Corrosion Mechanism of a Drill Pipe

A high temperature and pressure autoclave was used to simulate the drill pipe corrosion in situ field environment of Tarim oil field. The corrosion products and corrosion mechanisms of S135 drill pipe working in lignosulfonate mud were studied. The corrosion product film on the outside of the drill pipe was analyzed by XRD and SEM. The results showed that localized oxidation corrosion occurred on S135 drill pipe, the features were the ulcer-like corrosion, localized contiguous corrosion and pit corrosion. The main corrosion products were orthorhombic crystal system′s allcharite. The corrosion took place while the drill pipe standed on the derrick, where moisture in the mud cake clinging to the outside of drill pipe volatilized to the air and produced iron hematite, barite, bentonite powders and calcium powders. Three kinds of interrelated localized corrosion induding differential oxygen concentration corrosion, bimetallic corrosion and crevice corrosion occured.