-et -no2n as Aeparture from 7ucleate 8oiling (A78). 3ue rupture occurs rapidly due to S@>53 345M >645@43+7G (in fe2 minutes)
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Crac-ing occurs in ferrtic (CS or LS) 3emp 3emp %#0 (B90C) side of 2eld 2ith ust (00 SS or 7i signifcant thermal alloy) at high temp resulting from e*pansion 1 fatigue stress creep damage, fatigue crac-ing, in err to ust Eoint Sul/de stress crac-ing or @B disonding (?F@3 2ill not pre$ent crac-ing)
3hermal Shoc-
4rosion 1 4rosion"Corrosion
form of thermal fatigue crac-ing " "" 3hermal shoc- occurs 2hen high and non"uniform thermal stress de$elop in short time due to di= e*pansion or contraction, usually 2hen colder li;uid contacts a 2armer metal surface.
4rosion ccelerated mechanical remo$al of surface material y relati$e mo$ement, or impact from solids, li;uids, $apor etc.
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4rosion"Corrosion 2hen corrosion contriutes to erosion to remo$e protecti$e /lm or scale e*pose metal to further corrosion
Ca$itation
Mechanical atigue
orm of 45>S+>7 caused y the "" formation and instanteneous collapse of tiny $apour ules, the ule may contain $apor phase of li;uid, air or other gas, these collapsing ules e*ert se$ere localised impact forces and result in metal loss
Machanical degradation that occurs 2hen component e*posed to cyclic stresses for an e*tended period, resulting in sudden failure. 3hese stresses arise y mechanical loading or thermal cycling 2ell elo2 yield strength.
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6iration +nduced atigue
orm of mechanical fatigue in 2hich "" crac-s are produced as result of dynamic loading from $iration, 2ater hammer or Duid Do2.
5efractory Aegradation
8oth thermal insul and erosion resist "" refractories susceptile to mech damage (Crac-ing, spalling & erosion) and corrosion due to o*idation, sul/dation, and other high temp mechanisms
5eheat Crac-ing
Crac-ing of metal due to stress o$e :0 rela*ation during ?F@3 or inser$ice at ele$ated temp, mostly in hea$y 2all sections.
Gaseous >*ygen 4nhanced +gnitiion and Comustion
Many metals are Dammale in o*ygen & enriched air (%B >B) at lo2 pressures 2hich are non Dlammale in air. Spontaneous ignition of metals and non"metals can cause /res and e*plosion in >B rich gaseous en$ironments if not properly designed, operated or maintained.
4.2. Mechanical and Metallurgical Damages A!ected metallurg$ CS & .Mo steel (upto # Mo)
ot A!ected
A!ected "#uipment
8ainitic grades less susceptile Si & l ha$e negligile e=ect
#) hot piping and e;pt in CC, catalytic ref and co-er unit. B) e2 failures directly due to graphitization. ) Se$ere eye ro2 G3 lo2ers C5S. ) Seldom occurs on oiling surface tuing
CS, LS i.e. C"0.Mo, nnealed steels more hot piping and e;pt in CC, #"< Cr"Mo resistant than normalized catalytic ref and co-er Coarse grain more units resistant than /ne grain Si"-illed more resistant than l"-illed
?rimarily B.BCr"#Mo C"0.Mo, #Cr"0.Mo and (old gen prior to #.BCr"0.Mo not much #<:B particular a=ected suscepitle) and Cr" #Mo (lesser e*tent) Feld material more a=ected
#) e2 failures directlu related to 34. B) @ydroprocessing units (5eactors, hot feed 1 e= e*changers & hot @? seperators, CC reactors
>ld CS (pre #
Most li-ely in th- 2all $essel made from susceptile material not stress relie$ed.
Steels made y 8> and fully -illed 2ith l not susceptile
00 SS (e.g. 0, 0<, #0, #0S, 0 & 9), ASS li-e BB0, B0 and B0:
#) 5e/neries limit ferritic SS to non press parts .e.g. fractionation trays in CC, crude, co-er units. B) Crac-s 2hen 2eldings trays of 0<, #0 ) ASS @4 tues % 900
00 SS 2rought, 2elds and cast SS (@I, @? ha$ing high #0 "0 ferrite content) 00 Series (2ith #: Cr or more ) and Auple* SS
sigmatized 2rought materials still stuiale at operating temp
#) SS piping, cylcones, $al$es in @3 CC regen ser$ice. B) 00 SS o$eralys, 33S 2elds during ?F@3 for Cr" Mo ase metal. ) SS tues susceptile
>lder CS & LS prime concern (impurities) & 00 series SS also susceptile
Sec 6+++"# 4;pt suEect to re;uirement of Jcs 99 00 Series SS
SM4 Sec ! Ai$ # $essels efore Aec.#
ll Metals & lloys
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#) @3 4;pt operating ao$e creep range e.g. @eater tues, tue supports, hangers and furnace internals, CC reactor, @B reforming furnace tues. B) Lo2 creep ductility failures found in 2eld @H at nozzles cat reformer. ) ASM 2elds (er to ust) due to 34 stress.
ll materials of construction
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#) Mi* points of hot and cold streams e.g. @B mi* point in @? units, de" superheater or attemporators. B) 3 maEor prolem in co-e drum shells & s-irts. ) +n steam gen common location at attachment 2 S@ and 5@ tues. ) Steam soot lo2ers if frist steam e*it contain condensate
ll @ tues and "" common materials of construction
#) ll oilers & @ tues B) urnaces 2ith co-ing tendency crude, hea$y oil @? and co-er units /red harder to maintain outlet temp prone to localized heating. ) 5efractory lined e;upt in CC (refractory damage)
Caron steel and Lo2 alloy steel
ll steam generating units (ired oilers K F@8, @B reformers & CC units), ailures occur in super heaters and re"heaters during s1u 2hen condensate loc-s steam Do2.
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CS & LS 2elded to "" ust SS. ny material com ha$ing 2idely di=ering thermal e*p coe=
>$erlayed CrMo nozzles to solid SS pipe 2elds in @? reactor outlets K @B reformer #.BCr"#Mo pigtails to alloy !00 soc-olet of tues K alloy !00 o1l manifold to CS or #.BC5 transfer line K 00SS o$erlays in ?6 K all superheaters and reheaters ha$e AMF 2elds
ll metals & lloys
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#) CC co-ers, catalyic reforming and @? units in @3 ser$ice. B)Material 2ith lost ductility such as CrMo (temper emr) more susceptile. ) 4;upt suEected to accelerated cooling to minimize s1d time
ll metals, alloys & refractories
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#) ll types of e;pt e*posed to mo$ing Duid and1or catalyst are suEect to 4C B) Gas or Li;uid orn particles (slurry) in pumps 1 compressor ) @? euent piping 4C y ammonium isul/de depends on $el. ) Crude and 6AJ piping y naphthenic acid
Common materials e.g. Copper, rass, cast iron, CS, LS, 00, 00 SS & 7i ase alloys.
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?ump casings, pump impellers (L? side) and piping d1s ori/ces and C6s K restricted"Do2 passages y turulent Do2 (eg @ tues, $enturis, seals)
ll engineering alloys ""
#) 3hermal cycling daily cycles in oper li-e co-e drums K e;pt in intermittent ser$ice as au* oiler K ;uench nozzles B) Mechanical loading pump rotating shafts at -ey2ays K small dia piping in $iration K high ?A C6 or steam reducing stations can cause $iration prolem in piping
ll engineering materials
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#) Soc-et 2elds and small ore piping near pumps & compressors. B) ?S6 suEect to chatter, premat pop"o=, fretting, high pd C6s, @4 tues susceptile to $orte* shedding.
5efractory Matls inccl "" +nsulating ceramic /ers, castale, refractory ric- and plastic refractories.
CC 5eactor regenerator $essels, piping, cyclone, 2aste heat oiler, 8oiler /reo* and stac-s
LS (C5"Mo steels "" 2ith 6), 00 SS & 7i ased alloys e.g lloy !00 @
Mostly li-e to occur in hea$y 2all $essls in areas of high restraint i.e. nozzle 2elds and hea$y 2all piping K @SL steels are susceptile
#) CS & LS are Dammale in L? >B % #psig. B) ust SS diNcult to elo2 B00 psig. ) l is a$oided for Do2ing >B, if ignited urns ;uic-ly. ;uic-ly. ) 4asiest to ignite plastics, ruers and @C luricants. ) 3i a$oided in >B rich ser$ice, can sustaintain sustaintain com at #psi >B press.
Copper (%0) and 7i (%0) alloys are /re resistant 1 non Damm. lloy 00 highly resistant
>B is used in sulfur rec$ory units (S5J), CCJ, paritial o*idation units (?>) K >B piping, $al$es, regulators and impingement areas are $ulnerale
- All Industries Critical Factors
%re&ention
5andom (nodule) graphitization does not dding Cr K.: to LS lo2er creep resistance. Chain type reduces load earing capaility (rittle fracture). a" Feld @H graph occurs at lo2 temp. edge (4ye ro2) " 7on 2eld graph occurs along planes of local yeilding. 5eporting is ;ualitati$e (7SMS"7one, slight, moderate, se$ere) 5ate of S? depends on temp and initial microstructure
Mnimize long term e*posure
#) Susceptility due to elements Mn, Si, ?, Sn, S, s B) Signi/cantly reduces structural integrity of comp containing crac- li-e Da2
or old material #) Limit startup pressure to B of MA? elo2 M?3 (safe oper. en$elope). B) or 2eld repair, heating to ##0 and rapid cooling to 53 temp re$erses 34. or ne2 material #) 8est 2ay to Limit O for 8M & factor FM (#00 to # for B.BCr" #Mo) B) 7e2er less used 4;ui$alent ?hosphorus factor for FM & 8M.
#) Steels made y 8essmer or open hearth process, rimmed and capped steels 2ith higher impurities (C & 7) B) MaEor concern for e;uipment ha$ing crac-s (failure y rittle fracture). ) Can occur 2hen 2elding near crac-s and notches in susceptile matl.
#) 7ot an issue for ne2 steel 2ith lo2 impuritie and l % 0.0# to fully deo*idize stl. B) or old e;pt, pressurize 2hen temp % MAM3 ) ?F@3 or uttering of 2eld repairs of old e;uipment
#) +ncreasing ferrite increases susceptiility (increase in A833). B) Aamage is cumulati$e due to precip of emrittling intermetallic phase.
#) Jse of lo2 or non ferrite alloys SS B) 4mrittlment is re$ersile y heat treatment to dissol$e precipitates. Jse of ?F@3 ##00 follo2ed y rapid cooling.
#) Sigma phase occurs in ferritic & martensitic (e"Cr), austenitic (e"Cr"7i) and ASS in gi$en temp range. B) Sigma can form in fe2 hours in aust SS if suEect to ?F@3 (9<0 C) ) SS 2ith sigma sho2 complete lac- of fracture toughness y C67 P 00 ) ?recipitation of hard, rittle intermetallic compund
#) 8est 2ay to use alloys resistant to sigma formations or a$oid e*p to temp range. B) 00 SS desigmatized y solution annealing Q#<0 for hrs & 2ater ;uench. ) Control ferrite to "< for : ferrite and 0 still less. ) or SS clad CrMo, e*p time to ?F@3 to e limited
+mportant factors for 8 #) Material racture 3oughness y C67, B) Size, Shape & stress conc. of Da2 ) mount of 5 K stresses on Da2 3hic-er matl ha$e lo2er resist resist to 8. +n most cases, 8 occurs only elo2 the charpy impact transition temp.
#) Aamage (strain rate) is sensiti$e to load and temp. +ncrease of aout B or # of stress can cut remaining life in half or more, depending on alloy. B) Life ecome nearly in/nite elo2 3hresh temp ) Lo2 creep ductility is more se$ere for high 3S matl and 2elds K more li-ely in coarse grain matl K promoted y some carides in CrMo steels.
#) or ne2 e;pt est to use matl for lo2 temp (JCS 99 in sec 6+++) B) engineering study 2ith ?+ :< sec le$el # or B. B. ) Some reduction in 8 y ?F@3 if not done and for 2eld repair K Farm hydrotest then cold @3 to e*tend MS>3 #) Little to do e*cept Minimize metal temp for @ tues B) @igher ?F@3 to minimize creep crac-ing of metal 2ith LCA (#.BCr"0.Mo) (#.BCr"0.Mo) ) Creep resitant alloys for heater tues for longer life K Minimuze hot spots on heater tues and process side deposits K 63 and J3 th- or strap measure to assess 5L as per ?+ :<"#. ) or 4;pt, repair of creep damaged nozzles done y grinding out a=ected area, re2elding and ?F@3. ?F@3.
#) Iey factor are magnitude of temp s2ing and numer of cycles B) Start"up & shutdo2n increase susceptiility to thermal fatigue. ) Aamage promoted y rapid changes in surface temp (thermal shoc-). ) 7otches (2eld toe) and sharp corners act as initiation sites
#) 8est pre$ented y proper Aesign & >peration to minimize 3hermal Stresses & 3hermal Cycling. i.e. "% reduce stress conc, lend grind 2eld pro/le "% Controlled rate of heating 1 cooling during startup 1 SA "% A4 et2een ASM material to e considered. B) Aesign should incorporate De*iility e.g. a$oid rigid attach K drain on soot lo2er
#) Jsually Dame impingement or local #) in @, urner management o$erheating (ao$e design temp) and fouling 1 deposit control to B) 3h- loss due to corrosion reduces 3ime to minimize hot spot. failure. B) Jse di=use Dame urner ) in @? unit, install 3C in reactors. ) Maintain refractory in ser$iceale condition.
#) @eat Du* & Duid Do2 critical factors B) lame impingement from damaged or misdirected urners ) on Fater side anything that restricts Do2 (condensate, tue dent) cause A78 ) ailure occurs from hoop stress due to steam pressure at @3
#) Fhen A78 de$eolpes tue rupture 2ill ;uic-ly follo2, proper urner management to pre$ernt Dame impingement. B) 8F treatment to pre$ent restricted Duid Do2 ) 6+ of tues for ulging.
#) crac-ing occurs due di=erent C>4 12 ferr #) or @3, use 7+ ase /ller 2ith and aust di=er y B" (leads to high C>4 closer to CS & LS can stress at @H on ferr side) increase life of Eoint. B) stress on 2eld higher 2hen ust /ller B) +f 00 SS electrodes used used than nic-el /ller (C>4 closer to CS) AMF shuold e located in lo2er ) AMF ha$e narro2 mi*ed zone of high temp region. hardness near fusion line 2ith ferr and ) Consider uttering on ferr susceptile to @B crac-ing or SSC. (9.mm) & ?F@3 to minimiz ) C di=usion from ferr @H into 2eld hardness of mi*ed zone reduces creep strenght (at !00 to <0). ) +nstall pup piece of ) +n li; ash corrosion en$iron, ferr 2ill intermediate thermal e*p. preferentially corrode.
#) 3emp cycling may initiate fatigue crac-s #) ?re$ent Do2 interruption in (SS ha$e higher C>4 than CS or 7+ and more @3 line. prone) B) Minimize se$ere restraint. ) B) rature from stress ao$e RS result due to 3hermal slee$es to pre$ent restraint thermal e*p. li;uid impingement on ?8 ) 3hic- sections de$elop high thernal ) 5e$ie2 hot1cold inEection gradient points
#) Metal loss depend on $el, conc of impacting medium, size & hardness of particles, C5 of matl & nlge of impact. +ncreasing hardness of sustrate is common approach, ut not al2ays good indicator of impro$ed resistance to erosion corrosion B) or each en$ironment"material comination there is often threshold $eolocity for metal loss ) +ncreased corrosi$ity y temp, ?@ reduce protecti$e /lm staility and increase susceptiilyt to 4"C
#) impro$e desing (increase pipe dia to reduce $elocity, streamline ends, 2all th-) B) or 4rosion @ardfacing, surface hardening, erosion resistant refractory ) or 4C 8est mitigated y more C5 alloy or altering process (not y sustrate hardness only) ) higher Mo for 7C ) impingment plates and ferrultes in @
#) +nade;uate 7?S@ (min head re;uired to a$oid ca$itation). B) 3emp approaching oiing pt of li;uid result in ule formation. ) ?resence of solid or arasi$e particles is not re;uired for ca$itaion ut accelerate the damage.
#) 7ot signi/catnly impro$ed y material change. Modify design or operating change. B) 8est pre$ented y a$oiding as pressure to fall elo2 $ap press or change material properties (changing to more C5 or hihger hardness may not impro$e ca$it resist).
#) Aesign C initiate at surface notches or stress raisers under cyclic loading. Aesign is most imp for fatigue resist. B) Metallurg or 3i, CS, LS crac-ing 2ill not occur elo2 Stress 4ndurance limit (ratio of 4L to J3S is 0"0). ) ust SS & l dont ha$e 4L and L is de/ned y num of cyles at gi$en stress. ) iner grain ha$e etter fatigue resist than coarse grain (@3 such as ;uech K tempering impro$es 5). ) Ma* cyclical stress ampliude is determined for #09"#0: cylces (desired in lifetime) :) +nclusions in metal (dirty steel) ha$e accelerating e=ect on C.
#) 8est defense is good design that minimize stress conc in cyclic ser$ice. B) Select metal 2ith L for intended cyclic life. ) Mimimize grinding mar-s, nic-s, good /t"up and smooth transition of 2elds, mimize 2eld defects, remo$e urrs or lips y machining, use lo2 stress stamps and mar-ing tools.
#) high li-elihood of crac-ing 2hen input load synchronous to natural fre;. B) Lac- of stifness or support allo2s $iration and crac-ing initiated at stress raisers.
#) 6+ can e eliminated or reduced y design and Supports & 6irations dampening (matl upgrade not a solution). B) 6orte* shedding minimized at o1l of C6 and ?S6 y side ranch sizing and Do2 sta. ) 6iration may e shifted 2hen comp anchored, unless source remo$ed.
#) 5L4 should e designed for erosion, thermal shoc- and e*pansion. B) Ary out and curing should e as per manufacturer specs or S3M re;. ) nchors resistant to condensing sulf acids, @3 o*idation and C>4 near 8M. ) 5efractory resistant to erosion and arasion and needles compatile 2ith process en$.
?roper selection of refractory, anchors and /llers and design & +nstallation are the -eys to min ref damage.
#) 5C re;uires high stresses and more li-ely #) Ooints in hea$y 2all to e in thic- sections designed to minimiz restraint B) 5C occurs at 43 2here creep ductility is during 2elding and ?F@3. insuNcient to accomodate strain. B) Large grain size less result in ) 3rans$erse crac-s occured in B.BCr"#Mo" less ductile @H ma-ing matl 6 in SF 2elds only traced to contaminated susceptile to 5C. Du* (cases in B00!) ) $oid stress conc e.g. long ) 5C can occur during ?F@3 or in ser$ice at seam 2elds mismatch. high temp. ) or B.Bcr"#Mo"6 Gleele ) Crac-s are +7345G57JL5 2ithout 3ensile Screen 3est re;d. deformation. ) or !00@, inser$ice 5C ris9) Stalizing @3 and S5 of 00 SS for CL"SCC reduced using matching 2eld and ?3SCC can cause 5C. metal 2ith LK3iP0.:. 9) or !00@ operation% 0C matl re;uires stailiz heat treatment and S5 of 2elds 9) for thic-2all SS piping, a$oid ?F@3
#) ?rimary concern in high $el >B Do2 particulate entrainement and impinging on surface. >B $el in CS & SS piping should comply 2ith industry limits (depending on impigement or non impingement). B) +gnition temp for most alloys are near melt point in non Do2 condition. ctual system can su=er ignitiion under Do2 at room temp and lo2er due to particle impact. ) Contamination of >B system 2ith metal /nes or @C (oil or grease) can cause /re during startup ) impingment areas, elo2s, $al$es higher ris- of ignition in Do2ing >B.
#) >B /re are sudden e$ent, est pre$ention to -eep system clean after insp or maint. B) Maintain $elocity in recommend limit. $oid $el % #00 ft1sec 0 m1s). ) Jse only >B compatile luricants. ) Ao not open unnecessary open >B systems, for insp to a$oid contamination. ) Ao not use plastic pipe, minimize person during start up near >B system. 9) 3hin SS (P#1!T) a$oided in >B system.
Inspection Monitoring
Remar's
#) Can only e oser$ed y metallography. B) 4$aluation y full thicsample for metallography (5eplica inade;uate ) Surface or SS crac-s or micro$oid (ad$anced stage) diNcult to detect
Competing (o$e #0B ""% S?@ 8elo2 #0B ""% G?@)
#) Can only e oser$ed thru /eld metallogprahy or sample remo$al B) 5eduction in tensile strength and hardness may incidate spheroidization.
Competing (o$e #0B ""% S?@ 8elo2 #0B ""% G?@)
#) Con/rmed thru impact testing 7>74 (no e=ect on upper shelf energy). B) +nstall test loc-s of same heat no and impact test periodically ) 4nsure pressurization se;uence to a$oid 8 ) S4M fractographs sho2 +7345G57JL5 crac-ing due to impurity segragation at G8.
+nspection 7>3 JS4A to control Fhen deformation is at strain aging intermediate temp it is Aynamic Strain ging. 8lue rittleness also form of S
#) 7ot thru metallography ut 7>74 can e con/rmed y +mpact or end test B) 4$aluation y increase in hardness ) +mpact or end test of samples is positi$e indicator. ) Most emrittlement crac-ing during start up & shutdo2n P B00
#) >nly con/rmed y metall. 7>74 B) Crac-ing appears at 2elds during 3 & startup elo2 00 ) 3esting sample remo$ed from ser$ice is most positi$e indicator.
#) Crac-s are straight, non ranching de$oid of plastic deformation (clea$age) B) +nspection normally 7>3 JS4A to mitigate 8. ) susceptile $essels should e inspected for pre"e*isting Da2s1defects
3emper em K Strain age em K !! em K 3i hydriding K Sigma phase emrittlement
#) +nitial stage (creep $oids at Creep damage due to G8) y S4M metallography $ery @3 K 5eheat B) 8ulging of heater tues crac-ing efore /nal fracture. ) Creep damage micr$oid, /ssures and dim change not found y one techni;ue ut comination J3, 53, 4C dim measure & replica) used. ) 5emo$e sample & metallog to con/rm damage. ) or ?6 focus on 2elds of CrMo alloys in creep range (chec- y 63, ?3, F3M, J3) ) Chec- @ tues for diametric gro2th, ulges, crac-s, o2s, listers, 2all th- measurement
#) Surface crac-s, 2ide and Corrosion fatigue & often o*ide /lled due to temp Aissimilar metal crac-ing e*posure, single or multiple. B) Crac-s propagate 357S645S4 to stress and Aagger shaped and 3G. ) Crac-s follo2 toe of /llet 2eld ) Fater in soot lo2er lead to crazing pattern ) 63, ?3, M3, SFJ3 (for non intrusi$e) and special J3 for hea$y 2all
#) Localized deformation or ulging ( to #0 or more) depend on temp, alloy and stress le$el B) +S@ M>J3@ ailures y thinning at fractured surface. ) +n @, 6+, +5 montg, 3S3 of tues ) 5L4 monitor y heat indic paingt or +5 scan ) 5eactor ed and s-in 3C
Creep1 Stress rupture
#) S3@3 al2ays sho2 open ursts 2ith fracture edges dra2n to -nife"edge (ductile rupture) B) Microstructure al2ays sho2 se$ere elongation of grain y plastic deformation at time of failure. ) ?roperly maintain urners to a$oid Dame impingement.
Steam lan-eting can cause caustic corrosion (Causitic Gouging) K Short term >$er @eating.
#) Crac-s form at 2eld toe in 3hermal fatigue & @H of the ferrtic material, Corrosion fatigue & B) 3ues 2elds are prolem area Creep and SSC. ut support lugs of 00 SS to 00 SS are also a=ected ) or ne2 AMF 2elds, #00 ?3 after uttering, #00 J31 after ?F@3, #00 J31 53 & ?M+. ) or @ tues, 53 and SFJ3 such as top Danges
#) Surface initiating crac-s may 3hermal fatigue also appear as C5H4 C5CIS B) ?3 and M3 to con/rm crac-ing. )@ighly localized & diNcult to detect.
#) Localized th- loss in form of pits, groo$es, gullies, 2a$es, holes and $alleys (directional pattern). B) 63, J3 and 53 for metal loss ) Corrosion coupons and 45 online proes ) +5 scan for refractory loss
Specialized terminology or $arious orms e.g. Ca$itation, li;uid impingement erosion, fretting etc.,
#) Loo-s li-e sharp"edged pitting Li;uid +mpingement or or gouged appearance in lo2 4rosion pressure zone B) Ca$it pump sound li-e peles thrased. ccoustic montg. turulent areas for characteristic fre;. ) 63, J3 & 53 for th- loss. #) Signature mar- is clam Shell 6iration induced /ngerprint that has concentric fatigue. rings T8each mar-sT that results from Fa$esT of cracpropagation occuring during cycles ao$e threshold loading (single for Da2 2ith stress conc and multiple 21o stress conc). B) ?3,M3 & SFJ3 to detect fatigue crac-s at -no2n pt. ) 63 of small dia piping to detect oscillation ) 6i montg of rot e;upt ) +n high cycle fatigue, cracinitiation diNcult as cracinitiation is maEority of L.
#) Crac- initiate at high stress Mechanical fatigue & (thread or 2eld Eoint). 5efractory degradation B) or 5efractory damages, s-in temp measurement ) Chec- for $isile & audile signs of $iration, during start up, s1d, upset. Measure $iration. ) chec- pipe supports and spring hangers ) Aamage to insul Eac-eting can cause CJ+. ) 4*cessi$e crac-ing, spalling or lift"o= from the sustrate, softening or moisture degradation. B) +n erosi$e ser$ice, refract may e thinned e*posing anchors. B) 6isual inspection during shut do2ns K +5 scans
>*idation, Sul/dation and lue gas de2 point corrosion.
#) 5C is +7345G57JL5 and S8 lso referred to as Stress or emedded mostly in C>5S4" relief crac-ing and Stress G5+74A sections of 2eld @H. rela*ation crac-ing B) Surface crac-s y J3, ?3 & M3, 4M84AA4A crac-s found only through J3. ) +nspection for 5C in B.BCr" #Mo"6 reactor during farication typically done 2ith 3>A or manual SFJ3.
#) e*ternal heat damage 7ot applicale (glo2ing pipe or tint) is ind of int /re due to comustion of Dammale deris B) Forst situation 2hen pressure en$elope reached. >B /re can cause metal urning and struc damage. ) Sudden ignitiion of metals, it is diNcult to inspect in ad$ance. ) 8lac- light can e used to chec- @C contamination. ) Signs of e*t heat damage or $al$e malfunction indicati$e of prolems.
Corrosion Mechanism
Description
Gal$anic Corrosion Corrosion occurs at Eunction of dissimilar metals Eoined together in a suitale electrolyte or soil containing moisture
tmospheric corrosion
Corrosion that occrs from moisture associated 2ith atmos conditions. Marine and moist polluted industrial en$iron are most se$ere. Ary rural en$ironments cause $ery little corrosion.
CJ+
Corrosion of piping, presssure $essel and structural components due to 2ater trapped under insulation or /reproo/ng
Cooling 2ater corrosion
General or localized corrosion of metals caused y dissol$ed salts, gases, organic compounds or microiological acti$ity.
8oiler 2ater condensate Corrosion
General cprrosion and pitting in oiler system and condensate return piping
C>B Corrosion
C>B dissol$es in 2ater to form caronic acid 2hich lo2ers p@ & suNcient ;ty may promote general and1or pitting corrosion of caron steel
lue Gas Aue ?oint Sulfur and Chlorine in fuel 2ill form S>B, S> Corrosion and @CL in comustion and at lo2 temp these gases condense 2ith 2ater $apor to form sulfurous, sulfuric and hydrocholric acid to cause se$ere corrosion
Microiologically +nduced Corrosion (M+C)
Corrosion caused y li$ing organism such as acteria, algae or fungi often 2ith presence of tuercles or slimy organic sustances
Soil Corrosion
Aeterioration of metals e*posed to soils
Caustic Corrosion
Localized corrosion due to concentration of caustic or al-aline salts that usually occur under e$aporati$e or heat transfer conditions. General corrosion can occur depending on al-ali or caustic solution strength
Aealloying
Selecti$e corrosion 2here one or more constituents of alloy are preferentially attac-ed lea$ing lo2er density (dealloyed) porous structure. Component failure may occur due to degradation of mechanical properties.
Graphitic Corrosion Cast iron comprises of graphite particles in iron matri*. GC if form of dealloying in 2hich iron matri* is corroded, lea$ing corrosion product and graphite (2ith loss of strength, ductility and density). +t usually occurs under lo2 p@, especially in contact 2ith soil or 2ater high in sulfate.
4..*ni+orm or Temp. Range (F)
""
A!ected metallurg$
ot A!ected
ll metals e*cept most nole metals
Most nole metals
C5 increase 2ith temp Caron steel, LS and Cu upto B0 . o$e B0 alloyed l surfaces usually too dry for corrosion, e*cept under insulation
+nsulated piping 1 e;pt in intermittent ser$ice or operating at CS & LS #0 to 0 SS & ASS #0 to 00 or insulated comp corrosion ecomes se$ere at metal temp 12 B#B to 0 (insulation stays 2et)
Caron steel, LS, SS and Auple* SS
SS
Scaling potential for resh CS, all grades of SS, copper, 2ater, if process side aluminum, titanium and 7i temp %#0 (90C) ase alloys. 8rac-ish or salt 2ater temp % ## (9C) may cause serious scaling.
%rimaril$ C, some LS, some 00 Series SS and Cu ased alloys
+ncreasing temp incr C5 upto point 2here C>B is $aporized
Caron steel and lo2 alloy steels
00 SS are highly resistant 00 SS and ASS also resitant
@BS>c acid A? B!0 @CL acid A? #0
Caron steel, Lo2 alloy steels and 00 SS
organisms can sur$ice temps from 0 to B
Most common materials of construction incl caron and lo2 alloy steel, 00 SS, 00 SS, luminum, Copper & 7i ase alloys
Corrosion rate increase 2ith increasing metal temp
Caron steel, Cast iron & ductile iron
#) 4*posure to high ?rimarily caron steel, lo2 strenght caustic can cause alloy steels and 00 Series General corrosion of CS at SS. temp % #: and $ery high C5 ao$e B00.
lloy 00 and some 7i ase alloys e*hiit much lo2er C5
?rimarily copper alloys (rass, ronze, tin), lloy 00 and cast iron
?rimarily gray cast iron, ut also nodular and malleale cast iron (last t2o crumle 2hen attac-ed)
Fhite iron not suEect to this damage as there is no free graphite
,ocalied ,oss o+ Thic'ness - All Industries A!ected "#uipment
Critical Factors
@ susceptile if tues matl di=erent from 3S or aes and if salt 2ater cooling used K 8uried pipelines K ship hulls are typical locations
#) or GC, cond must e met, ?resence of electrolyte, di=erent alloys (KC) & electrical connection B) C5 high if small to C ratio. ) More nole material to e coated ) Same alloy may act as anode & cathode to surface /lms, scale or local en$iron.
#) ?iping & e;pt 2ith oper temp lo2 to allo2 moisture to e present. B) Coating poor condition B) 4;pt cycled 12 amient and high 1 lo2 oper temp. ) 4;pt shutdo2n for long period (unless mothalled) ) ?ipe resting on support may trap moisture. ) 8imetallic connections such as Cu to l
#) Critical factors include location (industrial, marine, rural)U moisture (humidity)U tempU presence of salts, sulfur compounds and dirt. B) Marine en$iron $ery corrosi$e (B0 mpy) & indust en$iron 2ith suDur compounds can form acid ("#0 mpy) ) +nland moderate C5 (#" mpy) ) Ary rural en$iron lo2 C5 (P#mpy) ) Cl, Dy ash, @BS from cooling to2er, furnace stac-s acceler corr.
#) 4;pt 2ith damaged insul, $ap arrier, 2eatherproof or mastic or protrusion thru insulation. B) 4;pt 2ith 2elded insul support rings, at ladder & platform clips, lifting lugs, nozzles. ) Aamaged or lea- steam tracing ) Local paint damage ) Aead legs, $al$es and /ttings ) missing caul-ing & insul plugs should e replaced and sealed.
#) ?oor design or installation allo2 2ater to trap can increase CJ+ B) Cyclic or intermittent ser$ice can increase CJ+ ) 4;pt operating elo2 A?, Cl leach from insulation, plant located in area of high rainfall or marine are prone to CJ+ ) 4n$ironment that pro$ide airorn contaminants li-e Cl, S>B increase CJ+
CF corrosion is concern 2ith 2ater"cooled @ and cooling to2ers across all industries.
#) CF corrosion and fouling closely related. B) increasing CF o1l temp increase fouling and corrosin rate. ) increasing >B increases CS corr. ) Lo2 $elocity (P ?S) li-ely to cause fouling. ccelerated corrsion y CF if used on shell side ) Cu1Hinc alloys can su=er SCC if ammonia or ammonium compound present in CF 9) 45F pipe can su=er 2eld 1 @H corrosion in fresh or rac-ish 2ater. :) 3i may su=er hydrding emrittle ment, generally ao$e #!0 2hen connected to anodic material.
4*ternal treatment system K deaerating e;upment K feed2ater lines, pumps, and economizers K steam generation system on oth the 2ater and /re sides K condensate return system.
#) 8F corrosion is usually result of dissol$ed gases, >B and C>B causing >B pitting corrosion and caronic acid corrosion B) Corrosion protection in oiler y continuous maintaining magnetite (e>) layer ) mmonia SCC can occur due to hydrazine, neautralizing amines or ammonia comp of Cu"Hn alloys
#) 8F and condensate sys. B) 4uent gas of shift con$ertors in @B plant 2hen temp drop elo2 de2 point 00 (C5V#000 mpy noted). ) >@ sys of regenertors on C>B remo$al plant
#) increasing partial press of C>B causes lo2er p@ and higher C5. B) Corrosion occurs in li; phase and 2here C>B condenses from $apor. ) +ncreasing Cr in steels o=ers no impro$ement in resist unitl min of #B reached.
#) ired heaters and oilers urning fuel 2ith S ha$e potential for @BS> A?C in economizer and stac-. B) @5SG 2ith 00 SS heaters can su=er CL"SCC from gas side if temp 2ater P @CL A? K if com turine atmosph include Cl (from cooling to2er drift)
#) Since all fuel contain S, sulfurous and sulfuric acid A? corrosion can occur if metal temp is elo2 A?. B) Ae2point of sulfuric acid depend on conc sulfur trio*ide in Due gas, ut typically B!0 (#!C). ) Ae2point of @CL acid depend on conc of hydrogen chloride, ut typically #0 (C).
#) Most often found in @, ottom of storage tan-s, piping 2ith lo2 Do2 and in contact 2ith soil. B) lso found in 4;pt 2hen hydrotest 2ater not remo$ed. ) Storage tan-s and 2ater cooled @ if CF treatment not proper. ) ire 2ater systems can e a=ected.
#) stagnant or lo2 Do2 conditions of 2ater promote m"organism gro2th. B) >rganisms can sur$i$e under se$ere cond e.g. lac- of >B, light or dar-, high salinity, p@ 0 to #B ) System ecome inoculated unless controlled ) ll organism re;uire source of C, 7 & ? for gro2th and thri$e on inorganic sustances (S, 7@, @BS) and organics (@C, organic acids). ) Lea-age of @BS or @C may lead to massi$e iofouling and corrosion
Jnderground piping and e;pt, uried tan-s, ottoms of storage tan-s and structures
#) 7o single parameter, multiple characteristics must e comined to estimate soil corrosion as in S3M S3? :#, ?+ 5? !0, !#. B) Soil resisti$ity used to estimate corrosi$ity. Soil 2ith high moisture, high dissol$ed salt conc, lo2 p@ are most corrosi$e. ) S" interface more susceptile ec of moisture & >B a$ailaility ) Gal$anic corrosion, dissimilar soil, stray current, M+C factors a=ect SC.
#) Most often in oilers, steam generators, @ B) ccel localized corrosin may occur in preheat @, furnace tues, transfer line in crude unit.
#) caustic sometimes added for neautralization or as reactant (may enter 8F 2hile regen of demins) B) Some process units use caustic soln to remo$e sulfur comp, or chloride comp. ) conc mechanism must e*ist to uild caustic strength (A78, e$ap and deposition)
#) underground C+ pipe e*posed to certain soils. B) in CF, @ tues (8rass, l rass) in some rac-ish and sea 2ater. ) 8F piping and aftter oiler comp incl ronze pumps, monel strainers, rass ?G.
#) Aealloying occurs usually 2ith $ery speci/c alloy"en$iron com. B) 4*tent of dezinci/cation increase 2ith increasing zinc content.
Graphitic corrosion can occur in soft 2ater, salt 2ater, mine 2ater, dilute acid and in u1g piping e.g. F piping, pumps, impeller, /re 2ater piping.
#) GC is usually limited to $ery speci/c m"structure"en$iron comination. B) Aamage occurs 2ith moisture or a; phase elo2 B00 (<C). ) Graphite is cathodic to +ron matri*, preferentially corrodes and protects graphite in 2ater or soils. ) Most damage in stagnant cond 2ith high sulfate.
%re&ention
Inspection Monitoring
#) 8est method is good design. Ai=erent alloys should not e in contact in conduct en$iron. B) Coating helpful ut more nole materal to e coated ) or piping, insulating olt slee$es & gas-ets may e used ) in G+ pipe, large to small C protects steel (elo2 #0)
#) cti$e material su=er general th- loss or cre$ice, groo$e or pitting corrosion B) node corrosion higher near Eunction ) 6isual inspection & J3 gauging are e=ecti$e to detect gal$anic corrosion.
Surface preparation and proper coating application are critical for long"term protection
#)ttac#)ttac- can e general or localized, if moisture trapped B) +f no coating, th- loss can e general y iron o*ide (red rust) scale forms. ) 63 and J3 for th- loss
#) Since maEority of matl prone, so est is to use paint1coating, paint1coating, maintain insulation 1 sealing. B) lame spray l coating on CS, corrodes preferentially y gal$anic action to protect CS. ) @igh ;uality non metallic coatings pro$ide long term protection. ) Lo2 Cl insul should e used on 00 SS. ) L foil 2rapped on SS piping and e;pt is e=ecti$e arrier under insulation. 9) Closed cell foam glass insul holds less 2ater than mineral 2ool.
#) CS & LS SuEect to localized pitting corrosion or th- loss. fter insul remo$al CJ+ appears as loose, Da-y scale B) 00 SS & ASS localized pitting. or 00 SS calcium silicate insul can cause Cl"SCC ) +nspection plan for CJ+ should e systematic approach, consider oper temp, type and age 1 cond of coating and insul, sign of insul, sealant damage. ) +f e*ternal co$ering in good condition, no reason to suspect damage ehind. ) Jse multiple techni;ues to de$elop cost e=ecti$e approach approach i.e. e.g. partial 1 full insul remo$al, J3 th-, ?ro/le 53 (small ore piping), 7eutron 8S for 2et insul, deep 4C insp, +5 scan for 2et insul, guided 2a$e J3
#) Aesign for process side inlet temp P #0 (90C) B) Min and ma* $elocity must e maintained in salt 2ater system ) Jpgrade tue metallurgy in high Cl, high process temp, lo2 $el systems ) ?eriodic cleaning of tue +A and >A for clean @3 surfaces ) CF should e on J"tue side to minimize stagnant areas.
#) CF corrosion can e general corrosion, pitting corrosin, M+C, ouling, SCC. B) Jn/rom corrosion of CS 2hen dissol$ed >B present. ) Localized corrosion may result from underdeposit corrosion, cre$ice corrosion or M+C. ) Corrosion of 45F 2eld appears as groo$ing along fusion line. ) Monitor $ariales that a=ect corrosion and founling i.e. p@, >B, C>C, io acit$ity, CF o1l temps, process lea-s ) @ J"factors (performance measure) pro$ide pro$ide info on scaling and fouling. ) 4C or +5+S inspection of tues. 9) Splitting representati$e tues.
#) >B sca$enging treatment treatment include #) Corr from >B is pitting type (redish ferrous (cat sodium sul/te or hydrazine) in o*ide) 2ith $ery small ;uantity. deaerator. B) Corr in cond return syst from C>B tends to B) +f scale 1deposit control e a smooth groo$ing of pipe (Eagged /r tree 1magnetite maintenance treatment type). scheme does not minimize C>B in ) Fater analysis commom montg tool to cond return system, an amine assure treatment system performance. inhiitor may e re;uired. ?arameter incl p@, conducti$ity, chlorine or residual iocide, and 3AS to chec- for lea-s in form of organic compounds. ) 7> proacti$e insp methods ) Aeaerator crac-ing chec- y FM?+
#) corrosion inhiitors can reduce corr in cond system. 6ap phase inhiitors re;d to protect against condensing $apor. B) increasing p@ % 9 can reduce corrosion in condesate sys. ) Jpgrading to SS for plant producing or remo$ing C>B. ) 00 SS and ASS also resistatn ) condensate sys e*periencing C>B corrosion usually due to operating prolems
#) Localized thinning or pitting corrosion of CS. Aeep pitting and groo$ing groo$ing in area of turulence 1 impingement. (M4S type pattern) B) 63, J3 and 53 for general & local th- loss in 2ater 2etting anticipated. ) ?referential 2eld corrosion re;uire angle proe J3 or 53 )Monitor 2ater analysis (p@, e e etc)
#) Maintain ac- end of oiler and /red heater ao$e sulfuric acid A? temp B) or @5SG a$oid 00SS in F heater if CL in en$ironment ) in oil /red oilers 2ater 2ash of ash, sodium caronate to e added to neutralize acid ash.
#) S corrosion of CS & LS 2ill cause general 2astage and shallo2 pits ased on ho2 sulfuric acid condenses. B) or 00 SS feed2ater heater @5SG, Cl"SCC 2ill ha$e surface rea-ing crac-s. ) J3 thic-ness of economizer tues ) SCC of 00 SS can e found y 63 & ?3.
#) System that contain 2ater should e treated 2ith iocide such as Cl, 8r, >, J6 light etc. (contd treatment re;d) B) Minimize lo2 Do2 or stagnant zone ) 4mpty hydrotest 2ater, lo2 dry to pre$ent moisture ) Frapping and C? of u1g struct e=ecti$e to pre$ent M+C. ) remo$al of deposits (pigging, lasting, chemical clean) and iocide treatment
#) M+C usually oser$ed as local pitting under tuercles or deposit. B) Cup shaped pits 2ithin pits in CS or susurface susurface ca$ities in SS. ) in CF system, treatment e=ecti$eness measured y ocide residual, microe count and $isual appearance. ) increase in loss of @ duty may indicate fouling from M+C. ) oul smelling 2ater sign of troule.
#) SC of CS minimized y use of #) SC appears as e*ternal thinning 2ith special ac-/ll, coating and C? (last localized pitting. t2o most e=ecti$e protection) B) ?oor coating is tell tale sign of SC. ) Most common method for monitog is to measure ?S? using ref electrode near structutre (corrected for +5 drop) ) C? should e performed as per 7C4 5? 0#9<. ) ?iping may e inspected y inline insp y inline inspection de$ices, guided J3, pressure testing (indirect) or $isually.
#) 8est pre$ented thru design. B) 5educe amount of free caustic ensuring 2ater Do2, urner management ot minimze hot spot on oiler tue, minimize al-aline salt ingress in condensers ) Caustic inEection designed to allo2 proper dilution 1 mi*ing. ) CS and 00 SS ha$e serious corrosion prolem % #0
#) >ften diNcult ot predict cond for dealloy in particular en$ironment. B) ddition of certain alloy elements can impro$e resist e.g. 3in inhiits dealloy of Cu alloys, admiralty rass inhiited y small amt of ?, s, S and dealumni/cation of l"8ronze pre$ented y heat treatment to produce α and β m"structure. ) Aepending on alloy"en$iron com, C? or arrier coating may e e=ecti$e.
#) AiNcult to predict if cond 2ill cause dealloying in particular en$iron or ser$ice. B) +nternal graphitic corrosion can e pre$ented y coating or cement lining. ) 4*ternal graphitic corrosion can e pre$ented y e*ternal coating or C? in se$erely corrosi$e coil.
#) 3ypically local metal loss as groo$es in oiler tue or L3 under insul deposits. B) Localized gouging along 2aterline, circumferential groo$e in $ertical tue. ) J3 th- useful for general corrosion ut diNcult to locate localized loss. ) J3 scan and 53 may e used. ) +nEection pt inspected as per ?+ :0. ) Steam gen e;pt may re;uire 63 2ih oroscope.
#) >fter there is color change or deep etched (corroded), ut some sho2 no dimensional or $isile change. B) ttac- may e uniform (layer type) or localized (plug type). )8rass dealloy e$ident y reddish Cu color, instead of yello2 rass color. ) Graphitic corr turns C+ charcoal gray, matl can e cut 2ith -nife. ) Metallography re;uired to con/rm A4. 9) Sign hardness red may accompany A4. :) ccoustic techni;ue (loss of metallic ring) and J3 attenuation applicale, ut not J3 thic-ness measurement. !) S of dealloyed comp should consider part rittle 2ith no mech strength
#) Aamage may e 2idespread or localized. B) damage may not $isually noted e$en if full thic-ness degraded. ) Aamage area easily gouged 2ith -nife. ) Metallograpy re;d to con/rm damage. ) J3 is not good for detecting damage. 9) ccoustic techni;ue (loss of metallic ring) and J3 attenuation applicale. :) Signi/catn red in hardness of dealloy.
Related Mechanism
Soil corrosion
Corrosion under insulation (CJ+)
tmospheric corrosion K >*idation K Chloride SCC
M+C K Cl"SCC K gal$anic corrosion
C>B corrosion, corrosion fatigue and erosion1erosion" corrosion
8oiler 2ater corrosion K caronate crac-ing
t lo2er temp @CL acid may condense and promote @CL corrosion of CS and Cl"SCC of 00 SS
Cooling 2ater corrosion
Gal$anic Corrosion
lso referred as Caustic gouging or ductile gouging. 5elated mech is Steam lan-eting (A78)
Aealloying often referred to y element remo$ed as dezinci/cation, destanni/cation, denic-li/cation and graphitic corrosion. lso referred to as Selecti$e Leaching.
lso -no2n as Selecti$e leaching, GC is form of dealloying of cast iron. Ao not confuse 2ith Graphitization.
Corrosion Mechanism
Description
>*idation
>B reacts 2ith CS and other alloys at high temperature con$erting metal to o*ide scale. >*ygen is present in air (B0) used for comustion in /red heaters & oilers.
Sul/dation
Corrosion of caron steel & other alloys from reaction 2ith sulfur compounds in high temp en$ironment. ?resence of @B accelerates (sul/dic) corrosion
Caruurization
Caron is asored into material at ele$ated temp 2hile in contact 2ith caronaceuos material or en$ironment.
Aecarurization
Metal Austing
Condition 2here steel loses strength due to remo$al of caron and carides lea$ing iron matri*. Aecarurization occurs during e*posure to high temps, during @eat 3reatment, e*posure to /res or @3 gases.
MA is form of carurization resulting in accelerated localized pitting in caruriz gases and1or process stream containing C and @B. ?it form on surface and may contain soot or graphite dust.
uel ash corrosion
ccelerated high temp 2astage of matls occurs 2hen contaminats in the fuel (S, 7a, I and1or 6) form deposits and melt on metal surfaces of /red heaters, oilers & Gas turines. Molten salts (slag) dissol$e surface o*ide and enhance transport of >B to surface to reform iron o*ide at e*pense of tue 2all or comp. ctual cause of 2astage is corrosion of clean unproteted steel
7itriding
hard, rittle surafce layer 2ill de$elop on some alloys due to e*posure to @3 process containing high le$els of 7B compounds such as ammonia or cyanides, particularly under reducing conditions.
4.4. /igh Te Temp. Range (F)
A!ected metallurg$
CS o*idation ecomes signif % #000 (!C)
ll caron steel and lo2 alloy steel. ll 00 & 00 SS & 7+ alloys 00 SS resist scaling up to also o*idize depending on #00 (!#9C) comp & temp
Sul/dation of e ase alloys usually egins ao$e 00
3ypically ao$e ##00 to allo2 C di=usion in to metal
ll caron steel, lo2 alloy steel, 00 & 00 SS. 7i alloys also a=ected depends on Cr Cu alloys form sul/de at lo2er temp than CS
Caron steel, lo2 alloy steel, 00 SS and 00 SS, Cast SS, 7i ase alloys 2ith signi/cant e content (alloy 900 & !00), @I1@? alloys
ot A!ected
Caron steel and lo2 alloy steels
Jsually occurs in temp range of <00 to #00 Aamge increases 2ith increasing temp.
Lo2 alloy steel, 00 SS, 7i alloys, @eat resistant alloys (Currentl$ no 'non metal hich is immune to MD at all conditions)
Corrosion occurs y this ll con$entional alloys used mechanimsn only if metal for process heaters and temp is ao$e temp of li; oilers susceptile. species
alloys of 0Cr" 07i sho2 impro$ed resistance
7itrid egins % 900 7itrid se$ere % <00
7i ase alloys (containg 0 to !0 7i) are more resistant
(%:0, preferential grain oundary nitrid may lead to micro"crac- and emrittlement)
Caron steel, lo2 alloy steel, 00 SS & 00 SS
perature Corrosion (0411F) - All Industries A!ected "#uipment
Critical Factors
ired heaters, oilers, comustion e;pt, piping operating % #000
#) +n general resist determined y Cr content. +ncreasing Cr le$el produce protecti$e o*ide scale B) ?resence of 2ater $apor can signifcant accelerate o*idn rate of some steel incl
#) ?iping and e;upt at high temp in sulfur containing stream. B) Common area of concern incl CC K co-er K $acuum K @? units ) @eaters /red 2ith oil, co-e gas (fuel) 2ith S ) 8oilers & high temp e;pt 2ith Sulfur containing gas
#) Susceptiility of alloy is y aility to form protecti$e sul/de scale. B) 5esistance determined y Cr. +ncreasing Cr increase resistance to sul/dation (7i alloys similar to SS 2ith similar Cr content). ) Sul/d primary due to @BS and other sulfur comp 2hich react to form @BS (C5 not ased on S alone). ) Sul/de scale o=ers protection depend on alloy & process se$ertiy
#) @ tues most common type of e;pt susceptile to carurization. B) Co-e deposit promote caruriz, particularly during deco-e cycles 2here temp e*ceeds normal oper temp. ) Caruriz found in Co-er units & catalytic reformers K ethylene pyrolosys and steam reformers. Caruriz occurs during deco-ing cycles.
#) 3hree conditions must e*ist (Carurizing en$iron K @3 % ##00 K susceptile material ) B) Cond fa$oring carurization incl high gas phase C acti$ity (@C, co-e, gas rich in C>, C>B, C@) and lo2 o*ygen potential (min >B or steam). ) +n CS & LS, C react for form hard, rittle surface that may crac- or spall on cooling. ) Carurization can cause loss of @3 creep ductility, loss of ament temp properties (toughness 1 ductility), loss of 2eldailiy and C5. ) 00 SS are more resistant than CS and LS due to higher Cr & 7i.
#) ny e;pt e*posed to high temp, heat treated or e*posed to /re. B) ?iping & e;pt in hot @B ser$ice in @? units, catalytic reformer, /red heater tues K ?6 components hot formed during farication can e a=ected.
#) Matl must e*pose to gas 2ith lo2 caron acti$ity so caron 2ill di=use to surface & react 2ith gas. B) Aepth of decar depends on temp and e*p time. Shallo2 decar can slightly decrease strength ut no e=ect on o$erall performance (@3@ may e present). ) Loss in room temp 3S and creep strength.
#) ?rimary @ tues, thermo2els andfurnace components in carurizing en$ironemnt B) Catalytic reformer heater tues, co-er unts, G3Ws, Methanol reformer outlet piping , hydrodeal-ylation furnaces and reactors
#) MA is preceded y carurization and rapid metal 2astage. B) MA in$ol$es comple* reactions 2ith reducing gas e.g. @B, C>, C. ) Mechanim of MA a" Saturation of metal y caruriz. "?recipitation of metal carides at G8 and metal surface. c"Aeposit of graphite from atmosph on to metal caride at surface d" Aecomp of metal caride under graphite K metal particles e" urther deposit of graphite catalyzed y metal particles ) MA can occur alternating reducing and o*idizing conditions ) +n high 7i alloy, MA occurs 21o formation of metal caride.
#) ny /red heater, gas turines urning fuel oils 2ith 6 and 7a. B) @ tues some times not a=ected due to s-in temp less than threshold temp of slag, ut hangers 1supports are a=ected. ) >il /red oilers on fuel 21o 6 less prone to Li;uid ash corrosion. ) or 2ater2all, if temp elo2 M? of pysrosulfate (:00), damage minimized. ) Steam generating press P#!00 psi nearly immune
#) Se$erity of damage depends on conc of contaminants in fuel, sulfur content and metal temp. B) li;uid species (slag) are di=erent for oil and coal ash. a"or oil ash, superheater and reheater corr y mi* of $anadium pento*ide and sodium o*ide or sodium sulfate (M? X #000). or coal ash, sodium & potassium iron trisulfate (M? X#00 t0 ##0). " or 2ater 2all corr in coal /red, li; species of pyrsosulfate of 7a & I. c" 5educing cond e.g. Due gas rich in @BS, C> and @B aggra$ate corr (B" times faster) ec protecti$e iron o*ides do not form readily (results in proous iron sul/de 2hcih is less protecti$e)
7itrid has een oser$ed in steam methane reformers, steam gas crac-ing (ole/n plants) and 7@ synthesis plants.
#) 3emp must e high engough for thermal rea-do2n of 7 from ammonia or other comp. B) @igh gas phase 7 acti$ity (high pp of 7B) promotes nitriding. ) 7itriding causes loss of @3 creep strength, amient mech properties (toughness 1 ductility), 2eldaility and corrosion resistance
%re&ention
Inspection Monitoring
#) 5esistance est y upgrading to more resist alloy. B) Cr is primary alloy element to resist o*idation. ) lso Si and l ut ad$erse e=ects on mech properties (used in special alloys for urner tips, heater supports)
#) CS, LS su=er thinning and co$ered 2ith o*ide scale on outer surface. B) 00 SS & 7+ alloy ha$e $ery thin dar- scale (generally no metal loss) ) Monitor process cond for @3 trend ) Monitor temp 2ith +5 scan or s-in 3C ) Measure th- loss 2ith e*ternal J3
#) 5esist generally achie$ed y upgrading to higher Cr alloy B) 4;pt constructed 2ith clad or solid 00 K 00 SS. ) l di=usion treatment of LS sometimes reduce sul/dation rates and scaling
#) Corrosion is most often in form of Jniform thinning ut can also e localized or high $el erosion corrosion. B) Sul/de scale co$ers component ) ?rocess cond monitg for increae in 3emp & sulfur le$els ) 3emp montg y s-in 3C or +5 scan ) 4*ternal J3 & ?ro/le 53 for thinning 9) ?M+ for alloy $erifcation and mi*up chec-
#) Select alloys 2ith strong o*ide layer or sul/de /lm formers (silicon & luminum) B) 5educe caron acti$ity of en$ironment thru lo2er temp and high >B1Sulfur partial pressures. ) Sulfur inhiits carurization and often added in small amounts into process streams of steam1 gas crac-ers of ole/n & thermal hydroal-ylation units
#) Aepth of carurization con/rmation y metallography B) Caruriz can e con/rm y sustantial increase in hardness and loss of ductility ) 6olumteric increase in ad$ance stage ) +ncr in erromagnetism of some alloys. ) ormation of metal carides depleting matri* of caride forming element ) +ntial stage inspection is diNcult (hardness and M5 from process side) K Aestruicti$e and magnetic ased tech (4C3) ha$e een used. 9) Aetermine increase of ferromagnetism (magnetic permeaility) useful for alloys paramagnetic initialy (austenitic) :) d$ances stages crac-ing y 53,J3 & magnetic techni;ue
#) Control the chemistry of gas phase and alloy selection (? 5? <#). B) LS 2ith Cr & Mo form stale caride & more resistant. ) Steels for @3 @B should e selected in a1c 2ith ?+ 5? <#.
#) Aamage $eri/ed y metallography. B) Aamage occurs on surface e*posed to gas ut thru 2all in se$ere case. B) Aecar layer free of caride, CS is pure iron. )ield metallography & replica (M5) can con/rm decar. ) Aecar results in softern con/rmed y @ardness testing
#) Sulfer (usually as @BS) forms protecti$e sul/de layer to minimize carurization & MA (retards Caron trasnfer from atmosph to metal & suppress & graphite nucleation & gro2th). B) Sulfur is catalyst poison in some units, so @BS in process not al2ays practical. B) l di=usion treatment to asemetal is sometimes ene/cial.
#) +n LS 2astage can e uniform ut usually in small pits /lled 2ith residue of metal o*ides and carides. B) Corrosion product is $olumnous caron dust contains metal particles, metal o*ides and carides. lo2 can s2eep dust lea$ing ehind pitted metal. ) +n SS &@S local attac- 2ith deep and round pits. ) Metallography sho2s metal is hea$y carurized under attac- surface. ) or heater tues compression 2a$e J3 eNcient method & scans large areas. ) 53 for pitting and 2all thinning 9) 6+ on internal surface :) iltering of cooled furnace or reactor euent may yeild metal particles tell tale sign of MA.
#) C can e pre$ented y lending or changing fuel sources (min contaminants) & maintain hot component elo2 temp of M? of deposits. B) 8urner design K management reduce Dame impingement and hot spots. ) +nEect special additi$es into fuel to incr M? of slag or /ring 2ith lo2 o*ygen. ) Change tue hanger & supprt to 0Cr 07i (ut design for lo2 stress rupture strength)
#) or CC of S@ & 5@ tues, ash deposit in t2o layers. @ard scale 2hen remo$ed steel surface has Talligator hideT appearance due to shallo2 groo$es. B) or 2ater 2all tues urning oil, appearance is series of circumf groo$es ro crac-s (actually $ shaped corrsosion fatigue crac-s). ) crac-s form due to thermal 1 corr fatigue as ash layers uilds, falls e*p and insul steel to temp spi-e y #00 . ) or coal ash, appearance is smooth interface 12 glassy slag and metal. ) 6isual inspection suNcient to detect hot ash corrosion. 9) Metal loss se$ere (#00"#000 mpy) 2ith presence of slag. 9) 3ues need grit lasting to remo$e tenacious glass li-e ash deposit for J3 thic-ness.
#) Changin to more resistant alloy 0"!0 nic-el usually re;d. B) +t is usually not practical to modify process to reduce 7B partial pressure or lo2er temp.
#) 7itrid con/ned to surface, has dull, dargray appearance. t initial stage, damage only seen 2ith metallography. B) +n ad$anced stage, matl e*hiit $ery high surface hardness, concern for cracde$elopment in nitride layer. )7itrid of LS upto #BCr cause increase in $olume. 7itride layer can crac- 1 Da-e. ) SS from thin rittle layer that may crac- or spall from stress. ) 7 di=uses in surface and forms needle li-e particles of iron nitride (e7, e7) only con/rmed y metallography. ) Change in surface color to Aull gray. 9) @ardness testing (00"00@8) can indicate nitriding. :) 7itrided layer magnetic, so chec- 00 SS for magnetism as screening. !) 4C3 in some cases K in ad$ance stage of crac-ing ?3, J3 & 53 for crac-ing.
Related Mechanism
>*id damage y Surface scaling (int o*id not in scope)
Sul/dation also -no2n as Sul/dic Corrosion. @igh temperature sul/dation (in @B ?resence)
Se$ere form of carurization -no2n as Metal Austing
@igh temperature hydrogen attac(@3@)
MA is also -no2n as Catastrophic carurization
@ot corrosion, hot ash corrosion, molten salt corrosion, oil ash corrosion and coal ash corrosion all terms used for this mechanism. Circumf crac-ing in 2ater2all tues is similar to thermal fatigue aggra$ated y a corrosi$e en$ironment
Simlar gas"metal reactions are Carurization & Metal dusting
Corrosion Mechanism
Description
Chloride SCC
Surface initiated crac-s of 00 series SS and some 7i ase alloys under comined action of tensile stress, temp & a;ueous Cl en$ironment (presence of dissol$ed >B increases crac-ing propensity)
Corrosion fatigue
Crac-s de$elop under the comined e=ects of cyclic loading and corrosion, often initiates at a stress concentration such as a pit in surface.
Caustic SCC (Caustic 4mrittlement)
SCC characterized y surface initiated crac-s in piping & e;pt e*posed to caustic (7a>@ & I>@), adEacent to non ?F@3 2elds
mmonia SCC
;ueous streams containing ammonia may cause SCC in some Cu alloys. CS is susceptile to SCC in anhydrous 7@.
Li;uid Metal 4mrittlement (LM4)
Crac-ing that result 2hen certain molten metals come in contact 2ith speci/c alloys. Crac-ing is sudden and rittle in nature.
@ydorgen 4mrittlement
Loss in ductility of high strength steels due to the penetration of atomic @B can lead to rittle crac-ing
4htanol SCC
Surface initiated crac-s of CS under com action of tensile stress and fuel grade ethanol (G4 S3M A!09) or G4 1 gasoline lend. Aissol$ed >B increases propensity for crac-ing
Sulfate SCC
Surface initiated crac-s in copper alloys in sulfate solutions o$er many years.
4.3. "n&iro Temp. Range (F)
SCC occurs at metal temp ao$e #0, increase in temp increases susceptility.
A!ected metallurg$
ot A!ected
ll 00 Series are highly susceptile. ASS more resistant. 7+ alloys resistant, not immune (7i content !"#B greatest susceptile)
CS, LS, 00 series 7>3 suscepile.
ll metals and alloys.
7i alloy % highly resistant and % near immune
Caron steel, lo2 alloy steel & 7i alloys are 00 SS are susceptile more resistant
ny 3emperature
Some Cu alloys in a;ueous 7@ or 7@ compunds (8rasses Cu"Hn including admiralty and l"rass are susceptile) CS in anhydrous 7@
Many common used matls i.e. Caron steel, lo2 alloy steel, high strength steel, 00 SS, 7i ase alloys, Cu alloys, l alloys, 3i alloys
<0"#0 Cu7+ and :0"0Cu7i are nearly immune 00 SS and 7+ alloys immune
CS, LS, 00 SS K ?recip 4=ect @ardenale (?@) SS and some pronounced from high strength 7+ ase alloys am temp to 00 (#
ll CS susceptile
7ot SCC ut general corr in some l and Cu alloys and ad$erse e=ect on non metal
Some Cu alloys (admiralty) rass more susceptile
<01#0 and :010 Cu7i more resistant 7on"Copper alloys immune
nment Assisted Crac'ing - All Industries A!ected "#uipment
Critical Factors
#) ll 00 series piping and ?6 components. B) SCC seen in 2ater"cooled condensers & process side of crude to2er >@ condsen. B) Arains in @? units are susceptile during start"up or shutdo2n if not purged. ) 4*ternal Cl"SCC on insul surfaces if 2etted. ) 8ello2s & tuing in @B recycle streams 2ith Cl
#) 7o lo2er limit for Cl, ec al2ays potential to concentrate. B) @eat transfer cond increase susceptiility as Cl can concentrate, 2et dry cond conduci$e to crac-ing ) SCC occurs ao$e B p@, lo2er p@ cause uniform corrosion. ) Stress may e applied or residual ) ASS ha$e impro$ed resistance o$er 00 SS ut not immune.
#) 5otating e;upt " gal$anic couples 12 impeller and shaft may cause pitting on shaft. ?itting act as S5 to cause (transgranular) crac-. B) Aeaerator crac-ing in late #
#) Crac-ing more li-ely in e$nirons that promote pitting under cyclic stress (thermal, $iration, A4). B) 3here is no fatigue limit in C. ) Corrosion promotes failure at lo2er stress and no of cycles than endurance limit. ) Crac- initiation sites incl pits, notches, surface defects, /llet 2elds, changes in section.
#) C4 found in 4;pt handling caustic, @BS & mercaptan remo$al units, e;pt that uses caustic for neutralization in sulfuric and @ al-ylation units. B) ailures occured in improper heat traced pipe & e;pt, heating coils. ) C4 occur due to steam cleaning in caustic ser$ice. ) 3races of caustic can conc in 8F and cause C4 of oiler tue in 2et and dry cond due #) Cu"Hn alloy tues in @4 K 7@ may e as contaminant or added as neutralizer. B) CS is used in 7@ storage tan-s, pipign & e;pt in refrg & some L> re/ning process.
#)Susceptiility is function of caustic conc, temp and stress le$el. B) if conc mecanism present, conc of 0 " #00 ppm suNcient for crac-ing. B) Stresses (approaching RS re;d) can e residual or applied. ?F@3 is e=ecti$e to pre$ent SCC. ) Crac- progragation rate increase dramatically 2ith temp (can go thru 2all in hours during temp rise). ) Special care 2ith steam tracing & steam out of non ?F@3 CS e;pt.
#) +n a /re molten metals may drip or contact 2ith susceptile matl li-e Hn gal$inzing, Cd electrical housing, melted Cu. B) LM4 couples (SS00 ru 2ith gal$ steel, +n re/nery, @g is found in crude oils can condense emrittling rass, alloy 00, 3i or l @ comp. ) LM4 of l comp occurred in L7G and cryogenic gas plant due to condensing li;uid mercury.
#) LM4 occurs in $ery speci/c com of metal and lo2 M? metals e.g. Hn, @g, Cd, ?, Cu and Sn. B) 6ery small ;uantity of molten metal suNcient to cause LM4 21o high 3S. ) 3S promotes crac- propagation rate, crac- may pass thru 2all in seconds of contact 2ith LM
#) or Cu alloy Hinc content of rass a=ects susceptiility, as zinc incr ao$e #. 2ater phase 2ith 7@ or 7@ compoung must e present, p@ %!., residual stresses, occurs at any temp, and >B in traces re;d. B) or Steel anhydrous 7@ 2ith P0.B 2ater cause crac-s in CS, SCC reported at "C in la test, ?F@3 eliminates susceptiility of most steels (3S P:0 -si), contamination 2ith >B increases tendency, high residual stress ma-e susceptile.
#) CS piping and $essels in 2et @BS ser$ices in CC, @?, amine, sour 2ater if 2elds not ?F@3. B) Storage sphere made 2ith slighly @S steel more susceptile. ) @igh strenth olts and springs $ery prone (%#0Isi 3S asor @B during electro plating and crac-) )Cr"Mo $essels in @? units crac-s at 2elds & @H 2hen hardness % B8@7
#) conditions re;d i.e. @B at critical conc in metal, micro structure susccetile to emrittlement, stress ao$e threshold B) @B can come from 2elding y 2et electrode 1 Du* (delayed crac-ing) K cleaning or pic-ling in acid K 2et @BS ser$ice or @ acid ser$ice K plating (@B Da-ing) K C? ) 3h- 2all components $ulnerale, ta-e logner for @B to di=use out. ) Jmtemp martensite & pearlite more susceptile than tempered martensite at same strength. ) CS se$erely @B charged as lo2er toughness.
#) Li-ely decrease y ?F@3 or applying coating B) $oid design 2ith local tensile stress, use of lap seam 2eld & cold 2or-ing
#) ield oser$ation @igh stressed, cold 2or-ed component 2ith stress conc are susceptile to crac-ing K crac-ing in G4 S3M A!09 2ith 2ater content K corr inhiitor e=ect not -no2n. B) La oser$ation (SS53) Aisso$led >B most imp in 4"SCC, no crac-ing in deaerated cond K ma* potential in 2ater content 0.#"0. y $ol K lends of G4 & gasoline 2ith as lo2 as B0 $ol G4 K gal$ coupling of old and ne2 steel increases 4"SCC K Cl content increase changes mainly from +G to 3G
#) Mostly @ tues in >@ distillation systems 2ith sulfates. B) Aamage oser$ed in Crude to2er >@ @
#) ?rocess must contain sulfates, 7@ is usually present in lo2 conc. B) Crac-ing occurs o$er many years e.g. #0"# years to cause tue lea-
%re&ention
Inspection Monitoring
#) Jse resistant matl (Auple* K 7ic-el ase) B) Fhen hydrotesting use lo2 Cl 2ater and dry thouroughly and ;uic-ly ) Coatings under insulation ) $oid design 2here Cl can deposit or stagnate ) @3 S5 of 00 SS may reduce residual stress possile ut sensitization prolem incr susceptility to ?3SCC, distortion and reheat crac-ing.
#) S8 crac-s can occur from process side or under insul. Matl sho2s no $isile signs of corrosion. B) SCC crac-s ha$e ranches and $isually detected y craze crac- appearance. B) Metallog sho2s typical transgranluar crac-s ut +GC of 00 SS also seen. ) Felds in 00 SS ha$e ferrite (duple* structure) more resistant to CL"SCC. ) racture surfaces ha$e rittle appear. ) Surface crac-s may e $isually seen. ?3 or phase analysis 4C preferred methods. 9) 4*tremely /ne crac-s diNcult to /nd 2ith ?3. ?olish or @? 2ater last may e re;uired. 9) J3 (53 not sensiti$e to detect /ne crac-s, ut at ad$anced stage)
#) 5otating 4;pt Modify corr en$iron y coatings 1inhiitors, minimize gal$anic e=ect, use more C5 material. B) Aearators ?roper F and condensate chemical control K minimize residual stress 2ith ?F@3 K smooth 2eld contour. ) Cycling oilers Slo2 start"up to minimize A"4*p and 2ater chemistry under control
#) C fracture is rittle, 3ransgranular as in SCC ut not ranched, multiple crac-s B) Crac-ing sho2s Little plastic deform at /nal fracture. ) +n cycling oiler, crac- on 2ater side of uc-stay attach 2eld 2ith 2ater2all, circular pattern, ulous in *"section. ) in sul/dizing en$iron, crac-s /lled 2ith sul/de scale ) 5otating 4;pt J3 K M3 for crac- detect 9) Aeaerators FM3, tight crac-s :) Cycling oilers uc-stays, J3 or 4M3
#) Crac-ing e=ecti$e pre$ented y ?F@3 of CS Q#000 (repair 2elds, int 1 e*t attach 2elds) B) 00 SS little ad$antage o$er CS, 7i alloys more resitant at higher temp or caustic conc. ) $oid steam out of non ?F@3 CS, 2ater 2ash /rst, use L? steam for short periods. ) +nEection sys design re;d to ensure caustic properly dispersed efore entering @3 crude preheat system
#) Crac-ing typically parallel to 2eld in ase metal, ut also in 2eld or @H. B) ?attern is spider 2e of small crac-s, 2hich initiate at 2eld Da2s. ) Crac-s con/rm y metallography as S8 intergrannular, typical occur in as"2elded CS and /ne, o*ide"/lled. ) Crac-ing in 00 SS typical transgranular and diNcult to distinguish from Cl"SCC. ) Crac- detection est y FM3, 4C, 53 or CM (surface prep y lasting re;d). ) ?3 not e=ecti$e for scale /lled crac-s and should not e used singly. 9) Crac- depth y SFJ3 K 43 for Crac#) or CJ alloys Cu"Hn alloys sho2 #) or Cu alloys Surface rea-ing crac-s may impro$ed resistance as Hn content sho2 8luish Corrosion product. @ tues sho2 decr P#, <0"#0 Cu7i & :0" single or ranched S8 crac-s, can 0Cu7+ nearly immune, SCC in intergranular or transgranular. steam ser$ice controlled y a) Monitor p@ and ammonia of 2ater to assess pre$enting ingress of air, 00 SS & susceptiility of Cu alloys. 7i alloys are immune ) @ tues 4C or $isual insp, rolled area B) or CS SCC pre$ented y adding susceptile 0.B min 2ater to 7@ (consider B) or CS 7on ?F@3 & @H, primarily $ap phase P 0.B), ?F@3, use lo2 intergranluar. 3S steel (P:0 -si) , 2eld hardness ) FM3 2elds in tan-s, 4*t SFJ3 using PV BB8@7, pre$ent ingress of >B 3>A, 43. in storage facilities
#) LM4 only pre$ented y protecting metal from coming into contact 2ith lo2 melting metal e.g. do not 2eld gal$ steel to 00 SS and protect from zinc coating o$erspray. B) >nce crac-ing initiated from LM4, grinding out a=ected area is not an acceptale /*.
#) M4 appears as rittle crac-s in other 2ise ductile material, con/rm only y Metallogarphy, Intergranular crac-s /lled 2ith LM metal. B) Spectrographic analysis to con/rm molten metal species. ) Aetect crac- y M3 for ferritic steel and ?3 for 00 SS and 7i ) 53 used to locate @g deposits in @ tues ec of high density
#) Jse LS steels and ?F@3 to temper microstructure, reduce hardness & stresses, impro$e ductility. B) Jse lo2 @B dry electrodes, a-e out metal 00 or higher to di=use @B. ) @ea$y 2all $essel re;uires control s1d & s1u procedures to cotrol pressursation se;uence. ) pply lining, SS cladding to pre$ent surface @B reactions in corrosi$e a;ueous seri$ce.
#) @4 crac- can intiate SS, ut mostly S8. B) Locations at high residual and tri"a*ial stress and conduci$e microstructure e.g. @H. ) >n macroscale little e$idence, some matl sho2 rittle fracture K in @S steels, crac-ing is often intergranular. ) or surface crac-s ?3,M3,FM3, J3 ) 53 not sensiti$e to @4 crac-s 9) if source of @B is lo2 temp a; en$ir, @B Du* can e monitored 2ith special instruments.
#) CS storage tan-s, piping & e;pt K transportation pipeline of G4. B) 4"SCC not reported in G4 manufacturer e;pt and tan-s or in transportation e;pt (arges, truc-s, railcars) K G4 lended 2ith unleaded gasoline (#0 $ol)
#) SCC appears as crac-s in $icinity of 2elds (parallel or trans$erse to 2elds) K crac-s tight and may e /lled 2ith corr product. B) Crac-s ranched & +G, ut 3G or mi*ed mode also reported, increased CL content shifts from +G to 3G. ) Microstructure of metal suEect to SCC are ferrite or ferrite K pearlite. ) FM3 preferred method, diNcult to detect y 63 tight crac-s /lled 2ith corr product. ) SFJ3 2here FM3 not feasile K CM 2ith less surface prep as in @H. 9) 4C3 not pro$en.
#) Life of @ tues lengthened y cleaning #1 years ut ltd pulish info a$ailale. B) <01#0 and :010 Cu7+ resist to 7@ SCC also resistant to sulfate SCC. )
#) 3ues sho2 single or ranched surface crac-s, cause slo2 lea-s (not rupture). B) 8y metallogrpahy, ranched 3G crac-s diNcult to distinguish from 7@ SCC. ) +nspect tues for crac-s y 4C or 63 ) 8ending sample of tues to detect shallo2 initial crac-s
Related Mechanism
Caustic SCC & ?SCC
Mechanical fatigue and 6iration induced fatigue
mine crac-ing & Caronate crac-ing simlar forms of al-aline SCC.
7
LM4 also called Li;uid Metal Crac-ing (LMC) 7i alloys are susceptile to 7i"7i sul/de eutectic that forms at ##:
lso -no2n as @B Da-ing, underead crac-ing, delayed crac-ing, @B assisted crac-ing, @+C. Sul/de SCC & @B SCC in @ closely related form of @B emrittlement
Similar to other reported in methanol and $arious al-aline a; solutions
7
Corrosion Mechanism
mine Corrosion
Description
General and1or localized corr principally on CS in amine treating processes. Corrosion is not caused y amine, ut from dissol$ed acid gases (C>B and @BS), amine degradation products, @eat Stale mine Salts (@SS) & contaminants.
mmonium ggressi$e corrosion in hydroprocessing 8isul/de Corrosion reactor euent streams and in units handling (l-aline Sour al-aline sour 2ater (Localized corrosion.) Fater)
mmonium chloride corrosion
General or localized corrosion, often pitting, occurring under ammonium chloride or amine salt deposits, often in the asence of a free 2ater phase.
@ydrochloric acid corrosion
@CL (a;. @CL) causes oth general and localized corrosion. Aamage in re/neries is most often de2 point corrosion as $apors containing 2ater & @CL condense from o$erhead stream of distillation, fractionation or stripping to2er. irst droplets can e highly acidic (lo2 p@) and gi$e high C5.
@igh temperature ?resence of @B in @BS streams increases @B 1 @BS corrosion se$erity of high temperature sul/de corrosion ao$e aout 00. 3his form of sul/dation results in uniform th- loss in hot circuits in hydroprocessing units.
@ydroDuoric (@) cid Corrosion
@ acid can result in high rate general or localized corrosion and may e accompanied y hydrogen crac-ing, listering and1or @+C1S>@+C
7apthenic cid Corrosion (7C)
@igh temperature corrosion that occurs primarily in crude and $acuum units, and d1s units that process certain fractions or cuts that contain naphthenic acids ( hot dry @C that do not contain free 2ater phase).
?henol (Carolic acid) Corrosion
Corrosion of caron steel can occur in plants using phenol as sol$ent to remo$e aromatic compounds from luricating oil feedstoc-s.
?hosphoric cid Corrosion (?C)
?hosphoric acid is used as catalyst in polymerization units. +t can cause oth pitting and localized corrosion of caron steels depending on 2ater content.
Sour Fater Corrosion (cidic)
Corrosion of steel due to acidic sour 2ater containing @BS at p@ . to :.0 (C>B may also e present)
Sulfuric cid Corrosion
S promotes general and localized corrosion of CS and other alloys. Caron steel @H may e*perience se$ere corrosion.
;ueous >rganic cid Corrosion
>rganic compounds in some crude oils decompose in crude furnace to from lo2 MF organic acids 2hich condense in distillation to2er >@ systems and contriute sigini/cantly to a; corrosion
3.. *ni+or Temp. Range (F)
A!ected metallurg$
C5 increase 2ith temp, ?rimarily caron steel. particularly in rich amine. 3emp ao$e aout BB0 (#0oC) can result in acid gas Dash and se$ere localized corrosion if pressure drop is high enough.
7@@S salts precipitate in CS is less resistant. reactor euent streams K L @ tues highly 2hen temp drop to #B0 to prone to erosion corrosion #0
Salts precipiate ao$e 2ater de2point 00, C5 increase 2ith incr temperature.
ll common materials susceptile, increasing resistance CS, LS, 00 Series SS, lloys 00, ASS, !00, and !B, lloys 9B, CB:9 and 3i
ot A!ected
00 Series SS are highly resistant.
00 Series SS, ASS, l alloys and 7i alloys are more resistant, (depends on 7@@S conc and $elocity).
ll common materials used in re/neries
3emperature ao$e aout 00 . +ncreases 2ith increase in temp and @BS conc.
@igh corrosion rates oser$ed % #0
lloy 00, 3i and some 7i ase alloys ha$e good resistance to dilute @CL. (3i performs 2ell in o*idiz conditions)
+ncreasing resistance caron steel, lo2 alloy steels, 00 Series SS, and 00 Series SS.
CS, Cu"7i alloys, lloy 00 7i ase alloys LS, 00 SS and 00 SS e.g. lloy CB:9 are susceptile to used corrosion 1 crac-ing and generally not suitale for @ ser$ice
7C occurs hot stream %B, ut reported as lo2 as 0.
Caron steel, lo2 alloy lloys 2ith steels, 00 SS, 00 SS and increasing Mo nic-el alloys. sho2 etter resistant 2ith Se$erity increase 2ith min B " B. temp up to :0, ut 7C depending on reported in hot co-er gas 37 of crude oil stream up to !00
Corrosion minimal elo2 B0
+ncreasing resistance caron steel, 0L, #9L and lloy CB:9.
CS and 010L SS corrode rapidly ao$e 0
C5 +ncrease 2ith +ncr in temp
+ncreasing resistance caron steel, 0L SS, #9L SS and lloy B0.
?rimarily a=ects caron steel
SS, CJ alloys and 7i alloys are usually resistant.
+ncreasing resistance Caron steel, #9L SS, lloy B0, @SC+, high nic-el C+ , lloy 8"B & lloy CB:9.
ll grades of caron steel are a=ected
Most C5 alloys crude to2er >@ system not a=ected
m or ,ocalied ,oss in Thic'ness - Re5ning A!ected "#uipment
Critical Factors
#) @BS, C>B and mercaptans remo$al units K crude, co-er, CC, @B reforming, hydroprocessing, and tail gas units. B) 5egen reoiler & regenerator at high tempK lean1rich @, hot lean amine piping, hot rich amine piping, solution pumps & reclaimers are prone to corrosion
#) C tied to operation of unit. CS is suitale, ut prolem due to faulty desing or operation. B) Most to least aggressi$e M4, AG, A+?, A4, MA4 ) Lean amine sol not corrosi$e (lo2 cond, high p@), ut @SS % B can increase C5. ) Lean amine sol contain @BS to maintain stale eS /lm. ) @BS, 7@, @C7 accelerate corr in 5>@C and piping. 9) @igh $el & tur cause local thic- loss, or CS limit "9 fps (rich amine) and B0 fps (lean amine)
#) @? Jnits 7@@S salts precipitate in reactor stream at #B0"#0 K fouling and $el corrosion at air cooler header o*, piping. B) CC Jnits 7@@s P B 2t ut $el & cyanides may remo$e protecti$e eS ) SFS K mine units @igh conc of 7@@S in stripper >@ piping, condenser, accumulator ) Aelayed Co-er @igh conc in gas conc plant d1s.
#) 8elo2 B 2t 7@@S conc, soln not generally corrosi$e, ao$e B incr corrosi$e 2ith incr $elocity. B) in @? & CC reactors, co-er furnace 7 con$erts to 7@ & reacts 2ith @BS to form 7@@S, at #0 it precipitates from gas stream cause fouling 1 plugging if not 2ashed. ) 7@@S salt deposit cause under deposit corrosion & fouling. ) >B & e in 2ash 2ater can lead to corrosion & fouling in @? reactor
#) Crude 3o2er >@ 3o2er top, top trays, >@ piping and @ face 7h and amina salts condensing from $apor phase. B) @? reactor K Catalytic 5eformer K CCJ K Co-er 4uent stream 7@CL salt fouling and corrosion.
#) 7@CL salts may precipitate 2hen cooled in hot streams and corrode piping & e;pt e$en % 2ater A? 00. B) 7@CL salts are hygroscopic and small 2ater cause high C5 % #00mpy. ) 7@CL and amine hydrochloride form hihgly corrosi$e acid soln 2ith 2ater.
#) Crude unit +n atmosph to2er >@ system, @Cl corr occurs as /rsr 2ater drop (lo2 p@) condense from $ap outlet. B) @? units Cl may enter as organic chloride in @C feed or recycle @B and react to form @CL K 7@CL salts can form in euent side as oht @CL & 7@ present. ) Cat reforming unit Cl may strip from catalyst, form @CL 2hich a=ect euent d1s e;pt.
#) Corrosion se$erity increase 2ith @CL conc and temp. B) ; @CL can form eneath 7@Cl or amine hydrochloride salt. @CL gas is not corrosi$e, ut 2ith 2ater forms @CL acid. ) CS and LS suEect to high corr 2hen e*posed to any conc of @CL at p@ P .. ) 00 SS and 00SS not usefully resistant at any con or temp. ) >*idizing agents (>B, erric, Cuprici ions) increase C5 particulary for lloy 00 & 8"B (not 3i). 9) 3i fails rapidly in dry @C ser$ice.
#) ?iping & e;pt in @3 @B 1 @BS streams incl all @? units e.g. desulf, hydrotreaters and hydrocrac-ing units B)C5 increase do2nstream of @B inEection points.
#) Sul/dation rate increase 2ith incr @BS content and increasing temp. B) C5 in gas oil desulfurizer and hydrocrac-er than naptha desulf y factor of B. ) Chorium content impro$es resist ut 2hen upto :"
#) ?iping and e;uipment in the @ al-ylation unit, Dare piping & d1s units e*posed to acid carryo$er. B) Most e;pt of CS e*cept @ acid regen to2er and acid relief neutral $essel of lloy 00 . ) @igh C5 in e;pt % #0 condesing $apors o= top of +sostripper, Aepropanzier, @ stripper. ) Se$ere fouling y e product in piping, @ and top of +sostripper and Aepropanizer to2er
#) CS forms protecti$e l scale in dry conc acid. Loss of scale y $el, tur causes high C5. B) ?resence of 2ater can destalize l scale to non protecti$e scale. ) ?rimary concern is @"in"2ater conc of acid phase ) 3ypical @ al-yl unit oper 2ith #" 2ater in acid i.e. <:"<< @"in"2ater at #0 at 2hich CS is used. ) C5 incr 2ith incr temp and decr @ conc (incr 2ater) 9) 54 in CS a=ect C5 i.e. C, Cu, 7i, Cr i.e. 8ase 1 2eld metal P 0.# 2t. 9) >B contamin increase C5 of CS and SCC of lloy 00
#) Crude and $acuum heater tues & transfer lines, 6ac otm piping, G> circuitsU @6G> and sometimes L6G> circuits. also reported in the LCG> and @CG> streams on delayed co-ing units processing high 37 feed. B) ?iping sys susceptile in high $el & tur (2elds K3F) and CAJ and 6AJ internals corrode in Dash zones y high $el droplets
#) 7eutralization num or 3otal cid 7umer (37) of crude is measure of acidity (organic acid content) as per S3M A"99. B) 37 may mislead due to family of acids & oiling points. 7C depend on acidity of stream not crude. ) S promote es and inhiits 7C upto a point. 7C is particular pro 2ith lo2 S crude & 37 X 0.#0. ) Corrosion most se$ere in t2o phase Do2, high $el or tur and hot $apor condensing in distill to2ers.
?henol e*traction facilities in lues plant.
#) Corrosion can occur in reco$ery section 2here spent phenol is separated. B) Ailute soln ("# phenol) are $ery corrosi$e in e*tract dryer cond. ) @igh $el promote localized corrosion.
#) ?iping and e;uipt in polymerization unit 2here 2ater mi*es 2ith catalyst B) Corrosion in lo2 $elocity area 2ith no circulation e.g. piping manifold, ottom of -ettle"type reoiler, partial penetration 2elds, @ 2here suNcient time to permit settling of acid droplets.
#) C conc, temp and contaminants. B) Solid ?hos acid catalysts are not corrosi$e to CS, cause se$ere corr 2ith 2ater. ) Corrosion can penetrate #1T th- steel tue in ! hrs. ) Most Corr proaly during 2ater" 2ashing oper at S1A. ) Cl can increase ?C
Concern in >@ systems of CC and co-er gas fractionation plant 2ith high @BS and lo2 7@ le$el
#) @BS conc in sour 2ater depends on @BS pp in gas, temp and p@. B) t gi$en press, @BS conc in sour 2ater decr as temp incr. ) +ncreasing conc of @BS decrease p@, elo2 . p@ corr is concern. ) o$e . p@, thin sul/de layer limts C5 or sometimes can promote pitting under deposit. ) @CL & C>B lo2er p@, 7@ incr p@ signi/cantly results in al-aline sour 2ater and 7@@S corrosion. 9) ir or o*idant increase C5 and produce pitting or underdeposit attac-.
#) S al-ylation units and 2aste 2ater treatment plants. B) rea of l-ylation unit reactor euent K reoiler, A+8 >@ systemK Caustic treating sections K 8ot of fractionation to2ers
#) CS C5 increase signi/cantly if $el % B" fps or acid conc P 9. B) Mi* point 2ith 2ater release heat and high C5 2here acid diluted. ) >*idizers greatly increase C5.
#) ll CS piping & e;pt in crude to2er, $acuum to2er, and co-er >@ system incl @, to2ers and drums. B) Corrosion occur 2here 2ater accumulates or 2ater droplets impinge and turulent areas e.g. 8otm of >@ @, oots of separtor drum, elo2s, tees, d1s of C6.
#) Lo2 MF acids incl formic, acetic, propionic and utyric acid. B) ormic and acetic acid are most corrosi$e, solule in naptha, once 2ater condenses lo2er the p@. ) ?resence may e mas-ed y other acids @CL, @BS>, @BC> etc. ) 3ype and ;uantity of organic acid in >@ system are crude speci/c, one source is decompose of napthenic acid in crude. ) Light > not as corrosi$e as +>. 3o calculate @CL e;ui$alent factor, multiply > ppm"2t y the factor, result 2ill e e;ui$alent content of @Cl (in ppm).
%re&ention
#) ?roper operation is most e=ecti$e 2ay to control corrosion, temp should not e*ceed limits. B) $oid uildup of @SS. ) Control local press drop to minimize Dashing, upgrade to 00 or 00 SS internals in asorer and regnenerators. ) >B in lea- causes @SS formation and hihg C5. ) ileter solids and @C 2ith amine sol.
Inspection Monitoring
#) CS & LS su=er uniform or localized thinning, localized underdeposit attac- K 3hinning 2ill e localized for high $el. B) 6isual , J3 for internal and J3 scans or pro/le radiography for e*ternal. ) Corrosion coupons and1or corr proes. K Montg should target hot areas unit. ) ouling of @ and /lters can e sign of corrosion prolem
Careful design 2hen 7@@S concentrations increase B2t & ao$e !2t K maintain $elocity #0 to B0?S for CS K use alloy !B & ASS 2hen $el % B0?S K Fater inE to dissol$e 7@@S K for SFS use 3i & lloy CB:9
#) General th- loss in CS K Localised corrosion at ends conc % B y 2t B) lo2 $el cause under deposit corr y 7@@s satls ) @ tues fouling K corrodes admiarility rass and Cu tues. ) sample to determine 7@@S concentration ) J3 and pro/le 53 of high and lo2 $elocity areas 9) +5+S, 54C, ML of air cooler CS tues and 4C of SS tues
#) Limiting salts and chlorides through desalting and 1 or adding caustic K 2ater 2ash to Dush salt deposits, K /lming amine inhiitors or neutralizations
#) Salts ha$e 2hitish, greenish or ro2n appearance. Fater 2ashing or steamout remo$e deposits so fouling may not e e$ident during $isual inspection. B) Corr under salts is $ery localized and results in pitting.K hihg C5. ) Loaclised corrosion diNcult to locate K 53 or J3 th- for 2all loss K Montg of feed streams and itentifying de2 point temp and later temp monitoring, K Corrosion proes or coupons are useful ut salt must deposit on proe
#) Crude units >ptimize crude desalt oper to reduce Cl (to B0 ppm or less in >@ accumulator 2ater) K Jpgrade to 7i alloys K 3i tues 2ill sol$e >@ conden prolem K caustic inEection d1s of desalter to reduce @CL K 7@ & neutralizing amine inEection in to2er >@ line. B) @? unit Minimize 2ater & Cl salts carryo$er K minimize Cl ions from @B in catalystic ref K use 7i alloy. ) Catalytic 5ef Fater 2ash @C stream to remo$e Cl K special asorent in Cl ed to remo$e CL from recycle @B
#) CS & LS su=er uniform thinning, localized corr or underdeposit attac-. B) 00 and 00 Series SS 2ill often su=er pitting attac- and 00 Series SS Cl"SCC. ) Serious corr found at mi* points 2here dry Cl contain stream mi* 2ith 2ater saturated stream or cooled to A?. ) L3 detection y J3 scan or pro/le 53 ) p@ of 2ater in atmosph to2er >@ accumulator chec-ed e$ery shift. Cl & e chec- less fre;uently. ) Fater phases in other units also checperiodic sampling from >@ durm of fract or stripping to2er. 9) ?roes or coupons and1or coupons for rate and e*tent of damage.
#) Aamage minimized y using alloys 2ith high Cr content B) 00 SS such as 3ypes 0L, #9L, B# and : are highly resistant
#) Jniform th- loss and eS scale formation (scale is times $olume of metal loss K tightly adherent gray scale) B) J3, 53, 63 for metal loss. ) >per temp /eld $eri/cation against deisgn temp K ?rocess simulation chec-s for @BS le$els
#) CS oper % #0 chec- for thloss & upgrade to lloy 00. B) Careful operation of unit to minimize 2ater, >B, sulfur and other contamnants in the feed. ) lloy 00 (solid or clad) e used to eliminate the prolems of listering and @+C1S>@+C. S5 to minimize chance of SCC. ) lloy CB:9 used 2here there is crac-ing prolems 2ith lloy 00.
#) Localized general or se$ere thinning of CS K Crac-ing due to @B Stress crac-ing listering and1or @+C1S>@+C damage. B) ouling due to iron Duoride scales. ) lloy 00 sho2s uniform th- loss ut not signi/cant scaling.K susceptile to SCC in moist @ $apors in presence of >B. ) J3 and 53 are used for th- loss. ) ?rograms to monitor small ore piping, Dange face corrosion, listering and @+C1S>@+C as per ?+ 5? :#. 9) Monitor 54 of CS & inspect for localized 1 preferential corrosion of 2elds as per 5? :#.
#) lending crude to reduce the 37 and1or increase the sulfur content, upgrade metallurgy or chemical inhiitors. B) or se$ere conditions, 3ype #:L SS or other alloys 2ith higher Mo may e re;uired. ) @3 7C inhiitors used 2ith moderate success ut e=ects on d1s catalyst to e assessed.
#) 7C is localized, pitting corrosion, or Do2 induced groo$ing in high $el areas. B) +n lo2 $elocity condensing conditions, alloys including CS, LS & 00 SS may sho2 uniform th- loss and1or pitting. ) J3, 53 for th- loss. ) Monitor 37 and sulfur content of crude charge and side streams to determine the distriution of acids in the $arious cuts. ) Corrosion Montg (45? & Coupons) K K @B proes. 9) Monitor streams for e & 7i content
#) 8est pre$ented thru proper matl selection and phenol sol$ent chemsitry control. B) >@ piping designed for ma* $elocity of 0fps in reco$ery section and maintian temp atleast 0 ao$e de2point. B) #9L may e used in top of dry to2er, phenol Dash to2er, that handle phenol"2ater. ) lloy CB:9 for high $el area 2here #9L inade;uate
#) General or localized corrosion of CS. B) 4rosion"corrosion or condensation corr oser$ed in to2er o$erhead circuits. ) J3 and 53 to monitor th- loss. ) 45 proes and corrosion coupons.
#) Selecti$e upgrading to C5 materials is only option 2here 2ater cannot e eliminated. B) 3ype 0L satsifactory in #00 conc upto #B0, #9L fe;d from #B0 to BB. ) 3ype #9L SS and lloy B0 e=ecti$e at concentrations up to ! at oiling temp.
#) General or localized thinning of CS. B) J3 and 53 for loss of thic-ness. ) Sample iron in 2ater from /rst column >@ recei$er. ) >nline 45 proes and1or corrosion coupons in 2ater dra2 from /rst column >@ condenser and reoiler.
#) 00 SS can e used at temp P #0 as Cl"SCC not li-ely. B) Cu and 7i alloys generally not susceptile to SFC ut Cu alloy $ulnerael to corrosin 2ith 7@.
#) Corrosion is typical general thinning, ut localized corrosion or underdeposit attac- can occur, if >B is present. B) Corrosion in C>B containing en$irons may e accompanied y caronate SCC ) 00 SS are susceptile to pitting attac- and cre$ice corrosion and1or Cl"SCC. ) J3 scan & ?ro/le 53 for L3. ) ?rocess and Corrosion montg, measure p@ of 2ater from >@ accumulator 9) ?roperly placed corrosion proes K coupons pro$ide rate and e*tent of potential damage.
#) Corrosion minimized thru materials selection and oper 2ithin design $elocities. B) lloys such as lloy B0, <0L and C"B:9 resist dilute acid corrosion and form a protecti$e iron sulfate /lm on the surface. ) cidic streams can e 2ashed 2ith caustic to neutralize acid.
#) General corrosion ut attac-s CS 2eld @H rapidly (attac-s 2eld slag). B) @B groo$ing may occur in lo2 Do2 or stagnant areas such as in storge tan-s or rail cars. ) +f C5 & $el high, there 2ill e no scale. ) Corr of steel y dilute acid is usually o$erall metal loss or pitting, ecomes se$ere 2ith increasing temp & $el. ) J3 or 53 inspection of turulent zones and hottest areas. 9) Coupons and 45 proes.
#) Corrosion y L> in crude >@ system can e minimized y inEecting neutralizer ut prolem 2ith changes in crude lend. B) ilming amines can pre$ent corrosion if it doesnt react 2ith >, ut it is not as e=ecti$e as neutralization. ) Jpgrading to C5 alloy
#) Light >C lea$es surface smooth and diNcult to distinguish from @CL corr. B) +n signi/cant Do2, surface smoothly groo$ed. ) J3 and 53 inspection for th- loss, L5J3 for long pipe run. ) or CS, damage is general thinning or hihgly localized 2here 2ater condenses. ) ?rocess monitoring for p@ and 2ater analysis in crude to2er >@ drum for >. 9) Corrosion proes and1or coupons.
Related Mechanism
mine stress corrosion crac-ing
4rosion , 4rosion" Corrosion
@CL Corrosion, Chloride SCC and >rganic acid corrosion of to2er >@ system
mmonium chloride corrosion K Chloride SCC and >rganic acid corr of distillation to2er >@ systems
@igh temperature sul/dation in the asence of @B
4n$ironmental crac-ing of caron steel and lloy 00 can occur in @. 5K @ydrogen stress crac-ing in @ K listering and @+C1S>@+C damage.
Sul/dation is competing mechanism mostly 2ith 7C. Fhere thinning occurs, it is diNcult to distinguish 7C & Sulidation.
7ot pplicale
7ot pplicale
Fet @BS damage and Caronate SCC
7ot pplicale
Aamage diNcult to di=erentiate from @CL corrosion. mm Chloride corrosion and Chloride SCC also related.
Corrosion Mechanism
Description
?olythionic cid Stress corrosion crac-ing (?SCC)
SCC normally occuring during S1A, S1J or during operation 2hen air and moisture are present. Crac-ing due to sulfur acids forming from sul/de scale, air & moisture acting on sensitized ust SS (adEacent to 2elds or high stress areas). SCC may propagate rapidly (min or hrs).
mine stress corrosion crac-ing
mine crac-ing is common term applied to crac-ing of steels in a;s al-anolamine systems used to remo$e @BS and1or C>B and mi*tures from $arious gas and li;uid @C streams. +t is most often found in non ?F@3 CS 2elds or cold 2or-ed parts.
Fet @BS Aamage (8listering 1 @+C 1 S>@+C 1 SSC)
our types of damage a) /2 6listering . @ atoms form during sul/de corrosion, di=use into steel, and comine to form molecule at lamination or or inclusion, too large to di=use out & press uilds to deform metal as surface ulges on +A, >A or 2ithin 2all th-. 7) /IC dEacent listers at di=erent depths de$elop crac-s, that lin- them, ha$e stair step appearance refer to as Tstep2ise crac-ingT. c) 8/IC9 Similar to @+C ut more damag form of crac-ing, appears as array of crac-s stac-ed on top of each other. 5esult is thru thcrac- perpendicular to to surface dri$en y high sress (5 or ). ppear in @H initiating from @+C or SSC. d) C9 orm of @+C result from asorption of atomic @B produced y sul/de corr. +t can initiate on surface at high hardness zone in 2eld metal (co$er pass not temp) and @H. ?F@3 is ene/cial to reduce hardness and residual stress. Jse preheat helps minimize hardness prolems.
@ydrogen Stress Crac-ing " @
4n$ironmental crac-ing that can initiate on surface of caron steel and @SL 2ith localized zones of high hardness in 2eld metal and @H as result of e*posure to a;ueous @ acid en$iron.
Caronate Stress Surface rea-ing crac-s occur adEacent to CS Corrosion Crac-ing 2elds under the comined action of tensile (CSCC) stress and corrosion in systems containing free 2ater phase 2ith caronate (some @BS also present). +t is a form of l-aline SCC.
3..2. " Temp. Range (F)
A!ected metallurg$
00 Series SS, lloy 9001900@ and !001!00@.
Crac-ing has een reported at amient temperatures 2ith some amines. +ncreasing temperature and stress le$el incr the li-elihood and se$erity of crac-ing.
Caron steels & Lo2 alloy steels
ot A!ected
8listering, @+C, and S>@+C Caron steel and lo2 alloy damage ha$e een found steels. to occur et2een amient and 00 or higher. SSC generally occurs elo2 #!0 (hihger if ; phase of @BS).
Caron steels & Lo2 alloy steels
lloy 00 not susceptile to crac-ing ut prone to +G SCC in non S5 cond.
+n C>B remo$al units, Caron steels & Lo2 alloy crac-ing may occur 2hen steels C>B content is ao$e B & temp e*ceed B00 (<C).
n&ironment Assisted Crac'ing - Re5ning A!ected "#uipment
Critical Factors
#) @4 tues, furnace tues and piping sensitized and in sulfur en$iron. B) @ urning oil, gas, co-e depending on sulfur le$els in the fuel. ) CC, hydroprocessing units (heater tues, hot feed1euent @ tues, ello2s), Crude and co-er units (piping).K 8oilers and @3 e;pt e*posed to sulfur comustion products
#) comination is re;uired of "en$ironment metal form sul/de scale e*posed to sulfur comp. +t reacts 2ith moisture and >B to form sulfur acids (?). 8" metal must e in sensited cond. C" stress 5esidual or applied B) Sensitization refers to chromium caride formation in grain oundary of metal in temp range :0 to #00. ) Lo2 C grades (P0.0) are less sussceptile and can e 2elded 21o sensitization. L grades do not sensizie if long term temp P :0
ll non"?F@3 caron steel piping and e;pt in lean amine ser$ice including contactors, asorers, strippers, regenerators and heat e*changers as 2ell as any e;uipt suEect to amine carryo$er.
#) Crac-ing more li-ely in M4 & A4 ut also found in MA4 & A+?. B) ?+ 5? < for ?F@3 re;uirement for amine ser$ices. ) Crac-ing most often in lean amine, rich amine crac-ing due to 2et @BS prolem. ) Some re/neries elie$e crac- not occur elo2 amine conc B" ut steam out can reduce limit to 0.B.
#) damage can occur in all re/nery 2here 2et @BS present. B) in @? unit, incr conc of 7@@S ao$e B incr potential of 8listering, @+C and S>@+C in $apor reco$ery unit of CC and co-er, fractionator to2er, asorer & stripper to2er, comp interstage separator, -o drum, @ etc prone ec of high 7@@S conc. ) SSC most li-ely in hard 2eld and @H, @S comp such as olts, relief $al$e springs, 00 SS $al$e trim, compressor shaft, slee$es etc.
#) p@ @B di=usion minimal at p@ :, @C7 in 2ater incr permeation in al-aline 2ater. a$ cond for damage " %0 ppm2 @BS dissol$ed in 2ater " free 2ater p@P and disso$led @BS " free 2ater p@%:.9, B0ppm2 dosl$d @C7 and some dissol$ed @BS. " %0.000 Mpa (0.0 psia) partial pressure @BS in gas phase " incr 7@ can %p@ 2here crac-ing can occur B) @BS ritrary $alue 0 ppm2 used for @BS conc that cause prolem ut e$en # ppm2 2as found suNcient for @B charging of steel. Susceptiility to SSC incr 2ith incr @BS pp % 0.0 psi 2ith 3S aout <0 -si or hardness % B:@8. ) 3emperature @B charging potential incr 2ith temp ut SSC potental ma* near am temp. ) @ardness Lo2 CS should ha$e 2eld hard P B00 @8 as per 7C4 5? 0:B (not suscept to SSC unless hardness % B: @8). 8listering, @+C and S>@+C not related to hardness. ) Steel ma-ing @+C often found in diry steel. Steel chemistry and manuf tailored to ma-e @+C resistant in 7C4 ?u !#< (ut #) 4;pt e*posed to @ acid at #) Susceptiility incr 2ith increasing any conc and hardness ao$e hardness % B: @8 highly prone. recomm limit. B) Crac-ing may occur rapidly in hours B) @SL (S3M #<"8:) olts after e*p to @ en$ironment. and compressor components. ) @ard microstructure may form in lo2 ) 8:M olts if o$ertor;ued heat input 2elds, @H, in LS or inade;uate ?F@3
#) Most pre$alent in CCJ Main fractionator >@ condensing & reDu* system B) SFS units in pump around return line to SFS to2er, >A of cold 2or-ed S"#:< cond tues ) ?iping and e;pt in potash caronate in Catacar and C>B remo$al units.
#) 5esidual stress le$el of CS and 2ater chemistry are critical factors. Jsually occurs at 2elds or cold 2or- area not stress relie$ed. B) Fater chemistry Li; 2ater phase present K p@ of sour 2ater !"#0 K @BS also present K +ncreasing 7@ and decreasing @BS increase li-elihood K Caronate ion ao$e threshold conc % #00 ppm2 K 2ith or 2ithout cyanides and polysul/de ) CCJ feed ;uality and operation a=ect crac-ing susceptility i.e. 7B higher in cases 2here SCC occur K crac-ing usualy in lo2 sulfur feed K mostly 71S ratio in feed of 0 to :0 ) +n C>B remo$al unit, crac-ing 2hen C>B content % B and temp e*ceed B00 (<C).
%re&ention
Inspection Monitoring
#) +f e;pt to e opened, Dush 2ith al-aline or soda ash soln to neautralized sulfur acids during s1d or purge 2ith 7B, 7@ (refer 7C4 5?0#:0). B) or furnace, -eep /reo* ao$e de2point to pre$ent acid forming on tues. ) L grades SS 0L1#9L1#:L sensitize if se$eral hours ao$e #000 or long term % :0. ) +mpro$ed resistance 2ith 3i & 7 sta grades e.g. SS B#, : and 7i alloys !B, 9B. ) 3hermal sta heat treatment at #90 sta SS 2elds ut diNc in /eld. 9) Susceptility y la corr test as per astm B9B prac C.
#) 3ypically occurs ne*t to 2elds, ut can also occur in ase metal (may not e e$ident until a lea- appears during s1u or in some cases, operation). B) Crac-ing is +7345G57JL5, corrosion or loss in th- is usually negligile. ) ?3 used to detect ?SCC after Dpper disc sanding to remo$e tight deposit. ) ?SCC is inspection challene ec crac- may not occur until shutdo2n. ) Montg for ?SCC during operation not practical ec condition not present.
#) ?F@3 all CS 2elds, repair 2elds and attachment 2elds as per ?+ 5? <. B) Jse solid or clad SS lloy 00 or other C5 alloys in lieu of CS. ) Fater 2ash non"?F@3 CS prior to 2elding, heat treatment or steamout.
#) Surface rea-ing crac-s primarly in 2eld @H ut also in 2eld & high stress areas. B) Crac- typically parelell to 2elds, ut inside 2eld trans$erse or long. B) t Set on 7ozzles crac-s radial to 8M and in set in nozzle parallel to 2eld. ) ppearance similar to @BS crac-ing ) ?ositi$e +A y metallography i.e. +7345G57LJ5 (>*ide /lled, ranched) ) Crac- detection est y F3M, CM. 9) ?3 not e=ecti$e for tight, scale /lled crac-s. :) SFJ3 for crac- depth (not ranched), and 43 for crac- gro2th.
#) 4=ecti$e arrier that protect steel sruface from 2et @BS can pre$ent damage including alloy cladding and coatings. B) common practice to use 2ash 2ater inEection to dilute @C7 conc in CC gas plant or con$ert @C7 to harmless thio cynate y inEect ammonium polysul/e. ) @+C resistant steel to reduce listering & @+C per 7C4 ?u !#<. ) SSC pre$ented y reducing hardness of 2eld and @H to B00@8 (Ma*) y preheat, ?F@3, F?S, and caron e;ui$alent (refer to 7C4 5? 0:B). ) ?F@3 can minimize S>@+C ut not listering and @+C. 9) Special corrosion inhiitor.
#) @B listers appear as ulges on surface of steel of ?6, found rarely on pipe and $ery rarely in middle of a 2eld. @+C can occur 2here$er listering or susurface laminations are present. B) +n ?6, S>@+C and SSC damage is most often associated 2ith 2elds. SSC also e found 2here zones of high hardness or in @S steel components. )?rocess condition e$aluated y ?4 and Corro specialist to identify e;pt prone to @BS damage. ) +nsp for @BS focusses on 2elds and nozzles (detection and repair outlined in 7C4 5? 0B<9). ) Crac- detection est y FM3, 4C, 53 or CM techni;ue. Surface prep usually not re;uired for CM. ) SFJ3 especially useful for insp and cracsizing. 45 instruments not e=ecti$e for cracdepth measuring. 9) 43 used to monitor crac- gro2th. :) Grinding or gouging crac- another method to crac- depht measure.
#) ?F@3 reduce residual stress and hardness. B) Lo2 strength CS 2ith 2eld hardness P B00@8 (7C4 S? 0:B susceptile if % B:8@). ) Jse CS 2ith C4 P0.. ) 8:M olts are lo2 strength and softer than 8:. ) Cladding or non metallic coatings for arrier to @B di=u 2ill pre$ent crac-ing..K
#) +7345G57JL5, S8 crac-s, usually associated 2ith 2elds and con/rmed y metallography only. B) FM3 for S8 crac-s. ) @ardness measurement est method to determine susceptiility. ) @igh hardness zone in 2eld co$er pass and attacment 2elds (not tempered)
#) ?ost"farication S5 heat treatment of aout #B00"#BBY as per F5C B pro$en method to pre$ent CSCC (for repair, int"e*t attachment 2elds). B) Crac-ing can e eliminated 2ith arrier coatings, solid or clad 2ith 00SS, use lloy 00 in lieu of CS. ) 2ater 2ash non ?F@3 prior to steam out or heat treatment in hot caronate ser$ice. ) Meta$anadate inhiitor to pre$ent crac-ing in hot caron system in C>B remo$al unit.
#) Crac-ing typically paralell to 2eld in @H or 8M 2ithin BT of 2eld. B) Crac-ing may also occur in 2eld. ) ?atternn is spider 2e of small crac-s K +7345G57JL5 K $ery /ne o*ide /lled crac-s similar to caustic SCC, amine SCC. ) Crac-s may e mista-en for SSC or S>@+C ut further a2ay from 2eld toe. ) Montg of p@ of CC sour 2ater is fastest and cost e=ecti$e method to locate areas prone to CSCC. 9) Monitg of C>" conc in sour 2ater. :) Crac- detect est y FM3 or CM. ?3 cannot /nd tight, o*ide /lled crac-s and should not e used. !) SFJ3 for crac- depth measure ut 45 instrument not suitale due magnetic o*ide in crac-.43 for crac- gro2th. <) Grinding out crac- is $iale method to measure depth (crac-s dont e*tend y grinding)
Related Mechanism
lso -no2 as ?olythionic cid Stress Corrosion Crac-ing (?3 SCC), +ntergranular Corrosion (+GC) and +ntergranular ttac(+G).
mine stress corrosion crac-ing is a form of l-aline SCC. Caustic SCC and caronate SCC are t2o other forms of SCC similar in appearance.
SSC is form of @B 4mrittlement K mine crac-ing & Caronate crac-ign are simlair and also confused sometimes 2ith 2et @BS crac-ing
Same mechanism that is responsile for SSC in 2et @BS en$iron e*cept that @ acid generating the @B
mine crac-ing and caustic stress corrosion crac-ing are to similar forms of SCC.
Corrosion Mechanism
@igh temperature @ydrogen ttac(@3@)
Description
@3@ results from e*posure to @B at ele$ated temperatures and pressures. 3he @B reacts 2ith carides in steel to form methane (C@) 2hich cannot di=use through steel. Loss of caride causes an o$erall loss in strength. C@ pressure uilds up, forming ules or ca$ities, micro/ssures and /ssures that may comine to form crac-s. ailure can occur 2hen crac-s reduce the load carrying aility of pressure part.
3itanium @ydriding 3i @ydriding is metallurgical phenomenon in 2hich hydrogen di=uses into titanium and reacts to form an emrittling hydride phase, result in complete loss of ductility 2ith no noticeale sign of corrosion or thic-ness loss.
3... Temp. Range (F)
A!ected metallurg$
ot A!ected
+increasing resistance CS, C"0.Mo, Mn"0.Mo, #Cr" 0.Mo, #.BCr"0.Mo, B.BCr"#Mo, B.BCr"#Mo"6, Cr"#Mo, Cr"0.Mo and similar steels.
00 SS, Cr,
>ccurs ao$e #9 (:C) 3itanium lloys and at a p@ elo2 , p@ ao$e ! or neutral p@ 2ith high @BS content K ao$e 0 in asence of moisture and >B
ther Mechanisms - Re5ning Indsutr$ A!ected "#uipment
Critical Factors
@? units, such as hydrotreaters (desulfuriz) and hydrocrac-ers, catalytic reformers, @B producing and cleanup units, such as pressure s2ing asorption units, are all susceptile. K 8oiler tues in $ery high pressure steam ser$ice.
#) @3@ preceded 2ith time period 2hen no changes in properties is noted. B) +ncuation period is time during 2hich damage is enough to e measured 2ith insp techni;ues. ) Cru$es for temp, @B pp and safe oper limits for CS, LS in ?+ <# (reasonaly conser$ati$e for CS up to #0,000 psi pp).
?rimarily in sour 2ater strippers and amine units in >@ condensers, @4 tues, piping and 3i eupt operate % #9 & also ao$e 0 (#::C) in the asence of moisture or >B K C? e;upt 2ith potential $alues P"0.<$ sce.
#) Gal$anic contact of 3i 2ith more acti$e metal li-e CS and 00 SS promote damage. B) >ccurs o$er time as @B asors and reacts to form emrittling hydride, 2ill contine until complete loss of ductility. ) Soluility of @B in pure 3i and alpha" eta alloys is limited (0"00 ppm) and once e*ceeded hydride forms. 8eta alloys more tolerant up to B000 ppm
%re&ention
Inspection Monitoring
#) Jse LS 2ith Cr and Mo to increase caride staility and minimize methane formation, also F & 6 stailizer. B) 7orma B to 0 safety factor approach 2hen using ?+5?<# cur$es. ) Se$eral failures of C"0.Mo, so its cur$ed remo$ed and not recommended for ne2 e;pt in hot @B ser$ice. ) 00SS o$erlay or clad at @B ser$ice if 8M does not ha$e ade;uate sul/dation resist K decrease in partial pressures for outgassing in shutdo2ns
#) @3@ can e con/rmed y special techni;ues incl metallography. B) @B1C reaction can cause surface. +f C di= limited, then internal decar, methan formation and crac-ing. ) +n early stage, ules 1 ca$ities can e detected y S4M (diNcult to distinguish 2ith creep ca$ities). 4arly @3@ only e con/rmed y metallogrpahy. ) +n later stage, /ssures or decar can e seen y microscope of replica metall. ) Crac-ing and /ssuring are intergranular & occur adEacent to pearlite (e caride). 9) Some listering due to molecular @B or methane in lamination $isile y 63. :) Aamage occur in 8M, 2eld and @H S> +7S?4C3+>7 +S 645R A++CJL3. !) J3 2ith $el ratio and 8J3 succesful to /nd /ssures or crac-ing only if damage reached pt 2hen micro$oid $isile at #00 magni/cation y microscope. <) 8ulging of cladding from 8M is tell tale sign that @3@ occured. #0) +n"situ metallog can detect only micro /ssure, /ssureing and decar near surface (ut decar may e due to @3). ##) Con$entional FM3 and 53 se$erely limited in aility e*cept ad$aced stage of crac-ing. 43 not pro$en method.
#) 3i should not e used in hydriding cond e.g. in mine and sour 2ater. B) +f gal$anic contact promotes hydriding, then use all 3i or electrically isolate to a$oid gal$anic couple ( may not pre$ent hydriding in al-aline sour 2ater en$ironments.)
#) 3i@ is metallurigcal change and only can e con/rmed y metallurgical techni;ue or mechanical testing. B) Zuic- test is end or crush test in $ice. 7omral 3i deform in ductile fashion and emrittled 2ill crac- 1 shatter 2ith no ductility. @ tues 2ill crac- 2hen tue undle is remo$ed or reroll done. ) Specialized 4C3 reported ale to detect hydriding damage. ) 7o other techni;ues other than the metallurgical or mechanical methods.
Related Mechanism
form of @3@ can occur in oiler tues and is referred to y the fossil utility industry as hydrogen damage.
@ydriding is a uni;ue to a fe2 materials including alloys of titanium and zirconium.
>*idation
General %#000f " +ron"ased thinning CS %#00 " alloys 2ith an 00SS o*ide layer co$ering the surface
Sul/dation @ydrogen accelerates corrosion" Jniform thinning ( localized sometimes ) 5e;uires Carurizati high on caron" acti$ity gas, lo2 o*ygen potential
*pgradin g more resistant allo$:
%00, P00 for copper alloys
+ron, nic-el and copper ased alloys
dd Cr
%##00
+ron"ased alloys
Lo2er temp, higher >B&S partial pressure
5e;uires """ Aecaruriz lo2 ation caron" acti$ity gas, CS 2ill e pure iron.
CS, LS
dd Cr, Mo
Metal Austing
ll
7o metal is immune" @BS forms protecti$e sul/de layer
?receded <00"#00 y carurizati on"pits /lled 2ith crumly residue of o*ides and carides in LS Aeep round pits in SS
uel sh
ll Contamina nts are S, 7a,I,6" Molten dissol$es o*ide layer & 0 Cr"0 7i more resistant
7itriding
+ts rare" CS, LS, 7itrogen Starts%900 00SS, di=uses , se$ere 00SS into %<00 surface forming needle"li-e particles of e7 and e7 hard rittle surface layer dull gray dry
+nEecting special additi$es
0"!0 7i
4n$ironme nt" ssisted Crac-ing Chloride SSC,
Surface %#0 initiated crac-s under the comined action of tensile stress, temperatur e and an a;ueous chloride en$ironme nt.
SS00
Jse lo2 chloride 2ater
Corrosion +nitiate Q atigue pits, notches, surface defect. rittle fracture ,3ransgran ular, ,not ranched.
""""
Caustic Surface """"" SCC crac-s ( 4mrittle adEacent to ment) non"?F@3" 2elds" +ntegranula r spider 2e and /lled 21o*ides" 3ransgranu lar in 00ss"0 to #00 ppm is suNcient for crac-ing
ll
CS, LS,00 SS
mmonia Copper ny range Copper SCC alloys alloys CS a;ueous, !. p@, >B, zinc%#, luish corrosion product, trans1inter granular crac-s[ CS" anhydrous ammonium , P.B 2ater, ir1>B, non ?F@3 2eld or @H
Aesign
?F@3, 7i alloys are resistant
?F@3 CS" 00SS, 7i alloys, <0" #01:0"0 Cu7i are immune" process control
Li;uid Metal 4mrittlem ent (LM4)
Li;uid Metal 4mrittlem ent (LM4) is a form of crac-ing that results 2hen certain molten metals come in contact 2ith speci/c alloys. Crac-ing can e $ery sudden and rittle in nature. Intergran ular crac'ing
Sour Fater (cidic)
Sulfuric cid
"""00 SS "Hinc Cu lloys "Mercury lloy 00 "Mercury
ll
?re$ented y protecting metal sustrates from coming into contact 2ith the lo2 melting metal.
@BS """ decreases p@ to ." general, localized pitting"SCC may occur in 00SS.
CS
SS,Cu alloys, 7i alloys
=ect CS" """" @H" Se$ere corrosion in CSQ%?S and1or %9 concentrati on" General corrosion
ll
7i alloys
;eneral"n&ironm entAssisted Crac'ing ?olythionic >ccurs :0"#0 Sensitize acid Stress during for austenitic CC (?SCC) shutdo2ns, sensitizatio steels startups, n 2hen e*posed to air& moisture" @H \L grade SS is less susceptile to sensitizatio n" +ntergranul ar crac-s.]
Jse chemically stale steel (B#ss, :, alloy !B and alloy9B)
mine Stress CC
?F@3, 5esistant alloys
>ccurs in %amient lean amines" M4, A4 mainly" concentrati on is not a factor" initiate +A on 2elds ( trans$ers e or longitudina l) or adEacent to @H" +ntergranul ar and /lled 2ith o*ides
CS, LS
Fet @BS Aamage (8listering1 @+C1S>@+C1 SSC)
?rocess (p@, @BS elo2 0, 2ash 2ater, ammonia &cyanides concentrati ons" ?F@3
ocus on 2eld seam and nozzles"
"C> RTACFM: =*T
@ydrogen 5esults y """ Stress e*posure Crac-ing" to a;ueous @ @ acid en$ironme nt" @H" +nterganula r" use CS 2ith Caron e;ui$alent (C4) P0.
?F@3, 5esistant alloys
FM3, @ardness testing
Caronate %B00 Stress Susceptiili Corrosion ty Crac-ing increases 2ith p@ and caronate concentrati on" ?ropagate parallel to 2elds, 2eld deposits, @H" +ntergranul ar and /lled 2ith o*ides
?F@3, 5esistant alloy
FM3, SFJ3
;eneral8ther Mechanis ms
Caused y P#!0f atomic hydrogen. @ B is formed due to corrosion.
@3@
3itanium hydriding
4*posure """ to hydrogen at ele$ated temperatur es and pressures" @ reacts 2ith carides to form methane" 00ss and %Cr are not susceptile to @3@" may cause decaruriz ation" +ntergranul ar 2ith listering sometimes .
@ydrogen di=uses into titanium to form hydride (rittle)" ?@P, ?@%!
CS, C"Mo, Cr"Mo
%#9f, % 3itanium 0 in alloys hydrogen atmospher e.
dd Cr&Mo
$oid titanium alloys in hydriding ser$ices
J3
J3
MG, hardness testing
M5, MG, hardness test
/eater tu7esCompress ion a&e *T:
63
Mg, hardness test, 63, magnetism (00SS)
%T> %hase anal$sis "C techni#ue s:
J3, M3FM3
=FMT>"C> RT ACFM>:% T ot ;ood
4C" Copper lloys, CS" FM3,SFJ 3 & 43
M3,?3
J3,53 ,Corrosion ?roes
53,J3, 45 proes
?3
ACFM=F MT> %T(not good):
