Sulfide stress corrosion cracking resistance of X65 pipeline steel welded joint in H₂S/CO₂ environment

An offshore nectural gas (NG) utilization project in Bohai Bay of China is carried out and API 5L X65 steel made in China is selected for the subsea NG transmission pipeline. Whereas, H₂S content in NG is increasing along with the exploitation of the field, and CO₂ content is up to 10%, so the subsea pipeline faces with stress corrosion cracking risks. Therefore, on stress corrosion cracking resistance of X65 pipeline steel welded joint in simulated H₂S/CO₂ environment was studied by referencing the test method of NACE TM0177 - 2005. Results show that the X65 pipeline steel welded joint has excellent performance of SSCC resistance in H₂S/CO₂ environment. However, a certain degree of SSCC sensitivity appeared at low temperature under acidic conditions. Some suggestions for controlling SSCC were presented in order to ensure the pipeline/ s safety in running, includes controlling NG transmission temperature in a appropriate range and reducing acid gas content as far as possible.