Corrosion failure analysis of stainless steel components for maleic anhydride plant

Failures of a flowmeter floater and a spherical valve installed at a pipe transporting maleic acid aqueous solution in a maleic anhydride plant were investigated by means of macroscopic and microscopic examinations, chemical composition analysis, and weight loss tests. The investigation results indicated that the components were made of AISI type 316L stainless steel. The damages of both the floater and the inner surface of the valve were caused by an extensive erosion–corrosion in maleic acid aqueous solution contaminated with sulphuric acid and chlorides, which originated from the feed blending coking benzene and the recycled process water, while that of the back surface of the floater as well as the outer surface of the valve was induced by general and pitting corrosion as a result of formation of a stagnation zone where the acidic chloride-containing solution collected. It was recommended to use a dechlorination device by resin adsorption technique for reducing the content of chloride ions in the maleic acid aqueous solution.