Developing alternative coatings for repair and restoration of pumps for caustic liquor transportation in the aluminum and nickel industry

Abstract

The damage caused by the combination of corrosion and wear processes on the materials that machine elements are produced causes huge losses in several industries such as mineral processing, chemical, petrochemical and power generation. Some devices that operate in harsh environments, such as centrifugal pumps for transportation of caustic liquor used in the industries of production of aluminum, undergo a rapid deterioration of their materials by the coexistence of corrosion and erosion at temperatures around 75°C. The aim of this work is to study new ways for the corrosive–erosive problems confronted by the aluminum and nickel industries. Several coating materials in powder or wire form applied by GMA welding and HVOF thermal spray techniques are compared in erosion and erosion–corrosion tests. Corrosion tests were performed for comparison. A solution of 1M NaOH was used as a corrosive medium to get the polarization curves The temperature of the electrolyte was 25°C. For pure erosion test, the slurry erosive agent was 4l of water and an erosive particle concentration of 400g/l. Particles of ferric oxide, HRC=40–50 and an average diameter of 600μm, were used as an erosive agent. The impact angle of 90° was tested, with an impact velocity of the abrasive particles of 31m/s. Tests were performed for each condition at a time of 2h at intervals of 20min. The results show that the best performance was that of the mixed stainless steel and cobalt alloys welded coating even though the general resistance to erosive–corrosive wear significantly favors cermets in relation to the other welded deposits.