The Study On Focusing Parameters Of Phased Array Ultrasonic Technology On Weld Defects

The phased array ultrasonic technology(PAUT) has the sound beam focusing capab ility, so it can greatly improve the sensitivity of defect detection. But using the different focusing parameters will bring great influence to the detection sensitivity and the detection results. For example, the inappropriate focus depth will cause the defect detection rate and detection sensitivity reduction. And under the China’s phased array ultrasonic standard, selecting the focus position is controversial in workpiece detection. In this paper, we use the OLYMPUS Omni Scan MX2 32:128PR phased array inspection instrument, with a large length of near field 5L64-A12 probe combined small defect burial test block TB7567-1, to study the defect detection results of focusing in the near field. And we using a small length of near field 2.25L32 probe and big defect burial test block T260, to research the focusing position’s effect for defect detection results. Combined with the analysis of computer simulation of the sound field distribution of the focusing, we explained the influence reason on the test results of the different focus depth.The results of the study show that, for the measurement of defect depth, the focal depth and length of the probe near field will make smaller impact on the defect positioning measurement results, the quantitative errors are less than 5%. When focus depth more than probe near field theory length, the defect depth detection results will relatively accurate. In the test block defect detection results show that the probe near field detection sensitivity is lower than far field defect detection sensitivity. It is suggested the effect of probe near field length and depth of the defect should be considered in phased array inspection standard of our country.At the same time, the study found that the 16 pieces of defects detection sensitivity are very high in actual weld seam testing which using the recommended focusing method. And there is very large measurement error of defect size measurement by conventional ultrasound-6db method. Based on the test results of the phased array focused sound field characteristics in the standard block, we puts forward the amplitude correction method for defect size measurement. Through the actual welding defect detection showed that the phased array focused method measurement accuracy is better than-6db measurement method for the defect depth in the range of 50-200 mm.This paper has certain guiding significance to create and apply the acceptance criteria of phased array technology.