PIPES
Getting the most out of AC pipework
The best and most efficient air condition system in the world cannot operate as it should if the pipework and components holding it together are not corrosion free. Internal corrosion in water containing pipes will lead to inefficiencies and potential breakdown, issues that can shorten an ac’s lifespan and result in downtime for the buildings relying on this cooling technology. From specification through to installation and ongoing maintenance, choosing the right pipe and components and then looking after them properly is essential for economical and sustainable HVAC that stands the test of time, explains Steve Munn, managing director for Hevasure.
T
he latest innovations in ac technology can often leave pipework and components in the shade. While maybe not as interesting as the box responsible for cooling, the lengths of metal that link components together in closed water systems have an essential role in allowing ac and HVAC equipment in general to meet their design requirements. If ac plants claims to be efficient, cost-effective and sustainable, it can only do this if the pipework and components are working as they should.
What’s key is that corrosion is kept at bay, chiefly by ensuring oxygen is kept out, particularly in closed circuit systems. This task begins from the moment pipework and component material is chosen, and continues throughout its working life where the role of the water treatment company becomes essential.
Testing your metal
AC systems are commonly plumbed together using mild, carbon or stainless steel pipework. Components such as valves and pumps can also be made from these materials, as well as brass, and heat exchangers are often constructed from aluminium.
All metals can be subject to corrosion attack to varying degrees, dependent on how a system has been installed and
18 September 2020
crucially, what happens during precommission cleaning, subsequent handover and ongoing maintenance. In recent years, thin-walled carbon steel has grown in popularity due to that fact it is light weight, cost-effective and easy to install. I’m a big supporter of carbon steel, but, while it is an excellent material for pipework, particularly in closed circuit systems, it can be very susceptible to damage. A few cases of bad press have left some specifiers and M&E contractors wary of carbon steel, but there really is no need – as long as it is used and maintained correctly. You might be forgiven for thinking thicker walled, mild steel, is a safer option (commonly used in older systems and for components, such as pumps). This material is still subject to corrosion, it’s just that wall penetration is less of an issue due to the thickness. The problem here lies with corrosion debris, which can be transferred around the system causing blockages and loss of efficiency. Where flow rates are low, corrosion debris settles creating the perfect conditions for microbes to flourish.
Even stainless steel and aluminium, which are passivated, can be vulnerable to corrosion. Aluminium loses its passivation if the pH of the water rises above 8.5 and stainless steel will undergo, pitting attack or even stress corrosion cracking in chlorinated waters. Brass components,
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