Digital holographic inspection for a straight pipe inner surface using multiwavelength illuminations

An inner surface of straight pipe has been investigated using digital holographic technique. Both contour images for surface profile and color reconstructed images are used to the detection of artificial defects made on the inner wall of copper pipe. For the inspection, a cone-shaped mirror glued to one end of a metal rod is inserted into the pipe and illuminated from the other open end of the pipe. The new algorithm in which a deviation of the cone-shaped mirror from the pipe axis can be directly evaluated from the experimental height profile reduces the amount of calculation for correcting the distorted experimental profile. The pipe inspection has been done using the developed images of both the color intensity image and height profile for the inner wall of pipe.