High Heat Input Welding of Offshore Structure

7/25/2019 High Heat Input Welding of Offshore Structure

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Procedures and Weld Proper t ies

W ith the right procedures , low-tem perature impac t properties

can be retained w ith high heat input submerged arc welding

B Y G . R 0 R V I K , M .

I.

O N S 0 I E N , A . O. K L U K E N A N D O. M . AKSELSEN

ert ies of h ig h heat in pu t (E > 3

deposi ted we ld metals have been

inc lud ing nondes t ruc ti ve

eva l

side bend testing, hardness mea

In addi t ion, metal lographic

ana l

m i n

0.015 w t -% T i ) con ta in

cons um ables , low we l d meta l

For many years the heat input in

k j / m m ,

in the we ld metal

such as the coarse ferri te sideplates

I.ONS0IEN,

A. O. KLUKEN

O.M. AKSELSENare with The Welding

SINTEF,

The Foundation for

Sci

Researchat the Norwe

tute of Technology, Trondheim,

suit

o f the s low coo l ing ra tes invo lved.

However, recent developments in

w e l d

ing consumables and steelmaking prac

t i ce , based on the phi losophy of control

l ing t ransformat ion behavior through for

ma t ion o f f i ne ly d ispersed no nm eta l l i c

inc lus ions (Refs . 1 -4) , have prov ided

materials w ith a cleavage resistance less

depend ent on the weld heat input . Under

such condi t ions, very f ine grains of pre

dominant ly ac icular ferr i te ( typical grain

s ize of 1-3

u.m)

may fo rm, resu l t ing in

exce l len t impac t p roper t ies . Based on

resul ts obtained in a previous invest iga

t ion (Ref. 5) (wi th a heat input between

5.2 and 8.0 kj /m m) , as we l l as re levant

l i te ra tu re da ta (Refs . 6 -13) , a p r imary

weld metal ac icular ferr i te volume frac

t ion of approximately 50% may give r ise

to a 35J(26 ft- lb) im pac t transit io n

t em

perature wel l below -40C

(-40F).

Appl i ca t ion o f h igh heat input in

welding of of fshore structures requi res,

however, informat ion on f racture tough-

KEY WORDS

Offshore Structures

Mic ros t ruc ture

High Heat Input

W e l d i ng

P W H T

Welding Procedures

Weld Metal Propert ies

SAW

Ti tan ium Content

FCAW

Mechanical Propert ies

ness proper t ies . The present inve s t iga

t ion was under taken w i th the ob jec t i ve

to examine the c rack t ip open ing d is

placeme nt (CTO D) f racture toughness of

procedure tes t we lds us ing submerged

arc we ld ing w i th bo th so l id and f lux

cored w e ld ing w i re , as we l l as sub

merged a rc w e l d i ng w i t h i r on pow de r

add i t ions (so l id w i re ) . Inc luded were

nondestruct ive evaluat ion and s ide bend

test ing,

together with hardness measure

ments, Charpy V-notch and tensi le test

ing. I t is shown that high impact and frac

tu re toughness may be ob ta ined in the

weld metal , both in the as-welded

c o n

di t ion and af ter postweld heat t reatment

(PWHT) .

M ate r i a l s and Ex per ime n ta l

Procedure

Materials and W elding

For the present investigation, f ive dif

f e ren t w e l d i ng c ons umab l es w e re s e

l ec ted .

Inc luded were th ree d i f fe ren t

c o m m e r c i a l l y a v a i l a b l e w e l d i n g c o n

sumables and two consum ables that rep

resent var ious mod i f i ca t ions (one h igh

in t i tanium, and one high in boron). A l l

we lds were depos i ted in doub le V -

g roov es on 60 -mm

(2.4-in.)

th ick base

plates corresponding to Statoi l Grade 1,

w i t h c hem i c a l c ompos i t i on gu i de l i nes

out l i ned in Tab le 1. The weld test as

sem bly is sh ow n in Fig. 1, and reveals

that4000-mm (13.12-ft) long welds were

depos i ted w i th a roo t open ing o f 2 mm

(0.00 8 in.) and a beve l angle of e i ther

40 or 50 deg. The app l ied w e ld ing pa

rameters a re summar ized in Tab le 2 .

These were adjusted to give heat inputs

of 3, 5 and 7

kj/mm

( 76 ,

1

27 and

1

78

kj / in . ) . Typ ica l macrographs are shown

in Fig. 2 for both low and high heat in-

W E L D I N G R E S E AR C H S U P P L E M E N T I 331-s


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Table 1 -

C

0.12

-Chemical Composition Guidelines for Statoil Grade 1

(Elements in wt- ) .

Si M n P S Cu Ni Cr

0.45 1.60 0.010 0.005 0.30 0.70 0.20

M o

0.08

V

0.006

Nb

0.03

Ti

0.03

Al

0.05

(a) Min im um 325 MPa y ie ld s t rength for 60 -mm p la te th ickness.

Groove geometry

2

Constraining plates

40 or 50

600

in. 300

60

J

3

r

0

Constraining

plates \ \

\

\

r

500

,

500 , 500

,

500 , 500 , 500 , 500 , 500

Welding

direction

4000

H

Fig.1 Weld test assembly dimensions in mm).

Table2WeldingParameters (Fill Passes).

Weld

No.

A

B

C

D

E

F

G

H

1

1

K

f

W i r e

OK 13.27

a

OK 13 .27

a

f AC

N i2

b

f AC Ni2

b

SD 3

a

SD 3

a

N W 2

b

N W 2

b

O K

13.27

a

OK 13.27

a

N W

10

b

N W

10

b

Diameter

(mm)

4.0

4.0

2.4

C

2.4

C

4.0

4.0

4.0

4.0

4.0

4.0

4.0

4.0

Flux

OK 10.62

OK 10.62

980

980

OP121TT

OP121TT

P 240

P240

OK 10.62

OK 10.62

P 240

P 240

Metal

Powder

OK 21.86

N o n e

N o n e

N o n e

PD 3 N iM o

PD 3 N iM o

N o n e

N o n e

OK 21.86

OK 21.86

N o n e

N o n e

Current

I (A)

700-750

700-725

450-500

500-525

700-750

750

800

820

650-700

780

800

850

Voltage

U ( V )

3 2 - 3 4

3 2 - 3 5

34-37

37

33

33

32

31

26-29

33

$1

32

Travel

Speed

(mm/s)

4 .7 -5 .8

33

3.3-3.8

2.8

7.5-8.3

5.0

3.6

3.6

5.8-6.7

5.0

5.0

3.8

Heat

InputE

(kj/mm)

5

7

5

7

3

5

7

7

3

5

5

7

G r o o v e

Angle

(deg)

50

5 0

40

50

50

50

40

50

50

50

40

40

a. So l id w i re .

b . F lux core d wi re (NW 2 and NW 10 represent var ious modi f ica t io ns o f the comme rc ia l Corevveld 70 wi re) .

c . 3 /32 in .

Exampleof weld macrograph. Left

Weld E; right

Weld H.

puts. The preheat ing and in terpass tem

peratures wer e 50 and 25 0C(122and

484F), respect ive ly. The root bead and

buf fer layers were deposi ted wi th a

1.2

mm (0 .045 in .) 80N i - 1 f l ux co red w i re

u s in g 7 5 % A r / 2 5 %

C 0

2

sh ie ld ing gas,

and a heat input of 1.7 k j /mm (43 k j / in . ) .

In the case o f submerged a rc we ld ing

w i t h i r o n p o w d e r a d d i t i o n s , p o w d e r

a mo u n t s o f ma x i mu m 9 k g / h ( 2 0 I b / h )

were added . One ha l f o f the p rocedure

we lds (2000-mm leng th ) was sub jec ted

to PWHT at 600C

(111 2F)

for 2

'/

h to

ob ta in i n fo rma t ion on the po ten t ia l e f

fects o f PWHT on weld meta l hardness,

tensi le st rength and duct i l i ty, as wel l as

impact and f racture toughness.

Testing

Al l nondestruct ive eva luat ion (NDE),

side bend and mechanica l test ing were

performed in conformance wi th the Sta

to i l Gu l l faks C spec i f i ca t i on (COI 7-A-

N-SP-304) . The nondest ruc t i ve exami

nat ion included u l t rasonic and magnet ic

par t ic le inspect ion.

The side bend test d imensions were

300 X 60 X 10 mm

(12

X 2.4 X 0.4 in.),

w i t h a f o r me r d i a m e t e r o f 3 0 mm

(1.2

in.) and a 180-deg bend ing ang le . Two

para l le l tests were carr ied out for each

wi re / f l ux comb ina t ion .

The room- tempera tu re tens i l e p rop

er t ies and Charpy V-notch (CVN) tough

ness at -40C were assessed for al l

w e l d s , w i t h sp e c i me n s ma ch i n e d f r o m

the welds as sche ma t ica l ly i l lust ra ted in

Fig. 3 . The tens i l e tes t spec imens ma

ch ined f rom f i l l passes were of 100-mm

(4- in . ) length (50-mm gauge length) wi th

a d iam eter o f e i ther 6 or 8 mm (0.2 4 or

0.31 i n . ) . Impact p roper t i es , based on

the ASTM Charpy V-no tch spec imen d i

mensions of

10

X

1

0 X 55 mm (0.4 X 0.4

X 2 .2 i n . ) , we re ex am ined in bo th the

root region and the f i l l passes, w ith three

paral lel tests for each posit ion.

Mach in ing o f B X 2B spec imens and

CTOD test ing were carr ied out in agree

men t w i th the Br i t i sh S tandard BS

5762 :1979 , wh ich i nc ludes p repara t i on

of the notch and fat igue precracking (this

is s im i la r to AST M Standard 1 290 -

8 9 , 1 9 8 9 , Standard Test Methods for

Crack Tip Opening Displacement

(CTOD) Fracture Toughness Measure

ments). T h e l o ca t i o n o f C T OD sp e c i

mens is show n in Fig. 4 (i.e., c rack p rop

aga t ion th rough the we ld me ta l ) . Th ree

par a l le l tests wer e run at -1 0C

(1

4F)

fo r each w i re / f l ux comb ina t ion .

3 3 2 - s I S E P T E MB E R 1 9 9 2


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Fatigue

precrack

Machined and

electro-discharged

nolch

Samplefor

chemical analysis

3 Location o f CVN specimens (schematic).

Fig. 4 Location of CTOD specimen s (schematic).

T h e w e l d me t a l ch e mi ca l co mp o s i

carbo n, su l fur, n i t rogen and oxy

wh ich were ana lyzed w i th a Leco

em atical ly in Fig. 4.

The meta l lographic examinat ion was

e in i t ia t ion (he., pr imary or

th F ig . 5 , and subsequ ent ly prepared

racture in i t ia t ion area was exam

rost ru cture in a JEOL 200 CX t rans

V

1 0

, i.e., 10-kg load) taken 1 mm (0.4

t ra

Results an d D iscussion

Procedure Welding

I n genera l , we ld ing w i th h igh hea t

inpu t was pe r fo rmed w i thou t techn ica l

prob lems, wi th a few except ions of mag

ne t i c b lo w. Poor s lag de tac hm en t has

been foun d in the case of a bevel a ngle

of 40 deg (Welds C and G), w hic h means

that h igh heat input we ld ing m ay requi re

a beve l ang le o f min imu m 50 deg . How

ever , th is does not necessar i ly g ive r ise

to an increase in the to ta l weld ing t ime.

This is due to the fact that very high de

posi t ion ra tes have been obta ined, as

shown by the da ta con ta ined in Tab le

3. Con vent ion a l submerged arc we ld ing

wi th 3

kj/mm

results in a deposit ion rate

of typ ic a l ly 7 to 8 kg/h

(1

5 to

1

8 Ib/h).

Th is leve l can be ra ised to

1

8 kg/h (40

Ib/h) in the case of submerged arc w e l d

ing wi th a f lux cored w i re using 7

kj/mm

hea t i npu t , o r conven t iona l submerged

arc we ld in g w i t h a so l i d w i re and i ron

pow der a ddi t ions using an arc energy of

5 k j /mm.

Thus, h igh hea t i npu t we ld ing may

give r ise to a subs tant ia l e nha nce m ent

of the deposi t ion ra te (i.e.,

1

50% ) . Th is

p rov ides a bas is fo r i ncreased p rodu c

t iv i ty. I t fo l lows that the product iv i ty po

ten t i a l i nvo l ved in h igh hea t i npu t i n

creases with increasing plate thickness.

NDE and Side Bend Test Results

Bo th the magne t i c pa r t i c l e and the

u l t rason ic i nspect ion revea led on ly a

few cases o f undercu ts and incom p le te

fus ion i n the roo t reg ion . However , a l l

we lds were accep tab le w i th respect to

the cu r ren t spec i f i ca t i on requ i remen ts .

The side bend test results were also ac

cep tab le , bo th i n the as-we lded cond i

t ion and after PWHT.

Weld Metal Chemical Composit ion

The chemica l compos i t i on o f we lds

A throug h L are out l in ed in Table 4 . An

inspect ion of the tab le reveals that the

weld meta l carbon content is s imi lar be

tween the consumab les (0 .0 6 -0 .0 8% C) .

Weld

Machined notch

3Typical Deposition Rates.

.

Technique

SAW/ I P

a

a

b

b

Heat Input

E (k | /mm)

3

5

5

7

Depos i t ion

Rate

(kg/h)

15

18

13

18

Fatiguecrack tip .

Fracture initiation

point

d e r a d d i t io n s .

welding

Sectioning plane to

identify microstructure

sampledby fatigue

crack

Sectioning plane to

identify microstructure

at fracture initiation

point

Fig. 5

Sectioning of CTOD specime ns for determination of brittle fracture initiation

(schematic).

W E L D I N G R E S EA RC H S U P P L E M E N T

I

3 3 3 - s


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Table

4

W e l d

No.

A

B

C

D

E

d

F

e

G

I I

1

J

K

t

Weld Metal Chemical Composition (Elements

inwt- )

a

C

0.07

0.07

0.06

0.06

0.06

0.07

0.07

0.07

0.06

0.06

0.07

0.08

a. All welds contain0.03

b. Elements n ppm.

Si

0.34

0.35

0.26

0.26

0.33

0.29

0.55

0.55

0.29

0.28

0.44

0.43

-0.05


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300

250

200

150

100

50

l l

Open Bars: As Welded

Filled Bars: PWHT

Root Region

ii

I

A B C D E F G H I J K L

WELD NO.

Weld metal CVN toughness at-40 C (root region).

300

O

o 250 -

u

w

O

3 0 p p m ) .

t e a l s o t h e v a r i a t i o n s i n t h e w e l d

a l u m i n u m a n d o x y g e n c o n t e n t s ,

i c h t o g e t h e r w i t h s i l i c o n , m a n g a n e s e

t i t a n i u m m a y i n f l u e n c e t h e r e s u l t

t r a n s f o r m a t i o n b e h a v i o r t h r o u g h

i n f l u e n c e o n d e o x i d a t i o n a n d s u b

n g r a i n s t r u c t u r e

T h e d a ta o b t a i n e d f r o m h a r d n e s s

( H V

1 0

)

a r e o u t l i n e d i n

5 a n d p r e s e n t e d g r a p h i c a l l y i n F ig .

h a r d

n e ss v a l u e s w e r e f o u n d ,

i.e.,

H V

1 0

w i t h i n t h e ra n g e f r o m 2 0 6 to 251

k g / m m

2

i n t h e a s - w e l d e d c o n d i t i o n , a n d

f r o m

197

t o 2 4 7 k g / m m

2

a ft e r P W H T .

T h i s o b s e r v a t i o n is n o t s u r p r i s i n g ,

c o n

s i d e r i n g t h e s l o w c o o l i n g r a te s i n v o l v e d

i n h i g h h e a t i n p u t w e l d i n g (t h e c o o l i n g

t i m e b e t w e e n 8 0 0 a n d 5 0 0 C is t y p i

c a l l y 3 0 t o 7 0 s ). I n g e n e r a l , P W H T g a v e

r i s e t o a s m a l l r e d u c t i o n o f t h e w e l d

m e t a l h a r d n e s s . A n e x c e p t i o n w a s f o u n d

f o r t h e t i t a n i u m - c o n t a i n i n g w e l d s G a n d

H .

I n c o n t r a s t t o t h e l o w h a r d n e s s l e v e l ,

r e l a t i v e l y h i g h y i e l d a n d t e n s i l e s t r e n g t h

v a l u e s h a v e b e e n o b t a i n e d T a b l e 5 .

T h i s p o i n t i s i l l u s t r a t e d i n F i g . 7 . P W H T

r e s u l t e d i n a r e d u c t i o n o f t h e w e l d m e t a l

s t r e n g t h , w i t h a n e x c e p t i o n f o r W e l d s C ,

G a n d H , w h e r e t h e y i e l d s t r e n g t h w a s

r a i s e d b y 5 0 t o 6 5 M P a ( 7 2 5 2 - 9 4 2 7

l b / i n .

2

) . A l s o , t h e t e n s i l e s t r e n g t h l e v e l

w a s i n c r e a s e d f o r t h e t w o t i t a n i u m - c o n

t a i n i n g w e l d s G a n d H b y 12 t o 3 5 M P a

(1 7 4 0 - 5 0 7 6 l b / i n .

2

) , b u t t o a s m a l l e r e x

t e n t t h a n t h e y i e l d s t r e n g t h . I t i s r e a s o n

a b l e t o s u g g e s t t h a t t h e s e r e s u l t s a r e

c a u s e d b y t h e h i g h t i t a n i u m c o n t e n t ,

p r o v i d i n g c o n d i t i o n s f o r s e c o n d a r y

h a r d e n i n g a s a r e s u l t o f p a r t i c l e p r e c i p i

t a t i o n . T h u s , i t i s n o t s u r p r i s i n g t h a t b o t h

t h e h a r d n e s s a n d t h e s t r e n g t h l e v e l a f t e r

P W H T a r e c l o s e l y r e l a t e d t o t h e w e l d

m e t a l T i c o n t e n t , as s h o w n b y F i g . 8 . I n

c o n t r a s t , w h e n c o n s i d e r i n g t h e v a r i a

t i o n s i n t h e w e l d m e t a l c o n c e n t r a t i o n o f

a l l o y i n g e l e m e n t s

( P

c m

v a l u e s r a n g i n g

f r o m 0.167 t o 0 . 2 1 3 ) , n o s t r a i g h t f o r w a r d

r e l a t i o n s h i p b e t w e e n a l l o y i n g l e v e l a n d

y i e l d o r t e n s i l e s t r e n g t h w a s f o u n d .

T h e t e n s i l e d u c t i l i t y w a s r e l a t i v e l y

h i g h ,

r e p r e s e n t e d b y e l o n g a t i o n a t f r a c

t u r e ( 5 0 - m m g a u g e le n g t h ) w i t h i n t h e

r a n g e f r o m 16 t o 2 8 % i n t h e a s - w e l d e d

c o n d i t i o n , a n d b e t w e e n

18

a n d 2 8 %

a f t e r

P W H T T a b l e

5 .

We ld Meta l Impac t Proper t ies

T h e C V N t e s t r e s u lt s a r e s u m m a r i z e d

i n T a b l e 6 , a n d p r e s e n t e d g r a p h i c a l l y i n

t h e f o r m o f v e r t i c a l b a r s i n F i g s . 9 ( f i l l

passes) and 10 ( r o o t r e g i o n ) . I t i s a p p a r

e n t f r o m F ig . 9 t h a t t h e n o t c h t o u g h n e s s

300

0.005 0.01 0.015 0.02 0.025 0.03

W E L D M E T A L T i C O N T EN T , w t %

12

Effect of weld me tal titanium content on CVN toughness at

E

E

y

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High Heat Input Welding of Offshore Structure