Corrosion of the inter-stage cooler shell in hydrogen compressors and protective measures

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Corrosion of the inter-stage cooler shell in hydrogen compressors and protective measures: In a chlor-alkali plant owned by a certain company, the material used for the inter-stage coolers in hydrogen compressors was 0Cr18Ni9. The medium involved was H2, with small amounts of impurities such as ammonium chloride (NH4Cl), chlorine gas (Cl2), sulfur dioxide (SO2), and carbon dioxide (CO2). The operating temperature was 140°C, while the operating pressures were 0.7 MPa and 1.6 MPa respectively. After operating for several cycles, corrosion and perforation occurred at the top of the device’s wall, leading to leakage and the shutdown of the entire unit, which resulted in significant economic losses. Analysis: Inspection and testing were conducted on the failed shell of the inter-stage cooler in the hydrogen compressor; it was concluded that the main causes of the failure were pitting (corrosion cavitation) and stress corrosion cracking (SCC) induced by ammonium chloride (NH4Cl) and chlorine gas (Cl2). With the promotion of Cl-, crack propagation-type stress corrosion cracking (SCC) caused by a small amount of hydrogen sulfide (H2S) may also occur. In the cooler, intergranular corrosion still exists due to the dispersed precipitated secondary phases present in the original austenitic structure. The original design of these two coolers used inappropriate materials, as 0Cr18Ni9 (304L) is not resistant to corrosion by boiling ammonium chloride; even 316L stainless steel is susceptible to pitting and stress corrosion. Measure: Dual-phase stainless steel resistant to pitting and stress corrosion should be selected. From a process perspective, it is necessary to minimize the concentration of halide ions in the environment, increase the pH value, and add an appropriate amount of corrosion inhibitor to prevent corrosion caused by the adsorption of chloride ions. By implementing the above measures, corrosion of the shell of the inter-stage cooler in the chlorine compressor section was effectively reduced, ensuring the stable operation of the chemical processing plant.