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- since 1996 -

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A leading UK manufacturer of Ultrasonic Probes, Accessories, Supplier of NDT Equipment and more.
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Technical Discussions
Anandh.P
India, Joined Jan 2015, 19

Anandh.P

India,
Joined Jan 2015
19
14:04 Feb-10-2015
Transducer crystal size

In AWS D1.1 it is given the crystal size to be used is 15 to 25mm length & width. what is the significance of that? Is it acceptable if we use smaller crystal(8x9) but maintaining the scanning over lap as 10% as required.

 
 Reply 
 
Paul Holloway
Consultant,
Holloway NDT & Engineering Inc , Canada, Joined Apr 2010, 227

Paul Holloway

Consultant,
Holloway NDT & Engineering Inc ,
Canada,
Joined Apr 2010
227
23:45 Feb-10-2015
Re: Transducer crystal size
In Reply to Anandh.P at 14:04 Feb-10-2015 (Opening).

Anandh,

Below is the relevant excerpt from AWS D1.1 (2010):

"6.22.7.2 Transducer Dimensions. The transducer crystal shall be square or rectangular in shape and may vary from 5/8 in to 1 in [15 mm to 25 mm] in width and from 5/8 in to 13/16 in [15 mm to 20 mm] in height (see Figure 6.17). The maximum width to height ratio shall be 1.2 to 1.0, and the minimum width-to-height ratio shall be 1.0 to 1.0."

The bulk of these requirements, in particular the limits on the height:width ratio for the probe, stem from changes made in 1980 to reduce scatter in discontinuity evaluations which were mostly attributed to transducer size. So while a 25mm wide by 15mm high would technically fall within the absolute limits, the W:H ratio for that configuration would be 1.66, and is out-of-spec given the limit is 1.2. Basically, they're just trying to control the size & shape of the transducer and have everyone on a relatively even playing field.

Annex S (UT Examination of Welds by Alternative Techniques) offers the operator the possibility of using alternate equipment as follows:

"Alternate equipment which utilizes computerization, imaging systems, mechanized scanning, and recording devices, may be used, when approved by the Engineer. Transducers with frequencies up
to 6 MHz, with sizes down to 1/4 in [6 mm] and of any shape may be used, provided they are included in the procedure and properly qualified."

The Engineer is defined as a duly designated individual who acts for, and in behalf of, the Owner on all matters within the scope of the code.

So it's possible to use smaller probes, but you've got to jump through some hoops to make it happen. Myself, I find the standard 5/8" square probe and snail wedge a nuisance to work with... I much prefer a 5MHz 1/2" dia. round attached to a nice Olympus short approach wedge. But alas, it's much easier to use the big probe & wedge than jump through those tiny, moving hoops.

1
 
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Anandh.P
India, Joined Jan 2015, 19

Anandh.P

India,
Joined Jan 2015
19
10:49 Feb-11-2015
Re: Transducer crystal size
In Reply to Paul Holloway at 23:45 Feb-10-2015 .

Mr Paul,Thank you so much for sharing the details. I am really thankful to all forum people/ experienced people sharing their knowledge and clearing other's doubts.
As you rightly said by using bigger size probe we can reduce the scanning time. but if the vendor is not having bigger size probe we are accepting smaller probes
Another clarification:In Table 6.2/6.3 the scanning levels given as sound path 65mm add 20db and the others.......
Now what I am doing is catching the 1.59 dia hole of V1/V2 block maximizing the hole indication, increasing the sensitivity upto 80% of FSH(ref db, evaluation of defect will be as per ref db only ).then adding only 6dbfor other losses.but here(6.2/6.2) it is mentioned add 20 db for every 65 mm of sound path....if we add this much db lot of unwanted echo's are coming for material A36,Thick 38.please clarify what I am doing is correct which is a deviation from standard

 
 Reply 
 
Rick Lopez
R & D,
John Deere - Moline Technology Innovation Center, USA, Joined Jul 2011, 190

Rick Lopez

R & D,
John Deere - Moline Technology Innovation Center,
USA,
Joined Jul 2011
190
14:55 Feb-11-2015
Re: Transducer crystal size
In Reply to Paul Holloway at 23:45 Feb-10-2015 .

Paul,
That is an interesting historical tidbit about the code's development (1980 probe size limitations). I must admit that I've never looked, but were these changes supported by a summary technical article from the time? I would dig it up if that were the case.
Best regards

 
 Reply 
 
Paul Holloway
Consultant,
Holloway NDT & Engineering Inc , Canada, Joined Apr 2010, 227

Paul Holloway

Consultant,
Holloway NDT & Engineering Inc ,
Canada,
Joined Apr 2010
227
02:25 Feb-12-2015
Re: Transducer crystal size
In Reply to Rick Lopez at 14:55 Feb-11-2015 .

Rick,

It's in the commentary section, this is the excerpt:

C6.22.7.2 Transducer Dimensions. In the 1980 code, transducer size and shape limitations were changed in an effort to reduce the scatter in the results of discontinuity evaluation, which is thought to be attributed solely to transducer size.

If you find a technical article from that era about this, please let me know. I'm interested too.

 
 Reply 
 
Andrew Hurrell
Consultant, Ultrasonic Transducer Production
Precision Acoustics Ltd, United Kingdom, Joined Apr 2000, 25

Andrew Hurrell

Consultant, Ultrasonic Transducer Production
Precision Acoustics Ltd,
United Kingdom,
Joined Apr 2000
25
13:20 Feb-12-2015
Re: Transducer crystal size
In Reply to Paul Holloway at 02:25 Feb-12-2015 .

In addition to the usage comments there is a purely transducer construction issue that is relevant here. A highly important, but sadly less widely known, factor is that piezo-ceramic resonators need to have a lateral dimension (e.g. diameter) to thickness ratio of at least 10:1. At aspect ratios less than this the parasitic (e.g. torsional) vibration modes take energy away from the fundamental thickness mode and devices become inefficient resonators.

25mm OD satisfies this aspect ratio constraint at 0.8 MHz and as frequency goes up, then the minimum diameter decreases proportially.Clearly most UT probes operate at higher frequencies than 0.8 MHz so should be well within the aspect ratio constraint

Hope this helps

 
 Reply 
 
hariharan m
hariharan m
13:26 Dec-09-2016
Re: Transducer crystal size
In Reply to Andrew Hurrell at 13:20 Feb-12-2015 .

my doubt is how to crystal dia and hight determined

 
 Reply 
 

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