Corrosion detection on pipelines by IR thermography

IR thermography is applied to detect hidden corrosion on carbon steel pipelines for oil transportation. The research is oriented to set up a robust technique to carry out in situ the early detection of corroded zones that may evolve either towards leakage or failure. The use of thermography associated with a transient thermal technique is investigated on 12.2 mm thick samples, machined to artificially create a reduction of wall thickness that simulates the effect of real corrosion in pipes. The extension and depth of the artificial defects is controlled by ultrasounds which represents the reference for the results obtained by thermography. Two approaches are proposed: the first is based on the processing of a single thermogram taken at the optimum time after a finite pulse heating of a large area of the external surface; the second technique is carried out by scanning the pipeline by means of a device composed of a linear lamp and a thermographic camera which move jointly over the surface to test. A suitable reconstruction provides a map of the tested surface with possible hot spots in correspondence with the corroded areas. The analysis of the thermal problem by Finite Element Method is used to optimize the experimental parameters. The experimental results demonstrate a detection capability starting from 15 % of wall thickness reduction. © 2011 SPIE.