Underwater wet welding is commonly used to repair corroded offshore ... air fillet
welds are examined in terms of strength, ductility, and failure modes.
Experimental study on strength and ductility of underwater fillet welds in repairing offshore steel structures Xiao Chen, Yasuo Kitane & Yoshito Itoh Dept. of Civil Engineering, Nagoya University, Japan
Results
Introduction Load-deformation 300 Fracture deformation
200
200
Longitudinal 0 0
1
2
3
Longitudinal 400 300
100
Chemical compositions (wt-%)
Weld orientation T: transverse L: longitudinal
TY A
CSY295: Corroded CSY295 C d d SY295. SY295 t: 6-8 mm, l: 20 mm.
"l $
"f s
Weld size
Ductility factor
0.72 0.96 1.41 0.56 0.43
0.016 0.013 0.020 0.013 0.015
-2
HAZ
DEPO
1
0.020 0.019 0.005 0.006 0.007
a
a
w, h =weld leg length, s =weld size, a=weld throat
Definition of weld size Maximum load of the specimen
Number of welds in the specimen
Pmax na l
Average weld length
Average throat thickness
Weld strength
TWA
TSA
TYW
TWW
TSW
0
0 05 0.05
01 0.1
Base plate
0 15 0.15
02 0.2
0 25 0.25
60% 41.0%
40%
30.4% 23.7%
20%
30.3%
21.3% 21.7%
6.9%
-40%
-50.6% -46.6%-50.3%
-60% -80%
Transverse Transverse
STK400
-23.8%
CSY295
-20%
SY295
0% SY295
Strength Strength increase increase
Ductility factor
-54.5% -50.8%
Longitudinal Longitudinal -84.5%
-100%
2
300 # m
(I)
#
300 # m
(I) DEPO
300 # m
(II) BOND
(III) HAZ
Underbead cracks
(II) (III) 300 # m
300 # m
(I) DEPO
(II) BOND
Ferrite+Perlite
300 # m
(III) HAZ
Martensite
Conclusions
s h
h =s
TYA
(b) LCW
-1 0
s
!w $
0 80 0.80
SYW295
DEPO
-3
w
w
Weld strength
fracture deformation of the first fractured weld
0.06 0.02 0.23 0.10 0.10
s
Specimen designation Ductility factor
Cover plate
-4
0.30 0.27 0.10 0.12 0.10
Base steel Y: SY295 W: SYW295 S: STK400 C: Corroded SY295 Welding environment A: in air W: underwater
S
(II) (III)
2
41 34 42 41 30
P
LCW-cover 500 Hv Max: 421 400 3000 200 100
DEPO
497 531 513 394 460
Mn
(I)
HAZ
273 349 392 362 410
Si
DEPO
Base plate
0.29 0.29 0.28 0.28 -
DEPO/BOND failure
200 100
Ducti Ducility ctilitydecrease decrease
HAZ
(a) LCA
LCW-base 500 Hv Max: 5222 400 300 200 100
213 212 213 203 -
0 60 0.60
1 2
Cover plate
500 400 300 200 100
HAZ
properties of steels Table Material 1. Material properties of steels
SY295 CSY295 SYW295 STK400 Electrode
0 40 0.40
-7 -6 -5 -4 -3 -2 -1 0 1 2
Specimen configuration
C
BOND failure
300
SYW295
0 20 0.20
Longitudinal weld specimen
Ultimate Material Young's Poisson's Yield stress, Elongation, stress, ! u modulus, ratio, v ! y (MPa) "! (%) E(GPa) (MPa)
LSW
400
0
LCA- cover Hv Max: 239
Loading
Clip gauge 9 t 9 12.7 t=12.7 or 6-8
Mechanical properties
LCW
-6 -5 -4 -3 --2 -1 0
200
Side view
Transverse weld specimen
LWW
500
1
200
12.7
200
LYW
-5 -4 -3 -22 -1 0
100 200
LSA
500 400 300 200 100
9 9
LCA
Hardness and microstructure
l= 40 or 20
75
Loading
Side view
LWA
LCA-base Hv Max: 213 3
Loading
LYA
600
Ductility factor
40 Clip gauge
DEPO/BOND failure
0 0 00 0.00
5l 5 l 5 40 40
Front view
Front view
BOND failure
200
Experiment program
1.5
Transverse
STK400
Repaired by welding patch plates
Weld strength (MPa)
Weld strength (MPa)
Corroded base
Corroded offshore steel structure
1
700
500
Underwater welder
0.5
Weld deformation (mm)
800
600
Weld
TYA TYW TWA TWW TSA TSW
Transverse 0 0
4
Weld deformation (mm)
Strength g and ductilityy
100
LYA LYW LWA LWW LCA LCW LSA LSW
100
Effect of underwater environment
Patch
A pplied load (kN)
Ultimate load
A pplied load (kN)
Underwater wet welding is commonly used to repair corroded offshore steel structures. The study presents an investigation on strength and ductility of underwater fillet-welded joints. Fourteen different types of weld assemblies are tested to failure, and weld hardness and microstructures are investigated. Differences between underwater and inair fillet welds are examined in terms of strength, ductility, and failure modes. Weldability of base steels in the underwater wet environment is also evaluated.
(1) Underwater fillet welds have larger strength but smaller ductility when compared with in-air welds. Strength increase ranges from 6.9% to 41.0%, while ductility decrease is nearly the same at 50%. (2) Underwater fillet welds on corroded SY295 steels show a drastic ductility decrease of 84.5%, resulting from mechanical mismatching and underbead cracks. (3) The weldability of SY295 steel is undesirable in underwater welding due to its high carbon equivalent.
Contact:
Department of Civil Engineering, Nagoya University Chikusa-ku, Furo-cho, 464-8603, Nagoya, Japan E-mail:
[email protected]
