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- since 1996 -

VOGT Ultrasonics GmbH
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Technical Discussions
Robbie
,
Australia, Joined Jun 2019, 11

Robbie

,
Australia,
Joined Jun 2019
11
02:05 Dec-13-2019
Button Probe Noise

Good morning everyone and happy Friday!! I have a question for the UT guru’s out there and your input is much appreciated! When scanning with a 5mhz twin crystal probe on a pipe that is 5mm (coated surface) the signal is relatively good, no dramas. When I put the button prob on (5Mhz) to examine slightly thinner material on the pipe (areas of internal corrosion) I have to be very very careful to not read the wrong signal as there is a large signal (80% fsh) before my actual 1st BWE. What causes this noise with the button probe as it’s also a twin crystal probe so there’s no initial pulse? Any input is much appreciated. Thanks

 
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Anmol Birring
Consultant,
Birring NDE Center, Inc., USA, Joined Aug 2011, 776

Anmol Birring

Consultant,
Birring NDE Center, Inc.,
USA,
Joined Aug 2011
776
04:46 Dec-15-2019
Re: Button Probe Noise
In Reply to Robbie at 02:05 Dec-13-2019 (Opening).

When you inspect from the side of internal corrosion there is no good contact. And the velocity in couplant is 1/4th of steel and that causes confusion. So probe on a 2 mm deep pit with couplant will be equivalent to 8 mm of steel
So the bottom line is the probe has to make full contact otherwise you will be lost

 
 Reply 
 
Paul Holloway
Consultant,
Holloway NDT & Engineering Inc , Canada, Joined Apr 2010, 218

Paul Holloway

Consultant,
Holloway NDT & Engineering Inc ,
Canada,
Joined Apr 2010
218
11:34 Dec-15-2019
Re: Button Probe Noise
In Reply to Robbie at 02:05 Dec-13-2019 (Opening).

Robbie, can you post a screenshot? Cross talk with dual crystal transducers is an issue, and the painted surface isn't doing you any favours. My recommendation for thin sections like that (~5mm) is to scrub with a single crystal 10MHz pen probe. I know it sounds a little nuts (scrubbing with a pen probe) but once you get used to it there's no turning back. I rarely use a dually anymore for complex internal corrosion, unless I'm just screening for later.

Cheers,
P

 
 Reply 
 
laurie
Australia, Joined Feb 2019, 34

laurie

Australia,
Joined Feb 2019
34
23:48 Dec-15-2019
Re: Button Probe Noise
In Reply to Robbie at 02:05 Dec-13-2019 (Opening).

To get good transmission and return you need smooth, "acoustically conductive" and parallel surfaces.

More gain can help but then you get an increase in noise which can be detected by the auto gate.

Start with the probe face, if its not flat and smooth or the insulating divider is chipped then you need to make it so. If you get to your wear limit then its time to get a new probe.

Then your contact surface, smooth off the paint if there are ripples, crazing, runs, etc, with some fine sandpaper. This will also remove the oxidized layer of paint which often significantly reduces transmission.
Having a parallel smooth surface on the inside isn't something you can control so a smaller probe will generally give you a smaller footprint which should be proportionately less rough than a larger probe and footprint and give you a better reflection.

 
 Reply 
 

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