An Investigation On Fretting Wear Mechanism And Prediction Model Of Steam Generator Tube Bundles

The heat transfer tube of pressurized water reactor steam generator is the key component between primary side and secondary side.Due to the flow-induced vibration of the tube bundles,there will be impact and sliding between the heat transfer tubes and the supports,leading to fretting wear of the heat transfer tubes.The tube plugging can happen due to thinning and rupture of fretting wear.This is an important failure reason of steam generator tube bundles,which can cause economic losses up to billions of dollars every year.Although there are many researches on fretting wear of tubes,the mechanism of fretting wear under impact-sliding is still not clear,and the prediction model for this kind of wear is still not perfect.Therefore,fretting wear and prediction model of Inconel 690TT heat transfer tubes in steam generators will be discussed this paper.In order to complete the research of impact-sliding fretting wear at high temperatures and room temperature,the experimental apparatuses of fretting wear in the two conditions were developed and designed in this paper.The device at room temperature can realize the research on fretting wear of heat transfer tube under the condition of simple impact,simple tangential sliding and impact-sliding.High temperature fretting wear experimental device was designed with a high temperature loading system and sealing structure which can solve the loading problem of high temperature two-direction excitation.The device can realize the impact-sliding fretting wear research at 300?.The fretting wear contact parameters between heat transfer tubes and supports were studied by fretting wear experiment at room temperature.Under the condition of different exciting amplitudes and exciting force ratio coefficients R_f,the displacements,contact forces,normal work rate and contact ratio of the tubes have been systematically analyzed.The dimensionless results show that with the change of dimensionless clearance C_r,the dimensionless work rate W_Nrin the form of trefoil hole,circular hole and anti-vibration bars all has peak values,but the positions are different.When the dimensionless clearance C_r>1.0,the dimensionless work rate W_Nr decreases rapidly,which is caused by the rapid drop of contact ratio R_c;when the excitation ratio coefficient R_f<0.4,the increase of work rate of three kinds of supports is not obvious,but when R_f exceeded,the increase trend of W_Nr can be found in all the three supports?By adding friction damping,the spring damping model is optimized and the double damping contact model is proposed.Using this model,numerical calculations were established with Newmark integral and mode superposition method,and the calculation results compared with the experimental results of single span with good accuracy and stability.In the single span numerical calculation,the influence of preload and position bias was studied.The results show that with the increase of preload the contact ratio R_cand the contact force F_impwill increase,but it will cause the decrease of the work rate W_N.The analysis of flow-elastic instability was also carried out under the condition of single span and multi span.The results show that below the critical flow velocity,the contact force and work rate will increase with the increase of clearance C due to the effect of fluid elastic force;the calculation results of U-shaped tube show that the work rate of the anti-vibration bars has obvious different characteristics due to the different load conditions and the asymmetric structure.To study the damage mechanism of impact-sliding wear of Inconel 690TT alloy tube as well as the influence factors such as load and temperature,fretting wear experiments at room temperature and high temperature were carried out in this paper.The results of sliding wear experiment at room temperature show that the distance of sliding is not easy to cause strong delamination,but increasing the normal load tends to induce serious delamination;the characteristics of worn surface and EDX results show that oxidation and wear promotes each other at room temperature;from the changes of microstructure and morphology of profile sub-surface,it can be seen that sliding has greater influence on the direction of grain boundary,while impact plays an important role in the formation of subsurface cracks and the shedding of wear debris layer.The main mechanism of impact-sliding wear in the high temperature steam environment of100??200?is the combination of adhesive wear and abrasive wear.As the temperature rises above 200?,the oxide layer increases the surface strength and plays a protective role.Abrasive wear is restrained,and adhesive wear can be more pronounced.Based on the statistical analysis of contact data,an impact sliding fretting wear model based on energy loss was established which considered the energy loss caused by impact.Through the verification of normal temperature and high temperature wear experiments,better prediction results are obtained under different loads compared with the Archard model.The impact and sliding effects can be found by characterizing the worn samples,and the microscopic explanation of the model is given.The wear depth prediction of anti-vibration bars in different positions of U-tube steam generator were established with the proposed model.The research methods and results in this paper can enrich the experimental data of fretting wear of steam generator tubes,and provide a basis for the numerical calculation.The proposed model provides a new idea for a more comprehensive analysis of fretting wear of heat transfer tubes,and the research results are of great significance for the design,manufacture,operation and maintenance of steam generators.