| There are a large number of butt welds with caps in engineering.In the process of radiography testing,it’s difficult to detect the planar defects.Otherwise,the detected defects cannot be accurately positioned.The traditional ultrasonic testing has the problems of coupling,signal identification and low detection efficiency.In order to solve these problems,phased array ultrasonic testing(PAUT)technology is used to inspect the butt welds with caps in this paper.By simulation,we analyzed the acoustic field propagation laws of the universal phased array probe with the wedge in welds and got optimized inspection parameters.Due to the limited space of inspection and for the implementation of larger area inspection,Imaging of butt weld is carried out using total focusing method(TFM).The specific research contents are as follows:30# steel butt weld testing block was machined with a dimension of 260 mm×30 mm×40mm,which had a 6 mm curvature radius and 2.4 mm cap height.Based on the sound velocity and attenuation coefficient of the block,and the simulation model was established to carry out PAUT research.The results show that the signal-to-noise ratio(49.1 dB)of the Φ2 mm SDHs detected with the obliquely incident wave on the base is much higher than that of the directly incident wave above the weld(3.1 dB).Furthermore,based on the model,we carried out a research of the obliquely incident wave and analyzed the acoustic field.The results show that with the increase of deflection angle,the detection coverage increases,the detection resolution increases first and then decreases,the detection sensitivity decreases at the same time.And as focusing depth increases,the detection coverage increases and the detection resolution decreases.The preferred detection parameters for the 20 mm SDH are: 40° to 60°deflection angle and 20 mm depth of focusing.Considering the limitation of oblique incident wave and the low signal-to-noise ratio of the direct incident wave,the A-scan signals were acquired using the universal phased array probe by water immersion.Based on the signals,differences of contour extraction were compared and analyzed among B-scan,Synthetic Aperture Focusing Technique(SAFT),Surface Adaptive Ultrasound(SAUL)and Total Focusing Method(TFM).Among these four methods,The results show that the maximum error and average error of SAFT contour extraction are 0.31 mm and 0.04 mm,respectively,which are also the smallest.The normalized standard error of TFM contour extraction is 0.98 mm,which is closest to 1 mm.Further imaging results of the SDH in the weld were compared based on extracted contour of these methods: The result of TFM is the best,That of B-scan and SAFT are the second,SAULis the worst.The amplitude and signal-to-noise ratio of the SDH are-14.22 dB and 17.56 dB by TFM,respectively.In order to improve the calculation efficiency of TFM imaging of butt welds,the signal threshold which is the maximum amplitude of 1/4 of all received signals for each transmitted signal was used to form the dynamic effective aperture(DEA)to participate in the imaging.The result shows that the extracted profile is completely consistent with that of full aperture(FA).The amplitude and signal-to-noise ratio of the Φ2 mm SDH in experiment are-21.39 dB and 7.51 dB,respectively.The amplitude and signal-to-noise ratio of the Φ2 mm SDH in simulation are-14.22 dB and 17.56 dB,respectively.Due to the presence of tool marks on the surface of the block,the experimental results are lower than that of simulation.On this basis,A research was carried out about the effect of weld size on image quality.The results show that when the height of the weld cap is 2.4 mm,with the increase of curvature radii,the amplitude and signal-to-noise ratio of the SDH increase,with the increase of cap height,the amplitude and signal-to-noise ratio of the Φ2 mm SDH decrease when the curvature radius of the weld cap is 18 mm.These phenomena are caused by structure and extracted contour errors. |
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