Balanced Field Electromagnetic Technique Fundamentals:
The Balanced Field Electromagnetic Technique was developed to enhance the signal responses produced from smaller defects such as cracks. The technology was originally used to detect cracking from the outside surface to inspect welds in DA Tanks, pressure vessels, tube stubs, and any other areas suspected to have cracking. In this technique, electromagnetic coils are wound and arranged in a balanced state. This balanced state is achieved by placing coils in both the "x" and "z" geometries at zero potential to each other. With the excitation coil in the "x" geometry and the sensor coil in the "z" geometry, a differential signal is produced over defected areas. In detail, the alternating current produced by the excitation coil is uniform and undisturbed when no defects are present. Thus the name Balanced Field Electromagnetic Technique. Conversely, the current is interrupted when a defect is present and forced to travel around it in a distorted fashion. It is this state of distortion that causes the coils to become unbalanced and thus producing an indication for the user that signals a defect. This distortion signal response can be measured and a crack depth can be calculated by comparison to a calibration standard.
With the technology based on electromagnetics, a polished surface is not required. Quality readings can be acquired through coatings such as paint, epoxy, and rubber. The actual probe does not need to be in contact with the test piece. Sometimes the probe is placed in a small cart with the probe base set slightly above the test piece. The probe can be pulled quickly across the test specimen at a speed up to 1 foot per second. The BFET method can test different types of metal by adjusting the test frequencies which range from 100HZ to 30,000HZ.
Benefits of BFET inspection:
1 Detects surface and subsurface cracking with or without coating.
2 Test speeds up to 1' per second.
3 Inspects Ferrous and non Ferrous materials.
4 Minimal surface preparation.
Prove up of this technique is typically done with Mag-Particle, and/or Shear Wave UT.
Alternative uses for BFET include detection of Graphetization, corrosion fatique cracking.
At TesTex we call our BFET system the Hawkeye.
The Balanced Field Electromagnetic Technique was developed to enhance the signal responses produced from smaller defects such as cracks. The technology was originally used to detect cracking from the outside surface to inspect welds in DA Tanks, pressure vessels, tube stubs, and any other areas suspected to have cracking. In this technique, electromagnetic coils are wound and arranged in a balanced state. This balanced state is achieved by placing coils in both the "x" and "z" geometries at zero potential to each other. With the excitation coil in the "x" geometry and the sensor coil in the "z" geometry, a differential signal is produced over defected areas. In detail, the alternating current produced by the excitation coil is uniform and undisturbed when no defects are present. Thus the name Balanced Field Electromagnetic Technique. Conversely, the current is interrupted when a defect is present and forced to travel around it in a distorted fashion. It is this state of distortion that causes the coils to become unbalanced and thus producing an indication for the user that signals a defect. This distortion signal response can be measured and a crack depth can be calculated by comparison to a calibration standard.
With the technology based on electromagnetics, a polished surface is not required. Quality readings can be acquired through coatings such as paint, epoxy, and rubber. The actual probe does not need to be in contact with the test piece. Sometimes the probe is placed in a small cart with the probe base set slightly above the test piece. The probe can be pulled quickly across the test specimen at a speed up to 1 foot per second. The BFET method can test different types of metal by adjusting the test frequencies which range from 100HZ to 30,000HZ.
Benefits of BFET inspection:
1 Detects surface and subsurface cracking with or without coating.
2 Test speeds up to 1' per second.
3 Inspects Ferrous and non Ferrous materials.
4 Minimal surface preparation.
Prove up of this technique is typically done with Mag-Particle, and/or Shear Wave UT.
Alternative uses for BFET include detection of Graphetization, corrosion fatique cracking.
At TesTex we call our BFET system the Hawkeye.
