Page 22
PocketMIKE Operating Manual
6.2 Flaws in the Specimen Being
Tested
If, during testing, the PocketMIKE suddenly reads a value which is
much thinner than the apparent thickness of the part, it may be reading
the distance to a flaw in the test piece, rather than the distance to the
backwall. If the cause is unclear, further examination of the part with
an ultrasonic flaw detection instrument or other suitable GE Inspcetion
Technologies method is recommended.
6.3 Condition of the Test Specimen’s
Surface
A regular pattern on the surface under test, such as machine grooves,
may cause a false thickness reading when using a dual element probe.
Higher frequency probes are especially sensitive to this condition. The
problem can usually be corrected by rotating the probe so that the
crosstalk barrier is at a right angle to the grooves.
It is possible for the surface of a test piece to be too rough to permit a
good reading. Excess couplant could be trapped between the probe and
surface under test, causing a false reading. A very rough surface may
prevent coupling altogether (no coupling indicator). This problem can
be corrected by grinding the surface until it is smooth enough to
permit good coupling.
6.4 Test Specimens with Curved
Surfaces
When measuring on curved surfaces, such as tubes or pipes, be sure to
keep the probe centered on the part and as stable as possible. As a rule,
smaller diameter probes improve coupling and minimize “rocking” on
curved parts. In some cases, special probes with contoured faces to
match surface curvature may be needed. Practice may be helpful to
develop the proper technique.
Page 22
PocketMIKE Operating Manual
6.2 Flaws in the Specimen Being
Tested
If, during testing, the PocketMIKE suddenly reads a value which is
much thinner than the apparent thickness of the part, it may be reading
the distance to a flaw in the test piece, rather than the distance to the
backwall. If the cause is unclear, further examination of the part with
an ultrasonic flaw detection instrument or other suitable GE Inspcetion
Technologies method is recommended.
6.3 Condition of the Test Specimen’s
Surface
A regular pattern on the surface under test, such as machine grooves,
may cause a false thickness reading when using a dual element probe.
Higher frequency probes are especially sensitive to this condition. The
problem can usually be corrected by rotating the probe so that the
crosstalk barrier is at a right angle to the grooves.
It is possible for the surface of a test piece to be too rough to permit a
good reading. Excess couplant could be trapped between the probe and
surface under test, causing a false reading. A very rough surface may
prevent coupling altogether (no coupling indicator). This problem can
be corrected by grinding the surface until it is smooth enough to
permit good coupling.
6.4 Test Specimens with Curved
Surfaces
When measuring on curved surfaces, such as tubes or pipes, be sure to
keep the probe centered on the part and as stable as possible. As a rule,
smaller diameter probes improve coupling and minimize “rocking” on
curved parts. In some cases, special probes with contoured faces to
match surface curvature may be needed. Practice may be helpful to
develop the proper technique.
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