Underfloor copper pipes: corrosion and pin holes

[Coddey]

Bungalow built in 2001. All copper pipework (water and heating) runs in channels of expanded foam polystyrene between a concrete floor and OSB boards. Pipe are lagged in stitched felt and what looks like bubble wrap with sand (?) over the top.

During the bathroom refit, I lifted up some of the OSB flooring to get access to the hot and cold bath feed and noticed the pipes were quite corroded with one or possibly two pin hole leaks.

How common is this for pipes of this age, or is it environmental? There is no way I can afford to life the entire floor of the property to inspect, let alone replace all the pipework.

Any advice on how to go forward?

 

[ShaunCorbs]

I would suspect the sand if it’s damp

 

[Coddey]

I would suspect the sand if it’s damp

As in the sand is the cause of the corrosion? The sand was damp but unsure why it was used?

 

[Basher]

Some background info published bybNPL:

https://www.npl.co.uk/getattachment/research/electrochemistry/corrosion-guides/Avoidance-of-corrosion-in-plumbing-systems-GPG8.pdf.aspx?lang=en-GB

 

[Coddey]

I had a read of that the other day. Quite comprehensive.

None of what they mention really matches what I have; however one of the types the reports notes is not found in the UK does look similar

It 'looks' to be mainly on the outside, but I won't be sure until I replace that section I can access. The sand was not in direct contact as the pipes are wrapped.

 

[Basher]

I had a read of that the other day. Quite comprehensive.

None of what they mention really matches what I have; however one of the types the reports notes is not found in the UK does look similar

It 'looks' to be mainly on the outside, but I won't be sure until I replace that section I can access. The sand was not in direct contact as the pipes are wrapped.

Were the pipes in your photo cleaned up (look quite bright), or is that the condition when you unwrapped them!?
Also are the pipes the same way up in the photo as they were when installed (ie would the pinhole have been on the side of the pipe originally?)
Is there anything slightly unusual about your water supply - very hard or soft or strong smell of chlorine etc?
Do you know the pH?

 

[Coddey]

Water is hard, although not extreme, no unusual smell. Not sure of the PH, but from a litmus paper test its around neutral (LP is not an exact science lol).

The image in my first post shows them in situ laying 5mm above the concrete floor looking from directly above. The insulation was removed from either side and the pipes were unwrapped. So the pin holes are on the top of the pipes.

Indeed, I did clean them up to see how bad the corrosion was. It was a lot worse than in the picture.
One clue is that a few mm to the right there is a T piece where the hot and cold feed go to the basin and to the left they exit under the bath.

Whilst there is corrosion across the full length of the pipe, it is significantly worse where its located under the floor wrapped up (see pic attached for this post).



I was thinking it could be condensation.

 

[Chuck]

Many possible causes. Maybe there was a single original leak, e.g. a badly made joint. The water from this got everything, including the sand wet. Depending on the type/source of the sand it may contain impurities, e.g. salt, that can be corrosive to copper in the presence of water. Or maybe bateria had a chance to grow and attack the copper. I can't be sure from the photos but it looks as though the pipes are touching at cross-over points. This can provoke leaks too.

You probably could get to the root cause with some lab tests and examination of pipe samples but they wont be cheap and whatever they say the solution is going to be the same. Remove the corroded pipework and repipe using the correct methods and materials, including a pressure test.

Nice report on causes of corrosion in copper pipework here:

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

with great pictures of each type. It's referred to in the NPL document and gives more details.

 

[Coddey]

I really appreciate the comments and advice, it’s been very informative. The white elephant in the room is - at the very least - the whole bathroom floor requires lifting to see the extent of the corrosion and then replace. Then at some point in the future, time, health, and funds permitting, inspect random areas throughout the property to see if the issue is present on the CE circuit.

It wouldn’t be so bad if the pipes were in the loft space, at least I would see damp patches indicating a leak. The layout I and other properties have in my street means these pin hole leaks could go undetected for quite a while under the floating floor.

Hopefully I will cut out the first section today. I’ll see if I can split the pipe length ways to see if it indicates or supports corrosion occurring from the environment outside (sand, damp, poor fitting etc.).