Are the cooling tubes of the monoblock soot?

Question

Do it yourself

I decided to clean the monoblock, I cleaned it, but I found not a big soot on the cooling tubes, you can probably find out what it is? how does this affect the operation of the monoblock? can be removed and is it necessary?
Photo
https://drive.google.com/file/d/0B8NQHZV3Bybyd256S...

Answer 1

Normal corrosion. The tubes have very thin walls, so it is better not to stick to them with sandpaper.

Answer 2

Nothing special, just oxide on a copper tube. You can not clean, the main thing is that this would not be on the surface of contact with the process

Answer 3

someone touched the tubes with their hands, and the copper oxidized, affecting only the appearance.