Eddy Current Inspection

One of the most diverse nondestructive testing (NDT) methods.


Many of today’s eddy current units have color screens along with memory to store and create eddy current reports and another feature are units having detachable probes. Most equipment is very portable for work on and around aircraft structures.   

Eddy current array (ECA) is a nondestructive testing technique that provides the ability to electronically drive multiple eddy current coils, which are placed side by side in the same probe assembly. Each individual eddy current coil in the probe produces a signal relative to the phase and amplitude of the structure below it. This data is referenced to an encoded position and time, and represented graphically as a C-scan image. Most conventional eddy current flaw detection techniques can be reproduced with ECA inspections; however, the remarkable advantages of ECA technology allows improved inspection capabilities and significant time savings. Eddy current array technology includes the following advantages:

  • A larger area on the aircraft can be scanned in a single-probe pass, while maintaining a high resolution
  • No need for complex robotics to move the probe; a simple manual scan is often enough
  • Imaging improves flaw detection and sizing
  • Complex shapes can be inspected using probes customized to the profile of the part being inspected

Conclusion

The eddy current method of inspection is taking the place of more time consuming and hazardous inspection methods such as radiography. In most cases eddy current inspections can be accomplished with one trained technician. Radiography in most states require two technicians for safety reasons along with the high costs of equipment and film processing chemicals and hazardous waste concerns. The eddy current process basically has no consumable materials involved such as gels, couplants, and chemicals, and most aircraft inspections are on the outer surface with no aircraft preparations. Many inspections requiring second, third and fourth layer skin inspections will be able to be accomplished at a high degree of certainty that aging aircraft components are airworthy. Any NDT inspector will advise you to thoroughly research all inspection equipment requirements, education and training, and aircraft manufactures requirements prior to accomplishing any type of inspection.

I consider myself fortunate because during my career as an NDT technician to have been able to use old and new eddy current inspection equipment. New techniques are constantly being introduced into the aerospace industry requiring shorter inspection times and at the same time requiring higher sensitivity to smaller defects. There is, as in any technical profession, a certain amount of technical training that must be regularly accomplished in order to maintain high inspection standards with a high degree of confidence in the technician and eddy current inspection equipment being used.

About the author

Mark Nistler is currently the NDT Shop Manager at Signature TECHNIAir, St. Paul, MN, with a total of 23 years experience in the NDT field. He is an American Society for Nondestructive Testing (ASNT) Level III certified in four methods: magnetic particle, fluorescent penetrant, radiography, and eddy current inspections. He also holds an A&P certificate and is currently the company Level III in Ultrasonics. Mark began his aircraft maintenance career in the U.S. Air Force performing NDT inspections on military aircraft such as the F-16, F-15, C-130, and H3 helicopters. He can be contacted at mark.nistler@signatureflight.com  or (651) 209-2720.

 

 

 

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