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1-6 Issue 05, 02/00 Krautkramer USN 52R/USN 52L
Effect of temperature variations
The velocity of sound within the test object also varies
as a function of the temperature of the material. This
can cause appreciable errors if the instrument has been
calibrated on a cold calibration block and is then used
on a warm or hot test object. Such errors can be
avoided either by warming the calibration block to the
same temperature before calibrating, or by using a cor-
rection factor obtained from tables.
Measurement of remaining wall thickness
The measurement of the remaining wall thickness on
plant components such as pipes, tanks and reaction
vessels of all types which have been corroded or
eroded from the inside requires a suitable test instru-
ment and special care in handling the probe.
The test operator must be told the nominal wall thick-
nesses and the likely amount of the loss due to erosion
or corrosion.
Assessing flaws using ultrasonics
In present-day test practice there are basically two
methods of assessing flaws.
If the diameter of the sound beam is smaller than the
extent of the flaw, then the beam can be used to scan
the boundaries of the flaw and thus determine its area.
If, however, the diameter of the sound beam is greater
than the size of the flaw, the maximum echo response
from the flaw must be compared with the maximum
echo response from an artificial flaw at the same depth
provided for comparison purposes.
Flaw boundary scanning method
The smaller the diameter of the sound beam from the
probe, the more accurately the determined flaw area
corresponds to the actual flaw area when scanning the
flaw boundaries with the sound beam from a probe.
If, however, the sound beam is relatively broad, the
determined flaw area can substantially differ from the
actual flaw area. Care should therefore be taken to se-
lect a probe which will give a sufficiently narrow beam
at the position of the flaw.
Introduction
Important notes
1-6 Issue 05, 02/00 Krautkramer USN 52R/USN 52L
Effect of temperature variations
The velocity of sound within the test object also varies
as a function of the temperature of the material. This
can cause appreciable errors if the instrument has been
calibrated on a cold calibration block and is then used
on a warm or hot test object. Such errors can be
avoided either by warming the calibration block to the
same temperature before calibrating, or by using a cor-
rection factor obtained from tables.
Measurement of remaining wall thickness
The measurement of the remaining wall thickness on
plant components such as pipes, tanks and reaction
vessels of all types which have been corroded or
eroded from the inside requires a suitable test instru-
ment and special care in handling the probe.
The test operator must be told the nominal wall thick-
nesses and the likely amount of the loss due to erosion
or corrosion.
Assessing flaws using ultrasonics
In present-day test practice there are basically two
methods of assessing flaws.
If the diameter of the sound beam is smaller than the
extent of the flaw, then the beam can be used to scan
the boundaries of the flaw and thus determine its area.
If, however, the diameter of the sound beam is greater
than the size of the flaw, the maximum echo response
from the flaw must be compared with the maximum
echo response from an artificial flaw at the same depth
provided for comparison purposes.
Flaw boundary scanning method
The smaller the diameter of the sound beam from the
probe, the more accurately the determined flaw area
corresponds to the actual flaw area when scanning the
flaw boundaries with the sound beam from a probe.
If, however, the sound beam is relatively broad, the
determined flaw area can substantially differ from the
actual flaw area. Care should therefore be taken to se-
lect a probe which will give a sufficiently narrow beam
at the position of the flaw.
Introduction
Important notes