Development of appearance inspection system for root pass welds of small-calibre pipes by image composition technique

Summary

It is often difficult to capture clearly full 360° views from partial images of welds in circumferential joints on the inside surface of small-calibre pipes or tubes (with an inside diameter of around 50–300 mm) with the aid of industrial endoscopes, because of their narrow-angle vision.

This study proposes an effective system to help inspect welds on the inside surface of pipes or tubes accurately and immediately through panoramic views being composed from their partial images. The partial images on the inside surface of pipes or tubes are taken with an instrument with an inbuilt ultrasmall-sized charge coupled device (CCD) camera developed as part of the study. The partial images are composed using the overlapping image data. If images are affected by geometric distortions, they cannot be composed because of the mismatch between overlapping areas. Such geometric distortions are therefore corrected by preprocessing. The developed system enables complete panoramic views of welds on the inside surface of small-calibre pipes or tubes to be photographed accurately and automatically, and thus overcomes the important deficiency of the conventional industrial endoscope's side view observation capability. The quality of photographed images and operating time reach a practical level.