Failure Analysis And Risk Assessment Of Furnace Tube In High Voltage Station

With the continuous development of the economy in China, the demand of electric power is also increasing. So the sustainable production and supply of electric power is essential to the development of economy. In our country mainly power source is thermal power, one of the three major equipments of which is power plant boiler. Therefore, sustained and stable operation of power stationboiler is very important to stable and rapid development of economy.But the study shows that unplanned downtime in the power station boiler accounted for over forty percent of the total, due to the boiler tube failure. This deeply troubled Chinese electricity production, as a result we need a simple and efficient method for failure analysis. In the condition of making the power station boiler normal operation, we can find out the cause of failure and avoid the occurrence of similar accidents. And we need a good method to reduce the inspection of the boiler, to reduce boiler accidents and to avoid unnecessary boiler accidents, preventing not occurring.In this paper, the failure of 12Cr1MoV steel superheater tube was deeply understood through the survey and analysis of diagnosis. Finally the main reason for failure of 12Cr1MoV steel superheater tube was found to be the furnace tube material problems. The direct cause of the accident was the oxide layer in the surface of the tube. Then, the heat transfer efficiency of the tube reduced and the heat concentrated. When stress increased in the oxide layer, the tube eventually ruptured because of error material having insufficient strength. According to the reasons of failure and the failure mechanism of superheater tubes, the problems of management of the boiler had been found. The material of the tube exist shoddy phenomenon, and it was not detected before the installation of the tube. At the same time, the dust, existing at the surface of the tube was not discovered and cleaned up, oxide layer formed and operation safety of the tube was affected.After the survey and analysis of diagnosis on the 20 steel water wall tube, it was found that the main reason of the failure of the 20 steel water wall tube is the quality of the water bad. The high content of impurities in the water making a layer of thick scale deposited in the wall and reducing thermal efficiency of the water wall tube. The tube in operation for fire was over temperature, creeping then burst after formation of the diameter in expansion. According to the reasons and the failure mechanism of failure of the water wall tube, it was found that the boiler water treatment that was not qualified, and there were no checks regularly to the water. The water wall tube scale layer became thick gradually, and the rupture final formed when the tube blocking.Using Solidworks flow simulation software to simulate and analysis the tube operating, the temperature and the stress distribution of the tube can be researched, the parts of the tube that is easy to failure was found, for example, at the corner of the tube, at the surface having dust, in the inner wall scaled.Finally, introduce risk-based inspection technology to carry out risk assessment for power plant boiler, explore the method of risk evaluation for boiler tubes using RBI technology. According to the formula:risk=failure probability x failure consequence, define risk, failure probability and failure consequence. At the same time difine the preliminary calculation method of failure consequence and influence factors of failure probability, including the similar equipment failure frequency, the correction coefficient, the evaluation system of correction coefficient and the residual life of the correction coefficient.