The effect of hydrogen fugacity on the hydrogen embrittlement sensitivity and hydrogen-induced cracking of X60 pipeline steel

Purpose This study aims to systematically evaluate the hydrogen embrittlement sensitivity and fracture mechanism evolution of X60 pipeline steel under varying hydrogen blending ratios (0–60%), providing essential insights for the safe design and operation of hydrogen-blended pipelines. Design/methodology/approach The hydrogen embrittlement behavior of X60 steel in long service was studied by hydrogen permeability test, slow strain rate tensile (SSRT) test, fracture toughness test, and fracture morphology analysis. Findings Hydrogen permeability indicates that vapor-phase hydrogen and stress–strain without impurities are not sufficient to cause significant hydrogen damage. When the hydrogen ratio is 20%, the length of SSRT fracture secondary crack is about 80% of the fracture, and the fracture morphology is quasi-cleavage. The J-Δa curve degenerated significantly, and the δ0.2BL decreased by 70.65%. The hydrogen embrittlement mechanism of X60 steel has undergone the evolution process from hydrogen-enhanced localized plasticity to hydrogen-enhanced decohesion and ultimately to hydrogen-induced cracking, and finally the fracture mode has changed from ductile fracture to brittle fracture. Originality/value This study provides a comprehensive analysis of the hydrogen embrittlement risk and fracture mechanism evolution in X60 steel, highlighting that a hydrogen blending ratio below 20% ensures controllable embrittlement risk in a 12 MPa environment. It offers critical data and theoretical support for the safe design and operation of hydrogen-blended natural gas pipelines, particularly in determining safe operational thresholds and protective measures.