Been reading the Eurostar thread with interest.
Similar question then ocurred about the failure of gas supplies in Luton and Barnet. Why the hell do they think it will take until after christmas to sort out a couple of broken pipes? Maybe there's some bit of high tech complexity in gas pipes that escapes me.
So they use Murphy Construction to do pipe repairs - interesting coincidence :)
Even an emergency/temporary replacement of 50m of pipe shouldn't take days ffs, unless they're gonna dig a trench with teaspoons! But then they don't seem to care fu about their customers these days :(
The fixing of the gas pipes isn't the bit that takes the time, a few hours at most. Excavation, repair, reinstatement. The main will have been turned off at the nearest Pressure Reduction Station, (PRS) to facillitate repair.
This will be the bit that escapes you: Not high-tech but complex. When gas mains fail the pressure over the entire district supplied will fall dramatically and with the deliberate isolation of said main there won't be many millibars around. Before pressure can be restored the district affected has to be clearly defined. Every house that has a gas supply has to be identified and visited. If N/A, revisited etc. If people are away, lots are, or the property vacant then it has to be isolated, and if the meter is not external then the service has to be cut off by excavating it first. The reason for all of this is that some people still have gas appliances with non-cut off pilot lights. If pressure was restored to such appliances, uncontrolled gas would fill the property. Missing even a single property is not allowed.
Gas and air must not be allowed to mix within the gas pipes or houses will be going bang all over the place. So if air has got into the pipes then a nitrogen purge is necessary to flush it out first, then the nitrogen flushed out with gas.
So once pressure has been restored with gas only in the mains then every house service has to be purged to get rid of any air nitrogen.
It is more complex than a water or electric main failing.
mark
You are not a customer of those responsible for the gas mains :-)
mark
blimey, tis indeed quite a palaver! "I know more now than I did before" Thanks, Mark.
Ive just googled the incidents you mention.
Looks like it is going to cost a fortune! It gives them something to do in the freezing conditions.
mark
The electrics have failed
You mean like part of Maryport last week:
mark used his keyboard to write :
I do appreciate a good explanation and that was a good one.
Thanks Mark ^^
Gas company handed out electric heaters, everyone went home and plugged them in, substation burned out. No gas or electric for many days.
When a major main replacement program was undertaken in Grimsby/ Cleethorpes a few years ago temporary overground yellow plastic pipe links were provided while sections were dug up and renewed. The overground temporary pipes were undersized! It caused havoc at one school site which the company I was working for at the time had serviced the boilers prior to the works. We got called every morning to boilers with blown gas burners failing to light. I went in early one morning and put a manometer on the supply before the boilers tried to start. When the boilers were supposed to start the pressure in the main was only 5millibar so of course the ignition failed. By about 09.30 the pressure was back up around 21mB and boilers operated normally but when the canteen kitchen started to operate the pressure fell to around 15mB and boiler ignition became erratic although heat was produced if the boilers were reset a couple of times. A couple of weeks later the relevant section of main was completed and the boiler problem went away.
In message , mark writes
As it seems to have done
now no gas or electricity
"non-cut off pilot lights" - that sounds very dangerous. Yet another reason why I won't have gas anywhere near the house. There have been three emergencies with my neighbours' gas supplies. I have an amusing video of workmen trying to seal a broken pipe.
The amount that comes out of an unlit pilot light doesn't pose much risk of anything.
I can only recall seeing these on *very* old cookers. I doubt that many are left at all but I suppose it's a chance that the gas company aren't prepared to take yet.
That's a bit extreme. Properly handled, it's acceptably safe and offers considerable savings for heating.
Are we talking about LPG/Propane here? Going to share your video? ;-)
Tim
not even after a few days in a small kitchen? mark
Sufficient natural air changes to avoid the concentration of gas in air reaching ignitable or explosive levels
In message , cynic writes
8% in round figures
Non-cut off gas fires too. Which are a lot bigger - 6kW input bigger for example :-)
Natural Gas is a) lighter than air b) very smelly due to additives. You can get auto-cutoff valves if there is a full-bore escape (vandalism of an outdoor pipe after the meter, BES do them - about =A340 well spent if drugged up copper thieves in your area).
LPG is a different matter a) heavier than air b) smell doesn't reach your nose, but can pool underfloors (basement, wooden ground floors) until it finds an ignition source such as a low level socket or low level socket timer and kaboom.
As to sealing a broken pipe, I suspect they use an "inflatable bulb" which expands into the pipe sealing it off (the pressure is 75mbar however the flow can be staggering if a large bore gas main). If it is cast iron then just wrap in a self-amalgamating wrap of some sort. When my mothers cast iron supply pipe was leaking the "apprentice" thought he had found it and then slammed his spade right through it, the Transco ACS at the time said "oh yeah, he's found it, clumsy sod". The apprentice is now working in the nuclear recycling industry now :-) Nice new yellow alkathene stuffed through.
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