Copper Corrosion on incoming main

[DIYinBerks]

Today our incoming water main sprung a leak, fortunately discovered quite quickly and fortunaterly just to the house side of the service valve. When I disassembled the leaking compression joint, I found the copper inside the fitting to be corroded away, and more corrosion just outside which had led to a pinhole. See image.

Corrosion

• DIYinBerks
• 19 Nov 2012
• 1

Left hand side was inside the compression fitting

I have read some of the posts on this topic, but am still wondering what might be causing this corrosion. Is it possible to tell from the image? Some additional info, which might be relevant based on the posts I read:
(1) The pipe itself is quite old, at least 1980's or earlier. Might go back to build date 1953.
(2) The house used to have a zinc cold water tank - taken out before we moved in, 1984.
(3) This part of the pipework is not bonded - there's a water softener with plastic pipework between the main and the rest of the house.
(4) We do see a bit of green staining on the WC's and bath; but quite slight.
I fixed the leak by replacing an inch or so of pipe - but should I be thinking about replacing more of the pipework - and if so how do I decide how much to replace?
Thanks!

 

[leakydave]

I have never seen anything like this before and would be interested to hear what other people think may have caused it.

 

[mfarrow]

Wikipedia's our hero:

- http://en.wikipedia.org/wiki/Erosion_corrosion_of_copper_water_tubes

Looks about the right age if you have soft water.

 

[DIYinBerks]

Thanks mfarrow,
Hmmm could be though doesn't sound exactly right. the article mentions turulance as the main cause: the service valve is in a straight run and as it's usually open I wouldn't have thought there would be much turbulence there. There are several elbows in the area, which would generate more turbulence; I only took one apart and there seemed no corrosion there; but I guess I should check the rest.
Our water is hard, so I think the comment in the article about overall lifetime - which fits the timing as you say - is probably not applicable. Maybe I should say hopefully not applicable, that will mean replacing a lot of pipework!
Anyone know a way to check the thickness without cutting the pipe?

 

[JohnD]

test it with a magnet. Could it be copper-plated steel?

 

[DIYinBerks]

No, not steel. There was lots of steel in the CH system when we moved in - leaked all over the place as it was soldered together with copper fittings (yes, true) but all the steel is gone now.

 

[Agile]

I would measure earth leakage currents around the house.

Also bond across the plastic parts.

 

[DIYinBerks]

That's good advice. I have made some tests for earth leakage currents and not found any yet.
But I do intend to bond across the water softener anyway; the lack of bonding only occurred to me after reading posts in this forum yesterday. Ironically, if lack of bonding has contributed to our problem, this is one of the few bits of plumbing in this house that I didn't do! I guess I should have thought to ask about bonding.

 

[mfarrow]

I would have thought this type of corrosion would be attributed to DC currents rather than AC. You haven't got one of those damp proof system that works by electrolytic action, have you?

Also, what type of electrical supply do you have? Is the earth cable attached to the DNO's cut-out, or do you have a rod in the ground?

It would be advisable getting the electricity external loop impedance tested, in case something's amiss and you're water pipe is acting as the main source of earthing.

 

[motco]

Thread revival! I have exactly the same problem as the original poster - in the Chilterns so near Berkshire and also with very hard water. I am fascinated by the possibility of galvanic corrosion because our incoming main sprung a leak on Christmas night in 2013. A local Thames Water approved contractor 'moled' a new incoming main in HDPE from the meter, through the basement wall into the house. I assume that and natural bonding by way of the old main being buried in soil has been lost due to the non-conductivity of polyethylene pipe. This new failure is only about three metres from the stopcock on the new HDPE pipe and is in a dry basement clipped to the ceiling. It has failed on a bend (not an elbow). In order to bond the cold water system is it sufficient to connect it to an earth spike? I have an earth spike very near my outdoor tap and that should have continuity through the fully copper system.

 

[Harry Bloomfield]

I have read some of the posts on this topic, but am still wondering what might be causing this corrosion.

Electrolytic action, at a guess, but I have little knowledge of it.

 

[JohnD]

In order to bond the cold water system is it sufficient to connect it to an earth spike?

No, that's not the way bonding works.

Inside your house, electrical equipment and cables must be earthed back to the main earthing point, usually inside or next to your consumer unit, or close to the incoming service head and meter.

The safety depends on them all being bonded together.

you can't rely on a copper pipe having continuity because at any time it might be cut and repaired, or a valve or section of plastic pipe might be added.

Your earth spike and outdoor tap, being outside the house, might not be at the same potential. The difference may be slight, sometimes it may be large, and it may change.

Your internal pipework must be bonded by connecting all metallic services entering the house, inside, close to their point of entry.

If you photograph the incoming supply, service head, company fuse, meter, and consumer unit, and the cables around and between them, we can most likely work out what kind of earthing system you have. It is usually fairly easy and cheap and you are not obliged to employ an electrician

useful points:
Look for a label or "badge" saying "PME" or "Protective Multiple Earth"
Are you in a built-up area or away from other houses
does your supply come in underground or overhead
is the supply head cast iron, brown plastic, black plastic, or grey plastic
what is the covering on the incoming supply cable
how old is your house

 

[motco]

Good grief John, what a full answer! Thank you for taking the time. The house is c.1968 as far as I know. It is the last in a row of detached houses and has a field adjacent in green belt and AONB. The supply is underground and the wiring is quite complex - although modern c/w RCDs and current breakers. It has been somewhat altered due to a swimming pool having been part of the property some years ago. Much plumbing and some wiring is now redundant. I have followed an earth conductor from a bonding point adjacent to the water main inlet to the boiler room. Every socket I have tested shows good continuity to local plumbing and each tests as having correct neutral, earth, and live with a simple plug in tester. To answer the remaining questions I have to delve into the basement and in the consumer unit cupboard. I wanted to thank you for your kind help as soon as I saw your post however, and I'll add to this when I have answers. Meanwhile I have ordered a pressure reducer as it is the cheapest way of both reading the mains pressure and, if need be, dropping it to an optimum level. More anon...

The supply head is black plastic and the covering of the incoming cable seems to be bituminised canvas. As for the earthing label, it's visible in this photograph:

 

[Harry Bloomfield]

Every socket I have tested shows good continuity to local plumbing and each tests as having correct neutral, earth, and live with a simple plug in tester.

Using what instrument? The only sure way to test the continuity of earth, is with an earth loop tester, with a wander lead.

 

[motco]

Using what instrument? The only sure way to test the continuity of earth, is with an earth loop tester, with a wander lead.

'Instrument' is overstating the sophistication of the device. It's a plug-in tester with a set of LEDs that light in a pattern confirming the presence of earth, live, neutral and the correct connection of the L & N. As for continuity, I haven't got a Megger or any specific electricians' tester, but I have a decent multimeter and an oscilloscope.