Failure Analysis on Fracture of the Water-Cooling Wall Tube in a Thermal Power Plant

By means of macroscopic examination, chemical composition analysis, mechanical property test, metallographic examination, fracture SEM analysis and so on, the fracture reasons of the water-cooling wall tube in a thermal power plant were analyzed. The results show that the fracture of the water-cooling wall tube was caused by the propagation of the fatigue cracks which initiated from the defect of the weld seam between the pipe and the fin. The cracks propagated along the side facing fire and the side unexposed to fire, and eventually resulted in transversal fracture of the tube perpendicular to the tube axis. The higher hardness of the weld seam and presence of incomplete fusion defect were the internal causes for the fracture failure. Constant start-up and shut-down and too frequent load fluctuation were the external causes for the fracture failure.