Study On The Application Of Residual Stress Measurement In Ultra Supercritical Boiler Water Wall Tubes

Ultra supercritical boiler has a vast space for development in thermal power plant.However, there are few relevant studies on manufacturing, operating and safety inspectiontechnique in our country. The incidents like cracking and explosion, which happened to thewater wall tubes, seriously affect the safe operation of ultra supercritical boiler. The residualstress produced during the manufacture and installation process has a significant impact onthe performance, structural strength, fatigue strength and resistance of stress corrosion.However, there are few of studies of the residual stress test for the tube with small diameterlike water wall tube. Therefore, the further study of residual stress test is very important forboiler quality and possible failure, and maintaining the safe operation of boiler.Residual stress with blind-hole method is composed by two parts: test of the strainrelease after drilling, and calibration of strain release coefficients. Therefore, taking the ultrasupercritical boiler water wall tubes of an thermal power plant as objectives, the followingresearch works are undertaken.First, finite element analysis with ANSYS software are carried out. The simulationcalibration results show that the absolute value of strain release coefficients increase with thestress level when the stress exceeds a certain value, and plastic deformation is then modifiedby using the energy parameter S. What’s more, the formula is derived which may calculate thestrain release coefficients for curved faces test by plane calibration results and curvature, sothat the application range of blind-hole method is expanded.Secondly, through the practical application of residual stress test for water wall tubes, acompleted test scheme is summarized, including the water wall field test method, calibratingexperiment method of strain release coefficients using the complete tube, and relevant erroranalysis and correction method. It shows that the calibrating experiment results agree wellwith the simulation calibration results within an error of7%, which means the method hashigh practical value.Finally, the analysis on residual stress test results shows that, the dominant residualstress of the water wall tubes is compressive stress, and20%of which is lower than-250MPa.It can determine that high residual stress level is one of the main causes of the cracking in thewater wall tubes, and measures should be taken to reduce the residual stress level of waterwall tubes and for reliable operation of boiler.