Plasma-Deposited Coatings Increase Corrosion Resistance of Steel Free

In the oil and gas industry, key components made of carbon steel (CS) are exposed to severe corrosion environments where high partial pressures of hydrogen sulfide (H₂S), carbon dioxide (CO₂), and chlorine (Cl) exist. To reduce and prevent corrosion to the pipes and other equipment, materials can be made of corrosion resistant alloys (CRAs), including nickel-based superalloys. The cost for materials made of CRAs, however, can be over 20 times more expensive than that for CS components.

Researchers at the Southwest Research Institute (SwRI) (San Antonio, Texas) explored the possibility of applying a CRA coating on CS for protection against the corrosive environment using a physical vapor deposition (PVD) process. UNS N10276 was selected as the coating material and deposited on commonly used UNS G41400 CS coupons using a plasma enhanced magnetron sputter (PEMS) process developed at SwRI, as well as a high power impulse magnetron sputtering (HiPIMS) process. The coating thickness varied from 0.1 to 11 µm. The coated coupons, along with uncoated ones, were then tested under two types of corrosive conditions. One set of tests involved cyclic polarization testing in simulated fracking solution and the other involved the exposure of samples to an autoclave test under high temperature and high pressure with H₂S, CO₂, and Cl for 30 days.

Preliminary results indicate that the baseline UNS G41400 samples (without a UNS N10276 coating) had a corrosion rate of 15.44 mpy (0.392 mm/y) after exposure, and many pits were observed on the samples’ surfaces. The maximum pit depth was 0.71 mils (0.018 mm). In contrast, under the optimal coating conditions, the UNS N10276-coated samples showed the mass loss corrosion rates of <0.5 mpy (0.0127 mm/y), and did not exhibit any pitting. These preliminary results indicate that using a CRA coating on CS can retain the strength of the base metal while greatly improving the corrosion resistance. In CORROSION 2014 paper no. 4147, “Corrosion Properties of Plasma Deposited Corrosion Resistant Alloy Coatings on UNS G41400 Carbon Steel,” by R. Wei, E. Trillo, J. Dante, and K. Coulter, the PEMS process is discussed and detailed corrosion test conditions and corrosion data are presented.

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