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Technical Discussions
Nathan Docwra
Nathan Docwra
15:29 Nov-12-2010
DAC Curve using IOW beam profiling block...

Can you create a DAC curve using an IOW beam profiling block?

I know you can physically do it - but is it allowed? The IOW profiling block has 1.5mm side drilled holes when the ASME DAC block has 3mm holes...

 
 Reply 
 
Peh Hoo Guan
NDT Inspector,
Malaysia, Joined May 2010, 12

Peh Hoo Guan

NDT Inspector,
Malaysia,
Joined May 2010
12
18:57 Nov-13-2010
Re: DAC Curve using IOW beam profiling block...
In Reply to Nathan Docwra at 15:29 Nov-12-2010 (Opening).

the 5 SDHs on IOW blocks are meant for DAC curve plotting for sure...so, the answer is YES, you can create DAC curve with it.

As for ASME block with larger diameter of holes on it, i won't think it would affect the accuracy tht much, but i guess, with slightly smaller diameter of 1.5mm on IOW block, it would be more sensitive..ur DAC would be more accurate..coz for smaller diamter hole, ur echo signal will drop faster as u move ur robe on the surface compared to bigger hole...

 
 Reply 
 
Michel Couture
NDT Inspector,
consultant, Canada, Joined Sep 2006, 868

Michel Couture

NDT Inspector,
consultant,
Canada,
Joined Sep 2006
868
20:01 Nov-13-2010
Re: DAC Curve using IOW beam profiling block...
In Reply to Peh Hoo Guan at 18:57 Nov-13-2010 .

Peh,

I don't think your statement is accurate as it relate to the accury of your DAC if you have a smaller diameter SDH. It will bo more sensitive for sure but accurate; I don't believe so.

Accuracy of a DAC is determined by setting up an accurate time base on your instrument and than when doing your DAC, to find which of the SDH has the most amplitude response, maximising the signal response and then increasing it to 80% FSH or to the amplitude level required by your code. Afterward, recording the amplitude of all your other SDH after of course having maximised them.

The key word here is to calibrate your instrumentt according to the code you are working to. Some codes will ask you to calibrate on a 1.5mm SDH other 3mm SDH yet others will request a 6mm SDH. Because when it comes to NDT, you always compare a known defect with an unknown. The known is the signal response from your SDH at that depth on your block , the unknown is what you come across during your inspection.

 
 Reply 
 
andrew cunningham
NDT Inspector
Canada, Joined Jun 2008, 238

andrew cunningham

NDT Inspector
Canada,
Joined Jun 2008
238
00:29 Nov-15-2010
Re: DAC Curve using IOW beam profiling block...
In Reply to Nathan Docwra at 15:29 Nov-12-2010 (Opening).

You need at least 3 reflectors to make a DAC.
So to use the 1.5mm SDH in the IIW you must hit it from 3 different distances.
1st close half leg.
2nd far half leg.
3rd on the skip.
You can create a DAC from the corner reflectors from the IIW then you set the 1.5mm or any other diameter hole to that DAC.
The modern day sets are all slightly different in their functions, but they all make all the DAC’s totally probe specific.
It is better to make the DAC from the IIW A5 block

 
 Reply 
 
Haridas sarvale
Haridas sarvale
15:46 Jan-12-2020
Re: DAC Curve using IOW beam profiling block...
In Reply to andrew cunningham at 00:29 Nov-15-2010 .

Dear sir.
,please send us process of making dac curve using iow beam profile block .
Thanks
Haridas.

 
 Reply 
 

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