Thick-walled Pressure Vessel Ultrasonic Time Of Flight Diffraction (TOFD) Detection Technology

Ultrasonic Time of Flight Diffraction (TOFD) with high precision, high rate ofdefect detection, detection of low cost and easy opration is suitable for detection ofthick-walled flat butt weld. But TOFD detection technology has some problems, such asbig surface blind, low detection rate of transverse defects, and difficults of defectsassessment. This paper is based on CIVA software simulation, combined with the actualengineering practice, proposed by using hierarchical scan on the surface of the blindultrasound creeping wave detection, non-parallel scanning non-parallel45°obliquescanning process to solve the problem of thick-walled pressure vessel detection, and theactual detection device, case and evaluation map.This papers is based on basic theory of ultrasonic diffraction time and imagingfeatures as well as key process parameters. By using CIVA simulation simulate TOFDsound field and the influence of critical process parameters for Ultrasonic field,proposed the TOFD detection technology, by using150mm Tablet butt weld defects as amodel to verify the response simulation analysis, and then verified by experiment, theresults showed that150mm Tablet TOFD detection need three separate testing, thethickness of the detection is divided into0to30mm (probe frequency5M, chip size6mm PCS110mm refraction angle70°),30~90mm (probe frequency5M, chip size6mm, PCS240mm refraction angle60°),90~150mm (probe frequency5M, chip size6mm, PCS260mm, the refraction angle70°)，high precision and has good thedetection results.TOFD detection surface blind ultrasonic pulse-echo testing, magnetic particletesting and ultrasonic creeping wave detection, the surface blind spot detection processas been applied by using TOFD detection on test block and the reference block andapplied in the Engineering Test. the results show that the8mm deep groove depth of3to10mm side hole can be found by using4MHz creeping wave probe and the front probefrom the center of the weld is40mm. the problem of the TOFD surface blind spot canbe solved by ultrasonic pulse-echo method and magnetic particle testing method incertain extent. Exceed detection in blind spot defects on the surface of the TOFD can bedetected by ultrasonic creeping wave detection, it is an effective supplemental detectionmethod to improve the application of TOFD detection.In this Paper, we proposed self-developed non-parallel scanning and oblique45°non-parallel scanning device to detect transverse defects. Experiments and engineering applications verified that By using non-parallel to the oblique non-parallel scanning cangreatly improve the lateral defect detection rate.In this Paper， the map features of the detected defects (pores, slag, lack of fusion,cracks) were regularity summaried, to provide a reference for the data assessment. Theresearch will provide a useful reference on thick-walled pressure vessel in TOFDdetection technology.