Processing thermography images for pitting corrosion quantification on small diameter ductile iron pipe

The condition of a metallic pipe is determined mainly by the extent to which it is corroded. Thus, the quantification of pitting corrosion in terms of metal loss is required for the understanding of pipe condition. There are different ways to quantify corrosion pit geometry. Direct methods measure the pit depth of pipe samples, which are sand/grit blasted to remove corrosion products, and are often adopted in laboratory. Indirect methods employ non-destructive inspection techniques to detect and quantify the corrosion without sandblasting, which is preferred for field test. In this study, the pulsed thermography is considered for fast quantification of pitting corrosion in a ductile iron pipe, which is sandblasted. The thermography testing generates a sequence of infrared images, which reflect the diffusion process of heat through pipe wall. This paper proposes a processing procedure to extract the corrosion information from the thermography images with phase congruency measurement and local binary fitting. The extracted feature is further related to the corrosion damage. Among all the features, the second principal component demonstrates a reasonably good linear relationship with metal loss of the pipe. The application potential is demonstrated by the experimental results.