insp of welded repairs

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NDT.net • July 2004 • Vol. 9 No.07

Inspection and Welding Repairs o !ressure Vessels

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Abstract

Repairs are reuired or pressure 8essels in order to restore its original intended operating condition' sae

operation and to prolong trou:le ree ser8ice lie. T3e 8essel condition deteriorate due to 8arious actors

5ainly (ec3anical !ro:le5s' !rocess Related !ro:le5s and ,orrosion !ro:le5s. Repairs are reuired to planned and carried out under t3e strict super8ision and control o a co5petent Inspector.

T3e paper :ries t3e 8arious steps in8ol8ed inDecision 5a;ing or t3e repairs depending on location and nature o deect <it3in t3e pressure 8essel as p

)"(% as <ell as )!I /0 code.

Welding procedure qualifications.

(aterials and Welding consu5a:les to :e used or procedure ualiication .

Reuire5ents and li5itations o controlled deposition <elding as an alternati8e to !W=T' or <3ere I5pac

testing is a reuire5ent.&y using pre3eating 5et3ods <3ere I5pact testing is not a reuire5ent .

(et3od o >Te5per :ead tec3niues> .(et3od o >=al :ead tec3niue>. NDT t3at can :e e5ployed :eore' during and ater <elding .

Necessity o !W=T and =ydrostatic tests .

Repairs and precautions during o8erlay <eld repairs.(et3ods and precautions to :e ta;en during alterations and re+rating o pressure 8essels.

)spects o reporting and re+inspection .

T3e !aper ai5s to :rie t3e interested audience in8ol8ed in <elding inspection and repairs o pressure 8est3at can :e conducted in "3ut do<ns <it3in ,3e5ical' Reinery' !etroc3e5icals and ?ertili@er industriesA

8arious 5et3ods o <eld repairs and related acti8ities suc3 as testing ater <elding.

Bey Words

-<ner user -<ner or a user organi@ation o t3e euip5ent.

RepairerT3e agency or organi@ation' appointed :y t3e o<ner user orrepairs o t3e euip5ent.

Inspector) co5petent inspection engineer 3a8ing ull ;no<ledge o t3e

pressure 8essel construction' in+ser8ice inspection <elding etc.

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Designer ) co5petent !ressure Vessel Design %ngineer.

,ode,ode or standard used or design construction and Inspection

o !ressure 8essel.

NDTinspector

) co5petent NDT inspector 3a8ing t3oroug3 ;no<ledge and

eCperience o NDT tec3niues in8ol8ed in ,onstruction andrepairs.

!W=T!ost Weld =eat Treat5ent gi8en to t3e !ressure 8essel duringconstruction or repairs.

.0 IntroductionRepair and 5aintenance o parts and co5ponents is a 5aor acti8ity in any process industry. Repair <eldin

can :e carried out as a logical procedure t3at ensures t3e part is usa:le and sae. I repairs are done <it3

proper care or precautions' it can a8oid pre5ature ailures' large <arranty clai5s' saety o property and personnel and result in satisied custo5ers. ?ailures o pressure 8essels are still o:ser8ed' <3ic3 result in a

costly do<n ti5e o production and product losses also so5eti5es it results in en8iron5ental 3a@ards and

unsae <or;ing conditions or disasters. %8ery o<ner user <ants to eCtract 3ig3est possi:le sae ser8ice liero5 euip5ent. T3e pressure 8essel repairs also cannot :e an eCception t3is p3ilosop3y. (odern pressure8essels are constructed in accordance to a recogni@ed code and esta:lis3ed a:rication and <elding practic

2.0 (et3od o Inspection and decision or repairs.

!ressure 8essels are designed to any recogni@ed code o design and construction. We 5ust under stand t3at3e design t3ic;ness can :e considera:ly lo<er t3an t3e actual ?a:ricated . During design itsel corrosion

allo<ance is added in t3e :ase 5etal t3ic;ness and t3e 5anuacturer a:rication c3ooses t3e neCt a8aila:le

t3ic;ness. T3ere:y <e 3a8e a eCcess t3ic;ness a8aila:le or t3e ser8ice <3ic3 result in a considera:ly lo<operating stress 8alue.

"teps in8ol8ed in t3e decision 5a;ing or repairs.

-perating conditions' Inspection 3istory' (aterial o construction o pressure 8essel .

Reasons or ailure .*ocation o t3e da5aged area :y 8isual inspection and e8aluation :y NDTs.

Re+e8aluate t3e need or repairs &ac; to design calculations1.

Repair (et3ods' ?or pressure retaining parts1 .!reparation o repair procedures.

Replace5ent o 5aor co5ponents.

2. -perating conditions' Inspection 3istory' (aterial o construction o !ressure 8essel) careul study o t3e operating para5eters and inspection 3istory and properly 5aintained internal

inspection reports' 5aterials o construction' its :e3a8ior <it3 t3e process luid' <elding tec3niues used

during construction' design consideration etc' also gi8es an adeuate conidence le8el a:out t3e use o pressure 8essel. "uc3 inor5ation is also useul or 5a;ing t3e repair decision. ,areully selected 5aterial

construction and t3e a:rication procedures' <elding procedures as <ell as inspection and certiication :y co5petent inspection aut3orities during a:rication stage' al<ays intend to gi8e suc3 inor5ation.

2.2 Reasons or ailures$ndesira:le pre5ature ailures can occur due to any one or 5ore o t3e ollo<ing reasons. ?aulty design'

aulty <or;5ans3ip' <rongly selected 5aterial o construction' <rong <elding tec3niues suc3 pre5ature

ailures generally occur in an early ser8ice period' <3ere as t3e nor5al ser8ice ailures are attri:uted tocorrosion' c3anges in t3e <or;ing para5eters' operation o t3e 8essel or <3ic3 it is not designed' i5purit

in t3e operating luids' 5etallurgical c3anges in t3e :ase 5etal etc. -nce t3e da5age is identiied t3e



pressure 8essels 5ust :e t3oroug3ly inspected to e8aluate t3e eCtent o da5age' need or repair and t3e rep

5et3od. T3oroug3 8isual inspection o t3e pressure 8essel can :e supple5ented :y a suita:le NDTeCa5ination' to locate t3e deects and t3e eCtent.

2.E *ocation o t3e da5aged area :y 8isual inspection and e8aluation :y NDT.

-n opening t3e euip5ent it is necessary to 5a;e it sae or entry as t3e re5aining luid or u5es o gases

could :e dangerous or 3u5an lie. T3e personnel 5ay :e reuired to stay or internal inspection t3ere cou :e possi:le repairs <3ere 3ot <or; is in8ol8ed' t3ere ore a sae entry per5it ro5 a co5petent aut3ority i

ro5 t3e saety and operation depart5ents. During internal inspection' so5e responsi:le operator s3ould

al<ays :e accessi:le to t3e inspector peror5ing internal inspection. "uc3 assistance can al<ays :e 3andyany critical situation. T3e eCternal surace s3ould :e c3ec;ed or any corrosion :elo< t3e insulation' o:8io

lea;ages' structural attac35ents' connections' oundations' lea; proo tig3tness o pressure relie 8al8es et

T3e internal surace s3ould :e reasona:ly cleaned so as to 8isually 8eriy its condition ' condition o t3reaconnections' ?lange connections' closures' internalsand da5age due to corrosion. Dierent corrosion

pro:le5s anticipated are pitting' line corrosion.' #eneral unior5 corrosion' groo8ing' #al8anic corrosion

?atigue' ,reep' te5perature' =ydrogen attac; %5:ritter5ent' "tress corrosion crac;ing' Inter+granular

corrosion' etc. T3e identiied da5age can :e supple5ented :y NDT or t3e eCtent' <3ere :y decision or

repairs can :e ta;en conidently' 8arious NDT possi:le' are $T t3ic;ness 5easure5ent' $T scanning' RT'(!I and *!T.

2.4 Re+e8aluate t3e need or repairs &ac; to design calculations1&ased on t3e NDT results o:tained' t3e sa5e can :e 8eriied :y t3e designer and inspector :y peror5ing

design calculations' to ensure t3at t3e re5aining t3ic;ness is still sae' and <3et3er t3e repairs are <arrant

or not. &ased on t3e re5aining t3ic;ness corrosion rates are calculated and t3e ()W! at t3e a8aila:let3ic;ness also calculated. I t3e ()W! reuired is lo<er t3at t3e calculated ()W! t3en t3e repairs are n

<arranted pro8ided t3e o<ner user is ready to carry out internal inspection as per neCt sc3eduled inter8al.

*ocation o deect is also i5portant. -n :ase 5etal a<ay ro5 t3e <eld 5etal' a 5onitor t3inning can :e lunattended. In e8ent t3ere are :orderline case t3e t3ic;ness can :e recalculated :y carrying our ull RT an

t3ere:y re8ising t3e Joint eiciency.

?ollo<ing design considerations are re8ie<ed during re+e8aluation!atc3 repairs <elded :y illet <elding can :e used on te5porary :asis. "uc3 repairs s3all :e c3ec;ed and8eriied :y t3e design %ngineer. T3e sa5e s3ould :e replaced <it3 per5anent 5easure at t3e neCt a8aila:l

5aintenance opportunity. ) ully encircle5ent lap oint 5ay :e considered as a per5anent repair 5et3od.

"uc3 ull encircle5ent patc3es s3all also :e designed to 5eet t3e code reuire5ents.(ini5u5 t3ic;ness o:ser8ed s3all :e e8aluated or ()W! and t3e corrosion rate' so as to decide t3e neC

inspection inter8al.

*ocation o locali@ed corrosion' suc3 as on t3e :ase 5etal' a<ay ro5 * sea5' )<ay ro5 , sea5' on t3e<eld oints' on cro<n portion o t3e 3ead' etc. t3ere:y' co5paring t3e original design reuire5ent. e.g. :y

carrying out * sea5 Radiograp3y' t3e oint eiciency can :e re8ised to and t3e re5aining t3ic;ness

accepta:le can :e re8ised.

T3e Inspector s3ould t3in; out all suc3 possi:ilities and ad8ise t3e o<ner user' so as to ta;e a precise udg5ent on t3e repair.

2./ Repair 5et3ods ?or pressure retaining parts1

T3e crac;s are gouged out or re5o8ed and <eld repairs can :e carried out ro5 :ot3 sides' i approac3 isa8aila:le'

T3e deep pits or locali@ed corrosion can :e <eld :uilt to restore t3e original t3ic;ness.

T3e larger area' <3ic3 cannot :e <elded :y :uild up' can :e replaced <it3 patc3 or a s3ell course or a 3ea"o ar "()W or #T)W 3as :een t3e 5ost <idely accepted <elding processes in t3e industry' or its



a8aila:ility o <elding euip5ent and s;illed <elders. =o<e8er ?,)W or #()W processes can also :e

used i suicient eCpertise and euip5ent are a8aila:le. Need less to state t3at any code reuire5ents' contractual reuire5ents or any statutory regulatory

reuire5ent 5ust :e co5plied during <eld repairs.

-riginal construction dra<ing' calculation data and inspection records are i5portant or repairs. I t3e

original construction data is not accessi:le' t3en an analysis o t3e :ase 5aterial' including pre8ious <elddeposits' :eco5es 5andatory. I di5ensions reuire close tolerances or i latness is critical' t3en

:enc35ar;s t3at <ill aid t3e repair <it3out causing eCcessi8e and eCpensi8e da5age to t3e <or; piece 5u :e esta:lis3ed.

T3e crac; in <eld oint or a deect in t3e :ase 5etal can :e repaired :y preparing a >$> or a >V> groo8e to

t3e ull dept3 and lengt3 o crac; and t3en ill up :y <eld 5etal deposit as descri:ed 3ere. I t3e crac; eCiin t3e stress concentration region t3en consult a co5petent pressure 8essel design %ngineer. ,orroded area

5ay :e restored :y <eld 5etal deposition as descri:ed 3ere.

2.F !reparation o a repair procedure

T3e repair procedure s3ould ta;e care o t3e reuire5ents o t3e :ase 5etal' <elding consu5a:les' seuen<eld deposits' reuire5ents o pre3eat' Interpass te5perature' post <eld 3eating' !W=T' i5pact test and t

NDT reuire5ents. T3e repair procedure s3all :e ualiied as per t3e recogni@ed code suc3 as )"(% sec using an eCperienced <elder. (aintain t3e records o procedure ualiication as <ell as peror5anceualiication.

I !W=T is reuired in original construction and it is not practica:le or ad8isa:le during repairs' t3en t3e

Inspector and t3e !ressure Vessel Design %ngineer s3all re8ie< t3e reason or original !W=T o t3eeuip5ent. I t3e -riginal reason <3y !W=T <as done is due to t3e ser8ice reuire5ents' t3en t3e

alternati8e 5et3ods gi8en :elo< 5ay :e a8oided' Details o Repair !rocedures and consideration are gi8e

E.0 o t3is article. It is allo<ed :y t3e Repair H Inspection code to a8oid t3e !W=T as <ell as !ressure tes

ater repairs.E.0 ,onsiderations or repair !rocedures ' 2

E. Repair procedure alternati8e to !W=T' !re 3eating 5et3od' <3ere i5pact testing is not done on t3e

original euip5ent.I5pact testing is not reuired <3en t3is <elding 5et3od is used.

T3is procedure is li5ited to !+#r. H 2A !E +#r. H 2 %Ccluding (n+(o steels1

T3e <eld area is pre 3eated and 5aintained at a 5ini5u5 /0 deg ,' during <elding. T3e te5perature is5easured to ensure 4> 5aterial or 4 ti5es t3ic;ness <3ic3e8er is greater1 ro5 t3e eac3 edge o <eld is

5aintained during <elding.

T3e 5aCi5u5 Interpass te5perature does not eCceed E/ deg ,,arry out <elding as per t3e ualiied procedure.

E.2 Repair procedure alternati8e to !W=T' <3ere i5pact testing is peror5ed on t3e original euip5ent.

W3en t3e original construction reuired i5pact test' Notc3 toug3ness testing as reuired :y t3e code o

construction is reuired. ) procedure need to :e ualiied separately :y using a groo8e <elding on t3e pla

"o5e additional reuire5ents t3at can :e considered o8er and a:o8e t3e supple5entary essential 8aria:leare

T3is procedure is li5ited to !A !E and !4 steels.)ll supple5entary essential ele5ents o )"(% "ection IG para W+2/0 are applied.

T3e <eld area is pre 3eated and 5aintained at a 5ini5u5 /0 deg ,' during <elding. T3e te5perature is

5easured to ensure 4> 5aterial or 4 ti5es t3ic;ness <3ic3e8er is greater1 ro5 t3e eac3 edge o <eld is5aintained during <elding.

T3e 5aCi5u5 Interpass te5perature does not eCceed E/ deg , .



(aCi5u5 3eat input s3all :e calculated and i5ple5ented during repairs. T3e 5aCi5u5 3eat inputs as per

ualiied procedure 5ust not eCceed during <elding.ualiication t3ic;ness or t3e plate 5aterial and t3e groo8es are as per t3e ta:le .

I t3e <elding is to :e done under N),% standard' (R 07/' t3en additional test or 3ardness 5easure to

applied.

?or "()W <elding process' electrodes <it3 additional supple5ental diusi:le 3ydrogen designator =K olo<er s3all :e used. T3e gas used in #T)W or #()W or ?,)W s3all eC3i:it a de< point no 3ig3er t3an

5inus /0 deg ,.

Welding s3all :e carried out as per controlled deposition' te5per :ead or =al :ead tec3niue.)ter co5pletion o <elding' <it3out allo<ing to reduce t3e pre3eat' t3e te5perature is raised to 2E0 to 2K

Deg ,. and 3eld or 5ini5u5 period o a:out 2 =rs to assist as =ydrogen :a;e out treat5ent.

T3e =ydrogen :a;e out treat5ent can :e o5itted i electrodes 3a8ing supple5ental diusi:le 3ydrogendesignator =4 are used.

)ter cooling t3e <eld 5etal' t3e eCcess layer o reinorce5ent is ground o to 5atc3 t3e surace contour

:ase 5etal.

Dept3 oTest #roo8e Repair groo8eDept3 ualiied. T3ic;ness o Test,oupon !late

T3ic;ness o &ase

(etal !late T1ualiied.

t L t L 2> $p to 2>

t L t M 2> ):o8e 2>

Ta:le ualiication t3ic;nesses or test coupon and test repair groo8e.

E.E Non+Destructi8e %Ca5ination and testing o repaired location.T3e prepared surace can :e c3ec;ed :y using (!I or *!T :eore <elding.

)ter co5pletion o <elding' ND% accepta:le to t3e )ut3ori@ed Inspector or t3e o<ner user are selected a

applied to ensure soundness o t3e <eld.

)ter repairs t3e need or pressure test is to :e decided :y t3e Inspector. T3e test te5perature and t3e5ini5u5 design 5etal te5perature o !ressure 8essel s3all :e careully e8aluated.

I =ydrostatic test is i5practica:le' t3en pneu5atic test s3ould :e considered <it3 appropriate saety

consideration.E.4 Repair to "tainless steel o8erlays and clad.

In e8ent any o8erlay or cladding area is re5o8ed' t3en t3e :ase 5etal gets eCposed to t3e ser8ice

en8iron5ent.T3e Inspector s3ould gi8e consideration to re5o8e t3e possi:le entrapped 3ydrogen i t3e ser8ice and t3e

:ase 5etal is prone to 3ydrogen entrap5ent' 3ydrogen e5:rittle5ent' Te5per e5:rittle5ent etc. ) 3eatin

treat5ent suc3 as =ydrogen :a;e out at 2E0 to 2K0Deg ,' or a:out 2 =rs. s3all :e gi8en.4.0 %Cecution o <elding repairs

T3e repairer' under close super8ision and sur8eillance o t3e Inspector' eCecutes actual repairs. T3e <rittenand ualiied procedures are strictly ollo<ed. In case t3e I5pact testing is speciied' t3e <elding para5et

are also 5onitored and ensured to :e <it3in t3e range at <3ic3 t3e procedure is ualiied."peciied ND% :eore <elding repairs and ater <elding repairs are carried out and s3all :e appro8ed :y t3

Inspector.

)ter repairs t3e inspection record and t3e 3istory o euip5ent' gi8ing details o repairs' is updated and ninspection sc3edule s3all :e reco55ended to t3e o<ner user.

/.0 Welding tec3niues ' 2



/. Te5per :ead <elding tec3niue

T3e 3eat aected @one o t3e :otto5 :ead due to t3e top :ead applied <it3 lo<er si@e electrode' lea8es lest3an 20 to E0 o t3e <eld 5etal cross sectional area as a > typical colu5nar grains> and t3e :alance is a

nor5ali@ed structure. T3e top layer o t3e reinorce5ent 5ainly consisting o colu5nar grains' is reuired

:e ground out' to 5atc3 t3e surace contour.

/.2 =al :ead <elding tec3niue')ter e8ery pass' t3e top 3al o t3e <eld :ead is ground o :eore applying t3e neCt layer. "uc3 3al :ead

tec3niue also ac3ie8s t3e si5ilar eect o te5per :ead tec3niue' :ut t3en t3e consu5ption o <elding

electrodes can s3oot up.F.0 ,onclusion

I <is3 to dra< t3e ollo<ing conclusions

Repairs o pressure 8essels are not al<ays <arranted' t3e decision o <elding repairs 5ust :e ta;en <it3 dconsideration to t3e location o deect' careully e8aluated and interpreted ND% results' Design ,alculatio

,onstruction condition suc3 as !W=T and I5pact test.

-nce t3e decision o <elding repairs is ta;en t3en it is necessary to docu5ent t3e repair procedure gi8ing

details o NDT test necessary' !er 3eat and !W=T' <elding seuence' 5onitoring t3e <elding para5eters

pressure test reuire5ents etc.!repare t3e inspection reports and ollo< up inspection at a predeined inspection inter8al.

7.0 R%?%R%N,%")!I /0 + !ressure 8essel inspection code.

)N"I N& 2E + National &oard Inspection code.

insp of welded repairs

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