November 2019

BCAS looks at what to consider when improving the compressed air distribution system. Improving compressed air distributions systems – things to consider A compressed air distribution system will be installed to deliver compressed air from the compressor house to the point or points of use. At the time of original design a number of factors will be taken into account including the total flow capacity of the system, operating pressures at points of use and exceptional flow demands. These factors will be used to determine the type of system, for example, a ring main, a combination of ring mains with sub headers or a simple single line system. In the same way that air receivers are a source of stored energy, so is compressed air piping. Therefore it is essential that: The system is designed properly to be safe and energy efficient. The system is installed correctly. Proper procedures are followed during commissioning to ensure the integrity of all the connections within the system. Correctly sizing the pipework at this stage is critical to ensuring the pressure drop across the system from the discharge at the compressor house to the points of use is no more than 0.2 bar, generally accepted as best practice. This is not a difficult process for an experienced compressed air engineer; however, as time goes by requirements often change driven by, new processes, updated equipment and variations to production patterns. As these factors are difficult to accommodate in the initial design their impact on the performance of the compressed air distribution system must be understood and monitored to ensure that compressed air continues to be generated and distributed. Managing expectations There are several key points when looking at pipework installation or modification it is key that both you and your contractor are working from the same understanding. The following are minimum requirements before embarking on a project: Agree an acceptable leakage rate at the contract stage The concept of ‘zero leakage’ is unacceptable unless related to a time factor and the accuracy of the test method The pressure at which the integrity test is conducted and its duration should be agreed When agreeing the test conditions the test pressure chosen should be related to; i. Design Pressure; ii. Actual operating pressure or; iii. PS’ which is identified as the ‘maximum allowable pressure’. Prior to any work a risk assessment method statement should be drawn up regarding safety of personnel. Set the criteria for the leakage test & the pressure (integrity) test both will be required. Who will be responsible for the follow up check. Carry out a risk assessment procedure on the system to establish which areas would be dangerous to personnel should there be a major leak or system failure. Jointing techniques In jointing many new modular piping may be similar in appearance, but the jointing procedure can be quite different. If not correctly carried out this presents a real risk of failure and consequent injury to personnel. Jointing must be carried out employing the process described by the manufacturer of the system or relevant British Standard. Your supplier should be able to advise you in accordance with your applications requirements and also set the testing appropriately at the quotation stage of your project. We have listed some detail for you below but for full detail please download the BCAS pressure and leak test guide from: www.bcas.org.uk Push-fit Joints This type of joint is made by mating a soft seal in some form of housing against either the inner or outer surface of the piping system. Box section modular aluminium pipes are connected to each other and fittings employing a double ‘O’ ring seal and dovetail clamping and jointing system. Screwed Joints Where pressure-tight joints are made on the threads – the BCAS publication “Pipe Joint Guide” identifies the thread types used for this type of jointing technique and the practices to adopt to ensure a satisfactory air-tight joint. Welded Joints The integrity of this type of joint rests solely with the quality of the welded joint. Therefore, a qualified and certificated welder in accordance with BS EN ISO 9606 should perform the welding procedure. ‘Press-fit’ Joints This is a mechanical pressed joint using an O-ring to make it fluid tight. The joint can be made by either hand force crimping tools or powered hand tools. Where flexibility is required, other systems may be more suitable. Hydraulic Friction Joints These are popular for pressures above 20 bar and extend into regions of 450 bar. The use of these fittings to make a joint with a pipe should follow the joint manufacturers’ instructions in every detail. Process, Controls & Plant Focus on: Compressed Air 24 | Plant & Works Engineering www.pwemag.co.uk November 2019

RkJQdWJsaXNoZXIy MjQ0NzM=