| The time of flight diffraction (TOFD) is an important technique used for evaluatingthe safety performance of welds quality and parts, which has been applied for imagingdetection of weld defects fast and efficiently. At present, the ultrasonic TOFD techniqueis mainly used in regular geometric shape of the welds detection like butt weld of platespecimen and butt weld of pipe ring. The Lateral wave and back wall as the referencewave, with a complete mathematical equations for the quantitatively and location of thedefects. However, there are many irregular geometry components which have differentweld structure. These components have different way in select lateral wave as well asquantitatively and location of the defects. Thus, the conventional TOFD technique wasno longer applicable on such components.In this paper, we investigate the unequal thickness butt weld plate, T-plate weld andthick-walled pipe ting weld, finite element method using the geometrical acoustic theoryanalysis software ABAQUS/Explicit and actual operation TOFD test were adopted.Based on the existing butt weld of flat ultrasonic TOFD detection principles andmethods, the corresponding amplitude (A-scan) of TOFD and the positioning andquantitative geometric mathematical model were analyzed and the gray scale imagingprinciple, B-scan and D-scan imaging detection method were introduced. Further, theultrasonic TOFD detection process optimization including TOFD detection accuracy,choice of probe, probe spacing setting and reduce surface blind area.The research of unequal thickness butt weld plate was established based onABAQUS, by modeling a simplified finite element model of unequal thickness weldingjoints, the acoustic wave was simulated by force source at specific angle. The wave fieldsnapshot show that the ultrasonic wave which was radiated from the side of thick platepropagated to the corner of the unequal thickness plat weld would produce a new lateralwave in the thin plate surface set the point of corner as source. It can be detectdefections by using the reference wave, the lateral wave and back wall echo, then carryout the actual operation TOFD inspection to the unequal thickness butt weld plate. Thewave field snapshot of thick and thin thickness ratio of4:1,3:1,2:1and the A-scansignals of TOFD show the effectiveness of this method. Referring to the finite elementmodels, artificial vertical hole defects were machined in unequal thickness butt weld plate,45°,60°,70°probe were used in TOFD inspection, the results shows that numericalsimulation and experimental results were correspond well. For unequal thicknessbutt weld plate,45°,60°probe are more appropriate according to the plate thickness.Transmitting and receiving probes placed on the wing simultaneously has beenproposed by the authors that successfully extends the application of TOFD to T-plateweld. The detection of connections between wing plate and web plate were carried outafter determining the lateral wave combining symmetric and asymmetric scanningdetection method, can effectively achieve a comprehensive test of T-plate weld.For the thick-walled pipe ting weld is consistent with the plate butt weld TOFDdetection method when the curvature of thick-walled tube and wall thickness have littleeffect on lateral wave, otherwise, it need to reselect the reference wave according to theroute of lateral wave. Since the blind surface area, it is hard to detect defects that wereexisted in the near-surface, but for the internal defects, it can be detected effectively.Research in this paper will provide a useful reference in promoting the application anddevelopment of ultrasonic TOFD detection method. |
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