Mechanistic studies of stress corrosion cracking of alloy 600 in high temperature high pressure water

276 Pages·2010·20.01 MB·English

by  Fabien Léonard

Study of Stress Corrosion Cracking of Alloy 600
in High Temperature High Pressure water
A thesis
submitted to the University of Manchester for the degree of
Doctor of Philosophy
in the Faculty of Engineering and Physical Sciences
2010
FABIEN LÉONARD
SCHOOL OF MATERIALS
Materials Performance Centre

Contents
Contents 3
List of Figures 7
List of Tables 13
List of Abbreviations 15
Abstract 18
Declaration 19
Copyright 20
Acknowledgements 21
Preface 23
Introduction 24
I Literature Review 27
1 Material presentation 29
1.1 Composition of alloy 600 . . . . . . . . . . . . . . . . . . . . . . . . 30
1.2 Microstructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
1.3 Thermal treatments . . . . . . . . . . . . . . . . . . . . . . . . . . 33
2 Stress corrosion cracking 37
2.1 Historical background . . . . . . . . . . . . . . . . . . . . . . . . . 39
2.2 Stages and morphology . . . . . . . . . . . . . . . . . . . . . . . . 40
2.3 Influencing parameters . . . . . . . . . . . . . . . . . . . . . . . . . 41
3
Contents
2.4 Modelling component life . . . . . . . . . . . . . . . . . . . . . . . 61
3 Mechanistic models 67
3.1 Slip-dissolution model . . . . . . . . . . . . . . . . . . . . . . . . . 68
3.2 Corrosion enhanced plasticity model . . . . . . . . . . . . . . . . . 71
3.3 Internal oxidation model . . . . . . . . . . . . . . . . . . . . . . . . 75
3.4 Model discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
II Techniques and Modelling 87
4 Experimental 89
4.1 Specimen orientation . . . . . . . . . . . . . . . . . . . . . . . . . . 89
4.2 Strain path . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
4.3 Mechanical testing . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
4.4 Stress corrosion cracking testing . . . . . . . . . . . . . . . . . . . 92
4.5 Grinding and polishing . . . . . . . . . . . . . . . . . . . . . . . . . 94
4.6 Crack depth analysis . . . . . . . . . . . . . . . . . . . . . . . . . . 95
4.7 Carbide distribution . . . . . . . . . . . . . . . . . . . . . . . . . . 97
4.8 Electron backscattered diffraction . . . . . . . . . . . . . . . . . . . 98
4.9 Misorientation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
4.10 Proving ring calibration . . . . . . . . . . . . . . . . . . . . . . . . 99
5 Finite element analysis 101
5.1 Experimental set-up . . . . . . . . . . . . . . . . . . . . . . . . . . 101
5.2 Finite element model . . . . . . . . . . . . . . . . . . . . . . . . . . 103
III Results 109
6 Material characterisation 111
6.1 Material description . . . . . . . . . . . . . . . . . . . . . . . . . . 111
6.2 Chemical composition . . . . . . . . . . . . . . . . . . . . . . . . . 112
6.3 Mechanical properties . . . . . . . . . . . . . . . . . . . . . . . . . 113
6.4 Carbide distribution . . . . . . . . . . . . . . . . . . . . . . . . . . 120
6.5 Grain boundary character . . . . . . . . . . . . . . . . . . . . . . . 122
6.6 Misorientation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
6.7 Strain path . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
7 Modelling results 133
7.1 Mechanical behaviour . . . . . . . . . . . . . . . . . . . . . . . . . 133
7.2 Output data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
4
Contents
7.3 Model assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
8 Stress corrosion cracking testing 143
8.1 Susceptibility assessment . . . . . . . . . . . . . . . . . . . . . . . . 143
8.2 Wedge-opening loading specimens. . . . . . . . . . . . . . . . . . . 144
8.3 Proving ring tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
8.4 Dead weight tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
8.5 Combination of constant load test results . . . . . . . . . . . . . . 154
8.6 Statistical analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
IV Discussion 159
9 Susceptibility vs microstructure 161
9.1 SCC susceptibility . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
9.2 Microstructural analysis . . . . . . . . . . . . . . . . . . . . . . . . 162
10 SCC testing vs strain path 169
10.1 Proving ring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
10.2 Strain path . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
10.3 Proving ring vs dead weight . . . . . . . . . . . . . . . . . . . . . . 172
V Conclusion 175
11 Summary conclusions 177
12 Future work 179
VI Appendices 181
A Calibrations of static autoclaves 183
B Statistical distribution fit 185
®
C MATLAB routines 189
C.1 β parameter calculation . . . . . . . . . . . . . . . . . . . . . . . . 189
C.2 Crack statistics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
C.3 Image analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
D FE model 195
E Grain boundary character analysis 205
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Contents
F Misorientation analysis 209
F.1 WF675 as-received . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
F.2 WF675 cold-worked . . . . . . . . . . . . . . . . . . . . . . . . . . 213
F.3 78456/337 as-received . . . . . . . . . . . . . . . . . . . . . . . . . 216
F.4 78456/337 cold-worked . . . . . . . . . . . . . . . . . . . . . . . . . 219
F.5 2360 as-received . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222
F.6 2360 cold-worked . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224
F.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227
G β parameter calculation details 229
H Santarini’s method 233
I Analytical model 235
J Lognormal distribution fit 237
K Fracture surfaces 243
Bibliography 253
Final word count: 30635
6
List of Figures
1.1 Applications of alloy 600 in PWR primary system . . . . . . . . . 30
1.2 Alloys of interest positioned on the Fe-Cr-Ni phase diagram . . . . 31
1.3 Ni-Cr-Fe phase diagram . . . . . . . . . . . . . . . . . . . . . . . . 32
1.4 Alloy 600 precipitates observed by TEM . . . . . . . . . . . . . . . 32
1.5 Influence of annealing temperature on alloy 600 microstructure . . 33
1.6 Effect of annealing temperature on a cold-worked microstructure . 34
1.7 Carbide precipitation diagram for alloy 600 . . . . . . . . . . . . . 35
2.1 Factors affecting stress corrosion cracking . . . . . . . . . . . . . . 37
2.2 Example of stress corrosion cracking in brass . . . . . . . . . . . . 38
2.3 Major submodes of stress corrosion cracking for alloy 600 . . . . . 38
2.4 Service and laboratory experience with SCC in alloy 600 . . . . . . 39
2.5 Steps of the stress corrosion cracking process . . . . . . . . . . . . 40
2.6 Stress corrosion cracking morphology of alloy 600 . . . . . . . . . . 41
2.7 Influence of nickel content on SCC of austenitic alloys . . . . . . . 42
2.8 Influence of nickel and chromium content on IGSCC . . . . . . . . 43
2.9 Influence of carbide distribution on SCC process . . . . . . . . . . 44
2.10 Examples of carbide microstructure types . . . . . . . . . . . . . . 44
2.11 Schematic representation of a chromium depleted zone . . . . . . . 45
2.12 Average crack growth rate as a function of cold work . . . . . . . . 46
2.13 Influence of cold work on SCC initiation time . . . . . . . . . . . . 47
2.14 Effect of processing orientation on SCC growth rate . . . . . . . . 48
2.15 IGSCC resistance limit as a function of grain boundary energy . . 49
2.16 Influence of grain size on IGSCC behaviour . . . . . . . . . . . . . 50
2.17 Arrhenius plot for initiation time and crack growth rate . . . . . . 52
2.18 IGSCC initiation time vs reciprocal temperature . . . . . . . . . . 53
2.19 Pourbaix diagram showing the domains of cracking in alloy 600 . . 54
2.20 Influence of hydrogen partial pressure on crack initiation . . . . . . 55
2.21 Influence of hydrogen partial pressure on crack propagation . . . . 55
2.22 Fracture surface with IGSCC as a function of applied potential . . 56
7
List of Figures
2.23 Influence of pH on crack velocity . . . . . . . . . . . . . . . . . . . 57
2.24 Influence of lithium on crack initiation . . . . . . . . . . . . . . . . 58
2.25 Influence of stress on initiation time and failure time . . . . . . . . 59
2.26 Crack growth rate as a function of the stress intensity factor. . . . 59
2.27 Correlation between initiation time and plastic strain . . . . . . . . 60
2.28 Evolution of crack growth rates as a function of the strain-rate . . 60
2.29 Comparative crack depths during SSRTs and constant-load tests . 61
2.30 Stochastic approach for vessel head nozzle . . . . . . . . . . . . . . 64
2.31 Schematic representation of the Monte-Carlo approach . . . . . . . 65
3.1 Schematic illustration of elements of slip dissolution model . . . . . 68
3.2 CGR values predicted by the slip-dissolution model . . . . . . . . . 70
3.3 Comparison of film repair kinetics and crack propagation rates . . 71
3.4 Steps of the corrosion enhanced plasticity model . . . . . . . . . . 72
3.5 Influence of hydrogen distribution around a dislocation . . . . . . . 73
3.6 Fracture surface of alloy 600 monocrystal and polycrystal . . . . . 74
3.7 Schematic representation of the internal oxidation model . . . . . . 76
3.8 Schematic representation of crack propagation . . . . . . . . . . . . 77
16 −
3.9 SIMS image with O at different depth . . . . . . . . . . . . . . 77
3.10 Grain boundary embrittlement by oxygen of unstressed alloy 600 . 78
3.11 Schematic representation of crack tip structure of alloy 600 . . . . 78
3.12 EDX analysis of a triple junction . . . . . . . . . . . . . . . . . . . 79
3.13 Arrhenius plot of oxygen induced cracking and IGSCC . . . . . . . 80
3.14 Temperature dependence of oxygen diffusion coefficient in nickel . 81
3.15 Scott and Le Calvar’s extrapolation for internal oxidation . . . . . 81
3.16 Representation of internal oxidation morphology in a Ni/Cr alloy . 82
3.17 Oxygen diffusion coefficient in nickel . . . . . . . . . . . . . . . . . 83
3.18 Oxide thickness and Cr depletion versus hydrogen overpressure . . 83
4.1 Specimen orientations for WF675 and 78456/337 materials . . . . 90
4.2 Geometry of the SCC specimens . . . . . . . . . . . . . . . . . . . 93
4.3 Representations of the section plane and geometrical notations . . 95
4.4 N(l,T) graphs from interrupted SSRT . . . . . . . . . . . . . . . . 97
4.5 Thresholding routine . . . . . . . . . . . . . . . . . . . . . . . . . . 98
4.6 Example of misorientation data processing . . . . . . . . . . . . . . 99
5.1 Proving ring set-up . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
5.2 Parts of the finite element model . . . . . . . . . . . . . . . . . . . 103
5.3 Analysis steps of the model . . . . . . . . . . . . . . . . . . . . . . 105
5.4 Abaqus mesh elements . . . . . . . . . . . . . . . . . . . . . . . . . 106
5.5 Distorted elements of the FE model . . . . . . . . . . . . . . . . . 106
5.6 Tied surfaces on specimen and pin . . . . . . . . . . . . . . . . . . 107
8