Magnetic Non-destructive Testing


Magnetic non-destructive testing is based on analysis of dispersion fields generated during test object magnetization in the area of a flaw. The technology allows performing instant diagnosis of ferromagnetic test objects with high efficiency. Tubes of small and large diameters, vertical steel tanks, rods and flat steel can be tested using the technology. Operating principle of magnetic flaw detectors for testing pipelines is based on the technology. The technology is non-contact and does not require advance surface preparation.

Operating principle

The technology operating principle is shown in Figure 1. The magnetic field source is a permanent magnet and generates magnetic flux in the test object. In the absence of flaws, magnetic field is almost completely inside the ferromagnetic test object and the magnetic field sensor (Hall sensor in Figure 1) detects absence of magnetic field. In the presence of flaws, a local change in the test object magnetic properties occurs; magnetic field tries to go round the area with a low magnetic permeability, and therefore partly comes to the surface, generating dispersion fields. The magnetic field sensor registers these fields. Thus, information about the presence of magnetic field in the sensor indicates the presence of a flaw under the sensor.
Figure 1. MFL technology operating principle

Main advantages of magnetic non-destructive testing

      • The technology do not require test object surface preparation
      • The technology is non-contact
      • High efficiency. For example, when testing gas pipeline efficiency is up to 10 running meters per second
      • High reliability during instant diagnosis