3D visual reconstruction of corrosion in underwater structure using alternating current field measurement technique

Corrosion is a common damage form in various underwater structures. However, the corrosions are usually covered by the coatings and attachments in the underwater environment. In this paper, the 3D visual reconstruction methods for evaluating the corrosion defect using the alternating current field measurement (ACFM) technique are presented. The FEM model is set up with corrosion and pitting defects to analyze the disturbed current field and the distorted magnetic field. A gradient imaging algorithm based on the Bz signal is proposed to reconstruct the surface morphology of the corrosion and the pitting defect. The inner contour of the corrosion defect is reconstructed using the Bx signal sensitive characteristics of probe lift -off. The calibration method is proposed to measure the depth of the pitting defect. The testing system is built, and the experiments are carried out to verify the 3D visual reconstruction methods. The maximum error of the surface area reconstruction is 8.13%. The maximum error of the corrosion inner reconstruction is 10%. The maximum error of the pitting depth is 3.25%.