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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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