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Gas main purging, commissioning and de-commissioning
Where alterations need to be made to a main, purging is the safe solution to remove the main totally of combustible gasses. On completion, the main can then be safely modified or totally removed without the worry of gas inside the main becoming ignited.
First the main or leg is disconnected at source, capped off and made safe. If the meter is removed it should be capped and made safe also.
The final end of the main or leg should be identified. A thorough investigation of site should be carried out to identify additional branches from the main and a simple line diagram created for reference and volume calculations.
The purge point end is connected to the purge point shown above by flexible hose. The source of the main is connected to a Purge Fan and operatives use 2 Way Radio to communicate.
When the fan is turned on fresh air is forced down the main which begins to purge the gas from the pipe. The gas flows out of the main into the flexible hose, through the purge rig and into the atmosphere. A special flare point is used to prevent flash backs should the gas be ignited.
An analyser and volume flow meter connected in line to the flare point shows the volume of gas / air purged from the main and the level of gas in the purging mixture. When the calculated volume is purged and the mixture reads only oxygen, the main is purged and can safely be removed.
A special procedure applies to mains with branches to ensure that 100% of the gas is safely removed from all legs of the pipework.
In the event of a failure of the fan blower component during operation, our engineers would continue to purge the main using Nitrogen gas.
Commissioning Of Mains
Purging requires an accurate measurement of the volume of the main to be commissioned.
When the new gas main has been pressure tested, certified and connected, the purge point is connected to the extreme of the main. The volume flow meter on the purge kit is reset and the gas is turned on.
The main is safely purged until the volume of air in the main is replaced with gas, hence the need to identify the volume before starting work.
The gas analyser can be used to confirm that the purge of air was successful and that no air remains inside the pipework.
Certification
Our Gas Safe operatives will issue Gas Safe paperwork to declare a safe gas main and provide Gas Safe commissioning paperwork for new installations.
Health & Safety
We have an excellent Health & Safety record and can provide high quality Health & Safety files including Site Specific Risk Assessments and Method Statements for all our works. We carry a full range of safety signage and barrier.
Construction Site Safety
Gas Operatives hold CSCS cards for easy site access.