Eddy current testing

Eddy Current Testing Coming of age By Jim Cox March 1998 During the period from 1775 to about 1900, several scientific experimenters investigated the many facets of electromagnetism. If we think about the tools that they must have used...

There are a lot of misconceptions about the limitations of eddy current testing. With the level of equipment and probe technology that has been achieved in the last few years, it is now possible to apply ECT to many test scenarios that previously could not be handled. Weld inspection for near surface flaws is a good example of this situation. With the right probes, both ferritic and non-ferritic weldments can be inspected. Another advancement that has taken place is the application of filtering and mixing technology to suppress unwanted non-flaw information.

Many aircraft inspection codes do not give eddy current its rightful place in the market. I suspect that this is normally based on the fact that no one wants to go back and re-address all of the paperwork that is required to upgrade those documents. When an EC test is applied with the proper probe and frequency choices, it can easily surpass the detection capability of many other NDE inspection processes. When the code phrasing uses something like ". . . demonstration of detectability equal to . . ." then you have the option of applying the most cost effective processes. Eddy current testing should come to mind at that point.

I have seen procedures that call for the same penetrant (PT) test to be performed multiple times to attempt to find tight cracks. The ECT inspection time would be much less and the flaw detection potential would be much higher in many of those cases. The same could be said for some inspections requiring magnetic particle (MT), or radiography (RT). Because a particular NDT method is listed as the code inspection does not necessarily mean that it is the best detection technique. Each situation should be evaluated on a cost vs. detection probability basis.

I doubt if Dr. Arago had any idea where his swinging magnet would take us. If you are not using ECT in your inspection processes on a regular basis, it may be time to get reacquainted with a very old technique that has truly come of age.

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