tnhrbtnhb - 23-5-2007 at 21:11
I need some help cleaning a copper cooling coil. I used silicone caulk to glue parts of the apparatus together and I didn't realize the acetic acid
it releases would be enough to corrode the copper... but there is plenty of green (oxide?) around the points that were glued :-(. It's all over
actually, the acetic acid vapor must have accumulated around the coil for some time.
This is bad because there is going to be food under a pan under the coil (water condenses on the coil and drips into a pan, but some will miss) and
copper is actually pretty poisonous - 1 milligram per day is the absolute "upper limit" that one should consume per day according to the FDA. So I
don't want any dissolving in the water and getting in the food.
So, how should I go about cleaning any water soluble copper off the tubing?
I thought of soaking it in hot water, but it's already attached to the apparatus and I don't know if I even could.
not_important - 23-5-2007 at 22:01
Water is likely the best way. Actually a rinse in dilute HCl to remove the basic copper salts, followed by a rinse in bicarbonate solution, then
several water rinses might be better.
You could try scrubbing with water and a small brush, followed by a good spray rinse. Do not let ammonia get around the equipment, you'll get more
copper corrosion.
If this is food processing gear, you should have used food grade caulk, or at least aquarium grade which does not outgas or leach out much. There's
other crap in caulk that you may not want leaching out and dripping into the product.
[Edited on 24-5-2007 by not_important]
Intergalactic_Captain - 24-5-2007 at 05:07
Strip off all the caulk and soak the copper in a tub of salt and vinegar...Hot vinegar works the best, if you can work with it. It may seem
counter-intuitive to use an acid to clean it, but trust me on this one - It's standard practice when cleaning copper pipe for building stills. The
last one I built began with a scrap 2"x5' pipe covered inside and out in green. I cooked up a paste of vinegar/flour/salt, packed the pipe full of
it, and left it for an hour - Rinsed it out, and it was shining like it was brand new.
Tsjerk - 24-5-2007 at 05:33
I've some experience with cleaning copper coins using vinegar and salt. Just use household vinegar and drop in a couple of tablespoons of salt for
every liter. I think for a copper pipe it would be enough to just throw the solution through a couple of times.
If you have a completly black copper coin and you hold it in the solution a couple of seconds it brand new again.
unionised - 24-5-2007 at 10:04
Cleaning the copper is a good start. Wet copper corrodes in air so you need to make sure it doesn't corrode again. IIRC the traditional way to do this
for copper saucepans was to coat them (inside) with tin.
zoomer - 24-5-2007 at 13:53
Catchup (ketsup) works really well, too. It's acidic + salty, and the thick stuff will stick in place long enough to clean the copper if you can't
reach it for mechanical cleaning. Just make sure to rinse well. 
Z
The_Davster - 24-5-2007 at 14:11
I have had to clean copper in a lab I used to work in, and we used very dilute nitric acid and steel wool. And this was on expensive equipment too,
the washings came off slightly green/blue, but noone seemed to care.
tnhrbtnhb - 24-5-2007 at 21:01
so far the ketchup looks best because the rest of the thing is made of aluminum (sorry I should have mentioned that.... it's basically a pressure
cooker with the cooling coil and valves built into the top.) or a flour paste so I don't want to put a highly salty solution in it (and I don't have
any nitric acid 
. It'll be a pain to apply it though so if anybody else has got
any more bright ideas.... .
I used food grade caulk, ("rtv 108") but apparently almost all non-toxic silicones give off acetic acid as a byproduct of the polymerization process
itself,.
I was worried for a moment that the copper would corrode even under normal circumstances but water pipes are typically bare copper in there, so it can
hardly be too bad right?
Does anybody have an easy way to test for the presence of copper in food? Then I could know what's happening (copper can cause nerve damage so I'd
better not "just try it an see"). Maybe I could mail some money and a sample to a friendly amateur chemist 
</rediculousnaiveoptimism> 'cause I probably don't have the equipment or chemicals.
I'm NEVER working with "food grade" bs again!