Research On High Temperature Corrosion And Method Of Residual Life Evaluation For T92 Steel Used In Superheater Tube Of Ultra Supercritical Boiler

With the continuous emphasis on environmental protection in our country,the ultra supercritical boiler with high efficiency and energy saving are being widely promoted.The operating parameters of ultra supercritical boiler are further improved and higher requirements for heat-resistant steel used in superheater tubes are also put forward.The high temperature corrosion resistance is an important safety index for the heat-resistant steel used in the thermal power boiler.In the complex high temperature corrosion environment,the heat-resistant steel should also have excellent high temperature strength and long service life.As the typical representative of the“third generation of martensitic heat-resistant steel”,T92 steel has quickly become preferred material on superheater tubes of ultra supercritical boiler from 2006 for its excellent performance and low prices.In order to better master the high temperature corrosion behavior of T92 steel used in superheater tube of ultra supercritical boiler and evaluate its residual life,T92 steel was chosen as the research object in this paper.Three aspects were studied by the methods of experimental research,theoretical analysis and numerical simulation:high temperature corrosion behavior of flue gas,high temperature corrosion behavior of steam side and the influence of the high temperature corrosion on the tube wall temperature,stress and the residual operating life.1.The high temperature corrosion behavior of T92 steel coated with mixed sulfate medium at 650℃and 700℃under different stress conditions was respectively examined by means of XRD,SEM,EPMA,EDS and kinetic curve of weighing.The results indicated that temperature had a significant effect on the high temperature corrosion of T92 steel.The effect of force allowed the development of defects on the surface of the sample and accelerated the corrosion of the matrix.The surface corrosion products were mainly composed of compound sulfates,Fe₂O₃ and chromate,and the mixed sulfates evaporated violently under the effect of high temperature.2.The corrosion behavior of T92 steel under different stress conditions in high temperature steam at 600°C and 650°C was studied by analytical methods of SEM and EDS.The results indicated that the corrosion process was mainly the diffusion process of O into the matrix.The corrosion layer products produced by the reaction were mainly the oxides formed by Fe,Cr and O.The temperature had a significant effect on the growth of oxide layer.The existence of stress promoted the development of the crack and increased the probability of oxide skin shedding.3.The relationship between the thickness of the oxide layer and the operating time of T92steel and the relationship between the thickness of the oxide layer and the tube wall temperature and stress were derived by theoretical analysis and numerical simulation.The C value of the Larson-Miller formula for T92 steel was calculated;based on the Larson-Miller formula,the tube wall temperature and stress variation law and the cumulative creep damage method,the residual life evaluation method of superheater tube was put forward.The residual life of T92steel superheater tube in a power plant was evaluated.Finally,based on the shedding characteristics of the oxide skin,the critical temperature change rate of T92 steel oxide skin was calculated,and operational management suggestions were proposed to provide reference for optimizing units operation and increasing service life.