Abstract: A 12Cr1MoV steel pipe of the low temperature reheater in a circulating fluidized bed boiler of a power plant in Xinjiang suffered from perforation and leakage. Through macroscopic and microscopic morphology observation, chemical composition analysis, microstructure observation, energy spectrum analysis, X-ray diffraction, and hardness testing, and in combination with the actual working conditions on site, the failure cause of the low temperature reheater steel pipe was analyzed. The results show that the failure pipe was perforated due to the accumulation of the contamination layer on the outer wall, causing pitting corrosion. The metal high temperature chlorides generated from the chlorine in the coal during combustion reacted with the black oxide film area on the outer wall, triggering "chlorine cycle and active oxidation". The dense protective film of Cr₂O₃ formed in the initial stage of the reaction was continuously destroyed and peeled off and was difficult to form again in the hot corrosion environment, ultimately leading to accelerated corrosion and perforation failure of the failure pipe.