TPT July 2008

currently available. For each tube produced, the LUT provides the wall thickness length-profile (at hot and room temperatures), the temperature length-profile and total length. When coupled to an outer diameter measurement device, the same system provides the outer diameter length-profile, resulting in full dimensioning of each tube. With a rotating tube or a swiveling probe(s), the LUT gives eccentricity length-profile. This operator can then used this information to make automated feedback correction of the production. The standard LUT system consists of six units: namely the generation laser unit, the detection laser unit, the detection unit, the control unit, the length measurement device and the inspection probe with a support structure. The LUT generation laser unit consists of high-power short-pulse laser for non-contact generation of ultrasounds. The laser is a Q-switch Nd:YAG operating at a wavelength of 1064nm (infrared). The laser is based on robust flashlamp technology, the same technology used for laser welding. The firing rate of the laser is currently limited to 100Hz and therefore the LUT can provide up to 100 measurements per second. The laser generation unit is an industrial-grade system with easy access for quick servicing. The LUT detection laser unit consists of a special frequency- stabilized laser source, uniquely designed for laser-ultrasonic detection. The detection laser is based on flashlamp technology, providing a high-power output that cannot be achieved with other types of lasers. The LUT uses the most powerful detection laser for laser-ultrasonic detection commercially available. This high-power laser, only manufactured by Tecnar, enables a flexibility to the LUT, which is claimed to be unparalleled by others

 Figure 4 : LUT probe at output of rotary sizer

systems. Such high power is needed for the detection of ultrasounds on highly scattering surfaces, such as those encountered for online tubes. As for the generation laser, the firing rate of the detection laser is 100Hz. The detection laser beam is delivered to the inspection probe via optical fibre. The detection laser unit itself is located in a control room, several metres away from the production lines. The detection laser unit is an industrial-grade system with easy access for quick servicing. The LUT control unit consists of a computer system to control and monitor the LUT. The extensive use of computers in the LUT allows for easy operation of the system by plant personnel. Very little interaction is needed between the LUT and the operator. In particular, no operator interaction is required to setup the system. A remote control unit is used to display the data at a key location on the production line, generally near the control panel of the process being monitored by the LUT. The LUT detection unit includes the components for processing the laser-ultrasonic signal and the optical pyrometer signal. The detection unit receives the signals from the LUT probe via optical fibres. The detection unit can therefore be located in a controlled area, away from the production line. The distance between the detection unit and the LUT probe can be up to 40 metres. The measured data is transferred to the LUT control unit via TCP/IP communication. The same data can be automatically transferred to any other location linked to the Ethernet network of the LUT and the plant. The data can therefore be directly interfaced to any available process control. The LUT inspection probe consists of the optical components, located on the plant floor, near the hot tube, that focuses the various laser beams onto the surface of the tube, and that collects all of the relevant light signals. As the inspection probe may be submitted to high temperature and vibrations, the probe was designed to contain mostly passive optical components and very little electronic components (mainly for laser safety). The optical components are mounted on an automated focusing device that allows the LUT to adjust to variation of tube outer diameter without the interaction of the operator. The inspection probe is mounted on a support structure to position it at an appropriate location. Several configurations of the support structure are available, from fixed structure to rapid scanning unit.

 Figure 3 : LUT probe mounted on fast scanning unit

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J uly 2008

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