1. Prediction of residual stresses in
pipe welds using FEM and its
effect on crack driving force
Niraj Deobhankar
Junior Research Fellow
Guide: Shri P. K. Singh
Reactor Safety Division, BARC
Final M. Tech Viva-voce
1

2. Content
• Introduction
• Objectives
• Experimental Details
• Finite Element Analysis
• Results
• Effect of residual stresses on crack driving
force
• Conclusions
2

3. Introduction
• Residual stresses are developed in weld joint due to
expansion during heating and contraction during cooling
along with constraints.
3

4. Introduction
• Due to rapid cooling and solidification of the weld metal
during welding, alloying and impurity elements segregate
extensively in fusion zone and heat affected zone resulting
in inhomogeneous chemical and metallurgical distribution.
• High amount of stresses are consequence of superimposing
of loading and residual stresses
• Residual stresses may lead to loss of performance in
corrosion, fatigue and fracture.
4

5. Objectives
• Produce girth welds of 304LN stainless steel pipes using Hot-wire
Gas Tungsten Arc Welding (GTAW) with narrow groove and cold
wire GTAW with conventional groove.
• Measurement and prediction of temperature during welding in the
weld joint and their comparison
• Measurement and prediction of residual stresses during welding in
the weld joint and their comparison
• Quantification of effect of residual stresses on crack driving force
5

6. Literature Review
6

7. Heat Transfer in Welding
7

8. Heat Transfer in Welding
Modelling of heat source depends on :
a. Desired accuracy of the heat source model
b. Purpose of prediction
c. Availability of information
8

9. Residual Stresses
9

10. Residual Stresses
10

11. Residual Stresses
11

12. Summary of Literature Review
European Network on Neutron Techniques Standardization
for Structural Integrity (NeT) conducted round robin
exercise for prediction of temperature and residual stresses
in bead on plate (austenitic stainless steel)
12

13. Experimental Details
13

14. Chemical Composition
Base Material: SS 312 Type 304LN, Filler Rod Material: ER 308L
Composition of Parent Material SS312 Type 304 LN
Compo
C Mn Si S P Cr Ni N
sition
%
0.021 0.79 0.33 0.003 0.004 18.26 8.45 0.10
Content
Composition of Filler Rod ER 308 L
Compositi
C Mn Si S P Cr Ni Mo Cu
on
% Content 0.017 1.72 0.37 0.011 0.023 19.88 10.02 0.24 0.19
14

15. CASE A: Bead on plate
15

16. CASE B: Hot wire GTAW with narrow groove
Distortion Measured Location
M-M’
Axial Distortion
N-N’
Thermocouple Positions
Distance On Outer On Inner
from edge side side
4 mm O1 I1
7mm O2 I2
10mm O3 I3
Residual stress measurement by blind hole drilling technique
Position form weld centre line
Configuration Surface A B C D
Narrow Inner 0 6 10 16
groove outer 0 3 7 Nil
16

17. CASE C: GTAW with conventional V groove
Thermocouple Positions
Distance On Outer On Inner
from edge side side
4 mm O1 I1
7mm O2 I2
10mm O3 I3
Residual stress measurement by blind hole drilling technique
Position form weld centre line
Configuration Surface A B C D
Conventional Inner 0 3 7 Nil
V-groove Outer 0 3 7 Nil
17

18. Process Parameters
Bead on Plate
Diameter of Wire Heat Input
Pass Voltage Current Velocity
Process filler rod (mm) Current (J/mm)
No (V) (A) (mm/min)
(A)
1 GTAW 2.4 13.5 160 0 63 2057
GTAW with Narrow groove
Wire Heat Input
Pass Diameter of Voltage Current Velocity
Process Current (J/mm)
No filler rod (mm) (V) (A) (mm/min)
(A)
Root GTAW 105 0 100 530
2 GTAW 105 110 550
3 GTAW 135 110 688
4 GTAW 140 100 782
5 GTAW 150 90 924
1.2 8.4
6 GTAW 145 15 90 896
7 GTAW 150 90 924
8 GTAW 145 90 896
9 GTAW 140 90 868
10 GTAW 150 90 924 18

19. Process Parameters
GTAW with Conventional groove
Diameter Heat
Pass Bead Voltage Current Velocity
Process of filler Input
Number Number (V) (A) (mm/min)
rod (mm) (J/mm)
Root 1 GTAW 3.5 12 110 30 2640
2 2 GTAW 12 110 35 2263
3
3 GTAW 14 110 38 2432
4
5
4 GTAW 14 120 45 2240
6
7
5 GTAW 15 130 47 2490
8 2.4
9
6 10 GTAW 15 130 46 2544
11
12
7 13 GTAW 16 135 51 2542
14 19

20. Residual stress Measurement
X- ray diffraction method
When a metal is under stress, applied or residual, the resulting elastic strains cause
the atomic planes in the metallic crystal structure to change their spacing.
The Blind Hole Drilling Strain-Gauge
(BHDSG) method
Removal of stressed material results in
the surrounding material readjusting its
stress state to attain equilibrium.
20

21. Finite Element Analysis
21

22. Thermal Analysis
• Quarter three dimensional finite element model
• 37,000 eight noded solid elements
• 34,394 nodes
Heat transfer to surroundings
by convection and radiation
Heat transfer to surroundings
by convection and radiation
22

23. Thermal Analysis
Heat transfer to surroundings
by convection and radiation
• Half three dimensional finite element model
• 1,29,301 eight noded solid elements
• 1,21,052 nodes
Heat transfer to
surroundings
by convection
and radiation
23

24. Thermal Analysis
Heat transfer to
surroundings by
convection and radiation
• Half three dimensional finite element model
• 1,52,588 eight noded solid elements
• 1,42,830 nodes
Heat transfer to
surroundings by
convection and
radiation
solidus temperature =13600C,
liquidus temperature =14400C
latent heat of fusion=270KJ/Kg
24

25. Thermal Properties
25

26. Heat Source
Power density distribution in double ellipsoidal
heat source
Parameters of double ellipsoidal heat source can
be verified using two criteria:
1. Peak Temperature
2. Weld pool dimensions
26

27. Thermal Analysis
Distribution of Temperature
27

28. Input to Mechanical Analysis
28

29. Mechanical Analysis
Conventional V- Groove
3594 four noded rectangular
elements
3336 number of nodes
Narrow Groove
4306 four noded rectangular
elements
4012 number of nodes
2D finite element model used for Mechanical Analysis
•Plain strain conditions were assumed.
•The parent and the weld material were assumed to have the same
temperature dependent mechanical and thermal properties.
29

30. Mechanical Analysis
• Temperature at which elements of the material to be filled gets transformed
to weld material was set to 13000C.
• Analysis was carried out for isotropic and kinematic hardening rule.
• Element Birth Technique:Stresses built up in the supposedly stress-free filler
material and a redistribution of the residual stresses in the previously laid
weld passes
low Modulus of Elasticity Transfer of strains from welded material to the
Yield Stress same as that of the parent material to be filled without generation of high
metal stresses.
Coefficient of expansion of filler No thermal stresses are generated in material to
material neglected be filled
30

31. Mechanical Analysis
Mechanical constraints in case
pipe weld joints
Mechanical constraints in
case of bead on plate
31

32. Material Properties
32

33. Material Properties
33

34. Results
34

35. Temperature in Bead on Plate
800
700
600
Temperature (°C)
500
400
300
200
100
0
0 200 400 600 800 1000
Time (sec) 35

36. Temperature
Pipe joint with narrow groove
Overall Temperature cycle at Temperature cycle at 4mm from
4mm from weld centre line weld centre line for first pass
36

37. Temperature
Pipe joint with conventional V groove
Overall Temperature cycle at Temperature cycle at 4mm from
4mm from weld centre line weld centre line for first pass
37

38. Distortions
Pipe joint with narrow groove
38

39. Residual stresses
Longitudinal stress
Transverse stress
Bead on plate
39

40. Residual stresses
40

41. Residual stresses
41

42. Residual stresses
42

43. Residual stresses
43

44. Residual stresses
44

45. Residual stresses
45

46. Residual stresses
46

47. Residual stresses
47

48. Residual stresses
48

49. Residual stresses
49

50. Residual stresses
Hoop residual stress on inner
surface
Axial residual stress on inner
surface
50

51. Residual stresses
Hoop residual stress on outer
surface
Axial residual stress on outer
surface
51

52. Comparison of residual stresses
Pipe joint with narrow groove
Residual stresses on inner surface
Residual stresses on outer surface
52

53. Comparison of residual stresses
Pipe joint with narrow groove
Comparison of hoop residual stresses with literature
[5] M. A. Wahab & M. J. Painterb, Numerical models of gas metal arc welds using experimentally determined weld pool shapes as
the representation of the welding heat source, International Journal of Pressure Vessels & Piping Vol. 73 (1997) 153-159
[11] John W.H. Price. Anna Ziara-Paradowska, Suraj Joshi, Trevor Finlaysonb, Cumali Semetaya, Herman Nied, Comparison of experimental
and theoretical residual stresses in welds: The issue of gauge volume, International Journal of Mechanical Sciences 50 (2008) 513–521
53

54. Comparison of residual stresses
Pipe joint with narrow groove
Comparison of axial residual stresses with literature
[5] M. A. Wahab & M. J. Painterb, Numerical models of gas metal arc welds using experimentally determined weld pool shapes as
the representation of the welding heat source, International Journal of Pressure Vessels & Piping Vol. 73 (1997) 153-159
[11] John W.H. Price. Anna Ziara-Paradowska, Suraj Joshi, Trevor Finlaysonb, Cumali Semetaya, Herman Nied, Comparison of experimental
and theoretical residual stresses in welds: The issue of gauge volume, International Journal of Mechanical Sciences 50 (2008) 513–521
54

55. Residual stresses
Heating
Cooling
55

56. Residual stresses
Hoop residual stress on inner
surface
Axial residual stress on inner
surface
56

57. Residual stresses
Hoop residual stress on outer
surface
Axial residual stress on outer
surface
57

58. Residual stresses
Pipe joint with conventional V groove
Residual stresses on inner surface
Residual stresses on outer surface
58

59. Comparison of residual stresses
Pipe joint with conventional V groove
Comparison of hoop residual stresses with literature
[5] M. A. Wahab & M. J. Painterb, Numerical models of gas metal arc welds using experimentally determined weld pool shapes as
the representation of the welding heat source, International Journal of Pressure Vessels & Piping Vol. 73 (1997) 153-159
[11] John W.H. Price. Anna Ziara-Paradowska, Suraj Joshi, Trevor Finlaysonb, Cumali Semetaya, Herman Nied, Comparison of experimental
and theoretical residual stresses in welds: The issue of gauge volume, International Journal of Mechanical Sciences 50 (2008) 513–521
59

60. Comparison of residual stresses
Pipe joint with conventional groove
Comparison of axial residual stresses with literature
[5] M. A. Wahab & M. J. Painterb, Numerical models of gas metal arc welds using experimentally determined weld pool shapes as
the representation of the welding heat source, International Journal of Pressure Vessels & Piping Vol. 73 (1997) 153-159
[11] John W.H. Price. Anna Ziara-Paradowska, Suraj Joshi, Trevor Finlaysonb, Cumali Semetaya, Herman Nied, Comparison of experimental
and theoretical residual stresses in welds: The issue of gauge volume, International Journal of Mechanical Sciences 50 (2008) 513–521
60

61. Effect of heat input on residual
stresses
At 4 mm from weld centre line
61

62. Effect of heat input on residual
stresses
Hoop residual stress on inner
Hoop residual stress on outer
surface
surface
Axial residual stress on inner
surface
Axial residual stress on outer
surface
62

63. Effect of Ri/t ratio on residual stresses
63

64. Effect of residual stresses on crack
driving force
64

65. Axial defect of finite length
Geometry functions at point A for a finite axial external surface crack in a cylinder
65

66. Part circumferential external surface
crack
Geometry functions at point A for a part circumferential external
surface crack in a cylinder
66

67. Normalised residual stress
67

68. Effect of residual stress on crack
driving force in case of finite axial
defect
68

69. Effect of residual stress in case of part
circumferential crack on external
surface
69

70. Conclusions
• Thermal cycle matches well with observations in all cases, although peak
temperature is slightly over-predicted. Reason for over-prediction can attributed
to the simplifications considered in heat dissipation in welding process.
• From comparison between residual stresses predicted using various strain
hardening rules, prediction using kinematic strain hardening rule comes close to
measured values.
• In case of bead on plate, residual stresses predicted using available FE code match
well with experimentally measured values. This helps in validation of the code to
be used in further investigation.
70

71. Conclusions
• In case pipe joints predicted residual stresses on inner surface match well
qualitatively.
• Residual stresses on outer surface follow the trend found in literature.
• Residual stresses in case of pipe joint using conventional groove is more than that
using narrow groove.
• With increase in heat input residual stresses increase in magnitude and hence
excessive heat input is detrimental to the weld joint.
• Ratio of inner radius with thickness does not alter residual stress pattern
drastically. But with increase in Ri/t ratio tensile nature of residual stresses
increases especially on outer surface.
71

72. Conclusions
• For pipe joints with different thicknesses but same Ri/t ratio and heat
input, residual stresses generated in pipe with larger thickness are low.
• Residual stresses contribute to crack driving force heavily and hence should be
accounted for.
72

73. Thanks a lot
73