# LC Resonant-Based Method for Permeability Interference Suppression in Magnetized Pipeline Eddy Current Testing

## TL;DR

This paper introduces an LC resonant method to reduce interference in eddy current testing of magnetized pipelines, improving the ability to distinguish between inner and outer wall defects.

## Contribution

The novel use of an LC resonant circuit to suppress permeability interference in magnetized pipeline ECT is proposed.

## Key findings

- The LC sensor shows insensitivity to permeability perturbations in magnetization response tests.
- The sensor achieves a standard deviation ratio of 2.25 and a peak-to-peak ratio of 4.42 for inner and outer wall defect signals.
- Amplitude thresholding with the LC sensor reliably distinguishes between inner and outer wall defects.

## Abstract

In the eddy current testing (ECT) of magnetized ferromagnetic pipelines, permeability perturbations near defects cause magnetic distortion that primarily modulates the imaginary part of the ECT sensor’s impedance, leading to confusion between inner and outer wall defect signals. To address this interference, this study thoroughly analyzes the modulation mechanism of permeability changes on impedance and investigates the feasibility of detecting solely the real part to enhance discrimination reliability. This understanding leads to the proposal of a solution employing an LC resonant circuit, capitalizing on its characteristic of zero imaginary part impedance at the resonant frequency, to effectively suppress the permeability-related signal interference. Experimental results demonstrate the effectiveness of the proposed approach: the magnetization response test confirms the insensitivity of the LC sensor to permeability perturbations, and the defect discrimination experiment shows that the sensor achieves a standard deviation ratio of 2.25 and a peak-to-peak ratio of 4.42 between inner and outer wall defect signals. The findings indicate that the LC resonant sensor can reliably distinguish between inner and outer wall defects through simple amplitude thresholding, thereby improving the reliability of inspections for magnetized pipelines in industrial applications.