Synergy effect of naphthenic acid corrosion and sulfur corrosion in crude oil distillation unit

► The corrosion of a carbon-manganese steel and a stainless steel in sulfur and/or naphthenic acid media was investigated. ► The corrosion rate of the carbon-manganese steel increased with the increase of the acid value and sulfur content. ► The critical values of the concentration of sulfur and acid for corrosion rate of the stainless steel were ascertained respectively. ► The stainless steel is superior to the carbon-manganese steel in corrosion resistance because of the presence of stable Cr5S8 phases.