Visual Reconstruction of Irregular Crack in Austenitic Stainless Steel Based on ACFM Technique

Abstract

For the advantages of corrosion resistance, high toughness and plasticity, the austenitic stainless steel is widely used in the petrochemical special equipment and offshore structure. The austenitic stainless steel usually services in high temperature, high pressure and corrosive medium environment. Various types of irregular cracks are easily introduced in the surface of the austenitic stainless steel, which threats the safety of the structure. Due to the property of non-magnetic, weak conductivity and coarse grain, it is still a challenge to detect and evaluate irregular cracks in the austenitic stainless steel using the nondestructive testing (NDT) method. The visual reconstruction method is presented to detect and evaluate the irregular crack in the austenitic stainless steel based on the alternating current field measurement (ACFM) technique. The austenitic stainless steel irregular crack ACFM finite element simulation model is set up. The distorted electromagnetic field around the irregular crack is analyzed. The vertical direction magnetic field (Magnetic field perpendicular to specimen, called Bz) image gradient field visual reconstruction method is presented to reconstruct the surface profile of the irregular crack. The irregular crack testing experiments are carried out to verify the efficiency of the visual reconstruction method. The results show that the current field induced by the ACFM probe gathers at the tips of the irregular crack in the austenitic stainless steel. The gathered current makes the vertical direction magnetic field Bz distorted. The Bz image gradient field can reflect the location of the gathered current. The surface profile of the irregular crack can be imaged visually and evaluated accurately by the Bz image gradient field visual reconstruction method.