The corrosion resistance of various coatings, surface treatments (from different nitriding processes), and sintered carbides (among traditional and new commercial grades) has been evaluated in highly sour environments and benchmarked against corrosion-resistant alloys. The laboratory testing consisted of series of 4,000 psi (20.6 MPa) autoclave tests with 1500 psi (10.3 MPa) hydrogen sulfide (H2S), temperatures up to 375°F (191°C), and exposures of 15 and 30 days. Corrosion was described both qualitatively (e.g., discoloration, pitting, spalling, corrosion byproducts) and quantitatively (i.e., with average weight-loss corrosion rates). For sintered carbides, crevice corrosion was also investigated to replicate the corrosion over stagnant sealing surfaces. Overall, this investigation establishes that (1) nitriding surface treatments are highly unequal and do not corrode more than well-established coatings currently in use, (2) certain coatings can be highly protective, especially when applied onto alloy substrates that are H2S weight-loss corrosion resistant, (3) carbide grades are less susceptible to weightloss corrosion despite major variations in performance. Through series of complementary tests, this investigation also concludes that some of the current materials technologies appear to remain fit-forservice for highly sour environments.
Key words: corrosion, nitriding, plating, spalling, tungsten carbide, hydrogen sulfide