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parallel with and perpendicular to the axial line) and select the minimum value of the readings as
the thickness measured.
10.5 Compound contour
In measuring materials with compound contour (such as elbows), the method introduced in 10.4
may be used. The difference is that there is the need to measure the second time to obtain two
readings and take the smaller reading as the thickness of the point measured.
10.6 Non-parallel surface
In order to obtain a satisfactory ultrasonic response, the other side of the test materials must be
parallel or on the same axial with the test surface. Otherwise, there will be errors or no reading at
all.
10.7 Temperature effect of test material
The thickness and ultrasonic wave transmission speed are all affected by temperature. If a high
accuracy is required, test block comparison method should be employed. This method is to correct
the measurement value by temperature compensation coefficient obtained by measuring test
blocks of the same materials at the same temperature.
10.8 High attenuation materials
In the fiber, porous, large-grained materials, the ultrasonic wave will be scattered and got energy
attenuation, the above phenomena will cause abnormal display and even no display (generally the
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abnormal displayed value is less than the actual one). In this case, it’s not suitable to apply the
gauge to this material.
10.9 Reference test block
For the calibration of the instrument, a test block with the thickness of 4.00mm is configured on
the TIME2110 cabinet, calibration method is scheduled in figure 4.3. The attached test blocks are
not enough for calibration while measuring different materials on various conditions. The more
similar the test block materials are to the tested materials, the more accurate the measurement is.
The ideal one is a series of test blocks with different thickness. This series can offer device
compensation calibration coefficient (such as material microstructure, heat treatment condition,
grain orientation, surface roughness). It’s very important to possess a series of test blocks to
guarantee the maximum accuracy.
In most cases, only one test block is enough to get satisfactory measurement precision. This test
block should be of the same material and similar thickness to the testing material. Select the testing
material whose thickness is well-distributed and measured by micrometer as a reference test block.
When the thickness of a thin material is close to the lower testing limit of the probe, a test block
can be employed to determine the exact lower limit (1.2mm for steel). Do not measure the
materials whose thickness is lower than the low limit. If the thickness range can be estimated, the
upper limit of the thickness of the test block should be selected.
When the material is thick, especially alloys with complex microstructure, a similar test block in
the series should be employed for proper correction.
Most of the casting and forging are directional in internal structure. The speed of sound may have
a little change along different directions. In order to solve this problem, the test block should have
