The Detection Of Deep Weld Defects Of Austenitic Stainless Steel Based On Ultrasonic Phased Arrays

Centrifugal casting austenitic stainless steel (CCASS) has been widely usedin today’s nuclear power and some of the chemical industry. Such welds have thecharacteristics with tissue Inhomogeneity, coarse, and apparent anisotropy. Itstraditional testing procedures cumbersome, slow, have long cycles, and have poordetect results, difficult to meet the rapid development of modern industry demand fornon-destructive testing. It is still a worldwide problem that researches an appropriatemethod to detect the CCASS weld defects.With the rapid development of ultrasonic phased arrays technology in recentyears, the studies of detect the CCASS weld defects using ultrasonic phased arraystechnology have been widely deployed worldwide. The ultrasonic phased arraystechnology has the advantage of high detection reliability, high detection resolution,high detection speed, and high detection efficiency, is suitable for CCASS welddefects inspection. Currently, some study fruits of Post-processing algorithms inultrasonic phased arrays were presented by some scholars. However, they seldompresented discussion about the imaging algorithms in this field. In addition, there werelittle reports of application the imaging algorithms in the existing ultrasonic phasedarrays detector.This paper based on the advanced ultrasonic phased arrays technology, used thetime reversal algorithm (TR) and the decomposition of the time reversal operatoralgorithm (DORT) witch are widely used in sonar and radar field, detect the CCASSweld defects with ultrasonic phased arrays. The major contributions and innovationsare as follows.(1) Through the research of wave equation, based on Matlab software,establishment the probe radiation acoustic field visual simulation model of ultrasonicphased arrays, and simulate the effect of important parameters (frequency:2MHz-5MHz, array element number:8-24, etc.) to the probe radiation sound field.(2) Made two austenitic stainless steel deep weld test blocks (high70-90mm,defects Maximum depth50mm, artificial defect diameter2mm). Used the ultrasonic phased arrays with different frequency (2MHz-5MHz) of transverse wave orlongitudinal wave detect the defects in the two test blocks. Verify ultrasonic phasedarray detector (OMNISCAN MX2) performance testing of austenitic stainless steeldeep weld defects. The results showed that low-frequency longitudinal wave angleprobe has higher SNR than other types probe about5-10dB.(3) This paper introduced the TR algorithm and the DORT algorithm which arewidely used in the field of sonar and radar. Description the principle andimplementation process of two algorithms detailed. Then simulated and Verifyed thecharacteristics of the TR algorithm and the DORT algorithm in the probe radiationacoustic field visual simulation model of ultrasonic phased arrays. The results provethat the TR algorithm can effectively focus the ultrasonic energy to the largest defectin the workpiece, while the DORT algorithm can detect multiple defects in theworkpiece and also has a better performance. The DORT algorithm can not directlyused in the existing ultrasonic phased array detector, but the improved DORTalgorithm can make up for this shortcoming. This paper also simulates and descriptsthe characteristics of the improved DORT algorithm.(4) Applied the TR algorithm and the improved DORT algorithm in thelaboratory existing ultrasonic phased array detector (OMNISCAN MX2,OMNI-M-PA16128). Experiment results showed that the TR algorithm and theimproved DORT algorithm can either improve the probe focusing effect effectively.While the focusing effect of the TR algorithm is better than the improved DORTalgorithm. The improved DORT algorithm still needs further improvements.