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(8) Surface characteristics of flaw (e.g. smooth or not)
(9) Optional methods of flaw detection
All of the flaw locating is based upon the measurement of the ultrasonic echo
signals. Constant sound velocity is a very important influence factor to test results,
so it is required for achieving higher measurement accuracy.
8.4.1 Material Influence
Among tested materials, steel for example, even includes many different kinds of
alloying components, its sound velocity is considered to be basically constant. But
in many other materials, such as lots of nonferrous metals or plastic, changes of
velocity are extremely distinct, thus affect measurement accuracy. If materials of
tested objects are not isotropic, sound velocity will be different in different direction.
In this case, average value of sound velocity within tested range must be used for
calculation. The average value is obtained by calculating the velocity of the
referenced test blocks with equivalent velocity to that of the workpiece.
8.4.2 Temperature Influence
Material sound velocity will change along with material temperature. If the
instrument is calibrated in a relative low environment temperature but applied in a
relative high environment temperature, in this situation the test result will deviate
from the actual one. To avoid temperature influence, the methods is to preheat
reference tested blocks before instrument calibration to achieve the same
temperature with environment for use; or the measurement result will be multiplied
by a temperature influence factor.
8.4.3 Surface Roughness Influence
Surface roughness of detected objects affects flaw detection. Influence will
increase along with roughness degree increases. The rough surface can cause
system error and accidental error, so multimetering is needed to avoid accidental
error when testing.
8.4.4 Attachment Influence
It needs to eliminate the attachment before flaw detection so as to make sure that
