Material and Fracture Surface Examination of T-Joint for High Pressure Hydrogen Piping that Caused Hydrogen Leakage in a High Pressure Hydrogen Facility

Abstract

This paper deals with the material and fracture surface examination of T-type joint for piping that caused hydrogen leakage in a high pressure hydrogen facility (Service pressure: 99 MPa). T-type joint is made of precipitation hardening martensitic 17-4PH stainless steel. The design fracture pressure of T-type joint is as high as 1050 MPa. Nevertheless, T-type joint caused hydrogen leakage in 150 MPa hydrogen gas whose pressure was 14 % of the design fracture pressure. Chemical composition analysis, microstructure observation and Vickers hardness measurement proved that 17-4PH of T-type joint was sound. Fracture surface observation showed that semi-elliptical crack surface was covered with quasi-cleavage and that peel-like defects were formed on taper surface. It was presumed from these points that hydrogen-leakage of T-type joint was caused by hydrogen-induced crack growth from peel-like defect in 150 MPa hydrogen gas.