Copper mains "thinning"

[meldrew's_mate]

Called to a customer's house at the weekend (and missed the 1st half of the Argie game ). He had a pinhole leak on the cold water mains. On trying to cut-out a section of pipe to make a repair using a standard Kopex cutter I found the pipe was so thin it would crush as the cutter rotated. It seems the pipe has been disolved so that the wall thickness is only about 0.3mm (new it was 0.7mm). I have seen this effect close to brass fittings, but not about 3m from the stopcock as in this case. The customer reported that a repair had been made 6 months previously, this being a compression brass "repair" connector.
My questions are:-
What causes the pipe to be eroded in this way?
What can be done to prevent further erosion?

I checked the main equipotential earth bond at the gas meter and found this to be very loose in the connection. There was no other earth wire emerging from the main earth terminal, so I doubt if the water main is earthed.
The house is very large, consumer unit and gas meter in the detatched garage, plastic water service pipe rising in the main house 10m away.

I intend to replace the damaged section with plastic and renew the equipotential bond to the house (yes, I'm competant & qualified to do so), can anyone tell me if these actions will prevent further corrosion to the rest of the internal mains copper?

PS I wrote this after getting bored with the Switzerland/Ukraine match, tried painting the walls but that was only slightly more interesting than the match

 

[fitz1]

it may have been standard of pipe at install. if u replace with plastic u will need to bond both sides of plastic pipe.

 

[doitall]

being as how your competent with sparky stuff

Check the pipes, including the gas etc with a clamp meter for residual currents.

 

[JohnD]

A DC current can erode metal objects, but AC usually won't.

 

[doitall]

He will be looking for a typical 20-40 m/amps reading.

 

[Agile]

A few mA is normal but I have seen some mains pipes with over an amp mains current flowing to earth.

Check the date of the install. There was some very poor quality copper during the Rodesian crisis 1970-1973 when Ian Smith declared UDI and blocked Zambian copper exports.

Tony

 

[Softus]

it may have been standard of pipe at install. if u replace with plastic u will need to bond both sides of plastic pipe.

Why would that be necessary? Doesn't the main bonding at the point of entry (i.e. before the plastic) satisfy the need to ground the pipe that's entering the equipotential zone?

 

[ChrisR]

Er, but,
Smith UDI was Rhodesia(Zimbabwe) 1970.
Copper crisis was Kaunda being unable to get copper out from Zambia through Angola, 1975.
So, ... oh never mind.


Doitall do you mean AC or DC?

AC will cause electrolytic corrosion, but usually more pitting than thinning.
Is it soft or hard water? Iron mains pipes at all?

 

[Nige F]

Historically I`ve come across this During the 70`s on pipe that was old ~@ the time and only a couple of instances here in Sussex..........so

 

[Agile]

The UDI was actually 1965 but only began to bite hard around 1970.

From internet:-

"""Zambia incurred massive costs from the survival of white supremacy across the Zambezi. Following (Southern) Rhodesia's Unilateral Declaration of Independence (UDI) in 1965, the United Nations imposed sanctions intended to isolate that country, but these bore much more heavily on Zambia. Copper exports were expensively rerouted northward, and a tarmac road and oil pipeline were built to Dar es Salaam, Tanzania. Trade with Rhodesia was steadily reduced, and the border was finally closed in 1973. A new coal mine and new hydroelectric schemes made Zambia largely independent of the Rhodesian-controlled power station at the Kariba Dam (built in 1959). In 1970–75 China built a railway from the Copperbelt to Dar es Salaam, which committed Zambia and Tanzania to extensive trade with China. """

Also older plumbers remember the problem as worst during early 1970s . Younger plumbers meet the steel and copper flashed steel pipes used around that time to get over the copper shortages.

Tony

 

[Nige F]

Tru-wel.......that`s the one- steel covered with ? total ****e..on one of the first jobs I was on as apprentice........lagged it with hair felt wrap under floors ...Big house on A22 in H*****D.......often wondered how long it lasted

 

[Kes]

Yes, stainless steel pipe, as brittle as you like and a real knee-killer to bend, even in a machine, soldered with Duz-All, a vicious liquid flux which turned your fingers green. Then the coated steel pipe, easier to bend and solder.

I remember taking some coated steel pipe out many years later, it was as good as new. Happy days, before H&S.

Rgds.

 

[meldrew's_mate]

...AC will cause electrolytic corrosion, but usually more pitting than thinning.
Is it soft or hard water? Iron mains pipes at all?

Hard water (~270ppm), plastic service pipe, house looks to have been built around 1970.

Thanks for your help and opinions. Subject closed as far as I'm concerned.


Incidentally, I once came across a gas service pipe earthing over 40A via the Suprima PCB (on a TNC-S electrical supply with faulty neutral spiking). PCB and gas valve didn't survive. Interesting fault, not least in seeing the woefull lack of skills exhibited by the various Board electricians who turned up.