Green deposit on copper pipe at fittings

[marbles]

Some copper water pipe solder fittings have a residue of green gunge around them, due to the finished solder joints not being effectively cleaned after soldering.after new CH installation around 5 years ago.

First Q: What is the green gunge (chemically)? Does the deposit have common or garden name? It must be a Cu compound, but how is it formed from solder flux, copper, solder & propane gas used in the torch?

Second Q: What is the most effective method of cleaning it off, especialy when it has been on the Cu pipes several years? I'd like to get the area around the fittings reasonably chemically clean. I fancy just cleaning with wire wool might leave a residue for the green to re-crystallize on.

Third Q: I thought I had cleaned the joints at the time, so how should soldered work be cleaned to avoid green film formation?

TIA

[Aidan]

Resues of acid/active flux, I believe. The active flux contains hydrochloric acid which removes the surface oxide layer & 'cleans'/pickles the pipe and fitting when heated, prior to the solder melting & running.

I don't know what the green compound is, I'm sure a chemist will be along shortly. If left inside a heating system, the acidic flux residues can cause serious problems with corrosion.

[Dave Plowman (News)]

It comes from the use of acid flux, and not cleaning any excess off afterwards. Shouldn't do any harm, though.

Water and wire wool or any other suitable abrasive. Car paint wet or dry paper if you have any lying around. Wash off with clean water afterwards.

You normally wipe the joint with a wet rag once the solder has set.

[Aidan]

Maybe a copper dihydrate? Starts off as a copper chloride CuCl2, a yellow-brown solid which slowly absorbs moisture to form a blue-green dihydrate (according to Wikipedia).

[Dave Plowman (News)]

Doesn't it get diluted by the water to the extent it can't do anything? It also seems to stop corroding the outside after a while - the reaction becomes used up.

[Aidan]

Unless flushed out &/or neutralised, I believe it makes the water acidic (pH

[The Natural Philosopher]

I'd say ots PROBABLY copper carbonate...sort of natural end point of any copper type oxide and CO2..

Ni. The reaon its around the joints is they they have a flux residue usually. And have been heated. If you WASH the joint and then wool it up, it stays good, usually

Darned good washing and some wire wool