关键词: 20# 碳钢, 2205双相钢, 氯化物, 有机氯, 腐蚀速率, 局部点蚀

Abstract: This study statistically examines 16 domestic and international corrosion failure cases in refineries induced by processing organic chloride-containing crude oil, focusing on affected units, equipment,and root causes. The corrosion behaviors of 20# carbon steel and 2205 duplex stainless steel (DSS) in varying NH₄Cl solutions and wet NH₄Cl salt deposits were investigated via thermodynamic calculations of NH₄Cl environments, mass loss tests, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), as well as characterization by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and 3D optical microscopy. Results indicate that atmospheric-vacuum distillation and hydrogenation units (including reforming pre-hydrogenation systems) are most vulnerable to corrosion during organic chloride crude processing, with heat exchangers and pipelines suffering localized leakage, ammonium salt deposition,and chloride stress corrosion cracking. Water washing mitigates salt deposition but generates a highly corrosive low-pH NH₄Cl environment: the pH of 5 000 mg/L NH₄Cl solution decreases from 5.17 (25°C) to 3.85 (150°C) with rising temperature. 20# carbon steel undergoes uniform corrosion in NH₄Cl solution, with controllable rates at low concentrations (<200 μg/g), but complete corrosion failure under wet salt deposits. 2205 DSS exhibits low general corrosion rates, yet its pitting breakdown potential drops sharply with increasing NH₄Cl concentration; EDS analysis confirms preferential corrosion of the austenite phase. Sulfides inhibit chloride corrosion: They promote protective film formation on carbon steel to reduce corrosion rates, and decrease pitting sensitivity of 2205 DSS.

Key words: 20# carbon steel, 2205 duplex stainless steel, chloride, organic chloride, corrosion rate, localized pitting corrosion