The Stress Analysis And Reliability Of Fatigue Calculations Of Boiler Drum In Power Station

The boiler, which is power machinery, is one of the three main machineries in thermal plants. The boiler is a kind of indispensable large industrial equipment, which is used in the heat production and conversion process. Boilers are not only used in the electric power industry, but also used in many industrial sectors. Boilers are widely used and play an important role in the industrial production. And the drum, as the pivot of boiler heating, evaporation and overheating, is the most important part of a boiler. Since the beginning of this century, the rapid development of the electric power industrial makes the peak-valley difference of the power grid bigger and bigger. Meanwhile, the requirements of the tasks about peak shaving which involve large capacity thermal power units are becoming more and more urgent. Therefore, the working conditions of drums, which are caused by the starting and stopping process of the units, become very harsh. Additionally, there are various kinds of defects in the manufacture, use, test, maintenance and etc. So the failure accidents of drums occur constantly. In order to avoid those accidents, boiler drums of power stations should be analyzed. First of all, on the basis of understanding and searching a certain number of data about drum failure accidents, this thesis adopts the "Fault Tree Analysis" method to conduct qualitative and quantitative analysis, which aim to find out the causes of the boiler drum failure of power stations. In this thesis, the minimal cut sets are calculated and the risk factors, which have a significant impact on the safe operation of the drum are determined. Precautionary measures of the boiler drum failure and employment advices are proposed.Secondly, a300MW natural circulation boiler drum of a power plant in Inner Mongolia is taken as the simulation object and the finite element analysis model is established. The data collected in the spot are fitted in function form which will be used as boundary condition of the calculation. The finite element software ANSYS is used to analyze seven unstable working conditions of the boiler drum, which are cold-quick starting, cold starting, hot starting, drum outfire, emergency shutdown, pressure fluctuation and normal shutdown. And then, the transient temperature, transient thermal stress, transient mechanical stress and total stress (by coupling thermal stress and mechanical stress) of those seven wording conditions will be calculated. As a result, the nephogram of the drum temperature field and the stress field varying with time can be obtained which are draw as curves.Thirdly, the calculation results are analyzed in order to find out the maximum temperature difference moment, the location with the highest temperature and the maximum stress position of the drum under various conditions. Then, the differences between thermal stress, mechanical stress and total stress are analyzed. The strength analysis of the drum structure is conducted too.Finally, based on the ANSYS transient analysis calculation results and the design fatigue curve in UK BS5500, the calculation of the low circle fatigue life of the drum is conducted.