Research On Thermal Fatigue Testing Method And Prediction Model Of Life Based On The Pipe Of Nuclear Power

Thermal fatigue phenomenon widely exists in the high temperature equipment,power mechanical devices and large scale integrated circuit. For example, nuclear powerplant pipes are subjected to cyclic temperature load of fluid boundary layer. It is easy forthe device to generate thermal fatigue crack due to the effect recently. And this results indamages of the pipeline and cause huge accidents. Consequently, it is so critical for thepipeline of nuclear power to analyze the crack which is generated because of thermalfatigue. The life prediction model of thermal fatigue is built through the research on thethermal fatigue of pipeline. And the pipes of nuclear power plant are analyzed directly.The using life of pipes is assigned. The components and parts will be maintenance andfixed in time. And nuclear power plant runs safely.The crucial device—U-type pipe in steam generator of nuclear power plant—is thetarget of research in this thesis. The U-type pipe of steam generator which belongs toNo.1looper is subjected to different temperature load coming from the fluid inside andoutside the tube. The thermal stress concentrates firstly on the U pipe. And this becomesthe basis of research on U-type pipe. In order to study the working process and damagemechanism, one thermal fatigue testing machine is designed according to the workingcircumstances of U-type pipe. The temperature load is totally simulated as well as on theU-type pipe. And the heating and cooling system are automatically accomplished byusing the relay controlling circuit. Specimen is heated and cooled following the timewhich is set before. The sensing line is trapped around the middle of specimen, and thespecimen is heated as the temperature. During the cooling process, the cooling water ispurred into the center hole of specimen. Temperature is uniformity and water does notsplash. Four specimens are placed around the bracket. Because two ends of specimen arerestrained, the direct relationship between cyclic life and thermal stress is built upprecisely. The testing machine is not only applied to the U-type pipe, but also thedifferent temperature cyclic load and different materials. It will be widely used for the accurate testing method and small shape. The testing data of huge device can be got byusing this testing machine, and it will be popular among the labs. The stress of thespecimen is simulated by using simulation software in this thesis. It is concluded that thetemperature and stress field are changing as the time pasts during the testing process. Thecyclic temperature amplitude and average temperature are considered into the lifeprediction in this thesis. And the effect of length of crack which is significant to predict istook into consideration. Consequently, the model of thermal fatigue life prediction isgained by taking those factors. It is clearer and more intuitive to predict life of thermalfatigue. And this leads to more precise results of thermal fatigue life prediction in thispaper.