Water in Gas mains!

I can't post in the Combustion Chamber.... and this isn't really a DIY gas question.....

There is a another incident in the news (Wirksworth, Derbyshire) whereby CADENT have had to isolate a number of customers from its network due to water in the gas mains after a water main leak.

I'm puzzled... how does this water get into the gas network (assuming that the gas pipe hasn't also been damaged)....but even if it were... wouldn't the pressure & flow of the escaping gas keep the water out?

CADENT now have to go to great lengths to individually isolate every customer from the mains, remove the water from the system & then individually reconnect each customer checking, I guess, that no appliance has been damaged or is burning incorrectly.

(Which I appreciate the logic & reasons for.... I just curious as to how the water enters the system in the first place!)

The gas main might be iron and corroded and water gets in. If you have ever seen water in the gas main the ugauge goes up and down and if the leak is underneath grass. You’ll see a dead patch of grass. Also the gas is low pressure compared to water main.

bellairaphon said:

Also the gas is low pressure compared to water main.

Click to expand...

The gas pressure in the house, post regulator is pretty low, only about 30mb ... but isn't the pressure in the street main a lot higher? I seen to recall in the region of about 7 BAR compared to around 2-3 BAR for the water main?

You’d be surprised how low the pressure is for much of the network - Water in pipes is an eternal PITA for the GDN’s. Sounds like they are having to do a purge and relight across all affected properties?

wizbongre said:

Sounds like they are having to do a purge and relight across all affected properties?

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Thats the way it reads. Yeap. 1500 properties affected.


https://www.bbc.co.uk/news/uk-england-derbyshire-49989697

I'm guessing that, with 1500 properties to serve, this ain't gonna be a 2" pipe...so you would have thought the pressure would be quiet high?

Gas pressure in the street isn't often incredibly high, on occasions I've seen crew 'repair' a damaged service, (pending proper repair), insulation tape wrapped around the pipe, and a plug of Denso tape in the open end have been 2 such fixes.

There was an incident in Corby, Northants in April 1997, where a contractor laying new water mains, had a 'Mole' that went AWOL, and smashed through an existing live water main, quickly followed by a live gas main. With the incident being geographically near the 'top' of the town, about 60000 gallons of water entered the gas system before it could be stopped. It took days to sort the mess out, with Gas engineers having to visit every affected property to restore the supply.

The cost of the incident ran into 6 figures I believe.

Water in Gas mains used to be quite common and the older cast mains had syphon points to drain water from the mains system, not so common now with the majority of the mains network is now PE, still a lot of cast out there though, and the Gas mains pressure in your village will never be anywhere near 7 Bar

Some water in gas mains was beneficial in the days of town gas to keep the joints gas tight.

From patent application GB2223551A for a joint sealing fluid that could be injected into gas mains. Read it HERE

The joints between adjoining lengths of existing cast iron gas main can be sealed by lead and yarn. The yarn forms a packing which when wet forms a good seal as the packing expands. When gas mains carried town gas the yarn was kept moist since town gas has a high moisture content. However., following the replacement of town gas with natural gas, the yarn has tended to contract as natural gas is much drier than town gas and has tended to absorb the moisture in the yarn. The contraction of the yarn has given rise to a tendency for the joints to leak.