Pay attention to pipework
21 November 2014
Although it’s not always properly considered, pipework can affect a compressor’s efficiency and its performance, as Andy Jones, managing director of Mattei, explains
Ensuring that a compressed air system runs efficiently and to optimum performance is about much more than investing in a modern, energy efficient compressor. The system’s pipework – in terms of the material it’s made from, the layout and its condition – has a huge role to play too.
Piping for compressed air systems can be made from a wide range of materials. When making a decision, it’s important not to be guided just by price; choosing the cheapest option can often prove to be false economy, as in the long run it could adversely affect efficiency, running costs and maintenance.
Traditionally, compressed air pipework was constructed from galvanised steel, a well-known and widely available material. However, its use has many limitations and restrictions, and there are drawbacks of pressure drops and reduced flow rates; galvanised steel is prone to rusting, which leads to contamination, reduces the effective cross-sectional area of the pipe (which restricts flow and increases pressure drops) and leads to premature blocking of pneumatic components and filters. Galvanised steel is also heavy, and the threaded joints require careful preparation. Furthermore, the inner surface won’t be smooth, giving rise to pressure drops and energy loss.
Aluminium could be regarded as a better solution than galvanised steel; aluminium is lightweight – typically being 70% lighter – yet it’s still robust. It is also quick and easy to install (only basic tools are required, without a requirement for welding or threading), reducing downtime. As aluminium is very flexible, modifications can easily be made to the system, if, for example, another branch line needs to be added at a later date.
Importantly, aluminium doesn’t rust. Any corrosion results in the formation of a layer of aluminium oxide, which is very stable and has good adhesion to the metal surface – actually protecting the material from further corrosion and oxidation. Providing it is not disturbed, once this layer is formed it won’t react any further.
High-performance plastic, for example ABS or polyethylene, is another option – as long as the piping has been specifically designed for use with compressed air. It is lightweight, non-corrodible and nontoxic, but can be subject to ultra-violet degradation.
Pipework made from stainless steel is also resistant to corrosion and rust, and offers high rigidity. It has a higher initial cost than other materials, so tends to be used in high specification, critical applications, such as food processing. Meanwhile, copper is particularly useful for medical applications, as it inhibits microbial growth, but its maximum diameter is 40mm.
It is important to seek advice from a compressed air specialist to ensure that appropriate pipework is specified. For further guidance, the British Compressed Air Society (BCAS) offers a fact sheet on pipe material selection, which illustrates the advantages and disadvantages of galvanised steel, aluminium, high-performance plastic, stainless steel and copper.
Whatever material is chosen, the efficiency of the system also depends on the layout and design of the pipework, and the joints and connections. The distance between the compressor and where the compressed air is used can have important implications in terms of system efficiency. Excessive lengths and bends lower efficiency, so pipe runs need to be suitably laid out. For systems where the point of use and the compressor are relatively close then a single line could be chosen, whereas larger systems with many points of use would benefit from a ring main.
Although smaller diameter pipe may save on capital cost, greater pressure drops in the system lead to a higher operating cost.
The pipework must also be in good condition, and in particular must be checked for leaks. We often see compressed air systems with about 150 to 300 leaks, and a company using 50m3 of compressed air per minute could potentially save around £63,000 by repairing them. Repairing leaks is a simple and cost-effective exercise (the average cost of a Mattei leak detection survey is less than 10% of the overall leakage costs).
While a new, correctly specified compressor can dramatically improve energy efficiency, in order to achieve optimum savings the system must be appropriately designed, and the pipework must be in good condition and made from an appropriate material.
As well as offering a range of energy efficient compressors, Mattei aims to raise awareness about related, cost-effective services that could improve efficiency without the need to finance a new compressor.