ANALYSIS OF THE REASONS FOR THE LEAKAGE OF A BOILER WATER-WALL TUBE IN A POWER PLANT

In the present research, the leakage causes of a boiler water-wall tube, with an outside diameter of 60 mm and a thickness of 6.75 mm, that transmits the water medium have been studied. Leakage occurred on the fire-facing side of the tube and close to the boiler. Various techniques including visual inspection, chemical composition analysis. Vickers hardness test, tube wall thickness measurements, mechanical performance testing, optical microscopy and energy-dispersive spectroscopy were carried out to verify the probable cause of failure. Deposits formed on the inner wall of the tube, which caused local heat-transfer performance of the tube to decrease, formed an overheating characteristic in the microstructure. and softened the tube wall and made the tube wall thinner near the leakage points. The softening of the tube wall reduces the measured hardness at the edge of the leakage point. In addition, due to the localized wall thinning and softening, the tube cannot withstand the stress flowing liquids and gases. with the result that the tube was bulging and deforming. Local overheating caused the degeneration of the initial ferrite-pearlite microstructure. In the microstructure near the leakage point of the water-wall tube, carbides were spheroidized and coalesced. According to the investigation, it was concluded that the local heat-transfer performance of the water-wall tube decreased and the tube performance deteriorated due to the deposits formed on the inner surface. The combination of localized overheating and tube wall thinning led to the tube's premature bulging and failure while running.