Analysis of Corrosion Reasons of 825 Nickel-Based Alloy Hydraulic Control Pipe in a Thermal Recovery Well

An 825 nickel-based alloy hydraulic control pipe of a thermal recovery well experienced corrosion failure after 3 months of operation. The corrosion reasons and mechanism of the failed pipe were studied by analyzing the chemical composition, mechanical properties and microstructure of the pipe and the morphology and composition of the corrosion products. The results show that the outer wall of the 825 nickel-based alloy hydraulic control pipe suffered severe pitting, the corrosion failure was caused by oxygen corrosion and sulfur corrosion, and sulfur was generated by the reaction of downhole H₂S with O₂ in steam injection.