Low-cycle Fatigue Life Estimation Of Power Plant Boiler Drum And Structure Analysis Of Pressure Piping

Fatigue failure in the power plant boiler drum and pressure piping is the common failure, which caused by fatigue loading and others. On the basis of the experimental studies of low-cycle fatigue, performed on the BHW-35 power plant boiler drum and 12CrMoV pressure piping respectively, the fatigue life evaluation methods are established in this paper. All studies can be concluded as follows.P-S-N curves of BHW-35 steel and of its weld metal are obtained with the total stain controlled low-cycle fatigue test and the probability and statistic method. The relations between the dummy stress amplitude and fatigue life can be easily developed. And then, the BHW-35 steel fatigue design curve can be obtained according with ASME criterion and BS5500 criterion.Compared ~vith the design curves provided by the ASME and BS5500 criterion, the curve got in this paper provides reliable direction for the fatigue design of boiler drum, which used on the altering generating power plant set. Stress concentration measure on the model of boiler drum with two nozzles was executed and the testing results were compared with the ASME criterion, experiential value and the value of finite element method respectively. This measurement result provides direction for evaluation of stress amplitude.With the experiment of surface crack growth of BHW-35 weld metal, the law of the surface crack shape variation when it grows was obtained, and the law of surface crack growth rate was also gotten. These direct the evaluation of the surface crack fatigue growth life and the critical value of its length. On the basis of all these research, the method of low-cycle fatigue life analysis and estimation for 4 lOT/H boiler drum was set up.With the superimpose model, the formula of the stress calculation of the elbows with elliptic section and nonuniform thickness was proposed in this paper. The formula is versified by the experiment of two elbows. The fatigue test of the l2CrMoV steel proved the method of evaluation the fatigue gro~vth life of the elbows suffering internal pressure.The model of exhaustion potential is reviewed and a new exhaustion potential model is suggested. Yang's elastic modulus drop is used to describe damage variable. The proposed model is found to accord with experimental data. These are elementary exploration for the use of damage mechanics on the fatigue life evaluation of the pressure suffering components of boiler such as boiler drum. And then a software system was developed under Visual C-r± environment for evaluation the fatigue life of boiler drum.These stud" can be concluded as following: on the basis of the BHW-35 steel P-S-N curve and its da'dN growth law the method of low-cycle fatigue life evaluation of 401 T/H boiler was proposed. And a mechanics model was suggested for calculating the stress of internal pressure suffering elbow. With the elbow fatigue test, a method of evaluation the fatigue growth life of pressure suffering elbow is recommended; and the elementary use of damage mechanics on the fatigue life evaluation of the boiler drum.