We have been living in a new house for more than a year, and the old one, in which we lived for 4 years while under construction, I now use as a workshop and a summer kitchen.
When I was equipping the site, half of the old house had to be demolished, and, accordingly, I had to intervene in the heating system, cutting out part of the radiators. The heating of this house was left from the old owners, the gravity system was cut out, and, apparently, was handed over for scrap, and instead of it, a one-pipe based on polypropylene pipes, several radiators and an old double-circuit functioned boiler.
At the time of buying the house, I found out that the renovation at that time was almost 2 years old and we lived here for another 4, totaling 6 years. Having disassembled the heating system, I was very surprised by the state of the pipes, they looked painfully lousy for their age...
And, this is after only 6 years! And a little later, I found out the answer why the pipes were in such a state ...
The photo may not represent colors, but it is a black, rough plaque that appears on pipes that are not protected from oxygen diffusion.
We have a set of rules SP 60.13330.2012 "HEATING, VENTILATION AND AIR CONDITIONING" (Updated edition of SNiP 41-01-2003), in clause 6.3.1 (SNiP p. 1) which says that in heating systems where the coolant is in contact with metal, pipes with an oxygen permeability of more than 0.1 g / (m3 per day) cannot be used:
Oxygen permeability or oxygen diffusion is the penetration of oxygen through the pipe walls and it is impossible to eliminate this situation without introducing additional barriers into the pipe structure. And the absolute absence of oxygen diffusion can boast of pipes only with an aluminum interlayer: PERT-Al-PERT and PPR-Al-PPR.
Yes, in glass fiber reinforced PPR pipes, linear expansion is really minimized, but the problem is that such PPR pipes have an oxygen permeability of 0.9 g / (cubic meters per day), which will be confirmed by any manufacturer, even if it is not in his interests. As you can see, this figure exceeds the requirements by 9 times, which in fact makes such pipes unsuitable for heating systems.
Oxygen, gradually penetrating through the pipe walls into the heating system, saturates the coolant with bubbles, and then accumulates in hard-to-reach places, initiating corrosion of steel elements, and, moreover, leads to blockages in system!
In addition to this, the air negatively affects not only the radiators, but oxygen bubbles also give rise to cavitation processes in the pumps, corroding the impeller:
Therefore, in heating systems it is necessary to use pipes with an interlayer of aluminum foil, because it is even better they did not come up with anything and aluminum is the only one hundred percent barrier between the coolant and oxygen. Now manufacturers place aluminum in almost all pipes, including cross-linked polyethylene, metal-plastic, and polypropylene. Even though such pipes are much more expensive, they guarantee us protection!
And that's all, I hope that the article was useful to you!