Cold weather warning

We may be in the depths of a bitterly cold winter, but compressed air systems still need to function safely and efficiently, as Chris Dee, executive director of the British Compressed Air Society (BCAS) explains

Whether you are a believer in the notion of climate change or not what is clear is that temperatures in the UK are falling steadily in recent winters. Some of the 'lows' of minus 18°C in parts of the UK just before Christmas 2010 where the 'normal' in winter was marginally below 0°C is an indicator that the weather is changing. In the north of England and Scotland the temperatures fell even further.

Last month was the coldest December documented for the UK since nationwide records began 100 years ago, the Met Office has confirmed. For central England, it was the second coldest December since 1659.

When compressed air systems are designed, items such as air receivers and coolers are encouraged to be sited outside the factory walls and preferably in the shade on the north side of the factory to benefit from cooling effects. Other equipment such as control valves, pipes and joints then provide the necessary connections into the factory building. Maybe the factory building is not heated for whatever reason so the incoming piping and the compressed air are still at ambient outside temperature.

In-service inspection is required according to written schemes of examination where periodicity of examination is identified along with particular examination techniques.

These are identified according to the known operating conditions as well as service and maintenance activities.

With the changes in winter temperatures there is a need to adopt system design practices and equipment design characteristics more usually seen in Scandinavian countries than in the UK.

As temperatures drop material properties change and aspects such as embrittlement leading to brittle fracture come into play.

Welded joints become a point of focus especially in air receivers. The population of air receivers in the UK numbers in the hundreds of thousands, many of some vintage.When ordering an air receiver how many people pay heed to the minimum temperature characteristic? Usually the only issue is the pressure and volume and the cost, so how many receivers are there with a minimum design temperature of perhaps 0°C or, in more recent years, probably -10°C.

With the recent low temperature experience in the UK even -10°C is not a low enough specification.

Before panic sets in and there is a rush to order a new air receiver with a lower temperature characteristic, stop and consult your competent person, the one who produced your written scheme for advice and/or your compressed air supplier.

Don't forget that valves which may have water vapour pass through them may now be frozen and possibly cause failure by cracking the body which will only be seen when the ice melts and the valve blows apart under pressure. Pressure relief (safety) valves may not function due to freezing as will be the case with automatic condensate drains.

Lagging water pipes and wrapping the hot water tank with an insulating jacket is okay for water systems but lagging compressed air pipes and wrapping an air receiver may seem a good solution to the cold but is not necessarily the best option. For existing compressed air systems the solutions to low temperatures need to be identified to be both cost effective and efficient. For new installations the issue of low temperature operation can be accommodated at the design stage as long as this characteristic is placed further up the list of priorities in view of recent experience. Consulting a BCAS AirSAFE registered company www.referenceline.com/bcas is one way of getting the advice and guidance necessary.

It may be cold outside but your compressed air system should still function safely and efficiently. For further independent advice, please contact the British Compressed Air Society.