Hydrogen Embrittlement Susceptibility of Base Metal and Welded Joint of X90 Steel under Cathodic Protection in Different Soil Environments

Hydrogen embrittlement susceptibility of base metal and welded joint of X90 steel in Korla and Beijing soil simulation solutions was studied in comparison by slow strain rate test (SSRT) under impressed current cathodic protection, in combination with microstructure observation and electrochemical polarization curve testing. The results show that the X90 steel base metal had fine grains, while the fusion line and coarse-grained zone of the heat-affected zone (HAZ) had relatively coarse grains for the welded joint of X90 steel. Under the cathodic protection at -0.9, -1.1 V (vs. SCE), the base metal showed low hydrogen embrittlement susceptibility in both soil simulation solutions. The hydrogen embrittlement susceptibility of welded joint was significantly higher than that of the base metal at the same cathodic protection potential, and the hydrogen embrittlement sensitivity in the Korla soil simulation solution was higher than that in the Beijing soil simulation solution. Under cathodic protection, the risk of hydrogen embrittlement would be increased by the coarse structure, uneven structure, high strength of materials and the high salinity of soil environment, among which high salinity of soil environment was the main factor.