在实验室模拟保温层下腐蚀的装置中, 于60~120 ℃对包裹保温层的20钢钢管在质量分数为0.01%~3%的NaCl溶液中分别进行120 h的浸润和浸泡腐蚀试验, 并通过失重法、扫描电镜观察及能谱分析等研究了20钢的保温层下腐蚀行为。结果表明: 随着温度的升高, 20钢的腐蚀速率先增大后减小, 高于100 ℃时在其表面形成致密腐蚀膜, 抑制了腐蚀的进一步发生; 在80 ℃恒温条件下, 随着NaCl溶液浓度的增加, 腐蚀先加剧后减缓; 由于高温下高浓度NaCl溶液在钢表面及保温层间大量结晶, 破坏了原有电化学腐蚀系统中氧含量的平衡, 使腐蚀速率大幅度下降; 干湿交替环境下的腐蚀较冷热交替和恒温环境的腐蚀更为严重。

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.