The weld is an important connection part of the tank bottom but during the process of manufacturing and through its use, it frequently produces defects and brings serious hidden danger in the process of safety production.

This paper develops a new magnetic flux leakage testing system for tank bottom weld defects and proposes an extraction method for the weld defect. It can be used in the detection and visual evaluation of the weld defects.

A continuous non-contact scanning method is used in the rectangular slot defect in the different regions of the weld by using a new magnetization system that is vertical to the travelling direction. The characteristics of the weld and the defect are transformed into accurate two-dimensional grayscale graphics through grayscale linear transformation. This is done through the combination of histogram equalization, Otsu’s method of binaryzation, morphologically removing small objects, edge detection, and then structuring a morphologically optimized edge extraction algorithm for edge detection on the grayscale. The displayed grayscale outline locates and quantifies the defects.

The results indicated that this method can directly indicate the defect shape, location and other information, the visual display of the magnetic flux leakage testing of the weld defects was also realized. It solved difficulties associated with the magnetic flux leakage method being used in the weld testing and showed how weld detection equipment can be used in the detection and visual evaluation of the weld defects.