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- since 1996 -

EKOSCAN
EKOSCAN is a French manufacturer specialized in equipment for ultrasonic Non Destructive Testing: Probes,UT boards & Scanners tailored for your needs
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Technical Discussions
Peter
Singapore, Joined Jan 2012, 117

Peter

Singapore,
Joined Jan 2012
117
08:02 Jan-20-2015
PAUT FOCAL DEPTH

Hi PAUT Experts,


I wanted to know whether is it really focal depth value that we choose really affects our inspection results. The usual formula use for focal depth calculation is 2T + 2T(10%). For example if i choose focal depth for 10mm thickness then i have to set 22mm ( 20mm + 2mm). I never see any diffrent in my inspection results even i set 50mm or 100mm. Its showing that how far i have to focus and as long as above the value of the given formula should be ok and can get better coverage. Please give your opinion.

Peter

    
 
 Reply 
 
Shahid Nisar
Engineering,
Saudi Arabia, Joined Feb 2009, 134

Shahid Nisar

Engineering,
Saudi Arabia,
Joined Feb 2009
134
12:11 Jan-20-2015
Re: PAUT FOCAL DEPTH
In Reply to Peter at 08:02 Jan-20-2015 (Opening).

Hi Peter
Beam Focussing can not be possible beyond N. It is also less than N So calculate your N based on your active aperture and you shall find your focussing capabilities of your system. There is no effect if focus depth entered in system is greater than N.
2T+2T(10%) is a general approach to initially scan without focussing the area of interest(in case of weld examination is range beyond 2T) for a uniform detection throughout. Once scanned then beam may be focussed at certain defect depth but it should not be greater than N.

    
 
 Reply 
 
mark
mark
16:14 Jan-20-2015
Re: PAUT FOCAL DEPTH
In Reply to Shahid Nisar at 12:11 Jan-20-2015 .

Peter,
Each angle in Phased array sectorial scan has different near field.
To get more information please see this article is written by Ed Ginzel: http://www.ndt.net/article/ndtnet/2014/4_Ginzel.pdf

    
 
 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
18:25 Jan-20-2015
Re: PAUT FOCAL DEPTH
In Reply to mark at 16:14 Jan-20-2015 .

It is interesting to note how some of the PA instrument software uses the term Focal Depth. Focussing is usually calculated for a specific plane. When I read "Focal Depth" I suspect that the software is only calculating the distance below the test surface. Some instruments allow you to enter the plane of focus or to enter that it is calculated in half-path (or simply along the beam axis). The limit in all cases is the near field distance, which varies when refraction occurs.

1    
 
 Reply 
 
Peter
Singapore, Joined Jan 2012, 117

Peter

Singapore,
Joined Jan 2012
117
04:03 Jan-21-2015
Re: PAUT FOCAL DEPTH
In Reply to Ed Ginzel at 18:25 Jan-20-2015 .

Hi Experts,


Thanks for the great explanation. I am currently using OMNISCAN MX2 and my usual calculation for focal depth is (2T + 2T (10%). Below are the setups which I planned to do on my OMNISCAN MX2. Based on the (2T + 2T (10%) formula my focal depth will be 47.17mm. This is what I learned at training centers. Can someone explain is there any other way to do the correct focal depth calculation to cover entire weldment ?


1. Start Element 32
2. Total Element 32
3. Angle Step 1
4. Probe 5L64-A12 ( Pitch Size : 0.6)
5. Thickness 21.44mm
6. Material CS
7. Minimum Angle 40°
8. Maximum Angle 70°


As per Mr Shahid Nisar advice, the near zone for 5L64-A12 probe will be around 142mm when my 32 element is active. In that case I am unable to focus above 142mm. My maximum focal depth will be 142mm. In that case can I key in 142mm which is maximum focal depth in my equipment whereby I am only going to activate 32 element for most of my thickness and do standard velocity, wedge delay calibration or do I need to calculate based on this formula (2T + 2T (10%) and do multiple calibration?


Peter




    
 
 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
16:15 Jan-21-2015
Re: PAUT FOCAL DEPTH
In Reply to Peter at 04:03 Jan-21-2015 .

Peter, I would first consider your applicable inspection standard. Most are based on the tradition of good workmanship. It would not be difficult to apply even the traditional manual UT criteria seen in ISO 11666, to a PAUT inspection. The underlying assumption in the old workmanship approach is to use a flat (unfocused) probe and we would construct a DAC or TCG and realte acceptance to these levels. Focussing a beam is not compatible with the general weld inspection and should be limited to special conditions where your region of interest is at the point of focus. The instructions you refer to from "training centres" seems to forget this consideration. These same instructors are probably also telling you how to also set up a TCG with an S-scan in the weld. But if you focussed at 25mm the beam pressure is maximised around 25mm. Beyond that it diverges and the pressure drops even faster after the focal spot. Now you have to add even more gain on the TCG than you would have if you did not focus the beam.
The "formal instruction" to always focus seems to have come from the early training days (only a decade ago) when the instructors saw the software asking for a value. So they made up a rule without considering the consequences for weld inspection. For my general weld inspections I simply entered 1000mm to ensure the software would NOT focus my beam. Then my beam approaches the same characteristics as would be had from a monoelement probe of the same aperture.

2    
 
 Reply 
 
Peter
Singapore, Joined Jan 2012, 117

Peter

Singapore,
Joined Jan 2012
117
02:38 Jan-22-2015
Re: PAUT FOCAL DEPTH
In Reply to Ed Ginzel at 16:15 Jan-21-2015 .

Dear Mr Ed Ginzel,

Thanks for the advice. Our inspection is according to ASME V for piping’s 20” and below and we are using calibration blocks with notches. Yes and I would agree with you. I never see any changes from my obtain results even though I key in the value from the formula or just key in 100mm. Both giving me the same results and it’s solely depend on TCG construction.

Another one more things are my sensitivity settings. Velocity and wedge delay usually plotted using radius or side drill holes and we don’t prefer to calibrate on the notches due to inconsistent reflection from the notches. Now we always stuck at sensitivity settings whereby we have to use notches for the sensitivity calibration. We facing the same problem whereby at different angles we are getting different sensitivities and most of the time we unable to get any reflection from the notches at highest angle which is 70degree. In that case we still have to go for sensitivity settings on side drill hole or radius. The TCG have to be plotted using manual TCG and not from TCG from the wizard. These are the difficulties we are facing currently.


Peter

    
 
 Reply 
 
Godson
Godson
12:30 Jun-17-2015
Re: PAUT FOCAL DEPTH
In Reply to Peter at 04:03 Jan-21-2015 .

Dear Peter,
According to your parameters,you are going to firing 32 elements only.. which means your active aperture is (no.of active elemnts ×pitch)=(32 × 0.6mm)=19.2mm.. Near zone for firing 32 elements is (A*A*F/4V)=(19.2 ×19.2 × 5)/4×5.89)=(1843.2/23.56)=78.23mm..
If u fire 32 elements in 5L64 probe your nearzone is o ly 78mm.. if u want,you can focus within 78mm only.. According to focus depth,we will get the results while we doing practical wise.. Basically UT is the comparision job.. just start to change your focus depth from your thickness(ur tk is 23mm) to 78mm..
Keep changing your FD and doing calibration.. so which focus depth gives you better sizing u can choose it.. this is one of the idea what i think...
If anybody knows some ideas please hesitate to share it..

    
 
 Reply 
 
Carlos Galan
Colombia, Joined Jan 2015, 3

Carlos Galan

Colombia,
Joined Jan 2015
3
15:44 Sep-16-2015
Re: PAUT FOCAL DEPTH
In Reply to Godson at 12:30 Jun-17-2015 .

Download

Hi
I use this formula in the Help menu OmniScan MX2 and book phased array testin

Carlos Galán
    
 
 Reply 
 
suresh kumar
Engineering, NDT LEVEL-3
NBTC, Kuwait, Joined Dec 2012, 18

suresh kumar

Engineering, NDT LEVEL-3
NBTC,
Kuwait,
Joined Dec 2012
18
09:36 Feb-21-2017
Re: PAUT FOCAL DEPTH
In Reply to Godson at 12:30 Jun-17-2015 .

HELLO GODSON,

(A*A*F/4V)=(19.2 ×19.2 × 5)/4×5.89)=(1843.2/23.56)=78.23mm.. as per ur concern, u r entered the velocity for longitudinal wave for near zone calculation.

but it supposed to be shear wave velocity is it?

    
 
 Reply 
 

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