Effect of applied potentials on the corrosion of X80 pipeline steel in simulated coastal soil solution

Abstract

In order to explore the corrosion mechanism of dual-phase X80 pipeline steel in the coastal soil simulation solution environment, the stress corrosion and electrochemical corrosion behavior of dual-phase X80 pipeline steel under different applied potentials (-750,-900 and -1 050 mV vs. saturated calomel electrode (SCE)) were studied by using polarization curve, slow strain rate tensile test (SSRT) and electrochemical impedance spectroscopy (EIS). The results show that dual-phase X80 pipeline steel is the most sensitive to stress corrosion (SCC) under -1 050 mV potential. SSRT exhibits brittle fracture, with circular or elliptical pits visible on the fracture at the ferrite region. This is due to the diffusion of hydrogen atoms generated by excessive cathodic reaction into the steel and aggregation at the boundaries of ferrite grains. When the hydrogen pressure generated by hydrogen gas precipitation exceeds the material strength, circular pits are generated and become elliptical under tensile stress. Meanwhile, EIS of sample, under-1 050 mV has the smallest simulated resistance, indicatingits worst corrosion resistance. The external potential of-750 mV can provide some electrochemical protection, yet it is not enough to reduce the stress corrosion of dual-phase X80 pipeline steel. The external potential of-900 mV can effectively inhibit the anodic dissolution of X80 pipeline steel. The strength and ductility of X80 pipeline steel after SSRT under-900 mV are both higher than those without external potential, exhibiting ductile fracture characteristics . Its EIS simulationresistances are the highest.Therefore, the optimal cathodic protection potential of dual-phase X80 pipeline steel in simulated coastal soil environment is about -900 mV vs. SCE. The study on the stress corrosion behavior of the dual-phase X80 pipeline steel in the simulated coastal soil environment can provide a theoretical basis for its safe service and provide a reference for corrosion suppression and protection in practical application.

Keywords

• metal materials engineering; dual-phase x80 pipeline steel; applied potential; coastal soil solution; stress corrosion