Experimental investigation on the stress corrosion cracking of FV520B welded joint in natural gas environment with ECP and SSRT

For the welded joint specimens of the steel FV520B used in natural gas impellers, the uniform experimental method is applied in the experiment of electrochemical corrosion potential (ECP) under a certain concentration of H2S and CO2, temperature and pressure to get some test data including electrochemical corrosion potential, current density, Tafel slope and polarization resistance. In addition, the stress corrosion susceptibility index has been measured by the experimental of slow strain rate tensile (SSRT). Combined with observation of crack and fracture morphology, the stress corrosion cracking mechanism of the martensitic stainless steel FV520B welded joints in the service environment is explored. The experimental results show that there are obvious tendency of stress corrosion cracking in welded joints and the relatively significant effects of temperature and CO2 concentration on corrosion current density and stress corrosion susceptibility. In the environment of 98 °C, 6 MPa, 30% H2S and 65% CO2, the stress corrosion susceptibility of welded joint specimens is the highest, and the fracture surfaces display brittle fracture behavior.