title: Helical comb magnetostrictive patch transducers for inspecting spiral welded pipes using flexural guided waves.
abstract: A wavefront analysis indicates that a flexural wave propagates at a helix angle with respect to the pipe axis. The expression for calculation of the helix angle for each flexural mode is given, and the helix angle dispersion curves for flexural modes are calculated. According to the new understanding of flexural guided waves, a helical comb magnetostrictive patch transducer (HCMPT) is proposed for selectively exciting a single predominant flexural torsional guided wave in a pipe and inspecting spiral welded pipes using flexural waves. A HCMPT contains a pre-magnetized magnetostrictive patch that is helically coupled with the outer surface of a pipe, and a novel compound comb coil that is wrapped around the helical magnetostrictive patch. The proposed wideband HCMPT possesses the direction control ability. A verification experiment indicates that flexural torsional mode T(3,1) at center frequency f=64kHz is effectively actuated by a HCMPT with 13-degree helix angle. Flexural torsional modes T(N,1) with circumferential order N equals 1-5 are selected to inspect a seamless steel pipe, artificial defects are effectively detected by the proposed HCMPT. A 20-degree HCMPT is adopted to inspect a spiral welded pipe, an artificial notch with cross section loss CSL=2.7% is effectively detected by using flexural waves.
authors.affiliation: Institute of Modern Manufacturing Engineering, Zhejiang University, China.
authors.forename: Xiaowei
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Institute of Advanced Digital Technologies and Instrumentation, Zhejiang University, China. Electronic address: tangzhifeng@zju.edu.cn.
authors.forename: Zhifeng
authors.initials: Z
authors.lastname: Tang
authors.affiliation: Institute of Modern Manufacturing Engineering, Zhejiang University, China.
authors.forename: Fuzai
authors.initials: F
authors.lastname: Lv
authors.affiliation: Institute of Modern Manufacturing Engineering, Zhejiang University, China.
authors.forename: Xiaohong
authors.initials: X
authors.lastname: Pan
keywords: Flexural waves; Helical comb magnetostrictive patch transducer; Helix angle; Spiral welded pipe