A novel MFL detection method based on low frequency AC magnetization for identification defect

• Published in: Journal of magnetism and magnetic materials Vol. 580; p. 170864
• Main Authors: Zhang, Shaoxuan, Feng, Jian, Lu, Senxiang, Dong, Xu
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.08.2023
• Subjects: corrosion induced defects (Cdft); Low frequency ACMFL; magnetic dipole; stress defects (Sdft); stress defects (Sdft); corrosion induced defects (Cdft); magnetic dipole; Low frequency ACMFL
• ISSN: 0304-8853
• DOI: 10.1016/j.jmmm.2023.170864

The reasons of structural failure of metal equipment are corrosion defects (Cdft) and stress defects (Sdft). But the sources and mechanisms of development of Cdft and Sdft are entirely different. The identification of Cdft and Sdft is a necessary prerequisite for the analysis of structural failures of metallic equipment. The magnetic domains move and rotate caused by Sdft and low frequency (f<30Hz) magnetic excitations. Both mechanical structural changes and magnetic excitation affect the magnetic domains. Under low frequency excitation conditions, the Cdft does not cause the magnetic domains to change. In this paper, an analysis of magnetic dipole density using magnetic domain variation and magnetic permeability variation is proposed. The low frequency alternating current magnetic flux leakage (ACMFL) method was used to identify Cdft and Sdft. The method combines the advantages of unsaturated excitation direct current magnetic flux leakage (DCMFL) and ACMFL with its low frequency characteristics. Simulations are used to determine the scanned surface signals. Multi-point and single-point experiments and as well as the corresponding simulations are used to verify the conclusions presented in this paper. In addition, this paper compares the difference between the proposed method and the DCMFL method using experiments, and also compares the difference between our proposed method and medium-high frequency ACMFL method. •The MFL method of low freq excitation is proposed, which can measure Sdft or Sdft.•A novel magnetic dipole model based on low-frequency excitation is proposed.