Report to API - The Technical Basis For API RP 941

TABLE OF CONTENTS

0HEXECUTIVE SUMMARY FOR THE TECHNICAL BASIS DOCUMENT ..................................................... 361H1

1H1.0 ABSTRACT ..................................................................................................................................... 362H5

2H2.0 INTRODUCTION .............................................................................................................................. 363H6 3H2.1 What is Hydrogen Attack? ............................................................................................................ 364H7 4H2.2 What is Fugacity and Why Is It Important .................................................................................. 365H11 5H2.3 Details of the Attack Progression .............................................................................................. 366H12

6H3.0 ATTACK OF MATERIALS CONTAINING FE3C ........................................................................... 367H20

7H4.0 METHANE PRESSURE RELATIONS WITH CEMENTITE .......................................................... 368H23

8H5.0 STEELS WITH MORE STABLE CARBIDES ................................................................................ 369H25

9H6.0 BEHAVIOR OF STEELS WITH COMPLEX ALLOY CARBIDES ................................................. 370H26

10H7.0 RESEARCH STUDIES .................................................................................................................. 371H27

11H8.0 STUDIES ........................................................................................................................................ 372H28

12H9.0 EFFECT OF STRESS .................................................................................................................... 373H32

13H10.0 EFFECT OF TEMPERATURE ....................................................................................................... 374H33

14H11.0 EFFECT OF HYDROGEN PRESSURE ........................................................................................ 375H34 15H11.1 Materials Issues ........................................................................................................................... 376H34

16H12.0 EXPOSURE TIME OR STRESS .................................................................................................... 377H35

17H13.0 EUROPEAN STUDIES .................................................................................................................. 378H36

18H14.0 NEW ANALYSIS OF MPC WORK ................................................................................................ 379H40

19H15.0 DEVELOPMENT OF P/T LIMITS NEAR THE CREEP RANGE AND ABOVE ............................ 380H42

20H16.0 A TECHNICAL BASIS ................................................................................................................... 381H43

21H17.0 DISCUSSION ................................................................................................................................. 382H45

22H18.0 FINAL COMMENT ......................................................................................................................... 383H47

23H19.0 OVERVIEW AND CONCLUSION .................................................................................................. 384H49

24H20.0 REFERENCES ............................................................................................................................... 385H51

25H21.0 FIGURES ....................................................................................................................................... 386H56

26HAPPENDIX A – BACKGROUND TO THE NELSON CURVES ............................................................... 387H124

27H1.0 HISTORY ..................................................................................................................................... 388H125

28H2.0 WHAT DATA IS AVAILABLE? ................................................................................................... 389H128

29H3.0 WHERE DID THE DATA COME FROM? .................................................................................... 390H129 30H3.1 API Publication 941 Fifth Edition Supplement 1 April 1998 ................................................ 391H129 31H3.2 Figure 1 Points C-0.5Mo Appendix A ..................................................................................... 392H130 32H3.3 File Correspondence but Points Not Plotted .......................................................................... 393H135 33H3.4 Points Plotted for 1-1/4Cr-1/2Mo and 2-1/4Cr-1Mo ................................................................. 394H138 34H3.5 Attack / No Attack Points .......................................................................................................... 395H139

35H4.0 DISCUSSION ............................................................................................................................... 396H141

36H5.0 CONCLUSIONS ........................................................................................................................... 397H145

37H6.0 FIGURES ..................................................................................................................................... 398H146

Report to API - The Technical Basis For API RP 941

38HAPPENDIX B – COMMONLY ASKED QUESTIONS ............................................................................. 399H157

39H1.0 HOW DO WE GET CARBON ACTIVITY AND CONTENT? ....................................................... 400H158 40H1.1 How Much Carbon Is Necessary To Exhaust The Carbide Formers? .................................. 401H161

41H2.0 ARE THE API RP 941 CURVES WHERE THEY BELONG? ..................................................... 402H162

42H3.0 WHAT VARIABLES MIGHT ADVERSELY INFLUENCE BEHAVIOR IN LONG TERM SERVICE? ................................................................................................................................... 403H163

43H4.0 WHAT OTHER FACTORS MIGHT PLAY A ROLE IN THE APPEARANCE OF HYDROGEN ATTACK? .................................................................................................................................... 404H164

44H5.0 WHY IS HYDROGEN ATTACK SEEMINGLY UNPREDICTABLE? .......................................... 405H165

45H6.0 WHY HAVEN’T THE NECESSARY CRITICAL EXPERIMENTS BEEN RUN? ......................... 406H166

46H7.0 WHAT IS ACTUALLY HAPPENING DURING EARLY STATES OF HYDROGEN ATTACK? . 407H167

47H8.0 REFERENCES ............................................................................................................................. 408H168

APPENDIX C – ESTIMATING DAMAGE RATES FOR LIFE ASSESSMENT ........................................ 169

48HAPPENDIX D – EFFECTIVE PRESSURES OF HYDROGEN IN STEEL COVERED BY CLAD/OVERLAY AND/OR CORROSION PRODUCT .................................................. 409H178

49HAPPENDIX E – OBSTACLES TO UNDERSTANDING HTHA ................................................................ 410H184

50HAPPENDIX F – APPLICATION AND SUMMARY OF PW PARAMETRIC MODEL ................................ 411H187

51H1.0 SUMMARY OF THEORETICAL KINETIC TREATMENTS ON BUBBLE GROWTH ................. 412H189 52H1.1 Diffusion Models - Grain Boundary and Surface Diffusion ................................................... 413H189 53H1.2 Coupled Diffusion and Creep Model ........................................................................................ 414H189

54H2.0 RELATIONSHIP BETWEEN THEORETICAL EQUATIONS AND ARRHENIUS TYPE EXPRESSIONS ........................................................................................................................... 415H191

55H2.1 Grain Boundary Diffusion (GBD) Process ............................................................................... 416H191 56H2.2 Surface Diffusion (SD) Process ................................................................................................ 417H192 57H2.3 Coupling Between GBD and SD Processes ............................................................................ 418H192 58H2.4 Power-Law Creep Process ........................................................................................................ 419H192 59H2.5 General Form of All Processes ................................................................................................. 420H192

60H3.0 DERIVATION OF ENGINEERING PARAMETER PW ................................................................ 421H194

61H4.0 EXAMPLE OF EXPERIMENTAL RESULTS RELATIVE TO THE ARRHENIUS TYPE EXPRESSION .............................................................................................................................. 422H196

62H5.0 APPLICATION OF THE PW PARAMETER – PREDICTION OF TIME DEPENDENT CRITICAL CURVES ...................................................................................................................................... 423H198

63H5.1 Discussion of the Values of and Q ....................................................................................... 424H198 64H5.2 Discussion of API RP 941 versus Parametric Equations for Several Materials .................. 425H200

65H6.0 APPLICATION OF THE PW PARAMETER – ESTIMATION OF THE EFFECT OF APPLIED STRESS ....................................................................................................................................... 426H205

66H6.1 Derivation of Pw Including the Stress ..................................................................................... 427H205 67H6.2 Effect of Applied Stress on the Critical Curve of 2.25Cr-1Mo Steel ..................................... 428H206

68H7.0 APPLICATION OF THE PW PARAMETER – ESTIMATION OF EFFECT OF OVERLAY ........ 429H207 69H7.1 Hydrogen Distribution in a Vessel Wall with Overlay During Operation .............................. 430H207 70H7.2 The Effect of Overlay on the Critical Curve ............................................................................. 431H208

71H8.0 CONCLUSIONS ........................................................................................................................... 432H210

72H9.0 REFERENCES ............................................................................................................................. 433H211

73H10.0 FIGURES ..................................................................................................................................... 434H212

Report to API - The Technical Basis For API RP 941

74HAPPENDIX G – OVERVIEW OF EUROPEAN RESEARCH .................................................................. 435H231

75H1.0 INTRODUCTION .......................................................................................................................... 436H232

76H2.0 NON-UNIFORM HYDROGEN ATTACK CAVITATION AND THE ROLE OF INTERACTION WITH CREEP ............................................................................................................................... 437H235

77H2.1 Introduction ................................................................................................................................ 438H235 78H2.2 Polycrystal Model for HA .......................................................................................................... 439H236 79H2.3 Method of Analysis .................................................................................................................... 440H242 80H2.4 Discussion .................................................................................................................................. 441H248 81H2.5 Conclusion .................................................................................................................................. 442H250

82H3.0 COMPARISON OF DELFT AND APPROACH REPORTED FROM JAPAN ............................. 443H252 83H3.1 Introduction to the Hydrogen Attack Models .......................................................................... 444H252 84H3.2 Calculation of the Methane Pressure ....................................................................................... 445H253 85H3.3 Comparison Between Methane Pressures .............................................................................. 446H254 86H3.4 Description of Void Growth Due to Diffusion.......................................................................... 447H255 87H3.5 Comparison of Predicted Void Growth Due To Diffusion ...................................................... 448H256 88H3.6 Creep As An Additional Deformation Mechanism .................................................................. 449H258 89H3.7 Conclusions ................................................................................................................................ 450H260

90H4.0 FIGURES ..................................................................................................................................... 451H261

91H5.0 REFERENCES ............................................................................................................................. 452H292

92HAPPENDIX H – SAMPLE PROBLEMS UTILIZING APPENDIX C AND DISCUSSION DEVELOPED BY SOME COMMITTEE MEMBERS DURING REVIEW OF THE REPORT ...................... 453H294

93H1.0 ESTIMATING DAMAGE RATES FOR LIFE ASSESSMENT: BASIC METHODOLOGY .......... 454H295

94H2.0 EXAMPLES: HYPOTHETICAL CASES USING APPENDIX C .................................................. 455H296 95H2.1 Case 1: Carbon Steel channel flange and shell welds discovered in 1.25Cr exchanger ... 456H296 96H2.2 Case 1A: 225 psia at 620

oF ....................................................................................................... 457H296

97H2.3 Case 1B: 225 psia at 750oF ........................................................................................................ 458H297

98H2.4 Case 2: Carbon steel pipe ......................................................................................................... 459H297 99H2.5 Case 3: C-0.5Mo exchanger channel cover ............................................................................. 460H297 100H2.6 Case 4: C-0.5Mo Methanator Short-Time Excursion ............................................................. 461H298 101H2.7 Case 5: Mn-0.5Mo exchanger with austenitic weld overlay/clad .......................................... 462H299 102H2.8 Case 5A: Consider Continued Operation at Current Conditions .......................................... 463H299 103H2.9 Case 5B: Operations wants to increase the operating conditions ....................................... 464H300 104H2.10 Case 6: 1Cr catalytic reformer reactor .................................................................................... 465H300 105H2.11 Case 7: Over temperature Conditions in a 2.25Cr 1 Mo Reactor ......................................... 466H300