Cause Analysis and Treatment Measures of Water Cooling Wall Pipe Leakage in a Power Station Boiler

The water-cooled wall pipe of a boiler in a power station leaked several times during the operation. The reasons for the leakage were analyzed by chemical composition analysis, microstructure observation, hardness testing and other methods. The results showed that the chemical composition and hardness of the failed pipe met the standard requirements, the microstructure was ferrite + pearlite, and the pearlite was slightly spheroidized. The leak points were located at multiple transverse cracks in the same pipe, and the cracks started near the spiral at the middle of the inner wall on the fire side. There was a scale layer on the inner wall of the water wall, and the furnace water was concentrated under the iron oxide scale and in the spiral gap, where the dissolved oxygen and the medium concentration increased sharply, resulting in electrochemical corrosion. The pipe wall on the fire side beared a large alternating thermal stress, and under the action of thermal fatigue load, cracks expanded at the corrosion defects of the inner wall, and the cracks passed through the combined action of fatigue and corrosion until they leaked.