Analysis Of Stress And Calculation Of Crack In 300MW Bioler Drum

Along with the increase of electric power plant capacity and the change of power consumption, the peak-valley difference of electrical network increases day by day, a lot of thermoelectricity generator units with high running parameters and large capacity have to take part in changing the loads and even to startup-halt for adjusting the peak output. The diameter and wall thickness of the boiler drum is relative big. During the process of starting or stopping and altering loads, especially under the accident, the pressure rising or dropping and temperature varying will make mechanical and thermal stress of the drum greatly change. The varying of the stress will result in fatigue damage to drum material and shorten the service life of the drum. For this reason, people had paid great attention to this and a lot of research work about drum was carried out. Among these work, the distribution of transient temperature field and stress field, the calculation and prediction of crack propagating are significant to ensure boiler in good condition and safety running.The thesis takes 300MW boiler drum of Zhuzhou Power Plant as object. Based on test data, the multi-disciplinary research across transient temperature field, transient stress field, predicting crack propagating etc was carried out. The thesis mainly carried on the discussion in the followed respects.Firstly, author built a calculating model with drop pipe, end cover of the drum, and calculated the effect by hanging strip and gravity of the drum to the stress field. The model was completed after comparing and analyzing the result of calculation. Then utilized the test data as border condition of the model. The three-dimensional finite element unit was adopted; ANSYS software were used and the transient temperature field, thermal stress, mechanical stress, total stress of the drum were calculated to the model.Secondly, the position of maximum stress of the drum was found out through the analysis of calculating result, some proportionate regulation between mechanical stresses or total stresses and steam pressure also found out. The results were compared synthetically to the different operating mode.Finally, the change of crack strength factors to cracks which have differentlength size in dangerous area was calculate and compared with that it was calculated by use of half oval surface crack formula. The COD method was applied and the critical size of crack was defined according to the fracture toughness of the material by Von misses stress calculated.The innovation in this thesis are as follows:1. The running parameters and test data of the drum during typical and accident operation was used as boundary condition for stress calculating and crack analyzing. Especially accurate measurement to the temperature of drum and considered the change of the water level in the drum were carried on, which have avoided the error owing of the distortion of border condition.2. Adopted the nodal coupling model to calculate the machinery stress and thermal stress of the drum to make sure the effect by the hanging strip for the first time.3. Calculated transient temperature and stress field and varying regularity underchanges load varying and other disturbance.4. Found out the position of maximal total stress and dangerous point in the drum. Calculated the critical size of crack and the yearly crack-propagating value at the point. This is important for periodicity checking and the treatment to cracks appeared in the drum.