Frequency optimisation of circumferential current field testing system for highly-sensitive detection of longitudinal cracks on a pipe string

The excitation frequency is a key parameter in electromagnetic non-destructive testing (ENDT). Due to the skin effect, the excitation frequency determines the penetration depth of the induced current field in the conductor, which may influence the detection sensitivity for different crack depths. In this paper, the detection sensitivity of the magnetic field in the axial direction (Bx) is set as the target parameter to optimise the excitation frequency of a circumferential current field testing system. The excitation frequency is optimised using a finite element method (FEM) model and verified by crack detection experiments. For this particular case study, the results show that 1 kHz is the optimum excitation frequency for the highly-sensitive detection of cracks using this circumferential current field testing system.