Thermal And Stress Analyses Of A Novel Coated Dual Pipe System With TGO Interface Morphology

In recent years,in order to achieve the national energy-saving and emission-reduction strategic goals,my country’s ultra-supercritical coal-fired power generation technology has increasingly developed in the direction of large capacity,high parameters,high efficiency and low emissions.For a long time,scholars at home and abroad have continuously pursued the further improvement of steam temperature and pressure,and are committed to the development of advanced ultra-supercritical coal-fired power generation technology at 630-700°C.However,the heat-resistant material technology for ultra-supercritical unit structures has become a technical bottleneck restricting the design and construction of advanced ultrasupercritical coal-fired power plants at 630-700°C.In order to break through this technical bottleneck,the traditional P91 heat-resistant steel pipe is covered with a thermal barrier coating made of Yttria-stabilized zirconia(YSZ),and a cooling steam pipe is arranged outside the pipe,designed a new type of coating double tube system.This paper takes a new type of high-efficiency coating double-tube system used in advanced ultra-supercritical power plants as the research object,and analyzes its hightemperature strength under steady-state working conditions.The research mainly uses multidisciplinary theories such as materials science,physics and mechanics.According to the failure mechanism of the thermal barrier coating,the influence of TGO on the temperature and stress distribution of the coating double tube system is analyzed from two aspects: theoretical analysis and finite element simulation..The main contents and conclusions of the research are as follows:(1)Based on the steady-state heat conduction equation of the multilayer cylinder model and the elastic stress and elastic thermal stress equations of the thick-walled cylinder,the heat transfer and stress analytical model of the double-tube system with TGO coating is deduced;it is ideal to use ABAQUS finite element software to establish each interface Flatten the finite element model of the interface coating double-tube system,conduct heat transfer and stress analysis on the finite element model,and compare the results with the analytical solution to verify the correctness of the model.The research results show that the hoop stress has a greater impact on the structural integrity of the system than the radial stress;the maximum Mises stress of the coated double-tube system with or without TGO is significantly different,and TGO has a great impact on the structural integrity of the system;The influence of thermal load on the structural integrity of the system is far greater than mechanical load.(2)Establish a finite element model of the coated double tube system with TGO cosine interface.First,analyze the influence of the cosine interface on the heat transfer and stress distribution of the system;then analyze the finite element simulation considering the effect of creep on the concentrated stress at the system TGO;finally The key parameters of the system(including the thickness of the TC layer,the coefficient of thermal expansion of the TC layer,and the temperature and pressure of the cooling steam)are variables,and their influence on the heat transfer and stress distribution of the system is analyzed.The research results show that during steady-state operation of the coated double-tube system,the hoop stress in the system is much greater than the radial stress;the maximum Mises stress occurs at the TGO/BC cosine interface near the peak of the TGO side,so TGO may cause the coating to fail One of the main reasons;thermal stress has a far greater impact on structural integrity than mechanical load;TC layer thickness and cooling steam temperature are the most sensitive factors leading to stress changes in the coating double tube system;when creep is considered in the TGO layer,TGO/BC The concentrated stress at the interface will be released due to creep.(3)Ignoring the lateral growth of TGO,analyze the stress distribution law of the TGO coating double tube system with gradual morphology under different TGO thicknesses,and the system stress distribution law under a certain TGO thickness and different TGO roughness;respectively take the TGO interface The amplitude,waveform and wavelength are variables,and the influence of the TGO interface morphology on the stress distribution of the coating double tube system is analyzed.Research indicates:In the case of a certain roughness,the maximum stress of the system gradually increases with the increase of the TGO thickness;the thickness of the TGO layer remains unchanged,and the increase of the TGO layer interface roughness leads to an increase in the stress at the TGO/BC interface;compared with TGO Layer thickness and interface roughness have a greater impact on the structural integrity of the system;When the waveform is used as the research variable of the interface morphology,the change of the waveform has less influence on the maximum Mises stress change of the system;when the amplitude is used as the research variable,the greater the amplitude of the interface,the greater the maximum Mises stress of the system;When studying variables,the maximum Mises stress of the system gradually decreases as the wavelength increases.(4)Use Photoshop,CorelDraw,UG,CAD and other image editing and 3D and 2D design software to extract the real interface morphology of TGO from the scanning electron microscope(SEM)photos of the thermal barrier coating,and import it into the finite element software ABAQUS for analysis The stress distribution law of the coating double tube system under the real morphology of TGO.The results show that the coating double tube system with the true morphology of TGO has the same stress distribution law as the coating double tube system with the cosine interface morphology of TGO,that is,the maximum Mises stress of the system is distributed at the convex part of the TGO/BC interface close to the TGO side,The combined effect of the thickness and roughness of the TGO layer causes the Mises maximum stress of the former system to be greater than that of the latter.