Analysis And Research Of Weld Defect Based On Ultrasonic TOFD

Welding is widely applied in various industries and has great influence on the development of national economy and the modernization drive.To ensure the safe and reliable operation of the welded structure,it is necessary to detect the possible defects in the weld.Ultrasonic TOFD(time-of-flight-diffraction)technique is the most effective method to detect welding defect due to its high defect detection rate,high measurement accuracy,high detection efficiency,intuitive data and permanent storage and equipment safety.But it is difficult to evaluate the weld defects qualitatively by TOFD and the transverse crack is easy missing in welds.In this paper,we studied the two problems of weld defect detection by TOFD.The characteristics of TOFD images with different weld defects were summarized by means of contrast test,and realized the qualitative evaluation of weld defect.The paper improved the traditional TOFD detection method,and proposed an oblique non-parallel scanning method to reduce the transverse crack's miss in weld,which was tested and verified.The main research contents are as follows:(1)Samples of a large number of different types of welding defects were prepared,during the ultrasonic TOFD detection experiment using ray detection for comparative verification,combined with TOFD detection D scan images and radiograph,analyzed and summarized the characteristics of typical weld defects according to the TOFD images.(2)Through the research of the cause of transverse crack's miss in TOFD detection,the paper improved the traditional TOFD detection method,and proposed an oblique non-parallel scanning method.In order to test the practicability of the method,improve the detection efficiency,the paper designed a special multi channel oblique scanning frame.(3)Samples of the transverse crack defect were prepared.CIVA software is used to simulate the sound field of the probe under different process parameters,and optimize the detection process parameters.The experiment verification was made by using the designed multi-channel oblique scanning frame to the simulated test block,the results showed that one chnnel for non parallel scanning,and another channel for the oblique non-parallel scanning with the angle from 30 degrees to 60 degrees of the multi channel oblique scanning frame can detect both longitudinal defects and transverse defects in weld.In this paper,the characteristics of typical weld defects are summarized,which can provide a theoretical basis for the judgment of defect types and the qualitative study of weld defects in the actual weld TOFD detection.The designed multi-channel oblique scanning frame can reduce the transverse crack's miss in weld,improve the detection data accuracy,and effectively simplify the scanning process,improve the detection efficiency.