copper pipe soldering question

[Pico Rico]

when you need to unsolder a pipe connection and then resolder to it, are there any tricks to the unsoldering, or to clean the joint of solder so you can put a new coupling on it to resolder?

[H0m eGu y]

There really is no advantage, and actually quite a bit of extra work and possibility to cause a fire, if you try to unsolder a copper pipe connection.

You are much better off cutting out the joint or the section you're working with and then solder new copper pipe in its place.

[Pico Rico]

well, I tend to agree, but it really depends on the existing configuration and location. In this instance, zero possibility of a fire, but cutting back further is more of a hassle.

[H0m eGu y]

Then it's just a matter of applying enough heat to melt the solder.

You will need to remove every last drop of water in the pipe, or you'll never be able to apply enough heat to melt the solder.

If you can or if you need to, shove some rags or paper towels in the pipe to soak up the water and then remove them.

Maybe drill a small hole right at the joint so water can drain out.

Is your problem getting the pipes disconnected?

Or are you asking how to re-connect or clean the surfaces once you've got them apart? The answer to that is sand paper.

[trader_4]

I'd also recommend the cut approach, but if it's too hard to cut then you can do what you propose. Just use a dry cloth to quickly wipe the end of the pipe clean of as much of the old solder as you can after heating it up. Make sure to flux the new fitting and old pipe. And then you may need to heat it to get the new fitting on.

[Pico Rico]

The latter. I am sure I can pull them apart, I just want to be able to slice a new fitting over a previously unsoldered part. Thanks for your comments.

[Pico Rico]

thanks for your comments. I will take a closer look and decide on the approach.

[Bill]

Yes, cover your bare skin and wear eye protection...cuz getting hit by hot solder can make even a bible-thumpin' mormon swear!

[nestork]

Pico:

You should know that copper rusts. It's just that the oxide that copper forms is very different than iron rust. Copper oxide remains well bonded to the parent metal (copper) and is fairly impermeable to both H20 and O2 molecules. So, the thicker the layer of brown copper oxide on copper, the better it protects the underlying parent metal from further oxidation. This is why copper water supply pipes in buildings will often outlast the buildings themselves.

Molten solder will bond well to bare copper, but not to copper oxide. So, the whole procedure of sanding the pipes and brushing out the fittings is to remove the copper oxide that has formed on the copper or brass since it was manufactured.

The primary purpose of soldering flux is to keep oxygen molecules away from the copper metal during the soldering process. The oxide film forms relatively slowly at room temperatures, but it's nearly instantaneous at soldering temperatures. The flux forms a physical barrier between the bare copper metal and the oxygen in the air while the joint is being heated, but at the soldering temperature, the flux is fluid enough to be displaced from the joint by the capillary pressure drawing the molten solder into the joint.

Now, a layer of solder over the copper will protect the copper from oxidation as well as flux will. So, if you take apart a soldered joint, you can wipe the solder off the pipe with a dry rag. But, there's no need to remove the old solder from the pipe or from the old fitting. You just treat the surface of the old solder as the new surface of the pipe.

In my opinion, it's best to flux the old solder just as you would a bare pipe or fitting. That's because flux contains a chemical called "zinc chloride". At soldering temperatures, zinc chloride becomes acidic and dissolves copper oxide much more readily than it dissolves copper metal. So, having plenty of flux in the joint is good insurance that there won't be any oxide in the joint to prevent the solder from bonding properly.

And, of course, just from the preceding, you should know to flux your pipes and fittings as soon after sanding or brushing them as possible. That way, there's the thinnest possible oxide film on the copper or brass to be dissolved by the zinc chloride, and therefore the best chance of leak-free solder joints. When people tell you to clean the old flux off the piping after soldering it's good advice because that old flux contains zinc chloride. It's just that at room temperatures, or even the temperature of a hot water supply pipe, the zinc chloride is very much less acidic, and would take forever and a day to do any harm to the piping.

[Guv Bob]

Standard plumbing trick is to wad up a slice or two of white bread into dough and shove it into the pipe up stream from the joint. This is helpful when you can't remove the blockage after the soldering is done. It will liquify and you can flush it out. ** Don't use "healthy" bread

- use plain soft white bread, no whole grains or seeds, and tear off the crust.

[bob haller]

easier to use sharkbites. No fuss no bother:) and PEX is dirt cheap, and tolerates freezing...

[clare]

drain all the water first, heat and dissassemble, wipe the heated end to remove all excess solder, leaving the pipe nicely tinned. Drilling the coupling you are removing helps drain the pipe.

[clare]

And the pipe gets too short because you cut it off, so you need 2 joints instead of one. No reason not to desolder if you can drain the pipe, and you have a good torch. By good, I mean a turbo-torch, not one of those crappy Bernzomatics from the sixties. I like MAPP on a Turbo for desoldering (and soldering) if I can't use the acetylene torch.

[Tony Hwang]

Hi, YTime is money. Sorry I won't reuse unsoldered joint.

[clare]

I prefer a damp rag. Heat to melt the solder, and a quick swipe gives you a perfectly tinned clean surface for soldering. A bit of "sal amoniac" on the rag helps if you want to get fancy.

[nestork]

I didn't know what "sal ammoniac" was either, so I googled it. It turns out that it's a relatively uncommon salt; ammonium chloride, and one of it's uses is to clean the soldering iron used to solder the lead strips together when making stained glass windows.

Clare How do you use this sal ammoniac and what difference does it make?

[clare]

It can take less time to dissassemble and salvage than to cut and patch.

[clare]

It is basically a flux that makes the tinned copper go together just like butter. Just a solution of sal amoniac and water to dampen the cloth.

[Stormin Mormon]

Nice and hot. When the fitting comes loose, immediately use a dry rag (cotton) to wipe the solder off the pipe / tube while it's still plenty hot. use a new fitting.

[Stormin Mormon]

The dry cotton rag will help remove all the solder from the old pipe. Have to be quick about it, while the solder is still melted.