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8.3.1 Detection Range
Signals gained from ultrasonic flaw detection only involves the part of tested
material which probe beam covers, conclusions from tested part applies to
un-tested part should be cautious. Generally, these conclusions only can be
adopted under the condition of proved to be correct by abundant experience and
statistical data. Beams can be full reflected form interface inside tested material ,
flaws and reflection point in deep area maybe not be detected. So it is very
important to keep the whole tested part of material covered by the probe beam.
8.3.2 Ultrasonic Wall Thickness Measurement
All of ultrasonic wall thickness measurement are based upon transmit time
measurement. Constant sound velocity of tested objects is required for accurate
measurement results. Tested materials made by steel (even various kinds of alloy
components),changes of sound velocity are very little and it will not influence test
precision but for high quality measuring. In other materials (e.g. nonmetal or
plastic), changes of sound velocity may be very large, so influence measuring
precision.
8.3.3 Surplus Wall Thickness Measurement
For surplus wall thickness measurement to factory facilities (e.g. interior corroded
pipeline, vessels and various reaction vessels), a suitable thickness gauge is
required, users should especially pay attention to probe’s selection and operation.
Operators should know related rated surplus wall thickness and possible wall
thickness loss.
8.4 Influence Factors of the Detection Precision
(1) Materials of the tested objects
(2) Temperature
(3) Surface roughness concentration
(4) Attachment
(5) Magnetic field
(6) Shape and characteristics of flaw
(7) Acoustic impedance of flaw
