Study On Failure Causes And Prevention Measuares Of Cracked Water Wall Tubes At Power Station Boiler

Boiler waterwall tubes failure is a frequent occurrence in power plants because of prolonged exposure to high temperature, high pressure and aggressive environment. The failure causes of a waterwall tube in a coal-fired boiler of WG220/9.81-13from a thermal power station in the Sinopec Chemical Company were analyzed, which is of great engineering significance.The investigation of cracked boiler tubes included mechanical properties tests, chemical compositions, optical microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) analysis. Analysis revealed that ruptures found in the tubes were caused by serious under-deposit corrosion due to the accumulation of scale deposits on the inner surface of waterwall tube, which led to thinning wall. The scaling resulted in overheating of the tubes and intensified corrosion.The thermal field and flow distribution in the boiler were studied utilizing the numerical simulation software in order to find out the effects of boiler’s operation parameters on the waterwall temperature. The results show that there is a high temperature entrainment zone of flue gas near the burner. With decreasing flow rate of the prime air, high temperature entrainment zone moved to the waterwall tubes and caused the waterwall’s temperature increasement.Finally, many preventive measures were taken to avoid the boiler tube’s frature and ensure the safe operation of boiler.