Shear Horizontal Guided Wave Corrosion Detection and Quantification in Pipes via Linear Scanning Magnetostrictive Transducers (MST)

Abstract

Shear horizontal (SH) guided waves are being widely considered as a promising tool for locating wall thinning corrosion in pipelike structures. One established approach to excite such waves in pipes is through the magnetostrictive transducers (MsT), which is an electromagnetic-based guided wave transducer that offers unique advantages over other transducer types. A common practice for fast screening of defects is using an automated probe positioning system. In this paper, we report the usage of a newly designed linear scanning MsT, where an iron cobalt (FeCo) strip of a predefined length wound with radio frequency (RF) coils is attached to the testing structure using shear wave couplants and a moving permanent magnet driven by a stepper motor is used to excite SH guided waves at predefined positions. In this fashion, manual manipulation of probe is minimized which significantly increases testing speed. The performance of the linear scanning MsT at corrosion inspection is evaluated experimentally by introducing “V” shaped gradual wall thinning patches of different depths and locations on a 406 mm outer diameter (OD) steel pipe with 10 mm wall thickness. The reflection and transmission amplitudes of SH modes, as well as indications from B-scan and synthetic aperture focusing technique (SAFT) images, are extracted for corrosion detection and quantification. Numerical modeling is also conducted to facilitate the understanding of SH waves interaction with defects.