On 11/03/2019 17:37, misterroy wrote:
What could have caused the heating pipe to corrode so badly that it failed? It was next to an external wall and lagged. The are a couple of lengths of the pipe lying outside the building unused for the same 6 years, other than the threaded ends, they look new.
image https://drive.google.com/open?id=1o8...cqBdRGYatmQb6R

Do you, by any chance, have an electro-osmotic damp proof course fitted?

I have had two instances of *earthed* components in contact with damp
masonry corroding in a similarly dramatic fashion. One was a galvanised
back-box (which I replaced by setting-in a plastic one), the other was
the screws and after that four six inch lengths of 316 stainless steel
6mm studding which I set into the rubble stone wall to support radiator
brackets.

I havn't had any trouble with other galvanised back boxes, but this one
was in a bit of wall which the DPC was spectacularly failing to protect.

However given the distribution of corrosion in your case I would be more
inclined to associate it with condensation within the insulation,
especially in the presence of salts.