harwig

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RESEARCH/DEVELOPMENT/RESEARCH/DEV

ELOPMENT/RESEARCH/DEV


ELOPMENT

ABSTRACT. Gas-sh ie lded f lux cored arcw e ld ing (FC AW -G ) has been i n use fo rm any years. Ho w ever, som e majo r issuess t i l l e x i s t r e g a r d i n g t h e a b i l i t y o f t h eFC AW-G p roc ess to d epos i t soun d w e lds

o n h i g h - i n t e g r i t y a p p l i c a t i o n s , e v e nt h o u g h i t o f f e r s s i g n i f i c a n t e c o n o m i e sdue to i t s h igh d epos i ti on r a te . O ne o f t hem a jo r i ssues w h en w e ld ing h igh - st r eng thstee ls w i th FCAW -G is the d i f fusib l e hy -d rogen po ten t i a l o f v a r i ous e lec t r odes .There have been q ues tion s regard ing them o is tu re c on ten t o f v a r i ous t y pes andc lassi f icat ion s of FCAW -G elec t rodes , es-pec ia l l y a f ter a tm ospher ic exp osure. Fewstudies have been p er formed to estab l isht h e e f f e c t s o f e l e c t r o d e c l a s si f i c a t i o n ,e lec t rode use, mois ture absorpt ion f romatm os pher i c ex posure and w e ld pa ram e-te rs on w e ld m e ta l d i f fus ib le hy d rogenc o n t e n t . L o w - h y d r o g e n sh i e l d e d m e t alarc weld ing (SM AW ) e lec t rodes , for ex -a m p l e , m u s t b e s t o r e d a t 2 5 0 F p e rAN SI /AW S D 1 .1 and h av e a pe rm i ssib lea tm os pher i c ex pos ure up to 9 h be fo rerebak ing is requi red.

The ob jec t i v es o f t h i s i nv es t i ga t i onw ere to d e term in e the e f fec t s o f w e ld pa -rameters on the resul ts o f the d i f fus ib leh y d r o g e n t e st p e r A W S A 4 . 3 - 9 3 f o rFC AW-G e lec t r odes, dev e lop an a tm os -pher i c ex p os ure test p roc edu re and ev a l -uate the atmospher ic exposure tes t pro-c e d u r e o n m i l d s te e l a n d C r- M o

FCAW -G elec t ro des . The m ois ture resis -t a n c e o f E 7 1 T - 1 , E 7 0 T - 1 , E 7 1 T - 5 a n dER70S-3 m i ld stee l e lec t rod es and E81 T-B2 , E91T-B3 and E80C -B2 C r -M o e lec -t rodes w as inv est igated us ing the atm os-p h e r i c e x p o s u r e t e st . T h r e e w i r e f e e dspeeds and th ree c on tac t t ube - to -w ork

dis tances were used to s tudy the ef fec tso f c u r r e n t a n d e l e c t r o d e e x t e n s i o n o nthe w e ld d i f f us ib le hy d rogen c on ten t o fa n E 7 1 T - 1 m i l d s t e e l e l e c t r o d e . W e l dv o l t age and t r av el s peed w ere ad jus ted

to m a in ta in a c on stan t a rc l eng th o f 14 i n .( 6 .3 5 m m ) a n d w e l d d e p o si t a r ea , r e-spec t i v e l y . D i f f us ib le hy d rogen c on ten to f t h e w e l d d e p o s i t w a s f o u n d t o i n -c rease a lm os t l i nea r l y as t he w e ld c u r -rent inc reased for the E71T-1 e lec t rode.The w e ld d i f f usib le hy d ro gen c on ten t i n -c reas ed f r om 2 .3 m L /100 g a t 140 A toa p p r o x i m a t e ly 1 1 . 6 m L / 1 0 0 g a t 3 4 5 A .C on t ra r y t o p ub l i shed l i t e ra tu re , t he e f -fec ts o f e lec t rod e ex tension w ere sm al la t a c ons tan t c u r ren t and a r c l eng th w i t hth i s e lec t r ode . I nc reas ed c on tac t t ube -to -w ork d i stanc e dec reased c u r ren t and ,h e n c e , t h e w e l d d i f f u si b l e h y d r o g e nc on ten t a t a c on stan t w i r e f eed speed .D i f f usib le hy d ro gen c on ten t o f t he w e lddepos i t dec reased w i th i nc reasing t im ein t he e lec t r ode ex tens ion c o lum n. Thed i f f us ib le hy d rogen c on ten t w as h ighe ri n w e l d s m a d e w i t h a l o n g e r c o n t a c tt u b e -t o - w o r k d i st an c e w h e n c o m p a r i n gtest s t ha t had equ a l t im e in t he e lec t r odeex tension c o lum n. Th i s w as be l i ev ed tob e a r e su l t o f t h e h i g h e r w i r e f e e dspeeds , w h ic h c hange the tem p era tu re

p ro f i l e i n t he e lec t rode ex tension .The atmo sph er ic expo sure test evalu-

ated the mois ture res is tance of severa lm i l d s te e l a n d C r- M o F C A W - G e l e c -t rodes f rom d i f ferent suppl iers . The tes t

used a sing le layer o f FCAW -G elec t rod etha t w as c a re fu l l y w ound on a pa in tedw i re spoo l . The spoo l w as ex pos ed tom o i s t u r e i n s i d e a f o r c e d a i r h u m i d i t yc ab ine t . D i f f usib le hy d rogen test s w erep e r fo r m e d o n w e l d s m a d e w i t h t h e seelec t rodes in the as - received and af ter ao n e - w e e k e x p o su r e c o n d i t i o n . T h e a t -m o s p h e r i c e x p o s u r e e n v i r o n m e n t w a scont ro l led at 80F (27C) and 80% re la-t i v e h u m i d i t y . T h e s e h u m i d i t y c a b i n e tparameters were based on the absorbedm o is tu re t est desc r ibed i n AW S A5 .1 -91se c t i o n s 1 6 . 2 t h r o u g h 1 6 . 6 f o r S M A Welec t rodes. A l l w e ld d i f f us ib le hy d rogent e st s w e r e p e r f o r m e d u si n g g a s c h r o -m atog raphy pe r AW S A4 .3 -93 . FC AW -Gelec t rodes w ere foun d to be suscept ib let o m o i st u r e p i c ku p i n a h u m i d e n v i r o n -m e n t . F o r e l e c t r o d e s p r o d u c e d t o t h esame c lass i f icat ion, some var iab i l i ty onw e ld d i f f usib le hy d rogen w as m easuredi n c o n s u m a b l e s su p p l i e d b y d i f f e re n tm a n u f a c t u r er s. F o r e x a m p l e , t h e w e l dd i f f us ab le hy d rogen c on ten t o f E71T-1elec t rodes after a one-w eek exposure in-c r e a s e d f r o m 4 t o 8 m L / 1 0 0 g f o r o n ee l e c t r o d e a n d i n c r e a s e d f r o m 8 t o 2 7m L/100 g for an other . Based on these re-

s u l t s , s t o r a g e a n d o p e r a t i n g r a n g e sshow n by m anu fac tu rer s t o p roduc e l owhy drogen w e ld depos i t s s hou ld be fo l -l ow ed c a re fu l l y w hen hy d rogen-assi stedc rack ing is a r isk . The e lec t rode shouldbe us ed w i th in t he c u r ren t r ange rec om -m e n d e d b y t h e s u p p l i e r o r w i t h l o w e rc u r r e n t s t o m i n i m i z e d i f f u s i b l e h y d r o -g e n . H a n d l i n g g u i d e l i n e s a n d a t m o s -pher ic exposure tes t procedures need tobe estab l i shed to i m p rov e the c on t ro l o fh y d r o g e n i n h i g h - i n t e g r i t y F C A W - Gw e ldm en ts .

Effects o f W eld in g Param eters and Elec t rod eA tm osph eric Exp osure o n the D i f fu sib le

H yd rogen C on ten t o f G as Sh ie lded Flu x Co red

A rc W el d s

B Y D . D . H A R W I G , D . P. LO N G E N E C KER A N D J. H . C R U Z

A v ar ie ty o f e lec t rodes w ere sub jec ted to atm ospher ic exp osure tests to determ in ethe i r suscept ib i l i ty to mois ture absorpt ion

K EY W O R D S

D i f f us ib le H y drogenH y drogen C rac k ingFlux Cored E lec t rodeM ois ture Resis tantL o w H y d r o g enCr-Mo E lec t rod eH u m i d i t yD . D . HA RW I G, i s w i t h Ed is on We ld i ng I nst i -

t u t e , Co lum bus , Oh io . D . P. LON GENECKER

and J. H . CRUZ a re w i t h Tower Au t omo t i v e ,

M i l w a u k e e , W i s.

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Introduct ion

The gas-sh ie ld ed f lux cored arc w eld-ing (FCAW -G) proc ess has been in u se fora p p r o x i m a t e l y 4 0 y e a r s ( R e f . 1 ) . T h eproc es s us es a c ons um ab le e lec t r ode ,l i k e t he gas m e ta l a rc w e ld ing (G M AW )process , except the e lec t rode is tubularand f i l l ed w i t h f l ux , i n add i t i on t o m e ta lp o w d e r s, i n st e a d o f b e i n g so l i d . T h i s

proc ess is prefer red by m any for h igh de-pos i t i on f l a t o r ou t - o f - pos i t i on app l i c a -t i ons. Fo r w e ld ing i n t he f l a t posi t i on , t hes lag prov ided by the f lux core is usual lym ore bas i c t o i nc reas e f l u id i t y , c on t r o lproper t ies and permi t bet ter outgass ing.For o ther weld ing pos i t ions , ru t i le e lec -trodes are preferred s ince the s lags arest i f fe r and p rov ide s uppor t f o r t he w e ldp o o l . L a r g e - d i a m e t e r r u t i l e e l e c t r o d e stha t p rov ide h igh e f fi c i enc y and h igh de -pos i t ion ra tes are a lso u sed in the f la t po-s i t ion. Rut i le e lec t rodes are more ac id icand t y p i c a l l y h av e l ow er im p ac t st r eng ththan bas ic e lec t rod es. Caut ion should b e

used wh en us ing rut i le e lec t rodes in thef la t w eld in g pos i t ion since th e st i f fer slagm a y i n h i b i t o u t g a s s i n g a n d p r o m o t eworm t rack ing (Ref . 2) . E lec t rode manu-fac tu re r s c on t i nu e to dev e lop FC AW-Ge lec tr odes tha t hav e im prov ed p roper t i esand a re approp r ia te f o r h igh - in teg r i ty ap -p l icat ions in a l l pos i t ions .

O ne of the m ajor issues to con sider inth i c k - s ec t i on o r h igh - in teg r i t y app l i c a -t i ons i s t he r es i s tanc e to hy d rogen-as -sis ted crack ing (H AC ). H ydro gen-assis tedc r a c k i n g c a n b e a p r o b l e m i n h i g h e rstrength s teels used in pressure vessels ,pip el in es and steel structu res (Ref. 1) . The

suscept ib i l i ty o f a weldment to hydrogenc rac k ing i s a f unc t i on o f t he hy d rogencontent , the weld and heat -af fec ted zone(HA Z) m ic ros truc ture and hardness, ser -v ice tem perature and w eld res tra in t . Toprevent hydrogen c rack ing, many fabr i -cators use low -hydrogen e lec t rodes, pre-heat the w eldm ent to reduce coo l ing rateand to p rom ote hy d rogen d i f fusion , andin som e cases pos tweld heat t reat (PW H T)to im prov e m ic rost r uc tu re and stab i l i z ethe d i f fus ib le hydrogen. Weld codes ands pec i f i c a t i ons s pec i f y r equ i r em en ts f o rw e ld hy d rogen c on t ro l th rough c ons um -able controls , preheat, interpass tempera-tu re and PW H T to r educ e the r i sk o f H AC .O f t hese requ i r em en ts , c on t r o l o f c on -sumables is c r i t ica l in the cont ro l o f d i f -fusib le hyd rogen below a cer ta in leve l de-p e n d i n g o n t h e w e l d i n g a p p l i c a t i o n .Som e cod es also spec i fy requ i rements forw e l d h e at i n p u t an d m a x i m u m w e l d an dHAZ hardness to cont ro l m ic ros t ruc ture.

This repor t presents deta i ls o f a pro-j ec t t o ev al u ate th e ef fe c ts o f w el d in g p a-rameters and e lec t rode atmospher ic ex -p o s u r e o n t h e d i f f u s i b l e h y d r o g e n

c on ten t o f gas s h ie lded f l ux c o red a r cw elds . The m ajor ob jec t ives of th is studyc an be s um m ar i z ed as f o l l ow s:

1 ) D e te rm ine the e f f ec t s o f w e ld ingparam ete r s on the d i f f us ib le hy d rogenc on ten t o f FC AW -G w e ld depos i t s.

2) D evelop a proc edure to assess thee f f e c ts o f F C A W - G e l e c t r o d e a t m o s -pher i c ex pos ure on the d i f f usib le hy d ro -gen c on ten t o f FC AW -G w e ld depos i t s.

3) D eterm in e the ef fec ts o f FCAW -Ge lec t r ode a tm os pher i c ex pos ure on thew e ld d i f f us ib le hy d rogen c on ten t f o r anum ber o f m i l d steel and C r-M o FC AW-G elec t rodes .

D i f f us ib le hy d rogen o f t he w e ld de -po si t is typ ica l ly m easured us ing the pro-c edures ou t l i ned i n AW S A4 .3 -93 (R e f.3) . Th is procedure permi ts d i f fus ib le hy -drogen to be measured us ing e i ther gasc h rom atog raphy o r a m erc u ry c o l l ec t i onm e t h o d . C o n si d e r a b l e w o r k h a s b e e ndon e w i th in t he AW S A5 c om m i t t ees t oa s s u r e d i f f u s i b l e h y d r o g e n t e s t i n g r e -pea tab i l i t y be tw een labs t h rough roun d-robi n test ing pro jec ts betw een e lec t rodesup pl iers and other l aborator ies (Ref . 4) .

Tw o AW S standards c ov e r FC AW -Ge lec t r odes: A5 .20 , Spec i f i ca t i on f o r C a r - bon Stee l Elec t r odes f o r F lux C o red A rc W e l d i n g (Ref . 5) , and A5.29, Speci f ica- t i on f o r Lo w A l l o y S tee l Elec t r odes fo r F l u x C o r e d A r c W e l d i n g (Ref . 6) (cur -r en t l y be ing r ev i s ed ) . Thes e s tandardsde f i ne t he r equ i r em en ts f o r w e ld p rop er -t i es, sh ie ld i ng gas and w e ld ing pos i t i on .A W S A 5 . 2 0 - 9 5 a l so i n c l u d e s h y d r o g e nc a tegory d esigna to r s as an o p t i on t o en -a b l e m a n u f a c t u r e s t o c e r t i f y t h a t t h ee lec t r ode i s genera l l y c apab le o f ac h iev -

i ng t he i nd i c a ted l ev e l o f d i f f us ib le hy -d rogen und er t he c las si f i c a t i on t est c on -d i t i o n s . T h e t h r e e h y d r o g e n c a t e g o r ydesigna t i ons are H 4 = 4 m LH 2/1 0 0 g; H 8= 8 m L H 2/1 0 0 g; H 1 6 = 1 6 m LH 2/1 0 0 g.

This sys tem has been or is be ing in-corporated in to the e lec t rode spec i f ica-t i o n s fo r sh i e l d e d m e t al a r c w e l d i n g(SM A W ), FC A W - G , G M A W a n d su b -m erged arc w eld in g (SAW ). These c lassi -f icat ions cer t i fy that the as - received d i f -f u si b l e h y d r o g e n c o n t e n t o f w e l ddepos i t s m ade pe r AW S A4 .3 -93 w i l l beless than th e c lassi f icat ion rat ing. The d i f -fus ib le hydrogen c lass i f icat ion sys tem isb a se d o n t h e l i n e a r b e h a v i o r o f w e l dc rac k ing susc ep t i b i l i t y t o t he l oga r i t hm o fthe d i f fus ib le hydrogen content (Ref . 4) .T h e r e f o r e , t h e H 4 c l a ssi f i c a t i o n i s a norder o f m agni tud e less than the H 8 c las -si f icat ion w i th respec t to the in f luenc e ofhy d rogen . M anu fac tu rer s a re now beg in -n in g to supply e lec t rodes using these des-ign ators (Ref. 7) .

The d i f fusib le hyd rogen content o f thew e l d d e p o si t m a d e w i t h a n FC A W - Gw eld ing p rocess is in f luenced by the as- re-

ce ived m ois ture content o f the e lec t rode,the absorbed m ois ture du e to s torage andatmospher ic exposure, the sh ie ld ing gasand th e w eldi ng param eters (Refs. 810 ).The hydrogen c lass i f icat ion in A5.20-95on ly add resses the as-received w eld hy -drogen co ntent . Spec i f icat ions that perm i tt he us e o f FC AW-G e lec t rodes l ac k r e -qu irem ents for the effects of electrod e use,exposure to the atmosphere and w eld pa-rameters. A tmospher ic expo sure con t ro lsand requi rem ents for the SM AW processhave been used for years to assure lo w hy-

W ELD IN G RESEARCH SU PPLEM EN T | 3 1 5 - s

F ig. 1 At m os pher i c ex posure FCAW-G e lec t rode s amp les i n hum id i t y c ab ine t .

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ELOPMENT

drogen in tegr i ty. For exampl e, an E7018MSM AW elec t rode m us t be s tored at 250 F(121 C) per AW S D 1.1 s truc tura l w eld ingcode and have a perm i ssib le atmo spher icex pos ure o f 9 h be fo re r ebak ing . M os t

AW S standards do no t i n c lude requ i r e -m en ts f o r sto rage o f FC AW -G c o ns um -ables. Ho w ever, Sec t ion 12 .6.7 of AW SD 1 . 5 - 9 6 b r i d g e w e l d i n g c o d e d o e s i n -c lude c on t ro l s f o r pac k ag ing , e lec tr odestorage and e lec t rode d ry ing; and equ ip-m ent for FCAW -G elec trode storage is alsonow avai lab le (Ref . 11) . Data is needed forFCAW -G to d eterm ine the ef fec ts o f a t -mospher ic exposure and other key para-meters on d i f fus ib le hydrogen content o ft he w e ld deposi t . Th i s da ta w ou ld he lpsupp or t the use of FCAW -G w hen used forh igh - in teg ri t y app l i c a t i ons. I t s hou ld beno ted tha t t he European s tandard

EN 758 :1992 a lso d ist inguishes hydrogenclass if icat ions and requires manufacturersto s tate in th eir sales l i terature an envelo peo f w e l d i n g c o n d i t i o n s f o r w h i c h t h ec la imed c lass is va l id a long w i th s torageguid el in es (Ref. 12).

F C A W - G e l e c t r o d e s h a v e b e e n r e -po r ted to abs o rb m o is tu re f r om a tm os -pher ic expo sure (Refs. 8 , 13 ) . The in i t ia lhy d rogen c on ten t o f the FC AW-G e lec -t r o d e r e p r e s e n t s t h e h y d r o g e n l e v e lshor t ly a f ter m anufac ture. FCAW -G elec -t rodes may absorb mois ture f rom the at -mosphere dur ing s torage or a t the works t a t i o n a f t e r o p e n i n g t h e p a c k a g i n g .

Som e lubr ic ants on the w i re sheath canc on ta in m o is tu re , w h ic h c on t r i bu tes t oh y d r o g e n i n t h e w e l d . M o i st u r e i s a b -so rbed i n to t he f l ux i ng red ien ts t h roughthe c rev ice in the w i re sheath. Seaml essFCAW -G el ec t rodes are more res istant tom o istu re abso rp t i on i n t he f l ux s inc e thef lux in gredients are not expo sed to the at -m o s p h e r e a f t e r p r o d u c t i o n . U n l i k eSM AW e lec t r odes, FC AW -G e lec t r odesdo not use mois ture-sens i t ive b inders inthe f l ux and hav e a m u c h s m a l l e r fl ux - to -

w i r e v o lu m e ra t i o (Re f . 13 ) . The refo re ,FC AW-G e lec tr odes shou ld be m ore r e -s is tant to mois ture absorpt ion comparedt o SM A W . M o i s tu r e c a n a l so b e i n t r o -duc ed i n to t he w e ld ing a r c t h rough the

sh i e l d i n g g a s a n d i m p r o p e r sh i e l d i n g(Ref . 14) . A tmospher ic exposure tes t inga n d g u i d e l i n e s a n d w e l d p a r a m e t e rguide l ines are requi red for h igh- in tegr i tyFC AW-G app l i c a t i ons.

The ef fec ts of FCAW -G w eld ing para-m eters (Refs. 810 , 14 ) and atmospher icexposure (Refs . 8 , 13) on d i f fus ib le hy -d rogen c on ten t o f t he w e ld depos i t hav ebeen inves t igated by severa l authors forbas ic , ru t i le and meta l cored e lec t rodes .I n g e n e r a l , t h e h y d r o g e n c o n t e n t o fFC AW -G w e lds has been repo r ted to i n -c rease w i th i nc reasing c u r ren t and de -c reasing tube- to-w ork d istance. A t shor ter

t u b e - t o - w o r k d i st a n c e a n d h i g h e r c u r -rents, there is less t im e for resis t ive heat-i n g t o e v a p o r a t e h y d r o g e n - c o n t a i n i n gresidu als f rom the w i re sur face. A lso ath igher cu r rent , i t is be l ieved th at the meta ldrops achieve smal ler d iameters , whichinc reas es the s u r fac e -a rea - to - v o lum erat io o f the d rop (Ref . 9) . Th is means hy -drogen leve ls inc rease faster in f in e drop sfo r a g i v en a r c env i r onm en t due to t hehigher d rop sur face area.

W h i te , et al. , s how ed tha t w e ld d i f -fus ib le hydro gen leve ls f rom u sing the ru-t i l e e l e c t r o d e s, s u c h a s E 7 1 T- 1 , w e r emore suscept ib le to parameter changes

than bas ic e lec t rodes , l ike E71T-5, andm eta l cored e lec t rodes (Refs. 9 , 1 0) . Theyc om pared the d i f f us ib le hy d rogen c on -ten t o f w e lds m ade us ing d i f f e ren t t ube -to-w ork d is tances and co ns tant cur rent .The tests w ere designed to m ainta in co n-s tant depos i t s ize and area by changingt r av e l s p e ed . A r c l e n g t h w a s n o t c o n -t r o l l ed bu t w as be l i ev ed to be approx i -m a te l y 3 m m (0 .118 i n . ) . The hy d rogenlevels were repor ted as a func t io n of bo thd e p o s i t an d f u s ed m e t a l w e i g h t . A W S

A4.3 r equ i r es hy d rogen to b e r epo r ted i nm i l l i l i t e r s pe r 100 g ram s o f w e ld depo si t .For the rut i le e lec t rodes , hydrogen leve li nc reased w i th d ec reasing tub e - to -w orkdis tance at cons tant cur ren t . Un der these

test cond i t ion s, h igher w i re feed speedsw ere requ i r ed to m a in ta in c ons tan t c u r -rent a t the longer tube- to-work d is tance.The hea t i ng t im e o r t he t im e the e lec -t rode spends in the e lec t r ica l ex tens ionb e t w e e n t h e c o n t a c t t i p a n d a rc w a slonger f o r t he l onger t ube - to -w ork -d i s -tance tests. Longer h eat ing t im e w as be-l i ev ed to ev apora te m ore hy d rogen f r omthe e lec t rode before i t entered the arc .W e l d d i f f u si b l e h y d r o g e n m e a su r e dw hen u sing the bas ic e lec t rode E71 T-5w a s n o t a f f e c te d b y t u b e - t o - w o r k d i s -tance o r cur rent . I t w as suggested that thef l uo r i de i n t he E71T-5 f l ux sub l im ed and

reduced the par t ia l pressure of f ree hy -d rogen i n t he a r c . A m e ta l c o red e lec -t rode, AW S E71 T-G, w as a lso tes ted an df o u n d i n s e n si t i v e t o t u b e - t o - w o r k d i s -t a n c e . H y d r o g e n c o n t e n t o f t h e m e t a lcored e lec t rode d epos i t w as sens i t ive tom e t a l t r an s fe r m o d e , w h e r e t h e sp r a yt r an s fe r m o d e p r o d u c e d m o r e w e l dmeta l hydrogen than shor t c i rcu i t t rans -fer.

A s im i lar inves tigat ion w as cond uc tedb y N u h n , et al. , w here a new E81T1-N i1 ,c o n t r o l l e d r o l l e d e l e c t r o d e w a s c o m -p a r ed t o c o n v e n t i o n a l r u t i l e F C A W - Ge lec t r odes (R e f . 8 ) . Bo th e lec t r odes

show ed s ens i ti v i t y t o t ube - to -w ork d i s-t anc e and c u r ren t w here t he new c on-t ro l led ro l led e lec t rode had lower as - re-c e i v ed w e ld d i f f usib le hy d rogen and w asm ore to lerant to change. Atmo spher ic ex -p o s u r e t e st s w e r e p e r f o r m e d o n t h i sFCAW -G elec t rode by u sing the absorbedm ois ture test condi t io ns spec i f ied in AW SA5 .1-91 for SMAW elec t rodes (Ref . 15) .This absorbed mois ture tes t spec i f ies atest i ng env i r onm en t o f 80% re lat i v e hu -m id ity at 80 F (27 C). Electro de exp osure

F ig. 2 Ef f ec t s o f c u r ren t on d i f f us ib le hy d rogen f o r an E71T-1 e lec t rode . A D i f f usib le hy d rogen (deposi t ed met a l ); B d i f f usib le hy d rogen

( tota l fused m etal ) .

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t i m e w a s f r o m se v e r al d a y s t o w e e k s,w h ic h w as c ons ide rab l y l onger t han the9-h test used on SM AW elec t rodes. Theex po sed e lec t r od es w ere then u sed tom ake d i f fus ib le hy drogen tests sim i lar tothe requi rem ents of AW S A4 .3. Resul tsf rom th is inves t igat ion showed the newcont ro l ro l led e lec t rode absorbed mois -tu re bu t a t a r a te m u c h l ow er than c on -vent ion al ru t i le e lec t rodes .

Siew er t (R e f . 13 ) add ress ed tec h -n iques fo r c on t r o l l i ng m o is tu re i n e lec -t r odes. The SM AW m o istu re c on ten t o ft h e c o v e r i n g i s d e t e r m i n e d b y t h e i n -c reas e i n w e igh t o f an abs o rp t i on t ubef i l l e d w i t h a n h y d r o u s m a g n e s i u m p e r -ch lo rate and is expressed as a percentageo f t he o r i g ina l w e igh t o f t he sam p le c ov -e r i ng . The AW S A5 .1 -91 abso rbed m o is -tu re t es t s pec i f i es t ha t e lec t r odes bep lac ed i n a f o r c ed a i r c i r c u la ti on c ab i ne ttha t has an env i r onm en t o f 80% re la ti v ehum id i ty a t 80F for 9 h. The e lec t rode iscon sidered m ois ture resis tant and c an begiven an R mois ture res is tant c lass i f i -

c a t i on i f t he e lec t r ode c oa t i ng m o is tu rec on ten t does no t ex c eed 0 .4 w t -%. Th i sm o is tu re c on ten t t y p i c a l l y r ep res en ts aw e ld m e ta l d i f f us ib le hy d rogen c on ten to f 10 m L /100 g (Re f . 4 ). Th i s m e thod hasbeen u sed for m any years and is easy top e r f o rm o n S M A W e l e c tr o d e s. Fo rFCAW -G elec t rodes , Siew er t sugges tedtha t the e lec t rodes be c u t 1 i n . ( 25 .4 m m )long to pe rm i t m o is tu re w e igh t t es t i nga f t e r m o i s t u r e e x p o s u r e . L i m i t e d d a t aw as p rov ided tha t show ed w e ld depos i t sm a d e w i t h a r u ti l e FC A W - G e l e c t ro d ew ere sus c ep t i b le t o m o istu re p i c k up f r omm o i s t u r e e x p o su r e . H o w e v e r, an a b -so r b e d m o i st u r e o r a t m o s p h e r i c e x p o -sure test and a moisture-res is tant rat ingdoes not ex is t for FCAW -G elec t ro des toda te , al t hough good c o r re la ti on has beenshow n b e tw een pe rc en tage m o istu re i nt h e w i r e a n d d i f f u s i b l e h y d r o g e n i nFC AW-G w e ld m e tal (Re f . 7 ) .

Experimen tal Approach

Th is i nv est i ga ti on w as pe r fo rm ed tod e v e l o p a p r e f e r r e d p r o c e d u r e f o r a t -m o s p h e r i c e x p o su r e t e st i n g F C A W - Gelec t rodes and to evaluate the ef fec ts o fw e ld pa ram ete r s on w e ld m e tal d i f f usib lehy d rogen c on ten t . Bo th m i ld s tee l andlow - a l l oy (C r -M o) e lec tr odes w ere ev a l -u a t e d s i n c e t h e l a t t e r c a n b e u s e d o nh igh - in teg r i t y p res s u re v es s e ls . An a t -m o spher i c ex po sure t est p roc edu re w asd e v e l o p e d t h a t d e f i n e s t h e p r e f e r r e dsample geometry , tes t condi t ions ( t ime,t em p e r at u r e an d h u m i d i t y ) a n d d o c u -m entat ion. I t is hoped th is data w i l l assis ti n t h e d e v e l o p m e n t o f h a n d l i n g a n d w e l dparameter gu ide l ines , a tmospher ic expo-sure l im i ts and an atmospher ic exposure

tes t i ng p roc edure f o rF C A W - G e l e c tr o d e s,the reby im prov ing thec on t ro l o f hy d rogen i nh i g h - i n t e g r i t y w e l d -ments .

The ef fec ts o f w eldparam eters w ere eval -ua ted by c onduc t i ng aser ies of tes ts us ing

t h r e e w i r e f e e dspeeds . A t eac h w i r efeed speed, tests w erep e r f o r m e d a t t h r e ec o n t a c t tu b e - t o - w o r k(TTW ) d istances . Thew e ld depos i t si z e w ash e l d c o n s t a n t b ym a i n t a i n i n g a c o n -st a n t w i r e - f e e d -speed- to- t ravel -speedra t i o . A r c l eng th w asalso h eld co ns tant a t 14i n . ( 6 . 3 5 m m ) . T h i scont ro l led tes t mat r ix

w a s p e r f o r m e d t oe v a l u a t e t h e s i g n i f i -c anc e o f c u r ren t , c on -tac t tube- to-work d is -t a n c e a n d w i r e f e e ds p e e d o n w e l d d i f -f usib le hy d rogen c on -t e n t . W e l d m e t a l h y -d r o g e n w a s r e p o r t e dp e r u n i t d e p o s i t a n dfused w e igh t t o ev a lu -ate the ef fec ts o f w eldpene t ra t i on a t h ighe rcur rents .

W e l d i n g w a s p e r -f o r m e d o n a L i n c o l ns idebeam s tat ion w i tha L i n c o l n D C - 1 0 0 0pow er supp ly . The d i -rec t cur rent e lec t rodep o s i t i v e p o l a r i t y w a sused . The w e ld ing gunw a s g a s c o o l e d a n dm o u n t e d i n a d i r e c td r i v e s e t u p t o m i n i -m iz e w i r e l i ne r c on ta -m in a t i on . A m ix tu re o f8 0 % A r - 2 0 % C O 2 w asused for the sh ie ld inggas. Shi eldi ng gas dewpo in t w as m a in ta inedb e l o w 6 0 C . T h ew eld in g gun w as set at 5 to 10 deg. (0 .08 7to 0.174 rad. ) drag angle to prov ide bet -t e r w e l d p o o l s h i e l d i n g a n d h e l p m i n i -m ize s lag bui ldup at the leading edge oft he w e ld p oo l . The c on tac t tube - to -w orkdi stance (TTW ) was set us ing gauges be-t w e e n t h e c o n t a c t t u b e a n d t h e w o r k -p iece. W ire feed speed and vo l tage w erec on t ro l l ed by a L inc o ln N A-4 c on t ro l l er.A c a l i b ra ti on c u r v e w as de te rm in ed be -

tw een the ac tua l w i re feed speed and theset w i re feed speed. Cal ib rated rea l - t im ed a t a a c q u i s i t i o n w a s u s ed t o m e a su r evol tage, cur rent and w i re feed speed du r -ing the parameter development s tudy Table 1. An E71T-1, 0 .045- in . (1 .14-mm)diam eter elec t rode w as used to evaluatethe ef fec ts o f weld ing p arameters on thew e ld d i f fusib le hy d rogen c on ten t . Th reew ire feeds speed s (W FS) and th ree con -tac t tube- to-wo rk d is tances were used to


F ig. 3 H ea t i npu t e f f ec ts on d i f f usib le h y d rogen (depos i t ).

F ig . 4 Ef f ec t s o f e lec t rode ex t ens ion t ime in c o lum n o n d i f f usib le

hy d rogen . A D i f f usib le hy drogen (depos i t ); B d i f f usib le hy -

drogen ( fused) .

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study the ef fec ts o f cur rent and e lec t rode

ex tension o n the d i f fusib le hyd rogen con-tent o f th is m i ld stee l e lec t rode. Elec t rodeex tension is the d i f ference betw een theTTW and arc length an d represents the re-g ion w here I2R preheat ing occu rs. In theelec t rode ex tension , i t is be l ieved that hy -drogen is evaporated f rom the w i re. A typ-i c a l TTW i s app rox im a te l y 34 in . (19.05m m ) f o r 0 . 0 4 5 - i n . ( 1 . 1 4 - m m ) d i a m e t e re l e c t r o d e s. C o n t a c t t u b e - t o - w o r k d i s-tances of 12 , 78 and 1 14 in . (12.7, 22.2 and28.6 m m ) w ere tested in th is inves tiga-t ion. A t a cons tant e lec t rode ex tens ion,the tim e in t he c o lum n i s de term ined b yd i v id ing t he e lec t r ode ex tens ion by t he

w ire feed speed. H igher cur rents (I ) typ i -ca l ly produce h igher d i f fus ib le hydrogencon tents because the t im e in the co lu mndecreases. W eld vo l tage (V) and t ravelspeed (TS) were adj us ted to m ainta in acon stant arc length of 14 i n . (6 .35 m m ) andw e l d d e p o s i t a r ea , r e sp e c t i v e l y . H e a ti npu t w as c a l c u la ted by t he f o rm u l a

H I = (V x I x 60 ) / TS

D i f f us ib le hy d ro gen test s w ere pe r -f o rm ed to t he r equ i r em en ts o f AW S A4 .3 -

93. The test coupo ns w ere made f rom 12 x

1 x 4 - i n . ( 12 .7 x 25 .4 x 101 .6 -m m ) th i c kpieces of SA36, plus s tart and stop tabs.T h e se sp e c i m e n s w e r e p r e b a k e d a t1100F (593 C) for 1 h to remo ve a l l resid-ua l hy d rogen i n t he bas e m a te r i a l . Theweight o f each spec imen was measuredbefore and af ter the d i f fus ib le hydrogenw eld tes t. The test spec im ens w ere heldin w a ter -c oo led c o pper j aw s. The w e ldw as m ade ac ross the 1 x 4 - i n . (25 .4 x101 .6-mm ) sur face of the spec im en, thenim m ediate ly quench ed in w ater. The slagw as w i r e b rushed o f f t he w e ld depos i t andthe spec im en w as then p lac ed i n l i q u idn i t rogen to inh ib i t loss of hydrogen. D i f -

fusib le h ydrogen w as m easured us ing gasc h r o m a t o g r ap h y u si n g a n O e r l i k o n -Yanaco h ydrogen analy zer. The accuracyof the d i f fus ib le hydrogen tes t us ing th isapproac h has been repo r ted to be ap -p rox im a te l y 1 m L /100 g (R efs. 4 , 16 ).Four w elds were mad e for each test con-d i t ion . These four samp les w ere p laced inhy d rogen-ana ly z e r c an i ste r s. D i f f us iont ime an d tem perature were 30 2F (150 C)for 6 h. The resul ts w ere repor ted b y de-pos i t (D W ) and fused (FW ) w eight . Thefused w eight was determ in ed by m easur -

ing the depo si t (D A) and nu gget (NA ) areaon a m e ta l l og raph ic c ros s s ec t i on andusing the f o l l ow in g fo rm u la :

FW = (N A / D A ) x D W

A n u m b e r o f c a r b o n a n d l o w - a l l o ystee l e lec t rodes w ere used in the atmo s-pher i c ex pos ure t es t s (Tab le 2 ) . Thes ee lec t r odes w ere ac qu i r ed f r om s ev e ra lmanufac turers to evaluate the suscept i -b i l i ty o f FCAW -G elec t rodes f rom d i f fer-ent sources to atmospher ic expo sure. O fthe m i ld s tee l e lec t rodes , severa l ru t i leE71T-1 e lec t rodes w ere c om pared to abas i c , E71T-5 e lec t r ode . The l ow -a l l oye lec t rodes w ere of the Cr -M o type. Fouro f t he f i v e C r-M o e lec t r odes w ere f l uxcored and o ne e lec t rode was meta l cored(E80C -B2) . I n add i t i on , a s o l i d G M AWelectro de (ER70S-3) w as used as a con trolsince so l id w i re shou ld n ot be as suscep-t ib le to mo isture p ick up as FCAW -G elec -t rodes. A tmo spher ic exposure test spec i -m ens w ere m ade by c a re fu l l y w ind ing as ing le layer o f e lec t rode on painted w i rebaskets. A p ainted w i re basket ree l wasused to inh ib i t rust ing of the reel and co n-taminat ion of the e lec t rodes . The atmos-pher ic exposure test spec im ens from thevar ious w i re e lec t rodes were p laced in-side a B lue M forced a i r cabinet that con -t r o l l ed t he a tm os phere t o 80% re la t i v ehum id i ty a t 80F Fig. 1 . A deta i led de-sc r ip t ion of the atm ospher ic expo sure testp roc edure i s p rov ided i n Ap pend ix A .

N o t e t h a t t h e e x p o s u r e c o n d i t i o n sw ere m ode led a f t e r the AW S absorbedm o i s t u r e te st f o r SM A W e l e c t r o d e s i nAW S A5 .1 , ex c ep t t ha t w e igh t ga in usingthe abs o rp t i on t ube tec hn ique w as no tper formed in th is inves t igat ion. Ins tead,t h e e x p o s e d e l e c t r o d e s w e r e d i r e c t l yu s e d t o m a k e d i f f u s i b l e h y d r o g e n t e s tw e lds ac c o rd ing to AW S A4 .3 u sing theparam eters in Table 3. N ote i t is d i f f icu l tt o r em ov e the fl ux f r om FC AW -G e lec -t rodes for w eight ga in analys is and m os tl ow -hy d rogen w e ld ing app l i c a t i ons a reeng ineered b ased on w e ld d i f f usib le hy -d r o g e n c o n t e n t . T h e p r o c e d u r e p r e -sen ted i n Ap pend ix A i s be l i ev ed to p ro -v ide a good sta rt i ng po in t f o r dev e lop in ga s t a n d a r d i z e d a t m o s p h e r i c e x p o s u r etest procedu re for FCAW -G elec t rod es.

The c o red e lec t r odes w ere p lac ed i n -si d e t h e h u m i d i t y c h a m b e r f o r o n e w e e k ,w h ic h w as j udged to be a r easonab l e ex -pos u re pe r iod f o r a FC AW -G e lec t r odev s. 9 h f o r SM AW e lec t r odes. The d i f -f usib le hy d rogen c on ten t o f the w e ld de -p o s i t fo r e a c h F C A W - G e l e c t ro d e w a sde te rm ined i n t he as - rec e i v ed and ex -pos ed c ond i t i on . I t shou ld be no ted tha ttw o e lec t r odes w ere t ested i n A ugus t o f1 9 9 6 , t h e n a g a i n i n A u g u s t o f 1 9 9 7 .Thu s, the ef fec ts o f shel f l i fe w as ben ch-

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m a r k e d f o r t h e se t w o e l e c t r o d e s. A l le lec t rodes w ere sto red i n an a i r - c ond i -t i o n e d r o o m i n si d e m e ta l c a n s w i t h o u tdes iccant . The as- received d i f fus ib le hy -d rogen c on ten t w as based on the da tew hen the e lec t rode pac k age w as opened

in t he l abo ra to r y , no t w hen the e lec t r odew a s m a n u f a c t u r e d . So m e e l e c t ro d ep a c k a g e s w e r e st o r e d a p p r o x i m a t e l yone y ea r be fo re be ing o pened fo r t es ti ng .

Results and D iscussion

The e f f ec ts o f w e ld ing p a ram ete r s onw e l d d i f f u si b l e h y d r o g e n c o n t e n t w a se v a l u a t e d u s i n g o n l y e l e c t r o d e ( A ) ,w h ic h w as an E71T-1 t y pe (Tab le 1 ) . Thed i f f us ib le hy d rogen c on ten t o f t he w e lddepos i t w as c o r re la ted to w e ld ing c u r -r en t , tim e in t he e lec t r ode ex tension c o l -u m n a n d h e a t i n p u t . D e p o s i t ar e a w a s

k e p t f a i r l y c o n s t a n t b y m a i n t a i n i n g aw i r e - f e e d - t o - t r a v e l - sp e e d r a t i o o f 3 5 .The e f f ec t s o f pene t ra t i on w ere ev a lu -a ted by c om par ing the d i f f us ib le hy d ro -g e n c o n t e n t o f b o t h t h e d e p o s i t a n df u se d m e t al . W e l d d i f f u si b l e h y d r o g e nc o n t e n t w a s f o u n d t o i n c r e a se a l m o stl i nea r l y as the w e ld c u r ren t i nc reased F ig . 2 . H ow ev er, c on t r a r y t o pub l i shedl i terature, the ef fec ts o f e lec t ro de ex ten-sion w ere sm a l l a t c ons tan t c u r ren t anda r c l e n g t h w i t h t h e E 7 1 T- 1 e l e c t r o d etes ted here. Inc reased contac t tube- to-w o r k d i s t a n c e d e c r e a s e d c u r r e n t a n dhenc e the d i f f usib le hy d rogen c on ten t a t

a c ons tan t w i r e f eed s peed . The w e ld de -pos i t d i f f usib le h y d rogen c o n ten t v a r i edf ro m 2 . 3 m L / 1 0 0 g a t 1 4 0 A t o a p p r o x i -m a te l y 11 .6 m L /100 g a t 345 A . Th i s c u r -r en t r ange i s t y p i c a l f o r an e lec t r ode th i ssi z e . The d i f f us ib le hy d rogen c on ten t f o rt h e f u s e d m e t a l i n c r e a s e d f r o m 2 . 0m L / 1 0 0 g t o a p p r o x i m a te l y 7 . 1 m L / 1 0 0g ov e r t he s am e c u r ren t r ange . The d i f -f e re n c e i n d i f f u si b l e h y d r o g e n c o n t e n tb e t w e e n t h e d e p o s i t a n d f u s e d m e t a lw as the greatest a t the h igher cu r rents

due to t he i n c reased bas e m eta l d i l u t i on .Th is e f fec t i s im p or tan t sinc e h ighe r c u r -r en ts p rodu c e s low er c oo l i n g r a tes andh igher h ea t i npu ts i n t hese c on stan t de -pos i t a rea test s. H ighe r w e ld d i f f usib leh y d r o g e n c o n t e n t s c a n o f t e n b e t o l e r -

ated at h igher heat inputs because them ic ros t r uc tu re m ay no t be as ha rd andm o r e h y d r o g e n c a n d i f f u s e o u t o f t h ew e l d d u r i n g a s l o w e r c o o l i n g r a t e.

The e f f ec t s o f c on tac t tube - to -w orkd i s t a n c e w e r e m o r e o b v i o u s w h e n t h ehea t i npu t w as c om pared to d i f f usib le hy -d rogen c on ten t o f t he w e ld depos i t F ig. 3 . W e ld d i f f usib le hy d rogen c on ten ti nc reas ed w i th i nc reas ing hea t i npu t a te a c h c o n t a c t tu b e - t o - w o r k d i s ta n c e .Longer TTW dis tances inc reased the re-sis tive h eat ing, dec reased the cur rent an dprodu c ed l ow er heat i npu ts ov e r t he w i r efeed speed range tes ted. From Table 1 , i t

w as apparen t t he TTW d is tanc e m u st bec los el y c on t r o l l ed t o c on t ro l hea t i npu t o fa w e l d m e n t . W e l d d i f f u s i b l e h y d r o g e ncon tent dec reased w i th inc reas ing e lec -t r ode t im e in t he e lec tr ode ex tension c o l -um n F ig . 4 . Based on the s lope fo reac h TTW c o nd i t i on , the d i f f usib le hy -d rogen c on ten t w ou ld b e sl i gh t l y h ighe ri n w e l d s m a d e w i t h a l o n g er T TW d i s-t anc e w h en c om par ing test s t ha t w ou ldhav e equa l t im e in t he c o lum n. Th i s tr endw as bel iev ed to be a resul t o f the h igh erw i re feed speeds and a lon ger d istancef rom the a r c , c hang ing the t em pera tu rep ro f i l e i n t he e lec t r ode ex tens ion . The

m o re t im e an e lec tr ode s pends at h ighe rtem pera tu re t he m ore e f f ec t i v e shou l d bethe hy d rogen rem o v a l . A t c ons tan t t im ein t he c o lu m n, t he sho r te r TTW d is tanc esshou l d h av e a h ighe r t em pera tu re p ro f i l ec o m p a r e d t o th e l o n g e r T T W d i s ta n c esinc e the s ho r te r TTW d is tanc e w i l l r e -c e i v e add i t i ona l h ea ti ng f r om the a r c andhad a l ow er c u r ren t .

The abo ve ef fec ts o f w eld param etersw ere for on e e lec t rode type and size. Thebehav io r o f o ther FCAW -G elec t rodes can

be expec ted to b e d i f ferent . The re la t ion-sh ip b e tw een w e ld pa ram eter s and w e lddi f fus ib le hydrogen contac t needs to beestabl ished for each typ e and size of e lec -t rode before a FCAW -G di f fus ib le hydro-gen c lassif icat i on c an be sat isf ied. For ex-

am p le f o r t he E71T-1 e lec t r ode tes tedhere, an H 8 c lassi f icat ion cou ld be g ivenov er a c u r ren t r ange f rom 140 to 275 A ,w h i c h w o u l d c o v e r a r a n g e o f w e l d i n gp o s i t i o n s. F u t u r e w o r k s h o u l d b e p e r -formed to develop these re la tion ship s.

FC AW-G w e ld depos i t s w ere f ound tobe suscept ib le to inc reased d i f fus ib le h y -drogen leve ls a f ter the atmospher ic ex -po sure test us ing the 80F and 8 0% re la-t i v e h u m i d i t y t e s t c o n d i t i o n s . A l ld i f f u s i b l e h y d r o g e n t e st s w e r e t e st e df r om e lec t r ode sam p l es, w h ic h w ere re -m ov ed f r om sto rage a f te r one w eek o f ex -p o s u r e i n s i d e t h e f o r c e d a i r h u m i d i t y

c ab ine t . The w e ld ing p a ram ete r s us ed o nthe a tm os pher i c ex pos ure t es t s am p lesw ere v ar ied depend ing o n the e lec t rodediameter (Table 3) . The d i f fus ib le hydro-gen c on ten t o f t he w e ld depo si t v a r i edb e t w e e n e l e c t ro d e m a n u f a c t u r e r , a n dsom e e lec t rodes tended to be m ore m o is -ture resis tant du e to the i r f lux i ng ch arac -ter ist ics . For examp le, the wel d d i f fus ib leh y d r o g e n c o n t e n t m a d e w i t h E 7 1 T - 1e lec t rodes a f te r one -w eek ex pos ure i n -c reas ed f r om 4 to 8 m L /100 g f o r e lec -t r o d e A a n d i n c r e a s e d f r o m 8 t o 2 7m L/100 g f o r e lec t rode B F ig. 5 . Thesetes ts were per formed in Augus t 1996, a

few m o n ths af t er t hey w ere r ec e i v ed f r omthe man ufac turers. These two e lec t rodesw ere r etested i n A ugus t 1997 and the r e -su l t s f o r e l e c t ro d e A w e r e t h e sa m e .H ow ev er, e lec tr ode B w as be l i ev ed to besaturated w i th m ois ture in that no d i f fer -e n c e w a s o b s e r v e d b e t w e e n t h e a s-sto red and one-w eek -ex pos ed w e ld d i f -fus ib le hyd rogen con tent a year la ter. A l lthe e lec t rodes were s tored in meta l cansin an a i r- c ond i t i on ed room , henc e i den -t i c a l c ond i t i ons . N o desi c c an t w as us ed

Fig. 5 Atm ospher ic exp osure test resul ts for m i ld s teel FCAW -G elec-

t rodes (note e lec t rod e test cod e and test date in parentheses) .

F ig . 6 At m os pher i c ex pos ure test resu l t s fo r C r -M o FCAW -G e lec -

t rodes (note e lec t rod e test cod e and test date in parentheses) .

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ins ide the cans but , based on these re-s u l t s , s h o u l d b e c o n s i d e r e d f o r s o m eelec t rodes after in i t ia l use wh en the e lec -t rode is p laced b ack in storage. Care mus tbe tak en to m a in ta in t he d r y c ond i t i onof the des iccant bags dur ing use and instorage. Tw o other E71 T-1 e lec t rodes ( Iand J) were tested w here the d i f fus ib lehy d rogen c on ten t o f the w e ld depos i t i n -c reased 10 mL/100 g for e lec t rode I and

4 mL/100 g for e lec t rode J af ter the at -m ospher ic exp osure test . From these re-su l ts , the suscept ib i l i ty to inc reased hy -d r o g e n f r o m a t m o s p h e r i c e x p o s u r ea p p e a r s t o b e a f u n c t i o n o f e l e c t r o d em anu fac tu re r , pac k ag ing m e thod , s to r -age tim e and pos sib l y d iam ete r. W i th inmanufac turers , the condi t ions that mayinf lu ence the rate of m ois ture absorpt ioni n c l u d e f a c t o r s s u c h a s p e r c e n t f i l l o fe lec t rode, t ightness of jo in t , ro l l ing vs .d raw ing , fl ux in g i ng red ien ts and l ub r i -c an t t y pes. There w ere no d i r ec t c om -par isons made to evaluate the ef fec ts o fe lec t r ode d iam ete r f o r a g i v en t y pe o f

e lec tr ode f r om one m anu fac tu rer ; t he re-fo re , no c on c lus ion c an be m ade w i th r e -spec t to d iam eter.

A b a s i c e l e c t r o d e F, E7 1 T - 5 , w a stested and fou nd to b e to lerant to the at -mospher ic exposure tes t . Th is e lec t rodehad a w e ld d i f f us ib le hy d rogen c on ten to f 3 t o 4 m L /100 g as -rec e i v ed and a f te re x p o s u r e . W h e t h e r t h e el e c t r o d e a b -so rbed m o is tu re o r no t w as no t de te r -m in ed , bu t c ou ld be de te rm ined by pe r -f o rm ing a w e igh t ga in m o istu re t est pe rthe p roc edure rec om m ended by S iew er t(Ref . 13) . The E71T-5 e lec t rod e has a f lu-o r i d e -base f l ux sy s tem , w h ic h w as re -po r ted to be to le ran t t o hy d rogen by l o w -er ing the par t ia l pressure of the hy drogeni n t h e a r c e n v i r o n m e n t . T h e l o w e r t h epar t ia l pressure of hydro gen, the low erthe equ i l i b r i um s o lub i l i t y o f hy d rogen i nthe w e ld poo l . To benc hm ark t he ac c u -racy of the d i f fus ib le hyd rogen tes ts per -form ed in th i s inves t igat ion, a so l id e lec -t r o d e ( ER 7 0 S - 3 ) w a s u se d w i t h t h eG M AW proc ess. Th i s e lec t rode L w as i nthe open s hop fo r s ev e ra l m on ths andhad a d i f f us ib le hy d rogen c on ten t o f 2m L / 1 0 0 g .

F i v e C r-M o e lec t r odes w ere a l so ev a l -ua ted us ing the a tm os pher i c ex pos uretest F ig. 6 . These e lec t rodes w ere re-c e i v ed w i th t he abov e ru t i l e e lec t r odesin t he s p r ing o f 1996 . The as - rec e i v edd i f f us ib le hy d rogen c on ten t o f t he w e lddepos i t w hen tes ted i n Augus t o f 1997(i .e. , w hen the e lec tr odes w ere rem o v edf rom the m anu fac tu re r s pac k ag ing ) v a r -i e d f r o m 7 t o 1 7 m L /1 0 0 g . T h e l at te r w a sc ons ide red a h igh hy d rogen l ev e l f o r aC r -M o e lec t r ode tha t c ou ld be us ed onh i g h - s t r e n g t h a p p l i c a t i o n s . A l l t h e s ee lec t rodes w ere supp l i ed i n t he 0 .04 5 -in . ( 1 .14 -m m ) d iam ete r . The e lec t r odes

tha t had the h ighes t w e ld hy d rogen c on -ten t i n t he as- rec e i v ed c o nd i t i ons w eree lec t r odes D and E . Elec t r odes D and Ed i d n o t s h o w a l a r ge i n c r e a se i n d i f -f usib le hy d rogen c on ten t o f the w e ld de -po s i t af ter the atmo sph er ic exp osure testp robab ly bec aus e o f a h igh i n i t i a l m o is -t u re c on ten t . The i n i t i a l m o is tu re c on ten tw as p robab ly a r esu l t o f t he p last i c bagand c a rdbo ard pac k ag ing m e thod . Elec -

t r o d e s G a n d H w e r e s u p p l i e d i n h e r -m e t i c a l l y s e al e d c a n s . T h e w e l d d i f -f usib le h y d rogen c o n ten t o f e lec t r ode Ginc reased f r om 7 to 13 m L /100 g a f t er t hea tm os pher i c ex po sure t est and s how edthe h igh est i nc rease o f t he C r -M o e lec -t rodes tested. Elec t rod e H w as a m eta l -c o r e d e l e c t r o d e , w h i c h a p p e a r s t o b emois ture res is tant in that the d i f fus ib leh y d r o g e n c o n t e n t o f t h e w e l d d e p o s i ton l y i nc reas ed approx im a te l y 1 m L /100g . Th i s w as w i th in t he s tandard o f dev i -a t i o n o f t h e d i f f u s i b l e h y d r o g e n t e s t .Elec t r ode K h ad a n eg l i g ib le i nc rease i nw e l d d i f f u si b l e h y d r o g e n c o n t en t a n d

app ears to be m ois ture resis tant , bu t th ise lec t r ode a l so had a f a i rl y h i gh i n i t i a l d i f -f u s i b l e h y d r o g e n c o n t e n t o f a p p r o x i -m a t e l y 1 1 m L / 1 0 0 g .

The resul ts f rom th is pro jec t c lear lydem on st rate that FCAW -G d epos i ts aresuscept ib le to inc reased d i f fusib l e hydro -gen leve ls a f ter a tmospher ic ex posure oft he e lec t rodes . A l t hough the p ro jec t d idno t address the sou rce and m echani sm o fd i f fus ion, i t is suspec ted that i t is du e tom ois ture p icku p. I t is possib l e that the ef -f ec t i s due to a sim p le abs o rp ti on m ec h -anism. I t is also equal l y po ssib le th at theef fec t is due to chemical reac t ions , thatoccu r over t im e as a resul t o f a tm ospher icexpo sure in vo lv ing th e s tee l sur faces, thel u b r i c a n t s a n d / o r t h e f i l l c o n s t i t u e n t s .Basi c f l ux c o red , m e ta l c o red and so l i de lec t rodes appear to be more to lerant toa t m o s p h e r i c e x p o s u r e t h a n r u t i l e f l u xc o red e lec t rodes . N ew f l ux c o red e lec -t r odes c on t i nu e to be d ev e loped tha t ap -pear to be mois ture res is tant . Addi t ionalw ork needs to be pe r fo rm ed to f u l l y c ha r -ac ter ize the ef fec ts o f f lux type, manu-fac tu r i ng m e thod ( i nc lud ing the e f fec t s o flub r icants ), e lec t rode d iam eter, sh ie ld ingg a s a n d w e l d p a r a m e t e rs. H a n d l i n ggu ide l i nes and an a tm os pher i c ex posuretest proc edure n eed to b e estab l ished toim prov e the c on t ro l o f hy d rogen i n h igh -i n t e g r i t y FC A W - G w e l d m e n t s. T h e at -m o sp h e r i c e x p o s u r e t e st i n g p r o c e d u r eu s e d h e r e i n A p p e n d i x A i s r e c o m -m ended as a star t ing po in t .

Conclusions

This pro jec t evaluated the ef fec ts o fw e l d i n g p a r a m e t e r s a n d e l e c t r o d e a t -m o spher i c ex pos ure on the d i f f usib le hy -d rogen c on ten t o f a r ange o f FC AW -Gw e l d d e p o s i t s . T h e m a j o r c o n c l u s i o n s

tha t c an be d raw n f r om the r esu l t s o f t h i sw ork a re as f o l l ow s:

1 ) We ld d i f f us ib le hy d rogen c on ten tw as found to increase alm ost l inear ly as thew eld cu rrent increased for the E71T-1 elec-trode tested here. The contact tube-to-w ork

dis tance had a sm all effect on di f fusible h y-drogen co ntent at constant current.2 ) We ld d i f f us ib le hy d rogen c on ten t

d e c r e a s e d w i t h i n c r e a s i n g t i m e i n t h ee lec t rode ex tension c o lum n. A t c o ns tan tt im e in t he c o lum n, t he hy d rogen c on ten tw as sl i gh t l y h ighe r w i t h w e lds m ade a th ighe r w i r e f eed s peeds and l o nger c on -tac t tube- to-work d is tances . The temper -ature prof i le in the e lec t rode ex tens ionm ay be respons ib le for th i s e f fec t .

3 ) FC AW -G w e lds are f ound to b e sus -cept ib le to inc reased d i f fus ib le hydro genc o n t e n t a f t e r a t m o s p h e r i c e x p o s u r e o fthe e lec t rodes . The range of d i f fus ib le hy -

d rogen i nc rease v a r ied f r om 19 m L /100g to neg l i g ib le l ev e l s depend ing on theelec t rode af ter a one-week exposure at80% re la t ive humid i ty a t 80F.

4 ) FC AW -G e lec t r odes a re f ound top rodu c e w e ld s w i t h h ighe r d i f f usib le hy -d rogen c on ten ts a f t e r be ing s to red fo ron e year in m eta l cans ins ide an a i r -con -d i t i o n e d ro o m .

5 ) We lds m ade w i th bas i c (E71T-5 )and m etal c o red e lec t r odes appear t o bem ore resis tant to in c reased d i f fusib l e hy -drogen contents af ter a tmospher ic expo-sure o f the e lec t rod es.

6) Handl ing guide l ines and an atmos-

pher ic exp osure test procedu re need to beestabl ished for FCAW -G el ec t rodes thatare in tended to be used in h igh- in tegr i tyappl i cat ions . Based on th is wo rk , i t is rec -o m m e n d e d t h e y b e p u r c h a s e d i n h e r -m i t ic -sealed conta iners and s tored, andused sim i lar ly to the prac t ices for low hy -d rogen SM AW e lec tr odes.

References

1 . W e l d i n g H a n d b o o k , Vol . 2, e ighth ed. ,Am er i can We ld in g Soc ie t y , M iam i , F la .

3 2 0 - s | SEPTEM BER 19 99




ELOPMENT

7/31/2019 HARWIG

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2 . W i d g e ry , D . 1 9 9 4 . Tu b u l a r W i r e W e l d - i n g, Woo dhead Pub l i sh ing L td .

3 . AN SI / AWS A4. 3 -93 , St andard Met hod s f o r De t e rm ina t i on o f t he D i f f usib le H y drogen Con tent of M artensi t ic , Bain i t ic , and Ferr i t ic St ee l W e ld M et a l P roduc ed by Arc W e ld ing ,1993 , Amer i can W e ld ing Soc ie t y , M iam i , F la.

4 . Ko t eck i , D . J. 1992 . H ydrogen recon-s idered. W eld ing Journa l 71(8 ) : 35 -43 .

5 . AN SI / AWS A5. 20 , Spec i f ic at ion for Car- bon St eel E lec trodes f o r Flux C ored A rc W e ld - i n g. Am er i can We ld ing Soc ie t y , M iam i , F la .

6. AN SI /AW S A5.29, Specif icat ion for LowAlloy Steel Fi l ler Electrodes for Flux Cored ArcWe ld ing . American W elding Society, Miam i, Fla.

7. Sierdz insk i , M . S. and Ferree, E. R. 1998 .N e w f l u x c o r e d w i r e s c o n t r o l d i f f u s i b l e h y -drogen levels . W eld ing Journa l 77(2 ) : 4548 .

8 . N u h n , N . G . , e t a l . 1 9 9 4 . D r y r u t i l ecored w ires real ly ex is t . Svetsaren48(2) .

9 . W h i t e, D . , et a l . 1 9 9 2 . T h e e f f e c t o fw e l d i n g p a r a m e t e r s o n d i f f u si b l e h y d r o g e nl e v e l s i n s t e e l w e l d s p r o d u c e d w i t h c o r e dw i res. I n t e rna t i ona l T rends i n W e ld ing Sc ienc e a n d T e c h n o l o g y C o n f e re n c e . G a t l i n g b u r g,Tenn.

1 0 . W h i t e, D . , et al. 1992 . The e f f ec t o fw e l d i n g p a r a m e t e r s o n d i f f u si b l e h y d r o g e nl e v e l s i n c o r e d w i r e w e l d i n g . W e l d i n g a n d

M et al Fabr i c a t i on (6).11. Czarneck i , J . 1998. Prevent ing the ef -

f ec ts o f mo is t u re con t am ina t i on i n f l ux -co redw i r e . Prac t i c a l W e ld ing Today 2(1 ): 4142 .

1 2 . E u r o p e a n S ta n d a r d p r E N 7 5 8 : 1 9 9 2 .W eld ing Cons umab le - Tubu la r Cored Elec - t rodes f o r Me t a l A rc We ld in g w i t h and w i t h - ou t a Gas Sh ie ld o f N on A l l oy and F ine Gra in Steels Cl ass i f icat ion.

13. Siew ert , T. A. 1985. M ois ture in w eld ingf i l ler materials. W elding Journal 64(2) :32-41.

14 . Kiefer, J. H . 199 6. Ef fec ts of mo is turecon t am in a t i on and we ld i ng paramet e rs on d i f -f usib le h ydrogen . W eld ing Journa l 75(5 ) : 155-s to 1 61 -s.

1 5 . A N SI /A W S A 5 . 1 -9 1 , Spec i f icat ion for Carbon St ee l Elec t rodes f o r Sh ie ld ed M et a l

A r c W e l d i n g , 1 9 9 1 , A m e r i c a n W e l d i n g So c i -ety , M iam i , Fla.

1 6 . W h i t e, D . , et al. 1992 . A st udy o f t hes igni f icance of measured values of d i f fus ib lehydrogen a t l ow leve l s. In ternat ion al Trends inW e ld ing Sc ienc e and Tec hno logy Con f e renc e .Gat l i ngburg , Tenn .

Appendix A

Test M ethod for A tmo spheric Expo-sure Test ing and D eterm inat ion ofD if fusible H ydrogen Content forCored Electrodes

Atm ospheric Exposure Testing

Samp le Preparat ion

Cored e lec t rodes should be receivedin the m anufac turer s standard p ackage. I tis prefer red for e lec t rodes to be supp l iedin sealed metal (moisture res is tant) cansto avoid contaminat ion before tes t ing.

Pa in ted w i r e bas k e t spoo ls sha l l beused for a tmo sph er ic expo sure test sam-ples . The spo ols shal l b e standard 1 2- in .s poo ls . A s ing le l ay e r o f t he e lec t r odesha l l be w ound on the spoo l so t ha t un i -

form exposure occurs over the e lec t rodesurface.

The m anu fac tu r i ng c ond i t i ons shou l db e r e co r d e d a n d sh o u l d i n c l u d e A W Sc lass, d iam eter, heat / lo t no . , date of m an-u f a c tu r e , b a k e d ( c o n d i t i o n i n g ) o r n o n -b a k e d a n d t i m e a n d t e m p e r a t u r e i n -v o l v e d i n c o n d i t i o n i n g.

Atm ospheric Exposure Test

The electrod e shall b e exposed in a suit-ably cal ibrated and control led environm en-tal chamb er for one w eek at 80F, mi nus 0,plus 5F and 8 0% RH, m inus 0, plus 5% .

T h e e n v i r o n m e n t a l c h a m b e r s h a l lm ee t t he f o l l ow ing des ign r equ i r em en ts:

1) The app aratus shal l b e an in su latedhum id i f i e r t ha t p roduc es the t em p eratu reof ad iabat ic saturat ion thro ugh regenera-t i v e ev apora ti on o r ev apora t i on o f w a ter.

2) The apparatus shal l have an aver -age ai r speed w i th in t he env e lope o f a i rsu r round i ng the c o red e lec tr odes o f 100to 325 f t /m i n .

3) The ap paratus shal l have a d r ip- f reearea w here the e lec t rode(s) can be p os i -t i oned w i th t he spoo l ax i s ho r i z on ta l andthe spoo l d iam eter posi t ioned as perpen-d icu lar as prac t ica l to the genera l a i r f low.

4 ) The appara tus s ha l l hav e a c a l i -b ra ted m eans o f c on t i nuous l y m easur ingand rec o rd ing the d r y bu lb t em pera tu reand e i t he r t he w e t bu lb t em pera tu re o rthe d i f f eren t i al be tw een the d r y bu lb andthe w e t bu lb t em p eratu re ov e r the pe r iodo f t im e requ i r ed .

5 ) T h e a p p a r a t u s s h a l l h a v e a n a i rspeed of a t least 900 f t /m i n over the w etbulb sensor un less the wet bu lb sensor

c a n b e s h o w n t o b e i n s en s i ti v e t o a i rs peed o r has a k now n c o r rec t i on f ac to rtha t w i l l p rov ide fo r an ad justed w e t bu lbread ing equa l t o t he t em pera tu re o f ad i -abat ic saturat ion .

6) The apparatus shal l h ave the w etbu lb sensor l oc a ted o n the s uc t i on s ide o fthe fan so that there is an absence of heatrad iat ion on the sensor.

The ex pos ure p roc edure s ha l l be asfo l l ow s :

1 ) The e lec t r ode s am p le ( s ) s ha l l beh e a t ed t o t e m p e r a tu r e , m i n u s 0 , p l u s10F abov e the dew p o in t o f t he c ham -ber a t t he t im e o f l oad in g and s to red i n a

desiccator.2 ) The e lec t r ode s am p le ( s ) s ha l l be

loaded in to t he c ham ber w i t hou t de layaf ter remo ved f rom the desiccator .

3 ) The e lec t r ode s am p le ( s ) s ha l l bep lac ed i n t he c ham ber w i t h i t s spoo l ax i sho r i z on ta l on 6 - i n . c en te r s, w i t h t he d i -a m e t e r o f t h e sp o o l p e r p e n d i c u l a r a sprac t ica l to the genera l a i r f low.

4 ) T i m e , t e m p e r a t u r e a n d h u m i d i t yshal l be co nt inuou sly recorded for a per iodthat the electrodes are in the ch amb er.

5) Coun t ing of the exposure t ime shal lstar t w hen the requi red tem perature andhum id i t y i n t he c ham b er a re estab l i shed .

6 ) A t t he end o f ex pos ure t im e , t hee l e c t r o d e s s h a l l b e r e m o v e d f r o m t h ec ham ber and p repared fo r d i f f usib le hy -drogen test ing, as spec i f ied in Sec t ion 2 .

The m anu fac tu rer sha l l c o n t r o l o the rtes t v a r i ab les t ha t a re no t de f i ned , bu tt h e y m u s t b e c o n t r o l l e d t o e n s u r e a

greater consis tency of results .

W elding and Preparation for Analysis

W eld Stat ion Setup

The w e ld s ta t i on us ed fo r m ak ing thedi f fus ib le hydrogen tes t samples shouldbe carefu l ly prepared to avo id tes t er rors.A d i r e c t d r i v e G M A W g u n sh o u l d b eus ed to m in im iz e w i r e l i ne r c on tam ina -t i on and s im p l i f y gun c lean ing be tw eentest r uns. The dew po in t and c om pos i t i ono f t he sh ie ld gas m us t be doc um ented byc ond uc t i ng ana ly si s o f a sam p le o r p ro -c u r e m e n t o f c e r t i f i e d g a s . G a s l i n e ss h o u l d b e t h o r o u g h l y p u r g e d p r i o r t ow e ld ing to r em ov e abs o rbed m o i stu re .

W e ld Param eter s

The w e ld ing gun c on tac t t ube shou ldbe modi f ied to assure e lec t r ica l contac tat the end of the tube. Contac t tube- to-w ork d i s tanc e s hou ld be w i t h in a 132 - i n .t o le ranc e . We ld v o l t age s hou ld be ad -j u ste d so th at th e arc l en gt h i s ap p ro x i -m a t e l y 18- i n . n o m i n a l . T h i s w i l l p e r m i tbet ter cont ro l o f the e lec t r ica l e lec t rodeex tens ion . Work ang le s hou ld be z e ro .T rav e l ang le s hou ld be z e ro t o 10 deg

drag (pu l l ) .W e ld c u r ren t f o r eac h e lec t rode w i l l

be con stant as a func t ion of e lec t rode d i -am ete r and w e ld p os i ti on . Thes e c u r ren tsneed to be es tab l ished. For exampl e, 280a n d 2 0 0 A c o u l d b e u s ed f o r w e l d i n g i nt h e f l a t a n d v e r t i c a l p o s i t i o n , r e s p e c -t i v e l y , w i t h 0 . 0 4 5 - i n . d i a m e t e r e l e c -trodes.

P r io r t o w e ld ing eac h d i f f us ib le hy -drogen sample, 3 f t (0 .9 m) of e lec t rodes hou ld be r an th rough the c on tac t t ubeand c u t o f f t o r em ov e w i r e t ha t m ay bebak ed be tw een test s f r om a w arm c o n tac ttube. D i f fus ib le hydro gen test ing shal l b e

per t he sec t i on be low .

D iffusible H ydrogen Analysis

D if fus ib le hyd rogen tests shal l b e per -f o rm ed to one o f t he m e thods g i v en i nA N SI / A W S A 4 . 3 , St a n d a r d M e t h o d f o r D e te rm i n a ti o n o f t h e D i f f u si b l e H y d r o - gen C on ten t o f M ar tensi t i c , B a in i t i c , and Fe rr i t i c Stee l We ld M e ta l Pr odu ced by A r c W e l d i n g .


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