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APPENDIX B-
APPLICATION NOTES
Measuring pipe and tubing
When measuring a piece of pipe to determine the thickness of the pipe wall,
orientation of the transducers is important. The transducer should be oriented so that
the gap (sound barrier) in the wear face is perpendicular (at a right angle) to the
length (long axis) of the tubing, allowing both sides of the transducer to make the
same amount of contact. The transducer orientation can either be parallel or
perpendicular for large diameter piping, as it’s much easier to ensure both sides are
making similar contact.
Measuring hot surfaces
The velocity of sound through a substance is dependent on its temperature. As
materials heat up, the velocity of sound through them decreases. In most
applications with surface temperatures less than about 200
F (100
C), no special
procedures must be observed. At temperatures above this point, the change in
sound velocity of the material being measured starts to have a noticeable effect upon
ultrasonic measurement.
At such elevated temperatures, it is recommended that the user perform calibration
on a sample piece of known thickness, which is at or near the temperature of the
material to be measured. This will allow the
ZX-5
to correctly calculate the velocity of
sound through the hot material.
Expansion and contraction of the transducer based on temperature, and a varying
temperature gradient, will also affect the measurement in a pulse-echo (P-E)
measurement mode. It is recommended that a “transducer zero” be performed often
to account for the delay line changing length and adversely affecting the accuracy of
the measurements.
When performing measurements on hot surfaces, it may also be necessary to use a
specially constructed high-temperature transducer. These transducers are built using
materials which can withstand high temperatures. Even so, it is recommended that
