Image analysis of cracks in the weld metal of a wet welded steel joint by three dimensional (3D) X-ray microtomography

Hydrogen is readily available in underwater wet welds due to the dissociation of water at high temperatures. Low weld metal toughness and thermal contraction during cooling can lead to the nucleation of cracks, which seriously affect the mechanical properties of the weld. In this paper, X-ray microtomography (μCT) and image analysis (IA) were employed to image and measure crack length and morphology in the weld metal of a wet welded low carbon steel joint. The images were corrected for noise and illumination. The cracks were segmented and post-processed to correct for artifacts. Size and shape parameters were measured and showed a large average value for the Feret diameter (385 μm) compared to average crack thickness (18 μm). Three dimensional (3D) renderings of the detected cracks revealed a spatial distribution in which densely cracked regions are separated by layers of crack-free material. The combination of μCT and IA proved to be a powerful tool to characterize a complex defect system in 3D, providing information that cannot be obtained with traditional 2D microscopy techniques.