Waygate Technologies Krautkramer USM 100, Руководство по эксплуатации, Страница: 28 / 330

1 Introduction Important information on ultrasonic testing
28 Rev. 9 (09/2023) Krautkrämer USM 100
Ultrasonic wall thickness measurement
All ultrasonic wall thickness measurements are based
on a time-of-flight measurement. Accurate measure-
ment results require a constant sound velocity in the test
object.
In test objects made of steel, even with varying alloying
constituents, this condition is mostly fulfilled. The varia-
tion of sound velocity is so slight that it is only of impor-
tance for high-precision measurements.
In other materials, e.g. nonferrous metals or plastics,
the sound velocity variations may be even larger and
thus affect the measuring accuracy.
Effect of the test object material
If the material of the test object is not homogeneous, the
sound waves may propagate at different velocities in dif-
ferent parts of the test object. An average sound velocity
should then be taken into account for the range calibra-
tion. This is achieved by using a reference block with a
sound velocity equal to the average sound velocity of
the test object.
If substantial sound velocity variations are expected,
then the instrument calibration should be adjusted to the
actual sound velocity values at shorter time intervals.
Failure to do so may lead to false thickness readings.