May 2013 Tube ProducTs InTernaTIonal
57
The case for
hot formed tubing
By David Martin, BSS Industrial
Before discussing applications, it is first important to
explain how hot form tubing is manufactured. Hot formed
(or hot finished) tubing goes through a process called
stretch reduction. This process permanently changes the
microstructure of the pipe, which means it can withstand more
manipulation and extreme temperatures. Hot formed tube
is heated up to specifically selected furnace temperatures
which recrystallise the fine grain microstructure of the tubing.
This means that the structure is more ‘relaxed’, and it is this
relaxed structure that makes hot form tubing more suitable for
extreme temperatures and demanding pressures.
Hot formed tube is more suitable in safety critical applications
or where the risk of failure would result in highly expensive
repair or refurbishment costs. For this reason, hot form tubing
is often used in any application involving extreme temperature
conditions. The unstressed grain structure of hot formed
tubing enables this hot product to operate efficiently, even
under immense pressure. By testing in accordance with
current legislation EN10217, the tubing has the capability to
operate in temperatures ranging from -7 to +260°C.
The stretch reduction process offers increasedmanoeuvrability,
rigidity and strength, even when under varying temperatures
and thermal loads. This is especially important when used
in vertical runs. In addition, the added strength and rigidity
reduces the risk of sagging between supports.
A further issue is the mixing of different types of tubing in a
single application. It is not uncommon to find installations
where a contractor has used a cold formed product at the end
of a run of hot formed tube for no other reason than “we had
some left over from another job”.
Unfortunately, the mixing of different types of steel tubing
in an air conditioning or central heating system leaves the
system at risk of failure, as the different types of steel tube
rarely work well together.
However, there are other issues surrounding the use of different
types of tube which simple differentiation by application will
not cure. Increasingly, in recent years, there has been a steady
increase in imported cold form tube from destinations as far
afield as India, Dubai and Turkey.
These imports still only account for approximately 15 per
cent of the market, but it is often impossible to understand
the exact chemical composition of the tube, and forged
certification is not uncommon.
Often, imported tube fails to conform to the minimum
technical requirements and is not sufficiently malleable or
strong enough for commercial applications, such as a central
heating system. Unfortunately the use of sub-standard tube
often only becomes clear once an office or industrial unit
fit-out has been completed and the tube fails, leaving the
potential of very costly remedial work.
H
ot formed tubing has been losing market share
to lower priced competitors as margin pressures
grip the construction industry. However, David Martin,
an expert in steel tubing at BSS Industrial, says that
hot formed tube has a key role to play in safety critical
applications and should not be overlooked purely on the
basis of cost.
Most users of steel tubing have traditionally taken the
view that “a tube is a tube is a tube”. In other words, one
steel tube is much the same as any other.
The reality, however, is very different. Different sizes and
chemical formations of steel tube make certain types
of tubing more suitable for safety critical applications
than others. Nowhere is this distinction more important
than with hot form tubing, which is commonly used
in commercial heating or air conditioning systems
generally up to and including 4" diameter.
Hot formed tube can operate in temperatures from -7 to +260°C
