A Novel High Sensitivity Sensor for Remote Field Eddy Current Non-Destructive Testing Based on Orthogonal Magnetic Field

Abstract

Remote field eddy current is an effective non-destructive testing method for ferromagnetic tubular structures. In view of conventional sensors' disadvantages such as low signal-to-noise ratio and poor sensitivity to axial cracks, a novel high sensitivity sensor based on orthogonal magnetic field excitation is proposed. Firstly, through a three-dimensional finite element simulation, the remote field effect under orthogonal magnetic field excitation is determined, and an appropriate configuration which can generate an orthogonal magnetic field for a tubular structure is developed. Secondly, optimized selection of key parameters such as frequency, exciting currents and shielding modes is analyzed in detail, and different types of pick-up coils, including a new self-differential mode pick-up coil, are designed and analyzed. Lastly, the proposed sensor is verified experimentally by various types of defects manufactured on a section of a ferromagnetic tube. Experimental results show that the proposed novel sensor can largely improve the sensitivity of defect detection, especially for axial crack whose depth is less than 40% wall thickness, which are very difficult to detect and identify by conventional sensors. Another noteworthy advantage of the proposed sensor is that it has almost equal sensitivity to various types of defects, when a self-differential mode pick-up coil is adopted.

Synthesis Study: Overview of Readily Available Culvert Inspection Technologies

“…A technological advancement from traditional Remote Field ECT is the use of orthogonal magnetic field excitation as compared to axial magnetic field excitation. The results indicate a large overall improvement in defect detection, specifically for axial cracks with depths less than 40% of wall thickness (Xu, Liu, Zhang, & Jia, 2014).…”

A Novel of Internal Corrosion Assessment Methods on Drinking Water Distribution Pipelines

“…Simultaneously, the exciter produces another indirect (external) field that travels through the wall of the pipe with a small attenuation. The change of field strength and attenuation depends on the thickness of the wall of the pipe thus from this change allows the determination of the thickness of the pipe wall [15] [18].…”

Review of Pulsed-Eddy-Current Signal Feature-Extraction Methods for Conductive Ferromagnetic Material-Thickness Quantification

“…While several techniques have been investigated for defect and crack detection of conductive materials [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20], when it comes to thickness quantification of conductive ferromagnetic materials, the Pulsed Eddy Current (PEC) technique, especially the detector coil-based PEC sensor architecture, has been commonly used [21][22][23][24]. The main reason for this associated with detector coil-based PEC sensors can be identified as it being possible to extract signal features that are proportional to the diffusion time constant of eddy currents [23] induced inside a ferromagnetic wall-like structure, and this diffusion time constant behaving as a function of the wall thickness [23].…”