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Technical Discussions
Nigel Armstrong
Engineering, - Specialist services
United Kingdom, Joined Oct 2000, 1094

Nigel Armstrong

Engineering, - Specialist services
United Kingdom,
Joined Oct 2000
1094
03:01 Nov-04-2005
Change of wedge velocity with temperature

I have read previous threads which discuss the change of sound velocity in materials with temperature change, but I cannot find any thread relating to the message subject. I seem to recall that sound velocity in Perspex or other similar wedge material is affected more by temperature than are metals. Is this correct? Has anybody any information on refracted angle change with changing temperature?


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

Tom Nelligan

Engineering,
retired,
USA,
Joined Nov 1998
390
05:29 Nov-04-2005
Re: Change of wedge velocity with temperature
Yes, it's a problem! Sound velocity in the polymers typically used to make wedges changes much more rapidly with temperature than sound velocity in metals. The wedge velocity decreases as it heats up, so the refracted angle in steel will increase. This velocity change can approach 50% per 50 degrees Celsius in some plastics, and will always be significant. The non-Perspex/acrylic materials used for high temperature wedges are somewhat more stable, but still can exhibit a significant velocity change when used at several hundred degrees. The situation is additionally complicated by the fact that the wedge will warm up and cool during testing, and that the heat distribution in the wedge will usually be uneven.

You can periodically check refracted angle with an IIW block that has been heated to the same temperature as the test piece, but of course that is not always practical. In theory, you could also heat up a block and wedge to various temperatures in a lab, record the refracted angle data, and then apply that data in the field after measuring the temperature of the test piece. But again, as a practical matter the constantly changing temperature of the wedge can make that difficult.

If you're doing high temperature testing, the linked application note that I wrote for the Panametrics-NDT web site might be of interest.

----------- Start Original Message -----------
: I have read previous threads which discuss the change of sound velocity in materials with temperature change, but I cannot find any thread relating to the message subject. I seem to recall that sound velocity in Perspex or other similar wedge material is affected more by temperature than are metals. Is this correct? Has anybody any information on refracted angle change with changing temperature?
------------ End Original Message ------------




    
 
 
Nigel Armstrong
Engineering, - Specialist services
United Kingdom, Joined Oct 2000, 1094

Nigel Armstrong

Engineering, - Specialist services
United Kingdom,
Joined Oct 2000
1094
03:47 Nov-05-2005
Re: Change of wedge velocity with temperature
Thank you for that info Tom. Possibly 50% velocity change per 50 degree Celsius is very concerning. I am looking at the trend in the opposite direction, i.e. with decreasing temperature. I am considering manual UT weld inspection, where potentially the probe may be in contact with a cold metal for several minutes at time. If the refracted angle changes significantly then this will play havoc with critical weld root inspections. Knowing that manual ultrasonics has cumulative measurement errors in the region of 2 - 4mm (even greater for heavy wall components), has anybody investigated the measurement inaccuracies caused by changing refracted angles? I guess with impending winter here in Central Asia it is a chance for me to take measurements out on site. Brrr!


----------- Start Original Message -----------
: Yes, it's a problem! Sound velocity in the polymers typically used to make wedges changes much more rapidly with temperature than sound velocity in metals. The wedge velocity decreases as it heats up, so the refracted angle in steel will increase. This velocity change can approach 50% per 50 degrees Celsius in some plastics, and will always be significant. The non-Perspex/acrylic materials used for high temperature wedges are somewhat more stable, but still can exhibit a significant velocity change when used at several hundred degrees. The situation is additionally complicated by the fact that the wedge will warm up and cool during testing, and that the heat distribution in the wedge will usually be uneven.
: You can periodically check refracted angle with an IIW block that has been heated to the same temperature as the test piece, but of course that is not always practical. In theory, you could also heat up a block and wedge to various temperatures in a lab, record the refracted angle data, and then apply that data in the field after measuring the temperature of the test piece. But again, as a practical matter the constantly changing temperature of the wedge can make that difficult.
: If you're doing high temperature testing, the linked application note that I wrote for the Panametrics-NDT web site might be of interest.
: : I have read previous threads which discuss the change of sound velocity in materials with temperature change, but I cannot find any thread relating to the message subject. I seem to recall that sound velocity in Perspex or other similar wedge material is affected more by temperature than are metals. Is this correct? Has anybody any information on refracted angle change with changing temperature?
------------ End Original Message ------------




    
 
 

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