Natural gas pipe sizing over 50 meter?

akingpage · Feb 28, 2012

I have had a bit of conflicting information on this, so far i have been told by several commercial engineers that seen as though I am able to run 35mm copper on my domestic ticket I can do the pipework myself as they are going to run the 60 meters from the u6 meter in 32 steel in any case?

I spoke to Gas safe and they have said that I can do the pipework run but the gas volumes would be too big for me to work on with my ticket so I will need a commercial engineer to purge the system, I was reading the trusty "essential gas safety" corgi book and it says that if I isolated the pipework at 0.035m³ intervals then I can purge each section and tightness test each section one by one ensuring I stay inside the domestic volumes for tightness testing?

How can I run the pipework myself if the maximum length of 35mm pipe I can run is 30 meters (insuring I stay within my 1mb differential pressure drop) my working out is just an example:

[Power]-[Flow rate ]-[Assumed diameter]-[Measured length]-[Effective length]-[Maximum length]-[Pressure drop]
[27kw]--[2.52m3/hr]------[35mm]-----------[30 meters]------[30 meters]--------[30 meter]-------[1mb]------

This working out tells me I cant install anything over 30 meters in length on a u6 meter because my pressure drop would exceed 1mb? (right or wrong?)
My questions are:
If I cant run the whole 60 meter in 35mm (due to potentially exceeding my 1mb pressure drop) how can a commercial engineer run the 60 meters in 32mm steel and stay within the 1mb pressure drop on a u6 meter?

Any help will be appreciated

Mike Jackson · Feb 29, 2012

I think you're getting yourself confused here. 30m of 35mm pipe will pass 8.5 cu m of gas per hour, and 30m of 32mm steel will pass 7.6 cu metres. This is over twice what you require so I would imagine 60m will leave you with a drop within specs.

Including the meter the maximum length of 35mm pipe that you can test and purge is about 17m including allowances for fittings. Without a meter the length is around 40m so you could in theory install, test and purge in sections. The problem is each section of pipe will require an isolating valve and test point. Also with volumes of .035 cu m a lit purge will be required.

tamz · Feb 29, 2012

35mm copper or 32mm steel will take 4.5m³ with a 1mb drop over 100m
Your 10m run of 22mm is too much. you have used up your 1mb drop on that.
32mm (1 1/4") steel is around £35 /6.5m length. Much cheaper (and better) than copper.

You can do it on a domestic ticket if you do it in sections. Test and purge as you go.

Run around 20m of 1 1/4" from the meter and valve it. (volume of 20m 1 1/4" pipe and meter inc allowance for fittings = 0.0325m³). Test and purge the section.
Run another 4 length of 1 1/4" (26m, volume 0.0318m³) and valve it again with a tee and test nipple in the section. Test and purge the section.
Run the 1 1/4" up to near the boiler then reduce to 22mm for the last couple of metres. Put a test point in the pipe work here too.

50m of 1 1/4" steel or 35mm copper will give a drop of around half a mb.