New Magnetostrictive Transducers and Applications for SHM of Pipes and Vessels

Abstract

The use of guided waves for long-range inspection of components is a rapidly growing area of the nondestructive evaluation service industry. Magnetostrictive sensors utilizing ferromagnetic strip material for the transduction effect have proven to be very effective for guided wave testing (GWT) on a variety of components. There is still a demand for enhanced sensor characterization and sensors with specific characteristics. The most challenging area is structural health monitoring (SHM) of components operating at elevated temperatures of at least 200°C. A new configuration of a sensor for generating and receiving transverse-motion guided waves swaps the biasing and time-varying magnetic field directions. This alternative design is a reversed Wiedemann effect magnetostrictive transducer. These transducers exhibit a number of unique features compared with the more conventional Wiedemann sensor, including: (1) the use of smaller rare earth permanent magnets to achieve large, uniform, and self-sustained bias fields; (2) the use of more efficient electric coil arrangements to induce a stronger time-varying magnetic field for a given coil impedance; (3) the ability to generate both transverse and longitudinal waves; (4) they can be used on pipes ranging from a few millimeters to several meters in diameter. In this paper, the new transducer design will be described and its performance will be analyzed in application to SHM of pressurized pipe operating at 200°C and automated omnidirectional scan of large storage tank walls.