Abstract: For the disadvantages existing in the current pipe flange welding, a method was proposed to of recognize the weld seam for pipe flange based on improved boundary following algorithm, which is divided into two steps of detecting the position of weld seam and then recognizing the weld seam accurately. At first, a method of curvature estimation was applied to position the weld seam in the detecting process. Secondly, a method to set irregular region of interest through dilation and mask in the original image was proposed based on the position of weld seam. And then the edge was thinned, and an algorithm was proposed to filter the pseudo edge. Experiments results showed that the proposed method is reliable and can recognize the weld seam accurately.