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643 views
02:27 Nov-12-2004
General
Square vs Round Transducers

Why does AWS D1.1 specify to use a square transducer and does not allow round transducers for doing shear wave inspections. CSA W59, the Canadian equivilent does not stipulate that sqaure transducers have to be used.

Why do AWS specify square?


 
06:05 Nov-13-2004

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1199
Re: Square vs Round Transducers ----------- Start Original Message -----------
: Why does AWS D1.1 specify to use a square transducer and does not allow round transducers for doing shear wave inspections. CSA W59, the Canadian equivilent does not stipulate that sqaure transducers have to be used.
: Why do AWS specify square?
------------ End Original Message ------------

I cannot state with authority as to WHY AWS imposes this rule, but perhaps it is just part of the "tradition" of the document being carried forward for nearly 50 years. In a correspondence with a committee member I was told that this was because square or rectangular elements have a "more uniform sound field". This is not true when you plot echo responses off ideal targets such as a FBH. Mechanical clamping in the corners of a rectangular probe is not the same as the clamping along the sides. The effect is that lobes occur. This is often seen on the ends of cylindrically focused immersion probes. The mechanical clamping on a round element is generally of better uniformity thereby providing a more uniform sound field than the square probes.

There are several issues with the old AWS D1 code that make it "different" from all the rest. One in particular is the way they treat amplitude correction with the strange formula for compensation of soundpath (the same rate of compensation is applied for all angles!). Other Codes tend to use a method of DAC compensation that allow for angle variations in echo-transmittance.
But AWS has finally updated itself in the 2004 edition. Annex K allows other options and even describes the more familiar DAC construction. But this is apparently so radical that it requires the approval of the engineer.
Ed


 


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