The role of passivating film in preventing slurry erosion-corrosion of austenitic stainless steel

Slurry erosion-corrosion tests were conducted on type 304 stainless steel in order to investigate whether the passivating film has any effect of decreasing the damage to the material. Two environments which contrasted with each other were chosen: a slurry consisting of silica sand particles and a 1 % sulfuric acid solution where the passivating film is stable, and a slurry of the same particles and a 5 % hydrochloric acid solution where it is not.As a result, the material was damaged at higher erosion-corrosion rates in the environment where the film was stable than in that in which it was not. Thus, the ability of the film to decrease the damage appeared to be denied. Nevertheless, the anodic polarization curve of the material in the 1 % sulfuric acid solution slurry revealed that the passivating film was mechanically broken by the impact of the particles but it was repaired rapidly enough to inhibit corrosion. Further it was found that in the 5 % hydrochloric acid solution slurry, erosion as well as corrosion was inhibited by chloride ions adsorbed on the surface.Consequently it was concluded that the passivating film has an ability to inhibit erosion-corrosion damage to a certain extent through inhibiting corrosion so long as it is chemically stable in the environment.