The effect of hydrogen on stress corrosion behavior of X65 steel welded joint in simulated deep sea environment

In order to investigate stress corrosion cracking (SCC) of X65 pipeline steel and its welded joint area in deep sea environment. The simulated methods were used to obtain the welded joint of hardening and softening tissue in heat affected zone (HAZ) by annealing at 1300 °C for 10 min and then, normalized in air and quenched in water respectively; the other was to get 1000 m depths of marine environment. The effect of hydrogen on SCC behavior of X65 pipeline steel in simulated deep sea environment was analyzed by a combination of hydrogen-charging, slow stain rate test (SSRT), scanning electron microscope (SEM) and electrochemistry. Results demonstrated that with the increasing of charging current density, Fracture of as-received appeared brittle characteristics and normalized and quenched steel generated micro cracks, Hydrogen-charging will enhance the SCC susceptibility of the steel in simulated deep sea environment. The corrosion potential of X65 steels was low in deep sea environment with hydrogen evolution reaction and showed some SCC sensitivity in deep sea environment. Heat treatment altered the microstructure of the steel, resulting in a change of SCC susceptibility. In particular, the quenched steel with a bainite micro-structure which had a higher SCC susceptibility than as-received and normalized steel in deep sea environment.