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- since 1996 -

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Technical Discussions
Rob Taylor
,
Australia, Joined Jun 2019, 12

Rob Taylor

,
Australia,
Joined Jun 2019
12
10:16 Jun-02-2020
Accurate sizing of defect height using UT

Hello gentlemen! I hope everyone is doing as well as we can be during this crazy time. I was hoping I could get some advice in through-wall (Height) sizing using manual UT. Iv been told the best way to size defect height is to first remove the scanning DB then move the probe forward until the signal drops to Dac..... and repeat moving the probes backwards and mark the index point... this measurement will give you the defect height. My problem with this method is we are working to iso11666 so when removing the scanning DB any discontinuity that is -10 dB and above can be rejected depending on plate thickness so using the Dac to size defect height can not be done? Any simple ways sizing of defect height would be appreciated.

Rob

 
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Paul Holloway
Consultant,
Holloway NDT & Engineering Inc , Canada, Joined Apr 2010, 248

Paul Holloway

Consultant,
Holloway NDT & Engineering Inc ,
Canada,
Joined Apr 2010
248
22:45 Jun-02-2020
Re: Accurate sizing of defect height using UT
In Reply to Rob Taylor at 10:16 Jun-02-2020 (Opening).

Hi Rob,

The amplitude of the indication may have very little bearing on it's size as a whole. I recommend the max amp technique:

https://www.ndt.net/forum/files/maximumamplitudetechniqueknownasmaxamp.pdf

Cheers,
Paul

 
 Reply 
 
John Pitcher
R & D,
Sonomatic Ltd, United Kingdom, Joined Sep 2016, 13

John Pitcher

R & D,
Sonomatic Ltd,
United Kingdom,
Joined Sep 2016
13
12:16 Jun-03-2020
Re: Accurate sizing of defect height using UT
In Reply to Paul Holloway at 22:45 Jun-02-2020 .

Have you considered increase the gain and look for diffracted signals from the top and bottom of the defect?
JohnP

 
 Reply 
 
Paul Holloway
Consultant,
Holloway NDT & Engineering Inc , Canada, Joined Apr 2010, 248

Paul Holloway

Consultant,
Holloway NDT & Engineering Inc ,
Canada,
Joined Apr 2010
248
01:45 Jun-04-2020
Re: Accurate sizing of defect height using UT
In Reply to John Pitcher at 12:16 Jun-03-2020 .

Hi John,

Max amp is basically tip diffraction. It's the only way to really get an accurate measurement. My PAUT instructor (Tim Armitt) showed me years ago how to size LOF from the "wrong side" using diffracted signals. From the near side, it's a screaming loud mirror-like reflector that completely dwarfs the tips. But from the other side, the tips are all you see. Crank it up!! :)

P

 
 Reply 
 

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