TPT July 2008

The choice of the support structure is dependant on the data needed and the location on the plant floor where the LUT is used. Figure 3 shows the probe mounted on a rapid swivelling device. This unit is used when circumference information is required at a location where the tube is not rotating (from the production process). 5. Implementation of LUT gauges The flexibility of the LUT allows it to be installed at locations not possible with other measuring technology. The first implementation of the LUT was installed directly at the output of a rotary sizer. In this location the main feature regarding the selection of LUT was the capability of the LUT to record data in the presence of large lateral motions (bouncing) of the tube. Being at the end of the manufacturing process (immediately before the cooling bed), the length-profile signatures allowed the operator to detect problems anywhere ‘upstream’ in the production line. LUT data enabled detection of problems such as splitting of the piercing mandrel and velocity imbalance of the rollers of the stretch-reducing mill. As of August 2004, this first implementation of the LUT has already inspected over 2,000,000 tubes. As an example of the use of the LUT, figure 5 shows a set of online tube length-profiles. The first length-profile (top) shows a case of bulging of the wall thickness in the centre section of the tube. The second (bottom) length-profile shows the tube produced once remedial action had been taken. Without the LUT, the conventional method of cutting the tube endings and manually measuring them would not have detected the extent of the defect in produced tube. A second location where the LUT has been installed is at the output of a free floating mandrel mill. In this instance, the important feature for selection of the LUT was the capability of the LUT to record data if the presence of a mandrel. As it is near the beginning of the manufacturing process, the length-profile data allowed the operator to detect problems at the piercing but also gave some information for correction of the specifications using the next processing steps. This configuration is currently in use in Japan. As described earlier, the LUT measures the wall thickness at a known distance from the start (top) of the tube. This distance is given by the length-measuring device included in the LUT. This ‘point’ measurement allows the operator to determine where, within the length of the tube, the problem has occurred. This can be indicative

of the source of the problem. In addition, the ‘point’ information can be use to locate specific features of the tube. For example, the LUT can provide the length of the plug for a plug mill and provide the possibility of feedback control for cutting of the plug. 6. Conclusion Laser-ultrasonic technology is the most advanced technology for the online wall thickness measurement of hot tubes. With the LUT, the Laser Ultrasonic Thickness gauge manufactured by Tecnar Automation Ltee, the technology is commercially available for use in harsh environments and has been used on a tube production plant since 2002. The LUT now allows for possible measurements of real wall thickness during a production flow at different locations, which were not available with previous technologies. Eccentricities of different orders and wall thickness fluctuations over the full length of the tube can be detected with the intention to readjust the process, to produce tubes with better quality and to save material. Thus, the measurement results allow for fast reaction on the process to avoid out of tolerance production. References Monchalin J-P, 1. ‘Progress towards the application of laser-ultrasonics in industry’ , Review of Progress in Quantitative Nondestructive Evaluation, vol 12, Edited by D O Thompson and D E Chimenti (Plenum Publishing Corporation, 1993), pp 495-506. C B Scruby and L E Drain, 2. ‘Laser-Ultrasonics: Techniques and Applications’ (Adam Hilger, Bristol, UK,1990) J-P Monchalin, 3. ‘Optical detection of ultrasound’ , IEEE Trans Sonics, Ultrasonics, Freq Control, UFFC-33, pp 485-499 (1986). A Blouin and J P Monchalin, 4. ‘Detection of ultrasonic motion of a scattering surface by two-wave-mixing in a photorefractive GaAs crystal’ , Applied Physics Letters, 65, 932-934, (1994).

This article was presented at the International Tube Association’s Tube Ukrainian conference in Dnepropetrovsk, Ukraine in 2007.

 Figure 5 : Set of wall thickness measurement with LUT for production correction

Ingenieurbüro Gurski-Schramm & Partner – Germany Fax : +49 203 37809 26 Email : info@gurski.biz Website : www.gurski.biz Tecnar Automation – Canada Fax : +1 450 461 0808 Email : mchoquet@tecnar.com Website : www.tecnar.com

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