Impact of Hydrogen Embrittlement on Minimum Pressurization Temperature for Thick-wall Cr-Mo Steel Reactors in High-pressure H2 Service—Initial Technical Basis for RP 934-F

API TECHNICAL REPORT 934-F, PART 1 FIRST EDITION, SEPTEMBER 2017

Impact of Hydrogen Embrittlement on Minimum Pressurization Temperature for Thick-wall Cr-Mo Steel Reactors in High-pressure H2 Service—Initial Technical Basis for RP 934-F

API TECHNICAL REPORT 934-F, PART 1 FIRST EDITION, OCTOBER 2017

Prepared under contract for API by: Dr. Richard P. Gangloff

Emeritus Ferman W. Perry Professor of Materials Science and Engineering Department of Materials Science and Engineering

School of Engineering and Applied Science University of Virginia, Charlottesville, Virginia

Special Notes

API publications necessarily address problems of a general nature. With respect to particular circumstances, local, state, and federal laws and regulations should be reviewed.

Neither API nor any of API’s employees, subcontractors, consultants, committees, or other assignees make any warranty or representation, either express or implied, with respect to the accuracy, completeness, or usefulness of the information contained herein, or assume any liability or responsibility for any use, or the results of such use, of any information or process disclosed in this publication. Neither API nor any of API's employees, subcontractors, consultants, or other assignees represent that use of this publication would not infringe upon privately owned rights.

API publications may be used by anyone desiring to do so. Every effort has been made by the Institute to assure the accuracy and reliability of the data contained in them; however, the Institute makes no representation, warranty, or guarantee in connection with this publication and hereby expressly disclaims any liability or responsibility for loss or damage resulting from its use or for the violation of any authorities having jurisdiction with which this publication may conflict.

API publications are published to facilitate the broad availability of proven, sound engineering and operating practices. These publications are not intended to obviate the need for applying sound engineering judgment regarding when and where these publications should be utilized. The formulation and publication of API publications is not intended in any way to inhibit anyone from using any other practices.

Any manufacturer marking equipment or materials in conformance with the marking requirements of an API standard is solely responsible for complying with all the applicable requirements of that standard. API does not represent, warrant, or guarantee that such products do in fact conform to the applicable API standard.

Users of this technical report should not rely exclusively on the information contained in this document. Sound business, scientific, engineering, and safety judgment should be used in employing the information contained herein.

All rights reserved. No part of this work may be reproduced, translated, stored in a retrieval system, or transmitted by any means, electronic, mechanical, photocopying, recording, or otherwise, without prior written permission from the publisher. Contact the Publisher, API Publishing Services, 1220 L Street, NW, Washington, DC 20005.

Copyright © 2017 American Petroleum Institute

Foreword

Nothing contained in any API publication is to be construed as granting any right, by implication or otherwise, for the manufacture, sale, or use of any method, apparatus, or product covered by letters patent. Neither should anything contained in the publication be construed as insuring anyone against liability for infringement of letters patent.

Questions concerning the interpretation of the content of this publication should be directed in writing to the Director of Standards, American Petroleum Institute, 1220 L Street, NW, Washington, DC 20005. Requests for permission to reproduce or translate all or any part of the material published herein should also be addressed to the director.

Generally, API standards are reviewed and revised, reaffirmed, or withdrawn at least every five years. A one-time extension of up to two years may be added to this review cycle. Status of the publication can be ascertained from the API Standards Department, telephone (202) 682-8000. A catalog of API publications and materials is published annually by API, 1220 L Street, NW, Washington, DC 20005.

Suggested revisions are invited and should be submitted to the Standards Department, API, 1220 L Street, NW, Washington, DC 20005, standards@api.org.

Contents

Page

Executive Summary xii

1. Background 1

2. Problem Statement 8

3. Objective and Scope 10

4. Acronyms and Abbreviations 4

5. Technical Analysis 11

6. Conclusions 92

Bibliography 94

Figures

1. Effect of loading format on: (top) the threshold for IHAC and (bottom) the growth rate vs stress intensity factor relationship for a modern pure 2¼Cr-1Mo steel containing 5 wppm predissolved H (CH-Total) and stressed at 23 °C 2

2. The effect of measured predissolved total H concentration (CH-Total) on KIH for

   the onset of IHAC under rising CMOD (dK/dt = 0.007 MPam) for laboratory step-cooled 2¼Cr-1Mo

   base plate and weld metal of several purity levels and tested at 23 °C 3

3. The effect of test temperature on KIH for the onset of IHAC under rising CMOD (dK/dt = 0.007 MPam) for 2¼Cr-1Mo base plate and weld metal of moderate purity and a single CH-Total of 5 wppm 3

4. The slotted compact tension specimen developed in Phase II for laboratory characterization of

   KIH and da/dt vs K for IHAC without H loss 5

5. Crack growth rate vs applied stress intensity for the slotted compact tension specimens of

   2¼ Cr-1Mo weld metal stressed under slow-rising CMOD at 25 °C 6

6. Effect of temperature on the rising CMOD threshold, KIH, for standard H2-precharged specimens of 2¼Cr-1Mo weld metal from Figure 3, as well as for the slotted compact tension specimen with three levels of electrochemically fixed total H concentration; 3.0 wppm (0.5 M H2SO4 + 10−3 M K2SO4, −5.0 mA/ cm2), 1.8 wppm (0.1 M NaOH, −15 mA/cm2), and 1.1 wppm (0.5 M H2SO4, −10 mA/cm2) on the slot surface 6

7. Effect of applied dK/dt, during rising CMOD, on KIH for low-J factor base plate and both low and moderate XB factor weld metal of 2¼Cr-1Mo steel, containing either 5 wppm or 3 wppm of precharged H (CH-Total) and stressed at 23 °C 7

8. An example of the intended pressurization vs temperature profile for safe-reactor startup, with the MPT of 150 °C established to minimize the likelihood of both catastrophic fracture due to temper embrittlement and subcritical crack propagation due to IHAC 8

9. Critical temperature for IHAC vs total dissolved H concentration, predicted specifically for a compact tension specimen fabricated from moderate-purity (“High Impurity”) 2¼Cr-1Mo weld metal 9

10. Correlation between measured KIH vs model-predicted concentration of H, trapped along the crack path with a binding energy, EB, of 38 kJ/mol and in the crack tip hydrostatic stress field, at a reference distance of FPZ = 9 µm ahead of the tip for moderate-purity 2¼Cr-1Mo base plate and weld metal subjected to laboratory step cooling to promote a typical level of temper embrittlement 14

    Contents

11. Correlation between measured KIH vs model-predicted concentration of H, trapped along the crack path with a binding energy, EB, of 59 kJ/mol and in the crack tip hydrostatic stress field, at a

    Page

    reference distance of FPZ = 9 µm ahead of the tip for moderate-purity 2¼Cr-1Mo base plate and weld metal subjected to laboratory step cooling to promote a typical level of temper embrittlement 15

12. Literature data for the effective diffusivity of H in the presence of trapping effects, DEff, for

    2¼Cr-1Mo weld metal (WM SMAW and WM SAW) and base plate (MB) 19

13. Amplification of the Figure 10 correlation between measured KIH and model-predicted

    concentration of H, CT (EB = 38 kJ/mol) at a reference distance of FPZ = 9 µm ahead of the tip for two similar heats of moderate-purity 2¼Cr-1Mo weld metal 25

14. Schematic diagram of the H concentration profile likely to be present in a stainless steel clad Cr-Mo steel reactor wall, after programmed outgassing 26

15. Figure 10 correlation between measured KIH vs model-predicted concentration of H, trapped along the crack path with a binding energy, EB, of 38 kJ/mol and in the crack tip hydrostatic stress field,

    at an FPZ reference distance of 9 µm ahead of the tip for moderate-purity 2¼Cr-1Mo steel 28

16. Model-predicted critical temperature for a cracked compact tension specimen of Cr-Mo steel, fabricated from either weld metal or base plate of moderate purity and H2 precharged to produce a homogeneously distributed total H concentration available for diffusion to the

    crack tip during loading 29

17. Standard Phase I compact tension specimen (1T-CT, 25 mm thick) and the novel 90-mm-thick compact tension specimen employed by Japan Steel Works researchers for Phase II IHAC

    laboratory testing 32

18. Measured values of KIH as a function of test temperature for 90-mm-thick compact tension specimens of 2¼Cr-1Mo base plate and weld metal subjected to slow-rising displacement

    rate at the indicated levels of dK/dt 33

19. The effect of test temperature on the extent of subcritical IHAC produced by slow-rising CMOD of 90-mm-thick compact tension specimens of H2-precharged 2¼Cr-1Mo Phase II

    weld metal (, dK/dt = 0.014 MPam/s) 34

20. Correlation between measured KIH vs the 2-D finite element model-predicted concentration of H, trapped along the crack path with a binding energy, EB, of 38 kJ/mol and in the crack tip hydrostatic stress field, at a reference distance of 9 µm ahead of the tip for moderate-purity

    2¼Cr-1Mo base plate and weld metal 38

21. Correlation between measured KIH vs the 2-D finite element model-predicted concentration of H, trapped along the crack path with a binding energy, EB, of 38 kJ/mol and in the crack tip hydrostatic stress field, at a reference distance of 9 µm ahead of the tip for moderate-purity

    2¼Cr-1Mo base plate and weld metal 39

22. Replot of the data presented in Figure 18, intended to show that KIC is very high for

    H-free 2¼Cr-1Mo steel, even when temper embrittled, provided that temperatures are greater

    than upper shelf values 40

23. Phase I steels examined showing the three broad categories of degree of temper embrittlement represented by Charpy impact FATT range for both weld metal and base plate of 2¼Cr-1Mo steel . 41

24. High-purity 2¼Cr-1Mo steels examined in JIP Phase I research 43

    Contents

25. Experimentally measured dependence of KIH on total dissolved H concentration

    from high-temperature precharging in high-pressure H2 for high-purity and laboratory

    Page

    step-cooled 2¼Cr-1Mo weld metal and base plate 44

26. Experimentally measured dependence of KIH on total dissolved H concentration from high- temperature precharging in high-pressure H2 for high-purity and laboratory step-cooled

    2¼Cr-1Mo weld metal and base plate 45

27. Correlation between measured KIH vs the concentration of H, trapped along the

    crack path with a binding energy, EB, of 38 kJ/mol and in the crack tip hydrostatic stress field (H = 2.5YS and HVH = 2.5 kJ/mol), at a reference distance of 9 µm ahead of the tip for modern

    higher-purity 2¼Cr-1Mo base plate and weld metal data presented in Figure 25 47

28. Correlation between measured KIH vs the concentration of H, trapped along the

    crack path with a binding energy, EB, of 38 kJ/mol and in the crack tip hydrostatic stress field (H = 2.5YS and HVH = 2.5 kJ/mol), at a reference distance of 9 µm ahead of the tip for the

    low-FATT 2¼ Cr-1Mo base plate and weld metal data presented in Figure 26 48

29. The effect of 2¼Cr-1Mo steel purity and temper embrittlement on the critical temperature for elimination of IHAC in H2-precharged compact tension specimens, as a function of total

    precharged H concentration and based on the values of CT-CRIT from Figures 15 and 29 49

30. The effect of 2¼Cr-1Mo steel purity and temper embrittlement on the critical

    temperature defined in terms of the crack tip FPZ diffusible H concentration at FPZ = 9 m, computed by a diffusion analysis and based on the values of CT-CRIT from Figures 15 and 28 50

31. Model prediction of critical temperature vs CH-Diff at the reference location of 9 m ahead

    of the crack tip, replotted from Figure 30 51

32. ABAQUS model predictions of diffusible H loss from a H2-precharged standard (25.4-mm-thick) compact tension specimen of 2¼Cr-1Mo steel exposed at several constant temperature and

    stress intensity levels 53

33. Correlation between measured KIH vs the concentration of H, trapped along the crack path

    with a binding energy, EB, of 38 kJ/mol and in the crack tip hydrostatic stress field (sH = 2.5sYS and sHVH = 2.5 kJ/mol), at a reference distance of 470 µm ahead of the tip for modern higher-purity

    2¼ Cr-1Mo base plate and weld metal data presented in Figure 25 54

34. Correlation between measured KIH vs the concentration of H, trapped along the crack path w ith a binding energy, EB, of 38 kJ/mol and in the crack tip hydrostatic stress field (H = 2.5YS and HVH = 2/5 kJ/mol), at a reference distance of 470 µm ahead of the tip for the low-FATT

    2¼Cr-1Mo base plate and weld metal data presented in Figure 26 55

35. The effect of crack tip analysis location on the predicted critical temperature for elimination of IHAC in H2-precharged compact tension specimens of low-FATT 2¼Cr-1Mo steel, as a function

    of total precharged H concentration and based on the values of CTs-CRIT from Figures 28 and 34 56

36. The effect of crack tip CH-Diff analysis accuracy for a cracked “structure” on the predicted critical temperature for elimination of IHAC using H2-precharged compact tension specimens of low-FATT 2¼Cr-1Mo steel, as a function of total precharged H concentration and based on the short-term laboratory value of CT-CRIT from Figure 34 57

    
    

    Contents

    
    

    Page

    
    

37. The effect of crack tip diffusible H concentration (CH-Diff 470 m), localized at the reference point of

    470 m ahead of the crack tip, on the predicted critical temperature for elimination of IHAC in a cracked section fabricated from low-FATT 2¼Cr-1Mo steel, as a function of total precharged

    H concentration and based on the short-term laboratory value of CT-CRIT = 1,000,000 wppm

    from Figure 34 58

38. The effect of crack tip diffusible H concentration (CH-Diff 470 mm), localized at the reference point of d470 mm ahead of the crack tip, on the predicted critical temperature for elimination of IHAC

    in a cracked section fabricated from moderate-FATT 2¼Cr-1Mo steel, as a function of total precharged H concentration and based on the short-term laboratory value of

    CTs-CRIT = 117,000 wppm taken from Figure 21 and enhanced to account for the increase

    in crack tip reference location from 9 mm to 470 mm 59

39. The H concentration distribution in the stainless steel clad Cr-Mo wall of a hydroprocessing reactor during: (a) operation at 450 °C in 14.7 MPa (2133 psi) H2, which produced

    CH-Total = 2.3 wppm H in the Cr-Mo steel at the interface with the stainless cladding, and (

    b) after cool-down to 25 °C, without H2 present and at two rates shown by the inserted time–temperature history 60

40. REACT diffusion model output of the diffusible H concentration distribution in the stainless steel clad Cr-Mo wall of a hydroprocessing reactor during: (a) operation at 450 °C in

    high-pressure (unspecified) H2, which produced CH-Diff = 2.1 wppm H in the Cr-Mo steel at the interface with the stainless cladding, and (b) after cool-down to 25 °C,

    without H2 present 61

41. The effect of total hydrogen concentration on the rising CMOD measurement of KIH for JIP Phase I 2¼Cr-1Mo base plate and weld metal of various purities that were temper embrittled

    by laboratory step cooling 64

42. 3-D finite element model prediction of A1 vs distance ahead of the crack tip along the specimen mid-thickness (top) and position along the crack front (bottom) for a standard compact tension specimen of H-precharged (initial CH-Diff = 2.0 wppm) 2¼Cr-1Mo steel that is isothermally exposed f

    or the indicated times at 25 °C. 1.0 wppm/in.1/2 = 0.627 wppm/cm1/2 66

43. Correlation between the 2-D values of the crack tip A1 parameter from Figure 42

    (and other FEA results), and the initial diffusible H concentration (of either 2.0 or 3.25 wppm) normalized by the effective H diffusivity and exposure time for H-precharged 2¼Cr-1Mo steel.

    1.0 wppm/in.1/2 = 0.627 wppm/cm1/2 67

44. Correlation between KIH and  = A1 exp(2000/T), where all data are reproduced from the

    JIP Phase I and Phase II results presented in Figure 10 for mid-FATT H precharged 2¼Cr-1Mo steel. 1.0 wppm/in.1/2 = 0.627 wppm/cm1/2 68

45. Correlation between KIH and  = A1 exp(2000/T) with temperature in degrees K for limited data reported for a modern low-FATT base plate of 2¼Cr-1Mo steel, which is a subset of the large

    data base presented in Figure 26. 1.0 wppm/in.1/2 = 0.627 wppm/cm1/2 69

46. FEA mesh for H diffusion analysis associated with an ID crack in a stainless steel clad Cr-Mo reactor vessel in elevated-temperature, high-pressure H2 service, including the

    shutdown and startup time–temperature profile in the inset 71

    
    

    Contents

    
    

    
    

47. Diffusible H concentration, represented by the A1 parameter, vs distance from the

    tip of an ID surface crack located either (top) 5.4 mm or (bottom) 23.7 mm inward from

    the pressure vessel ID surface based on REACT FEA for the conditions shown in Figure 46 and results shown in Figure 40.  is 0.88 (Figure 43), DEff = 1.0 x 10−6 cm2/s, and

    Page

    CH-Diff = 0.65 CH-Total. 1.0 wppm/in.1/2 = 0.627 wppm/cm1/2 72

48. The operating-time dependence of the H concentration similitude parameter, , for two crack depths in a stainless steel clad Cr-Mo reactor vessel subjected to the shutdown and startup

    cycle shown in Figure 46 73

49. The predicted operating-time dependence of MPT, defined by the ratio of constant critical 

    (selected parametrically) to A1 from FEA of the cracked pressure vessel represented in

    Figures 46 and Figure 47 for a single crack depth 73

50. Predictions of the AG model showing the effect of crack tip diffusible H concentration

    (CH-Diff 470 m), localized at the reference point of 470 m ahead of the crack tip, on the predicted critical temperature for elimination of IHAC in a cracked section fabricated from low-FATT

    2¼Cr-1Mo steel, as a function of total precharged H concentration and based on the

    short-term laboratory value of CT-CRIT = 1,000,000 wppm from Figure 34 75

51. Comparison of experimental and Gerberich-model-predicted values of threshold stress intensity factor, typically KTH for the steels investigated, as a function of the reversibly trapped

    and stress enhanced H concentration adjacent to the crack path 77

52. Blind prediction of KTH for Cr-Mo steel using: (a) uniformly dissolved CH-Total available

    for diffusion to the 470 m reference location, followed by partition to the crack tip stress field

    and trapping at sites adjacent to the IHAC path, (b) average values of all model parameters for

    the 300 to 700 MPa yield strength steels shown in Figure 51 and Table 6, and (c) at 25 °C 79

53. The effect of measured total H concentration (CH-Total) on KIH for the onset of IHAC under rising CMOD (dK/dt = 0.007 MPam) for 2¼Cr-1Mo base plate and weld metal of several purity

    levels, laboratory step cooled to simulate temper embrittlement and IHAC tested at 25 °C 80

54. Comparison of measured KTH for moderate-purity temper embrittled Cr-Mo steel

    (red trend line from Figure 53 for step-cooled specimens) with micromechanical model

    results (blue dotted line) 81

55. Comparison of measured KTH for moderate-purity Cr-Mo steel (red trend line from Figure 53 for step-cooled temper embrittled specimens) with micromechanical model results

    (blue dotted line) for the H concentration located at dFPZ = 9 mm 82

56. Comparison of measured KTH for high-purity Cr-Mo steel (red trend line from Figures 25 and 26 for step-cooled specimens) with micromechanical model results (blue dotted line) 83

57. Comparison of measured KTH for high-purity Cr-Mo steel (red trend line from Figures 25 and 26 for step-cooled specimens) with micromechanical model results (blue dotted line)

    for the H concentration located at FPZ = 9 m 84

58. Calibrated prediction of KIH for high-purity Cr-Mo weld metal and base plate as a function of the concentration of stress field and crack path trap site enhanced H concentration, CT, at the

    9 m crack tip reference location 85

59. Calibrated prediction of KTH for moderate-purity temper embrittled Cr-Mo weld metal

    and base plate plotted as a function of the concentration of stress field and crack path trap site enhanced H concentration, CT, at the 9 m crack tip reference location 87

    
    

    Contents

    
    

    
    

60. Alternate best fit prediction of measured KTH for moderate-purity temper embrittled

    Cr-Mo steel (red trend line from Figure 53 for step-cooled temper embrittled specimens) with micromechanical model results (blue dotted line) for the H concentration located

    Page

    at FPZ = 9 m 88

61. Alternate prediction of KTH for moderate-purity Cr-Mo steel as a function of the concentration of stress field and crack path trap site enhanced H concentration, CT, computed using the model parameters fit to the KIH vs uniformly dissolved initial total H concentration, CH-Total,

    represented in Figures 53 and 60, and Task 1.0 master correlation value of EB (38 kJ/mol) 89

62. Calibrated fit prediction of KTH for moderate-purity temper embrittled Cr-Mo weld metal and base plate plotted as a function of the concentration of stress field and crack path trap site

    enhanced H concentration, CTs, at the 9 mm crack tip reference location 90

63. Schematic representation of model-predicted master correlations for four temperatures,

e.g. from left to right: 400 K (red), 343 K (green), 298 K (blue), and 250 K (orange) inspired

by the quantitative predictions shown in Figure 62 91

Tables

1. Definition of the Trap-affected H Diffusivity vs Temperature, Diffusible H Concentration, and Plastic Deformation at the Crack Tip of 2.25Cr-1Mo Weld Metal (YS = 508 MPa) for FEA Diffusion Modeling Using ABAQUS 18

2. Estimated Stress-enhanced Diffusible H near the Crack Tip from the 3-D Fixed K Diffusion Model to Approximate the Effect of dK/dt. DH = f(CH, T, P) 21

3. Estimated Stress-enhanced Normalized Diffusible H [CH-Diff- / CH-Diff Bulk (t=0)] at the Crack Tip

   of H2-precharged Standard Compact Tension from the 3-D Fixed K Diffusion Model to Approximate

   the Effect of Slowly Rising Load at a dK/dt of 0.007 MPam/s. DH = f(CH, T, P) 22

4. 2-D Diffusion Model Prediction of Peak Diffusible H Concentration near the Crack Tip for

   Standard and Slotted Compact Tension Specimens As a Function of Stress, Time, and Temperature.

   DH = f(CH, T, eP) 35

5. Comparison Between 2-D and 3-D Hydrogen Diffusion Model Predictions 36

6. Parameters Used to Predict Threshold Stress Intensity Factor for IHAC in Steels of Varying

Tensile Yield Strength Using Gerberich’s Decohesion Model 77

EXECUTIVE SUMMARY

The objective of this study, in support of API Recommended Practice 934-F [Guidance for Establishing a Minimum Pressurization Temperature (MPT) for Heavy Wall Reactors in High Temperature Hydrogen Service During Startups and Shutdowns], is to establish the technical basis for determining a minimum pressurization temperature (MPT) necessary to avoid internal hydrogen-assisted cracking (IHAC) of weld metal and base plate of temper embrittled 2¼Cr-1Mo steel in high-pressure H2 service. The threshold condition for the onset of subcritical crack propagation—and its dependencies on dissolved hydrogen concentration, temperature, and steel purity/temper embrittlement—are targeted as particularly important to pressure vessel safe operations. A second objective is to improve the underlying data base for fracture mechanics fitness-for-service (FFS) modeling of IHAC. Both analyses are built on the conservative rising displacement threshold stress intensity factor for IHAC (KIH).

This investigation has accomplished five tasks, leading to the following conclusions and key figures taken from the body of this report. These conclusions are sufficient to establish the API 934-F section on MPT to conservatively avoid IHAC in 2¼Cr-1Mo steel.

Task 1.0—Summarize and clarify the technical approach, assumptions, data, and modeling results used in Phase II JIP research to quantitatively establish the H concentration and temperature dependencies of the threshold stress intensity, KIH, for IHAC and the concentration dependence of MPT for moderate- impurity 2¼Cr-1Mo steel.

Task 1.0—Summarize and clarify the technical approach, assumptions, data, and modeling results used in Phase II JIP research to quantitatively establish the H concentration and temperature dependencies of the threshold stress intensity, KIH, for IHAC and the concentration dependence of MPT for moderate- impurity 2¼Cr-1Mo steel.

1. Measured threshold stress intensity factor (KIH) for the onset of IHAC increases with decreasing bulk- dissolved H concentration and increasing temperature, as proved by experimental results for multiple specimen geometries of 2¼Cr-1Mo steel.

   
   

2. The H concentration and temperature dependencies of KIH are explained physically by the interactive effect of each variable on the concentration of H (CT) that is enhanced at a reference location in the crack tip fracture process zone due to localized hydrostatic stress and microstructure sites for H trapping that constitute the crack path.

   
   

3. The steps necessary to predict CT as a function of total dissolved H concentration and temperature, proposed by Al-Rumaih in a joint industry program (JIP) Phase II PhD study at the University of Virginia, are validated as fully correct and are clarified to provide the scientific basis for engineering applications that seek to avoid IHAC. This analysis was guided by mechanistic consideration of H trapping and embrittlement in the crack tip region of a complex steel microstructure.

4. A master experimental correlation exists between measured KIH and diffusion-model-predicted CT for moderate-purity temper embrittled [6 °C < fracture appearance transition temperature (FATT) < 43 °C] 2¼Cr-1Mo, including a critical level of locally trapped H below which KIH rises toward KIC (CT-CRIT). The

   critical H concentration is marginally lower for weld metal compared to base plate, with each

   microstructure temper embrittled by laboratory step cooling. Figure 15 follows, specific to CT predicted at 2CTOD ahead of the crack tip; FPZ = 9 m:

   
   

   
   

5. The master KIH vs CT correlation provides the basis for a critical temperature, TCRIT, above which IHAC is not observed and that is the foundation for MPT determination. The TCRIT increases with increasing CH-Total dissolved in the “structure” at high temperature, with a quantitative dependence reported in Phase II work specific to the compact tension geometry and moderate-FATT 2¼Cr-1Mo weld metal and base plate. Figure 16 follows based on KIH vs CT in Figure 15. Diffusion analysis (see Task 4.0) is required to apply this specific result to a cracked reactor vessel in H2 service.

Task 2.0—Validate the Phase II correlation of KIH and critical temperature vs H concentration, based on new analyses of post-Phase-II IHAC data.

Task 2.0—Validate the Phase II correlation of KIH and critical temperature vs H concentration, based on new analyses of post-Phase-II IHAC data.

1) Japanese experiments with unusually thick and H2-precharged compact tension specimens of moderate- purity temper embrittled 2¼Cr-1Mo weld metal and base plate (22 °C < FATT < 43 °C) quantitatively validate the master correlation between KIH and CT. Figure 21 follows showing agreement between these thick-specimen results (,) and the small-specimen master curve from Figure 15, each related to

FPZ = 9 m:



 





 





♣













Task 3.0—Enhance the Phase II analysis of KIH vs crack tip H concentration, and thus MPT, by describing the interaction between temper embrittlement and IHAC using JIP Phase I data so as to predict the influence of modern steel purity.

Task 3.0—Enhance the Phase II analysis of KIH vs crack tip H concentration, and thus MPT, by describing the interaction between temper embrittlement and IHAC using JIP Phase I data so as to predict the influence of modern steel purity.

1) Results of extensive JIP Phase I IHAC experiments, conducted with H2-precharged compact tension specimens of multiple high-purity lots of laboratory step-cooled 2¼Cr-1Mo weld metal and base plate (−90 °C < FATT < −28 °C) are well correlated by a master correlation between KIH and CT, as verified by additional literature KIH data.