TPT September 2012

Article

External resonant circuit

If impeders cannot be used in individual sections due to a lack of space, a separate contact unit makes it easy to change from induction welding to contact welding with automatic contact adjustment and wear indication. Contact wear is monitored and compensated by position encoders. Extensive process expertise gained from using EloWeld TM HF generators with virtually all high-frequency weldable materials and tube sections over several decades enables users to produce perfect welds thanks to fully reproducible frequencies matched to production processes and defined welding energy. SMS Elotherm supports customers with the services of experienced commissioning specialists who provide system operators with the necessary system and process knowledge.

Tube seam annealing with pilot line for orbital correction of the inductor position

welded tubes with wall thicknesses of up to 25mm. Calculation programs enable process-orientated system design in the project engineering phase, which usually avoids the need for inductor changes. The basic requirements here are the right frequency, the heating conductor width, orbital inductor tracking and inductor zones with sufficient length. The induced power is individually calculated and controlled by multizone technology with EloMat TM L-LC converters (from the circuit architecture: L for pre-choke and LC for parallel resonant circuit). In contrast to existing single-converter technology with the same power modules, this enables maximum power induction in every heating phase without surface overheating. It is therefore important to ensure for every material specification that the inner seam is reliably heated at least in the width of the wall thickness to above AC3 – end of austenite formation at approximately 785°C. EloMat TM L-LC converters offer a constant high power factor (cos phi > 0.95) regardless of load conditions, including partial load operation. Mains harmonics are distinctly reduced by using 12-pulse L-LC converters. Heat treatment of the high-frequency welded seam region is necessary in order to match its mechanical properties to those of the tube. In the past, single-stage induction seam annealing was followed by normalising in a continuous furnace. Multi-stage induction annealing with water quenching, also known as double annealing, yields a fine grain structure and therefore high impact strength. Multi-stage annealing provides a high statistical confidence level in the event that tube manufacturers are held liable due to possible annealing defects. Double annealing with quenching station

Inline seam annealing and normalising

Modern process-optimised EloSeam TM tube seam annealing systems enable inline induction annealing of high-frequency

Seam annealer for API tubes with NC-controlled positioning axis

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September 2012