TO-BA-e-2020
29
10
Instructions for use
10.1 Measurement of large and small pipes
When measuring a pipe section to determine the thickness of the pipe wall, the
alignment of the transducers is important. If the pipe diameter is larger than approx. 4
inches, the measurements should be carried out with the transducer arranged so that
the gap of the contact surface is perpendicular (at right angles) to the longitudinal axis
of the pipe. For smaller pipe diameters, two measurements should be made, one with
the gap perpendicular to the contact surface and the other with a gap parallel to the
longitudinal axis of the pipe. The smaller of the two displayed values is considered to
be the thickness at the respective point.
10.2 Measurement of hot surfaces
The speed of sound propagation through a material depends on its temperature. As
the materials heat up, the speed of sound propagation decreases. For most
applications with surface temperatures below about 100 °C, no special procedures are
required. At temperatures above 100 °C the change in the speed of sound of the
material to be measured has a significant effect on the ultrasonic measurement. At
such elevated temperatures, it is advisable to perform a calibration procedure on a
sample of known thickness that is at the temperature of the material to be measured
or at a comparable temperature. This will allow the instrument to correctly calculate the
speed of sound propagation through the hot material.
For measurements on hot surfaces it may be necessary to use a specially designed
high temperature transducer. Such transducers are made of materials that can
withstand high temperatures. However, it is recommended to leave the probe in
contact with the surface only as long as necessary for a stable measurement. When a
transducer comes into contact with a hot surface, it begins to heat up, and thermal
expansion and other effects can affect measurement accuracy.
