January 2012 Tube Products International
43
products & developments
Composite tubes
Hoesch Schwerter Profile GmbH
develops its products in collaboration
with specific fields of industry and
customers. Modern power stations
and industrial plants are just two areas
where special steel solutions are used
that are required to withstand extreme
loads.
The classic seamless steel tube for
pressure vessels represents a key
construction element in the building of
thermal plants.
The requirements for boiler construction
steels become significantly more
exacting if – instead of conventional
boiler fuels such as coal, oil or gas –
other sources of energy are used that
result in strongly-corrosive combustion
products. For instance, boiler tubes
in a waste incineration plant are not
only exposed to thermal loads, but
are also subject to corrosive attack,
fundamentally triggered by the chemical
element chlorine.
For this specific application, the
conventional boiler tube used in plant
construction with its proven component
strength was equipped with a ‘coating’
using a corrosion-resistant austenitic
material. The intention behind this
combination of materials is to allow
the C-steel (carbon steel) to handle the
thermal-mechanical load on the tube,
while the austenite provides protection
against corrosion from the prevailing
environment.
‘Combined materials’ tubing of this
kind is often referred to as composite.
If produced using the extrusion
process, the term used to describe
this is co-extruded tubing. When the
corrosion-resistant layer is applied to
the tube body by welding, the term
used is clad pipe.
Clad pipes have one or two layer
corrosion-resistant outer covering,
approximately 2.5mm thick. This is
applied using fusion welding, which
creates overlapping welding beads.
During welding there is an intermixing
of a few tenths of a millimetre between
the C-steel and the austenite; in
metallurgical terms this is equivalent
to a ‘dilution’ of the high-alloy layer
material. Since it is obtained via the
liquid phase, the layer material is
characterised by a casting structure
typical of welding.
The development of composite tubing
pursued by Hoesch Schwerter Profile
GmbH was undertaken with the aim of
overcoming the known disadvantages
peculiar to clad pipes.
The composite tube is characterised
chiefly by the following properties:
•
C-steel component and austenitic
layer of the extrusion billet are
manufactured in a common hot
forming process at around 1,150 to
1,250°C. The metallurgical connection
between the two materials is achieved
in the solid state using pressure-
accelerated solid state diffusion
•
A diffusion zone approximately 10μm
thick forms between the materials,
which is responsible for a high-
strength, oxide-free metallurgical
bond of materials
•
The fine microstructure configuration
of the layer and base material is
preserved, with no variation in the
alloy concentration
•
Smooth surface structures avoid
deposition of corrosion-promoting
ash and salt particles from the flue
gas
•
Special cross-section forms such as
fin tubes, omega tubes or double
omega tubes are possible
•
Cold bending is possible, since
there is no cast structure created by
cladding
•
Internal and external layer possible
Hoesch Schwerter Profile GmbH
–
Germany
A growing perforating business
Sönnichsen, Norway, is an established
manufacturer and marketer of welded
precision tubes in the north European
market. The company’s perforating
line is the latest stage of a continued
expansion of service offering to provide
added customer value.
In the company’s production facilities,
located 100km south of Oslo, close to
the Swedish border, tubes are produced
according to European standard, with a
high percentage of the production tailor
made to customer specification. While a
significant proportion of the production
has traditionally been sold cut to length,
Sönnichsen’s new perforating line
has added an additional service for
customers.
The
highly
automated
perforating line is equipped with
robots for feeding tubes into
the unit, repositioning the tubes
if required and handling the
perforated tubes. Weld seams
are detected by an automated
visual detection system,
allowing the line to be operated
with a minimum of operator
assistance.
The perforating line can perforate one to
four faces of the tube and accommodate
lengths up to approximately 3.2m.
The unit can perforate up to four tubes
simultaneously and is therefore well
suited for long series. The company
reports that its new service has been
well received by customers, particularly
in the shop fitting sector.
Sönnichsen as
– Norway
Sönnichsen now offers a perforating service
