Prediction Of Residual Stresses In Pipe Welds

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Prediction Of Residual Stresses In Pipe Welds

  1. 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. 2. Content• Introduction• Objectives• Experimental Details• Finite Element Analysis• Results• Effect of residual stresses on crack driving force• Conclusions 2
  3. 3. Introduction• Residual stresses are developed in weld joint due to expansion during heating and contraction during cooling along with constraints. 3
  4. 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. 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. 6. Literature Review 6
  7. 7. Heat Transfer in Welding 7
  8. 8. Heat Transfer in WeldingModelling of heat source depends on :a. Desired accuracy of the heat source modelb. Purpose of predictionc. Availability of information 8
  9. 9. Residual Stresses 9
  10. 10. Residual Stresses 10
  11. 11. Residual Stresses 11
  12. 12. Summary of Literature ReviewEuropean Network on Neutron Techniques Standardizationfor Structural Integrity (NeT) conducted round robinexercise for prediction of temperature and residual stressesin bead on plate (austenitic stainless steel) 12
  13. 13. Experimental Details 13
  14. 14. Chemical Composition Base Material: SS 312 Type 304LN, Filler Rod Material: ER 308L Composition of Parent Material SS312 Type 304 LNCompo C Mn Si S P Cr Ni N sition % 0.021 0.79 0.33 0.003 0.004 18.26 8.45 0.10Content Composition of Filler Rod ER 308 LCompositi 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. 15. CASE A: Bead on plate 15
  16. 16. CASE B: Hot wire GTAW with narrow grooveDistortion 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 lineConfiguration Surface A B C D Narrow Inner 0 6 10 16 groove outer 0 3 7 Nil 16
  17. 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 I3Residual stress measurement by blind hole drilling technique Position form weld centre lineConfiguration Surface A B C DConventional Inner 0 3 7 Nil V-groove Outer 0 3 7 Nil 17
  18. 18. Process Parameters Bead on Plate Diameter of Wire Heat InputPass 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 InputPass 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. 19. Process Parameters GTAW with Conventional groove Diameter Heat Pass Bead Voltage Current Velocity Process of filler InputNumber 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. 20. Residual stress MeasurementX- ray diffraction methodWhen a metal is under stress, applied or residual, the resulting elastic strains causethe 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. 21. Finite Element Analysis 21
  22. 22. Thermal Analysis • Quarter three dimensional finite element model • 37,000 eight noded solid elements • 34,394 nodesHeat transfer to surroundingsby convection and radiation Heat transfer to surroundings by convection and radiation 22
  23. 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. 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 radiationsolidus temperature =13600C,liquidus temperature =14400Clatent heat of fusion=270KJ/Kg 24
  25. 25. Thermal Properties 25
  26. 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. 27. Thermal Analysis Distribution of Temperature 27
  28. 28. Input to Mechanical Analysis 28
  29. 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 sametemperature dependent mechanical and thermal properties. 29
  30. 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 passeslow Modulus of Elasticity Transfer of strains from welded material to theYield Stress same as that of the parent material to be filled without generation of highmetal stresses.Coefficient of expansion of filler No thermal stresses are generated in material tomaterial neglected be filled 30
  31. 31. Mechanical Analysis Mechanical constraints in case pipe weld jointsMechanical constraints incase of bead on plate 31
  32. 32. Material Properties 32
  33. 33. Material Properties 33
  34. 34. Results 34
  35. 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. 36. Temperature Pipe joint with narrow grooveOverall Temperature cycle at Temperature cycle at 4mm from4mm from weld centre line weld centre line for first pass 36
  37. 37. Temperature Pipe joint with conventional V grooveOverall Temperature cycle at Temperature cycle at 4mm from4mm from weld centre line weld centre line for first pass 37
  38. 38. DistortionsPipe joint with narrow groove 38
  39. 39. Residual stressesLongitudinal stressTransverse stress Bead on plate 39
  40. 40. Residual stresses 40
  41. 41. Residual stresses 41
  42. 42. Residual stresses 42
  43. 43. Residual stresses 43
  44. 44. Residual stresses 44
  45. 45. Residual stresses 45
  46. 46. Residual stresses 46
  47. 47. Residual stresses 47
  48. 48. Residual stresses 48
  49. 49. Residual stresses 49
  50. 50. Residual stressesHoop residual stress on inner surface Axial residual stress on inner surface 50
  51. 51. Residual stressesHoop residual stress on outer surface Axial residual stress on outer surface 51
  52. 52. Comparison of residual stresses Pipe joint with narrow groove Residual stresses on inner surface Residual stresses on outer surface 52
  53. 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 asthe 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 experimentaland theoretical residual stresses in welds: The issue of gauge volume, International Journal of Mechanical Sciences 50 (2008) 513–521 53
  54. 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 asthe 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 experimentaland theoretical residual stresses in welds: The issue of gauge volume, International Journal of Mechanical Sciences 50 (2008) 513–521 54
  55. 55. Residual stressesHeatingCooling 55
  56. 56. Residual stressesHoop residual stress on inner surface Axial residual stress on inner surface 56
  57. 57. Residual stressesHoop residual stress on outer surfaceAxial residual stress on outer surface 57
  58. 58. Residual stressesPipe joint with conventional V groove Residual stresses on inner surface Residual stresses on outer surface 58
  59. 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 asthe 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 experimentaland theoretical residual stresses in welds: The issue of gauge volume, International Journal of Mechanical Sciences 50 (2008) 513–521 59
  60. 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 asthe 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 experimentaland theoretical residual stresses in welds: The issue of gauge volume, International Journal of Mechanical Sciences 50 (2008) 513–521 60
  61. 61. Effect of heat input on residual stresses At 4 mm from weld centre line 61
  62. 62. Effect of heat input on residual stressesHoop 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. 63. Effect of Ri/t ratio on residual stresses 63
  64. 64. Effect of residual stresses on crack driving force 64
  65. 65. Axial defect of finite lengthGeometry functions at point A for a finite axial external surface crack in a cylinder 65
  66. 66. Part circumferential external surface crackGeometry functions at point A for a part circumferential external surface crack in a cylinder 66
  67. 67. Normalised residual stress 67
  68. 68. Effect of residual stress on crackdriving force in case of finite axial defect 68
  69. 69. Effect of residual stress in case of part circumferential crack on external surface 69
  70. 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. 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. 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. 73. Thanks a lot 73

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