Analysis of electrochemical hydrogen permeation through X-65 pipeline steel and its implications on pipeline stress corrosion cracking

Electrochemical hydrogen permeation tests were performed to measure the hydrogen permeation current through the X-65 pipeline steel in the electrolytes simulating the soil conditions to initiate near-neutral pH stress corrosion cracking (SCC) in pipelines. The hydrogen permeation current was analyzed following the constant concentration model. It is shown that, AQDS, simulating the organic compound in the soil, inhibits hydrogen permeation by decreasing the sub-surface hydrogen concentration, while sulfide promotes hydrogen permeation by inhibiting the hydrogen recombination and thus increasing the sub-surface hydrogen concentration. The steel specimen is more susceptible to stress corrosion cracking in the soil solution with a higher sub-surface hydrogen concentration, indicating that hydrogen is involved in near-neutral pH SCC in pipelines. It is suggested that hydrogen promotes the cracking of the steel, accompanying with the anodic dissolution on the crack sides and at the crack tip.