Non-Destructive Testing

Non-destructive testing has gained significant importance in modern industrial processes with its primary aim at reducing down time and enhancing safety and productivity.  Magnetic methods for NDT include magnetic flux leakage (MFL), electromagnetic acoustic transducer (EMAT) and hysteresis testing.

Each of these methods is sensitive to different defect configurations; while some are sensitive to surface cracks, others are sensitive to volume defects and yet others to internal stresses.  In each of these techniques, a magnetic field (time varying or static) is induced in the part to be tested and the response is analyzed to determine and characterize defects.

The MFL method is sensitive to surface cracks that impede the 'flow' of magnetic flux in ferromagnetic material -e.g. steel.   In this test method, a static magnetic field is impressed on the part to be tested.  Surface cracks cause a change in magnetic reluctance in the closed magnetic circuit resulting in a change in the amount of flux 'leaked' into air immediately outside the surface of the part.  Hall effect sensors are typically used to measure the leakage field.  Analysis of the leakage field over the surface thus permits characterization of the defect.

The EMAT method launches a surface acoustic wave in the ferromagnetic part.  Acoustic waves reflected from the defect couples back into the EMAT transducer through the magneto-elastic properties of the material.

The hysteresis method is sensitive to bulk properties.  In this method, an appreciable volume of the ferromagnetic part is subjected to a full magnetization cycle.  Changes in the hysteresis loop parameters, such as coercivity and remanence, are used as indicators of change in the physical properties in the bulk material.

Dexter Magnetic Technologies has a wide expertise in the design of optimal magnetic circuits and can assist you in designing your next non-destructive testing system. 

For further inquiries, please e-mail us at info@dextermag.com -or- call us at:  800-345-4082 (In North America) or +44 (0) 1189 602430 (In Europe).