Effect of residual and external stress on corrosion behaviour of X80 pipeline steel in sulphate-reducing bacteria environment

X80 pipeline steel has a wide application prospect. This steel is easily affected by sulphate-reducing bacteria (SRB) in neutral soil and causes stress-corrosion cracking. Based on the results of static and dynamic electrochemical tests, the corrosion behaviour and mechanism of X80 pipeline steel under the synergistic effect of stress and SRB in Shenyang soil environment were investigated through slow strain rate testing, electrochemical impedance spectroscopy, potentiodynamic polarisation technique and surface analysis techniques. Results showed that internal residual and external tensile stress accelerate the corrosion of X80 steel, and the effect of SRB is influenced by the stress type. When only residual stress is applied, the SRB adsorption film plays a certain protective role, which reduces the corrosion sensitivity of X80 steel, and its corrosion mechanism is the anode dissolution of the film rupture. When tensile stress is applied, stress and SRB play a role in the stress concentration at the crack tip, thereby increasing the corrosion sensitivity of X80 steel. The corrosion mechanism is then the activated anode dissolution.