Water in gas

[Jim K...]

Water pressure in fractured water main higher than gas pressure in adjacent fractured gas main?

[John]

How can this happen?

A burst water pipe caused problems that left hundreds without gas in Wirksworth earlier this week.

More than 900 homes were were affected when water from a burst main entered the gas network on Tuesday, October 8.

[Andrew]

Happened in West Sussex in 1986.

Some workers using a hydraulic mole (which hammers its# way through the ground), went through both a water main and a medium pressure gas main.

Water spurted out of cooker hobs and gas boilers etc.

BG shut off the gas to a large part of West Sussex South of Horsham.

The police commandered our village carpark so that BG could use it as a base for all their vehicles and they brought people in from all over the UK to visit every house and shut off all gas appliances. Anyone at work came home to find a note saying that the hole in their drive or pavement was where BG had dug down and cut and capped the gas supply to the house.

After fixing the damage and flushing out the water they has to purge and repressurise the entire area and then revisit every house to get gas appliances running again.

I did find a HSE report on the incident once, but have forgotten where it was kept.

[Brian Gaff]

Well one way is that in many older systems the gas pipes are knackered. When they dug up our road after reports of gas it transpired that our clay soil was all that was containing a lot of the gas supplies, since the pipes had rusted away, indeed as they disturbed the pipes gas started to bubble up in peoples gardens and killed some plants, including one of my roses. They have since used plastic pipes to replace them all, but as I have no gas installed, they just left a stop end here ready in case its needed in future. I was amazed that they let it go this far, but apparently its not uncommon for water leaks to get into the clay and leach out in the gas supply, even to cut it off on low spots. Both gas and water have extensive contracts going on replacing the now very old pipes, in the case of gas because they are obviously steel and rusting away, and in the case of water mainly due to them being made of lead, which although probably safe after all this time does deteriorate of course. Brian

[Brian Gaff]

It was not as serious as that here, merely cut off the supply. Brian

[Harry Bloomfield, Esq.]

Brian Gaff presented the following explanation :

Our old system had 70 year old steel pipes running along the back gardens. Leading up to their replacement 3 years ago, they regularly came along with a sniffer in case of serious leaks.

3 years ago, they laid a new plastic main at the front, along the road, then up drives to the individual meters. There were too many garages and extensions built over the original pipe route at the rear.

[Steve Walker]

Lead pipes in soft-water areas never get a coating and remain soluble. The water companies use phosphate dosing to prevent the water dissolving small quantities of lead (I designed some of the dosing rigs in this area). Other than that, lead pipes can last hundreds of years, as lead is very stable.

SteveW

[Harry Bloomfield, Esq.]

Jim GM4DHJ ... explained on 11/10/2019 :

Understandable I suppose. I doubt they had in mind when the laid the original pipes, that there would be much need to build so many extensions and garages.

When the laid the new pipe, the homes to our right have a drive, but there is no easy underground route to get a pipe from the front, to the rear where their meters are. The result was gas feeds run on the surface down the sides of those houses.

I gave the installers leave to run next doors supply pipe up my drive, with my own buried supply pipe.

[Martin Brown]

Water flow undermined support for the gas pipe, it sagged and broke open at a joint. I doubt if much (any) water would get into the gas pipe at least until the gas pressure was turned off to prevent an explosion.