GE 37 400, Technical Reference And Operating Manual

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Important information on ultrasonic testing 1 Introduction
USM 36 Issue 2 (12/2013) 1-5
Technical test requirements
Every ultrasonic test is subject to specific technical test
requirements. The most important ones are:
● the definition of the scope of inspection
● the choice of the appropriate test method
● the consideration of material properties
● the determination of limits for recording and evalua-
tion.
It is the task of the those with overall responsibility for
testing to ensure that the inspector is fully informed
about these requirements. The best basis for such infor-
mation is experience with identical test objects. It is also
essential that the relevant test specifications be clearly
and completely understood by the inspector.
GE regularly holds specialized training courses in the
field of ultrasonic testing. The scheduled dates for these
courses will be given to you on request.
Limits of testing
The information obtained from ultrasonic tests only re-
fers to those parts of the test object which are covered
by the sound beam of the probe used.
Any conclusions from the tested parts to be applied to
the untested parts of the test object should be made with
extreme caution.
Such conclusions are generally only possible in cases
where extensive experience and proven methods of sta-
tistical data acquisition are available.
The sound beam can be completely reflected from
boundary surfaces within the test object so that flaws
and reflection points lying deeper remain undetected. It
is therefore important to make sure that all areas to be
tested in the test object are covered by the sound beam.
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 variation of sound velocity is so slight that it is only