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Technical Discussions
Sergey
NDT Inspector,
EAST METAL ltd, Latvia, Joined Sep 2017, 4

Sergey

NDT Inspector,
EAST METAL ltd,
Latvia,
Joined Sep 2017
4
23:30 Sep-02-2017
Probe index

Hello,
I have a problem. My probe 80° 4 MHz (official 77°) is showing index beyond measuring scale. The scale is 17 mm, index about... 20 or so. I tried the same probe (same manufacturer, same angle) - also index is too far. I tried another UT device (same model, same manufacturer) with both probes - the same situation. All other angles and frequencies have no problems. Both devices - GE Krautkramer USM 36. Both probes also GE, absolutely the same.
My colleague tried both GE probes on his Olympus Epoch 600 and got index of 12 mm.
What could be my problem?

    
 
 Reply 
 
Anmol Birring
Consultant,
Birring NDE Center, Inc., USA, Joined Aug 2011, 746

Anmol Birring

Consultant,
Birring NDE Center, Inc.,
USA,
Joined Aug 2011
746
04:28 Sep-03-2017
Re: Probe index
In Reply to Sergey at 23:30 Sep-02-2017 (Opening).

How are you measuring the index point and is this S or L wave ?

    
 
 Reply 
 
massimo carminati
Consultant, AUT specialist
IMG Ultrasuoni Srl, Italy, Joined Apr 2007, 691

massimo carminati

Consultant, AUT specialist
IMG Ultrasuoni Srl,
Italy,
Joined Apr 2007
691
09:53 Sep-03-2017
Re: Probe index
In Reply to Sergey at 23:30 Sep-02-2017 (Opening).

I doubt it is a matter of instrument. 80s probes are difficult probes to use and I always recommend creeping waves instead.

    
 
 Reply 
 
Sergey
NDT Inspector,
EAST METAL ltd, Latvia, Joined Sep 2017, 4

Sergey

NDT Inspector,
EAST METAL ltd,
Latvia,
Joined Sep 2017
4
11:53 Sep-03-2017
Re: Probe index
In Reply to Anmol Birring at 04:28 Sep-03-2017 .

We call it V1 block. (I am very new in UT, especially in english terminology, pardon me) this is S wave I guess (the one with ~3250 speed in steel) This block has r100 to catch the peak of signal and an arrow showing exit point on the scale of a probe.
I also tried to catch 15 mm depth side drill hole. It shows depth (y) correctly, and beam (S) also, and calculation and measuring still give me index more than 17 mm. On Both USM 36. On Epoch 600 it shows correctly.

    
 
 Reply 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1268

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1268
16:35 Sep-03-2017
Re: Probe index
In Reply to Sergey at 11:53 Sep-03-2017 .

Sergy, at such a high refracted angle in shear mode on the "V1" block, you may in fact be seeing a larger response from the Rayleigh mode (surface wave). This mode will have a slower velocity than the shear mode and if your instrument is using the "assumed" velocity of 3240m/s to make trigonometric calculations then it could result in the instrument software making an incorrect positioning of the exit point.
Using the hole at 15mm depth as a target to verify the trigonometry calculations uses the shear component of the wavefront and avoids the surface wave (which does not penetrate more than about 1 wavelength under the surface).
To see if it is the Rayleigh wave you are using on the "V1" block, rub your finger on the surface in front of the probe. If the signal is damped by your finger movement, then it is probably the Rayleigh mode.

1    
 
 Reply 
 
Paul Holloway
Consultant,
Holloway NDT & Engineering Inc , Canada, Joined Apr 2010, 191

Paul Holloway

Consultant,
Holloway NDT & Engineering Inc ,
Canada,
Joined Apr 2010
191
19:54 Sep-03-2017
Re: Probe index
In Reply to Ed Ginzel at 16:35 Sep-03-2017 .

zoom image
Further to Ed's advice, here is the wave mode in action.

-Paul
1    
 
 Reply 
 
Joe Buckley
Consultant, ASNT L-III, Honorary Secretary of BINDT
Level X NDT, BINDT, United Kingdom, Joined Oct 1999, 522

Joe Buckley

Consultant, ASNT L-III, Honorary Secretary of BINDT
Level X NDT, BINDT,
United Kingdom,
Joined Oct 1999
522
23:20 Sep-03-2017
Re: Probe index
In Reply to Sergey at 23:30 Sep-02-2017 (Opening).

You say your colleague gets more like the 'expected' results with the same probes. Might be worth confirming he is also using the same test block.I have seen small amounts on anisotropy on V1 blocks (shouldn't be, but...) It wouldn't take much to make a difference.

1    
 
 Reply 
 
Sergey
NDT Inspector,
EAST METAL ltd, Latvia, Joined Sep 2017, 4

Sergey

NDT Inspector,
EAST METAL ltd,
Latvia,
Joined Sep 2017
4
19:58 Sep-04-2017
Re: Probe index
In Reply to Joe Buckley at 23:20 Sep-03-2017 .

My colleague used another V1 block.
I remind that I got a good result on my V1 for all probes except 80.

    
 
 Reply 
 
Sergey
NDT Inspector,
EAST METAL ltd, Latvia, Joined Sep 2017, 4

Sergey

NDT Inspector,
EAST METAL ltd,
Latvia,
Joined Sep 2017
4
20:29 Sep-04-2017
Re: Probe index
In Reply to Ed Ginzel at 16:35 Sep-03-2017 .

I found exactly the same picture on the screen as Paul shows. But the difference between signals is not so big (about 4 dB) Peak of the higher signal shows index ~20. The peak of the lower signal shows index 13.
I managed to calibrate and build DAC after that. Ready for work.
Thank you a lot!

    
 
 Reply 
 

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