ElektroPhysik
E-17
Application Notes
9.
Application Notes
9.1
Measuring Pipe and Tubing
When measuring a piece of pipe to determine the
thickness of the pipe wall, orientation of the transducers
is important. If the diameter of the pipe is larger than
approximately 100 mm/ 4 inches, measurements should
be made with the transducer oriented so that the gap in
the wearface is perpendicular (at right angle) to the long
axis of the pipe.
For smaller pipe diameters, two measurements should
be performed, one with the wearface gap perpendicular,
another with the gap parallel to the long axis of the pipe.
The smaller of the two displayed values should then be
taken as the thickness at that point.
perpendicualar
parallel
9.2
Measuring Hot Surfaces
The velocity of sound through a substance is dependant
upon its temperature. As materials heat up, the velocity
of sound through them decreases. In most applications
with surface temperatures less than about 100°C
(200°F), 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 a calibration procedure (refer to
section „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 MINITEST
403 to correctly calculate the velocity of sound through
the hot material.
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 the probe be left in
contact with the surface for as short a time as needed to
acquire a stable measurement. While the transducer is
in contact with a hot surface, it will begin to heat up itself,
