Variables affecting unstable fracture load of cracked pipes under hydrogen environment

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This paper presents an analytical equation for the reduction of the unstable fracture load for a cracked pipe due to hydrogen embrittlement. The proposed equation shows that the reduction of the unstable fracture load due to hydrogen embrittlement depends not only on the toughness reduction due to hydrogen embrittlement but also on plastic tensile properties and the degree of plastic yielding at fracture of a pipe without hydrogen embrittlement (quantified using the proximity parameter for plastic collapse). Note that the proximity parameter for plastic collapse is affected by the pipe and crack geometries, loading condition and fracture toughness before hydrogen embrittlement. Two case study results are presented using published material data. The first case considers stainless steel data to demonstrate the effect of the toughness reduction due to hydrogen exposure and the degree of plastic yielding at fracture on the reduction of the unstable fracture load for a cracked pipe under hydrogen embrittlement. The second case uses two sets of API 5L X42 and X70 pipeline steel data to illustrate the effect of plastic tensile properties.