copper pipe corrosion

Maougnassous · May 2, 2013

I have a problem of copper corrosion in both the hot and cold water which leave blue stains on sinks etc.As it is in both hot and cold water I have concentrated on the cold water supply to find out where it is coming from. Where the water enters the building there is a galvanised metal pipe soldered directly to the copper piping without a dielectric joint . Is it possible that could cause corrosion of the copper ? If so , how would I fit a dielectric joint at this point . The galvanised pipe only extends about 30 cm. out of the ground so I can't take it back to the previous joint.

Dotty · May 2, 2013

I'd get all the galvo stripped out if I was you, it'll only get worse.

You got any decent plumbers over there?

Maougnassous · May 2, 2013

Hi , thanks for the quick reply . Do you think that could be the cause of the problem ? I have researched the internet about problems relating to copper/galvo joints bit I have only seen reference to corrosion of the galvo . Your solution sounds simple but it would be quite a task to find out the route of the pipe and would be quite a big and costly job so I'd like to be sure that that is the problem .

Dotty · May 2, 2013

Absolutely. Fresh oxygenated water and ferrous pipwork, galvanised or not, are never a good combination.

'Fraid it's gonna cost you a few euros my old mate!

Maougnassous · May 2, 2013

If that is the problem would fitting a dielectric joint be a cheaper solution ? If so , how ?

Maougnassous · May 4, 2013

I'm going to do as you say because as you say galvanised steel is not good news but I still don't understand the process .After an extensive search of the internet I've only found mention of corrosion of the galva caused by electrolyisis and only when the water is flowing from copper to galva . In my case the water is flowing from galva to copper and it's the copper that is corroding . I can't find reference anywhere on the net to this kind of problem . Can anybody explain please ?

lame plumber · May 4, 2013

galavanic action and electrollosis (can't spell), or rusting/corrosion to the simple folks here. In simple terms dont mix your metals.

Cello · May 4, 2013

The direction of water flow is not important where electrolytic corrosion is concerned. Copper connected to zinc will result in corrosion of the zinc (or the underlying steel if that is exposed) and not the copper. If this is occurring, the corrosion will be localised to the area of immediately adjacent to the joint as the electric current which causes the corrosion takes the shortest path. It is therefore likely that the copper corrosion you describe is from a different cause? I wonder about the quality of the water supply? If it is acidic (perhaps from a borehole??) that will cause corrosion. Another cause is the use of low quality copper pipework. I seem to remember a countrywide outbreak of copper corrosion during the 1970's when copper shortages lead to the use of inferior material. The advice to avoid mixed metals, wherever possible, is a good one.

...Robert

Maougnassous · May 4, 2013

O.K. I'll be more specific . There's a stopcock underground in front of the gate . It is connected to polyethylene
piping . It seems that it then branches underground , one branch going to the boiler and the othe branch going to the cold water circuit . When I test the water at the boiler there is no trace of copper . The other branch is somehow connected to a galvanised pipe because that is what is sticking out of the ground and it is soldered to the copper cold water circuit . Less than one metre from this joint is a tap and I tested the water there and found it has 1.8 mg/l of copper . So what is going on ? I'm going to somehow dig up and get rid of this galvanised pipe but I just wondered if anyone could explain what is happening .

Cello · May 5, 2013

1.8 mg/l is very high. Also, if the corrosion is producing this level of copper in the water after only 1 metre of travel (I assume that the water has not been static for a long period) the corrosion rate is unusually high. Did you have a complete water analysis performed? There are certain water compositions that exacerbate cuprosolvency. Best, as you say, to remove the mixed metals problem then, at least you have eliminated that problem. Some years ago, I encountered excessive cuprosolvency at a property in Redditch. The problem was solved using a controlled solubility phosphate product called "Micromet". One further thought... as the copper level is so high near the supply pipe, is there any possibility that the high copper level is originating much further upstream? If you have a neighbour on the same supply, might be worth checking if he has a similar problem??

Maougnassous · May 5, 2013

Thank you all for the advice . As I said , at the stopcock the pipe is polyethylene . It then branches underground and one branch goes to the boiler at the other end of the building , and the other goes to the main water circuit . At the boiler there is no copper , so what I've decided to do is to stop the branch which goes to the water circuit and then connect this circuit to the arrival of the water at the boiler . I shall also make sure that the whole thing is well earthed to be on the safe side . It will remain a bit of a mystery but at least that should get rid of the problem .

WHPES · May 5, 2013

Are you on a private water supply? I have encountered copper corrosion in areas where ammonium or aluminium salts are present in the water supply, or where the water is mildly acidic (included dissolved CO2).