Purge old gas pipe before removal?

[wookey]

I have taken up my parquet and screed which has revealed the old 1" iron gas pipe underneath. I want to get rid of this as it's in the way of my nice new insulation, which is going to involve angle-grinding it into sections in order to get it out . It's been disconnected from the meter.

What I'm not sure about is whether there is any point trying to purge it of gas first or just decide that the small volume of gas in it isn't going to do any harm. All the info in gas fitter training about gas purging is about making sure a new installation has been filled with methane and there is not an explosive mixture (so you calculate the correct volume to feed through from the mains).

I found nothing on the correct procedure for removing lines, even though in principle the same issue applies: if you just uncap it and leave it, at some point it will be an explosive mixture, before it eventually isn't again. I have no idea what the diffusion rate is and this whether this is a good idea, given a desire to start hacking at it tomorrow or the day after. At least if it's left full, and you open the door whilst hacking at it, there's probably not much risk. (total pipe volume is about 5.6 litres, or 0.2 cubic ft).

I could contrive to fill it with 6L of water or pump 6L of CO2 or air through (although I don't have a handy source of CO2) , but wonder if it's worth the effort. Anyone know what an appropriate procedure is?

[AGT]

https://gaspipes.co.uk/services/gas-testing-purge/

[ALAN/ALAN D]

How long is it. ?
Has it been open / vented at both ends. ?
Have you still got a gas supply to the house. It is not connected in any way to the gas system. ?

If its been open vented at both ends for a long time. Fill it with water and cut it out with grinder.

[wookey]

Sorry forgot to say there is about 10m of pipe (hence the 5.6l internal volume). It basically runs the length of the house via a spur to the original gas fire and two generations/locations of kitchen hob/oven.

No it's not been vented. Yes it is definitely disconnected, but not very long ago. There is still a gas meter connected to an (unused these days) boiler with 22mm copper pipe. You can see where the iron pipe used to connect. The whole meter+boiler is due to be removed sometime in the next year or so so I can stop paying a pointless standing charge.

AGT: yes I did see that page, but it seems like they are mostly talking about larger installations than domestic houses. It does imply that one should make an effort to get the gas out first, but in my experience fitters don't do this before they start soldering up gas pipe with torches so they don't seem very bothered about naked flames near recently-cut gas pipes, so long as they are not still pressurised. A pipe full of gas isn't dangerous. A long-term gas-leak in a closed-up building is, and a pipe with just the right (wrong) amount of air in could be....

[John_S]

Presumably it is either open or capped ar the disconnected end, if it is capped, remove the cap.
At the other end, remove the appliance so that the end is open,
Stick a short length of hose pipe in one end and blow half a dozen deep breaths into the old gas pipe and it will be purged.
Seal hose with gaffer tape if necessary.

Probably overkill, but this would eliminate all risk.

[ALAN/ALAN D]

Ref " Presumably it is either open or capped ar the disconnected end, if it is capped, remove the cap.
At the other end, remove the appliance so that the end is open,
Stick a short length of hose pipe in one end and blow half a dozen deep breaths into the old gas pipe and it will be purged.
Seal hose with gaffer tape if necessary.

Probably overkill, but this would eliminate all risk. "

Run a short length of hose pipe. YELLOW. From the old disconnected pipe near gas meter to an open door / window outside.
Use YELLOW P.V.C. tape to seal the bit of hose pipe that you put inside the iron pipe.
Each appliance that is connected to the Old iron pipe.
Disconnect.
Open any valves fitted / Remove any Capped fittings and blow half a dozen deep breaths into the old gas pipe and it will be purged.
Doooo the same on all appliance things that were connected.

The Yellow P.V.C. tape / Yellow hose pipe. Was a wind up. You can use other colours.

I have cut into 24 inch diameter pipes over a thousand metre long and welded various fittings onto it. That needed a bit more purging.

[AGT]

Can it be pulled up and the sections kind of bend up and wiggled backwards and forwards to get shorter length.

I would do this and if I was worried I might fill the pipe with water and then cut.

[wookey]

I do even have some of that 20mm yellow gas pipe they use to retrofit old iron installations so I can do it with kosher pipe :-)

So I left it to vent for about 30 hours, then gave it a few puffs and chopped it out. No problem. (except that the pipe is thicker than the depth of my angle-grinder so it was a bit of a pain to actually get out).

Cheers for the suggestions.