Stress corrosion behavior of B+F dual-phase X80 pipeline steel in different soil environments

The stress corrosion behavior and immersion corrosion behavior of B+F dual-phase X80 pipeline steel in simulated near-neutral and alkaline soil solutions were studied by slow strain rate tensile (SSRT) test, immersion corrosion test and polarization test. The results show that the strength and ductility of the samples in alkaline soil solution are weaker than those in near-neutral soil solution, and the elongation loss (I delta) and area shrinkage loss (I psi) are 2.81 and 2.76 times of those in near-neutral soil solution. Bainite and ferrite (B+F) dual-phase X80 pipeline steel is more sensitive to stress corrosion in alkaline soil solution than in near-neutral soil solution. The protective properties of the passive film determine the corrosion dynamics, because the more complete and uniform the passive film formed, the better the corrosion resistance. In both soil solutions, the cracks are mainly transgranular. The results of polarization and immersion experiments are consistent. The linear corrosion rate in alkaline solution is higher than that in near-neutral solution in immersion test. The corrosion pit of the sample is concentrated in bainite area in near-neutral solution while weak part around inclusions is preferentially corroded and forms large corrosion holes in alkaline solution. Therefore B+F dual-phase X80 pipeline steel is easier to corrode in alkaline soil solution.