Copper pipe corrosion

[George A2Y]

Only for curiosity as the repair has already been done.
When plumbing my, Circa 1900 stone built cottage, 27 years ago I had to run a 1/2" cold feed from the kitchen attic through a gable wall to the main building. As the hole I drilled was not large enough to accommodate standard pipe insulation I decided to wrap it with some closed cell foam (50mm x 6mm) & secure that each end with gaffer tape, in an attempt to isolate & insulate.
I recently had a pin hole leak in the middle of this pipe but was surprised to see that the corrosion was from the outside - in and quite distinctly follows the spiral where the foam butted together.
Any idea what's been going on?
There would have been condensation with it being a cold feed but I think any loose mortar in the joint would be miniscule.

 

[Mikes]

It's hard to see from the photo's but it could have been a type of phenolic foam insulation that you used. It's a recognised problem with phenolic foam applied to pipework which can 'sweat' as the moisture starts a reaction with the material. The insulation is now made with an internal coating to prevent this (didn't used to be coated). Even so, there are some companies that won't allow phenolic foam on any cold services.

 

[Kram]

Condensation and wet foam may have degraded and became acidic?

When I redid the shower 10+ yeears ago, sanded off the nasty white paint, polished up the pipe and gave it a brush of clear coat, still looks perfectly shiny, hasnt yellowed, degraded or any sign of corrosion.

 

[123hotchef]

Petro tape is what i wrap pipes like that in. Protects the copper well

 

[Ross365]

You quite often see old foam in radios and electronic gear which has gone "tacky" and caused corrosion. Seems to be problem that has been solved and tends to be seen in stuff from the 60's & 70's.

 

[tom2207]

look at the foam surround on certain hi fi cones , it seems ok but if you so much as look at it the wong way , it just turns to dust ,,, literally .

 

[Farside]

You quite often see old foam in radios and electronic gear which has gone "tacky" and caused corrosion. Seems to be problem that has been solved and tends to be seen in stuff from the 60's & 70's.

There's a plague of it affecting 70s cameras now.

 

[Morris]

look at the foam surround on certain hi fi cones , it seems ok but if you so much as look at it the wong way , it just turns to dust ,,, literally .

Had a pair of Royds do that.

 

[George A2Y]

Thanks, Mikes & Kram, that sounds the most likely explanation, don't think I used that technique anywhere else, so all should be good!

 

[gaz1]

old method grease the pipe before you wrap it

closed sell or the wrap never works as youve just seen but greasing the pipe does as it keeps moisture away from the tube