Hydrogen Cracking and Stress Corrosion of Pressure Vessel Steel ASTM A543 by Ali Hamad AlShawaf A thesis submitted to the Faculty and the Board of Trustees of the Colorado School of Mines in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Metallurgical and Materials Engineering). Golden, Colorado Date Signed: Ali Hamad AlShawaf Signed: Dr. Stephen Liu Thesis Advisor Golden, Colorado Date Signed: Dr. Ivar E. Reimanis Interim Department Head Department of Metallurgical and Materials Engineering ii Table of Contents Chapter 1: Introduction ......................................................................................................... 1 1.1 Research Scope ........................................................................................................... 1 1.2 Justification for Research Performed ............................................................................ 1 1.1 Plant Process Operation ............................................................................................... 5 1.1.1 Alkalinity of Boiler Water ........................................................................................ 5 1.1.2 pH Level of Boiler Water ........................................................................................ 5 1.1.3 Dissolved Oxygen in Boiler Water .......................................................................... 6 1.1.4 Dissolved Solids in Boiler Water ............................................................................ 6 Chapter 2: Literature Review ................................................................................................ 9 2.1 Hydrogen Damage ....................................................................................................... 9 2.1.1 Hydrogen Cracking Models .................................................................................. 10 2.1.2 Temperature Range for Hydrogen Cracking ........................................................ 11 2.1.3 Sources of Hydrogen ........................................................................................... 11 2.1.4 Presence of Hydrogen in the Weld ...................................................................... 12 2.1.5 Weld Overmatching Condition ............................................................................. 13 2.1.6 Weld Undermatching Condition ........................................................................... 13 2.1.7 Hydrogen Solubility and Diffusivity in HSLA Steel ................................................ 14 2.1.8 Hydrogen Trap Sites ............................................................................................ 14 2.1.9 Hydrogen Interaction with Grains & Grain Boundaries ........................................ 16 2.1.10 The Influence of Grain Size & Alloying Elements.............................................. 16 2.1.11 Microstructural Susceptibility ............................................................................ 17 2.1.12 Effect of Hydrogen on Mechanical Properties: .................................................. 18 2.1.13 Hydrogen Damage Prevention ......................................................................... 21 2.2 Weldability Testing ..................................................................................................... 22 iii 2.2.1 Implant Testing .................................................................................................... 24 2.2.2 Carbon Equivalent ............................................................................................... 25 2.2.3 Previous Research Studies on Implant Test of HSLA Steels ............................... 26 2.3 Hydrogen Charging .................................................................................................... 33 2.3.1 Electrochemical Charging .................................................................................... 33 2.3.2 Hydrogen Recombination (Poison) ...................................................................... 34 2.4 Fracture Surface Morphology In The Presence of Hydrogen ..................................... 34 2.5 Residual Stresses ....................................................................................................... 34 2.6 Corrosion .................................................................................................................... 36 2.6.1 Corrosion in Water-contained Pressure Vessels .................................................. 38 2.6.2 Stress Corrosion Cracking (SCC) ........................................................................ 40 2.6.3 Slow Strain-Rate Testing ..................................................................................... 41 2.6.4 Corrosion Prevention and Protection ................................................................... 42 Chapter 3: Experimental Procedure ................................................................................... 44 3.1 Material Specification ................................................................................................. 44 3.2 Heat Affected Zone (HAZ) Experimental Simulation................................................... 44 3.2.1 Gleeble® 3500 Simulation of HAZ ....................................................................... 44 3.2.2 Furnace Simulation of HAZ .................................................................................. 46 3.3 Hydrogen Charging Set-up ......................................................................................... 47 3.4 Hydrogen Analysis Using LECO H Analyzer ............................................................. 49 2 3.5 Etchant Used for Preparing the Metallographical Samples ........................................ 50 3.6 Weldability Implant Testing ......................................................................................... 51 3.6.1 Gas Metal Arc Welding (GMAW). ........................................................................ 52 3.7 Tensile Testing of simulated HAZ Subzones-Alliance Machine .................................. 52 3.8 Corrosion Study of Q&T HSLA Steel .......................................................................... 53 3.8.1 Slow Strain Rate Testing...................................................................................... 53 iv 3.8.2 Electrochemical Test Using Gamry Machine ....................................................... 55 Chapter 4: Weldability and Mechanical Properties ............................................................. 57 4.1 Weldability Implant Testing ......................................................................................... 57 4.1.1 Implant Test Equipment Construction .................................................................. 58 4.1.2 Implant Test Results ............................................................................................ 59 4.2 Mechanical Properties Results ................................................................................... 60 4.2.1 Pre-charged Furnace Simulated Samples ........................................................... 60 4.2.2 Pre-charged Gleeble® Simulated Samples ......................................................... 69 Chapter 5: Fractography & Metallography Analyses .......................................................... 74 5.1 Introduction ................................................................................................................. 74 5.2 Results and Discussion .............................................................................................. 74 5.3 Metallography of Furnace and Gleeble® Samples ..................................................... 76 5.3.1 LePera Colored Etchant ....................................................................................... 91 Chapter 6: Numerical Simulation of Implant Testing .......................................................... 93 6.1 Numerical Simulation Introduction .............................................................................. 93 6.1.1 Simulation Considerations ................................................................................... 94 6.1.2 Rosenthal's Equations ......................................................................................... 95 6.2 Mathcad Calculations ................................................................................................. 97 6.3 ESI-SYSWELD Simulation ......................................................................................... 98 6.3.1 Material Database Manager ............................................................................... 100 6.3.2 Thermal and Mechanical Parameters in SYSWELD .......................................... 102 6.3.3 Modeling of Moving Heat Source (Arc) .............................................................. 105 6.4 Simulated Implant Testing ........................................................................................ 108 6.4.1 Parameters Used in the Simulation .................................................................... 112 6.4.2 Thermo-physical Properties ............................................................................... 113 6.4.3 Mechanical Properties ....................................................................................... 113 v 6.5 Description of the Welding Conditions – Bead-on-Plate Welding Simulation ........... 113 6.5.1 Temperature Distribution and Obtaining Thermal Cycle .................................... 115 6.5.2 Imposing Thermal Cycle on Implant Pin Simulation ........................................... 115 6.6 Simulation Results for Pressure Vessel Steels ......................................................... 119 6.6.1 ASTM A516 Gr. 70 Steel Simulation Results ..................................................... 124 6.6.2 ASTM A533 Steel Simulation Results ................................................................ 126 6.6.3 ASTM A36 Steel Simulation Results .................................................................. 128 6.6.4 ASTM A543 Steel Simulation Results ................................................................ 128 6.7 Discussion of Implant Simulation Results ................................................................. 131 Chapter 7: Corrosion Study of Q&T HSLA A543 Steel ..................................................... 136 7.1 Introduction ............................................................................................................... 136 7.2 Results and Discussion of SSRT .............................................................................. 139 7.3 Electrochemical Impedance Spectroscopy (EIS) ...................................................... 147 7.3.1 Results and Discussion ...................................................................................... 150 Chapter 8: Research Summary ........................................................................................ 159 8.1 Hydrogen Cracking ................................................................................................... 159 8.2 Surface Mobility Mechanism Causing Pits ................................................................ 159 Chapter 9: Conclusions .................................................................................................... 165 9.1 Microstructure, Mechanical Behavior and Weldability Studies ................................. 165 9.2 Numerical Modeling .................................................................................................. 165 9.3 Corrosion Study ........................................................................................................ 166 9.4 Suggested Mitigations .............................................................................................. 166 Chapter 10: Future Works .................................................................................................. 167 Chapter 11: Appendices ..................................................................................................... 178 vi List of Figures Figure 1.1. A longitudinal cross-section through the weld showing the crack, which exhibits a jagged path. ................................................................................................................................. 3 Figure1.2. A schematic showing the general assembly of the pressure vessel, E is ethylene, EO is ethylene oxide. ................................................................................................................... 7 Figure 1.3. Schematic of two drums boiler to generate Boiler Feed Water BFW [5]. ................... 8 Fig. 2.1. Schematic showing location of hydrogen-induced cracks in carbon steel weldments [9]. ............................................................................................................................................. 10 Figure 2.2. (A)The hydrogen sites in the steel: a) Trap sites. b) Subsurface. c) Surface. d) GB, vacancies. e) Dislocations. f) Combined Hydrogen, (B)the common hydrogen models [10]. ........................................................................................................................................... 12 Figure 2.3. Causes of cold cracking in base metal [15]. ............................................................ 13 Figure 2.4. a) Amount of hydrogen absorbed by the molten weld pool varies with concentration in arc atmosphere at 1900oC. b) Solubility of hydrogen in weld metal decreases as temperature decreases [15]. ................................................................................ 15 Figure 2.5. Hardness as function of carbon content as a function of martensite formation in carbon steel with rapid cooling [13]. .......................................................................................... 18 Figure 2.6. Hardenability curves for five carbon steels as determined by end-quench testing [13]. ........................................................................................................................................... 19 Figure 2.7. True-stress-strain curve relation with the strain hardening. ..................................... 20 Fig. 2.8. Effect of grain size on mechanical properties. ............................................................. 22 Fig. 2.9. Hydrogen hardening as observed during the hydrogen charging [31]. ........................ 23 Figure 2.10. Schematic representation of an Implant test specimen after welding. The rod is loaded by tension. ..................................................................................................................... 24 Figure 2.11. The CSM Implant test set up. The plate on top of the set-up is the weld plate. With the weld plate removed, the notched rod is shown in the small photograph. ..................... 25 Figure 2.12. Carbon equivalent values located on the Graville chart. ........................................ 26 Figure 2.13. Implant test result showing the different charging percentage of hydrogen. .......... 27 Figure 2.14. A chart of the model that developed by Coe and Chano [36]. ............................... 27 Figure 2.16. Implant testing results of the five grades of HSLA steels [38]. ............................... 28 vii Figure 2.17. Implant specimen showing the variable parameters used to build up the numerical model [39]. ................................................................................................................ 30 Figure 2.18. No evidence of cracking in the HAZ and fusion zone [40]. .................................... 31 Figure 2.19. Preheat temperature as a function of hydrogen content [42]. ................................ 31 Figure 2.20. The Percentage of hydrogen diffusion in one of the steel [46]. .............................. 33 Figure 2.21. Intergranular fracture surface of two different materials a) 2507 duplex stainless steel, b) HSLA AISI 4135 steel [54,55]. ..................................................................................... 35 Figure 2.22. The distribution of residual stresses over the diameter of a quenched bar and radial directions due to (a) thermal contraction and (c) both thermal and transformational volume changes [9]. .................................................................................................................. 37 Figure 2.23. Typical distributions of temperature and longitudinal stress ( ) during bead on x plate welding showing residual stress development [9]. ............................................................ 37 Figure 2.24. The galvanic series showing active and inactive metals. ....................................... 39 Figure 2.25. Stress corrosion cracking factors. .......................................................................... 40 Researchers have classified the SCC of HSLA steels into two categories, intergranular SCC (IGSCC) and transgranular SCC (TGSCC). Both intergranular and transgranular SCC may take place, but the crack always follows a general macroscopic path that is normal to the tensile component of stress. ...................................................................................................... 40 Figure 2.26. A schematic of the slow strain-rate test set up. ..................................................... 42 Figure 2.27. Stress corrosion cracking factors. .......................................................................... 42 Figure 3.1. Gleeble® 3500 thermo-mechanical simulation system. ........................................... 45 Figure 3.2. Heat treatment temperatures cycles in Gleeble® 3500. .......................................... 46 Figure 3.3. One inch-thick plates for furnace heat treatment. .................................................... 47 Figure 3.4. Cathodically hydrogen charging set-up. .................................................................. 48 Figure 3.5. Hydogen concentrations vs. time for pre-charged specimens analyzed by LECO analyzer. .................................................................................................................................... 49 Figure 3.6. LECO H analyzer machine. .................................................................................... 50 2 Figure 3.7. Implant weldability test set-up constructed in the welding laboratory. ..................... 51 Figure 3.8. Gas metal arc welding (MIG welding or GMA welding). .......................................... 52 Figure 3.9. Mechanical tensile test using the Alliance machine. ................................................ 53 Figure 3.11. Geometry and dimensions of tensile test specimen for SSRT (in mm). ................. 54 Figure 3.12. Electrochemical test showing the flask and Gamry set-up. ................................... 56 viii Figure 4.1. Implant test design and dimensions recommended by ASM handbook [76]. .......... 57 Figure 4.3. The implant test parts, a) general implant test set-up, b) applied load reading, c) load cell, d) weld bead on implant plate, e) load plates, f) jack sysetm. .................................... 61 Figure 4.4. Schematic showing how the implant test is conducted. ........................................... 62 Figure 4.5. Implant test results for all three conditions (0% H , 1%H and 2% H ). ................... 63 2 2 2 Figure 4.6. Fracture locations in different conditions. ................................................................ 64 Figure 4.7. Microhardness measurements on the implant pin without hydrogen charging, the sample did not fail. ..................................................................................................................... 65 Figure 4.8. a) the hydrogen diffusion in austenitic materials is lower than ferritic materials, b) hydrogen cracking after the weld [15]. ....................................................................................... 66 Figure 4.9. Mechanical tensile test results for the furnace samples. ......................................... 68 Figure 4.10. Tensile strength and microhardness results for the furnace samples. ................... 69 The samples were machined according to the standardized low force mode in Gleeble® machine. The dimensions were 6 mm diameter and 80 mm length. The samples were used to produce the different subzones in the HAZ along the implant pin. Two more temperatures were added to assure covering all the regions in between the different microstructures. .......... 69 Figure 4.11. Modified tensile test results using constant load for the furnace samples. ............ 70 Figure 4.12. Modified tensile test results using constant load for each simulated furnace sample. ...................................................................................................................................... 71 Figure 4.13. Fracture locations in different conditions. .............................................................. 72 Figure 5.1. Schematic showing the possible features happening in the fracture surface. ......... 75 Figure 5.2. The base metal (ASTM A543 steel) and the high temperature simulated specimens (CGHAZ and FGHAZ) with different hydrogen charging. ......................................... 77 Figure 5.3. The low temperature simulated specimens with different hydrogen charging. ........ 78 Figure 5.4. The base metal (ASTM A543 steel) and the high temperature simulated specimens (CGHAZ&FGHAZ) with different hydrogen charging at higher magnification. ......... 79 Figure 5.5. The low temperature simulated specimens with different hydrogen charging at higher magnification. ................................................................................................................. 80 Figure 5.6. Gleeble simulated samples charged with 5 ppm H for ASTM A543 steel .............. 81 2 . Figure 5.7. Gleeble simulated samples charged with 5 ppm H at higher magnification 2 showing the high hydrogen intergranular cracking in the CGHAZ and reduces as going to low temperatures in red arrow. ......................................................................................................... 82 ix Figure 5.8. Different microstructures (subzones) generated by the weld during implant testing. ....................................................................................................................................... 84 Figure 5.9. Different HAZ subzones microstructures produced by the furnace. ......................... 85 Figure 5.10. Microstructure of the base metal ASTM A543 steel showing the martensite and bainite with some ferrite. ............................................................................................................ 86 Figure 5.11. The Vickers hardness reading along the implant pin for ASTM A543 steel. .......... 86 Figure 5.12. Different microstructures produced by the Gleeble®. ............................................ 88 Figure 5.14. As-etched microstructures for a) 1200oC and b) 1100oC, CGHAZ simulated samples. .................................................................................................................................... 89 Figure 5.16. As-etched microstructures for a) 760oC and b) 725oC, and c) 500oC simulated samples. .................................................................................................................................... 90 Figure 5.17. Lepera etchant for the CGHAZ and FGHAZ samples, ferrite is blue, bainite is brown, MA consituent is white. .................................................................................................. 92 Figure 6.1. Heat flow around weldment for (a) thick plate and (b) thin sheet. ............................ 94 Figure 6.2. Schematic temperature variations around weld pool. .............................................. 95 Figure 6.3. Rosenthal assumption: point heat source geometry [85]. ........................................ 96 Figure 6.4. Rosenthal equation showing the effect of doubling the welding speed on isotherm pattern [84]. ............................................................................................................................... 97 Figure 6.5. Graphical repersentation of the calculations resulted in the form of isotherms using Rosenthal equation. ......................................................................................................... 99 Figure 6.6. Welding advisor: Component (base metal and welding metal) properties, welding process parameters, cooling behavior, and clamping condition are addressed. ...................... 101 Figure 6.7. Material database manager- start window. ............................................................ 103 Figure 6.8. Material database manager- start window- chemical composition, thermal conductivity, and yield stress. .................................................................................................. 104 Figure 6.9. Goldak double ellipsoid heat source model [89]. ................................................... 106 Figure 6.10. The weldline in SYSWELD simulation. ................................................................ 107 Figure 6.11. Recommended dimensions for implant test pin in ASM Metals Handbook. ......... 108 Figure 6.12. Simulated model showing the dimensions used in SYSWELD. ........................... 110 Figure 6.13. First model simulation showing the geometry and the mesh distrinution. ............ 111 Figure 6.14. The two models used for the simulation and computational analysis. ................. 112 Figure 6.15. Simulated welding parameters and conditions .................................................... 116 x