Characterisation of pitting corrosion by white light interferometry

An improved method is described for obtaining detailed information on the size and shape of many corrosion pits by examination with White Light Interferometry. The entire surface is first imaged at low resolution by automatically stitching individual images into one composite image. Specially written software analyses the image and determines the location of all corrosion pits. The program then guides the white light interferometer in making high resolution topographic images of each pit. The images are analyzed to give any desired data about the pit geometry, such as depth, maximum width, projected area, volume, etc. Curves showing the depth distribution for each pit can be generated along with detailed topographic images of all pits. The technique does not work for pits that undercut the surface, and there is a practical size limit of about 20 cm2. The method is therefore best suited for studying the early stages of pit propagation.