Hydrogen gaseous effects on fracture resistance of API-X70 estimated by XFEM

Hydrogen embrittlement has been recognized as one of major degradation mechanisms causing the decrease of ductility and fracture toughness of several kinds of materials. In accordance with the demand for hydrogen fuels, it becomes more important to ensure safety of relevant facilities like pressure vessels, storage tanks and so on. The objective of this study is to examine fracture resistance of American Petroleum Institute (API)-X70 steel under highly pressurized hydrogen gaseous condition. The extended finite element method (XFEM) was adopted to predict J-R curves via a crack growth simulation approach. At first, preliminary analyses for SM490A carbon steel were carried out to demonstrate applicability of the XFEM, of which result was comparable to test data within 14 %. Subsequently, iterative numerical analyses were conducted to calibrate appropriate damage parameters for the API-X70 steel by using notched round bar specimens. Finally, crack growth simulations of 1T-compact tension (CT) specimens were performed adopting the calibrated parameters. JIC values determined from predicted J-R curves were compared with 1/2T-CT CTOD test data and relevant constraint effect was discussed.