TS 2000 Tube Scanner

 Demonstration Preview

The Low Frequency Electromagnetic Technique works by injecting a low frequency magnetic field into a metal plate or tube and measuring the distortions in the resulting magnetic field that occur over a flaw.  This injection can be achieved by using an external horseshoe shaped driver coil.  This driver coil is placed such that the return path for the magnetic field is through the area to be tested.  Flaws are detected by measuring the magnetic field directly over the flaw area with sensor coils.  A flaw or defect causes the magnetic flux lines in that area to be distorted or different than expected.  This distortion can be measured as a change in phase and/or amplitude.  With suitable calibration tables the flaw can be analyzed and a determination of the flaw’s depth and shape can be made.  By using several sensors in the scanner array it is possible to display a 3D image of the collected data so that the shape and depth of the flaw can be determined. 

Low frequencies (< 30 Hz.) are used on carbon steel plates because the high magnetic permeability and conductivity of carbon steel greatly resists the penetration of higher frequencies into the metal.  By using low frequencies, the penetration of the magnetic field is more uniform throughout the plate wall thickness and defects on both the top and bottom sides of the plate can be seen.  Because the sensor coils detect magnetic fields, the effects of residual plate magnetism and noise from outside magnetic fields can be greatly reduced by increasing the magnetic field from the horseshoe shaped driver coils.  As with other types of electromagnetic NDT; the lower the frequency, the higher the penetration.  Conversely, the higher the frequency: the lower the penetration.  Select a frequency that gives the best signal to noise ratio, as well as the greatest response when gaining on the test piece and then lifting the scanner off of the test piece. 

By adjusting the test frequency, different types of metal can be tested including aluminum, stainless steel, and carbon steel. 

Generally, carbon steel specimens up to 3/4" thick can be tested with the Low Frequency Electromagnetic Technique.

Applications:

n  Boiler Waterwalls n  Reheaters/Superheaters n  Storage Tanks n  Pipelines n  Service Water Piping n  Fire Protection Piping n  Coal Mill Piping n  General Piping n  Pressure Vessels n  Heat Exchanger Shells