Water Main Break

[eddiememphis]

I had a text last night from a neighbor about the sewer back up. Then the President of the HOA asked why there were light in front of my building. I walked the dog and found a kid from the city standing in a geyser park. It was pretty cool, with the flashing lights and little burbles popping up as we chatted about old cast pipes giving up the ghost.



A very poor picture. The main had ruptured about eight feet away from this. It was pouring up, from under the asphalt, and down into the storm drain the city guy had opened.

There were six other spots where it went from a bubbling to geysering as we waited for the "meter" guy to show up and shut it off.

Today, the men showed up, tore up the asphalt, found the breech, cut it out and patched it.

I took a picture of the hole.



I didn't ask the guy the orientation of the hole. It looks to me that it deteriorated from the outside.

So to my questions...

1- What is the pressure on the city side of the meter?

Homes need a regulator to keep the pressure around 60 psi. This would lead me to think the city side is slightly or possibly much higher, but I can't find much information about it.

2- Does this picture look like a weak spot in the pipe or abrasion from movement? Does a 4" cast pipe move at all during the on/off cycling? What about last year's break causing this?

I am not looking to blame anyone. I just love to figure out how thing work.

[fitterjohn]

looks to me like something was rubbing on it. 90% of the leaks i get in copper are from rubbing. wires are the worst, the copper pipe will rub through before you can rub through wire insulation. that being said i dont deal in cast pipe

[FoxtArt]

By no means an expert, very far from one...

I have had to personally replace quite a bit around my house. The alkaloids in the soil around this part of the state do something crazy to it. After a lot of years/decades, it ceases to act quite like metal. I've had two 4" lines that popped laterally, or split I guess is the better way to put it. Cast iron pipe cutters no longer worked well. Sawsall no longer worked well.

Sledgehammer though - excellent to get it out. And there was no doubt it was cast, I still have some pieces around, but it performed like an imaginary substance between ceramic and iron. Nearby there is a site that has had their cast main (18" maybe?) leak on more than a dozen occasions, and I'm sure it's the same underlying cause.

Anyway, over a long enough period of time, in some places, the metal can get quite brittle and it can split or rupture very easily in those places. No idea what caused that specific one, though, as you don't live here.

ETA: Around here the municipal pressure can exceed 100PSI. But we also have mountain sources and elevated tanks, so it's not apples to apples.

[Grant H.]

Chemical reaction deterioration is more likely than actual abrasion. Yes, water hammer and repeated on/off can cause pipes to move some, but if it was properly backfilled/buried, that effect is mitigated for the most part.

I spent some time in the O/G world working with the guys that were responsible for Cathodic Protection of pipelines (building comms and monitoring solutions for them) and it is incredible what varying soil conditions can do to cast iron, steel, and even epoxy coated steel pipe.

Most municipal water systems run between 80-100psi on the city side, usually favoring 80-90psi. Most large water towers (pressure, not storage) are 180-200' tall (every 100' gains approx 50psi). I had a lot of fun installing radios on top of water towers.

[TRnCO]

The water pressure on any given water line, even within any one water district, can vary from zone to zone. In other words, there are usually several zones within a city and each zone could have a different water pressure.

Hard to tell, but that break could've been caused by a nick when the pipe was installed initially, and over time simply deteriorated much quicker in that one spot then the rest of the pipe.

As Grant said above and to be a little more accurate, for each foot of rise water gains .433 psi. In other words, 100' of rise will give you 43.3 psi.

[ray1970]

Not really a corrosion guy myself but looks like external corrosion of the pipe likely caused a significant reduction in the wall thickness of the pipe in that area. There?s a reason certain industries employ pipe coatings and cathodic protection. Delivery of clean water under low pressure isn?t likely to kill anyone or ruin the environment so I guess just burying metal pipe straight in the ground is perfectly fine.