Stress Analysis Of Crack Failures Of Down-fired Supercritical Boiler Water Wall

In recent years,problems of water wall deformation,crack and accident of water wall leakage have happened frequently in the down-fired supercritical boilers of BWBC,which is a serious hazard to the safety and stable of boiler operation and the production and operation of the power plant.Therefore,make a full investigation of the accident and make stress analysis of the water wall is necessary and helpful to provide effective advice and treatment for the existing problems and design optimization for follow-up projects.At the same time,it is beneficial to improve the product quality and update the technology of W flame boiler of Babcock & Wilcox Beijing company.The research background of this thesis is the frequent splitting and transformation of the three supercritical W flame boiler water wall of BWBC.Taking the No.2 boiler of C project,No.1 boiler of B project and No.2 boiler of D project as the main research objects,the expansion data during the shutdown and start process of boilers,deflection of buckstay,DCS data and the load of constant spring hanger on the furnace arch are collected.By study these data,the factors that may cause the increase of the stress of the water wall of the boiler are found.In order to study the influence of temperature distribution and deformation of buckstay on the stress level of water wall,with the finite element method,tube-bar models of the furnace are built.Data of water wall temperature and buckstay deformation are put into the finite element calculations as boundary conditions.Results show that in the selection of the water wall temperature measurement range,the temperature distribution will cause a stress value of 268 MPa on the water wall,which has exceeded the material yield limit.The uneven of temperature distribution is one of the main reasons of the crack of water wall.Results also show that the deformation of buckstay in project C will cause a stress value of 70 MPa on water wall.This proves that the deformation of buckstay is not the main reason of the crack,but it will cause the deformation of the water wall.The reason of the deformation of buckstay comes from the temperature difference between inside and outside flange and invalid of the post.In the study of the stress level effect on the water wall by furnace arch hanger,strain measurement technique is used to measure the load of the rod in cold and hot condition.Then a shell model is build.Through the analysis of the measurement data,combined with the finite element,the paper points out the design defect of hanging on furnace arch of A,B,C project.By comparison of calculation results from combination of different load conditions and hanger design conditions,suggestions of hanger design on down-fired supercritical boiler furnace arch are given.The new design can effectively reduce the stress level of the water wall and reduce the risk of fatigue damage in the normal operating conditions and most of the running time of the boiler.Through the summary of the analysis,suggestions to avoid water wall crack and to reduce the water wall deformation are given.