The Study Of Thermal Fatigue Damage And Life Forecast Of Heat Exchange Pipes In Nuclear Power Station

Since entering the new century，Chinese national economy is developing quickly, thequantity demanded of the energy is growing day and day. It produces a lot of flue gas andpollutes the environment severely, when using the coal and other fossil fuel to generateelectricity. The nuclear power is being paid more and more attentions because of non-pollution,high safety factor and convenient distribution. However the heat exchanging pipes in thenuclear power station are always generating thermal fatigue damage, which has become thepotential safety hazard of the nuclear power station. The damages are caused by the mixture ofthe low-temperature water and high-temperature water in the pipes that makes the temperatureof the pipe internal surface changing periodically.The thermal fatigue phenomenon is complex and has a lot of influence factors. There isno theory which can evaluate the thermal fatigue quantificationally and accurately. So theexperimental study is very important. Simulate the periodic change of the temperature fieldaccurately, establish the temperature field and stress field in the interior of the samples andconsequently, simulate the initiation of the thermal fatigue crack and developing processaccurately, by means of establishing a set of reasonable testing apparatus. The thermal fatiguetest can provide relational dates for the manufacturing technique and thermal fatigue lifeforecasting of the samples, changing the structure and the choice of material.On this task, design a kind of thermal fatigue testing apparatus with external constraintswhich can make the temperature of the samples change periodically and restrain all theconstraints. This testing apparatus makes up by samples, heating system, cooling system,control system, temperature measurement system and pedestal. The samples are cavitycylinder with thin-wall, which can conform to the actual working conditions of the heatexchanging pipes and are installed on the pedestal by the round nuts. The heating system iscentral assembly unit and uses electromagnetic induction heating way to heat the samples. Thecooling system uses forced water cooling way. The heating time and cooling time are operatedby the control system.This paper bases on the electro-magnetic induction theory and discuses the relevantparameters of the induction coil and the relevant parameters of the electrical power generating system to the influence of the temperature field by the software of finite element analysis. Anduse the testing apparatus to verify the temperature field obtained by the finite element analysis.Therefore, get the data of thermal fatigue circulation life, thermal fatigue crack initiation andextending length. Take advantage of the mechanics of fracture theory and base on the Parisformula to obtain the prediction model of the residual life of the endurance crack propagationat the same time.By the experimental verification, the heating system of the testing apparatus iscompletely in conformity with the requirement of the thermal fatigue test and can generatehomogeneous one-dimensional temperature field on the samples, insuring the reliability of thetest results. Establish the prediction model of the residual life of the endurance crackpropagation of the heat exchanging pipes which can understand thermal fatigue life in depth. Itis convenient to maintain components and parts and insures the safe operation of the reactor inthe nuclear power plant.