Corrosion Behavior of 20 Steel under Insulation in Different Simulation Conditions

Infiltration and immersion tests were carried out for 20 steel tube in 0.01wt%-3wt% NaCl solution at temperature range of 60-120 ℃ for 120 h in a experimental simulation device of corrosion under insulation (CUI). Corrosion behavior of the steel was analyzed by scanning electron microscopy, energy dispersive spectrometer and weight loss method. The results show that CUI rate of the 20 steel increased first and then decreased with increasing the temperature, the dense corrosion film formed on the steel surface above 100 ℃ which inhibited the further corrosion. CUI rate of 20 steel increased first and then decreased with increasing the NaCl concentration under 80 ℃ constant temperature condition. It was due to the effect of high temperature and the crystallization of high concentration NaCl solution between metal surface and insulation layer, leading to the oxygen concentration balance destruction in the original electrochemical corrosion system and finally decreasing the corrosivity in CUI system. Corrosion of 20 steel in dry-wet environment was more serious than those in hot-cold and constant temperature environment.