TPT January 2016

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Technology News
58 January 2016
Improved precision in pipe
and pipe end heating
THE heat treatment of pipes and pipe
ends is an important process step, which
occurs in the manufacture of a variety
of different high quality products. There
is a distinction to be made between
preheating beforemechanical processing
like drilling, sealing, threading or forming
to increase/decrease the diameter and
heat treatment to harden the metal,
eliminate residual stresses or achieve a
structural transformation.
Induction heating offers many
advantages in comparison with
conventional heating systems. The
main benefits are process reliability,
high throughput and, in particular,
the possibility to generate a precise
temperature profile. The particular
challenge is to provide a homogeneous
predefined temperature distribution for
different diameters, wall thicknesses or
irregular geometries in one installation.
Only by an interaction between
experience, know-how and high-grade
components is it possible to meet the
high requirements regarding precision
and quality.
EMA Indutec, as a manufacturer of
modern induction heating systems, is
specialised in the area of pipe and pipe
end heating, offering technical solutions
with improved precision and efficiency.
One of the most important factors
to ensure a high product quality is the
precision of the temperature distribution
at the heat treatment. Particularly in
the case of pipe and pipe end heating,
it is important to generate a defined
temperature for a certain period and
only in a specific region. For example in
the case of local thermal stress relief, a
simple rule of thumb gives an exposure
to approx. 610°C for a period of 1h for
each 25mm of thickness (minimum of
1h for any thickness). At the same time,
neighbouring regions should remain
cold.
In this manner, selective heat
treatment is fundamental to achieve
the demanded mechanical properties
of the final product. Conceptually, this
approach demands: precise heat source
distribution with highest power at the
surface (to compensate the heat loss to
the environment) but also heat generation
inside the volume to guarantee a
uniform temperature distribution in
radial direction; high power density for
fast heating to avoid an undesirable
spread of temperature in axial direction;
and an intelligent regulation which
controls rapidly all process parameters,
with regard to the desired temperature
distribution.
Especially for pipe end heating,
induction technology offers a reliable
solution. However, the difficulty is to
hold the desired temperature profile for
a period of time retaining the required
accuracy. In this regard EMA Indutec
developed a technology for highest
precision, which has already been
proven in a large number of different
applications.
EMA Indutec pursues continuous
improvements by finding innovative
solutions for processes and products.
In this respect, multi physical numerical
simulations are used to analyse different
technical concepts including all relevant
process parameters in a virtual model.
In order to achieve optimum levels
of precision and accuracy the most
suitable solution will then be chosen
from a large number of possible
variations. In this way numerous
induction heating systems have
been implemented successfully.
An example of a heating plant
for pipe ends is shown above right.
The main issue was to increase
or decrease the diameter and
achieve a specific wall thickness.
Providing defined thermal
conditions by the induction heater,
the material flow can be selectively
controlled during the forming
process. A variation of this installation
type was designed for stress relief heat
treatment. The plant’s flexibility allows
both preheating for forming and for
thread cutting. As a result two individual
heating systems can be replaced saving
space and costs.
Pipe bending is also a widespread
application for the induction technology.
In order to prevent cracks, deformations
or other damages during the bending
process the pipe is preheated
sequentially to approximately 1,000°C.
The usual procedure consists of an
integrated induction heater, which
is shown for large diameters (see
below left). The pipe is transported
continuously through the coil, which
is heated with high precision only in a
defined narrow area.
The process for manufacturing
high quality pipes and tubes had to
fulfil very demanding requirements
in terms of precision during the heat
treatment. The induction technology
offers many advantages in comparison
to conventional heating systems.
However, only an accurate technical
design guarantees high standards of the
final product.
Based on decades of experience
combined with modern computer-aided
calculation and simulation methods
EMA Indutec sets new standards of
accuracy. This new generation of
induction heating system has proven
successful in manufacturing tubes and
pipes but can be also transferred to
other industrial applications.
EMA Indutec GmbH – Germany
Website:
Induction plant for
pipe end heating
Bending machine for pipes with
integrated induction heating system
By Dr-Ing Peter Turewicz, Dipl-Ing Joachim Brettel and Dr Jürgen Kern