Study of the Hydrogen Delayed Fracture of Mooring Chain Steel using Strain Rate Testing

The delayed fracture behaviour of a high-strength offshore mooring chain steel was investigated by a conventional strain rate test (CSRT). The hydrogen was electrochemically pre-introduced to the steel, and the hydrogen content in the specimen was measured by thermal desorption analysis (TDA) after fracturing during the CSRT. The results showed that when the hydrogen content was less than 3.0 wppm, the fracture stress decreased slowly and linearly. As the hydrogen content exceeded 3.0 wppm, the fracture stress decreased rapidly but remained linear. With increasing of hydrogen content the fracture mode changed from ductile to brittle intergranular. The dependence of local maximum fracture stress on local hydrogen content obtained from the CSRT and slow strain rate test (SSRT) was similar when the local hydrogen content was less than 3.0 wppm. However, when the hydrogen content was more than 3.0 wppm, at a given nominal fracture stress, the local hydrogen content for the CSRT was lower than that for the SSRT.