Fatigue Performance of Sour Deepwater Riser Welds-Artigo Apenas Texto

7/21/2019 Fatigue Performance of Sour Deepwater Riser Welds-Artigo Apenas Texto

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Fatigue performance of sour deepwater

riser welds: crack growth vs. endurance

Colum M. Holtam

TWI North America LLC,Houston, Texas, USA

David P. Baxter

Atkins Oil & Gas,

Abereen, U!

"a#er #resente at AS$% 'th International Con(erence on Ocean, O((shore an Arctic %n)ineerin), O$A% *'++,

otteram, The Netherlans, -une +./*0, *'++, "a#er 10.23+

!stractSteel catenar4 risers 5SCs6 are increasin)l4 use in ee#7ater oil an )as e8elo#ments9 SCs can be sub:ect to

lo7/stress hi)h/c4cle (ati)ue loain), (or exam#le (rom 7a8e an tial motion, 8ortex inuce 8ibration 5;I;6 ano#eratin) loas, an corrosi8e en8ironments 5internal an external69 When the #rouction (luis are sour, hi)her

(ati)ue crack )ro7th rates 5<CGs6 are ex#ecte an there(ore shorter o8erall li(e com#are to #er(ormance in air, as

a result o( the interaction bet7een (ati)ue crack )ro7th an sul#hie stress crackin)9 Success(ul esi)n o( risers is

criticall4 e#enent on the a8ailabilit4 o( a##ro#riate ex#erimental ata to =uanti(4 the extent to 7hich (ati)ue li8es

are reuce an rates o( (ati)ue crack )ro7th are increase9 Historicall4 there has been a iscre#anc4 bet7een

ex#erimental sour (ati)ue enurance ata an (racture mechanics/base estimates o( the corres#onin) stress/li(e 5S/ N6 cur8es9

This #a#er summarises the results o( recent sour <CG tests on C/$n #i#eline steel9 Tests 7ere #er(orme uner

conitions o( increasin) a##lie stress intensit4 (actor ran)e 5>!6, on s#ecimens containin) shallo7 initial (la7s an

at 8er4 hi)h stress ratios 56, to obtain ata close to threshol9 In man4 cases it is material beha8iour at these lo78alues o( >! that ominate the (ati)ue li(e 5e.g. ;I; loain)69 The <CG ata are then com#are to sour (ati)ue

enurance ata, both #ublishe an (rom a TWI -oint Inustr4 "ro:ect 5-I"69 The obser8e en8ironmental reuction

(actor 5%<6 (or enurance tests is com#are to that ex#ecte (rom the i((erence in (ati)ue crack #ro#a)ation rates,to examine 7hether <CG ata mi)ht #ro8ie an alternati8e means o( #reictin) %<s9

This #a#er o((ers 8aluable insi)ht into current best #ractice methos (or )eneratin) sour <CG ata 7hen =uali(4in)

)irth 7els (or sour ser8ice, an the relationshi# bet7een (ati)ue crack )ro7th an (ati)ue enurance9

"ntroduction

Steel catenar4 risers 5SCs6 are increasin)l4 use in ee#7ater oil an )as e8elo#ments9 SCs can be sub:ect to

lo7/stress hi)h/c4cle (ati)ue loain), (or exam#le (rom 7a8e an tial motion, 8ortex inuce 8ibration 5;I;6 ano#eratin) loas, an corrosi8e en8ironments 5internal an external69 When the #rouction (luis are sour 5 i.e. contain

7ater an H*S6, hi)her (ati)ue crack )ro7th rates 5<CGs6 are ex#ecte an there(ore shorter o8erall li(e com#areto #er(ormance in air, as a result o( the interaction bet7een (ati)ue crack )ro7th an sul#hie stress crackin)9 Sour

#rouction (luis are common in oil an )as a##lications an there(ore success(ul esi)n is criticall4 e#enent on

the a8ailabilit4 o( a##ro#riate ex#erimental ata to =uanti(4 the extent to 7hich (ati)ue li8es are reuce an rates o(

(ati)ue crack )ro7th are increase9

In man4 cases it is material beha8iour at lo7 8alues o( a##lie stress intensit4 (actor ran)e 5>!6 that ominate the

(ati)ue li(e 5e.g. ;I; loain)69?+@ %x#erimental crack )ro7th rate ata 5aN/>!6 are t4#icall4 etermine in

simulate o#eratin) en8ironments, an u##er boun cur8es can be use in (racture mechanics calculations tocalculate critical (la7 siBes9 %x#erimental ata at lo7 8alues o( a##lie >! are o(ten etermine usin) a ecreasin)

>! t4#e test, 7here the crack is relati8el4 ee# b4 the en o( the test9

At lo7 8alues o( >! 5i.e. a##roachin) threshol6 crack )ro7th rates in A"I 2L )rae D2 C/$n #i#eline steel

etermine uner conitions o( ecreasin) >! ha8e been sho7n to be substantiall4 lo7er than those etermine

http://www.twi.co.uk/services/technical-information/published-papers/fatigue-performance-of-sour-deepwater-riser-welds-crack-growth-vs-endurance/#ref1




uner conitions o( increasin) >! 5 Figure 169?*@ This is belie8e to be ue to an in(luence o( crack e#th 5attribute to

bulk h4ro)en char)in) (rom ex#ose sur(aces69?*/0@ The reuce in(luence o( a sour en8ironment at lo7 >! has

similarl4 been re#orte else7here9 ?2,D@

Figure #. $our fatigue crack growth rate data generated under conditions of increasing and decreasing %&'illustrating a possi!le crack depth effect at lower %& ()*++,mm-/0/#MPam+.12.304 (rrows indicate increasing

crack depth in each test2.

It is #ossible to com#are the results o( <CG tests in a sour en8ironment 7ith (ati)ue enurance ata base on the

#reicte )ro7th o( #ostulate (la7s9 An en)ineerin) critical assessment 5%CA6 is a (racture mechanics/basea##roach that is use to e8aluate the si)ni(icance o( a (la7, base on a #articular combination o( material, stress an

en8ironmental conitions9 An %CA can there(ore #ro8ie maximum allo7able (la7 siBes at the manu(acture an

installation sta)e to ensure that, (or exam#le, )irth 7el (la7s o not reach a critical siBe urin) the #ro:ecte li(e o(

the com#onent9 This i((ers (rom con8entional (ati)ue esi)n #hiloso#h4 7hich uses a stress/li(e 5S/N6 a##roach,

7hereb4 an enurance cur8e is )enerate (rom a series o( re#resentati8e tests9 S/N esi)n cur8es can be (oun in ES

FD'3?F@ an N; "/C*',?3@ (or exam#le, an 7ill t4#icall4 be base on the statistical mean o( the ex#erimental ataminus t7o stanar e8iations o( lo) N9 The S/N a##roach can be use to assess the #er(ormance o( a nominall4

e(ect/(ree 7el, althou)h :oint misali)nment can be allo7e (or9 Ho7e8er, (or 7els 7ith kno7n e(ects, an %CA

a##roach is re=uire to emonstrate ae=uate (ati)ue li(e9

The assume <CG usuall4 takes the (orm o( a "aris la7 7hich relates the crack )ro7th #er c4cle 5aN6 to the

ran)e o( stress intensit4 (actor 5>!6 7here >! ! max / ! min an m an C are constants 5%=uation +69 ?.@

It has #re8iousl4 been emonstrate that the assume <CG la7 has a si)ni(icant in(luence 7hen #er(ormin) %CAs

on internal sur(ace/breakin) e(ects in SCs o#eratin) in a sour en8ironment an sub:ect to ;I; (ati)ue loas9 ?+@ It

7as sho7n that i( the a##arent iminishe in(luence o( a sour en8ironment at lo7 >! 7as inee a true

re#resentation o( material #er(ormance uner such conitions, then si)ni(icantl4 lar)er initial (la7 siBes coul be

tolerate b4 closel4 (ittin) the <CG cur8e to the ex#erimental ata at lo7 >!9 A lar)er allo7able initial (la7 siBe

leas to (e7er re#airs an cut/outs, 7hich means (aster installation an si)ni(icant cost sa8in)s9






























Historicall4 there has been a iscre#anc4 bet7een ex#erimental sour (ati)ue enurance ata an (racture mechanics/

base estimates o( the corres#onin) stress/li(e 5S/N6 cur8es9 The aim o( this #a#er is to e8aluate 7hether the results

o( recent <CG tests in8esti)atin) the near/threshol 5lo7 >!6 beha8iour o( C/$n #i#eline steel in a sour

en8ironment can be use to more accuratel4 #reict sour (ati)ue enurance beha8iour9

Comparison of fatigue crack growth rate and fatigue

endurance data

Figure 2 sho7s the results o( recent <CG tests on A"I 2L )rae D2 C/$n #i#eline steel in air an in a souren8ironment,?+'@ #lotte alon)sie the #re8ious ex#erimental ata (rom Figure 19 Tests 7ere #er(orme uner

conitions o( increasin) >! on s#ecimens notche in the #arent material9 ;er4 hi)h stress ratios 56 7ere use 5u# to

'9.6 to (acilitate )eneratin) ata at lo7er >! 5(rom +''Nmm/*$"am'92 to D2'Nmm/**+$"am'9269

Figure 0. 5esults of increasing %& tests at high stress ratio and starting at low %& in air and in a sour

environment' plotted alongside data from a decreasing %& test in a sour environment.3#+4 (rrows indicate

increasing crack depth in each test2.

The sour

en8ironment

7as ientical

to that use (or

the #re8ious

tests in Figure1, an 7as

base on NAC%

T$'+FF

solution E9?++@

This consistso( 2JNaCl

an '90JNa

acetate, an is

acii(ie to #H

90/9D usin) acetic aci9 The basic solution 7as saturate 7ith a mixture o( FJ H *S in N*, to )i8e a #artial #ressure

o( '9''F$"a 5+#si6 H*S, an there 7as a continuous #assa)e o( )as throu)h the test solution to maintain saturation9All tests 7ere carrie out at *2KC 5KC69 The air tests 7ere carrie out at a reasonabl4 hi)h loain) (re=uenc4 52/

+'HB6, since the results are not ex#ecte to be sensiti8e to (re=uenc49?+*@ <or the tests carrie out in a sour

en8ironment the loain) (re=uenc4 7as reuce to '9+HB 57hich is com#arable to 7a8e or ;I; loain)6 to allo7

time (or the en8ironment to interact 7ith the s#ecimen9

It can be seen that there 7as no a##arent reuction in the in(luence o( the sour en8ironment at lo7 >! 5 Figure 269

The most a##ro#riate a8ice, there(ore, is to use an u##er boun cur8e base on ex#erimental crack )ro7th rate ata5aN/>!6 obtaine uner increasin) >! conitions in a re#resentati8e sour en8ironment9 A more in/e#th

iscussion o( the test methos use an anal4sis o( the ex#erimental results is #ro8ie else7here9 ?+'@

A -oint Inustr4 "ro:ect 5-I"6 inclue both <CG an stri# (ati)ue enurance testin) o( A"I 2L )rae D2 C/$n

steel 7els in air an in a sour en8ironment9?+@ The results o( these tests ha8e been con(iential since the conclusion

o( the #ro:ect in *''2 but became #ublishable in *'+'9 ata (rom the stri# (ati)ue tests in air an in a sour

en8ironment are #lotte in Figure 3?+@ alon)sie the Class % mean an esi)n 5i.e. mean minus t7o stanar

e8iations o( lo) N6 cur8es (rom ES FD'39?F@ The s#ecimens teste in air emonstrate better (ati)ue stren)th than theClass % mean cur8e9?F@ The sour ata sho7e the (ati)ue stren)th to be reuce b4 a (actor o( a##roximatel4 0' on

li(e9 All tests in a sour en8ironment 7ere #er(orme at a loain) (re=uenc4 o( '9*HB9 Ho7e8er, (or the sour test

#er(orme at an a##lie local stress ran)e o( 0D$"a the loain) (re=uenc4 7as increase (rom '9* to +9'HB a(ter*,0*,.'. c4cles9

































Figure . Fatigue endurance data in air and in a sour environment. 3#4

There 7as an a##arent im#ro8ement in (ati)ue #er(ormance o( the sour test s#ecimens at the t7o lo7est stress ran)es9

It 7as s#eculate that these tests ma4 ha8e initiall4 been belo7 the threshol (or crack )ro7th, so crackin) i not )et

uner7a4 until corrosion ha notche the 7el root toe (urther9 Alternati8el4 these lo7 stress tests ma4 inicate a real

an is#ro#ortionate reuction in crack )ro7th rate at lo7 >!9 The4 coul also be ue to ex#erimental scatter alone9

<CG tests 7ere carrie out uner increasin) >! conitions 5(rom >! ''Nmm /*.$"am'92 to +*''Nmm/

**$"am'9269 The sour en8ironment use 7as ientical to that escribe abo8e an tests 7ere #er(orme at ambient

tem#erature 7ith '92 an loain) (re=uencies o( '9+, '9* an +9'HB9 Attem#ts to )enerate ata at lo7er >! 7ere

re#orte as bein) lar)el4 unsuccess(ul 5ue to crack (oulin) b4 corrosion ebris69 At ''Nmm /*.$"am'92 a sli)htl4

hi)her <CG 7as obser8e at '9+HB than the other t7o (re=uencies, but this retare until all three (re=uencies (ell inline 7ith each other9 e)ression anal4sis o( all the sour ata )a8e "aris la7 coe((icients o( m 9*0 an C 9F2x+' /

+ (or >! in Nmm/* an aN in mmc4cle 5 Figure 469

Figure *. 5egression anal6sis of the increasing %& tests in a sour environment. 3#4

One o( the conclusions o( the -I" 7as that <CG testin) 7as not a reliable metho o( #reictin) en8ironmental

reuction (actors 5%<s6 / o(ten re(erre to as knocko7n (actors / (or )irth 7els in a sour en8ironment, (or the

ran)e o( )ro7th rate in8esti)ate9?+@ A )reater in(luence o( the sour en8ironment 7as obser8e urin) enurance

testin) than #reicte usin) (racture mechanics methos usin) the sour (ati)ue crack )ro7th cur8e in Figure 49 It is

7orth notin) that (or the stress ran)es consiere 50D$"a u# to *''$"a6 much o( the earl4 crack )ro7th

5#articularl4 at lo7 stress6 takes #lace at 8alues o( >! less than ''Nmm /*.$"am'92, (or 7hich no <CG ata 7ereobtaine9 Ho7e8er, in the tests #resente in Figure 2, <CG ata ha8e been success(ull4 measure at lo7er 8alues o(

>! an it is #ossible there(ore, that <CG testin) ma4 no7 correlate more closel4 7ith the (ati)ue enurance ata9

In orer to com#are the relati8e #er(ormance o( a material urin) (ati)ue crack )ro7th an (ati)ue enurance testin),

a "aris la7 cur8e can be use to #rouce a (racture mechanics base estimate o( the corres#onin) S/N cur8e, 7ithin

the (rame7ork o( ES F.+'9?+0@ Calculations ha8e been #er(orme usin) TWIMs so(t7are CAC!WIS% 0, 7hich is

(ull4 com#liant 7ith the latest 8ersion o( ES F.+'9?+0@ A #ro)ramme o( enurance testin) usin) stri# (ati)ue s#ecimensin a sour en8ironment is ex#ensi8e an time consumin) an no such tests ha8e been #er(orme in the current 7ork9

Com#arisons are there(ore ra7n 7ith the enurance ata (rom the #re8ious -I"9

"nput parameters

"nitial flaw dimensions


















An internal sur(ace/breakin) (la7 7as assume to be locate at a )irth 7el, close to the 7el root toe9 The 7el 7as

assume to be a (ull #enetration )irth 7el #rouce usin) mechanise #rocesses9 A t4#ical exam#le is sho7n in

Figure 59 Wels are kno7n to contain small 7el toe intrusions, t4#icall4 '9+2/'90mm ee#, ?+2,+D@ 7hich #ro8ies a

con8enient u##er an lo7er boun estimate o( initial (la7 siBe to be use in an assessment, assumin) similar (la7s

7ere #resent in the stri# s#ecimens teste in the -I"9 In the anal4ses, t7o i((erent as#ect ratios o( initial (la7 hei)ht5a6 to (la7 len)th 5*c6 7ere assume '9+ an '99 <inal (ailure 7as consiere to ha8e occurre 7hen a sur(ace crack

#ro#a)ate hal( 7a4 throu)h the s#ecimen thickness, i9e9 7hen the (la7 hei)ht reache +'9mm base on a +0in9 riser

7ith 7all thickness *'9Dmm9

Figure 1. 76pical pipeline girth weld produced using mechanised welding processes

ES F.+' #ro8ies a sim#li(ie <CG e=uation (or C/$n steels in air, 7here m 9' an C 29*+ x +' /+, to (acilitate

initial screenin) assessments that can be com#are irectl4 7ith calculations base on (ati)ue esi)n rules (or 7elesteels 5e.g. ?F@69 Ho7e8er, these coe((icients corres#on to an u##er boun cur8e9 The corres#onin) mean 8alues 5(or

'926 are m 9' an C *92 x +' /+9?+F@ This sim#li(ie la7 7as use to calculate the initial (la7 siBe that 7oul

(orce a calculate S/N cur8e to (it a Class % mean cur8e9 <or an as#ect ratio o( a*c '9+, the calculate initial (la7

siBe #resent close to the 7el root toe in orer to )et the same li(e as that (rom a Class % mean cur8e 7as '9+*mm x

+9*mm 5usin) the stanar * $k solution (or an internal sur(ace/breakin) (la7 ?+0@69 This is com#arable to t4#ical

7el toe intrusions?+2,+D@

an #ro8ies a e)ree o( con(ience in the initial (la7 siBes assume in the anal4ses9

$tress intensit6 magnification factor due to presence of weld (Mk factor2

The local stress intensit4 ma)ni(ication (actor at the 7el toe is characterise usin) the #arameter $ k 9 Stanarsolutions (or sur(ace/breakin) (la7s are #ro8ie in Annex $ o( ES F.+', ?+0@ eri8e (rom * 5an (or certain

)eometries 6 (inite element anal4ses9 $k is e#enent on 7hat is terme the attachment len)th, 7hich in the case

o( an internal sur(ace/breakin) (la7 in a (ull #enetration #i#eline )irth 7el is the 7ith o( the 7el root #rotrusion9

<or the #ur#oses o( this 7ork, a 7el root 7ith o( 0mm 7as ao#te9 $ k is a maximum near the sur(ace an its

in(luence ecreases as (la7 e#th increases9 $k is calculate automaticall4 7ithin CAC!WIS% 0 (or the selecte

attachment len)th an in the current 7ork the stanar * solutions (or an internal sur(ace/breakin) (la7 in a (lat #late 7ere use 5$99*9*6,?+0@ assumin) a (ull #enetration 7el9 While it is ackno7le)e that the solution 7oul

#ro8ie a less conser8ati8e solution, it re=uires the ratio o( attachment len)th 50mm6 to 7all thickness 5*'9Dmm6 to be

)reater than or e=ual to '92, 7hich is rarel4 the case (or #i#eline )irth 7els9

Fatigue crack growth law

Figure 6 sho7s a t7o/sta)e "aris la7 base on a re)ression anal4sis o( the sour <CG ata )enerate uner

increasin) >! conitions 5 Figure 26 7ith m 09D0 an C +90' x +' /+2 (or Sta)e A an m *9DD an C 39 x +'/++

(or Sta)e E 5(or >! in Nmm/* an aN in mmc4cle69 The threshol 8alue o( stress intensit4 (actor ran)e 5>! TH67as assume to be DNmm/**$"am'92 in line 7ith the )uiance in ES F.+' (or steels in air9 Ho7e8er, the threshol

7as remo8e (rom the anal4ses at lo7 a##lie stress ran)es to initiate crack )ro7th9

Figure 8. 7wo-stage mean crack growth relationship in a sour environment !ased on the latest experimental

fatigue crack growth rate data (Figure 22' plotted alongside the results of increasing %& tests in a sour

environment from the previous 9"P. 3#4

The com#arable sour <CG ata (rom the -I" are also #lotte in Figure 6 9 It is not immeiatel4 clear 7h4 the <CGs

obser8e in the -I" are lo7er than those obser8e in the current 7ork9 Althou)h the -I" teste s#ecimens notche inthe 7el 5as o##ose to s#ecimens notche in the #arent material in the current 7ork6 recent anal4sis has sho7n that,

(or this material/en8ironment combination, #arent material, 7el metal, heat a((ecte Bone 5HAP6 an simulate

HAP microstructures exhibit broal4 similar (ati)ue crack )ro7th beha8iour9 ?@

Fatigue stresses

<or each assume initial (la7 siBe, assessments 7ere carrie out uner constant am#litue loain) at a##lie stress

ran)es corres#onin) to the sour (ati)ue enurance tests in the -I"9 The number o( c4cles to (ailure 5e(ine as 7hen

the crack #ro#a)ate hal( 7a4 throu)h the s#ecimen thickness6 7as calculate, to allo7 sour S/N cur8es #reicte 8ia

%CA 5i.e. (racture mechanics6 to be #lotte9































5esults

Tables 1 an 2 sho7 the (ati)ue li8es #reicte 8ia %CA (or each initial (la7 siBe base on the sour <CG cur8e (rom

the -I" an the t7o/sta)e sour cur8e (rom <i)ure D res#ecti8el49 Also inicate in Tables 1 an 2 are the 8alues o( >! at the onset o( crack )ro7th an at (ailure 5e(ine as 7hen the crack #ro#a)ate throu)h hal( 7all69 The actual

obser8e (ati)ue li8es (rom the sour enurance tests in the -I" are also sho7n (or com#arison9 The corres#onin)

calculate sour S/N cur8es are #lotte alon)sie the sour ex#erimental ata in Figure 7 5-I" sour crack )ro7th cur8e6an Figure 8 5t7o/sta)e sour cur8e69

7a!le # Fatigue lives predicted via engineering critical assessment !ased on the previous oint industr6 proect

sour crack growth curve assuming t6pical initial surface-!reaking defects to !e present at a girth weld' close to

the weld root toe.

"nitial

flaw si;e

(mm2

spect

ratio'

a/0c

$tress

range

(MPa2

ctual life -

9"P data

(c6cles2

Predicted

life (c6cles2

%& at start

of life

(,mm-/02

%& at

failure

(,mm-/02

'9+2 x +92 '9+

0D ,3F.,2+* F,00',''' 2' *D*

D' +,2,2F. ,+0',''' DD 0

3+ *+*,.D' +,+.',''' 3. 0D0

++' FD,D2* 00+,''' +*' D*'

+0D *F,+.3 +FD,''' +D' 3+'

*'' .,.+' D,''' *+. +,'+

'90 x 09' '9+

0D ,3F.,2+* 0,0F',''' D+ *D2

D' +,2,2F. +,3.',''' F. 0D

3+ *+*,.D' F+2,''' +'F 0D3

++' FD,D2* *D2,''' +02 D'

+0D *F,+.3 +'D,''' +. 300

*'' .,.+' 3,''' *D0 +,'.F

'9+2 x '92 '9

0D ,3F.,2+* .,3*',''' 0' *D

D' +,2,2F. 0,+2',''' 2* 0'

3+ *+*,.D' +,2F',''' F+ 0D*

++' FD,D2* 23*,''' .D D+3

+0D *F,+.3 **,''' +*F F3F

*'' .,.+' 3,2'' +F0 +,'0*

'90 x +9 '9

0D ,3F.,2+* D,''',''' 03 *D2

D' +,2,2F. *,2',''' D D

3+ *+*,.D' .2.,''' 32 0D2

++' FD,D2* 22,''' ++2 D+D+0D *F,+.3 +0*,''' +2 3*F

*'' .,.+' 2+,''' *+' +,'3+

7a!le 0 Fatigue lives predicted via engineering critical assessment !ased on the latest two-stage sour crack

growth curve assuming t6pical initial surface-!reaking defects to !e present at a girth weld' close to the weld

root toe.

"nitial

flaw si;e

(mm2

spect

ratio'

a/0c

$tress

range

(MPa2

ctual life -

9"P data

(c6cles2

Predicted

life (c6cles2

%& at start

of life

(,mm

-/0

2

%& at

failure

(,mm

-/0

2'9+2 x +92 '9+ 0D ,3F.,2+* 2,*0',''' 2' *'



D' +,2,2F. +,2',''' DD +'

3+ *+*,.D' 32,''' 3. 0F

++' FD,D2* .F,''' +*' 2D

+0D *F,+.3 *.,''' +D' F'+

*'' .,.+' .,''' *+. .FD

'90 x 09' '9+

0D ,3F.,2+* *,*'',''' D+ *0F

D' +,2,2F. D02,''' F. 0

3+ *+*,.D' +D2,''' +'F 02*

++' FD,D2* 00,''' +02 2.'

+0D *F,+.3 +2,''' +. F.0

*'' .,.+' 2,3'' *D0 +,++'

'9+2 x '92 '9

0D ,3F.,2+* 3,3*',''' 0' **0

D' +,2,2F. *,2F',''' 2* *3'

3+ *+*,.D' D00,''' F+ 0*F

++' FD,D2* +D',''' 3* 2.'+0D *F,+.3 0D,''' +'3 F'

*'' .,.+' +,''' +F0 +,'+*

'90 x +9 '9

0D ,3F.,2+* ,D',''' 03 *20

D' +,2,2F. +,'D',''' D *

3+ *+*,.D' *D3,''' 32 00+

++' FD,D2* D.,''' ++2 2.'

+0D *F,+.3 *+,2'' +2 F*'

*'' .,.+' F,0'' *+' +,'F'

Figure <. $-, curves predicted via engineering critical assessment calculations using the oint industr6 proect

sour crack growth curve' plotted alongside fatigue endurance data for specimens tested in a sour environment.

3#4

Figure =. $-, curves predicted via engineering critical assessment calculations using the latest two-stage sour

crack growth curve' plotted alongside fatigue endurance data for specimens tested in a sour environment. 3#4

Figure 7 con(irms the (inin) (rom the -I" that <CG testin) 7as not a reliable metho o( #reictin) %<s (or )irth

7els in a sour en8ironment, (or the ran)e o( )ro7th rate in8esti)ate9 As hi)hli)hte #re8iousl4, crack )ro7th ata7ere not )enerate at su((icientl4 lo7 8alues o( >! to accuratel4 moel the onset o( crack )ro7th9 Interestin)l4

ho7e8er, better correlation is obser8e at lo7er stress as these tests exhibite better (ati)ue #er(ormance9 An initial

(la7 siBe o( '90mm 7ith a*c '9+ #ro8ies the closest a)reement 7ith the ex#erimental ata, but the %CA #reiction

is still obser8e to o8er/estimate the (ati)ue li8es in a sour en8ironment, 7hich is non/conser8ati8e9

When the anal4sis 7as re#eate usin) the t7o/sta)e sour (ati)ue crack )ro7th cur8e (rom Figure 6 there 7as a

ramatic im#ro8ement in the a)reement bet7een the %CA #reictions an the ex#erimental ata 5 Figure 869 O8erall

there 7as excellent correlation bet7een the sour S/N cur8es #reicte 8ia %CA an the ex#erimental ata9 Theobser8e %< 5(or enurance tests6 is com#arable to that ex#ecte (rom the i((erence in (ati)ue crack #ro#a)ation

rates9 It 7oul seem that the sour en8ironment has a similar e((ect on total (ati)ue li(e as it oes on crack #ro#a)ation

alone9 %xaminin) Figures 7 an 8, the #reicte sour S/N cur8es are not si)ni(icantl4 in(luence b4 the choice o(

initial (la7 as#ect ratio9

The (racture mechanics/base #reictions #resente in Figure 8 su))est that <CG ata ma4 #ro8ie an alternati8e

means o( #reictin) %<s9 <urther re8ie7 an com#arison o( <CG an (ati)ue enurance beha8iour in a sour

en8ironment is unoubtel4 re=uire, to con(irm the #resent inication that the t7o are irectl4 #ro#ortional9Ho7e8er, there are relati8el4 (e7 #ublishe S/N ata (or steels in a sour en8ironment, #articularl4 at lo7 stress9 ?+3/*+@













Euitra)o et al?*+@ in8esti)ate the in(luence o( a sour en8ironment on (ati)ue enurance in both the lo7 an hi)h c4cle

(ati)ue re)imes, incluin) tests on A"I 2L )rae D2 C/$n steel 7els in the same sour en8ironment escribe

abo8e9 Tests 7ere also #er(orme at lo7 stress ran)es9 The results o( the #ertinent stri# (ati)ue enurance tests in air

an in a sour en8ironment are re#rouce in Figure 99 Loain) (re=uenc4 7as +HB com#are to '9*HB in the -I"9

Figure >. Fatigue endurance data for P" 1? grade @81 C-Mn steel weld specimens tested in air and in a sour

environment. 30#4

The obser8e #er(ormance in air 7as si)ni(icantl4 better than that obser8e in the -I" an ha a shallo7er cur8e,

7hich is consistent 7ith 7hat one mi)ht ex#ect (rom hi)h =ualit4 )irth 7els9 Euitra)o et al teste )irth 7els

#rouce in the +G #osition b4 a mechanise G$AW #rocess a(ter a STT root #ass9 The 7els teste in the -I" 7ere

#rouce in the *G #osition 7ith GTAW root an G$AW (ill an ca#9 Ho7e8er, the resultin) sour S/N cur8e 7as

si)ni(icantl4 stee#er9 It 7as conclue that the use o( a constant slo#e 5 i.e. one/sta)e6 S/N cur8e re#resents aconser8ati8e sour esi)n assum#tion9

The abo8e #ublishe ata #ro8ies another use(ul test case (or the %CA #reictions usin) the t7o/sta)e sour (ati)ue

crack )ro7th cur8e9 Table 3 #resents the results o( this anal4sis in a similar (ashion to Tables 1 an 2, this time

alon)sie the actual obser8e (ati)ue li8es (rom the sour enurance tests re#orte b4 Euitra)o et al9 ?*+@ The

corres#onin) sour S/N cur8es are #lotte alon)sie the sour ex#erimental ata in Figure 109

7a!le Fatigue lives predicted via engineering critical assessment !ased on the latest two-stage sour crack

growth curve assuming t6pical initial surface-!reaking defects to !e present at a girth weld' close to the weld

root toe.

"nitial

flaw si;e

(mm2

spect

ratio'

a/0c

$tress

range

(MPa2

ctual life -

Buitrago et al

data (c6cles2

Predicted life

(c6cles2

%& at start

of life

(,mm-/02

%& at

failure

(,mm-/02

'9+2 x +92 '9+

+2 *,2'',''' / / /

*' F,F32,0. *2',''',''' ** +'*

' *,23F,.0+ 3,+02,''' +DF

0'*,*'0,F &

+,++F,0F0+','0',''' 00 **

2' .'F,F. ,2D',''' 22 *20

F' F*,2. F2*,''' FF 3'

+'' *',.*+ +03,''' ++' 2'0

+D+ F+,D+' *',''' +FD 3D3

'90 x 09' '9+

+2 *,2'',''' / / /

*' F,F32,0. +'2,''',''' *D ++'

' *,23F,.0+ +D,''',''' 0' +D2

0' *,*'0,F &+,++F,0F0

0,*+',''' 2 *+3

2' .'F,F. +,0.',''' DD *0.

F' F*,2. +3,''' .* 3'

+'' *',.*+ D2,2'' +* 2F

+D+ F+,D+' +',.'' *+ .+'

'9+2 x '92 '9 +2 *,2'',''' / / /

*' F,F32,0. 0*+,''',''' +F +'2

' *,23F,.0+ D0,+'',''' *D +0F

0'

*,*'0,F &

+,++F,0F0 +D,33',''' 2 *'2

2' .'F,F. 2,..',''' 00 *0











F' F*,2. +,*D',''' D+ 0

+'' *',.*+ *0D,''' 3F 2F

+D+ F+,D+' ',3'' +0' .'*

'90 x +9 '9

+2 *,2'',''' / / /

*' F,F32,0. +F,''',''' *+ +'F

' *,23F,.0+ *D,.',''' + +F'

0'*,*'0,F &

+,++F,0F0D,.0',''' 0* *+D

2' .'F,F. *,0D',''' 2* *2'

F' F*,2. 2**,''' F .'

+'' *',.*+ +'0,''' +'2 2+

+D+ F+,D+' +2,''' +D. 3++

Figure #+. $-, curves predicted via engineering critical assessment calculations using the latest two-stage sour

crack growth curve' plotted alongside fatigue endurance data for specimens tested in a sour environment.

30#4

The S/N cur8es #reicte 8ia %CA are much shallo7er than the #ublishe test ata9 Conse=uentl4, (ati)ue

#er(ormance is uner/estimate at hi)h stress an o8er/estimate at lo7 stress9 Table 4 #resents #reicte (ati)ue

li8es base on Sta)e E onl4 (rom Figure 6 9 This re#resents a conser8ati8e u##er boun sour crack )ro7th cur8e9 The

corres#onin) sour S/N cur8es are #lotte alon)sie the sour ex#erimental ata in Figure 119 The slo#e o( the

#reicte S/N cur8es no7 more closel4 matches that o( the ex#erimental ata an (ati)ue li8es are consistentl4 uner/estimate9

Figure ##. $-, curves predicted via engineering critical assessment calculations using an upper !ound sour

fatigue crack growth curve' plotted alongside fatigue endurance data for specimens tested in a sour

environment 30#4

7a!le * Fatigue lives predicted via engineering critical assessment !ased on an upper !ound sour crack growth

curve assuming t6pical initial surface !reaking defects to !e present at a girth weld' close to the weld root toe.

"nitial

flaw si;e

(mm2

spect

ratio'

a/0c

$tress

range

(MPa2

ctual life -

Buitrago et al

data (c6cles2

Predicted

life (c6cles2

%& at start

of life

(,mm-/02

%& at

failure

(,mm-/02

'9+2 x +92 '9+

+2 *,2'',''' 3,2'',''' +D 30

*' F,F32,0. ,.D',''' ** ++

' *,23F,.0+ +,02,''' +D3

0' *,*'0,F &+,++F,0F0 D*D,''' 00 **0

2' .'F,F. 0D,''' 22 *3*

F' F*,2. +0+,''' FF 3F

+'' *',.*+ 20,''' ++' 2+F

+D+ F+,D+' +2,0'' +FD 3.3

'90 x 09' '9+ +2 *,2'',''' 2,3'',''' *' 3

*' F,F32,0. *,F+',''' *D ++*

' *,23F,.0+ .*',''' 0' +D3

0'*,*'0,F &

+,++F,0F0

0*.,''' 2 **2

2' .'F,F. *F,''' DD *3*









F' F*,2. .F,''' .* .3

+'' *',.*+ F,2'' +* 2D0

+D+ F+,D+' +',2'' *+ 33*

'9+2 x '92 '9

+2 *,2'',''' +','',''' + 3

*' F,F32,0. 0,3'',''' +F ++*

' *,23F,.0+ +,D',''' *D +DD

0'*,*'0,F &

+,++F,0F0FD',''' 2 **2

2' .'F,F. 0*',''' 00 *3*

F' F*,2. +F+,''' D+ 30

+'' *',.*+ DD,''' F0 22

+D+ F+,D+' +3,F'' +0' .''

'90 x +9 '9

+2 *,2'',''' F,*3',''' +D 32

*' F,F32,0. ,3',''' *+ ++*

' *,23F,.0+ +,+2',''' + +D30'

*,*'0,F &

+,++F,0F022,''' 0* **0

2' .'F,F. *.D,''' 2* *3

F' F*,2. +*',''' F F.

+'' *',.*+ 0D,2'' +'2 20

+D+ F+,D+' +,''' +D. 30'

Discussion

S/N cur8es ha8e been #reicte 8ia (racture mechanics usin) a t7o/sta)e sour <CG cur8e, e8elo#e (romincreasin) >! tests startin) at 8er4 lo7 >!9 There 7as excellent correlation bet7een the #reicte S/N cur8es an

the results o( sour stri# (ati)ue enurance tests (rom a #re8ious TWI -I"9 This su))ests that <CG an (ati)ueenurance beha8iour in a sour en8ironment are irectl4 #ro#ortional, an <CG ata ma4 #ro8ie an alternati8e

means o( #reictin) %<s9

Ho7e8er, the same #reicte S/N cur8es i not correlate as 7ell 7ith enurance ata #ublishe b4 Euitra)o et al9 ?*+@

This is #erha#s not sur#risin) consierin) the si)ni(icantl4 better air #er(ormance emonstrate b4 the 7els teste

b4 Euitra)o et al9 It 7as sho7n that the initial (la7 siBes assume in the abo8e anal4ses 7ere com#arable to the siBe

o( (la7 re=uire to achie8e the same li(e as a Class % mean cur8e, base on a sim#li(ie mean crack )ro7th cur8e (or

steels in air9?+F@ Ho7e8er, the 7els teste b4 Euitra)o et al exceee Class % mean #er(ormance, there(ore smallerinitial (la7 siBes 7oul nee to be assume in orer to (orce a calculate S/N cur8e to (it the ex#erimental air cur8e9

Also, re(errin) to the actual (ati)ue li8es in a sour en8ironment re#orte in Tables 3 an 4, the 8alues o( >! at the

start o( li(e 7ere si)ni(icantl4 lo7er than +''Nmm /*$"am'92, the lo7est 8alue o( >! (or 7hich actual <CG ata

has been measure 5 Figure 269 Aitional test ata are there(ore re=uire at lo7er 8alues o( >! 5i.e. Q+''Nmm/

*$"am'9269 "ossible (re=uenc4 e((ects ha8e also not been ex#lore in this #a#er9 Ao#tin) an u##er boun sour

crack )ro7th cur8e 5i.e. Sta)e E (rom the t7o/sta)e cur8e6 im#ro8e the correlation bet7een the #reicte S/Ncur8es an the ex#erimental ata an ensure a conser8ati8e #reiction o( (ati)ue li(e9

<urther in8esti)ation is re=uire to establish 7hether the obser8e %< 5(or enurance tests6 is com#arable to that

ex#ecte (rom the i((erence in (ati)ue crack #ro#a)ation rates9 Ho7e8er, there are a number o( lucrati8e bene(its i(

<CG ata can #ro8ie an alternati8e means o( #reictin) %<s9 <or exam#le, sour corrosion <CG tests are, in

)eneral, consierabl4 chea#er an =uicker than (ati)ue enurance tests9 I( (racture mechanics calculations base on

ex#erimental <CG ata can be sho7n to #ro8ie accurate estimates o( (ati)ue enurance ata in sour en8ironmentsthen si)ni(icant cost an time sa8in)s mi)ht be achie8e urin) the initial sta)es o( ee#7ater e8elo#ment #ro:ects9

<urthermore, inustr4 is increasin)l4 intereste in )eneratin) corrosion (ati)ue ata at realistic ser8ice 5 i.e. lo76

stress ran)es9 Sour (ati)ue enurance tests uner constant am#litue loain) are o(ten un(easibl4 lon) an ex#ensi8e

ue to the lo7 (re=uenc4 re=uire in corrosion (ati)ue testin)9 <CG testin) at lo7 >! ma4 #ro8ie an alternati8e

means o( in8esti)atin) (ati)ue beha8iour in this re)ime9









There is much ebate re)arin) the conce#t o( %<s 5or knocko7n (actors69 It is #ossible that t7o i((erent 7elin)

#roceures ma4 exhibit a i((erent (ati)ue enurance in air, but a similar #er(ormance 7hen teste in a sour

en8ironment9 The better #er(ormin) 7el 5in air at least6 is there(ore assi)ne a )reater (ati)ue li(e reuction (actor,

an a some7hat more strin)ent sour esi)n cur8e9 In other instances, (ati)ue #er(ormance in air ma4 si)ni(icantl4

excee that re=uire9 The etermine (ati)ue li(e reuction (actor, bet7een stri# tests in air an in a sour en8ironment,can then be 8er4 lar)e9 A##l4in) this reuction (actor to the esi)n cur8e results in a 8er4 strin)ent sour esi)n cur8e,

an #enalises the use o( a )irth 7elin) #roceure that results in )oo 5in air6 (ati)ue #er(ormance9 The onl4 7a4 to

eliminate the uncertaint4 7ith eri8in) %<s (rom small scale stri# (ati)ue s#ecimens alone is to conuct (ull scale(ati)ue tests in a sour en8ironment9 To ate such tests ha8e not been (easible but a -I" aime at conuctin) such tests

commence in *'+'9

?+'@

Conclusions and recommendations

Sour corrosion (ati)ue beha8iour o( C/$n #i#eline steels is a com#lex research area in(luence b4 numerousen8ironmental an mechanical 8ariables9 This #a#er #ro8ies encoura)ement that it ma4 be #ossible to use (racture

mechanics calculations base on ex#erimental <CG ata to #ro8ie su((icientl4 accurate an conser8ati8e estimateso( (ati)ue enurance in sour en8ironments9 Althou)h (urther re8ie7 an com#arison is re=uire, the #otential bene(its

o( bein) able to #reict total (ati)ue li(e 8ia <CG ata :usti(4 the continue in8estment in this area, #articularl4 the

e8elo#ment o( <CG test methos in sour en8ironments9

5eferences

+9 Holtam C $, Eaxter ", Ashcro(t I A an Thomson C, *''.R MIn(luence o( (ati)ue loain) on theen)ineerin) critical assessment o( steel catenar4 risers in sour ee#7ater oil an )as e8elo#mentsM, !e4

%n)ineerin) $aterials, ;ols9 0+/0+0, ##+/*2, Trans Tech "ublications, S7itBerlan9

*9 Holtam C $, Eaxter ", Ashcro(t I A an Thomson C, *'+'aR M%((ect o( crack e#th on (ati)ue crack

)ro7th rates (or a C/$n #i#eline steel in a sour en8ironmentM, International -ournal o( <ati)ue * 5*'+'6 ##*33/*.D, %lse8ier9

9 Holtam C $, Eaxter ", Ashcro(t I A an Thomson C, *'+'bR M<ati)ue crack )ro7th #er(ormance o(

sour ee#7ater riser 7elsM, "roceein)s o( the *'+' ee# O((shore Technolo)4 5OT6 International

Con(erence, Houston, USA9

09 Holtam C $, Eaxter ", Ashcro(t I A an Thomson C, *'+'cR MAn in8esti)ation into (ati)ue crack

)ro7th test methos in a sour en8ironmentM, International -ournal o( O((shore an "olar %n)ineerin) 5ISSN

+'2/23+6, ;ol9 *', No9 *, -une *'+', ##9 +'/+'.9

29 Eristoll " an oele8el -, +.F3R M<ati)ue o( o((shore structuresR e((ect o( sea7ater on crack #ro#a)ation in

structural steelM, "roc Con( %uro#ean O((shore Steels esearch9

D9 Webster S %, Austen I $ an u % -, +.32R M<ati)ue, corrosion (ati)ue an stress corrosion o( steels (or

o((shore structuresM, %CSC e#ort No9 %U .0D', %CSC Steel "ublications, %uro#ean Commission,

Erussels9

F9 ES FD'3, +..R MCoe o( #ractice (or (ati)ue esi)n an assessment o( steel structuresM, Eritish Stanars

Institution, Lonon9

39 N; "/C*', *''2R M<ati)ue esi)n o( o((shore steel structuresM, et Norske ;eritas9

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acce#te9





++9 NAC% T$'+FF, *''2R MLaborator4 testin) o( metals (or resistance to sul(ie stress crackin) an stress

corrosion crackin) in H*S en8ironmentsM, Item No9 *+*+*, NAC% International, USA9

+*9 <rost N %, $arsh ! - an "ook L ", +.F0R M$etal (ati)ueM, Ox(or Uni8ersit4 "ress9

+9 Slater G, "ar)eter - an Eaxter ", *''2R M<ati)ue #er(ormance o( corrosion resistant steel catenar4

risersM, (inal re#ort, 8olume +, TWI re#ort no9 +0+0*D'29

+09 ES F.+', *''2R MGuie to methos (or assessin) the acce#tabilit4 o( (la7s in metallic structuresM, Eritish

Stanars Institution, Lonon9

+29 Si)nes % G, Eaker G, Harrison - an Eurekin < $, +.DFR M<actors a((ectin) the (ati)ue stren)th o(

7ele hi)h stren)th steels, Eritish Welin) -ournal, +0 56 +'3/++D9

+D9 Watkinson <, Eo)er " H, an Harrison - , +.F+R MThe (ati)ue stren)th o( 7ele :oints in hi)h stren)th

steels an methos (or its im#ro8ementM, "roc9 con(erence on (ati)ue o( 7ele structures, "a#er F, .F/++,

Eri)hton, D/. -ul4 +.F', Abin)ton, U!R Welin) Institute9

+F9 !in) N, Stace4 A an Shar# - ;, +..DR MA re8ie7 o( (ati)ue crack )ro7th rates (or o((shore steels in air

an sea7ater en8ironmentsM, O$A% / ;olume III, $aterials %n)ineerin), AS$%9

+39 Euitra)o - an Weir $ S, *''*R M%x#erimental (ati)ue e8aluation o( ee#7ater risers in mil sour ser8iceM,ee# O((shore Technolo)4 Con(, Ne7 Orleans, USA9

+.9 $c$aster <, Eo7man -, Thom#son H, Phan) $ an !in4on S, *''3R MSour ser8ice corrosion (ati)ue

testin) o( (lo7line an riser 7elsM, O$A% *''3/2F'2., "roc o( *Fth Int Con( on O((shore $echanics an

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*'9 $c$aster <, Thom#son H, Phan) $, Walters an Eo7man -, *''FR MSour ser8ice corrosion (ati)ue

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%n)ineerin), San ie)o, Cali(ornia, USA9

*+9 Euitra)o -, Huak S an Eaxter , *''3R MHi)h/c4cle an lo7/c4cle (ati)ue resistance o( )irth 7els insour ser8iceM, O$A%*''3/2F202, *Fth International Con(erence on O((shore $echanics an Arctic

%n)ineerin), ISEN '/F.+3/3*F/3, AS$%9

Fatigue Performance of Sour Deepwater Riser Welds-Artigo Apenas Texto

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