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- since 1996 -

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Technical Discussions
creed
NDT Inspector,
n.n., Joined Jul 2009, 29

creed

NDT Inspector,
n.n.,
Joined Jul 2009
29
04:48 Dec-06-2012
Eddy current testing for welds

Hi everyone,
I have quick questions related to Weld Eddy Current Tesing:
1. " When we use 100kHz probe, Can we detect subsurface defects within 2mm depth? because we used the calibration block with 2mm depth slot signal is reference level (eg. 80% of full screen)?
2. With the thin thickness of parent metal in weld testing will affect to the ECT signal? and How to control if YES?
Eg: the weld with the parent metal thickness is 2 or 3mm whilst we us ED slot calibration block with 5mm thick.
Thanks

 
 Reply 
 
John Hansen
Director, - Eddy Current Technology
ETher NDE Ltd, United Kingdom, Joined Oct 1999, 73

John Hansen

Director, - Eddy Current Technology
ETher NDE Ltd,
United Kingdom,
Joined Oct 1999
73
10:32 Dec-06-2012
Re: Eddy current testing for welds
In Reply to creed at 04:48 Dec-06-2012 (Opening).

1) At 100 kHz in Carbon Steel (Ferromagnetic) the Standard Depth of Penetration (aka skin depth) is about 0.03 mm. This means that as standard then eddy current can only be considered a surface method.

2) I think your question is now answered unless your material is non-magnetic.

All the best

John Hansen

 
 Reply 
 
Franlk Lund
R & D,
United Kingdom, Joined Apr 2005, 219

Franlk Lund

R & D,
United Kingdom,
Joined Apr 2005
219
11:45 Dec-06-2012
Re: Eddy current testing for welds
In Reply to creed at 04:48 Dec-06-2012 (Opening).

Creed,

1. The calibration slot starts from the inspection surface, so it gives a path for the interrogating current to penetrate into the test block by going down and up the flanks of the slot. If your slot is on the other side of the block, then the interrogating current in the slotless surface is not interrupted and will not see the slot.

2. Things get different when your 2mm deep vertical slot penetrates to the other side of the 2mm thick test piece. Of course, a slanted defect can have a 2mm pocket depth without penetrating a 2mm thick plate.

Cheers,
Frank

 
 Reply 
 
creed
NDT Inspector,
n.n., Joined Jul 2009, 29

creed

NDT Inspector,
n.n.,
Joined Jul 2009
29
22:41 Dec-06-2012
Re: Eddy current testing for welds
In Reply to John Hansen at 10:32 Dec-06-2012 .

Thanks John and Franlk.
Your answers make me feel open-minded. Prior I had stupid perpective in checking thin material might affected to signal.
Cheers.

 
 Reply 
 

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