Applied Science, Faculty of
Engineering, School of (Okanagan)
DSpace
UBCO
Piche, Austin
Master of Applied Science - MASc
University of British Columbia
The objective of this thesis was to investigate the effects of hydrogen-enriched natural gas (HENG) blend on the microstructure and mechanical properties of an API 5L X42 pipeline that is currently being used in FortisBC’s infrastructure. The seam welded X42 pipeline is a commonly used material in North America’s natural gas infrastructure and is manufactured through hot rolling and connected with submerged arc welding (SAW) along the seam. A decommissioned Vintage Grade 290 pipe was manufactured in the same way as the X42 material which was also used for this study. The introduction of hydrogen gas into other X-series pipeline systems has shown the potential to cause hydrogen embrittlement (HE) which can lead to premature failure. This embrittlement could degrade the mechanical properties and be one of the main reasons for a shortened life cycle, causing repairs to occur more frequently. In this study, the ultimate tensile strength, yield strength, percent elongation, area reduction, fracture surface, microhardness, and phase compositions were all tested on both the X42 base and Vintage Grade 290 welded material. These properties were obtained through tensile tests, Vickers hardness testing, and analysis on a scanning electron microscope. Tensile test samples were obtained in the longitudinal direction in the pipe wall with the welded samples in the hoop direction perpendicular across the weld. These samples were induced in various hydrogen and natural gas blends for different prolonged periods. Induction blends consisted of 0%, 5%, and 20% hydrogen concentration by molar mass mixed with natural gas. The samples were then held in these enriched environments for periods of 2 weeks, 2 months, and 6 months. The results revealed that both the hydrogen concentration and time of exposure have small impacts on various properties of the material in the X42 base material. As for the Grade 290 weld, the hydrogen concentration and exposure time did not impact the mechanical properties of this material. To iii analyze the hydrogen susceptibility of the material, a 2% and 3% factor of embrittlement was determined for the X42 and Grade 290 respectively. Microstructural analysis of the pipeline at various locations was conducted utilizing an optical microscope, scanning electron microscope, and energy dispersive X-ray spectroscopy. These revealed the phases and chemical composition present in the X42 base material and the Vintage Grade 290 fusion zone (FZ), heat affected zone (HAZ), and base metal (BM) regions. Micro-hardness testing on the X42 showed that hydrogen could diffuse into the material and increase the hardness near the exposed surface. This hardness increase was not present in the Vintage Grade 290 HAZ and FZ.
EFFECTS OF BLENDED HYDROGEN ENRICHED NATURAL GAS ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF A X42 STEEL PIPELINE AND GRADE 290 WELD by Austin Piche B.A.Sc., The University of British Columbia, 2020 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in THE COLLEGE OF GRADUATE STUDIES (Mechanical Engineering) THE UNIVERSITY OF BRITISH COLMUBIA (Okanagan) December 2020 © Austin Piche, 2020 ii The following individuals certify that they have read, and recommend to the College of Graduate Studies for acceptance, a thesis/dissertation entitled: EFFECTS OF BLENDED HYDROGEN ENRICHED NATURAL GAS ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF A X42 STEEL PIPELINE AND GRADE 290 WELD submitted by Austin Piche in partial fulfillment of the requirements of the degree of Master of Applied Science. Examining Committee: Dr. Dimitry Sediako, School of Engineering, Mechanical Engineering ______________________________________________________________________________ Supervisor Dr. Lukas Bichler, School of Engineering, Mechanical Engineering ______________________________________________________________________________ Supervisory Committee Member Dr. Jian Liu, School of Engineering, Mechanical Engineering ______________________________________________________________________________ Supervisory Committee Member Dr. Ahmad Rteil ______________________________________________________________________________ University Examiner iii Abstract The objective of this thesis was to investigate the effects of hydrogen-enriched natural gas (HENG) blend on the microstructure and mechanical properties of an API 5L X42 pipeline that is currently being used in FortisBC’s infrastructure. The seam welded X42 pipeline is a commonly used material in North America’s natural gas infrastructure and is manufactured through hot rolling and connected with submerged arc welding (SAW) along the seam. A decommissioned Vintage Grade 290 pipe was manufactured in the same way as the X42 material which was also used for this study. The introduction of hydrogen gas into other X-series pipeline systems has shown the potential to cause hydrogen embrittlement (HE) which can lead to premature failure. This embrittlement could degrade the mechanical properties and be one of the main reasons for a shortened life cycle, causing repairs to occur more frequently. In this study, the ultimate tensile strength, yield strength, percent elongation, area reduction, fracture surface, microhardness, and phase compositions were all tested on both the X42 base and Vintage Grade 290 welded material. These properties were obtained through tensile tests, Vickers hardness testing, and analysis on a scanning electron microscope. Tensile test samples were obtained in the longitudinal direction in the pipe wall with the welded samples in the hoop direction perpendicular across the weld. These samples were induced in various hydrogen and natural gas blends for different prolonged periods. Induction blends consisted of 0%, 5%, and 20% hydrogen concentration by molar mass mixed with natural gas. The samples were then held in these enriched environments for periods of 2 weeks, 2 months, and 6 months. The results revealed that both the hydrogen concentration and time of exposure have small impacts on various properties of the material in the X42 base material. As for the Grade 290 weld, the hydrogen concentration and exposure time did not impact the mechanical properties of this material. To iv analyze the hydrogen susceptibility of the material, a 2% and 3% factor of embrittlement was determined for the X42 and Grade 290 respectively. Microstructural analysis of the pipeline at various locations was conducted utilizing an optical microscope, scanning electron microscope, and energy dispersive X-ray spectroscopy. These revealed the phases and chemical composition present in the X42 base material and the Vintage Grade 290 fusion zone (FZ), heat affected zone (HAZ), and base metal (BM) regions. Micro-hardness testing on the X42 showed that hydrogen could diffuse into the material and increase the hardness near the exposed surface. This hardness increase was not present in the Vintage Grade 290 HAZ and FZ. v Lay Summary The consumption of raw materials and harmful effects of fossil fuels used as an energy source has pushed the world to a state of global warming that may not be recoverable. Now sustainable, renewable, clean energy sources are the goal of the future. Hydrogen as an energy source is an obtainable method to achieve these goals. Hydrogen burns more efficiently, hotter, and cleaner, producing electricity, heat, and water as by-products which can be captured and utilized. This is why the incorporation of hydrogen gas into natural gas is a stepping stone towards a more sustainable future. This research has focused on the feasibility and effects of the hydrogen natural gas blend on current materials being used in pipelines. This was done by conducting many tests that would determine the durability of the material, relative to its initial properties, while being exposed to various conditions. vi Table of Contents ABSTRACT ............................................................................................................................................... III LAY SUMMARY ......................................................................................................................................V TABLE OF CONTENTS ....................................................................................................................... VI LIST OF TABLES ................................................................................................................................... IX LIST OF FIGURES .................................................................................................................................. X LIST OF SYMBOLS AND ABBREVIATIONS............................................................................. XIII ACKNOWLEDGEMENTS ..................................................................................................................XV DEDICATION ........................................................................................................................................ XVI CHAPTER 1: INTRODUCTION ......................................................................................................... 1 1.1 BACKGROUND AND STATEMENT PROBLEM ............................................................................ 1 1.2 OBJECTIVE AND SCOPE .................................................................................................... 4 1.3 METHODOLOGY ............................................................................................................... 5 1.4 NOVELTY ......................................................................................................................... 5 CHAPTER 2: LITERATURE REVIEW ............................................................................................ 7 2.1 INTRODUCTION....................................................................................................................... 7 2.2 HYDROGEN EMBRITTLEMENT (HE) IN PIPELINE MATERIALS................................................... 8 2.3 FACTORS AFFECTING HE ........................................................................................................ 8 2.3.1 Microstructure and chemical compositions ................................................................... 8 2.3.2 Grain boundaries and crystallographic texture ............................................................ 10 2.3.3 Composition of the pipeline materials ......................................................................... 12 2.4 MECHANISMS THAT AFFECT HE ........................................................................................... 16 2.4.1 Hydrogen enhanced decohesion model (HEDE) ......................................................... 16 2.4.2 Hydrogen enhanced localized plasticity (HELP) ......................................................... 17 2.4.3 Adsorption induced dislocation emission (AIDE) ....................................................... 17 2.5 HYDROGEN IMPACT ON STEEL PIPELINE .............................................................................. 18 2.5.1 Mechanical Properties .................................................................................................. 18 vii 2.5.2 Hydrogen assisted fatigue ............................................................................................ 19 2.5.3 Hydrogen effect on the initiation and growth of defects in transmission pipelines ..... 21 2.5.4 Diffusion and solubility of gases in steels ................................................................... 21 2.6 CONCLUSIONS FROM CHAPTER 2 .......................................................................................... 22 CHAPTER 3: TESTING PROCEDURE .......................................................................................... 24 3.1 INTRODUCTION..................................................................................................................... 24 3.2 MATERIAL USED .................................................................................................................. 24 3.3 X42 & GRADE 290 MATERIAL TESTING PROCEDURES ......................................................... 25 3.3.1 Tensile Testing ............................................................................................................. 25 3.3.2 Vickers Hardness Testing ............................................................................................ 28 3.3.3 Fracture Surface Procedure .......................................................................................... 32 3.3.4 Microstructural Procedure ........................................................................................... 33 3.4.5 Surface Oxide Procedure ............................................................................................. 37 CHAPTER 4: RESULTS AND DISCUSSION ................................................................................ 39 4.1 MECHANICAL PROPERTIES ................................................................................................... 39 4.1.1 Tensile Tests Base X42 ................................................................................................ 39 4.1.2 Tensile Tests Vintage Grade 290 ................................................................................. 43 4.1.3 Microhardness Tests Base X42 .................................................................................... 47 4.1.4 Microhardness Tests Vintage Grade 290 ..................................................................... 51 4.2 FRACTURE ANALYSIS ........................................................................................................... 54 4.2.1 HE Susceptibility ......................................................................................................... 55 4.2.2 Base X42 material ........................................................................................................ 57 4.2.3 Grade 290 material ....................................................................................................... 61 4.3 MICROSTRUCTURAL ANALYSIS AND PHASE COMPOSITION .................................................. 62 4.3.1 Phase composition ....................................................................................................... 62 4.4 SURFACE OXIDE ANALYSIS .................................................................................................. 66 4.5 STATISTICAL ANALYSIS ....................................................................................................... 68 4.5.1 Tensile Tests ................................................................................................................ 70 CHAPTER 5: CONCLUSIONS .......................................................................................................... 77 viii 5.1 CONSTRAINTS ...................................................................................................................... 79 5.2 FUTURE WORK ..................................................................................................................... 80 BIBLIOGRAPHY ................................................................................................................................... 82 APPENDICES ......................................................................................................................................... 90 APPENDIX A: RAW X42 TENSILE DATA ..................................................................................... 90 APPENDIX B: RAW GRADE 290 TENSILE DATA.......................................................................... 95 APPENDIX C: RAW X42 MICROHARDNESS DATA ...................................................................... 98 APPENDIX D: RAW GRADE 290 MICROHARDNESS DATA ......................................................... 101 APPENDIX E: RAW X42 AND GRADE 290 FRACTURE ANALYSIS DATA .................................... 108 ix List of Tables Table 1 Chemical breakdown by mass fraction percent of elemental requirements to meet standards [52] ........................................................................................................................ 13 Table 2 Summary of inclusion types and methods used to find them through other studies [49]. Reprinted from International Journal of Hydrogen Energy, Vol 43 / Issue 31, Enyinnaya Ohaeri, Ubong Eduok, Jerzy Szpunar, Hydrogen related degradation in pipeline steel: A review, 14584-14617., Copyright (2018), with permission from Elsevier ........................... 15 Table 3 Chemical composition (%) of API 5L X42 Steel and Vintage Grade 290 used in present investigation .......................................................................................................................... 25 Table 4 Mechanical properties found in this research compared to API standards ...................... 25 Table 5 Phase compositional range (shown in wt%) of various phases and inclusions found in base X42 material ................................................................................................................. 64 Table 6 Phase compositional range (shown in wt%) of various phases and inclusions found in Grade 290 welded material ................................................................................................... 66 Table 7 Rust analysis on 2 and 6 month samples ......................................................................... 67 Table 8 Analysis of variance (ANOVA) table for two-factor tests .............................................. 69 Table 9 ANOVA analysis for the UTS of X42 ............................................................................. 71 Table 10 ANOVA analysis for the UTS of Grade 290 weld ........................................................ 72 Table 11 ANOVA analysis for the YS of X42 ............................................................................. 72 Table 12 ANOVA analysis for the YS of Grade 290 ................................................................... 73 Table 13 ANOVA analysis for the %EL of X42 .......................................................................... 73 Table 14 ANOVA analysis for the %EL of Grade 290 ................................................................ 74 Table 15 ANOVA analysis for the RA of X42 ............................................................................. 74 Table 16 ANOVA analysis for the RA of Grade 290 ................................................................... 75 Table 17 ANOVA analysis for the brittle area percentage of X42 ............................................... 75 Table 18 ANOVA analysis for the brittle are percentage of Grade 290 ....................................... 76 x List of Figures Figure 1 An overview on the research performed in this thesis ..................................................... 4 Figure 2 (A): Optical, (B and C) transmission electron micrograph of X80 pipeline steel [28]. Reprinted from International Journal of Hydrogen Energy, Vol. 42/ Issue23, Teng An, Huangtao Peng, Pengpeng Bai, Shuqi Zheng, Xiangli Wen, Lin Zhang, Influence of hydrogen pressure of fatigue properties of X80 pipeline steel, 15669-15678.,Copyright (2017) with permission for Elsevier ....................................................................................... 9 Figure 3 Inverse pole figure orientation maps in three different regions around hydrogen induced cracks [32]. Reprinted from Corrosion Science, Vol 111, Mohammad Masoumi, Cleiton Carvalho Silva, Hamilton Ferreira Gomes de Abreu, Effect of crystallographic orientations on the hydrogen-induced cracking resistance improvement of API 5L X70 pipeline steel under various thermomechanical processing, 121-131., Copyright (2016), with permission from Elsevier ......................................................................................................................... 11 Figure 4 Various types of hydrogen trapping sites in the material [49] Reprinted from International Journal of Hydrogen Energy, Vol 43 / Issue 31, Enyinnaya Ohaeri, Ubong Eduok, Jerzy Szpunar, Hydrogen related degradation in pipeline steel: A review, 14584- 14617., Copyright (2018), with permission from Elsevier ................................................... 16 Figure 5 ASTM standard dimensions for the base material tensile tests coupons with the small size specimens of 6mm dimeter chosen [56] ........................................................................ 26 Figure 6 Modified ASTM sub-size standard dimensions, in mm, for the welded material tensile test coupons .......................................................................................................................... 26 Figure 7 3D model showing location of welded sample in reference to the weld ........................ 27 Figure 8 Progression of sample step for sub-size flat welded tensile coupons ............................. 27 Figure 9 Tensile set-up of the MTS test machine used for the pulling tests ................................. 28 Figure 10 Image of Vickers micro-hardness machine (United Testing System Canada Limited SXHV-1000 TA) ................................................................................................................... 28 Figure 11 Minimum recommended spacing for Vickers Indentations [57] .................................. 29 Figure 12 Location of Vickers indentations on base X42 sample specimen ................................ 30 Figure 13 Location of Vickers indentations on weld sample specimen, within regions .............. 31 Figure 14 Location of Vickers indentations on weld sample specimen, across regions ............... 31 xi Figure 15 A) Image of fracture surface with yellow line representing the outer circle used for area. B) Red represents the brittle area with black being ductile.......................................... 32 Figure 16 Image of the orientations taken for microstructural analysis ....................................... 33 Figure 17 SEM image of X42 in the longitude direction (A), radial direction (B) ...................... 34 Figure 18 Nital etching the surface of the samples at different time lengths ............................... 35 Figure 19 Image of FE-SEM Tescan Mira 3 XMU machine used ............................................... 36 Figure 20 Image of the sputter coater Cressington 208 HR used ................................................. 36 Figure 21 Image of the Zeiss optical stereoscopic microscope (OSM, model 37081 Gottingen) 37 Figure 22 Rust accumulation on 6 month samples for 0%,5%, and 20% ..................................... 38 Figure 23 Scale used for measuring rust accumulation ................................................................ 38 Figure 24 The average ultimate tensile strength for tensile specimens of the base X42 material for the ten enrichment conditions ......................................................................................... 40 Figure 25 The average yield strength for tensile specimens of the base X42 material for the ten enrichment conditions ........................................................................................................... 40 Figure 26 The average elongation for tensile specimens of the base X42 material for the ten enrichment conditions ........................................................................................................... 41 Figure 27 The average area reduction for tensile specimens of the base X42 material for the ten enrichment conditions ........................................................................................................... 42 Figure 28 The average ultimate tensile strength for tensile specimens of the Grade 290 welded material for the ten enrichment conditions ........................................................................... 44 Figure 29 The average yield strength for tensile specimens of the Grade 290 welded material for the ten enrichment conditions ............................................................................................... 45 Figure 30 The average elongation for tensile specimens of the Grade 290 material for the ten enrichment conditions ........................................................................................................... 46 Figure 31 The average area reduction for tensile specimens of the Grade 290 material for the ten enrichment conditions ........................................................................................................... 46 Figure 32 Vickers hardness results on the base material exposed to 0% H2 ................................ 48 Figure 33 Vickers hardness results on the base X42 material exposed to 5% H2 ........................ 49 Figure 34 Vickers hardness results on the base X42 material exposed to 20% H2 ...................... 50 Figure 35 Vickers hardness results on the base X42 material with exposure time of 6 months for 0%, 5%, and 20% H2............................................................................................................. 51 xii Figure 36 Vickers hardness results on the Grade 290 material. (A) No exposure, (B) exposure concentration of 0%, (C) exposure concentration of 5%, (D) and exposure concentration of 20% H2, in the base, HAZ, and FZ region for 2 weeks, 2 months, and 6 months. ............... 52 Figure 37 Vickers hardness across the weld for (A) 0%, (B) 5%, (C) and 20% .......................... 53 Figure 38 Embrittlement factor of X42 for the enrichment conditions ........................................ 56 Figure 39 Embrittlement factor of Grade 290 for the enrichment conditions ............................. 57 Figure 40 Brittle and ductile locations on the fracture surface of A) Original X42 sample B) Conditioned 6 month 20% H2 X42 sample ........................................................................... 58 Figure 41 A) Brittle cleavage and B) Ductile dimpled fracture mechanisms ............................... 58 Figure 42 ImageJ analysis between two X42 samples A) 2 weeks at 0% B) 6 months at 20% ... 59 Figure 43 Brittle area percentage of X42 for the ten enrichment conditions................................ 60 Figure 44 Brittle and ductile locations on the fracture surface of a Grade 290 welded sample ... 61 Figure 45 Brittle are percentage of Grade 290 for the ten enrichment conditions ....................... 62 Figure 46 Microstructure of the X42 pipeline material with ferrite and pearlite present ............. 63 Figure 47 Locations of scattered inclusions with a magnified photo of a singular one................ 64 Figure 48 SEM image of X42 with the layering pattern from hot rolling, lighter grey is ferrite, darker is pearlite .................................................................................................................... 65 Figure 49 SEM image of Grade 290 A) Base metal region B) HAZ region with lighter grey pearlite, dark is ferrite C) FZ region with light bainite and dark ferrite ............................... 66 xiii List of Symbols and Abbreviations AIDE Absorption Induced Dislocation Emission ANOVA Analysis of Variance API American Petroleum Institute ASTM American Society for Testing and Materials BCC Body Centered Cubic BM Base Metal CCS Carbon Capture and Storage CSL Special Coincidence Lattice CT Compact Tension EDS Energy Dispersive Spectroscopy F Factor of Embrittlement FCG Fatigue Crack Growth FE-SEM Field Emission Scanning Electron Microscopy FZ Fusion Zone GB Granular Bainite GHG Greenhouse Gas HA-FCG Hydrogen Assisted Fatigue Crack Growth HE Hydrogen embrittlement HEDE Hydrogen Enhanced Decohesion Model HELP Hydrogen Enhanced Localized Plasticity HENG Hydrogen Enriched Natural Gas HIC Hydrogen Induced Cracking ISO International Organization for Standardization LAGB Low Angle Grain Boundaries xiv NG Natural gas PF Polygonal Ferrite PSL Product Specification Levels RA Area Reduction SAW Submerged arc welding SEM Scanning Electron Microscope UTS Ultimate Tensile Strength, MPa WM Welded Metal YTS Yield Tensile Strength, MPa %EL Percent Elongation xv Acknowledgements I would like to thank my supervisor Dr. Dimitry Sediako for the opportunity, support, and encouragement he provided me over the last two years in the completion of my Master’s degree and thesis. I would also like to thank Dr. Lukas Bichler for providing access to high-end research and laboratory equipment. Thank you to the UBCO School of Engineering for providing the opportunity and chance to further my learning career. I would like to acknowledge Josh Stroh for training me on equipment while I was a research assistant. He engrained in me the importance of conducting testing to meet a high standard. I also greatly value the time and assistance offered by the UBCO Machine Shop Technicians, Durwin Bossy and Raymond Seida, for their expert knowledge and advice while I was machining samples. I also had the opportunity to work alongside some great colleagues turned friends with Josh Stroh, Sina Kianfar, Kyle Lessoway, Jordan Kozakevich, Nick Sabry, and Kris Mackowiak that were around to keep things light when testing wasn't always going to plan. Also, a thank you to everyone else who helped along the way with my studies. Special thanks are owed to my parents, who have supported me throughout my years of education, both morally and financially. Lastly I would like to thank my girlfriend Alyssa for the long study nights together and moral support throughout the years. xvi Dedication This thesis is dedicated to My Parents Andrea and Michael Piche Who supported me throughout my journey 1 Chapter 1: Introduction 1.1 Background and Statement Problem The last decade witnessed significant growth in awareness for fuel scarcity, greenhouse gas emissions, and global warming. Thus, the need arises to implement a new energy carrier that would provide the same energy value and contribute to reducing CO2 emissions. Reducing CO2 emissions and other harmful by-products to become more environmentally friendly has become the goal of many world leaders and scientists. One such potential fuel is hydrogen, which is becoming increasingly popular [1-3]. With technology, the use of hydrogen has been largely growing and will continue to do so as the demand increases [67]. This means that it will be produced in large quantities and will certainly need to be transported from the production location to the end-user. State of the art breakthroughs has given hydrogen gas the ability to be used in a variety of different applications. Hydrogen can help to decarbonize transportation, supply industry and residential energy needs, be used for structure heating, and is a major component in the manufacturing process of fertilizers for feedstock and polymers [66]. It can also be used in fuel cells that power commercial or passenger vehicles as well as other modes in the transport sector. Hydrogen is a sustainable energy source with the ability to burn cleaner, hotter, and more efficiently than the current combustion processes used for energy and transportation. Current methods to transport hydrogen are dangerous, very energy intensive, and inefficient [68]. With the demand growing, there is a need to transport the product in larger volume. Existing methods cool and compress the hydrogen gas, then transport it with commercial trucking in pressurized tanks. This method is both inefficient and dangerous, as it is highly energy intensive to contain the gas while putting civilians and the workers at risk. Trying to transport pressurized containers with the possibility to explode because of the pressure by roadway or train has a high-risk factor with the 2 potential for mistakes and accidents due to human error. Using existing infrastructure such as pipelines to transport hydrogen is a cost-effective way to distribute the product. Experience indicates that implementing new technology does not essentially require drastic change; it can be achieved by small modifications to existing methods and infrastructure. There are suggestions to inject hydrogen into the existing natural gas pipelines, which permits a fast and cost-effective transition to hydrogen energy transport and a way to distribute the product while benefiting from what is already developed [4-6]. Mixing of the hydrogen gas into the natural gas infrastructure would allow for more efficient, cost-effective distribution and is the best comprehensive method for large scale use of hydrogen. The hydrogen can then be stored in the pipeline networks and subsequently converted back to water in a fuel cell to generate electricity during periods of peak demand [1]. The mixture of gases also results in a lighter medium that is easier to pump throughout the lines. Unfortunately, most high-pressure gas and oil pipelines are carbon and high-strength steel (ferritic steels), which are susceptible to hydrogen embrittlement (HE) [7-9]. The concern is that hydrogen gas tends to make steels brittle through a process known as hydrogen embrittlement. This process can have catastrophic effects on the metal and result in premature failure. An extensive leakage risk assessment conducted by the National Renewable Energy Laboratory [54] concluded that blending hydrogen gas into the existing natural gas (NG) infrastructure with a concentration below 20% resulted in an overall risk that is not significant. With the need to lower harmful emissions and meet government regulations, the demand for hydrogen systems and usage will continue to grow, requiring larger volumes to be transported through pipelines. Since pipelines are the ideal method of transporting hydrogen, more research is needed to understand the long- term effects of hydrogen blended with natural gas on X42 pipelines. There are limited amounts of research with a mixed consensus on what the hydrogen gas does to the mechanical properties of 3 lower strength X-series steels. X-series steel pipelines are mainly used for low to medium pressure oil and gas transmission. The material is a low alloy steel that is referred to by the minimum required yield strength. For example, X42 is a steel that has a minimum required yield strength of 42 ksi. The three main alloying elements in this series are carbon, silicon, and manganese. Since steel makes up to 46% in miles of all pipeline types in the USA [54] and a large portion in Canada and other regions [69], it is important to know the impact of the hydrogen enriched natural gas blend (HENG) on the steel. With X42 and its equivalent Grade 290 being one of the most commonly used materials, the need to determine if it and the welds are suitable for being used in the transportation of HENG application is imperative. In this thesis, an X42 and Grade 290 steel pipeline was induced by various amounts of hydrogen and Natural gas blends (0, 5, and 20 mole %) for specific periods (2 weeks, 2 months, and 6 months) to see the effect of the blend on the mechanical properties of the steel. Phase analysis and microstructure of the X42 steel alloy was evaluated using Scanning Electron Microscope/Energy Dispersive Spectroscopy (SEM/EDS) testing. The hardness of the specimens was found through the use of a Vickers micro-hardness tester. Material characteristics such as tensile and yield strength were assessed using an MTS tensile testing machine. The tensile testing also allowed elongation, area reduction, and hydrogen susceptibility of the material to be measured. Fracture analysis was evaluated using ImageJ on the notched and dog bone tensile specimens to evaluate the percent of the brittleness of the failure surface. Rust analysis was conducted to find the rate of growth relative to the base material as accumulation appeared on the higher percentage samples that were exposed to the mixed environment longer. The microstructure in all conditions consisted of a body-centered cubic D-Iron phase and Pearlite phase which is alternate lamellae of Ferrite (D) and Cementite (Fe3C). Throughout the microstructure, there were 4 many other inclusions of various forms mainly falling under aluminum, silicon, calcium, manganese, sulfur inclusions. 1.2 Objective and Scope The objective of this thesis was to determine the effect of a hydrogen/natural gas blend on X42 pipeline steel and Grade 290 welds. This thesis accomplished the scope by evaluating the outcome of the tensile strength of both at room temperature, microhardness indentation, the phase present in the material, and ImageJ analysis of the fracture surface. Figure 1 expresses a break down overview of the work conducted in this study. Figure 1 An overview on the research performed in this thesis Tensile Test ASTM E8 Vickers Hardness ASTM E92 Tensile Test ASTM E8 Microstructural analysis Mechanical testing To determine if the HENG concept is feasible for application X42 Steel Tests Mechanical testing Optical Microscopy SEM/EDS Vickers Hardness ASTM E92 Microstructural analysis Grade 290 Weld Tests Fracture Analysis Fracture Analysis Effects of HENG on mechanical properties and microstructure of X42 Optical Microscopy SEM/EDS 5 1.3 Methodology The overall approach to the research conducted was to determine the effects of hydrogen- enriched natural gas on the properties of pipeline steels. The purpose of studying the effects of hydrogen-enriched natural gas is to identify what occurs when different concentrations are exposed to the pipeline material for prolonged periods of time. To determine these effects, quantitative mechanical properties of materials currently being used in FortisBC’s distribution lines were tested and analyzed. This was done by conducting tensile tests, microhardness tests, SEM imaging, and other image analysis. Exposure time and hydrogen concentration variables were manipulated at three different levels, each to assess the impact on the properties. This was the most suitable approach as it allows for an initial feasibility study to be conducted on a budget to see if the different levels are practical in a large scale commercial operation. The work followed ASTM standards where possible for reliability and repeatability. Statistical analysis and data gathered were analyzed to produce criteria that would meet the validity and reliability of this research. Data collection was usually in the form of raw numerical data that was then gathered, organized, and processed in excel documents into finalized graphs for simple evaluation. Different tests used various methods that are further explained in the experimental procedures. 1.4 Novelty The combination of the hydrogen-enriched natural gas implemented into the X42 pipelines is an innovative step forward in the transportation and future use of hydrogen. This new field studies the effects of different hydrogen concentrations and durations on the microstructure and mechanical properties of an X42 pipeline. The implementation of hydrogen-enriched natural gas can unlock the potential to a vast field of new opportunities such as: • More efficient method of transporting hydrogen 6 • The ability to leave hydrogen in the natural gas system to be used by consumers as a cleaner efficient fuel source • Aspiration to start consumer use of hydrogen fuel cell vehicles • Hydrogen cells in vehicles could be collectively used to power commercial buildings during the day increasing vehicle utilization • Used in mobile applications as power packs This work is novel as it represents the first attempt to conduct a feasibility study by implementing hydrogen gas into an existing natural gas infrastructure. It investigates the effect of the hydrogen blend on the mechanical properties and microstructure of X42 base and Grade 290 welded material. Literature has done some similar testing on higher strength X-series pipeline materials but none have been conducted in this manner on X42. No research combines the external exposure of materials to a hydrogen enriched natural gas at the concentration and time used in this work to determine its effects on the X42 and Grade 290 material. 7 Chapter 2: Literature review 2.1 Introduction Hydrogen’s use and capabilities are ever-growing as a clean source. There are many benefits of adding hydrogen to natural gas, which include: • Significant reduction of greenhouse gas emissions (GHG) if hydrogen is produced from a renewable source such as solar, biomass, wind, and nuclear power [54] • HENG has some advantage of greenhouse gas emissions with hydrogen production from fossil fuels with Carbon Capture and Storage (CCS) [54] • Potential benefits of selective extraction of hydrogen rely on the performance of the separation technology and subsequent use of the hydrogen, which is dependent on purity [54] • Benefits of the improvement of air quality by reducing sulfur dioxide, oxides of nitrogen, and particulate emissions if hydrogen replaces conventional fuel in transportation [54] • Potential benefit of developing a greener natural gas if the HENG mixture is used in existing industrial and household appliances [54] • Reduce the cost of energy source transmission and use in commercial fertilizers and chemical components [66] However, there are some challenges faced with the implementation of hydrogen into a natural gas infrastructure. When typical steel pipelines are exposed to hydrogen, a process called hydrogen embrittlement occurs in which the hydrogen makes the material brittle. Typically, hydrogen- related damages occur at a level of stress lower than what is normally seen on a certain metal under operation conditions without hydrogen [54]. The hydrogen affects pipeline steels properties, specifically the microstructure, mechanical properties, fracture, and fatigue properties. This 8 section will cover topics that are widely studied in the technical literature and cover areas of interest that are relevant to the work conducted in this research. 2.2 Hydrogen embrittlement (HE) in pipeline materials Hydrogen can degrade the fracture behavior of most structural materials under certain conditions. The degradation of the material’s mechanical properties by hydrogen is called hydrogen embrittlement [2]. If the embrittlement occurs as a result of hydrogen located within the bulk of alloy during the application of load, it is referred to as “internal hydrogen embrittlement”. Moreover, the embrittlement might also result from the exposure of the material under load to the hydrogen-containing environment, referred to as “external hydrogen embrittlement”. The embrittlement exhibits a brittle fracture mode reducing the tensile strength of the material [2, 21]. There are established means by which hydrogen mitigates into the pipeline materials: (i) absorption of molecular hydrogen from the environment; (ii) introduction of hydrogen in the material during processing (such as welding or heat treatment); and (iii) generation of hydrogen on the surface as a result of a chemical reaction (i.e. corrosion or precipitation) which is called hydrogen reaction embrittlement, also known as hydrogen-induced cracking (HIC). The resulting hydrogen can either form blisters in the sub-surface region or gaseous methane in the interior [22-24]. 2.3 Factors affecting HE 2.3.1 Microstructure and chemical compositions Thermomechanical processing leads to a wide range of microstructures and anisotropy of mechanical properties in high strength pipeline steels. The formation of each microstructural component in the material is dependent on the processing parameters, especially the cooling rate after hot-rolling [25]. These microstructures are often comprised of ferritic pearlite, polygonal ferrite, quasi polygonal ferrite, acicular ferrite, bainitic ferrite, bainite, and martensitic 9 microstructural phases [26]. Fast cooling rates and low transformation temperatures produce bainitic ferrite while higher transformation temperatures and slower cooling rates often generate polygonal ferrite microstructure. A comparison was made between three API grade pipeline steels (X60, X80, and the X100 grade) for their susceptibility to the hydrogen embrittlement [27]. The results showed that there is a distinct susceptibility to loss of ductility after charging, and this tends to increase with the strength level of the steel at a charging current density above 0.44 mAmm-2. Cathodic hydrogen charging is based on the principles of an electrochemical cell. Samples are submerged in an electrolyte while the sample acts as the cathode and another material acts as an anode. The electrical potential applied produces hydrogen ions to concentrate on the surface of the sample and drives the diffusion of the hydrogen ions. All three pipeline steels exhibited fine cracks parallel to the major rolling direction after charging and an increasing amount of brittleness on the fracture surface. The typical microstructure of X80 pipeline steel consists of polygonal ferrite (PF) and granular bainite (GB), see Figure 2 [28]. Figure 2 (A): Optical, (B and C) transmission electron micrograph of X80 pipeline steel [28]. Reprinted from International Journal of Hydrogen Energy, Vol. 42/ Issue23, Teng An, Huangtao Peng, Pengpeng Bai, Shuqi Zheng, Xiangli Wen, Lin Zhang, Influence of hydrogen pressure of fatigue properties of X80 pipeline steel, 15669-15678.,Copyright (2017) with permission for Elsevier Studies have shown that microstructural banding comprising of ferrite pearlite phases heighten susceptibility to hydrogen blistering [29]. However, if we alter the microstructure by thermomechanical processing into equiaxed ferritic pearlites, ferritic granular bainite, and bainitic A B C 10 ferrite, the drastic reduction in the blistering effect of hydrogen was observed. Also, the presence of the martensitic phase in the pipeline material increases the susceptibility to hydrogen embrittlement. This is because such a microstructure is highly strained with excess interstitial carbon trapped within the lattice, which promotes hydrogen attack. The distribution of austenite and carbide within the martensitic lathes enhances the hydrogen diffusion. Also, it is established that the non-metallic inclusions and precipitates aid hydrogen attack on pipeline material by providing sites for the accumulation of hydrogen [6]. Hence, the processing which governs the microstructure of the material greatly affects the hydrogen embrittlement properties. 2.3.2 Grain boundaries and crystallographic texture The distribution of grain boundaries and preferred orientation of the grains, known as texture, are important factors that influence the hydrogen attack on pipelines. In this regard, it is of interest for the grain boundaries as well as crystallographic texture to be optimized for the specific application. Often the thermomechanical processing of the material is done to increase the low angle grain boundaries (LAGB) and special coincidence lattice (CSL) boundaries, possessing low energy and less susceptibility to hydrogen attack. Thermomechanical treatment of pipeline steel also results in extensive deformation, recrystallization, and phase transformation which leads to change in the properties and performance under severe conditions. Despite the non-uniformity of the texture evolution after hot rolling, grain boundaries containing <101> and <111> planes parallel to the surface of pipeline steel are most resistant to hydrogen degradation [31, 32]. Venegas et al. [31] investigated the effects of microstructure local texture and grain boundary distribution on the HIC in API-5L-X46 pipeline steel using SEM and EBSD. It was found that the paths for intergranular crack propagation in this material are mainly high angle (high-energy, disordered) grain boundaries, while transgranular propagation occurs by cleavage along the <111> planes. 11 Masoumi et. al [32] observed preferential HE and crack propagation along the regions dominated by the small grains in X70 pipeline steel as shown in Figure 3. It is attributed to the fact that smaller grains contain excess grain boundaries and more dislocations which trap the hydrogen and act as a zone for crack initiation and propagation. These microstructural characteristics are created through the manufacturing process which contributes to the features seen in the material. It is important to study the features present in X42 as it can help to determine how the material responds to the susceptibility of HE. Based on the conducted literature review, the crystallographic texture may have a strong connection to the hydrogen-induced cracking. A layered texture for the X42 pipeline is expected due to the heavily reduced cross-sectional area from the rolling process. This in turn may influence hydrogen-induced cracking. Figure 3 Inverse pole figure orientation maps in three different regions around hydrogen induced cracks [32]. Reprinted from Corrosion Science, Vol 111, Mohammad Masoumi, Cleiton Carvalho Silva, Hamilton Ferreira Gomes de Abreu, Effect of crystallographic orientations on the hydrogen-induced cracking resistance improvement of API 5L X70 pipeline steel under various thermomechanical processing, 121-131., Copyright (2016), with permission from Elsevier 12 2.3.3 Composition of the pipeline materials There are a few different standards followed throughout the world for pipelines but the most commonly used and met are from the American Petroleum Institute (API) and in Canada is the Canadian Standard Association (CSA Z245.1). This institute has regulations and requirements to monitor the quality and standards that need to be met by a certain grade of pipe. Seen in Table 1 is a chemical breakdown by mass fraction percent of the required amounts of each element present to be classified under the API 5L PSL1 standard. Table 1 shows some of the X-series steels and their respective mass fraction breakdown. It can be seen that as the percentage of carbon and manganese increases so does the series number from X42 to X70. Increasing these elements in turn increases the yield strength of the material. This is not an exhaustive list with more tables available for different heat treatments used or different standards that are required to be met such as the API 5L PSL 2 standard. 13 Table 1 Chemical breakdown by mass fraction percent of elemental requirements to meet standards [52] Steel Grade Mass fraction, % based on heat and product analyses a,g C Mn P S V Nb Ti max b max b max max max max max Seamless Pipe A 0.22 0.9 0.3 0.3 - - - B 0.28 1.2 0.3 0.3 c,d c,d d X42 0.28 1.3 0.3 0.3 d d d X46 0.28 1.4 0.3 0.3 d d d X52 0.28 1.4 0.3 0.3 d d d X56 0.28 1.4 0.3 0.3 d d d X60 0.28 e 1.4 e 0.3 0.3 f f f X65 0.28 e 1.4 e 0.3 0.3 f f f X70 0.28 e 1.4 e 0.3 0.3 f f f Welded Pipe A 0.22 0.9 0.3 0.3 - - - B 0.26 1.2 0.3 0.3 c,d c,d d X42 0.26 1.3 0.3 0.3 d d d X46 0.26 1.4 0.3 0.3 d d d X52 0.26 1.4 0.3 0.3 d d d X56 0.26 1.4 0.3 0.3 d d d X60 0.26 e 1.4 e 0.3 0.3 f f f X65 0.26 e 1.45 e 0.3 0.3 f f f X70 0.26 e 1.65 e 0.3 0.3 f f f a. Cu ≤ 0.50%; Ni ≤ 0.50%; Cr ≤ 0.50%; and Mo ≤ 0.15% b. For each reduction of 0.01% below the specified maximum concentration for carbon, an increase of 0.05% above the specified maximum concentration for Mn is permissible, up to a maximum of 1.65% for grades ≥ L245 or B, but ≤ L360 or X52; up to a maximum of 1.75% for grades > L360 or X52, but < L485 or X70; and up to maximum of 2.00% for grade L485 or X70 c. Unless otherwise agreed NB + V ≤ 0.06% d. Nb + V + Ti ≤ 0.15% e. Unless otherwise agreed f. Unless otherwise agreed, NB + V = Ti ≤ 0.15% g. No deliberate addition of B is permitted and the residual B ≤ 0.001% Table 2 also has a summary of inclusion types found and their effects on hydrogen trapping and hydrogen induced cracking (HIC) from different studies. The majority of the inclusions found were Al-Si and MnS inclusion with some also finding Al, Si, Ca-Al-O-S/Si, or various oxides. Across the majority of the findings in Table 2, all authors refer to cracks either initiation at the inclusions, or a detrimental localized corrosion occurring, which are both significant in HIC 14 forming. Inclusions sites are harmful because hydrogen is known to concentrate which is the start of the HIC process. 15 Table 2 Summary of inclusion types and methods used to find them through other studies [49]. Reprinted from International Journal of Hydrogen Energy, Vol 43 / Issue 31, Enyinnaya Ohaeri, Ubong Eduok, Jerzy Szpunar, Hydrogen related degradation in pipeline steel: A review, 14584-14617., Copyright (2018), with permission from Elsevier S/No Pipeline steel Inclusion analysis technique Inclusion types found Findings 1 X70 SEM and EDX analysis after slow strain rate tensile test in acidic soil solution Al and Si enriched inclusions For cracks to initiate at inclusions, their morphology and composition should be such that encourage hydrogen trapping and pressure build up at interface. Si-enriched inclusions were quite coherent with pipeline steel matrix and did not initiate cracks, but cracks initiated at Al-enriched inclusion due to incoherency with pipeline matrix. 2 X100 SEM, EDX and localized electrochemical impedance spectroscopy (LEIS) techniques before and after immersion in NS4 solution (neutral pH bicarbonate solution) Si-O enriched, Al-Si-S-Ca-O enriched, Mg- Al-Ca-O enriched, and Al-Si-Ca-O inclusions Inclusions of Si-O type were coherent with steel matrix and did not result in any obvious localized corrosion. Whereas, other inclusions containing relatively less Si-O experienced localized corrosion attack after complete dissolution or fall-out of inclusions with increasing immersion time. 3 X100 Hydrogen charging with 0.1 M H2SO4 solution at different current densities in the absence of stress and inclusion analysis by SEM and EDX Mixture of Ca- Al-O-S, MnS, and oxides of Al and Si inclusions HIC occurred at critical hydrogen charging concentration of 3.24 ppm at mainly Si and Al oxide enriched inclusions instead of elongated MnS and Ca-Al-O-S inclusion. The reason being higher degree of non- cohesiveness between Si and Al inclusions. 4 X80 Electrochemical hydrogen permeation test in 0.5 M H2SO4 and polarization measurement with SEM and EDX inclusion characterization. Mainly Si and Al-Si enriched inclusions The high presence of irreversible hydrogen traps (inclusions) at the weld heat affected zone predisposed pipeline steel to preferential anodic dissolution. Inclusion analysis showed that hydrogen related localized corrosion occurred mainly around those enriched with Si and Al-Si. 5 X120 HIC susceptibility measurement according to NACE TM0284-2003 and hydrogen permeation test. Microstructure and inclusion studies were performed with SEM and EDX respectively. Primarily Al2O3 or MnS inclusions Microstructure and inclusions were significant in influencing HIC. Variations in amount of inclusions (irreversible trap sites) resulted in differences in HIC susceptibility for different X120 pipeline steel specimens (with varying alloying composition) as a result of changes in hydrogen diffusion pattern. 6 X70 Electrochemical hydrogen charging with 0.5 mol/L H2SO4 and AS2O3 p hydrogen permeation studies Oxides of Ca and Al with nitrides of Ti and Nb Uniform distribution of NbN and TiN was observed, but cracks were mainly associated with oxides of Ca-Mn-Al. Nitrides and carbide precipitates of Ti and Nb contributed to precipitation strengthening of pipeline steels. Also, observed precipitates are smaller than oxides or oxysulfides of Ca and can accommodate more hydrogen beside them to cause HIC. 16 2.4 Mechanisms that affect HE Despite having studies that date back over a century on this topic, the mechanism responsible for the failure of the material due to hydrogen is still debatable. Hydrogen degradation depends on its trapping behavior in the pipeline materials. These trap sites in the material include defects, dislocations, vacancies, precipitates, grain boundaries, alloying elements, and interfaces shown in Figure 4. It is proposed that no single mechanism of the following models specifically explains the entire phenomena known as HE, but a combination of systems being explained in the different theories are used for each specific case. Figure 4 Various types of hydrogen trapping sites in the material [49] Reprinted from International Journal of Hydrogen Energy, Vol 43 / Issue 31, Enyinnaya Ohaeri, Ubong Eduok, Jerzy Szpunar, Hydrogen related degradation in pipeline steel: A review, 14584-14617., Copyright (2018), with permission from Elsevier 2.4.1 Hydrogen enhanced decohesion model (HEDE) HEDE is characterized by a smooth brittle fracture of the material surface with limited plasticity. Induction of hydrogen weakens the metal-metal bonds leading to decohesion instead of slip. HEDE is one of the most frequently proposed mechanisms in HE of steels [33, 34]. The material failure with a reduction in the bond strength is due to the segregation of the hydrogen at grain interfaces. When the applied stress is greater than the cohesive strength along the interface, 17 the presence of impurities results in the reduction of gross cohesive strength which leads to initiation or propagation of the cracks. 2.4.2 Hydrogen enhanced localized plasticity (HELP) HELP is a hydrogen embrittlement mechanism that manifests as crack propagation via coalescence of micro-voids in a localized manner. Beachem [37] was the first to propose that despite the brittle macroscopic appearance of hydrogen cracks, highly localized deformation processes may constitute the fracture process. Based on this concept, HELP models were developed by several studies [10, 38, 39] and they found that hydrogen atmospheres attached to dislocations decrease the barrier to dislocation movement which eventually leads to an increase of the localized plasticity. Even though it is very difficult to prove the HEDE and AIDE mechanism, there have been several experimental investigations of direct evidence of the HELP model. The revealing results have been obtained with the technique of in situ TEM observations. The experiments were conducted for BCC, FCC, and HCP, metals in which TEM foil was strained in situ in a specialized TEM with an environmental cell allowing it to be exposed to hydrogen gas while under strain. It was found that hydrogen increased the dislocation mobility under conditions of constant stress. In stressed specimens, dislocation mobility could be increased by the addition of H2 to the environmental cell and decreased by the removal of H2 and restoration of vacuum [10]. 2.4.3 Adsorption induced dislocation emission (AIDE) The AIDE embrittlement mechanism acts on the adsorption of hydrogen causing a weakening of interatomic bonds over several atomic distances. The model states that crack growth under sustained or monotonically increasing stresses occurs not only by dislocation emission from 18 crack tips but also involves nucleation and growth of the micro-voids ahead of the tip [51]. This void formation contributes to crack growth which allows cracks to propagate more rapidly and cause premature failures. 2.5 Hydrogen Impact on Steel Pipeline 2.5.1 Mechanical Properties The hydrogen effect on the mechanical properties of structural steels and alloys is well known and several studies have been conducted [16, 40, 41]. However, there are some contradictions in the reported studies. Some studies found the strengthening effects of hydrogen on material [12] while others reported weakening of the material, in the decreasing of the yield strength [42]. This circumstance is caused by the difficulty to take into account all possible factors, such as the specimen size and conditions of their hydrogenation, control of hydrogen concentration in material, loading conditions, and other factors that influence the study of the phenomenon. It should be noted that in the majority of the conducted studies, the actual value of hydrogen concentration in the material was unknown and the level of material hydrogenation was assessed indirectly [43]. This identifies limitations of used methods and received results. Meng et al.[44] investigated the hydrogen effects on X80 pipeline steel in high-pressure natural gas/hydrogen mixtures. The mechanical properties of X80 pipeline steel were tested with hydrogen/gas blend with different hydrogen concentrations of 0, 5.0, 10.0, 20.0, and 50.0% at the pressure of 12MPa. The results indicate that added hydrogen does not affect ultimate tensile strength and yield strength. On the contrary, the decreases of elongation and reduction of area were observed with increasing hydrogen. The fractographs of the tension specimens implied the brittle fracture characteristic of quasi-cleavage in hydrogen blends compared to the ductile characteristic of dimples in nitrogen gas. Furthermore, the textured microstructure caused by hot rolling 19 influenced the HE, and the notch specimens seemed to be more sensitive to the texture than the smooth specimens. 2.5.2 Hydrogen assisted fatigue Previous investigations indicated that hydrogen-induced acceleration of fatigue crack growth, which is caused by natural gas pressure fluctuations, is the most likely type of failure in the mixed gas-hydrogen pipelines [44, 45]. Given the importance of this failure mode, the measurement of fatigue properties of the pipeline steel in hydrogen gas is of crucial importance. The typical crack growth rate behavior of a material is described through ΔK- da/dN with three distinguishable regimes including stage I (threshold regime), stage II (Paris regime), and state III (final fracture) [46]. The stage II fatigue crack growth domain is quantitatively described through Paris law as shown in Eq.(1): 𝑑𝑎 𝑑𝑁 = 𝐶(𝛥𝐾)𝑚 Eq.(1) Where 𝑑𝑎 𝑑𝑁 is crack growth per cycle, the material coefficients C and m are obtained experimentally, ΔK is the stress intensity factor range and can be expressed is Eq.(2) as: 𝛥𝐾 = 𝐾𝑚𝑎𝑥 − 𝐾𝑚𝑖𝑛 = 𝐾𝑚𝑎𝑥(1 − 𝑅) where 𝑅 = 𝐾𝑚𝑖𝑛 𝐾𝑚𝑎𝑥 Eq.(2) Where 𝐾𝑚𝑎𝑥 and 𝐾𝑚𝑖𝑛 are the maximum and minimum stress intensity factors during the cycle and R is stress ratio. Fatigue crack growth rate testing is conducted on Compact Tension (CT) specimens, in accordance with the ASTM E647 standard [47]. 20 Alvaro et al. [20] investigated the effects of hydrogen on the fatigue crack growth behavior of the Fe-3 wt%Si alloy and a pearlitic-ferritic X70 pipeline steel under in-situ electrochemical H charging condition. In situ H-charging enhanced the fatigue crack growth rate for the Fe-3 wt%Si material up to 1000 times and up to 76 times for the X70 pipeline steel compared to testing in air. The results indicated the time-dependent nature of the H-induced degradation interaction: a lower frequency leads to more severe degradation of the FCG process. Post-mortem fractography clearly showed a shift in crack growth mechanisms: the FCG mode of both Fe-3 wt%Si alloy and X70 steel changed from transgranular to Quasi-cleavage; IG type fracture was limited in Fe-3 wt%Si and absent in X70, indicating that the grain boundaries are not preferential paths for crack propagation. An et al. [28] investigated the effect of hydrogen on the low cycle fatigue and FGC properties of X80 pipeline steel, varying the hydrogen partial pressure from 0MPa to 8MPa at a total pressure of 12MPa. It was found that the cycles to failure of X80 decreased exponentially with increasing hydrogen pressure. Crack initiation happened at about 3000 cycles with the hydrogen partial pressure of 0.6MPa at the maximum load of 20kN. Another study by the National Renewable Energy Lab (NREL) [54] states that accelerated fatigue crack growth is more severe at ambient temperature compared to elevated temperatures. The study also mentions that the presence of hydrogen reduces the cyclic stress intensity factor ΔK and fatigue life, therefore, making the fatigue cracking a great concern in pipelines that commonly fluctuate in pressure. 21 2.5.3 Hydrogen effect on the initiation and growth of defects in transmission pipelines The concern of injecting hydrogen into transmission lines is that they operate at a much larger pressure than in the distribution system. Transmission lines are sometimes located within close proximity to largely populated areas. Therefore, the risk factors and considerations were different at the time of installation of the initial natural gas system. This could result in larger and maybe more possible areas of defects which, with the addition of hydrogen, will exploit as a weakness. Cracks that can grow from existing defects such as corrosion, sharp defects in the weld, or inclusions are more susceptible to propagating under the influence of HE as it reduces the ductility strength of the material. The sharp defects are of major concern as typical cyclic stresses can accelerate crack growth. This accelerated crack growth due to HE can change the characteristics of the failure mode from a preferential leak before rupture to a catastrophic failure. The NREL [54] found that adding up to 50% hydrogen into natural gas transmission pipelines may not cause a catastrophic failure. They also showed with a risk assessment that the material defects risk factor increased from 34.16%with NG to 39.16% with the introduction of hydrogen between 20%-50% and further to a risk factor of 54.16% when hydrogen was greater than 50% [54]. Some work states that transportation of pure hydrogen in low-pressure transmission lines has no occurring problems [54]. Others mentioned that low-strength pipeline alloys, such as X42, are highly susceptible to hydrogen assisted fatigue crack growth (HA-FCG) [55]. 2.5.4 Diffusion and solubility of gases in steels Diffusion of hydrogen, or any gas, is driven by the gradient difference in concentration and will continue to diffuse until uniform concentration has been reached. Fick’s first law of diffusion states that mass diffusivity is driven by a concentration gradient as demonstrated in Eq. (3) [62]: 22 𝐽𝐴𝑥 ∗ = −𝐷𝐴𝐵 𝜕𝐶𝐴 𝜕𝑥 Eq. (3) Where 𝐽𝐴𝑥 is the mass diffusivity of material A in material B, 𝐷𝐴𝐵is referred to as the binary diffusion coefficient, and CA and CB are the concentration of species A and B respectively. Fick’s first law assumes that D is a constant, which in only true for dilute solutions but is a good assumption for diffusion in solids. The mass diffusivity of hydrogen in iron is 0.26 𝑥 10−12𝑚2/𝑠 at a temperature of 15oC [62]. This diffusion constant is highly dependent on temperature and when the temperature increases so does the constant. Permeability is another important aspect of the rate at which hydrogen flux passes through the material. The permeability of the gas is inversely proportional to the square root of pressure as seen in Eq. (4) [62]: 𝑃 = 𝐽 𝑙 √𝛥𝑝𝐻2 Eq. (4) Therefore, under the concept of gas diffusion into steel, the three most important factors considered when implementing hydrogen into an existing system are temperature, pressure, and concentration of the fluid. 2.6 Conclusions from Chapter 2 X-series pipeline steels, specifically X42, has been widely used in natural gas transmission and distribution lines because of their strength, affordability, and durability. The material properties for prolonged exposure to natural gas are known, with well-established service intervals. The introduction of hydrogen brings a new aspect to the table that potentially changes the material properties. Hydrogen embrittlement is affected by factors such as the composition of the pipeline material, microstructure and chemical compositions, grain boundaries, and 23 crystallographic texture. The exact model for the failure of the material due to hydrogen is still highly debatable, but generally can be classified into one of three models: HEDE model, HELP model, or AIDE model. The impacts of hydrogen on the materials properties and fatigue characteristics itself are also controversial as some studies claim a detrimental effect, while others declare improvements [12, 20, 28, 42, 44, 45]. The diffusion of the hydrogen gas is hard to measure, but it is directly driven by a gradient that is dependent on temperature, pressure, and concentration of the fluid. 24 Chapter 3: Testing Procedure 3.1 Introduction In this chapter, an overview of the experimental procedures will be discussed. This includes both the X42 base and Vintage Grade 290 welded API 5LX X42 material. It will discuss tensile testing, Vickers hardness, fracture surface analysis, microstructural and phase evaluation, and surface oxide accumulation analysis. 3.2 Material Used The API 5L X42 Steel used in this study was provided by FortisBC and it is currently the most common type of material used in their pipeline system to date and commonly used in industry. In Table 3 the chemical composition of the API 5L X42 steel and Vintage Grade 290 material is shown. API 5L X42 which will now be referred to as X42 base steel. The Vintage Grade 290 material is the metric equivalent of the imperial X42 and will be referred to as Grade 290 weld from now on. The Grade 290 material is a previously decommissioned pipeline that has previously been exposed to natural gas for it service life. These pipeline materials are in agreement with the American Petroleum Institute (API) specifications that adhere to the International Organization for Standardization (ISO) 3183 [52, 65]. Table 4 shows the mechanical property standards set by API, along with other important properties and the numbers gathered in this study. These materials are commonly used in pipeline infrastructure because of their high strength, corrosive resistance, ductile characteristics, and resistance to brittle crack propagation. 25 Table 3 Chemical composition (%) of API 5L X42 Steel and Vintage Grade 290 used in present investigation Fe C Si Mn P S Cr Ni Cu Ti Mo V B Nb CE X42 Bal 0.16 0.27 1.19 0.017 0.003 0.040 0.007 0.010 0.002 0.004 0.001 0.001 0.002 0.365 Grade 290 Bal 0.21 0.25 0.93 NA NA 0.100 0.065 0.149 - 0.019 0.035 0.001 0.002 0.424 Table 4 Mechanical properties found in this research compared to API standards This Study (X42 Base) This Study (Vintage Grade 290 Weld) API 5L-X42 Standard Ultimate Tensile Strength (UTS) (MPa) 517-536 533-537 > 414 [52] Yield Strength (YS) (MPa) 321-348 444-466 > 290 [52] Elongation (%EL) 32-37 14-17 > 20 [52] Area Reduction (RA) 73-75 11-15 - Vickers Hardness (HV) 161-230 168-224 170 [53] The X42 steel underwent assessment in ten different conditions. “Original” is referred to as the reference material that did not undergo any induction and is used as a controlled point. The other enriched environmental conditions will be referred to as 2 weeks at (0%, 5%, 20%) , 2 months at (0%, 5%, 20%), and 6 months at (0%, 5%, 20%). The percentage amount refers to the molar percent of hydrogen blended into natural gas. Tests in this study were conducted with an internal inducing pressure of 60psi. In consideration, FortisBC currently operates transmission pipelines at a pressure of 585-2160psi, while distribution lines operate at a pressure less than 100psi. 3.3 X42 & Grade 290 Material Testing Procedures 3.3.1 Tensile Testing Tensile tests were conducted on two different types of samples, the round smooth tensile coupons shown in Figure 5 for the X42 base material and the sub-size flat dog bone specimens shown in Figure 6 for the Vintage Grade 290 welded samples. The difference in size and type of 26 coupons was due to the limitation in the geometric size of the pipe as the weld was in the longitude direction. Both the X42 base material round coupons and Grade 290 welded flat sample specimens were prepared and tested as per ASTM E8/E8M-16a [56]. The Grade 290 samples were a modified sub-sized version of the standard as this was the only possible way to retrieve a welded sample due to limited thickness and geometrical characteristics of the pipe. The dimensions of the X42 and Grade 290 samples are shown in Figure 5 and 6 respectively. Figure 5 ASTM standard dimensions for the base material tensile tests coupons with the small size specimens of 6mm dimeter chosen [56] Figure 6 Modified ASTM sub-size standard dimensions, in mm, for the welded material tensile test coupons The sample extraction location of the welded coupon is shown in a 3D model in Figure 7. Illustrated in Figure 8 the progression of the flat weld tensile samples with a similar process followed for the round specimens but in the longitudinal direction. 27 Figure 7 3D model showing location of welded sample in reference to the weld Figure 8 Progression of sample step for sub-size flat welded tensile coupons The tensile tests were conducted using the MTS Landmark 370 servo-hydraulic testing system (Model 370.10, 25kN load cell) pulling at a constant strain rate of 0.02mm/mm/min. Figure 9 demonstrates the particular tensile test set-up used for pulling the X42 base and Grade 290 welded coupons. The tensile tests were conducted three times for the X42 material and four times on Grade 290 welded samples for each one of the environmental conditions for reproducibility and repeatability of the results obtained. 28 Figure 9 Tensile set-up of the MTS test machine used for the pulling tests 3.3.2 Vickers Hardness Testing Vickers micro-hardness values were obtained using the United Testing System Canada Limited SXHV-100 TA Vickers micro-hardness machine shown in Figure 10. These tests were conducted according to Vickers hardness testing standard ASTM E92-17 [57]. Figure 10 Image of Vickers micro-hardness machine (United Testing System Canada Limited SXHV-1000 TA) A couple of important features to note in this standard is that the sample needs to be highly polished and completely flat in order to get a clean diamond shape. The method used to do so is 29 further explained in depth in section 4.1.3. The force application that the indenter pushes with and the dwell time that the force is held for are important and can influence the results. The force used in the testing of the base material was 25g or 0.24525N with a holding dwell time of 15 seconds. The spacing between indentations and distance to the edge, as shown in Figure 11, is required to be 2.5 times the Vickers diagonal. This force and dwell time was chosen as it allowed many indentations close to the edge of the sample where the hydrogen effect was expected to be observed. Figure 11 Minimum recommended spacing for Vickers Indentations [57] A total of forty-four measurements were taken on each X42 base specimen with different interval spacing as the test progressed further towards the middle. Four different lines starting at 40𝜇m, 50𝜇m, 60𝜇m, and 70𝜇m, were used to get an accurate representation near the surface wall. These lines are 90o apart in relation to each other. The closest indentation to the wall starts at 40um progressing to the furthest at 4000um towards the center. All lines have the first 6 points with 40um interval spacing, the next 4 with 400um, and the last a distance of 600um away from the most recent point. This allowed a progression of points from 40um -270um with 10um spacing, 30 from 300um-1800um with 100um of spacing, and 2400um-4000um with 600um of spacing. The location of these indentations is shown Figure 12, with the results discussed in section 4.1.3. Figure 12 Location of Vickers indentations on base X42 sample specimen The Grade 290 welds were processed with a slightly different procedure but follow all the same steps outlined in the ASTM E92-17 standard [57]. The outline locations of these indents are shown in Figure 13 within the welded regions and in Figure 14 across the regions. The force used within the regions was 0.981N with a holding dwell time of 15 seconds. The force used across the regions was 4.905N with a dwell time of 15 seconds. The lower force of 0.981N was used due to limited space, which required closer points to the exposed surface, better representing the penetrative effect of HENG. The large force of 4.905N was used across the region to limit the 40um 400um 900um 50um 40um 400um 1400um 40um 400um 1900um 70um 400um 2200um 40um 60um 31 fluctuation due to phase dependence. The locations of the test within the regions is demonstrated below. Four rows were indented in each region, the first point is 75um from the wall followed by the next 6 points being 75um apart from each other and the last 6 being 225um apart. This starts at the outer wall and moves towards the center. This is then repeated in each of the regions. Figure 13 Location of Vickers indentations on weld sample specimen, within regions The tests across the Grade 290 weld were conducted in two lines of 41 points at the center of the sample to avoid any influence from the penetrative effects of the HENG blend. With the increased weight for these indentations, the distance between indentations was required to increase to 200um, following ASTM standard E92-17 [57]. A schematic diagram of these locations can be seen in Figure 14. Figure 14 Location of Vickers indentations on weld sample specimen, across regions HAZ HAZ 3400um 75um 225um FZ Base Material Base Material 3400um 200um 200um FZ Base Material Base Material HAZ HAZ 8000um 32 3.3.3 Fracture Surface Procedure The same MTS tensile testing machine mentioned previously and a SEM machine were also used in the fracture surface procedure. The notched tensile samples used to evaluate peak load was the fractured surface area analyzed. Each half of the broken notched tensile samples were cut down to fit and be mounted inside the SEM. The fracture analysis started with retrieving SEM images. All photos were taken at the same magnification magnitude of 100x and under exposure of 28.7 contrast and 92.3 brightness level. Next ImageJ, a processing software, was used as it can determine the brittle-to-ductile surface area using a greyscale. This greyscale was used to determine the brittle section to total area which was then converted to a brittle percentage. The total area calculation was determined by finding the area of an oval based on two different diameters and can be shown as the yellow circle in Figure 15 A. In Figure 15 B the image shows the red, representing the brittle flat darker grey and the black being the litter grey ductile fracture characteristic. Figure 15 A) Image of fracture surface with yellow line representing the outer circle used for area. B) Red represents the brittle area with black being ductile A B 33 3.3.4 Microstructural Procedure Microstructural analysis was conducted on the X42 and Vintage Grade 290 steel to determine the phases present in the X42 base, and the Grade 290 fusion, HAZ, and base material regions. The analysis was conducted on all ten conditions to see if the percentage of hydrogen or the amount of time affected the microstructure. First analysis was looking at the surface normal to the longitudinal and radial direction as shown in Figure 16 and 17. Figure 16 Image of the orientations taken for microstructural analysis These two orientations were analyzed to determine if there was any noticeable difference in the two directions. As shown in SEM images in Figure 17, there is no evident difference in the features between the longitude and radial facing direction. Therefore, it can be determined that analysis in the longitude direction is a fair representation of the material. 34 Figure 17 SEM image of X42 in the longitude direction (A), radial direction (B) Once manageable size pieces were cut, the sample was then mounted in a quick cure acrylic. Next sanding and polishing took place while following the rules laid out in the ASTM standard E3-11 [58]. The process started with 240 grit sandpaper, then moving up to 400, 600, and 800 grit when ready. Afterwards, a diamond polishing paste was used to further remove scratches at a diamond size of 9um, 6um, 3um, finishing with 1um. The polished samples were etched using a Nital solution of 5% Nitric acid and 95% alcohol while following ASTM Standard E407- 07(2015) [59, 60]. Figure 18 shows an optimum submergence time of 40 seconds resulted in the clearest images. A B 35 Figure 18 Nital etching the surface of the samples at different time lengths Afterwards, the specimens were rinsed with distilled water and dried with warm convective air to remove any leftover water and prevent water spots. The images used in evaluating the optimum etching time in Figure 18 were taken with a Zeiss optical stereoscopic microscope (OSM, model 37081 Gottingen). The images and phases discussed in this report were obtained using a field emission scanning electron microscope (FE-SEM), Tescan Mira 3 XMU, that uses an accelerating voltage of 20,000V to evaluate the microstructure. A Cressington 208 HR sputter coater was used to sputter the specimen’s surface with 10nm of platinum. The coating makes the sample electrically conductive and does not allow for a charge to buildup on the surface while scanning resulting in a clear image. Images of these machines are shown in Figure 19-21. 36 Figure 19 Image of FE-SEM Tescan Mira 3 XMU machine used Figure 20 Image of the sputter coater Cressington 208 HR used Once these samples are sputter-coated, input into the SEM machine, and scanned an Oxford energy dispersive X-ray spectroscopy (EDS) detector was used to determine the composition 37 analysis of the phases present. An Oxford Instruments Aztec data acquisition and processing software along with the EDS composition of the phases were used to compare literature values to the stoichiometry of each phase. Figure 21 Image of the Zeiss optical stereoscopic microscope (OSM, model 37081 Gottingen) 3.4.5 Surface Oxide Procedure Oxide analysis was conducted on the X42 samples by measuring the weight of surface oxide relative to the 2 weeks samples where it started to appear. The rust was measured by a sanding process that removed the rust from a section of the sample then weighed the amount removed. The weight of the rust removed was then measured to determine the overall weight of accumulated rust on the surface of the entire sample. Figure 22 and 23 shows the accumulation of rust on the samples and scale used to measure the removed amount. 38 Figure 22 Rust accumulation on 6 month samples for 0%,5%, and 20% Figure 23 Scale used for measuring rust accumulation 39 Chapter 4: Results and Discussion The following section covers the results from the testing experiments conducted on the X42 and Vintage Grade 290 welded pipeline material. 4.1 Mechanical Properties This section will discuss the results of the mechanical properties, specifically on the (UTS), (YS), (%EL), and (RA), and microhardness for both the base X42 and Grade 290 welded material. 4.1.1 Tensile Tests Base X42 Tensile testing was conducted for each of the enriched conditions with the results discussed and presented in the following section. Three ASTM standard samples were pulled within each testing condition. The average and standard deviation for UTS, YS, %EL, and RA can be seen in Figure 24 to Figure 27. The UTS for the base X42 material in Figure 24 stays relatively constant for all the enrichment conditions. The data shows a recurring trend with a slight increase in the UTS with the time induced from the 2 weeks to 6 months exposure time. This minor increase with longer exposure time is within the standard deviation. A very similar observation can be made for the YS of the X42 material. The yield strength is relatively constant for all conditions, with a little increase in longer exposure time as seen in Figure 25. This increase again is within the standard deviation and is minor in magnitude. The difference in magnitude from the low to high extremes in UTS is 3.5% and YS is 8.5%. The UTS and YS from this testing can be determined to have an average of 527MPa and 336MPa respectively. These values directly correlate with the 523MPa UTS and 331MPa YS seen in the original X42 material used as a reference as well as the values provided from the SIAM Steel Pipe Company Limited testing and certification sheets [64]. 40 Figure 24 The average ultimate tensile strength for tensile specimens of the base X42 material for the ten enrichment conditions Figure 25 The average yield strength for tensile specimens of the base X42 material for the ten enrichment conditions When considering the effects of the HENG blend on the YS and UTS of the X42 material, the small increase in strength can be related to exposure time in the environment rather than the hydrogen concentration, which has very minor effects. Statistical analysis backs this conclusion with results in section 4.5.1.1 UTS and 4.5.1.2 YS, showing that the variation is not significant. The elongation measured on the overall length of each of the three samples was obtained and averaged. As can be seen in Figure 26, similar patterns in the UTS and YS appear for %EL. 41 The %EL remains relatively the same with a slight tendency to decrease in the 0% condition with longer exposure time. In the 5% and 20% conditions this trend is only shown between the 2 weeks and 6 months samples as the 2 months values stand out and increases. The important information from this graph is that the decrease seen is because of longer exposure times and not a result of hydrogen concentration. The difference between conditions is within the standard deviation of the samples, therefore hydrogen exposure for a prolonged time has no distinguishable to minor effects. This is confirmed with statistical analysis performed in section 4.5.1.3 %EL. The average elongation across all conditions in this testing of 34% also corresponds with the certified value given of 36% from SIAM Steel Pipe Company Limited [64]. Figure 26 The average elongation for tensile specimens of the base X42 material for the ten enrichment conditions Area reduction is measured by reduction in the initial cross-sectional area to the final area at breakage in the gauge length region. Shown in Figure 27 the RA remains relatively consistent across all enriched conditions. There is an increase in RA in the 5% and 20% samples that is the same trend seen in UTS, YS, and opposite in the %EL. The RA increases slightly with exposure time, with this amount remaining within the standard deviation. Therefore, it can be said that no 42 distinguishable effects from exposure time or hydrogen concentration are seen in the RA, as identified in the statistical analysis in section 4.5.1.4 RA. Figure 27 The average area reduction for tensile specimens of the base X42 material for the ten enrichment conditions When considering the effects of the hydrogen blend on the UTS, YS, %EL, and RA it can be shown in the graphs that the noticed minor changes are correlated with the exposure time and not the hydrogen concentration itself. The hydrogen not having an impact on the material is expected for the UTS and YS characteristics as literature has stated that the lower strength steels are more resistant to hydrogen embrittlement. Where the results start to deviate from literature is with regard to %EL and RA. This work demonstrates that no detrimental effects or significant changes are noticed in these characteristics, whereas some literature has shown a noticeable decrease. The %EL and RA discussion in these results coincide with the remarks made about the UTS and YS as there are very minor to no differences noticed between the conditions. Statistical analysis supports this conclusion with results in section 4.5.1.4 RA identifying no significant variation. 43 4.1.2 Tensile Tests Vintage Grade 290 Mechanical properties for the weld of the Vintage Grade 290 pipeline material were also tested. Seen in the graphs below are the UTS, YS, %EL, and RA. Since the testing was conducted on samples made from decommissioned pipeline, the enriched conditions between the welded original Grade 290 reference material and all 0% hydrogen concentration conditions have been induced to the same environmental gasses. Also, since the weld material was made at a different time under similar conditions, a direct comparison between the Grade 290 and X42 materials is not possible. Due to the limited knowledge of its history, these two materials cannot be guaranteed to be the same. Figure 28 shows the UTS results for the Grade 290 weld material under the different enriched conditions. There is no trend seen in this data with the magnitudes of each being the same. The difference in the high and low extremes is 537MPa and 525MPa or about 2%. This difference is within the standard deviation of the data and the UTS of the Grade 290 welded material is determined to not be affected by the hydrogen concentration or exposure time. Statistical analysis backs this conclusion with results in section 4.5.1.1 UTS showing that there is no significant variation. 44 Figure 28 The average ultimate tensile strength for tensile specimens of the Grade 290 welded material for the ten enrichment conditions There is no increasing or decreasing trend present in the data for the YS on the welded samples. The results shown in Figure 29 do not directly follow any trend made thus far. The high and low extremes for the YS is 466MPa and 445MPa respectively with a difference of about 5%. The difference in the data between the enrichment conditions is within the standard deviation and the reference original Grade 290 is in the middle of the two extremes. Therefore, the Grade 290 YS is not affected by different hydrogen concentrations or exposure time. Statistical analysis verifies this conclusion with results in section 4.5.1.2 YS showing that there is no significant variation. 45 Figure 29 The average yield strength for tensile specimens of the Grade 290 welded material for the ten enrichment conditions When considering the effects of the HENG blend on the UTS and YS of the Grade 290 welded material. It can be determined that the hydrogen concentration and exposure time do not affect them. Elongation measured on the gauge length of four samples was obtained and averaged. As can be seen in Figure 30, similar patterns found for the Grade 290 UTS and YS appear for %EL. The %EL remains the same with an increase in hydrogen concentration and exposure time. There is a slight variation that is within the standard deviation of the samples, therefore noting no distinguishable change. Statistical analysis of the welded %EL backs this conclusion with results in section 4.5.1.3 %EL showing that there is no significant variation. 46 Figure 30 The average elongation for tensile specimens of the Grade 290 material for the ten enrichment conditions The RA, shown in Figure 31, remains relatively consistent across all enriched conditions for the Grade 290 weld. The results across all conditions are within the standard deviation of testing. Therefore, no distinguishable effects from time exposure or hydrogen concentration are seen in the RA of the Grade 290 weld. Statistical analysis supports this conclusion with results in section 4.5.1.4 RA showing that there is no significant variation. Figure 31 The average area reduction for tensile specimens of the Grade 290 material for the ten enrichment conditions 47 When considering the effects of the HENG blend on the mechanical properties of the Grade 290 welded material, the induced concentration levels and exposure times do not affect the mechanical properties. 4.1.3 Microhardness Tests Base X42 Microhardness testing was conducted on all the enriched condition samples to determine the penetrative and detrimental effects of the hydrogen blend on the X42 pipeline material. Indentation testing was conducted according to ASTM standards on Vickers hardness testing [57]. The locations of the indents were conducted from the outside wall of the sample towards the middle as explained in section 3.3.2 Vickers Hardness Testing. Figure 32 shows the results of the indentations on the original base X42 sample along with the 2 weeks, 2 months, and 6 months induction times for 0% HENG blended. Indicated in the line of the original X42 the overall trend, with the exception of one outlier, does not increase or decrease in progression from the outer edge to the middle of the sample. The fluctuation on this line however is due to the specific hardness of the phases present in the material. The phases are discussed in depth later but the ferrite phase was found to be softer than the pearlite phase at an average of 170HV and 220HV respectively. Vickers ASTM standard testing is conducted by maintaining at least a minimum distance of 2.5 times the diamonds diagonal between points. Since Vickers hardness tests are on the magnitude of micrometers, the same as the size of phases, different amounts of one phase relative to the other get indented. This leads to a different percentage of each present for each indent resulting in a fluctuation between different points. With multiple points tested through the process used, the phase dependence can be ruled out as a contributing factor since the points are taken with no bias to the specific location of the indent but determined by distance from the last point. The overall trend of the line is what shows the effects 48 of the HENG blend. When no hydrogen is exposed to the samples the Vickers hardness of the material is approximately in the 165-185HV range. Figure 32 Vickers hardness results on the base material exposed to 0% H2 The graph in Figure 32 illustrates that the Vickers hardness does not change with the induction of the 0% HENG blend for all induction times used with respect to the original base X42. This is largely due to the limited amount of time that the samples are induced for as any effects that could occur do not have enough time to cause a difference. In the 5% HENG graph in Figure 33 the lines overall trends slopes down to the right for only two conditions. In the longer times induced by 2 and 6 months, it can be seen that the Vickers hardness is larger near the surface on the samples until approximately a penetrative depth of 150um. This is however not apparent in the 2-week sample as the trend of the line remains flat. When 5% hydrogen is exposed to the base X42 samples, the Vickers hardness for the 2 and 6 month specimens starts in the 200-215HV range, with the 2-week specimens remaining at 170- 185HV. All samples eventually converge in the 170-185HV range. 49 Figure 33 Vickers hardness results on the base X42 material exposed to 5% H2 The difference between the conditions seen here are related to the exposure time. The 2 months and 6 months samples show an increased surface hardness, while the 2 weeks remains flat at the 5% range. Once the enriched condition is increased to 20% hydrogen, the effects are more noticeable as the overall trends of the lines start at a harder Vickers value and decrease towards the center. The 2 and 6 months sample start in a range of 210-225HV before eventually settling to a hardness of 175-190HV at approximately the 300um distance from the edge. The 2 weeks sample starts at about 185-200HV then decreases to a range of 175-190HV at about 80um. 50 Figure 34 Vickers hardness results on the base X42 material exposed to 20% H2 Figure 34 shows that at a higher HENG concentration of 20% the increased hardness is well demonstrated by 2 and 6 months but also slightly noticeable by 2 weeks induced. The larger hardness values in the 2-week exposure at 20% lead to a development that both the hydrogen concentration and exposure time can affect the Vickers hardness of the base X42 material. Further analysis of the results is done by pairing the data regarding the different hydrogen concentrations for the longest period of 6 months. In Figures 32 to Figure 35 it is evident that the Vickers hardness is increased near the surface for 5% and 20% conditions but not for 0%. This indicates that the concentration of hydrogen also affects the Vickers hardness. 51 Figure 35 Vickers hardness results on the base X42 material with exposure time of 6 months for 0%, 5%, and 20% H2 Therefore, conclusions can be made from the above graphs and discussion that both time of exposure, demonstrated in Figure 32-34 and increased hydrogen concentration, demonstrated in Figure 35, have an influence on increasing Vickers hardness of the X42 material up to a depth of approximately 300um. 4.1.4 Microhardness Tests Vintage Grade 290 Vickers hardness testing was also conducted on the Vintage Grade 290 weld and followed the same ASTM standards and procedures that were in place for the base material testing. The indent locations on this material were conducted differently. Two tests were done, one within the welded regions (Base, HAZ, FZ) and one across regions, meaning direction across the weld (Base- HAZ-FZ-HAZ-Base). Diagrams of how this was performed and indent locations can be seen in section 3.3.2. As previously mentioned, since the material used to conduct the tests on the Grade 290 section is a previously decommissioned pipeline the 0% results will only be shown for the reader’s purpose. They will not be discussed for this section as the material has undergone the same enriched conditions as the base Grade 290. 52 4.1.4.1 Within Regions An average of four points indented at each distance from the wall was calculated to limit the variation due to the phase dependent hardness. Figure 36A represents the Vickers hardness in the base, HAZ, and FZ region of the original Grade 290 sample and provides a reference point. In this graph, it can be seen that the FZ and HAZ have a larger Vickers hardness throughout its depth compared to the base metal Grade 290. Figure 36B shows the Vickers hardness of the HAZ and FZ for a hydrogen blend of 0% at times induced for 2 weeks, 2 months, and 6 months. In this graph the hardness of the FZ region is larger than the HAZ by about 10-20HV. This trend generally follows in the remaining two graphs of 5% and 20% hydrogen in Figure 36C-D. Figure 36 Vickers hardness results on the Grade 290 material. (A) No exposure, (B) exposure concentration of 0%, (C) exposure concentration of 5%, (D) and exposure concentration of 20% H2, in the base, HAZ, and FZ region for 2 weeks, 2 months, and 6 months. The general trends of the lines within the regions remain relatively flat as the distance from the outer exposed surface increases. If there was a change in hardness because of hydrogen it would A C B D 53 be noticeable nearest to the exposed surface where the concentration is highest due to diffusion of hydrogen into the material. It can be stated that there are no noticeable effects of the HENG penetration on the BM, HAZ, or FZ regions. The FZ also shows that it is harder than the HAZ. 4.1.4.2 Across Regions The data presented in Figure 37A-C represents the Vickers hardness for the 0%, 5%, and 20% hydrogen blends for each of the induced conditions. The general trend of the graphs depicts that the hardness increases as the location of the FZ is approached, peaking for a maximum hardness in the FZ, then decreasing again as the distance moves out of the region. The dashed lines in the graphs represent the general Vickers hardness profile that each of the respective conditions follows. With the hardness points all following the same general trend and overlapping, it is clear that the HENG does not have an effect on the Grade 290 weld Vickers hardness across the regions. Figure 37 Vickers hardness across the weld for (A) 0%, (B) 5%, (C) and 20% The microhardness testing demonstrated that the hydrogen blend does, to some extent, have an impact on the Vickers hardness of the base material, but no measurable effect was observed A C B 54 through the weld. This is demonstrated on the base samples with the surface of the samples showing an increased hardness in all 20% hydrogen induced times and in the 5% hydrogen blend at 2 and 6 months. This effect of hydrogen impacting the hardness, however, did not appear to be present in the data for the FZ and HAZ regions. As for hardness in the specific regions, the results demonstrate that the FZ is the hardest followed by the HAZ and base Grade 290 material. Throughout all the Vickers hardness testing, exposure time is the only controlled testing variable that seemed to have an impact across all test conditions for the X42 material with no variables impacting the Grade 290 weld. 4.2 Fracture Analysis The fracture surface of the broken X42 and Grade 290 metal for the tensile specimens was observed by scanning electron microscope (SEM) to understand the failure mechanism under different levels of hydrogen blending. An ImageJ processing software was used to determine the brittle to ductile areas of the fracture. This allowed for a brittle area percentage to be determined for the enrichment conditions of the X42 and Grade 290 samples. The fracture analysis was conducted on the round notched and flat dog bone tensile samples. The samples were pulled in tension until failure, then an image was taken of the fracture surface with an SEM. Six fracture surfaces were analyzed for the X42 and eight for the Grade 290 material for each environmental condition. This resulted in a total of 60 X42 surfaces and 80 Grade 290 fracture surfaces to measure. The averages for each condition along with the hydrogen embrittlement susceptibility of the X42 and Grade 290 are presented and discussed below. 55 4.2.1 HE Susceptibility To quantify the hydrogen effects, a factor of embrittlement (F) was defined which is based on the respective reduction of area observed under hydrogen/gas mixture or gas as written in Eq. (5) [20]: 𝑅𝑎 = 1 − (𝑆𝑓𝑖𝑛/𝑆𝑜) and 𝐹 = 𝑅𝐴𝑔𝑎𝑠−𝑅𝐴(𝑔𝑎𝑠ℎ𝑦𝑑) 𝑅𝐴𝑔𝑎𝑠 Eq. (5) where Sfin is the broken section of the specimen after rupture. S0 is the initial section of the specimen. RA is the average reduction of area of the specimen tested under gas or under hydrogen blending with gas. With this, a chart is formulated to quantify how effective the hydrogen conditions are on the material relative to a controlled reference test condition. The embrittlement factor for the X42 material is seen in Figure 38. This graph shows that the largest embrittlement factor is a little over 2% for the 2 weeks at 20% hydrogen concentration. The remaining exposure conditions have an embrittlement factor below or around 1%. Some conditions also even exhibit a negative embrittlement factor technically meaning that those specific conditions are less prone to the hydrogen embrittlement than the reference material. There are no trends seen in these results as exposure time and hydrogen concentration increases. Therefore, it can be concluded that the environmental conditions tested here do not significantly impact the embrittlement of X42. 56 Figure 38 Embrittlement factor of X42 for the enrichment conditions The factor of embrittlement for the Grade 290 material can be seen in Figure 39. These results have embrittlement factors that are slightly larger in magnitude compared to the X42 material. While the largest embrittlement factor of -6% is in the negative direction, this means that the condition is less susceptible to hydrogen embrittlement. Therefore, we need to consider the largest positive embrittlement factor that has hydrogen present as the area of interest. For Grade 290 this is the 6 months at 20% condition with a factor of about 3%. This is only 1% larger than 57 the 2% embrittlement factor seen in X42. Therefore, with this magnitude being relatively low, the Grade 290 embrittlement is also not affected by the hydrogen conditions. Figure 39 Embrittlement factor of Grade 290 for the enrichment conditions 4.2.2 Base X42 material The difference in fracture characteristics between brittle and ductile is depicted in Figure 40 and 41. The brittle region appears as a flat, dull area, with the ductile region emerging as a dimpled more shiny region. 58 Figure 40 Brittle and ductile locations on the fracture surface of A) Original X42 sample B) Conditioned 6 month 20% H2 X42 sample Figure 41 A) Brittle cleavage and B) Ductile dimpled fracture mechanisms The red area shown in Figure 42 is what ImageJ determines as the brittle area based on the reflectiveness of the surface using a greyscale. When comparing the images in Figure 42, B shows A B Brittle fracture Ductile fracture Brittle fracture Ductile fracture A B 59 a much more predominate red around the outer circle than image A. This reveals that there are more brittle fractures near the outer edge of the sample where the sample is exposed to the hydrogen. These results are in agreement with the Vickers hardness testing results that were discussed previously. Both tests demonstrate the higher hydrogen concentrations for the 6 months induction period of the exposed surface does show a little effect due to hydrogen. This increased hardness and brittle fracture area was especially seen around the outer edge of the sample. Figure 42 ImageJ analysis between two X42 samples A) 2 weeks at 0% B) 6 months at 20% The data presented in Figure 43 represents the brittle percentage area of the fracture surface analyzed on the X42 material for all enrichment conditions. The data shows the 2-week results being relatively the same as the original X42. The 2 and 6-month results show that the brittle area percent becomes larger with an increase in hydrogen concentration. In Figure 43 it is evident that the brittle percentage for the X42 material is larger in the 5% and 20% enrichment conditions with respect to the original X42 reference point. This means that the broken surface in these samples contained more brittle fractures that covered a larger area than the original X42. When looking at the 0% condition, the brittle percentage is the same as the original reference. In the 5% condition, A B 60 an increase is noticed with the 2 months having a brittle percentage of 63% and the 6 months at about 65%. At a higher concentration of 20% hydrogen, both the 2 months and 6 months conditions have increased to about 67% of the surface area representing a brittle fracture. This is a point to make note of with the similarity in magnitude between the 2 and 6-month columns at 20%. With these two different periods having the same amount of fracture surface it could mean at some point in time between 2-6 months at a hydrogen concentration of 20% an equilibrium is reached. This equilibrium could represent the point at which the hydrogen can no longer influence the brittleness of the fracture surface. This would have to be confirmed with further testing at longer induced conditions and maybe under higher hydrogen concentrations. When comparing two photos of the analysis between 2 weeks at 0% and 6 months at 20% it is seen that the latter has much more brittle fracture present, as shown in Figure 42. Figure 43 Brittle area percentage of X42 for the ten enrichment conditions These results demonstrate that the 2 week time period was too short for environmental conditions to affect the material, assuming that both time and hydrogen percentage may affect the brittle area percentage of the X42 material. With the increase from different testing conditions, the material responds with a more brittle fracture characteristic. The AIDE model most accurately 61 represents the circumstances seen here. The adsorption of hydrogen from the enriched environment may cause a weakening of interatomic bond dislocation through nucleation and growth of the micro-voids ahead of the crack tip. This model helps to explain why the brittle area percentage increased with the addition of hydrogen. 4.2.3 Grade 290 material The fracture surface of the Grade 290 weld is shown in Figure 44. It can be seen that the fracture surface is ductile with very little cleavage fracture areas. The data presented in Figure 45 represents the brittle percentage area of the fracture surface for the Grade 290 weld. Figure 44 Brittle and ductile locations on the fracture surface of a Grade 290 welded sample When analyzing the brittle area percentage for the Grade 290 material, different conclusions are made when compared to the X42 area. Figure 45 shows that there is no increasing or decreasing trend present in the brittle area percentage data with respect to the original Grade 290 reference. The small variations in this data set are all within the standard deviation therefore, 62 the HENG blend does not affect the brittle area percentage of the Grade 290 weld. This is in agreement with the Vickers hardness testing results seen earlier on the welded regions as those results also did not exhibit any effect due to the HENG blend. Although the X42 and Grade 290 material cannot directly be compared the brittle fracture amount in the welded region is also about four to six times lower than seen in the fracture surface on the base X42. Figure 45 Brittle are percentage of Grade 290 for the ten enrichment conditions 4.3 Microstructural Analysis and Phase Composition This section will cover and discuss the phases present in the base X42 material and Vintage Grade 290 regions as well as the chemical composition of the phases. 4.3.1 Phase composition The chemical composition of the material was measured using EDS, point, line, and mapping elemental analysis. The analysis was conducted on 4 major sections of the material, one being the base X42 and three more in the Grade 290 welded material. These can be classified as base X42, base Grade 290, HAZ, FZ. The chemical compositions of both materials can be found in Table 3. 63 The SEM micrographs of the base X42 pipeline material are shown in Figure 46. EDS composition in the weight percentage of the phases found in the base X42 material are shown in Table 5. Figure 46 Microstructure of the X42 pipeline material with ferrite and pearlite present Only two phases were found in the base X42 material throughout the different enrichment conditions. All samples and areas analyzed consisted of polygonal BCC ferrite and ferritic pearlite, which is a laminar structure of ferrite and cementite. The lighter grey polygonal ferrite makes up the majority of the material in the samples. The remaining portion consists of laminar pearlite phase, with the exception of some scattered inclusions, as shown in Figure 47. This breakdown is consistent with the literature on similar alloys and X42 [61]. Multiple locations throughout the samples and near the edges were analyzed on both the SEM and optical microscope. It was found that the size and morphology of the phases and inclusions present in the base X42 material for all enrichment conditions remain the same. When analyzing the microstructure under the optical Polygonal Ferrite Pearlite (Fe, Fe3C) Pearlite (Fe, Fe3C) Polygonal Ferrite Inclusion 64 microscope, as visualized in Figure 48, the layering pattern of ferrite and pearlite phases are visible from the hot rolling mechanical processing. Table 5 Phase compositional range (shown in wt%) of various phases and inclusions found in base X42 material Specimen Phase Fe C Mn O Si S Ca Al Mg Original Base X42 Ferrite (Fe) 97-99 - 1-3 - - - - - - Pearlite (Fe & Fe3C) 80-88 9-15 1-2 1-3 0-1 - - - - Inclusions Mn/S 20-67 13-15 14-42 - - 13-26 1-6 - 1-3 Al/Mn/S 8-36 - 12-17 - - 9-11 1-7 18-23 2-4 Al/Ca 5-26 5-8 1-3 - 2-7 1-6 13-27 15-26 2-6 Si/C 27-66 18-29 - - 18-40 - - - - Mn/C 40-57 15-24 8-15 - - 5-9 0-1 4-6 0-1 Figure 47 Locations of scattered inclusions with a magnified photo of a singular one 65 Figure 48 SEM image of X42 with the layering pattern from hot rolling, lighter grey is ferrite, darker is pearlite In the Grade 290 material, there are three regions to analyze, the BM, HAZ, FZ. The base material found in the Grade 290 weld had the same phases and structure present as in the base X42 material. When examining the transition from base material to the HAZ, the phases become smaller as a different structure appears. The HAZ region consists of a smaller ferrite and pearlite phases shown in Figure 49B. The FZ consists of a bainite structure with granular and lamellar ferrite with pearlite as also found in Figure 49C[61]. A breakdown of these phases and the chemical composition in weight percentage is shown in Table 6. 66 Table 6 Phase compositional range (shown in wt%) of various phases and inclusions found in Grade 290 welded material Specimen Phase Fe C Mn O Si Base Grade 290 Ferrite (Fe) 97-99 - 1-3 - - Pearlite (Fe & Fe3C) 80-88 9-15 1-2 1-3 0-1 HAZ Ferrite (Fe) 97-99 - 1-3 - - Pearlite (Fe & Fe3C) 80-88 9-15 1-2 1-3 0-1 FZ Ferrite (Fe) 97-99 - 1-3 - - Bainite 84-92 7-14 1-2 - - Pearlite (Fe & Fe3C) 80-88 9-15 1-2 1-3 0-1 Seen in Figure 49B the HAZ region shows the ferrite and pearlite phases. These phases are about half the size of the same phases that are present in the base region of the Grade 290 material. Figure 49 SEM image of Grade 290 A) Base metal region B) HAZ region with lighter grey pearlite, dark is ferrite C) FZ region with light bainite and dark ferrite 4.4 Surface Oxide Analysis The accumulation of rust analysis was conducted on the round X42 tensile samples as seen in Figure 22 with the results presented in Table 7. This was completed by removing and weighing Polygonal Ferrite Pearlite Polygonal Ferrite Pearlite Polygonal Ferrite Bainite A B C 67 the rust accumulated on the samples. When compared to the 2 months 0% samples, a noticeable amount of accumulation was found on the 2 months 20% and all 6 months samples. The results demonstrated that in both periods induced, the difference between 0% and 5% is very small if not unnoticeable. The change is seen with respect to hydrogen concentration between 0% and 20%. The 2 months 20% samples have 2.54 times more accumulation with the 6 months 20% samples having 3.68 times more with respect to the 0% concentrations. When considering the time effect, the results show that there is still 4.18 times more rust in the 6 months 0% samples relative to 2 months 0% conditions. The worst condition, 6 months at 20% H2, had as much as 15.36 times more rust accumulated on the sample relative to 2 months at 0%. Table 7 Rust analysis on 2 and 6 month samples 2-Month Sanded Area mm2 Before (g) After (g) Difference (g) Total Rust/Samples (g) Relative to 0% Relative to 2 Month 0% 2-Month 0% 1005.09 0.6013 0.6019 0.0006 0.0011678 1 2-Month 5% 828.14 0.6008 0.6013 0.0005 0.0011791 1.01 2-Month 20% 981.97 0.6134 0.6149 0.0015 0.0029700 2.54 6-Month 6-Month 0% 954.87 0.6727 0.6751 0.0024 0.0048793 1 4.18 6-Month 5% 969.68 0.6953 0.6978 0.0025 0.0050171 1.03 4.30 6-Month 20% 805.66 0.6627 0.6701 0.0074 0.0179365 3.68 15.36 68 Therefore, the data shows that time of exposure directly leads to more rust accumulation. Also more rust is accumulated when the hydrogen concentration is increased from the 0 to 20% samples within each time of exposure. This means that both time and concentration contribute equally to about 4 times an increase in surface oxidation. The X42 samples were retrieved from a pressurized pipe apparatus using a band saw with a lubrication system. The second set of tests with the Vintage Grade 290 samples apparatus used a dry cut without lubrication. The accumulation of rust seen may be a result of the experimental procedure used (an artifact), or due to the effects of hydrogen. A further assessment would need to be conducted to determine the causing effect of this rust accumulation. 4.5 Statistical Analysis A two-factor ANOVA with a fixed-effects model was used in this research to investigate the statistical significance of the yield and tensile strength, elongation, area reduction, and brittle percentage area. These were analyzed at treatments A being three time frames (2 weeks, 2 months, and 6 months) and at treatments B, three levels of environmental gas (0% H2, 5% H2, and 20% H2) then directly comparing them to the original baseline obtain by the virgin material. The varying amounts of treatment A (time) and treatment B (H2 concentration), with both A and B being three levels and having 3 repeats. N is the total number of observations and the null and alternative hypothesis were: 𝐹𝑜 = 𝑀𝑆𝐴/𝑀𝑆𝐸 Ho: To=T1=…=Ta = 0 H1: at least one Ti ≠ 0 𝐹𝑜 = 𝑀𝑆𝐵/𝑀𝑆𝐸 Ho: ßo=ß1=…= ßa = 0 H1: at least one ßj ≠ 0 𝐹𝑜 = 𝑀𝑆𝐴𝐵/𝑀𝑆𝐸 Ho: (Tß)ij = 0 for all i, j 69 H1: at least one (Tß)ij ≠ 0 Therefore if Fo > F0.025,(a-1)(b-1), ab(n-1) one would be able to reject the null hypotheses Ho, and the time and/or concentration would have a significant influence, and if Fo < F0.025,(a-1)(b-1), ab(n-1) we cannot reject Ho and the treatments do not have an effect. For the ANOVA analysis of the tensile tests, the null hypotheses (Ho) of To=T1=…=Ta = 0 means that for the different enrichment conditions the outcome of the results is the same. Indicating that there is no effect of the material from the HENG. Therefore, whenever the F is less than the Fcrit in the following tables, it statistically means that there is no effect due to HENG. With the two factors, hydrogen concentration and exposure time, there may be a difference in response between the levels of one factor that is not the same at all levels of the other factor. This dependence between the two is called an interaction and this feature statistically allows to see if one variable is being influenced by the other. The ANOVA tests conducted for this work are all done so with a level of significance of 𝛼 = 0.05. The formulas used in these calculations for the corresponding results are shown in Table 8. Table 8 Analysis of variance (ANOVA) table for two-factor tests A T-test was used to determine the differential effect of results obtained through the manual versus automatic Vickers hardness indenter. This was done by conducting twenty indentations on 70 a single virgin X42 sample on each machine. Two rows of ten were conducted in alternating order to make sure that the results did not vary by direction or location. It was determined that the automatic Vickers hardness indenter was more accurate during this differential testing. 4.5.1 Tensile Tests This section will cover the statistical analysis of the results on the UTS, YS, %EL, RA, and brittle area percentage for the tensile test conducted. Statistically determining the pattens and trends through ANOVA analysis combined with comprehension of the data is the best interpretation of the results to form a conclusion. It uses non-bias methods to quantitatively show if a variable effects the outcome of the results. 4.5.1.1 UTS Seen in Table 9 is the two factor with replications ANOVA analysis for the UTS of the X42. The F-value is lower than the Fcritical for the H2 variable meaning that the hydrogen concentration does not influence the UTS of the X42. However, the F-value of the time variable highlighted in red is much larger than the Fcritical meaning that exposure time was a variable that caused a meaningful enough statistic change. This change is seen and backed up in the results with a small increase in UTS of X42 in Figure 24. The third row in the ANOVA table shows the interaction between the two variables of hydrogen and exposure time. Statistically, the F-value is less than the Fcritical meaning that the interaction between the two variables is not important enough to be statistically significant. 71 Table 9 ANOVA analysis for the UTS of X42 Seen in Table 10 is another two factor with replications ANOVA for the UTS of the Grade 290 weld. This analysis demonstrates that the hydrogen concentration variable does not play a role in significantly affecting the mean UTS of the material. There is also not a significant interaction between the two variables. Time is the only variable that statistically is determined to differ the averages between the enrichment conditions. This statement though is contradictory to the discussion about the UTS of the Grade 290 weld in the results. However, when analyzing both the statistical method and the data shown in Figure 28, it can be determined that time is showing significant here because of the deviation between the conditions is so small. Since the average values of the UTS for the 2 weeks and 2 months data are almost the same, between 533-536MPa. When the 6 months averages are slightly lower at 526-530MPa statistically the ANOVA analysis deems this as a big enough change to be significant due to the time variable. When in reality the difference of a few megapascals fits within the standard deviation of this chart. Utilizing both methods, graphically and statistically, it is determined that time also does not have an impact on the UTS of the Grade 290 weld. 72 Table 10 ANOVA analysis for the UTS of Grade 290 weld 4.5.1.2 YS Seen in Table 11 is the two factor ANOVA test with replication for the YS of the X42. The F-value of the hydrogen variable and interaction is much less than Fcritical meaning that the hydrogen concentration or interaction between the two variables does not affect the YS. However, the F-value of the time variable is larger than the Fcritical showing that exposure time caused a meaningful enough statistic change. This is apparent on the graph in Figure 25 and complies with the UTS results of the X42. Table 11 ANOVA analysis for the YS of X42 Seen in Table 12 is the two factor ANOVA test with replication for the YS of the Grade 290. The F-value of the exposure time and interaction is less than Fcritical meaning that the concentration time or interaction between the two variables does not affect the YS. However, it shows that the F-value of the hydrogen concentration is larger than the Fcritical meaning that there is a statistical change. When considering this statement and analyzing the graph in Figure 29, it is clear that the YS starts lower for the 0% conditions, slightly increases for 5%, then decreases again 73 for the 20% conditions. The graph supports the statistical analysis, but there is no trend present as it increases then decreases again for a higher concentration. This change is also near the standard deviation of the samples and because of utilizing both methods, it is determined that hydrogen concentration also does not affect the YS of the Grade 290. Table 12 ANOVA analysis for the YS of Grade 290 4.5.1.3 %EL Table 13 shows the two factor with replications ANOVA analysis of the %EL for X42. The F-value of hydrogen concentration and interaction between the variables is less than the Fcritical and therefore is determined to not affect the %EL. As is discussed in the results from the graph in Figure 26 , the exposure time was noticed to slightly affect the %EL. This is backed up here as the F-value, highlighted, is just slightly larger than the Fcritical. Establishing that both statistical analysis and the data agree that the %EL is slightly affected because of exposure time. Table 13 ANOVA analysis for the %EL of X42 Table 14 shows the two factor with replication ANOVA analysis of the %EL for the Grade 290. It demonstrated that hydrogen concentration, exposure time, and the interaction between the 74 two variables do not affect the %EL results of the Grade 290 weld. The data in Figure 30 confirm this statistical analysis as the variation between the conditions is within the standard deviation and the condition averages are relatively the same. Resulting in no distinguishable change to the Grade 290 %EL because of these variables. Table 14 ANOVA analysis for the %EL of Grade 290 4.5.1.4 RA Table 15 shows the two factor with replication ANOVA analysis of the RA for the X42. The data from the table shows that hydrogen concentration, exposure time, and the interaction between the two variables do not affect the RA results of the X42. This is because the F-value is smaller than the Fcritical for each source of variation meaning that the changing factors are not significant enough to change the data. The statistical results match the results determined from Figure 27 that no distinguishable effects of time exposure or hydrogen concentration are seen in the RA. Table 15 ANOVA analysis for the RA of X42 75 Seen in Table 16 is the two factor with replication ANOVA analysis for the RA of the Grade 290 weld. The table demonstrates that hydrogen concentration, exposure time, and the interaction between the two variables do not affect the RA results of the Grade 290 weld. This statistical analysis agrees with the results seen in Figure 31 where no distinguishable effects from time exposure or hydrogen concentration are seen in the RA of the Grade 290 weld. Table 16 ANOVA analysis for the RA of Grade 290 4.5.1.5 Brittle Percentage Area Seen in Table 17 is the two factor with replication ANOVA analysis for the brittle percentage area of X42. The table shows that for both hydrogen concentration and exposure time the F-value is larger than Fcritical. This means that these variables caused an important enough statistical change to affect the brittle area percentage. This is also demonstrated in the results shown in Figure 43 as it can be seen that both hydrogen concentration and exposure time increase the averages. Therefore, both statistical analysis and the graph data match with one another and the brittle area percentage is influenced by hydrogen and time. Table 17 ANOVA analysis for the brittle area percentage of X42 76 Table 18 shows the two factor with replication ANOVA analysis for the brittle percentage area of the Grade 290 weld. The hydrogen concentration and interaction between the two variables do not affect the brittle area percentage results. The statistical analysis indicates that the exposure time influences the results as the F-value is larger than the Fcritical. When considering the data in Figure 45 it is apparent that the 2 months averages are lower than the 2 weeks and 6 months averages. That is the reason why the time variable is coming up as an important factor. However, there is no general increasing or decreasing trend seen in the graph along with the difference in the averages being within the standard deviation. Table 18 ANOVA analysis for the brittle are percentage of Grade 290 77 Chapter 5: Conclusions The effects of HENG on X42 steel pipeline was investigated in this study. The mechanical properties (UTS, YS, %EL, RA, and hardness), microstructural properties (fracture surface, phase composition, crystallographic structure), and surface oxide analysis of the material was evaluated on the base X42 and Grade 290 welded sections of the pipe. The listed properties were determined to be of importance with little previous research conducted to date. The conclusions made are listed as follows: 1) Upon exposure to the hydrogen-enriched environment, the UTS and YS of the base X42 material showed a small increase in strength, not because of hydrogen concentration, but because of increased exposure time in the hydrogen-rich environment. The range of the UTS and YS is 517-536MPa and 321-348MPa respectively. This increase is of the same magnitude as the standard deviation. 2) Similarly, the reduction of %EL noticed in the base X42 material was not a result of the increasing hydrogen concentration but mostly because of longer exposure time. This change is within the standard deviation of the test results, so the effects of HENG results in little to no difference in %EL. 3) RA was not distinguishably affected by duration of exposure to HENG or hydrogen concentration. 4) The Grade 290 exhibited no noticeable change to the mechanical properties while being exposed to HENG for prolonged periods of time. 5) HENG blend has a measurable impact on the surface hardness of the material. The base X42 material samples showed about 10% increase in surface hardness, reaching 210-220 HV for 5% blend HENG and up to 215-230 HV for the 20% HENG. 78 6) The hardness measurements revealed that FZ is the hardest, reaching about 224HV. The HAZ and base Grade 290 have reduced hardness, at 5-10% lower relative to the FZ region. The effect of HENG impacting the hardness did not appear in the data for the Grade 290 FZ and HAZ regions. 7) Both time and hydrogen concentration affect the brittle area percentage of the X42 material, increasing it from ~57% to 60-67%. This effect may reach a potential equilibrium between the two fracture modes. The HENG blend does not affect the brittle area percentage of the Grade 290 weld. 8) Both the X42 and Grade 290 did not show a significant increase in the embrittlement factor with the largest cases being 2% and 3% for the respective metals. This observation demonstrates that the material is not effected by the exposure to hydrogen under the tested conditions. 9) The X42 and base Grade 290 material have the same phases and structure consisting of ferrite and pearlite forming in a layered pattern due to hot rolling. The HAZ has the same phases, with grains that become smaller in size and have a more randomized crystallographic pattern. The FZ consists of a bainite structure with pearlite, granular ferrite, and lamellar ferrite. The bainite phase explains the increase in hardness observed in the FZ region. The transitions between these microstructural zones do not have definitive boundaries, allowing these phases to morph from one region to the next. 10) Time of exposure and hydrogen concentration directly leads to significant rust accumulation with respect to the 2 month 0% enrichment condition. In this analysis, hydrogen was acting as a catalyst for the surface oxidation, caused by to the moisture that 79 was introduced during sample retravel. The oxidation observed was not therefore directly related to the exposure to HENG. This researched project confirmed feasibility. The HENG does not significantly impact the material, and is safe to continue with further studies. 5.1 Constraints There are a few constraints in this research that need to be taken into consideration. Aspects such as the exposure time, concentration levels, inducing pressures, and sample ratio size were limiting factors that restricted the scope of work. The induction time for the samples were only studied for up to 6 months and the hydrogen concentration was only up to 20% HENG blend. The possible impacts of the hydrogen enriched natural gas in long term periods such as 5 years, 20 years, or the duration of its service life may be different. Another constraint on the work had to do with the inducing pressures. The 60 psi inducing pressures were the maximum safe allowable pressure to be legally pressurized in the testing pipe apparatuses without needing to have specific equipment. Certified pressure chambers are required to induce the samples at the larger natural gas pipeline operating pressures of 585-2160psi. There are also constraints with the embrittlement factor method as it is dependent on the reduction of cross sectional area. The samples used in this research had a set consistent surface-to-volume ratio and other surface-to-volume ratios could influence the embrittlement factor and mechanical properties. This is because a higher ratio could cause the factor to increase as there is more exposed material that could be impacted by the embrittlement. These constraints are important factors to consider when taking into account the results presented in this work. 80 5.2 Future Work Through the studies and testing conducted in this work on the X42 and Grade 290 pipeline material, some other questions have been raised that are outside the initial scope of the work. Two areas of future interest that have emerged from this research are to analyze fatigue characteristics and to study material exposure to high pressures, relevant to the operating conditions of the pipeline in service application. Fatigue testing is of importance due to the cyclic loading conditions that pipelines undergo, especially in climates such as British Columbia where the imposed HENG project is to take place. The pipeline would undergo cyclic loading through pressure and temperature changes that occur daily and seasonally. Temperature changes in this region of the world are known to change drastically every day or even over a year, which can range between 40 to -40 degrees Celsius. Pressure changes in the line can even change throughout the day as the fluid inside the pipe is pumped at different pressures or can expand due to temperature changes. All of these variations put extra stress and fatigue on the pipeline material, which needs to be studied to determine how the material properties change these conditions. Fatigue tests can also be used to determine the crack propagation speeds and crack growth data, identify critical locations, or demonstrate the safety of a structure that may be susceptible to fatigue. Another aspect of the work that needs to be further investigated is the penetrative effects of the HENG into the material under full operating pressure. Tests in this study were conducted at an internal pressure of 60psi. This is approximately 10~36 times lower than the 585~2160psi that FortisBC currently operates some pipelines at, which is a significant difference. Fick’s laws of diffusion and diffusion constants operate on the aspects that concentration difference drives the rate and speed at which gases diffuse into metals. The increased pressure difference can 81 dramatically increase the diffusion rate of gases into a material. 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Retrieved from https://www.borusanmannesmann.com/media/2147/bmb-line-pipe-hat-boru-brosuru- 2020-nisan.pdf 90 Appendices Appendix A: Raw X42 Tensile Data 91 92 93 94 95 Appendix B: Raw Grade 290 Tensile Data 96 97 98 Appendix C: Raw X42 Microhardness Data Microhardness Original X42 2 W 0% 2 W 5% 2 W 20% Site Location (um) Vickers Average Error Vickers Average Error Vickers Average Error Vickers Average Error 1_1 40 181.1 176.525 4.575 175.6 174.125 1.475 182.6 181.65 0.95 185.6 198.55 12.95 2_1 50 175.3 175.54 0.24 170.3 181.04 10.74 188.4 180.18 8.22 220.7 195.06 25.64 3_1 60 177 175.54 1.46 176.3 181.04 4.74 171.6 180.18 8.58 201 195.06 5.94 4_1 70 172.7 173.7 1 174.3 181.04 6.74 184 181.66 2.34 186.9 196.54 9.64 1_2 80 171.6 172.44 0.84 208.7 184.66 24.04 174.3 182.9 8.6 181.1 189.2 8.1 2_2 90 171.9 172.42 0.52 175.6 191.32 15.72 190 183.7 6.3 193 187.48 5.52 3_2 100 169 173.28 4.28 188.4 190.78 2.38 194.6 182.02 12.58 184 187.2 3.2 4_2 110 176.9 173.96 2.94 209.6 189.24 20.36 175.6 183.38 7.78 192.4 189.9 2.5 1_3 120 177 172.64 4.36 171.6 190.64 19.04 175.6 179.7 4.1 185.5 193.4 7.9 2_3 130 175 172.64 2.36 201 189.76 11.24 181.1 177.08 4.02 194.6 194.58 0.02 3_3 140 165.3 170.08 4.78 182.6 183.24 0.64 171.6 179.06 7.46 210.5 192.62 17.88 4_3 150 169 167.74 1.26 184 185.42 1.42 181.5 179.06 2.44 189.9 192.9 3 1_4 160 164.1 168.12 4.02 177 179.28 2.28 185.5 179.14 6.36 182.6 190.5 7.9 2_4 170 165.3 170.18 4.88 182.5 182 0.5 175.6 182.5 6.9 186.9 184.34 2.56 3_4 180 176.9 170.475 6.425 170.3 182.6 12.3 181.5 182.72 1.22 182.6 183.76 1.16 4_4 190 175.6 173.325 2.275 196.2 183.14 13.06 188.4 181.28 7.12 179.7 186.46 6.76 1_5 200 177.375 177.375 187 183.74 3.26 182.6 183.84 1.24 187 184.74 2.26 2_5 210 175.5 178.425 2.925 179.7 186.78 7.08 178.3 181.86 3.56 196.1 184.44 11.66 3_5 220 181.5 180.625 0.875 185.5 182.94 2.56 188.4 177.74 10.66 178.3 184.44 6.14 4_5 230 181.1 181.3 0.2 185.5 179.86 5.64 171.6 178.02 6.42 181.1 184.32 3.22 1_6 240 184.4 184.5 0.1 177 179.58 2.58 167.8 175.92 8.12 179.7 182.2 2.5 2_6 250 184 185.25 1.25 171.6 176.8 5.2 184 173.9 10.1 186.4 184.1 2.3 3_6 260 191.5 183.175 8.325 178.3 174.96 3.34 167.8 176.96 9.16 185.5 182.46 3.04 4_6 270 179.65 179.65 171.6 176.94 5.34 178.3 185.32 7.02 187.8 184.2 3.6 1_7 300 172.8 180.025 7.225 176.3 177.48 1.18 186.9 185.9 1 172.9 181.78 8.88 2_7 400 170.3 182.275 11.975 186.9 180.02 6.88 209.6 189.66 19.94 188.4 181.92 6.48 3_7 500 185.5 179.88 5.62 174.3 182.5 8.2 186.9 189.94 3.04 174.3 179.76 5.46 4_7 600 200.5 178.62 21.88 191 184.92 6.08 186.6 186.88 0.28 186.2 181.98 4.22 1_8 700 170.3 181.36 11.06 184 185.22 1.22 179.7 179.82 0.12 177 181.28 4.28 2_8 800 166.5 178.58 12.08 188.4 183.92 4.48 171.6 179.24 7.64 184 182.64 1.36 3_8 900 184 175.86 8.14 188.4 178.78 9.62 174.3 178.44 4.14 184.9 181.34 3.56 4_8 1000 171.6 177.92 6.32 167.8 182.18 14.38 184 175.56 8.44 181.1 183.18 2.08 1_9 1100 186.9 179.2 7.7 165.3 182.6 17.3 182.6 177.76 4.84 179.7 184.06 4.36 2_9 1200 180.6 177.74 2.86 201 181.44 19.56 165.3 178.02 12.72 186.2 186 0.2 3_9 1300 172.9 177.74 4.84 190.5 182.74 7.76 182.6 176.88 5.72 188.4 183.64 4.76 4_9 1400 176.7 173.48 3.22 182.6 183.74 1.14 175.6 175.48 0.12 194.6 181.5 13.1 1_10 1500 171.6 171.94 0.34 174.3 177.1 2.8 178.3 178.72 0.42 169.3 179.36 10.06 2_10 1600 165.6 172.76 7.16 170.3 175.8 5.5 175.6 178.42 2.82 169 178.92 9.92 3_10 1700 172.9 172.54 0.36 167.8 172.58 4.78 181.5 181.92 0.42 175.5 173.56 1.94 4_10 1800 177 170.32 6.68 184 171.52 12.48 181.1 183.36 2.26 186.2 174.56 11.64 1_11 2400 175.6 171 4.6 166.5 171.78 5.28 193.1 183.9 9.2 167.8 175.34 7.54 2_11 3000 160.5 170.74 10.24 169 173.88 4.88 185.5 181.66 3.84 174.3 175.04 0.74 3_11 3600 169 169.175 0.175 171.6 171.35 0.25 178.3 181.8 3.5 172.9 172.25 0.65 4_11 4000 171.6 167.033333 4.56666667 178.3 172.966667 5.33333333 170.3 178.033333 7.73333333 174 173.733333 0.26666667 99 Microhardness 2M 0% 2M 5% 2M 20% Site Location (um) Vickers Average Error Vickers Average Error Vickers Average Error 1_1 40 174.3 172.625 1.675 216.8 209.5 7.3 214.9 220.65 5.75 2_1 50 179.1 172.96 6.14 215.8 205.58 10.22 216.8 216.4 0.4 3_1 60 166.8 172.96 6.16 211.3 205.58 5.72 220.5 216.4 4.1 4_1 70 170.3 174.04 3.74 194.1 200.2 6.1 230.4 214.36 16.04 1_2 80 174.3 175.14 0.84 189.9 195.96 6.06 199.4 213.98 14.58 2_2 90 179.7 177.72 1.98 189.9 192.3 2.4 204.7 211.12 6.42 3_2 100 184.6 179.64 4.96 194.6 191.78 2.82 214.9 207.14 7.76 4_2 110 179.7 179.64 0.06 193 190.32 2.68 206.2 208.14 1.94 1_3 120 179.9 177.4 2.5 191.5 187.74 3.76 210.5 204 6.5 2_3 130 174.3 174.54 0.24 182.6 184.48 1.88 204.4 199.32 5.08 3_3 140 168.5 171.9 3.4 177 183.44 6.44 184 194.62 10.62 4_3 150 170.3 170.72 0.42 178.3 183.12 4.82 191.5 191.12 0.38 1_4 160 166.5 170.18 3.68 187.8 183.7 4.1 182.7 188.54 5.84 2_4 170 174 171.5 2.5 189.9 187.86 2.04 193 192.62 0.38 3_4 180 171.6 172.56 0.96 185.5 190.1 4.6 191.5 188.9 2.6 4_4 190 175.1 173.58 1.52 197.8 192.8 5 204.4 190.48 13.92 1_5 200 175.6 172.84 2.76 189.5 189.4 0.1 172.9 190.68 17.78 2_5 210 171.6 175.04 3.44 201.3 187.96 13.34 190.6 189.18 1.42 3_5 220 170.3 177.12 6.82 172.9 185.5 12.6 194 184.24 9.76 4_5 230 182.6 179.68 2.92 178.3 185.28 6.98 184 187.96 3.96 1_6 240 185.5 182.28 3.22 185.5 183.62 1.88 179.7 187.22 7.52 2_6 250 188.4 182.08 6.32 188.4 185.78 2.62 191.5 186.4 5.1 3_6 260 184.6 178.72 5.88 193 188.1 4.9 186.9 185.82 1.08 4_6 270 169.3 174.18 4.88 183.7 189.08 5.38 189.9 186.4 3.5 1_7 300 165.8 170.3 4.5 189.9 187.06 2.84 181.1 185.48 4.38 2_7 400 162.8 169.5 6.7 190.4 184.12 6.28 182.6 184.04 1.44 3_7 500 169 170.76 1.76 178.3 188.6 10.3 186.9 184.36 2.54 4_7 600 180.6 172.46 8.14 178.3 189.54 11.24 179.7 187.06 7.36 1_8 700 175.6 173.96 1.64 206.1 188.84 17.26 191.5 186.48 5.02 2_8 800 174.3 176.2 1.9 194.6 192.74 1.86 194.6 187.14 7.46 3_8 900 170.3 173.38 3.08 186.9 196.64 9.74 179.7 189.18 9.48 4_8 1000 180.2 171.08 9.12 197.8 194.38 3.42 190.2 187.68 2.52 1_9 1100 166.5 171.08 4.58 197.8 192.84 4.96 189.9 187.68 2.22 2_9 1200 164.1 173.2 9.1 194.8 192.56 2.24 184 191.3 7.3 3_9 1300 174.3 172.3 2 186.9 189.52 2.62 194.6 190.64 3.96 4_9 1400 180.9 174.12 6.78 185.5 185.36 0.14 197.8 188.06 9.74 1_10 1500 175.7 175.46 0.24 182.6 186.6 4 186.9 191.74 4.84 2_10 1600 175.6 174.4 1.2 177 186.02 9.02 177 190.9 13.9 3_10 1700 170.8 172.28 1.48 201 184.58 16.42 202.4 187 15.4 4_10 1800 169 171.66 2.66 184 184.58 0.58 190.4 184.74 5.66 1_11 2400 170.3 169.9 0.4 178.3 186.1 7.8 178.3 186.32 8.02 2_11 3000 172.6 168.24 4.36 182.6 180.22 2.38 175.6 183.22 7.62 3_11 3600 166.8 168.24 1.44 184.6 180.22 4.38 184.9 181.425 3.475 4_11 4000 162.5 168.24 5.74 171.6 180.22 8.62 186.9 182.466667 4.43333333 100 Microhardness 6M 0% 6M 5% 6M 20% Site Location (um) Vickers Average Error Vickers Average Error Vickers Average Error 1_1 40 177 180.275 3.275 199 207.35 8.35 213.1 211.2 1.9 2_1 50 186.4 178.8 7.6 222.4 205.1 17.3 213.8 211.94 1.86 3_1 60 170.8 178.8 8 208.1 205.1 3 207.8 211.94 4.14 4_1 70 186.9 182 4.9 199.9 209.38 9.48 210.1 212.4 2.3 1_2 80 172.9 179.84 6.94 196.1 206.12 10.02 214.9 214.54 0.36 2_2 90 193 179.24 13.76 220.4 207.12 13.28 215.4 214.54 0.86 3_2 100 175.6 174.68 0.92 206.1 204.52 1.58 224.5 217 7.5 4_2 110 167.8 176.08 8.28 213.1 206.2 6.9 207.8 215.58 7.78 1_3 120 164.1 171.8 7.7 186.9 198.98 12.08 222.4 214.06 8.34 2_3 130 179.9 170.74 9.16 204.5 195.74 8.76 207.8 211.42 3.62 3_3 140 171.6 173.4 1.8 184.3 189.64 5.34 207.8 207.84 0.04 4_3 150 170.3 177.96 7.66 189.9 190.86 0.96 211.3 201.34 9.96 1_4 160 181.1 179.22 1.88 182.6 190.16 7.56 189.9 196.18 6.28 2_4 170 186.9 181.12 5.78 193 194.52 1.52 189.9 192 2.1 3_4 180 186.2 184.24 1.96 201 193.92 7.08 182 191.4 9.4 4_4 190 181.1 188.22 7.12 206.1 194.78 11.32 186.9 191.12 4.22 1_5 200 185.9 186 0.1 186.9 193.04 6.14 208.3 189.08 19.22 2_5 210 201 182.82 18.18 186.9 188.62 1.72 188.5 187.26 1.24 3_5 220 175.8 180.66 4.86 184.3 184.5 0.2 179.7 185.54 5.84 4_5 230 170.3 177.8 7.5 178.9 184.5 5.6 172.9 181.96 9.06 1_6 240 170.3 171.32 1.02 185.5 185.72 0.22 178.3 179.08 0.78 2_6 250 171.6 172.52 0.92 186.9 185.66 1.24 190.4 178.8 11.6 3_6 260 168.6 173.86 5.26 193 189.44 3.56 174.1 179.88 5.78 4_6 270 181.8 176.28 5.52 184 189.14 5.14 178.3 178.54 0.24 1_7 300 177 175.26 1.74 197.8 189.26 8.54 178.3 173.86 4.44 2_7 400 182.4 174.04 8.36 184 188.56 4.56 171.6 172.1 0.5 3_7 500 166.5 171.58 5.08 187.5 186.34 1.16 167 173.04 6.04 4_7 600 162.5 170.76 8.26 189.5 181.9 7.6 165.3 174.66 9.36 1_8 700 169.5 168.6 0.9 172.9 180.22 7.32 183 175.46 7.54 2_8 800 172.9 170.96 1.94 175.6 179.7 4.1 186.4 177.98 8.42 3_8 900 171.6 173.6 2 175.6 178.3 2.7 175.6 182.02 6.42 4_8 1000 178.3 175.88 2.42 184.9 178.58 6.32 179.6 179.48 0.12 1_9 1100 175.7 176.42 0.72 182.5 178.86 3.64 185.5 175.92 9.58 2_9 1200 180.9 177.22 3.68 174.3 180.92 6.62 170.3 175.6 5.3 3_9 1300 175.6 178.08 2.48 177 179.06 2.06 168.6 174 5.4 4_9 1400 175.6 179.14 3.54 185.9 178.5 7.4 174 170.2 3.8 1_10 1500 182.6 177.36 5.24 175.6 180.74 5.14 171.6 169.3 2.3 2_10 1600 181 176.7 4.3 179.7 180.46 0.76 166.5 169.38 2.88 3_10 1700 172 177.66 5.66 185.5 177.86 7.64 165.8 169.44 3.64 4_10 1800 172.3 177.14 4.84 175.6 178.4 2.8 169 170.24 1.24 1_11 2400 180.4 174.56 5.84 172.9 178.24 5.34 174.3 171 3.3 2_11 3000 180 174.48 5.52 178.3 174.84 3.46 175.6 171.9 3.7 3_11 3600 168.1 174.48 6.38 178.9 174.84 4.06 170.3 171.9 1.6 4_11 4000 171.6 174.48 2.88 168.5 174.84 6.34 170.3 171.9 1.6 101 Appendix D: Raw Grade 290 Microhardness Data Original Microhardness Line Original Sight 1 Sight 2 Sight 3 Sight 4 Average SD DEV Sample 1 12:55 Site Depth From Edge (um) Site (500g) Location (um) Line1 Line2 Average Base (100g) 1 75 176 172 180 175 175.75 3.30403793 1 -4000 176 205 190.5 2 150 175 192 168 176 177.75 10.1447852 2 -3800 188 173 180.5 3 225 166 174 170 183 173.25 7.27438428 3 -3600 177 181 179 4 300 173 166 167 183 172.25 7.80491298 4 -3400 188 182 185 5 375 172 172 172 175 172.75 1.5 5 -3200 186 181 183.5 6 450 171 168 187 166 173 9.55684746 6 -3000 178 179 178.5 7 525 162 177 175 173 171.75 6.70198975 7 -2800 186 188 187 8 750 168 190 179 179 179 8.98146239 8 -2600 174 180 177 9 975 166 175 182 182 176.25 7.58836829 9 -2400 193 189 191 10 1200 167 173 167 188 173.75 9.9121138 10 -2200 180 170 175 11 1425 173 175 181 187 179 6.32455532 11 -2000 182 186 184 12 1650 169 171 161 188 172.25 11.3541476 12 -1800 186 198 192 174.729167 7.53730041 13 -1600 180 194 187 HAZ (100g) 1 75 201 195 190 187 193.25 6.13052472 14 -1400 204 193 198.5 2 150 193 205 205 181 196 11.4891253 15 -1200 215 203 209 3 225 185 206 195 193 194.75 8.65544145 16 -1000 225 203 214 4 300 189 204 209 191 198.25 9.77667292 17 -800 206 197 201.5 5 375 188 213 209 190 200 12.832251 18 -600 194 203 198.5 6 450 198 203 198 184 195.75 8.18026079 19 -400 193 210 201.5 7 525 196 195 196 183 192.5 6.35085296 20 -200 212 208 210 8 750 194 201 195 184 193.5 7.04745817 21 0 213 210 211.5 9 975 196 193 191 186 191.5 4.2031734 22 200 221 226 223.5 10 1200 193 205 198 182 194.5 9.67815409 23 400 204 207 205.5 11 1425 202 192 196 181 192.75 8.84590301 24 600 190 192 191 12 1650 191 204 195 192 195.5 5.91607978 25 800 228 203 215.5 194.854167 8.2588248 26 1000 192 195 193.5 Weld (100g) 1 75 195 196 203 196 197.5 3.6968455 27 1200 191 200 195.5 2 150 203 187 210 199 199.75 9.63932916 28 1400 194 188 191 3 225 197 199 200 206 200.5 3.87298335 29 1600 192 208 200 4 300 173 196 206 208 195.75 16.0494029 30 1800 192 208 200 5 375 167 195 194 195 187.75 13.8413631 31 2000 218 212 215 6 450 183 195 193 193 191 5.4160256 32 2200 202 192 197 7 525 176 190 200 195 190.25 10.3400516 33 2400 194 199 196.5 8 750 192 189 194 206 195.25 7.45542308 34 2600 195 183 189 9 975 190 196 200 204 197.5 5.97215762 35 2800 193 187 190 10 1200 196 183 206 203 197 10.2306728 36 3000 182 180 181 11 1425 170 194 199 191 188.5 12.7671453 37 3200 182 199 190.5 12 1650 155 199 197 206 189.25 23.1570724 38 3400 170 172 171 194.166667 10.203206 39 3600 178 189 183.5 40 3800 177 188 182.5 41 4000 170 179 174.5 Microhardness 102 Sight 1 Sight 2 Sight 3 Sight 4 Average SD DEV Sight 1 Sight 2 Sight 3 Sight 4 Average SD DEV Site Depth From Edge (um) Base (100g) 1 75 182 184 182 175 180.75 3.94757309 177 190 187 190 186 6.164414 2 150 181 181 179 179 180 1.15470054 201 185 189 179 188.5 9.29157324 3 225 185 176 182 179 180.5 3.87298335 176 179 180 187 180.5 4.65474668 4 300 184 177 176 177 178.5 3.6968455 176 181 196 179 183 8.90692614 5 375 182 182 180 179 180.75 1.5 181 184 184 187 184 2.44948974 6 450 184 180 185 177 181.5 3.6968455 183 187 188 210 192 12.1928941 7 525 182 185 179 178 181 3.16227766 198 187 200 189 193.5 6.45497224 8 750 180 171 180 180 177.75 4.5 176 190 194 187 186.75 7.71902412 9 975 185 188 179 189 185.25 4.5 182 184 182 170 179.5 6.40312424 10 1200 183 173 173 180 177.25 5.05799697 183 199 179 187 187 8.6409876 11 1425 178 177 177 179 177.75 0.95742711 186 191 182 173 183 7.61577311 12 1650 187 201 190 175 188.25 10.6887792 188 183 176 187 183.5 5.44671155 180.770833 3.89461907 185.604167 7.16171973 HAZ (100g) 1 75 178 186 179 181 181 3.55902608 184 180 192 177 183.25 6.5 2 150 180 184 187 185 184 2.94392029 185 187 180 188 185 3.55902608 3 225 179 193 185 197 188.5 8.06225775 150 183 182 180 173.75 15.8823802 4 300 189 192 181 184 186.5 4.93288286 188 177 186 180 182.75 5.12347538 5 375 193 180 201 186 190 9.05538514 181 188 192 186 186.75 4.57347424 6 450 183 185 181 185 183.5 1.91485422 186 183 177 183 182.25 3.77491722 7 525 189 187 193 184 188.25 3.77491722 181 188 202 188 189.75 8.80814017 8 750 189 185 184 195 188.25 4.99165971 182 192 188 193 188.75 4.99165971 9 975 180 185 178 177 180 3.55902608 181 186 181 189 184.25 3.94757309 10 1200 188 187 181 181 184.25 3.77491722 179 185 184 185 183.25 2.87228132 11 1425 178 188 175 175 179 6.164414 186 177 181 185 182.25 4.11298756 12 1650 186 182 193 196 189.25 6.39661369 182 184 195 185 186.5 5.8022984 185.208333 4.92748952 184.041667 5.82901778 Weld (100g) 1 75 211 190 201 198 200 8.67947771 178 193 191 194 189 7.43863787 2 150 195 215 200 196 201.5 9.25562892 186 197 190 189 190.5 4.65474668 3 225 196 208 193 215 203 10.2956301 198 198 188 190 193.5 5.25991128 4 300 191 202 205 212 202.5 8.73689495 171 194 189 197 187.75 11.6440256 5 375 195 203 231 197 206.5 16.683325 187 199 194 188 192 5.59761854 6 450 192 221 203 193 202.25 13.4505266 190 208 200 187 196.25 9.60468636 7 525 197 199 196 206 199.5 4.50924975 190 203 189 185 191.75 7.80491298 8 750 203 206 216 206 207.75 5.67890835 184 198 199 184 191.25 8.38152731 9 975 198 202 199 201 200 1.82574186 198 194 185 184 190.25 6.8495742 10 1200 189 215 192 213 202.25 13.6473441 188 180 193 192 188.25 5.90903263 11 1425 207 202 212 200 205.25 5.37742193 183 189 190 181 185.75 4.42530602 12 1650 188 212 197 202 199.75 10.0124922 193 197 181 183 188.5 7.72442015 202.520833 9.01272013 190.395833 7.10786664 Microhardness 2W 0% 2W 5% 103 104 Sight 1 Sight 2 Sight 3 Sight 4 Average SD DEV Sight 1 Sight 2 Sight 3 Sight 4 Average SD DEV Site Depth From Edge (um) Base (100g) 1 75 190 180 199 194 190.75 8.05708798 176 191 192 174 183.25 9.56991815 2 150 187 183 185 189 186 2.5819889 170 184 203 185 185.5 13.5277493 3 225 181 175 180 180 179 2.7080128 176 183 176 192 181.75 7.58836829 4 300 184 187 174 204 187.25 12.4733048 184 186 178 187 183.75 4.03112887 5 375 179 180 190 190 184.75 6.07590871 182 188 181 193 186 5.59761854 6 450 178 217 171 190 189 20.2484567 188 192 187 180 186.75 4.99165971 7 525 189 193 188 179 187.25 5.90903263 179 187 185 185 184 3.46410162 8 750 181 201 197 229 202 19.9666388 185 190 189 191 188.75 2.62995564 9 975 178 189 178 170 178.75 7.80491298 188 193 201 186 192 6.68331255 10 1200 183 188 185 181 184.25 2.98607881 180 189 183 189 185.25 4.5 11 1425 188 248 174 176 196.5 34.8855271 182 170 182 186 180 6.92820323 12 1650 183 192 192 216 195.75 14.1509717 183 176 175 193 181.75 8.30160627 188.4375 11.4873268 184.895833 6.48446851 HAZ (100g) 1 75 188 180 180 185 183.25 3.94757309 189 180 184 181 183.5 4.04145188 2 150 171 198 191 188 187 11.4600756 175 194 189 192 187.5 8.58292879 3 225 174 186 181 184 181.25 5.25198375 189 189 205 206 197.25 9.53502316 4 300 179 182 186 185 183 3.16227766 194 202 196 205 199.25 5.12347538 5 375 177 194 186 184 185.25 6.99404509 192 199 202 196 197.25 4.27200187 6 450 178 183 188 179 182 4.54606057 199 199 192 190 195 4.69041576 7 525 175 185 185 192 184.25 6.99404509 181 203 194 207 196.25 11.5289491 8 750 173 194 189 183 184.75 9.03234927 183 184 192 193 188 5.22812905 9 975 196 187 187 184 188.5 5.19615242 194 196 197 194 195.25 1.5 10 1200 197 211 201 193 200.5 7.72442015 194 197 193 200 196 3.16227766 11 1425 187 187 177 191 185.5 5.97215762 189 193 194 183 189.75 4.99165971 12 1650 190 200 191 189 192.5 5.06622805 186 181 199 199 191.25 9.17877988 186.479167 6.27894737 193.020833 5.98625768 Weld (100g) 1 75 204 200 186 200 197.5 7.89514619 167 196 198 191 188 14.3061758 2 150 188 196 195 194 193.25 3.59397644 207 196 223 193 204.75 13.573872 3 225 200 209 182 215 201.5 14.3874946 199 158 216 193 191.5 24.3652758 4 300 190 215 181 202 197 14.7648231 196 191 192 214 198.25 10.7199192 5 375 197 200 182 220 199.75 15.6284996 208 206 204 191 202.25 7.67571929 6 450 204 197 196 217 203.5 9.67815409 192 198 201 196 196.75 3.77491722 7 525 197 199 186 191 193.25 5.90903263 201 199 191 197 197 4.3204938 8 750 194 202 198 214 202 8.6409876 189 201 187 194 192.75 6.23832242 9 975 204 201 185 199 197.25 8.4212034 208 205 197 197 201.75 5.6199051 10 1200 202 196 219 211 207 10.0995049 195 186 175 185 185.25 8.18026079 11 1425 209 193 201 196 199.75 6.99404509 199 192 200 189 195 5.35412613 12 1650 203 195 194 196 197 4.0824829 196 195 188 199 194.5 4.65474668 199.0625 9.17461254 195.645833 9.06531118 Microhardness 2M 0% 2M 5% 105 106 Sight 1 Sight 2 Sight 3 Sight 4 Average SD DEV Sight 1 Sight 2 Sight 3 Sight 4 Average SD DEV Site Site Depth From Edge (um) 1 Base (100g) 1 75 173 191 175 185 181 8.48528137 167 177 200 179 180.75 13.8654246 2 2 150 178 200 183 187 187 9.41629793 165 171 173 172 170.25 3.59397644 3 3 225 190 185 182 201 189.5 8.34665602 177 182 161 178 174.5 9.25562892 4 4 300 183 185 178 180 181.5 3.10912635 169 162 164 194 172.25 14.7958327 5 5 375 188 183 174 191 184 7.43863787 191 165 150 161 166.75 17.3661548 6 6 450 176 179 174 188 179.25 6.18465844 183 188 154 176 175.25 14.997222 7 7 525 180 180 187 177 181 4.24264069 171 198 161 188 179.5 16.6232769 8 8 750 180 178 174 171 175.75 4.03112887 173 160 169 183 171.25 9.53502316 9 9 975 164 177 170 179 172.5 6.8556546 165 165 175 172 169.25 5.05799697 10 10 1200 172 179 177 177 176.25 2.98607881 153 163 160 179 163.75 10.9962115 11 11 1425 192 174 194 178 184.5 9.98331942 162 192 188 184 181.5 13.4039795 12 12 1650 184 180 178 183 181.25 2.75378527 182 154 183 182 175.25 14.1745076 13 181.125 6.15277214 173.354167 11.9721029 14 HAZ (100g) 1 75 176 183 178 189 181.5 5.8022984 184 185 165 175 177.25 9.32291085 15 2 150 177 185 189 184 183.75 4.99165971 181 160 169 170 170 8.60232527 16 3 225 185 189 183 189 186.5 3 179 171 164 169 170.75 6.23832242 17 4 300 187 180 183 183 183.25 2.87228132 170 174 190 160 173.5 12.4766448 18 5 375 189 193 190 186 189.5 2.88675135 207 180 161 171 179.75 19.7547463 19 6 450 181 197 186 189 188.25 6.70198975 184 179 162 174 174.75 9.42956344 20 7 525 185 191 180 187 185.75 4.57347424 210 156 167 174 176.75 23.3719918 21 8 750 183 201 189 176 187.25 10.5948101 178 177 171 174 175 3.16227766 22 9 975 182 188 203 191 191 8.83176087 196 162 183 159 175 17.6068169 23 10 1200 189 187 193 179 187 5.88784058 174 170 173 188 176.25 8.01560977 24 11 1425 184 180 184 186 183.5 2.51661148 176 155 167 188 171.5 13.96424 25 12 1650 189 199 185 185 189.5 6.60807587 183 153 175 186 174.25 14.9080515 26 186.395833 5.4389628 174.5625 12.2377917 27 Weld (100g) 1 75 214 209 205 211 209.75 3.77491722 196 220 195 196 201.75 12.1757957 28 2 150 195 197 215 205 203 9.09212113 231 203 167 184 196.25 27.439327 29 3 225 201 202 212 199 203.5 5.8022984 216 200 207 191 203.5 10.5987421 30 4 300 189 193 202 190 193.5 5.91607978 200 202 204 204 202.5 1.91485422 31 5 375 201 197 198 205 200.25 3.59397644 175 184 193 202 188.5 11.61895 32 6 450 202 198 216 200 204 8.16496581 185 173 204 188 187.5 12.7671453 33 7 525 188 195 194 188 191.25 3.77491722 190 197 199 206 198 6.58280589 34 8 750 188 210 195 203 199 9.55684746 178 190 172 194 183.5 10.2469508 35 9 975 195 218 214 195 205.5 12.2338329 187 177 202 194 190 10.6144556 36 10 1200 209 215 186 210 205 12.9357386 194 205 194 192 196.25 5.90903263 37 11 1425 198 182 192 189 190.25 6.65206735 185 196 196 203 195 7.43863787 38 12 1650 190 179 189 208 191.5 12.0692447 206 185 200 185 194 10.6770783 39 199.708333 7.79725058 194.729167 10.6653146 40 41 Microhardness 6M 0% 6M 5% 107 108 Appendix E: Raw X42 and Grade 290 Fracture analysis Data X42N1-1 Area total 4036173.147 N1-2 Area total 3811701.435 N2-1 Area total 4,246,922.76 N2-2 Area total 3,878,501.69 N3-1 Area total 4,151,273.54 N3-2 Brittle Area 2153016.79 Brittle Area 2413706.806 Brittle Area 2459693.4 Brittle Area 2146906.917 Brittle Area 2259849.299 Brittle Percent 53.34% Brittle Percent 63.32% Brittle Percent 57.92% Brittle Percent 55.35% Brittle Percent 54.44% 2 Weeks N4-1 Area total 4,150,183.10 N4-2 Area total 3,920,655.39 N5-1 Area total 4,436,554.30 N5-2 Area total 4,086,933.19 N6-1 Area total 4,128,623.60 N6-2 Brittle Area 2263163.916 Brittle Area 2140856.576 Brittle Area 2731368.041 Brittle Area 2234053.95 Brittle Area 2395749.74 Brittle Percent 54.53% Brittle Percent 54.60% Brittle Percent 61.57% Brittle Percent 54.66% Brittle Percent 58.03% N7-1 Area total 4,235,980.89 N7-2 Area total 4,166,427.03 N8-1 Area total 4,416,880.14 N8-2 Area total 4,325,795.58 N9-1 Area total 3,895,347.08 N9-2 Brittle Area 2400253.216 Brittle Area 2311893.646 Brittle Area 2648242.936 Brittle Area 2799525.757 Brittle Area 2362822.537 Brittle Percent 56.66% Brittle Percent 55.49% Brittle Percent 59.96% Brittle Percent 64.72% Brittle Percent 60.66% N10-1 Area total 4,282,639.73 N10-2 Area total 4,121,878.35 N11-1 Area total 4,074,050.61 N11-2 Area total 4,435,378.42 N12-1 Area total 4,621,888.79 N12-2 Brittle Area 2771022.632 Brittle Area 2733422.383 Brittle Area 2186052.152 Brittle Area 2584220.065 Brittle Area 2757005.585 Brittle Percent 64.70% Brittle Percent 66.31% Brittle Percent 53.66% Brittle Percent 58.26% Brittle Percent 59.65% 2 Months N13-1 Area total 4,201,034.52 N13-2 Area total 4,357,632.03 N14-1 Area total 4,335,744.20 N14-2 Area total 4,169,001.93 N15-1 Area total 4,283,396.29 N15-2 Brittle Area 2542419.657 Brittle Area 2538839.819 Brittle Area 2628451.279 Brittle Area 2516851.847 Brittle Area 2481606.88 Brittle Percent 60.52% Brittle Percent 58.26% Brittle Percent 60.62% Brittle Percent 60.37% Brittle Percent 57.94% N16-1 Area total 4,358,596.17 N16-2 Area total 4,378,354.74 N17-1 Area total 4,356,820.96 N17-2 Area total 4,214,675.00 N18-1 Area total 4,232,720.70 N18-2 Brittle Area 2769371.074 Brittle Area 3162181.09 Brittle Area 2481897.516 Brittle Area 2428227.183 Brittle Area 2589937.778 Brittle Percent 63.54% Brittle Percent 72.22% Brittle Percent 56.97% Brittle Percent 57.61% Brittle Percent 61.19% N19-1 Area total 3,944,205.01 N19-2 Area total 4,257,758.30 N20-1 Area total 4,211,301.44 N20-2 Area total 4,306,648.31 N21-1 Area total 4,550,446.39 N21-2 Brittle Area 2623804.827 Brittle Area 2691364.327 Brittle Area 2784134.112 Brittle Area 2977841.811 Brittle Area 3016002.271 Brittle Percent 66.52% Brittle Percent 63.21% Brittle Percent 66.11% Brittle Percent 69.15% Brittle Percent 66.28% 6 Months N22-1 Area total 4,258,859.53 N22-2 Area total 4,490,991.85 N23-1 Area total 4,559,614.19 N23-2 Area total 4,303,010.56 N24-1 Area total 4,454,519.24 N24-2 Brittle Area 2458063.641 Brittle Area 2683142.457 Brittle Area 2779064.995 Brittle Area 2589595.086 Brittle Area 2831183.188 Brittle Percent 57.72% Brittle Percent 59.74% Brittle Percent 60.95% Brittle Percent 60.18% Brittle Percent 63.56% N25-1 Area total 4,710,016.69 N25-2 Area total 4,332,236.09 N26-1 Area total 4,492,925.16 N26-2 Area total 4,356,930.63 N27-1 Area total 4,389,541.50 N27-2 Brittle Area 2692017.109 Brittle Area 2847078.149 Brittle Area 3004528.843 Brittle Area 2915446.727 Brittle Area 2949459.578 Brittle Percent 57.16% Brittle Percent 65.72% Brittle Percent 66.87% Brittle Percent 66.92% Brittle Percent 67.19% N28-1 Area total 4,673,047.01 N28-2 Area total 4,555,410.23 #2 N28-1Area total 4,492,110.47 #2 N28-2 Area total 4,387,784.59 Brittle Area 3085127.778 Brittle Area 3199816.934 Brittle Area 2960889.248 Brittle Area 2909808.875 Brittle Percent 66.02% Brittle Percent 70.24% Brittle Percent 65.91% Brittle Percent 66.32% 109 110
Thesis/Dissertation
eng
Mechanical Engineering
Vancouver : University of British Columbia Library
Attribution-NonCommercial-NoDerivatives 4.0 International
Graduate
Effects of blended hydrogen enriched natural gas on the microstructure and mechanical properties of a X42 steel pipeline and Grade 290 weld
Text