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569 views
03:30 May-02-2008

Gowri santhosh Palika

NDT Inspector,
Royscan engineering pte ltd,
Singapore,
Joined May 2008
51
DAC

Hi,
To make DAC curve, we have to consider half skip, full skip and one and half skip distances. what is the necessity to take one and half skip distance?


 
08:08 May-02-2008

Michel Couture

NDT Inspector,
consultant,
Canada,
Joined Sep 2006
818
Re: DAC ----------- Start Original Message -----------
: Hi,
: To make DAC curve, we have to consider half skip, full skip and one and half skip distances. what is the necessity to take one and half skip distance?
------------ End Original Message ------------

One of the reasons you want your signal amplitude for 1 1/2 skip distance is that you have a better representation with 3 points than 2. You are covering a greater distance. I know many codes requires that you inspect only in the first skip, but personnaly, I do go to 1 1/2 skip because of the Near Field. I've seen times when I couldn't see properly my signal after my IP, but the indication was quite visible after the first skip. Your indication may actually blend itself with your IP.

Presently, at one of my client's shop, we do inspection using Longitudinal Wave and our calibration is set to 100% Backwall. But the code also says that if your Initial Pulse cover more than 1/3 of the metal path, your calibration should be of at least 6 Backwall Reflections for the reason I have expressed ealier.

You've probably have noticed that your IP is always somewhat wider than your Backwall or your indications.

Hoping this will be of help...
Michel


 


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