Implementation of Ductility and Microstructural Attributes for Evaluation of Fracture and Fatigue Performance of API X Grades in High Pressure Gaseous Hydrogen Transmission Pipeline Environments

Abstract There is a strong interest in hydrogen as an energy source to contribute to combatting climate change. Hydrogen diffusion into the steel with assistance through various mechanisms of corrosion and pressure will degrade the mechanical properties, primarily critical ductility properties of fracture toughness and fatigue, through embrittlement or hydrogen induced cracking. Fracture toughness as a measure of crack arrest performance through required Charpy (TCVN) performance represents a principal mechanical property requirement of the pipeline. Ductility performance, regardless of the environment, which consists of % RA, fracture toughness, fatigue, etc. is driven primarily by metallurgical components of the through-thickness microstructure such as average high angle grain boundary (HAGB) size and homogeneity of the HAGB’s . A relationship can perhaps be developed of ductility attributes such as TCVN performance in air vs. fracture toughness ductility performance in hydrogen. This relationship of TCVN ductility performance in conjunction with through-thickness microstructural components with fracture toughness performance in hydrogen will be used to propose an additional “Option C” qualification to the ASME B31.12 Code for Hydrogen Piping and Pipelines. This paper will present the background analysis, evaluation, development of the logic, proposed B31.12 code language and how to implement the logic.