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Technical Discussions
S.Williams
S.Williams
13:44 Nov-30-2018
Calibration using curved wedges

How does one calibrate the time base with an IIW block or rompas block which is flat using a curved wedge as required by ASME V?

    
 
 
Paul Holloway
Consultant, UT Level 3
Holloway NDT & Engineering Inc , Canada, Joined Apr 2010, 171

Paul Holloway

Consultant, UT Level 3
Holloway NDT & Engineering Inc ,
Canada,
Joined Apr 2010
171
14:51 Nov-30-2018
Re: Calibration using curved wedges
In Reply to S.Williams at 13:44 Nov-30-2018 (Opening).

zoom image


ERVW blocks at ASNT 2018

Hi Shawn:

Timely question, I'm in the process of writing a series of articles on calibration for piping. Effective and code-compliant calibrations on curved piping was one of the main reasons behind the design of the ERVW piping calibration blocks available from PH Tool (https://www.phtool.com/store2/proddetail.asp?prod=ERVW%2EPIPE%2ESDH)

Chapter 1 of the article is here:
http://www.hollowayndt.com/news/2018/11/27/notches-vs-side-drilled-holes-chapter-1-echo-dynamics

Because the wedge is an essential variable, you must use the same wedge during calibration as examination. So you can't calibrate with a flat wedge on an IIW-Type or Rompas then switch to a contoured wedge (which I think was the point of your question).

So put away the IIW/Rompas and grab your piping calibration block that you're using for DAC/TCG.

Velocity calibration: don't bother. Unless your piping material is exotic, just start with the nominal shear wave velocity. There is really little value to performing a velocity calibration because the value you'll end up with should be within a few percentage points of nominal anyways. This can always be verified after calibration.

Wedge delay/zero offset: this can be difficult with standard notch blocks because of the mode conversions around 60 degrees. In fact, if you hit a notch at 60-62 degrees, you may notice the peak of the echo dynamic occurs before the backwall (corner trap, "B0" on an Omniscan). This is because the signal at 60 is actually so weak due to mode conversion that the signal is actually stronger at lower angles (e.g. 55 degrees), even though the middle of your beam at 60 degrees is lined up with the corner trap. It will be more pronounced with conventional UT because it's a single-point calibration. With phased array, you may be able to get away with it as the curve-fit from the calibration wizard is based on the entire angular sweep and may blur out the "bump" that occurs around 60 degrees. You'd have to verify this yourself on whatever system/blocks you are using.

Hope that helps,
Paul
4    
 
 
Ali
NDT Inspector,
Iran, Joined Mar 2013, 93

Ali

NDT Inspector,
Iran,
Joined Mar 2013
93
19:08 Nov-30-2018
Re: Calibration using curved wedges
In Reply to S.Williams at 13:44 Nov-30-2018 (Opening).

You can also use curved V2 calibration block for wedge delay calibration of piping welds.

2    
 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1252

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1252
23:41 Nov-30-2018
Re: Calibration using curved wedges
In Reply to S.Williams at 13:44 Nov-30-2018 (Opening).




Shawn, as Ali noted, it is possible to obtain an IIW-Type block with a curved surface. As long as the apex of the curvature is accurately made so that the distance from the centre of radius at the apex to the 100mm radius is 100mm, your wedge delay and time-base calibration should be correct. There are good instructions in the ISO 2400 and ISO 19675 documents (for calibration block fabrication) to ensure that the calibration block velocities are held within a small range of tolerance. Therefore the velocity settings on your instrument should provide a good calibration. The calibration will require that your mid-point of the radiused wedge be centred on the curved contact. As long as the curvature of the block is smaller than the curvature of the wedge this will be possible. A reasonably small curvature on the cal block would be about 25mm radius.
In the attached image I made in Civa you can see how a wedge, radiused to 100mm fits on a 25mm radius surface. If the radius of the wedge is smaller than the radius of the block you will not be measuring the true wedge delay as there will be gap formed between the wedge and block. Assuming you can fill that gap with couplant it adds to the delay being detected by the instrument and the calculation for wedge delay will be incorrect in your calibration.
2    
 
 
S.Williams
S.Williams
19:05 Jan-31-2019
Re: Calibration using curved wedges
In Reply to Ed Ginzel at 23:41 Nov-30-2018 .

So how is everyone checking their exit points and beam angles? Is everyone using curved blocks. What range of diameters can you use a curved shoe on or does every diameter require it's own curved shoe?

Reminds of when ASME changed the cal block requirements so that you needed to have the same diameter and schedule then changed it back to the way it is now. I hope they change this back as well.

    
 
 
Paul Holloway
Consultant, UT Level 3
Holloway NDT & Engineering Inc , Canada, Joined Apr 2010, 171

Paul Holloway

Consultant, UT Level 3
Holloway NDT & Engineering Inc ,
Canada,
Joined Apr 2010
171
19:57 Jan-31-2019
Re: Calibration using curved wedges
In Reply to S.Williams at 19:05 Jan-31-2019 .

Download Making Sense of Wedge Curvature (an afternoon nap)

Shawn,

The ASME rules for wedge curvature actually make a lot of sense, it's just the way that they've worded it is really poor in the 2017 edition.

I wrote an article that I think explains it in a little less confusing way (attached pdf).

Paul
    
 
 
Edward Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1252

Edward Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1252
20:34 Jan-31-2019
Re: Calibration using curved wedges
In Reply to S.Williams at 19:05 Jan-31-2019 .

Shawn, the issues relating to small diameter pipe girth-weld inspections are indeed frustrating. In the January 2019 issue of NDT.net, I have a rather lengthy paper where I tried to consider many of these parameters. https://www.ndt.net/article/ndtnet/papers/Modelling-Probe-Wedge-and-Pipe-Geometry-as-Critical-Parameters-in-Pipe-Girth-Weld-Ultrasonic-Inspections-Using-Civa-Simulation-Software.pdf
Getting away from notches is, I think, a good idea. Making specific provision for curved wedge requirements is also , I think, a good idea.
Perhaps discussing these issues will inspire the improved availability of reference blocks with curved surfaces such as Ali described back in November.

    
 
 
S.Williams
S.Williams
21:05 Jan-31-2019
Re: Calibration using curved wedges
In Reply to Edward Ginzel at 20:34 Jan-31-2019 .

Can you purchase pre-curved shoes?

    
 
 
S.Williams
S.Williams
21:06 Jan-31-2019
Re: Calibration using curved wedges
In Reply to Paul Holloway at 19:57 Jan-31-2019 .

Thanks Paul, the article helped. I am still confused how people are checking the index point and beam angle without having a curved IIW block.

    
 
 
Edward Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1252

Edward Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1252
21:35 Jan-31-2019
Re: Calibration using curved wedges
In Reply to S.Williams at 21:05 Jan-31-2019 .

You can certainly order them from most manufacturers. I doubt they are off-the-shelf since the manufacturer will not know what diameter you want then to be and many options are possible.

    
 
 
nick bublitz
Other, Phased Array Analysist
VeriPhase, USA, Joined May 2010, 123

nick bublitz

Other, Phased Array Analysist
VeriPhase,
USA,
Joined May 2010
123
23:18 Jan-31-2019
Re: Calibration using curved wedges
In Reply to S.Williams at 21:05 Jan-31-2019 .

Most manufacturers will have standard curvatures available for the popular probe types, custom exact wedges can also be ordered but will usually cost more and have a longer lead time. Here are a few links to a few different manufacturers' charts.

https://www.olympus-ims.com/en/probes/wedges/#!cms[tab]=%2Fprobes%2Fwedges%2Fvalues

https://sonatest.com/products/transducers/phased-array-transducers

1    
 
 

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