Study on the Synergistic Effect of Several Sulfur Compounds to the Corrosion Attack of Copper in Liquefied Petroleum Gas

During the process of liquefied petroleum gas (LPG) exploitation, various sulfide-containing gases are produced, which significantly bring about corrosion attacks to copper equipment and facilities. Investigations on the effects of sulfides, hydrogen sulfide (H2S), carbonyl sulfide (COS), and ethanethiol (C2H6S) on copper corrosion and synergistic mechanisms are of great significance for LPG production. This paper studied the synergistic corrosion effects of mixed sulfide-containing gases in LPG on copper plates, including the influence of H2S + COS, H2S + C2H6S, as well as H2S + COS + C2H6S. The results showed that there exists an apparent synergistic effect between different sulfide-containing gases, which decreased the critical point of corrosion and enhanced the severity of copper corrosion. SEM observation on corrosion products with the addition of different sulfide-containing gases demonstrated that the microstructures of corrosion products are significantly different, which reveals different corrosion mechanisms. By characterizing the corrosion products on copper surfaces, corresponding corrosion mechanisms were proposed. Individual H2S reacts with copper directly as chemical corrosion. The presence of water leads to the dissolution of H2S into water film at the copper surface and results in electrochemical corrosion in nature. COS tends to decompose into acidic gas H2S and CO2, which accelerates the electrochemical corrosion at the copper surface. C2H6S can react with copper directly as chemical corrosion. A mixture of different sulfur-containing gases enhanced the corrosion attack by synergistic effect.