Abstract

Hydrogen is one of the promising energy carriers for achieving a carbon neutral society. The pipeline system is positioned as a major type of infrastructure which will be indispensable for mass transportation of gaseous hydrogen. It is acknowledged that existing natural gas pipelines can be used safely to transport hydrogen blends up to 10 or 20 %. However, it is also known that the mechanical properties of steels are significantly degraded by hydrogen embrittlement, even under small partial pressures of hydrogen. Material degradation is considered in the hydrogen pipeline code ASME B31.12. This code requires evaluation of the fracture and fatigue properties of linepipe materials used under hydrogen, and a critical assessment is conducted so that fracture of the pipeline can be avoided during its service life. In the present study, the hydrogen absorption properties, fracture toughness and fatigue crack growth properties under a 25 MPa hydrogen gas environment were investigated by using 3 kinds of linepipe steels manufactured by different methods. The materials were API X65 linepipe steel, which were manufactured as ERW, LSAW and seamless (SMLS) linepipes. Although all the materials showed a bainitic ferrite generally called, each microstructure had distinctive characteristics attributable to the manufacturing process. While all the linepipe steels showed better fracture toughness and fatigue crack growth rates than the ASME B. 31.12 design curve, their hydrogen absorption properties, fracture toughness in hydrogen gas and fatigue crack growth properties in hydrogen gas differed due to their crystal structures, even though the strength grade of the materials. In the steels used in this study, the fracture toughness and fatigue crack growth characteristics under a hydrogen atmosphere were insensitive to the influence of absorbed hydrogen, and were considered to be influenced by the material factors that determine the fracture toughness and fatigue crack growth characteristics in the atmosphere.

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