Resistance of Thermal Spray coatings in Cour Environments: A Comparison of Tungsten Carbide, Chromium Cardbide and Inconel 625

An important problem for the petrochemical industry is the behaviour of materials in aggressive environments, when hydrogen sulphide, carbon dioxide and sand, which contribute to corrosionerosion of the surface, are present.

Generally, the use of hard materials such as thermal sprayed tungsten carbide and chromium carbide reduces this problem, in particular from the point of view of erosion.

Therefore it is very important to identify a correct procedure to determine the actual behaviour of thermal spray coatings in sour environments, defined as fluids containing water as a liquid and hydrogen sulphide (H2S), and in which carbon dioxide (CO2) gas is also present.

This paper presents a proposed procedure to test coated samples in sour environments by immersion in acidified sodium chloride solution saturated with hydrogen sulphide and carbon dioxide at ambient pressure and temperature. The method is based on the determination of the weight loss and surface damages of the sample.

The comparison of the behaviour in sour environments of HVOF (High Velocity Oxygen Fuel) sprayed tungsten carbide cobalt-chromium based, chromium carbide nickel-chromium based and Inconel 625 is considered. The results of these tests have shown that the materials considered kept for 720 h in the conditions described above did not suffer serious damage.