Copper pipe corrosion

[SlimD]

Got called to a leaking stopcock recently. Fine jet of water spraying out from compression joint. On closer examination I found the copper had corroded under the olive.
Please see photos.
Anyone seen this before?
Is this pinhole corrosion?

 

[Ric2013]

Yes. Working in a house in Machynlleth. Removal of the stopcock to replace washer had revealed severe corrosion of the brass valve seat and I had to replace the stopcock. In doing this, I found evidence of pinholing of the pipework on the wet side of the olive not unlike what you have shown. Luckily I had already decided to renew the pipework from the alkathene mains to a bit beyond the stopcock. The damage did appear to be limited to the section of pipe inside the stopcock compression fitting though.

 

[king of pipes]

Have had it several times myself to keeps us busy. Cheers kop

 

[SlimD]

Anyone know why it is only in the part that's inside the stopcock? Could the copper be reacting to something in the brass stopcock? It seems unlikely.

 

[Chuck]

Anyone know why it is only in the part that's inside the stopcock? Could the copper be reacting to something in the brass stopcock? It seems unlikely.

The causes of this type of corrosion don't seem to be well understood. High water-velocity and turbulence are often cited as causes and/or aggravating factors. If this is going to occur anywhere then near the stopcock is a likely place. Make sure the replacement stopcock is good quality and properly sized and the cut ends of any pipes are carefully deburred.

I think it's important to avoid/remove burrs when jointing pipes but not everybody seems to bother these days.

Water pH is another possibility, particularly if it is from a private supply such as a well, but this wouldn't explain why the corrosion only occured near the stopcock.

 

[Last Plumber]

Anyone know why it is only in the part that's inside the stopcock? Could the copper be reacting to something in the brass stopcock? It seems unlikely.

Read about the reactivity series. (Brass is an alloy of Copper and Zinc). It looks to me like electrolytic corrosion. Impurities in Copper tube can react more than usual in certain circumstances. Chuck mentioned the PH value of water which can be a contributory factor in the corrosion process but other things such as the presence of different metals, salts etc also play a part.
It is a long time ago that I learned about the corrosion processes involved in Plumbing and I am no expert but if you read up on it, you will probably find answers to your question.



Hope this helps

 

[Moffski72]

Yeah, have seen it a few times. Usually on borehole supplies tbh, but I wonder if it was an old stopcock whether it was dzr brass (ie: no zinc) or not? Maybe electrolysis of the copper where the two metals are touching?

 

[Stigster]

Here is a link to the most comprehensive study I can find on corrosion in copper tubing in plumbing installations. It makes for interesting reading if you like such things.

http://www.fwr.org/copper.pdf

 

[justlead1]

In the situation you describe erosion corrosion is the likely cause. If the water is forced through a small area (the stopcock) down stream of the valve small jets of water can erode the pipe. Similar to cavitation. ( a bit like pinching the end of a hose pipe and forming jets of water. )
Water that's cupro solvent can cause pin holes in copper but this situation doe's not need pressure to happen. When found, normally associated with well water, (Green lines on the bath under the tap can give a measure of cupro solvency.)