TPT September 2012

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September 2012 149
Article
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 EloWeldTM 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.
Inline seam annealing and
normalising
Modern process-optimised EloSeamTM tube seam annealing
systems enable inline induction annealing of high-frequency
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 EloMatTM 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.
EloMatTM 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.
Double annealing with
quenching station
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.
External resonant circuit
Seam annealer
for API tubes with
NC-controlled
positioning axis
Tube seam annealing
with pilot line for
orbital correction of
the inductor position