Optimum Surface Roughness of Aluminum Coating to Protect Equipment from Corrosion with Arc Thermal Spray Aluminum Methods

Abstract

Oil and gas production equipment, especially offshore which is often exposed to seawater vapor is susceptible to corrosion on the surface. Aluminum coating can be used to solve this problem. In this study, an Aluminum coating of 200 - 250 μm thickness is produced using arc thermal spray technology, with 95.05% aluminum wire as feedstock and a standoff distance of spraying ~300 mm to make the material corrosion-resistant. The substrate surface coarsening is done by grit blasting technique using abrasive aluminum oxide at 140-280 mm spray distance and 3-6 bar pressure. Observations were carried out in four samples with different surface roughness variations: Surface roughness of substrate about 30-50 μm, Surface roughness of substrate about 60-80 μm, Surface roughness of substrate more than 120 μm, and Surface roughness of the substrate material as it is with no blasting, about 3-27 μm. The adhesion strength of aluminum coating on the non-blasting substrate has the smallest value and fails in a series of tests. Surface roughness of 60-80 μm produces the best adhesion. The adhesion strength is influenced by the mechanical interlocking bond between the coating and the substrate. The rougher surface has a stronger interlocking bond that increases adhesiveness. However, the excessively high surface roughness reduces the bond strength. The adhesion strength of the aluminum coating increases with increasing surface roughness of the substrate to a certain degree of roughness that does not exceed 80 μm. The better the adhesion of the coating, the more protected the material will be from corrosion.