Investigation of mode conversion of SH waves at the welded tabular ends of a fuel storage tank

Abstract

Storage tanks are an essential part of petrochemical plants. Most storage tanks are cylindrical, and the base plate is welded at the edge. The bottom plate of the tank is eventually exposed to the environment and soil, leading to corrosion over time. The tank bottom metal loss is one of the defects caused by corrosion initiated by the welded tubular end of the storage tank. Inspecting the storage tank corrosion defect is imperative to avoid undesirable losses. In recent years, the electromagnetic acoustic transducer (EMAT) has become an effective non-contact and non-couplant inspection tool for applying Non-destructive Testing (NDT) & structural health monitoring (SHM). Generally, the guided wave method is preferred to inspect the defect by reflecting propagating wave (SH) modes. It has been observed that the reflected wave modes converse into different modes at a certain reflection angle due to the defect orientations and the welded ends. Due to mode conversion, identifying the defect position with SH wave modes is challenging. This study investigates the influence of mode conversion on the reflected wave from the welded tabular ends of the storage tank. A numerical model has been developed to investigate the SH wave propagation, reflection, and mode conversion due to defects and welded tabular ends. Further, an experiment has been performed with a chevron PPM-EMAT for generating SH wave to validate and compare the simulation results.