Sulphur-induced corrosion in Duplex stainless steel: A case study in a petroleum refinery

From the introduction of its first-generation, Duplex (austeno-fenitic) steel has seen a steady increase in popularity [1]. Recently, the production of highstrength, corrosion resistant super-duplex coil hasbeen implemented in several applications. The case study we present in this paper concerns its use in a set of tubes of a heat exchanger affected by corrosion. The tubes material, S31803 Duplex stainless steel, is particularly suited to applications where corrosion is likely due to chlorides and/or sulphides being present. The heat exchanger operates in a chloride environment due to marine water on the inner side while the outer side is in contact with a hydrocarbon mixture rich in sulphur. It also has high resistance to general, pitting, crevice and erosion corrosion and to corrosion fatigue. The aim of our study is to understand the corrosion mechanism occurring and the factors responsible (e.g. the presence of chlorides, sulphides etc.) using several techniques for the experimental characterisation of the materials including optical microscopy and SEM (scanning electron micrography).