Enhancement of microCT images of steel cracks using mathematical filters

Abstract

MicroCT has become a powerful and widely used tool for non-destructive testing and can be used for mapping the complex 3D structures of cracks and their interactions. The materials of most oil and gas transport pipes, buried or submerged, such as high strength low alloy steels, for example, are likely to suffer corrosion degradation and fracture due to the corrosive environment. Similarly, cracks are one of the most severe types of discontinuity in a welded joint since they are strong stress concentrators. High tensile stresses develop in the weld region as a result of the localized thermal expansion and contraction, associated with the welding thermal cycle. To better characterize the cracking behavior, it is important to gain information about the evolution of the 3D crack network. However, the search for improving image quality in the inspection of steel samples using X-ray beams is still challenging because of spreading effects that can cause noise in the 3D image. For this purpose, we performed microCT tests to verify cracks due corrosion and loss of weld adhesion cracks applying mathematical filters to improve the final image quality. To enhance details of the grey scale microCT slices, the image was improved using anisotropic diffusion (AD) and unsharp mask (UM) filters, which have been found to be highly effective for enhancement of digital fractured media. With the results was possible to verify cracks around 0.66 mm for corrosion cracks and 4.27 mm for cracks due to loss of weld adhesion, as well as the cracks network in the 3D visualization of the inspected materials.