Magnetic Induction Testing
Magnetic induction testing is a non-destructive testing method used to check ferromagnetic materials for defects or irregularities, including cracks, corrosion, pitting and material loss. It is commonly used in industries such as oil and gas, automotive, aerospace and manufacturing.
The principle is based on the fact that magnetic fields tend to follow the path of least resistance. When a magnetic field is applied to a ferromagnetic material, the field will flow through the material unless it encounters a defect or anomaly. When the magnetic field encounters such a defect, it is diverted or leaked from the material, resulting in a detectable signal. The technique is relatively fast, provides real-time results, and is suitable for both laboratory and field inspections.
Fig 1. Electromagnetic induction.
Magnetic Induction Test Procedure
- Magnetization: The test sample is magnetized by direct current (DC) or alternating current (AC) magnetization. DC magnetization is typically used for surface inspection, while AC magnetization is more suitable for detecting subsurface defects.
- Leakage Field Detection: After magnetization, a magnetic field sensor or flux detector is used to measure the magnetic field at or near the surface of the material under test. Any deviation or change in the magnetic field indicates the presence of a defect.
- Data analysis: The measurements obtained from the magnetic field sensor are analyzed to determine the size, shape and location of the defect. This analysis can be performed visually or with the aid of specialized software.
Magnetic Induction Test Methods
- Eddy Current Testing (ECT)
ECT creates eddy currents in conductive materials by means of an alternating magnetic field. Defects can be detected by measuring the magnetic field produced by these currents. ECT is frequently used to find flaws in conductive materials, both surface and subsurface.
- Magnetic Flux Leakage (MFL)
A ferromagnetic material is subjected to a strong magnetic field in MFL. Defects cause the magnetic field to become distorted, which produces a visible leakage flow. MFL is frequently used to check for corrosion and other flaws in big ferromagnetic constructions, such as tanks and pipelines.
- Magnetic Particle Testing (MPT)
In MPT, a material is made magnetic and then ferromagnetic particles are applied to its surface. Defects are present because the particles are drawn to regions of magnetic flux leakage. MPT is a technique used in ferromagnetic materials, such as castings, forgings, and welds, to identify discontinuities at the surface and near the surface.
- Barkhausen Noise Test (BNT)
The Barkhausen effect, which occurs when a ferromagnetic material is exposed to a fluctuating magnetic field, and causes a fast shift in the material's magnetic induction strength, is the basis for BNT. Defects can be found by measuring and analyzing the noise produced by these modifications. In ferromagnetic materials, BNT is used to assess material hardness, residual stress, and grinding burns.
- AC Magnetic Field Measurement (ACFM)
ACFM is an electromagnetic technique that utilizes alternating current to create a magnetic field in a material, allowing changes in the field to be measured to identify defects. ACFM is used to detect surface and near-surface defects in conductive materials.
Fig 2. Test platform of magnetic induction strength. (Alvim T, et al. 2022)
In addition, the experts in our magnetic induction testing laboratory also provide a variety of custom services to your needs and requirements. Let's discuss the custom services with our experts for free.
Reference
- Luan B, et al. "High Precision Magnetic Levitation Actuator for Micro-EDM." Actuators. 2022, 11(12), 361.
Note: this service is for Research Use Only and Not intended for clinical use.
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