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Technical Discussions
Nick Roussos
Greece, Joined Aug 2019, 3

Nick Roussos

Greece,
Joined Aug 2019
3
21:27 Jul-11-2020
UT crack height measurement
zoom image



Dear friends,
I want to measure the height of some sharp cracks that are perpendicular to the inner surface of a high-pressure pipe. Although the measurements seems to be relative accurate for small cracks I haven't been able to measure satisfactorily large cracks (I have a sectioned sample where I can measure the real height of the cracks). Any ideas please?
Thanks in advance

 
 Reply 
 
John Pitcher
R & D,
Retired, United Kingdom, Joined Sep 2016, 14

John Pitcher

R & D,
Retired,
United Kingdom,
Joined Sep 2016
14
23:18 Jul-11-2020
Re: UT crack height measurement
In Reply to Nick Roussos at 21:27 Jul-11-2020 (Opening).

Nick,
My first thought would be to use TOFD to measure the depth of the tip. If you scan across the crack and can resolve the tip.
Alternatively you could use a PA probe and use TFM to image the defect. I always think of TFM as multi TOFD and SAFT combined therefore very accurate.
JohnP

1
 
 Reply 
 
Paul Holloway
Consultant,
Holloway NDT & Engineering Inc , Canada, Joined Apr 2010, 253

Paul Holloway

Consultant,
Holloway NDT & Engineering Inc ,
Canada,
Joined Apr 2010
253
13:09 Jul-12-2020
Re: UT crack height measurement
In Reply to Nick Roussos at 21:27 Jul-11-2020 (Opening).

I agree with John, just use tip diffraction with your regular shear wave probe. It's super easy and accurate.

1
 
 Reply 
 
Anmol Birring
Consultant,
Birring NDE Center, Inc., USA, Joined Aug 2011, 832

Anmol Birring

Consultant,
Birring NDE Center, Inc.,
USA,
Joined Aug 2011
832
17:25 Jul-12-2020
Re: UT crack height measurement
In Reply to Nick Roussos at 21:27 Jul-11-2020 (Opening).

Comments.
1. TOFD is most accurate but will require two probes in pitch catch
2. Second option is Phased Array but make sure to focus properly
3. Pulse echo with conventional probe as shown in your diagrams is no good for sizing

1
 
 Reply 
 
Paul Holloway
Consultant,
Holloway NDT & Engineering Inc , Canada, Joined Apr 2010, 253

Paul Holloway

Consultant,
Holloway NDT & Engineering Inc ,
Canada,
Joined Apr 2010
253
21:52 Jul-12-2020
Re: UT crack height measurement
In Reply to Anmol Birring at 17:25 Jul-12-2020 .

Anmol, I use tip diffracted signals in PE mode all the time for sizing cracks and it works great.

 
 Reply 
 
levi Porter
R & D,
Dacon Inspection Technologies, Thailand, Joined Jan 2017, 67

levi Porter

R & D,
Dacon Inspection Technologies,
Thailand,
Joined Jan 2017
67
05:38 Jul-13-2020
Re: UT crack height measurement
In Reply to Anmol Birring at 17:25 Jul-12-2020 .

Hi Nick,
As suggested a simple angle beam setup should be satisfactory for height sizing to within +- 1mm true crack height.

I suggest a broadband highly damped higher frequency transducer (5-10Mhz) depending on your material and thickness.

Note: Cracks that propagate to within a few millimetres of the inspection surface may be difficult to size with PE. In this case I suggest a dual element angle beam setup.

 
 Reply 
 
Manfred Richter
Consultant,
Richter & Tomasi Ltd., Brazil, Joined Jan 2008, 34

Manfred Richter

Consultant,
Richter & Tomasi Ltd.,
Brazil,
Joined Jan 2008
34
15:29 Jul-13-2020
Re: UT crack height measurement
In Reply to levi Porter at 05:38 Jul-13-2020 .

zoom image



Nick,
The pictures self explain the diffraction sizing technique. Have attention for the wave fase in RF screen.
Regards
 
 Reply 
 
Andrew Crawford
Andrew Crawford
02:21 Jul-14-2020
Re: UT crack height measurement
In Reply to Nick Roussos at 21:27 Jul-11-2020 (Opening).

If you have a TFM option then using TTT will give you a very accurate result. Way higher POD than normal PAUT but given the stochastic nature of UT it would depend on the crack. The TFM option is by far the quickest and easiest to deploy in my experience.

 
 Reply 
 
Anmol Birring
Consultant,
Birring NDE Center, Inc., USA, Joined Aug 2011, 832

Anmol Birring

Consultant,
Birring NDE Center, Inc.,
USA,
Joined Aug 2011
832
18:02 Jul-14-2020
Re: UT crack height measurement
In Reply to Paul Holloway at 21:52 Jul-12-2020 .

Paul - Pulse echo works well on notches, but on cracks it can be hot or miss.

 
 Reply 
 
Paul Holloway
Consultant,
Holloway NDT & Engineering Inc , Canada, Joined Apr 2010, 253

Paul Holloway

Consultant,
Holloway NDT & Engineering Inc ,
Canada,
Joined Apr 2010
253
13:42 Jul-15-2020
Re: UT crack height measurement
In Reply to Anmol Birring at 18:02 Jul-14-2020 .

Anmol, can you explain why it would be hit or miss? I just completed a performance demonstration where I used tip diffraction to size real cracks quite successfully. It's best to use multiple angles and skews and then compare results to find the best facet for accuracy.

Thanks,
P

 
 Reply 
 
Levi Porter
R & D,
Dacon Inspection Technologies, Thailand, Joined Jan 2017, 67

Levi Porter

R & D,
Dacon Inspection Technologies,
Thailand,
Joined Jan 2017
67
11:29 Jul-16-2020
Re: UT crack height measurement
In Reply to Paul Holloway at 13:42 Jul-15-2020 .

zoom image



Hi Paul and All,
It's my opinion that pulse echo would be a go to tool for crack sizing but there are a few situations where it may not work. I'd like to explore further and this type of discussion may be valuable to some of the readers who may be interested or will be interested in the future.

•The crack tip is so small that the returned signal amplitude is insufficient to break the electronic or material noise (see attached picture INO48 B. Credit: TY - BOOK
AU - Zhai, Ziqing
AU - Olszta, Matthew
AU - Toloczko, Mychailo
AU - Bruemmer, Stephen
PY - 2015/08/01
T1 - Precursor Corrosion Damage and Stress Corrosion Crack Initiation in Alloy 600 During Exposure to PWR Primary Water)

•The through-wall propagation of the crack brings it into the transducers material boundary ultrasonic ring-down
○Likely this could be an issue with thin wall material.
Possible solution: Use a duel element angle beam
probe.

•The crack base signal and ring-down are so large the tip signal amplitude is enveloped in the base signal
○This could happen with very shallow cracks. Possible
remedy: Use highly damped and/or high frequency
transducer.

I'm sure there are other situations and scenarios left out. These same limitations would likely apply to TOFD but possibly TFM could be more accurate or remove some limitation of cracks in close proximity with material boundary.


For visualization of the crack tip diffraction please see the following page of photoelastic visualization by Mr. Edward Ginzel:

https://www.ndt.net/search/docs.php3?id=13899
2
 
 Reply 
 
Edward Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1307

Edward Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1307
14:03 Jul-16-2020
Re: UT crack height measurement
In Reply to Levi Porter at 11:29 Jul-16-2020 .

Levi, your illustrations contain some good examples where tip diffraction sizing can be weak. The illustrations labelled "d" and "f" show cracks with dendritic ends. These will not provide a single source diffraction pattern and will make it difficult to define the endpoint of a crack. Crack-tip format will have a significant effect on signal characteristics. Many years ago my brother worked on scanning of SCC crack colonies. In one of his experiments he used a 50 MHz PVDF probe and managed to show a "fuzzy cloud" forming around the tips of cracks. This seemed to be associated with a change in grain structure and initiation of crack propagation.

2
 
 Reply 
 
Paul Holloway
Consultant,
Holloway NDT & Engineering Inc , Canada, Joined Apr 2010, 253

Paul Holloway

Consultant,
Holloway NDT & Engineering Inc ,
Canada,
Joined Apr 2010
253
23:03 Jul-16-2020
Re: UT crack height measurement
In Reply to Edward Ginzel at 14:03 Jul-16-2020 .

Ed and Levi,

Great points and illustrations. Definitely agree.

I have a few 9.5mm thick weld samples with HAZ cracks up to 1mm deep. Indeed, these are difficult to size. With a 10MHz focused beam phased array probe I can resolve down to just below 1mm then I lose the tip in the corner.

(I can hear Andrew Crawford telling me to "try TFM, mate!")

Cheers,
P

 
 Reply 
 
levi Porter
R & D,
Dacon Inspection Technologies, Thailand, Joined Jan 2017, 67

levi Porter

R & D,
Dacon Inspection Technologies,
Thailand,
Joined Jan 2017
67
03:50 Jul-17-2020
Re: UT crack height measurement
In Reply to Edward Ginzel at 14:03 Jul-16-2020 .

Mr. Edward Ginzel,
It's interesting you brought up PVDF transducers. I see you said it was your brother who performed this testing, but please answer a few questions if possible. Was this a duel element setup with a PZT4/5 transmission element? I have been considering the thought of creating this type of transducer, and your feedback would be appreciated.

 
 Reply 
 

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