TPT March 2016

T E CHNOLOG Y

Passive thermography as an in-line NDT method THE use of an in-line non-destructive testing system offers many advantages. For example, the mill can be stopped as soon as problems occur and the amount of faulty tubes can be reduced, resulting in the saving of scrap. Based on the physical principles, the use of eddy current systems for in-line testing is limited to the detection of irregularities on the surface of a weld seam. Critical faults such as cold welds, root forming problems and variations of penetration depth or symmetry are not detectable by the use of eddy current. To detect these and other critical welding irregularities, as well as process disturbances, HKS Prozesstechnik began to develop the ThermoProfilScanner thermo line camera for welding applications in 2007. This robust, compact and lens-free IR-measuring device is placed directly behind the welding point and measures the temperature in a line with a scan frequency up to 400Hz. The constantly captured thermo profiles across the welding seam are evaluated and checked against the maximum temperature, the width of temperature zone, symmetry, profile position and form differences. Irregularities of the weld seam and process disturbances are detected due to the incorrect heat input and/or disturbed heat distribution. Even pressure changes of the forming rolls, damaged forming rolls and worn out bearings inside a tube mill can be detected. Since the system was developed with several protection mechanisms it can be used in arc-, laser beam- and electron beam-welding processes. Brazing and electric resistance welding applications are also possible. In the example illustrated, a tube with a cold weld was welded inside an HF-ERW (HFI) mill. With a welding speed up to 600fpm the fault was only detectable by using an in- line system. By evaluating the emitted thermal radiation the welding irregularity is detected and becomes visible in the thermogram as well as in the parameter curves. Based on the physical effects, the faulty part was not detected with an eddy current system. HKS Prozesstechnik GmbH – Germany Email: sales@hks-prozesstechnik.de Website: www.hks-prozesstechnik.de ThermoProfilScanner detects cold weld (seam picture, thermogram and calculated parameter curves)

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M ARCH 2016