Pulsed magnetic flux leakage method for hairline crack detection and characterization

Abstract

The Magnetic Flux leakage (MFL) method is a well-established branch of electromagnetic Non-Destructive Testing (NDT), extensively used for evaluating defects both on the surface and far-surface of pipeline structures. However the conventional techniques are not capable of estimating their approximate size, location and orientation, hence an additional transducer is required to provide the extra information needed. This research is aimed at solving the inevitable problem of granular bond separation which occurs during manufacturing, leaving pipeline structures with miniature cracks. It reports on a quantitative approach based on the Pulsed Magnetic Flux Leakage (PMFL) method, for the detection and characterization of the signals produced by tangentially oriented rectangular surface and far-surface hairline cracks. This was achieved through visualization and 3D imaging of the leakage field. The investigation compared finite element numerical simulation with experimental data. Experiments were carried out using a 10mm thick low carbon steel plate containing artificial hairline cracks with various depth sizes, and different features were extracted from the transient signal. The influence of sensor lift-off and pulse width variation on the magnetic field distribution which affects the detection capability of various hairline cracks located at different depths in the specimen is explored. The findings show that the proposed technique can be used to classify both surface and far-surface hairline cracks and can form the basis for an enhanced hairline crack detection and characterization for pipeline health monitoring.

A Method for Detecting Surface Defects in Railhead by Magnetic Flux Leakage

“…Tsukada proposes a method using a sensor probe consisting of a semicircular yoke with induction coils at each end and a gradiometer with two anisotropic magnetic resistance sensors for detecting the components perpendicular to the steel surface [15]. Okolo studies the influence of sensor lift-off on the magnetic field distribution, which affects the detection capability of various damages and proposes a quantitative approach based on the Pulsed MFL method [16].…”

Pipe Cracks Detection Methods – A Review

“…The accuracy and practical application of the MFL system have been experimentally evaluated for detecting surface and remote cracks of a sample made of low carbon steel, with a thickness of 10 mm [9]. A large current around the pipe circumference was supplied, using the Helmholtz coil magnetization method to generate a strong magnetic field saturated around the wall of the pipe.…”

Enhancement method of magnetic flux leakage signals for rail track surface defect detection

“…Wu et al [12] used a ferromagnetic support in a pipeline MFL detection system. Okolo and Meydan [13] proposed a quantitative approach based on impulse excitation to inspect farsurface hairline cracks.…”