The erosion–corrosion behaviour of high velocity oxy-fuel (HVOF) thermally sprayed inconel-625 coatings on different metallic surfaces

The minimization of cost and the enhancement of reliability of rotating and stationary fluid machinery equipment that are subjected to highly erosive and corrosive environments is mandatory in the oil and gas production industries. This can be achieved by minimizing the material damage resulting from the combination of solid particle impingement and corrosion. The high velocity oxy-fuel (HVOF) process is one method of producing metallic coatings to protect metallic surfaces from high temperature, wear, and corrosive environments. Stainless steel components coated with Inconel-625 are very common in the oil/gas industry. In this study, the erosion–corrosion characteristics of HVOF thermally sprayed Inconel-625 powder coatings were evaluated when applied on three different metallic surfaces: (a) plain stainless steel (SS), (b) spot-welded stainless steel (SW-SS), and (c) a composite surface of stainless steel and carbon steel welded together (C-SS-CS). These coated surfaces were tested in a jet impingement rig under two fluid conditions: (i) free from added solids, (ii) containing 1% silica sand. Weight loss measurements were used to provide a measure of the amount of material loss that each coated surface experienced, and the influence of time during impingement testing was taken into consideration. The surface morphology and the elemental composition of the coating before and after the erosion–corrosion test were examined using the SEM and EDS techniques. The results indicated that the coating over both spot-welded and plain stainless steel surfaces exhibited a similar degree of weight loss. However, the coating on the composite surface experienced a greater degree of weight loss. Microscopic observations of the fracture surfaces showed that the metal removal of the tested surface was concentrated around the unmelted and the semi-melted particles of the deposit.