TPT July 2008

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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
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
 Figure 4: LUT probe at output of rotary sizer