Eddy Current Inspection

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

“Can you quick check this part for a possible crack?” If only I had a nickel for every time I heard that phrase. In my 23 years of inspecting aircraft for cracks and corrosion, I would have to say eddy current inspection is the most diverse, time-saving inspection method used in today’s fast-paced aircraft inspection world. 

Here is an easy-to-follow explanation of eddy current testing in which I will answer a few typical questions such as:

  • What is eddy current inspection?
  • Who can do eddy current inspection?
  • How can I get certified to do eddy current inspection?
  • What are the eddy current inspection applications that would help me or my facility?
  • What is the latest technology in eddy current inspections?

These are all good questions every director of maintenance or maintenance facility should ask themselves when they’re looking for a possible way to expand their inspection capabilities.

What is eddy current inspection?

“Eddy current” is a nondestructive testing (NDT) method that uses electricity and magnetism or electromagnetic induction to create a magnetic field in the article under inspection. Some of the most common benefits of using the eddy current method include:

  • Sensitive to small cracks and other defects
  • Detects surface and near surface defects
  • Inspection gives immediate results
  • Equipment is very portable
  • Method can be used for much more than flaw detection
  • Minimum part preparation is required
  • Test probe does not need to contact the part
  • Inspect complex shapes and sizes of conductive materials

Some of the limitations of using the eddy current method include:

  • Only conductive materials can be inspected
  • Surface must be accessible to the probe
  • Skill and training required is more extensive than other techniques
  • Surface finish and roughness may interfere
  • Reference standards needed for setup
  • Depth of penetration is limited
  • Flaws such as delamination that lie parallel to the probe coil winding and probe scan direction are undetectable

Who can accomplish eddy current inspections and how can I get certified?

Eddy current inspections can only be accomplished by qualified and certified NDT personnel as stated in NAS 410 “Certification & Qualification of Nondestructive Test Personnel.”

At a minimum the technician performing eddy current inspection is required to have 40 hours of formal classroom training and 1200 hours of on the job experience before performing eddy current inspections on aircraft and accepting or rejecting parts. Most technicians are tested every three to five years. Inspectors must complete a general knowledge exam (40 questions), a specific examination (30 questions), and a practical examination all given by a Level III NDT examiner.

Additional training may be required for certain aircraft manufacturers. Specific training on complex eddy current procedures is mandatory to maintain continuity on all inspection accomplished on critical aircraft components such as; vertical and horizontal stabilizer attach points, wing to fuselage attachments, and engine turbine discs, just to list a few.

Education for eddy current certificated inspectors generally comes from attending a two year engineering program, an NDT technical school, or military technical school with NDT military work experience.

Eddy current inspections are currently used in all aspects of aircraft NDT inspections. Cessna, Gulfstream, Bombardier, Falcon Dassault, and Hawker Beechcraft are just a few aircraft manufacturers that currently use eddy current inspection procedures to maintain high standards of crack free components in the aircraft industry. These same manufacturers are creating many new eddy current procedures as new aircraft and new technology becomes more computerized. An example would be eddy current array inspection procedures. These inspections can be used for multi skin corrosion detection as well as remaining skin thickness after corrosion removal.

What is the latest eddy current technology?  

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