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Technical Discussions
Arjun Vijay
NDT Inspector,
India, Joined Sep 2019, 2

Arjun Vijay

NDT Inspector,
India,
Joined Sep 2019
2
18:19 Nov-22-2019
PAUT Calibration Difficulty With Notch For Piping Job

Dear experts,
I have been calibrating my OmniScan MX2 machine for PAUT inspection on piping. My calibration block thickness is 38mm. It us provided with top and bottom notches with a depth of 10% of thickness. Iam using 5L64A12 probe and SA12N55S wedge. I have made a sectorial group having angle ranges from 42 to 68 degree. As iam doing my wedge delay calibration with bottom notch 55 degree to 63 portion is not getting calibrated properly, all other angles are ok. Even If I calibrate wedge delay somehow, then Iam suffering in sensitivity calibration. During sensitivity calibration as i pick signals from bottom notch, the amplitude decrease gradually from 45 to 55 degree as it is supposed to be, but after 55 degree the problem starts, my echo amplitude suddenly starts to drop to 2 to 3% and even 0%. My questions are
1.why Iam facing this problem?
2. Is this a normal problem during calibration with notch?
3. Can anyone suggest a solution?

 
 Reply 
 
Anmol Birring
Consultant,
Birring NDE Center, Inc., USA, Joined Aug 2011, 751

Anmol Birring

Consultant,
Birring NDE Center, Inc.,
USA,
Joined Aug 2011
751
14:52 Nov-23-2019
Re: PAUT CALIBRATION DIFFICULTY WITH NOTCH FOR PIPING JOB
In Reply to Arjun Vijay at 18:19 Nov-22-2019 (Opening).

Good Observation.
There is a difference between the notch and hole reflectors. The main difference is that notch has two reflections, the bottom of the block and the face of notch. And when the S-wave reflected angle from one the faces falls below 32.1 degrees (for refracted angle exceeding 57.9 degree), there is mode conversion and a step drop in reflection as the waves split to L- and S- waves. That is why the wedge delay and sensitivity calibrations are done on holes where there is no mode conversion.
Hope the explanation is clear, otherwise let me know and I will send some figures.

 
 Reply 
 
Arjun Vijay
NDT Inspector,
India, Joined Sep 2019, 2

Arjun Vijay

NDT Inspector,
India,
Joined Sep 2019
2
15:06 Nov-23-2019
Re: PAUT Calibration Difficulty With Notch For Piping Job
In Reply to Anmol Birring at 14:52 Nov-23-2019 .

Thank you sir for the information. It would be more helpful if you provide me with images. So how can I overcome this problem sir. Since my client is telling me (even the code) to use only notch for calibration since it is a piping job. If my wedge delay and sensitivity calibration is not proper then surely my TCG also will be in trouble. Give me a solution sir.

 
 Reply 
 
Edward Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1282

Edward Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1282
15:28 Nov-23-2019
Re: PAUT Calibration Difficulty With Notch For Piping Job
In Reply to Anmol Birring at 14:52 Nov-23-2019 .

Anmol, I noted that Arjun has indicated that he is doing his wedge-delay calibration on the notch too. Wedge delay should be done using a constant metal path so a target like a SDH or a fixed radius should be used for wedge delay calculations.

 
 Reply 
 
Anmol Birring
Consultant,
Birring NDE Center, Inc., USA, Joined Aug 2011, 751

Anmol Birring

Consultant,
Birring NDE Center, Inc.,
USA,
Joined Aug 2011
751
17:10 Nov-24-2019
Re: PAUT Calibration Difficulty With Notch For Piping Job
In Reply to Arjun Vijay at 15:06 Nov-23-2019 .

Because of mode conversion on notch you will be limited to a range from 32.1 to 57.9 degrees for a smooth calibration curve.
In reality you don’t need wedge delay as there is no issue with depth measurement.
For sensitivity calibration on notch, there will be a big jump at 57.9 deg.
ASME code allows holes for piping. See Alternate piping Block in ASME V art 4, 2017.

1
 
 Reply 
 
Paul Holloway
Consultant,
Holloway NDT & Engineering Inc , Canada, Joined Apr 2010, 200

Paul Holloway

Consultant,
Holloway NDT & Engineering Inc ,
Canada,
Joined Apr 2010
200
00:02 Nov-26-2019
Re: PAUT Calibration Difficulty With Notch For Piping Job
In Reply to Arjun Vijay at 18:19 Nov-22-2019 (Opening).

zoom image


The blue smear of the notch (sigh)

As Anmol has pointed out, calibrating for sensitivity on a vertical notch will result in mode conversion around 60 degrees. This means a significant drop in amplitude while "tracing the green line" during sensitivity/TCG calibration. As a result, the TCG will boost those signals sky high, and you can end up with the "blue smear".

For really thin wall thickness, you have no choice, you'll have to use notches. That's because you can't drill a 2.38mm hole through a 5.5mm wall thickness and expect to have any reasonable amount of steel left. However, in every other case I prefer side-drilled holes. And as Anmol has pointed out, they are perfectly valid and allowed by ASME without any qualification or special consideration.

I've written a couple articles about this exact scenario which you can find here:

http://www.hollowayndt.com/news/2018/11/27/notches-vs-side-drilled-holes-chapter-1-echo-dynamics

http://www.hollowayndt.com/news/2019/6/17/notches-vs-side-drilled-holes-chapter-2

 
 Reply 
 
Peter
Singapore, Joined Jan 2012, 121

Peter

Singapore,
Joined Jan 2012
121
03:49 Nov-26-2019
Re: PAUT Calibration Difficulty With Notch For Piping Job
In Reply to Paul Holloway at 00:02 Nov-26-2019 .




Dear Experts,

ASME V SECTION T-434 referred. ASME allows the use of Side drill hole for piping blocks below 20” if the sensitivity of side drill hole equivalent or greater than required notch sensitivity. As per below example, the depth of notch is at 6.78mm for half skip distance. For side drill hole we shall choose 1 1/4t(9.52mm) as a first point for TCG to achieve sensitivity equivalent of greater. Please correct me if I am wrong. Thanks.

Example:-
a) Pipe : 3inch schedule 80
b) Thickness : 7.620mm
c) Notch depth at ½ skip( 11% depth) located at 6.78mm
d) SDH depth 1/4t(1.9mm), 1/2t(3.81mm), 3/4t(5.72mm), 1 1/4t( 9.52mm)



Peter
 
 Reply 
 
Joe Buckley
Consultant, ASNT L-III, Honorary Secretary of BINDT
Level X NDT, BINDT, United Kingdom, Joined Oct 1999, 524

Joe Buckley

Consultant, ASNT L-III, Honorary Secretary of BINDT
Level X NDT, BINDT,
United Kingdom,
Joined Oct 1999
524
07:41 Nov-26-2019
Re: PAUT Calibration Difficulty With Notch For Piping Job
In Reply to Paul Holloway at 00:02 Nov-26-2019 .

Very useful article Paul.

Does anyone know of a ‘theoretical’ discussion article on notch mode conversion?

N.B. noticed the pdf link on the second one doesn’t work.

 
 Reply 
 
Matthias Dreifeld
NDT Inspector, CEO
Dreifeld Materialprüftechnik, Germany, Joined Sep 2005, 100

Matthias Dreifeld

NDT Inspector, CEO
Dreifeld Materialprüftechnik,
Germany,
Joined Sep 2005
100
10:37 Nov-26-2019
Re: PAUT Calibration Difficulty With Notch For Piping Job
In Reply to Paul Holloway at 00:02 Nov-26-2019 .

That's because you can't drill a 2.38mm hole through a 5.5mm wall thickness and expect to have any reasonable amount of steel left.

----

Paul, cant you just drill a 1 mm hole and calculate the dB difference?

 
 Reply 
 
Edward Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1282

Edward Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1282
14:47 Nov-26-2019
Re: PAUT Calibration Difficulty With Notch For Piping Job
In Reply to Joe Buckley at 07:41 Nov-26-2019 .

Joe, Ulrich Mletzko provided an interesting replty in a 2010 Forum topic on the corner reflector (https://www.ndt.net/forum/thread.php?admin=&forenID=0&msgID=33354&rootID=33327#33354). Ulrich's comments describe the quantification of losses at the critical mode conversion angles.

 
 Reply 
 
Miguel Diaz
Miguel Diaz
17:45 Nov-27-2019
Re: PAUT Calibration Difficulty With Notch For Piping Job
In Reply to Peter at 03:49 Nov-26-2019 .

Buen día Peter.

Mis disculpas por escribirte en mi idioma pero estoy seguro que con las herramientas actuales puedes leerme sin problemas y puedo explicarte mejor.

Primero, si estás realizando una inspección bajo el código ASME en tuberías, debes usar el bloque ASME para tuberías el cual aparece en T-434.3 con las dos alternativas que aparecen para ellos: el de solo entallas o muescas (notch) y el de agujeros de lado (SDH) pero este segundo, siempre que se permita por su espesor... entonces en espesores muy delgados no se deben usar perforaciones sobre todo por la imposibilidad de perforar y porque no siguen una curvatura en la sección transversal del tubo... eso se puede hacer para espesores altos, diría yo, sobre 38mm incluso mayores.

En cuanto a la dificultad para calibrar el sistema con entallas, esto se debe más a las leyes focales que deseamos calibrar o poner a punto. Si la calibración resulta dicil debemos replantear las aperturas, voltajes, ángulos, etc... si no mejora por ningún lado entonces puede ser un tema de frecuencia y tamaño de los elementos...

 
 Reply 
 
Paul Holloway
Consultant,
Holloway NDT & Engineering Inc , Canada, Joined Apr 2010, 200

Paul Holloway

Consultant,
Holloway NDT & Engineering Inc ,
Canada,
Joined Apr 2010
200
19:22 Nov-27-2019
Re: PAUT Calibration Difficulty With Notch For Piping Job
In Reply to Matthias Dreifeld at 10:37 Nov-26-2019 .

Matthias,

I suppose you could, but then you'd have one more step and a demonstration to document to your auditor. Depending on how versed they are with UT, you may end up with more questions than you want to answer. I find it's easier to try to play "in bounds" as much as possible.

Cheers,
P

 
 Reply 
 
Paul Holloway
Consultant,
Holloway NDT & Engineering Inc , Canada, Joined Apr 2010, 200

Paul Holloway

Consultant,
Holloway NDT & Engineering Inc ,
Canada,
Joined Apr 2010
200
19:38 Nov-27-2019
Re: PAUT Calibration Difficulty With Notch For Piping Job
In Reply to Peter at 03:49 Nov-26-2019 .

Hi Peter,

The paragraph you quote is specifically for reflectors which do not meet the requirements of either the standard notch block (Fig. T-434.3-1) or the side-drilled hole block (Fig. T-434.3-2). Side-drilled holes are perfectly valid without any additional qualification provided they meet T-434.3-2.

If, however, you wanted to use curved holes, slots, or maybe even just holes that were a different size than specified in T-434.3-2 then you'd have to prove the resultant sensitivity was equal or greater over the sound path range used. This usually means a documented procedure qualification reviewed and accepted by your auditor.

Best regards,
Paul

 
 Reply 
 
Peter
Singapore, Joined Jan 2012, 121

Peter

Singapore,
Joined Jan 2012
121
02:12 Nov-29-2019
Re: PAUT Calibration Difficulty With Notch For Piping Job
In Reply to Paul Holloway at 19:38 Nov-27-2019 .

Hi Mr Miguel Diaz,

Thanks for the advice. I manage to convert from Spanish to English to understand the informations better. Thanks again.

Hi Mr Paul,

Thanks

Peter

 
 Reply 
 

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