temperature effects on plastic wedges

[ NDT-net Forum ]
[ Follow Ups ] [ Post Followup ] [ Help ]

temperature effects on plastic wedges
Posted by: John Brunk (PID_323), E-mail: jbrunk@kcp.com, on October 11, 2000 at 15:55 :
When performing angle beam testing of metals, there is a change in beam angle with temperature. This happens because the velocity change in plastic wedge materials for a given temperature change is larger than the change in the metal.
Beam angle increases with increasing temperature. The effect is most likely to be noticed when testing at high temperatures with a 70 degree wedge. Surface waves can drive you crazy. It has to be almost too cold to work to get
longitudinal waves with a 45 degree wedge. The more common problem is to be wrong about the location of the reflector because of the change in beam angle. I don't have the data with me and won't trust my memory for the numbers; but
I wrote an article about this for Materials Evaluation about 1987. I noticed this problem a couple of years earlier working outside in Wyoming in the winter. Different plastics used for wedges have different temperature coefficients.
If you keep your angle beam calibration reference at the same temperature as the test object, and keep track of the actual angle and attenuation as the temperature changes, that should take care of most problems unless you really have
to have a specific beam angle for a good reason. Attenuation changes can also be due to effects on the couplants.

Follow Ups:

Re: temperature effects on plastic wedges William Friedman 05:12 10/12/2000 (0)

Post a Followup:

Name:

E-Mail:

Subject:

Comments:
: When performing angle beam testing of metals, there is a change in beam angle with temperature. This happens because the velocity change in plastic wedge materials for a given temperature change is larger than the change in the metal. : Beam angle increases with increasing temperature. The effect is most likely to be noticed when testing at high temperatures with a 70 degree wedge. Surface waves can drive you crazy. It has to be almost too cold to work to get : longitudinal waves with a 45 degree wedge. The more common problem is to be wrong about the location of the reflector because of the change in beam angle. I don't have the data with me and won't trust my memory for the numbers; but : I wrote an article about this for Materials Evaluation about 1987. I noticed this problem a couple of years earlier working outside in Wyoming in the winter. Different plastics used for wedges have different temperature coefficients. : If you keep your angle beam calibration reference at the same temperature as the test object, and keep track of the actual angle and attenuation as the temperature changes, that should take care of most problems unless you really have : to have a specific beam angle for a good reason. Attenuation changes can also be due to effects on the couplants.

Optional Link URL: Example: "http://www....html". Alternative write "http://www.ndt.net/wshop/attach/filename.htm" if you transfered a filename.htm via FTP

Link Title: is important! Information on my Home Page

Optional Image URL: http://www....gif

Attention! Please click the button only once. This may take a moment to process
[ NDT-net Forum ] [ Help ]

Optional Link URL:	Example: "http://www....html". Alternative write "http://www.ndt.net/wshop/attach/filename.htm" if you transfered a filename.htm via FTP
Link Title: is important!	Information on my Home Page
Optional Image URL:	http://www....gif