Analysis on Leakage Reasons of Buried Pipes in a Circulating Fluidized Bed Boiler

Means such as macro examination, chemical composition analysis, metallographic analysis, hardness test, fracture analysis and XRD analysis were used to analyze the leakage reasons of the buried pipes in a circulating fluidized bed boiler after use of 1.1×10⁴ h. The results show that the limescale layer at lower curved section was very thick, which caused long-time overheating of outer wall of the buried pipes. So pearlite spheroidization and decarburization phenomenon occurred, and the strength and hardness of the pipe wall seriously decreased. At the same time, the medium in the hearth had larger flushing action to outer wall of the buried pipes at the lower curved section, which accelerated the wall thickness thinning rate here. The above reasons led to the early leakage failure of the buried pipes at the lower curved section.