低碳钢在LNG电站烟气介质下的应力腐蚀原因分析

Reason analysis for corrosion of low carbon steel in flue gas from an LNG power plant

某液化天然气电站余热锅炉尾部受热面发生多次腐蚀泄漏。通过裂纹形貌观察、腐蚀产物分析、腐蚀性元素测量和管壁温度有限元计算等表明,裂纹具有典型应力腐蚀(SCC)形貌特征,腐蚀类型为沿晶SCC。导致SCC的原因是,机组调峰运行启停过程中的某些时段给水或烟气温度较低,使管外壁温度低于烟气露点从而导致烟气结露,形成SCC液态环境。SCC腐蚀的主导组分是CO2水溶液。

Leakage occurred many times at the tail heated tubes in heat recovery steam generator （HRSG）of a power plant.Thus,much analysis were performed,such as crack morphology obser-vation,corrosion product analysis,corrosive element measurement and tube wall temperature field FEM calculation.The results show that,the cracks have the stress corrosion cracking （SCC） characteristics and the corrosion type is intergranular fracture SCC.During a certain period of unit startup and shutdown for peaking operation,the low temperature of feed water or flue gas causes the tube outer wall temperature decreases to lower than the flue gas dew point,so the flue gas dews and the SCC solution emerges on outer wall of the tube.The CO2 solution is considered as the dominant component resulting in SCC.