Research Of Detection And Characterization Methods For Stress Corrosion Cracking Damage By Acoustic Emission

304 austenitic stainless steel has good corrosion resistance and workability,which is widely used in the petrochemical industry's key equipment.However,the vicious and uncertainties of service environment make 304 stainless steel prone to stress corrosion cracking(SCC).So it is necessary to carry out stress corrosion cracking damage detection research.As a non-destructive technique,acoustic emission can effectively judge the existence of stress corrosion damage,identify the stage of corrosion damage and evaluate the damage status of corrosion,and ensure the safety of the structure.In paper,304 stainless steel as the research object,acoustic emission techniques as a means to carry out stress corrosion damage related research,and experimental research and numerical analysis is used to achieve the 304 stainless steel stress corrosion damage detection and damage type of acoustic emission signal characterization.The main research contents include:(1)304 stainless steel stress corrosion cracking sensitivity researchThe relationship between the concentration of sodium chloride,sulfuric acid and the rate of tension and the sensitivity index are studied by stepwise regression.The experimental design of slow rate tensile test was carried out by uniform experimental design and seven groups of experiments were carried out.The mechanical parameters and the acoustic emission parameters as the sensitivity index respectively,the quantitative relationship model between the two sensitivity index and the influencing factors are established,which could provide guidance for the selection of parameters such as the corrosion solution and the tension rate.(2)Acoustic emission testing and analysis of 304 stainless steel in SCCThe four-point constant strain test and the slow strain rate tensile test are used to simulate the stress corrosion cracking process.The final four-point bending test obtained the pitting corrosion expansion stage and the slow strain rate tensile test obtained the crack initiation stage.Acoustic emission parameters are used to find out the relationship between parameters and stress corrosion process.K-means clustering shows that AE signals in two types of experiments are effectively divided into four categories.According to the characteristics of each type of signal,relationship is established with signal type and stress corrosion damage types,and the acoustic source parameters of each damage mode in stress corrosion process are obtained.(3)Genetic Clustering Algorithm Corrosion Acoustic Emission Signal ProcessingThe traditional K-means clustering has a poor effect on dealing with data with discrete values.Combining genetic algorithm and K-means clustering method,the two experimental acoustic emission signals are further analysis.Data in the four-point constant strain experiment has discrete points,and the clustering effect is superior to the traditional K-means clustering.Two clustering methods are effective for slow rate tensile experimental data and processing results are similar,both effectively obtained stress corrosion damage model and signal parameters between the two methods the same effect.(4)Stress corrosion cracking damage assessmentIn order to determine the state and severity of stress corrosion damage in 304 stainless steel,acoustic emission signal parameters are extracted.The severity of damage was obtained by using damage matrix,and four grades is divided.The damage matrix can be used to obtain the stress corrosion damage state at any time,which can provide references for the structural safety judgment.