Abstract Scope |
Water - glycol fluids are used for the hydraulic power control of subsea, downhole valves, and for the preservation of oilfield mechanical parts. These fluids have been designed to provide good compatibility with low-alloy steels and common corrosion-resistant alloys, but their effects on corrosion is unclear after surface diffusion treatments, especially on stainless steel and nickel-based alloys. In this investigation, surface modification by nitrocarburizing is applied on martensitic grade of stainless steels (13Cr, S13Cr and 17-4PH) and Ni-based alloys (935, 925, 718, 625+), with goals to establish the environmental performance of these alloys in clean and seawater-contaminated hydraulic fluids. Crevice corrosion immersion tests and electrochemical polarization technique are complementarily used to measure the environmental performance of these alloys, the effects of the surface treatments, and establish widely accepted yet incompletely documented industry practices. |