An Online Monitoring Technique for Long-Term Operation Using Guided Waves Propagating in Steel Pipe

Abstract

Nondestructive testing (NDT) techniques are widely used as a reliable way for preventing failures and helping in the maintenance design and operation of critical infrastructures and complex industrial plants as nuclear power plants (NPPs). Among the NDT techniques, guided waves (GWs) are a very promising technology for such applications. GWs are structure-borne ultrasonic waves propagating along the structure confined and guided by its geometric boundaries. Testing using GWs is able to find defect locations through long-range screening using low-frequency waves (from 5 to 250 kHz). The technology is regularly used for pipe testing in the oil and gas industry. In the nuclear industry, regulators are working to standardize monitoring and inspection procedures. To use the technology inside an active plant, operators must solve issues like high temperatures (up to more than 300 °C inside a light-water reactor's primary piping), high wall thickness of components in the primary circuit, and characteristic defect typologies. Magnetostrictive sensors are expected to overcome such issues due to their physical properties, namely, robust constitution and simplicity. Recent experimental results have demonstrated that magnetostrictive transducers can withstand temperatures close to 300 °C. In this paper, the GW technology will be introduced in the context of NPPs. Some experimental tests conducted using such a methodology for steel pipe having a complex structure will be described, and open issues related to high-temperature guided wave applications (e.g., wave velocity or amplitude fluctuations during propagation in variable temperature components) will be discussed.