Hydrogen Effect on Linepipe Steel and Material Compatibility to a High-pressure Hydrogen Pipeline

In this paper, the basic material behavior and mechanical properties of linepipe steel under high-pressure hydrogen were investigated. A hydrogen exposure test was first conducted to evaluate hydrogen absorption into the steel from gaseous hydrogen at pressures of up to 25 MPa. It was found that about 0.1 ppm hydrogen was absorbed into the steel, which is the level of hydrogen absorption in a mildly sour environment. This result reminds us of the possibility of hydrogen stress cracking; accordingly, the proper material is recommended for hydrogen use. Then, fracture toughness and fatigue crack growth tests were conducted using a recently produced Grade X65 longitudinal submerged arc welded linepipe with a fine-grained bainitic microstructure, revealing excellent performance of fracture and fatigue resistance under a 21 MPa high-pressure hydrogen condition. Fatigue crack growth analysis of the hydrogen pipeline was finally conducted based on the American Society of Mechanical Engineers hydrogen pipeline design code.