There are countless pipelines in facilities of such as oil and gas, chemical processing, and related industries. Steel tube pipe general (STPG) for pressure service is a commonly used pipe, and they are jacketed with thermal insulations. Due to penetration of water, corrosion under insulation (CUI) that occurs on surface of the pipe is a major problem. At present, it is difficult to detect the CUIs without removal of the insulations from the pipes by conventional non-destructive testing (NDT) technique.
Therefore, we have developed a novel non-contacting ultrasonic guided wave testing (UGWT) technique that enables us to inspect defects on the STPG pipes in the insulation. To realize this inspection, we developed a magnetostriction-based UGWT technique, which utilized the magnetostrictive effects of the STPG pipe itself. In this method, we use electromagnets to give remnant magnetic field in the pipe, at which the magnetostrictive effect occurs by applying pulse magnetic field, leading to generation of guided wave. We utilized a high-sensitive HTS-SQUID gradiometer to receive magnetic signal generated at the remnant field by the inverse magnetostrictive effect due to the guided wave propagating in the pipe.
In this talk, we firstly introduce the conventional magnetostriction-based UGWT technique, which pastes nickel thin films on a pipe as magnetostrictive transducer. We developed this technique to the non-contacting UGWT technique using the remnant field of the pre-magnetized STPG370 pipe in place of the nickel film. Pre-magnetization conditions, such as shape of the electromagnets, current amplitude to the electromagnets, were derived from electromagnetic field simulation. We demonstrated non-contacting transceive of T(0, 1) mode guided waves using the novel technique. We also demonstrated defect detection using this technique and discuss feasibility of this technique for practical use.

Keywords: steel tube pipe general, magnetostrictive effects, ultrasonic guided wave testing, HTS-SQUID gradiometer