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“ping”. The ping then propagates through the wall of the tube, is re ected by the back wall until it reaches to front surface, the point of origin. The forward and back propagation of the ping is repeat several times, until the sound energy is fully absorbed or scattered by the material of the tube. Each time the ping arrives at the surface, it affects a second laser, the detection laser, which “records” the signal. The detection laser acts as a microphone, listen- ing to the arrival of the pings. By measuring the time between the reception of two successive pings, one may determine the time of propagation of the sound within the bulk of the tube. Knowing the velocity of sound in the hot material, the wall thickness at the precise location of genera- tion of the ping may be measured. Repeating the process along the length of the tube provides an accurate thickness pro le.
Since laser light is used to both
generate and detect the ultra-
sonic pulse, the measurement is
non-contact and, therefore, not
affected by tube motion or tube
temperature. In addition, since
the ultrasound is re ected by the
back wall of the tube, the pres-
ence of a mandrel inside tube
has no effect on the wall thick-
ness measurement accuracy. As the product is moving under the probe, measurements are taking along the length of the tube, given the oper- ator a wall thickness pro le as shown in Figure 2. The operator can then use the information to determine if the product at this location is within the target speci cations or if remedial actions are required.
INFORMATION FROM WALL THICKNESS PROFILE
With the information provided with each wall thickness pro le, the operator can quickly, in a rst step, verify that the wall produced is within the nominal target values. The operator may then stop produc- tion to react if out of speci cation conditions are observed and reduce the production of “scraps”. Production yield may also be increasing by tracking the length of heavy or light wall at both ends of the tube. Using the wall thickness pro le, operator may adjust production param-
Fig. 2 Typical wall thickness pro le
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Fig. 3 Pro le with heavy ends
ITAtube Journal No2/July 2018
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