Use this URL to cite or link to this record in EThOS:
Title: Modelling and experimental investigation of magnetic flux leakage distribution for hairline crack detection and characterization
Author: Okolo, Chukwunonso
ISNI:       0000 0004 7224 125X
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2018
Availability of Full Text:
Access from EThOS:
Access from Institution:
The Magnetic Flux Leakage (MFL) method is a well-established branch of electromagnetic Non-Destructive Evaluation (NDE) extensively used to assess the physical condition of ferromagnetic structures. The main research objective of this research work presented in this thesis is the detection and characterization of the MFL distribution caused by rectangular surface and far-surface hairline cracks. It looks at the use of the direct current and pulsed current techniques to investigate the presence of hairline cracks in ferromagnetic steel pipelines, by comparing the Finite Element Modelling (FEM) technique with practical experiments. First, the expected response of an MFL probe scanned across the area of a hairline crack was predicted using the 3D FEM numerical simulation technique. The axial magnetization technique is employed and the characteristics of the surface and far-surface leakage field profile (Bx, By, Bz) was simulated. The optimization of the magnetization and sensing methodologies were crucial to ensuring accurate numerical results. The performance of the modelled MFL inspection system on detecting and characterizing both surface and far-surface hairline cracks was confirmed using real low carbon steel plates, with well-defined artificial hairline slots. The experimental findings showed that the MFL signals caused by a 0.2 mm deep surface and 0.4 mm deep far-surface hairline cracks, with a constant width and length of 0.2 mm and 10 mm respectively, is detectable. The transient responses in the time and frequency domains, yielded information relating to different cracks located at different depths within the test specimen. The MFL sensor used was able to detect the inspected hairline cracks at 9 mm lift-off, which makes the newly developed system effective and beneficial in applications where large lift-off distances are required. The pulsed current inspection approach significantly reduced the power consumption and thermal effects by 50%, compared to the direct current approach. Also, the experimental results were within 10% of the simulated results.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available