Fracture properties and fatigue life assessment of API X70 pipeline steel under the effect of an environment containing hydrogen

Abstract

A series of fracture toughness and fatigue crack growth rate tests were performed on the X70 pipeline steel base and weld metals under 10 MPa of a natural/hydrogen gas mixture with 1% H2 blends. It is observed that the 10 MPa gas mixture with 1% H2 causes a significant reduction in the fracture toughness in both metals. The fatigue crack growth rates are markedly accelerated under the gas mixtures with 1 % hydrogen blend compared with the tests performed in ambient air. The obtained fracture parameters serve as inputs for fatigue life assessment analyses under the effect of a hydrogen-containing environment. The observed design fatigue life depends strongly only on the environmental conditions. The design fatigue strength of the structural pipeline exposed to hydrogen is much shorter than that under ambient air owing to the decrease in fracture toughness properties and acceleration of the fatigue crack growth rate.