Corroded Pipe?

[Monkfish]

Hi, I had a new boiler installed about 5 months ago. The plumbers ran a new 22mm copper pipe from the gas supply alongside the existing 22mm copper pipe for the flow and return (30 years old).

Since the installation I have been losing around 1/10 bar pressure per week (sealed system) and have been topping up the pressure thinking that the system was just taking its time to stabilize. I was slightly worried it might be a small leak, but as I could find no signs I ignored the pressure drop.

This week I noticed the telltale sign of water dripping from a light socket. Investigating, I found a floor beam that was soaked just where the three pipes mentioned above passed through it (inconveniently right under a partitioning wall).

Further along the pipe I noticed a small bead of flux had been left bridging the return pipe and the new gas pipe. Cleaning off this flux I noticed a small pin hole in the return pipe (which later investigation revealed was about to breach the pipe). Thankfully, there was no such hole in the gas pipe (which seems strange as both are copper). Cutting out the pipe from under the wall revealed similar flux residue and many more holes (as shown in the image). This was the source of the leak.

Now I could have imagined that the return pipe which is over 30 years old had slowly corroded under the wall and the new pressurised system finally forced the water through, but the hole further up was clearly caused by a bead of flux left during the upgrade 5 months ago.

Is it normal for a small bead of flux to eat its way through a copper pipe in this period of time or could there be some additional electrolysis action between the gas pipe and the water pipe (both are earth at the boiler)?

 

[WHPES]

I doubt it is all down to flux. If it is about 30 years old there was a copper shortage and inferior imported copper tube was used. This had inclusions of carbon and slag which causes cold water pitting (and hot water pitting) of the copper to form the telltale pinholes.

See

Wapedia - Wiki: Cold water pitting of copper tube

The chances are the rest of your water pipe is in a similar condition.

 

[wards]

have to agree with monkfish,once you have had the old pipework replaced remember to treat the water with fresh inhibitor HTH
si

Re: Corroded Pipe?
have to agree with monkfish,once you have had the old pipework replaced remember to treat the water with fresh inhibitor HTH
si
grrr i meant whpes

 

[WHPES]

A few areas I cover in the North York Moors have problems with pitting of copper pipe. This usually manifests in the pipe nearest to the supply, particularly on horizontal runs. Copper cylinders become eaten through and immersion elements soon rot. The only satisfactory remedy is to repipe in plastic and fit stainless cylinders and incolloy heating elements.

I have had water samples sent for anyalysis and we have found presence of ammonium salts and carbonic acid (as in fizzy drinks). Pitting is likely initiated through stagnation as described in my last link.

 

[oldplumber]

you mention sealed system, if vented previously the extra pressure starts to accelerate losses not previously noticed in the old pipework. Everything rots eventually as your system is now showing, and I have noticed certain area around me have acidic water which just eats immersion heaters (6 - 12 months and they are dust)

 

[Monkfish]

The rest of the pipe looks okay on the outside and so does the inside of all the pipe I've removed. God I hope this isn't going to happen elsewhere as most of the piping is sealed under concrete flooring and behind tiled walls.

So you think the pressure is accelerating internal corrosion that has been developing over the years in the old pipe. I guess that bead of flux could just have been corrosion blown from the tiny hole.

Maybe it will just be that short run of piping. They used to be the heat-exchanger pipes linking the immersion tank to the boiler, but we never used them, so they had stagnant water sitting in them for at least 20 years. Now they are being used as the flow & return of the new boiler.

I use Sentinel X100 + X200. The X200 won't make things worse will it?

 

[Blackcatgas]

The rest of the pipe looks okay on the outside and so does the inside of all the pipe I've removed. God I hope this isn't going to happen elsewhere as most of the piping is sealed under concrete flooring and behind tiled walls.

So you think the pressure is accelerating internal corrosion that has been developing over the years in the old pipe. I guess that bead of flux could just have been corrosion blown from the tiny hole.

Maybe it will just be that short run of piping. They used to be the heat-exchanger pipes linking the immersion tank to the boiler, but we never used them, so they had stagnant water sitting in them for at least 20 years. Now they are being used as the flow & return of the new boiler.

I use Sentinel X100 + X200. The X200 won't make things worse will it?

Also dont forget that self cleaning flux (Laco) etc is more active when its heated which is why the heating pipe could be more afected than the gas pipe at room temperature.
If Iam doing all new copper piping with no new to old connections I like to use a less agressive flux like fluxite, I still use laco though and try to wipe off any excess.

 

[WHPES]

You may find it's just a certain section which dates from a certain job.

Does any of your other pipework have any of the telltale green patches on the outside?