Effect of Hydrogen Partial Pressure on the Hydrogen Embrittlement Susceptibility of Type304 Stainless Steel in High-pressure H2/Ar Mixed Gas

Slow strain rate testings (SSRTs) were carried out on Type304 stainless steel (Type304SS) in room temperature mixed gasses controlled to various pressure levels of up to 75 MPa, and the variation of embrittlement susceptibility of the tested steel under various hydrogen partial pressure was measured. Regardless of gas composition and at a hydrogen partial pressure level of 0.3 MPa or more in the gasses, elongation as well as relative reduction of area lowered, and brittle fracture surfaces appeared with accompanying quasi-cleavage. The critical P-H2 at which Type304SS embrittles in a room temperature inert gas environment with mixed hydrogen is inferred to be between 0.05 and 0.1 MPa. From a conservative judgment it is concluded that hydrogen embrittlement fractures would be unlikely to occur to members made of Type304SS when P-H2 is around one tenth of the atmospheric pressure or lower (i.e. 0.05 MPa).