| At present,austenitic stainless steel has been widely applied into a plenty of special fields owning to the outstanding advantages in its property.However,the reliability and lifespan of operating devices are directly influenced by the welding quality in its weld zone.In addition,the technique of ultrasonic phased array has been widely applied into detection of austenitic stainless steel weld for its excellent beam deflection and focusing performance.Nevertheless,owning to the fact that there exits numerous setting conditions about detection parameters and the detection process is so complicated that the detection rate of defect can be greatly affected..Therefore,in this paper,related experimental researches were conducted on the defects in depth of 10mm-50 mm in austenitic stainless steel weld with thick wall.Besides,a quantitative analysis on its detection rate was carried out by POD as well.The main tasks accomplished by this paper are as followed.(1)To compare the focusing effect of adjustable probes parameters in actual detection,the acoustic simulation model of linear array probe is established by Matlab software.Moreover,the influence of various frequencies and array elements on beam performance and focusing effect is researched by utilizing accumulative sound intensity of beam in Y-axis direction.(2)The microstructure differences in separate regions of customized austenitic weld specimen are analyzed by metallographic tests.Besides,by comparing the ultrasonic phased array detection results,the influence of microstructure in weld zone on propagation rule of ultrasonic wave is studied.The results show that the grain size in weld zone is thick,where the grain is complicated in structure with an obvious behavior of anisotropy.Additionally,it is found by experiments that at the same depth,the gain value in weld zone is about 10 dB greater than that of the one in base-material zone,with a gap of 17.8db at most and 10.3db at least at the same depth.Hence,it can be obtained that there exist a severe attenuation effect on the propagation of ultrasonic wave in weld zone.(3)The detection effect of varied defects are compared by setting differentdetecting parameters of ultrasonic phased array detector.Besides,the echo wave signal detected in varied depth in weld zone is post-processed by matching pursuit method.It is revealed by the results that for defect detection in weld zone,the detection effect gets better by adopting the mode of longitudinal wave,low frequency and multiple array elements.What's more,by matching pursuit method,not only can the noise signal be restrained effectively,but also the SNR of defect signal gets improved.Besides,the noise signal which was annihilated at 50 mm depth can be extracted,which reinforcing the defect information without missing the detection of defects.(4)Probability of detection(POD)is selected to serve as the index to quantitatively assess the influence of various factors on detection rate.Next,by utilizing the POD model based on signal response data,the varied factors that influence the detection rate of ultrasonic phased array detection are investigated from aspects of probe frequency,array element,detection material and defect size and so on.The results indicate that the defect detection capacity enhances with the increase of array elements and defect sizes.While,the defect detection capacity decreases with the increase of probe frequency and structural noise of detection material. |
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