Research On Weld Testing Technology And Image Processing By TOFD

The ultrasonic time of light diffraction (TOFD) technique has high detection precision, strong reliability and low error rate, especially the feature for accurate quantitative determination of defect size. Thus it is suitable for nondestructive detection of moderately thick welds and fairly effective particularly for quantitative determination of the cracks with high risk and planar cracks. The technique has been widely applied to nondestructive detection for weld defects and well developed.In this thesis, the weld testing technology and image processing by TOFD are studied. At the first, this paper introduces the TOFD technology principle, the theory how to show the image and the system parameters setting. Based on the experiment, a set of experimental system for TOFD welding testing was designed. A series of TOFD images with different initial positions and different gains were obtained via slight change of probe’s initial detecting position each time. Then, these TOFD pictures were processing by registration based on the original data.This paper introduces the image registration on detail. According to the actual situation, the shift-and-add (SAA) noise reduction method was studied. This method can reduce the noise effectively in weld detection TOFD image. The SAA method was proposed by Bates and Cady for reconstructing diffraction-limited images in stellar speckle interferometry. Then, the matching algorithm was further improved by using the sub-pixel registration algorithm, which can make the registration accuracy achieve sub-pixel level. Meanwhile, various algorithm which can reduce image noise in the TOFD D-scan image was proved through experiments.In addition, the paper details the characteristics of the SIFT algorithm and implementation process. The SIFT algorithm is applied to the TOFD image processing, and getting the description of the feature points and matching the feature points on TOFD images. This algorithm which need to do a more accurate picture TOFD image registration provides an initial algorithm and conditions for the subsequent.