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08:30 Mar-02-2001
IceClampers
UT Thickness Testing

When taking UT readings on pipe using a dual probe, why is it prefered to keep the axis of the probe perpindicular to the axis of the pipe being tested.



    
 
09:45 Mar-02-2001

Tom Nelligan

Engineering,
retired,
USA,
Joined Nov 1998
390
Re: UT Thickness Testing : When taking UT readings on pipe using a dual probe, why is it prefered to keep the axis of the probe perpindicular to the axis of the pipe being tested.
.

Because that orientation optimizes sound coupling. The barrier that separates the transmitter and receiver sides of dual probes is a dead zone. When you couple any flat probe onto a small-radius cylinder, the actual area of contact is only a thin line. If you hold the dual so that the barrier is parallel to the axis of the pipe, much of that narrow contact area is occupied by the barrier, and only a small amount of energy transfers into the pipe. But if you hold the dual so that the barrier is perpendicular to the center axis, then you have an area of contact that spans the full active width of the probe and maximizes sound transmission in and out.

It's a good idea to get into the habit of holding the dual perpendicular to the axis in all cases, but it becomes most important as the pipe diameter gets smaller (especially on diameters under 25 mm or 1 inch).

--Tom Nelligan





    
 
02:00 Mar-02-2001

Raúl Navarrete

Consultant, teacher ndt inspector
METAL-MET, C.A.,
Venezuela,
Joined Jul 2000
8
Re: UT Thickness Testing : When taking UT readings on pipe using a dual probe, why is it prefered to keep the axis of the probe perpindicular to the axis of the pipe being tested.
.

This is also due the correction pattern. When you hold the probe parallel to the pipe axis, the way of the sound will follow the curve of the pipe diameter. If you hold it perpendicular to the axis, the path way will be on a straight pattern, not folloing any curve. So the correction to be made (because is a dual transducer) is easier and accurate than the another one. So that is why you MUST use the probe with its axis perpendicular to the pipe axis.




    
 


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