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- since 1996 -

Materials Research Institute
Consulting to the NDT industry.
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Technical Discussions
Terry White
Terry White
06:49 Oct-17-2007
Transducer failures

My company has experienced a recent spate of ultrasonic transducer failures due to blistering of the epoxy facing of cylindrically focused immersion transducers, 3 in the last two months. One transducer was not quite one year old. The other two were approximately 5 years old. Does anyone know of a possible cause of transducer blistering? Perhaps an additive or change in chemical composition of the water? Are there any known chemicals which could attack the epoxy faces of transducers? Could sodium sulfite be a cause?


 
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Tom Nelligan
Engineering,
retired, USA, Joined Nov 1998, 390

Tom Nelligan

Engineering,
retired,
USA,
Joined Nov 1998
390
08:16 Oct-17-2007
Re: Transducer failures
Chemicals in your water could be a possibility, but are you soaking the transducers continuously? Epoxy blistering can happen even in distilled water over a long period of time if transducers aren't given a chance to dry out, due to water absorption in the lens epoxy which causes it to swell and blister. If you' were soaking two of them more or less continuously for five years, I'd expect it.

In the case of Panametrics-NDT immersion transducers, we publish a recommendation that they should not be submerged for more than 8 hours at a time, followed by 16 hours of drying. That's a VERY conservative recommendation that will usually insure many years of service, and many of our customers are happy with a more liberal duty cycle, but the point is that epoxy-faced immersion transducers can indeed suffer blistering in pure water if they're soaked long enough without a drying period.


 
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Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1300

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1300
03:06 Oct-18-2007
Re: Transducer failures
I would like to first concur with Tom and then just add that if the water temperature has been elevated (e.g. 25-35C) it may accelerate the situation

----------- Start Original Message -----------
: Chemicals in your water could be a possibility, but are you soaking the transducers continuously? Epoxy blistering can happen even in distilled water over a long period of time if transducers aren't given a chance to dry out, due to water absorption in the lens epoxy which causes it to swell and blister. If you' were soaking two of them more or less continuously for five years, I'd expect it.
: In the case of Panametrics-NDT immersion transducers, we publish a recommendation that they should not be submerged for more than 8 hours at a time, followed by 16 hours of drying. That's a VERY conservative recommendation that will usually insure many years of service, and many of our customers are happy with a more liberal duty cycle, but the point is that epoxy-faced immersion transducers can indeed suffer blistering in pure water if they're soaked long enough without a drying period.
------------ End Original Message ------------




 
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