TPi May 2014

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May 2014 Tube Products International 39
products & developments
Composite
tubes
Hoesch Schwerter Profile develops
products in collaboration with specific
fields of industry and customers.
Modern power stations and industrial
plants are 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 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 carbon steel to handle the thermal-
mechanical load on the tube, while
the austenite provides protection
against corrosion from the prevailing
environment.
Clad pipes (where the corrosion-
resistant layer is applied to the tube
body by welding) have one or two layers
of 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 carbon 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
particular to clad pipes.
The carbon steel component and
austenitic layer of the extrusion billet
are manufactured in a common hot
forming process at around 1,150-
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 also possible, since there is
no cast structure created by cladding.
Hoesch Schwerter Profile GmbH –
Germany
Extruded tubing with internal and external layer
New name for continuous weld product
Wheatland Tube, a manufacturer of
steel pipe and tube solutions, has
announced a new name for its
continuous weld (CW) pipe. Wheatland
CW pipe will now be manufactured and
sold under the SureThread™ brand
name.
“This name speaks to the
excellent threading and fabrication
characteristics of CW pipe,” said Mark
Magno, president of Wheatland Tube’s
pipe division. “Many of our customers
tell us that our CW pipe ‘threads like
butter’ and doesn’t have hard spots
commonly seen on imported ERW
pipe, so the SureThread name just
made sense.”
SureThread pipe features a uniform
grain pattern and smooth surface that
the company says is proven to cause
less wear and tear on tools and dies
than traditional ERW pipe.
SureThread is used for mechanical
and low-pressure applications, as well
as steam, water, gas and air lines
applications. Wheatland Tube is North
America’s only full-line producer of
SureThread ASTM A53 CW and electric
resistance weld (ERW) standard steel
pipe.
“We recently surveyed contractors,
and 72 per cent of respondents
indicated they believe our SureThread
product to be easier on their tools.
That means reduced wear and tear,
which helps tools last longer,” added
Mr Magno.
Wheatland Tube – USA