Corrosion type, reasons and influential factors of the tail heated surface tube of the low carbon steel under the flue gas medium in LNG(Liquefied Natural Gas) power station HRSG(Heat Recovery Steam Generator) were researched through cracks morphology observation, corrosion products analysis, corrosion elements measurement and tube wall temperature field FEM calculation. Results showed that the crack initiated from the outer wall of the tube and propagated toward the inner wall with the arborescent morphology. Intergranular embrittlement ruptured. Rock type feature and secondary crack were observed on the fracture. Mud pattern and polygonal figure of the corrosion products were present. According to these morphology characteristics, the crack was identified as stress corrosion crack, and corrosion type was SCC(Stress Corrosion Cracking). Reasons of SCC were that low feed water or flue gas temperature during a certain period of the unit startup and shutdown for peaking operation brought about the temperature of the outer wall of tube below the flue gas dew point, and the flue gas became dew and corrosion solution emerged on the outer wall of tube. The SCC component was CO2 solution according to the corrosion products. S and Cl elements were found in the outer wall of tube, but their effects on SCC are still needed more researches.
Measurement Method for Organic Halogens and its Application to Flue Gas Monitoring