Method for predicting creep life of power boiler heatproof material

Abstract

The invention discloses a method for predicting the creep life of the refractory steel of the station boiler, which proposes a creeping cavity nucleus model and then further proposes a calculating method of the corrected semidiameter of the critical creeping cavity. The calculating method adopts econometric analysis by microexamination, calculating the semidiameter of the critical creeping cavity according to the change on the core quantity and size of the serial nucleation like the carbide and the occluded foreignsubstance in the whole operational period of high temperature creep of the refractory steel; and then calculating the actual-growing cavity semidiameter according to the change on the core quantity and size of the serial nucleation of the actual fracture specimen (or actual pipe section specimen that are periodically inspected), thus gaining the fracture time by calculation with a good accordance with the practical value.

Description

technical field [0001] The invention belongs to the technical field of material science and engineering application, and relates to a method for predicting the creep life of heat-resistant materials of power plant boilers. Background technique [0002] As we all know, in order to protect the environment, save energy and slow down the tendency of global warming, the development of high-efficiency supercritical, ultra-supercritical steam parameters, and super-large-capacity steam cycle power generation units has become the fundamental way out for the world's electric power development. People have clearly realized that only by increasing the steam parameters can the efficiency of the generator set be effectively improved, and to realize the reliable operation of the generator set under higher steam parameters, it is necessary to research and develop high-temperature heat-resistant materials suitable for high steam parameters . [0003] Heat-resistant ...

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Problems solved by technology

[0007] The linear extrapolation method of the enduring strength isotherm is to obtain the relationship between the short-term stress, fracture time and temperature of the material by increasing the stress and temperature, and then extrapolate the relationship between the long-term stress, fracture time and temperature. The extrapolation method is the basic method for the design of high-temperature components at present, but because the prediction technology is sensitive to the working stress, the relationship between creep life and stress has been questioned. Therefore, there are many deficiencies in the life evaluation of high-temperature components using this technology; The representative of the parameter extrapolation method is the Larson-Miller extrapolation formula, which estimates the long-term creep strength at lower temperatures through creep rupture tests at higher temperatures and lower stresses. This method is used in the design of actual high-temperature components However, it is generally stipulated that the extrapolated life with L-M parameters should be less than 3 times of the longest test point; at the same time, the L-M formula assumes the lack of physical theoretical basis for creep rupture, does not consider stress relaxation and tissue deterioration, and in low stress areas It cannot be extrapolated, the prediction of creep life is relatively conservative, and the extrapolation accuracy is not high enough; in addition, based on the methods related to the creep process, such as: void nucleation and growth, free carbide composition and graphitization, etc. The measurement techniques for the change of phase characteristics mainly include the creep cavity method, M 6 C precipitation rate method and carbide spheroidization rate method, these methods have similar theoretical basis

For example, the creep void method is mainly to establish the relationship between the material creep void damage and creep life. It is generally believed that the long-term creep damage is the intergranular fracture damage caused by the nucleation and growth of voids on the grain boundary. The void fraction corresponds to a certain creep life fraction. Since the diversity of creep void nucleation and the influence of carbides are not comprehensively considered, there is a certain gap between the calculation model and the actual creep fracture microstructure, which cannot be accurate. Prediction of creep life of boiler pipes in power plants makes it impossible to perform relatively accurate life assessment and prediction on the life of high-temperature components, which affects the long-term operation safety of power plants

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