Failure of stainless steel 410S product stripper trays in a petroleum refinery due to ammonium bisulfide corrosion

Trays in the product stripper of an atmospheric residue desulfurization plant failed prematurely after three years of service. This study investigates the failure of the tray made of stainless steel SS 410S. Comprehensive analyses were conducted, including optical and scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), chemical analysis, and hardness testing. SEM and EDS analyses revealed that the tray was covered with a multi-layered corrosion product scale comprising sulfides and oxides of iron and chromium. The outer corrosion product scale layer was composed of iron sulfide, without the participation of chromium, while the inner corrosion product layer contained chromium sulfides. The outer iron sulfide scale layer was relatively porous, whereas the underlying chromium-containing scale layer was more compact. The scale formation due to the corrosion reaction and subsequent scale removal led to significant thinning and perforation of the tray. The chemical composition, microstructural evaluation, and hardness measurements did not reveal any abnormalities in the tray material. The findings of the investigation indicate that the failure of the tray resulted from aggressive ammonium bisulfide corrosion. Recommendations to prevent the recurrence of failure of trays include reducing the contents of ammonium bisulfide in the process environment and upgradation of the material of the tray to a more corrosion-resistant material.