14:58 Apr-09-2009 TomNelligan Engineering, retired, USA, Joined Nov 1998 390
Re: Low Temperature Thickness measurementIn Reply to Joe Buckley at 01:39 Apr-09-2009 (Opening).
We too get asked about that sort of thing on occasion, typically involving corrosion testing of pipes and tanks in cryogenic systems, and the big problem is finding a viable couplant that remains a liquid or gel at such low temperatures. Most high temperature dual element transducers that are designed to work on surfaces at plus several hundred degrees Celsius will tolerate short-term contact with surfaces at minus a hundred degrees, so the transducer doesn't have to be a limitation. The same design considerations that protect high temperature duals from thermal expansion effects would normally protect them from thermal contraction as well. But we don't have a couplant to recommend. I have suggested to customers that they might look into exotic lubricants to see if there's anything that might work (other than graphite lubricants, which aren't a good acoustic couplant), but to date no one has ever gotten back to me with a suggestion.
18:17 Apr-09-2009 R Duwe NDT Inspector, API-510, 570, 653 MISTRAS, USA, Joined Jan 2009 148
Re: Low Temperature Thickness measurementIn Reply to Jim Kovarik at 16:21 Apr-09-2009 .
Couplant: Have you tried silicon oil? Another possible ULT couplant is alcohol. At dry ice temps, isopropyl has a moderate viscosity, should work well. Hopefully, your calibration block is also at the low temp.