TPI May 2013

The case for hot formed tubing By David Martin, BSS Industrial

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.

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. 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

57

www.read-tpi.com

May 2013 Tube ProducTs InTernaTIonal