Hot stuff — the case for hot-formed tubing!

BSS Industrial, steel pipe, pipework, hot formed tube
Hot-formed tube steel tube sourced from market-leading manufacturers such TATA Steel can mitigate the risk of expensive failure.

Hot-formed steel tubing has been losing market share to cheaper competitors as margin pressures grip the construction industry. However, David Martin of BSS Industrial stresses 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-formed tubing, which is commonly used in commercial heating or air-conditioning systems, generally up to and including 4 in diameter.

Before discussing applications, it is important to explain how hot-formed tubing is manufactured. Hot-formed (or hot-finished) tubing goes through a process called stretch reduction. This process permanently changes the micro-structure 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 micro-structure of the tubing. This means that the structure is more relaxed and it is this ‘relaxed’ structure that makes hot-formed 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-formed tubing is often used in any application involving extreme temperature conditions. The unstressed grain structure of hot-formed tubing enables this product to operate efficiently, even under immense pressure. By testing in accordance with current legislation EN 10217, the tubing has the capability to operate in temperatures ranging from -7 to +260°C.

The stretch-reduction process offers increased manoeuvrability, 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-formed tube from as far afield as India, Dubai and Turkey.

These imports still only account for about 15% of the market, but it is often impossible to understand the exact chemical composition of the tube, and forged certification is not uncommon. Imported tube often 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.

What’s more, the British Standards, whilst reducing the risk of non-conformity, offer only limited security for tube users. The variation in product quality from one end of EN 10253 and EN 10217 to the other is vast.

My advice to tube users is therefore twofold. First, in safety-critical applications where the risk of failure is a significant refurbishment cost, hot-formed tube sourced from leading manufacturers such TATA Steel, which manufactures the Install+ range of hot-formed products, can mitigate the risk of failure.

Secondly, it is important to use only tube that can be fully traced throughout the supply chain. Cheap imported steel tube may appear to offer a cost-effective alternative, but its lack of traceability could leave contractors at the mercy of costly legal proceedings if the tube fails.

In the current economic environment, the temptation for contractors is to try to buy more cost effectively in order to try and maintain a margin, and steel tubing would appear to offer just such an opportunity.

However, this policy is not without serious implications if the wrong tube is used in an application or, worse, low-grade imported tube is used. Cold-formed tube, manufactured by a reputable company, bought through a reputable distributor and used in a suitable application is perfectly acceptable, but its use must be application specific.

I would urge all users of steel tube to take the advice of a good distributor before specifying steel tube, as not all tube is the same.

David Martin is an expert in steel tubing at BSS Industrial.

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