The Influence of Microstructures on the Corrosion Properties of X80 Pipeline Steel in Near-Neutral pH Soil

The influence of microstructures with different heat treatments on corrosion properties of X80 pipeline steel was investigated in near-neutral pH soil using electrochemical measurement and surface analysis(SEM, EDS and XRD). The results showed that the microstructure of X80 steel affected the properties of corrosion product layers. Generally, X80 steels with heat treatments had a higher corrosion rate than the as-received steel. The increase of pearlite content enhanced the corrosion of ferrite through a galvanic effect. The appearance of upper bainite and martenite increased further the activity of the steel. The corrosion product layer formed on as-received X80 steel was compact and complete, provided an effective protection to the underneath steel. However, the corrosion product layers on the heat-treated X80 steels were generally inhomogeneous, loose, porous and defective, and provided minor protectiveness. The cathodic/anodic reactions of X80 steel are dominated by the oxygen reduction and formation of iron oxides that deposit on the steel surface which was through a physical block effect to afford the protection.