Study On Acoustic Emission Detection And Evaluation Method For Welding Cold Cracks Of High Strength Steel

In order to meet the demand of large-scale,lightweight and safe production of petrochemical equipment and promote the development of energy saving and green industry,low alloy high strength steel with good comprehensive performance has been widely used,and the demand is still increasing.In the manufacturing of petrochemical equipment,welding is an indispensable procedure,and the cold crack is easy to appear in the welding structure of low alloy high strength steel.So it is necessary to inspect and evaluate the weld before it is put into production so as to ensure the safety of the equipment and personnel.In this paper,the weld of SPV490 Q low alloy high strength steel plate is studied.According to the characteristics of elastic stress wave release in the process of crack formation and fracture,acoustic emission technology is used to detect the weld.The acoustic emission signals of cold crack are analyzed and evaluated from two aspects of parameters and waveforms.An acoustic emission detection and evaluation method for cold crack of low alloy high strength steel has been established to ensure the weld quality of the pressure equipment and has the engineering application value.The main contents of this paper are as follows:1.According to the formation mechanism of cold crack and the testing methods,the evaluation method of cold crack acoustic emission is studied by using the experimental data of the sloping Y groove,and the test data are applied and verified by the rigid flat test data.2.To describe the change of acoustic emission signals of welding seam,the change of acoustic emission impacting cumulative count statistical parameter with time is used.Analyzing the amplitude time and the impact count time experience chart,the amplitude of the acoustic emission signal and the distribution of the impact count are obtained at the stage of birth and the formation of the crack formation.And these methods are as a sufficient condition for the further judgement of the cold crack.3.Because some acoustic emission parameters have certain correlation when the signal is characterized,the method of principal component analysis is used to simplify the data scale,which can reduce the data dimension,reduce the time of data analysis and improve the efficiency.The support vector machine classifier which is directly based on the acoustic emission signal parameters and the support vector machine classifier based on the principal component are established by using the known sound emission crack signal and the characteristic parameters of the interference signal as the training set.The results show that the recognition efficiency of the support vector machine based on the principal component is better.4.The recursive analysis of the acoustic wave after the wavelet denoising is carried out.The support vector machine classifier based on the recursive parameters of the acoustic emission waveform information and the support vector machine classifier combined with the principal component analysis,recursive analysis and support vector machine technology are respectively established.The results show that the latter has better recognition effect,and the cold crack recognition method based on the acoustic emission waveform information is more accurate than the identification method based on parameter information.5.An acoustic emission detection method and evaluation method for cold crack of SPV490 Q low alloy high strength steel is established.The method is applied to plate rigid restraint test and the effectiveness of the method is proved.