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Material for Welded Tubes
and Pipes:
The material of the tube depends on
the application of the customer and decisive factors
are the maximum operating temperature of method of application and corrosion
from the
environment and the working pressure.
The following table shows some commonly used tube materials and the maximum
operating
temperature recommended by underwriters laboratories, USA (UL 10300). ( Other
tube
qualities are also used occasionally).
The maximum operating temperatures only apply when the tube are operating under
oxidizing
conditions in pure air. When used in corrosive liquids or other atmospheres the
choice of
material and maximum operating temperature must be based on appropriate
corrosion
tables.
Copper and Copper based alloys:
Copper tubes are mainly used for heating water and other non corrosive liquids
and the heat
exchanging applications.
Brass tubes have today a very limited use for small immersion heaters where the
price is
more important than the quality.
The finished tubular elements are often nickel- plated. Chrome-plating and
tinning also occur.
The tubes are normally used in semi-hard condition as soft annealed tubes are
too easily
bent and the filling operation requests straight tubes.
Furthermore, the heat conductivity of the insulating powder is improved due to
higher density
after reduction of semi-hard tubes.
Monel tubes are more corrosion resistant than copper tubes and are mainly used
in liquids
which may corrode other types of alloys.
Aluminum:
Aluminum tubes are generally used in tubular elements which have to be pressed
into grooves
or soldered to other aluminum surfaces. Typical examples are elements for
flat-iron soles and
aluminum frying pans. Other applications are elements for de-frosting and floor heating.
The aluminum tubes should be in a semi-hard condition for the same reasons as
the copper
tubes and to avoid low powder density and excessive elongation when compressed by
rolling or
swaging.
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