Elcometer CG60DL Operating Instructions Manual page 46

If the diameter of the pipe is larger than approximately 100 mm (4"), measurements should be made with
the transducer oriented so that the gap in the wearface is perpendicular (at right angles) to the long axis of
the pipe.
If the diameter of the pipe is small, two measurements should be performed, one with the wearface gap
perpendicular to the long axis of the pipe, another with the gap parallel to the long axis of the pipe (Figure
8). The smaller of the two displayed values should then be taken as the thickness at that point.
Perpendicular Parallel
Figure 8. Transducer positioning on small diameter pipe
18.2 MEASURING HOT SURFACES
The velocity of sound through a material depends upon the temperature of the material. As materials heat
up, the velocity of sound in the material decreases. In most applications with surface temperatures less than
approximately 100°C (~200°F), no special procedures are required. At temperatures above 100°C
(~200°F), the change in sound-velocity of the material being measured starts to have a noticeable effect
upon the accuracy of ultrasonic measurement.
At such elevated temperatures, it is recommended that the user perform a calibration procedure (see
"Calibration" on page 17) on a sample piece of known thickness, which is at, or near, the temperature of the
material to be measured. This will allow the gauge to correctly calculate the velocity of sound through the
hot material.
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