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Old 12-11-2008, 12:28 PM   #1
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do soldered joints ever break after ?


this may sound like a stupid question but ...

last night i made a soldered joint that appeared questionable. it was tucked away in a hard-to-reach corner and, in order to fit the elbow, i had to force both pipes in a little bit. that is never a good thing because the tension translates onto the fitting pressuring one side more than the other so the flux/solder gets unequally distributed (at least theoretically).

while applying solder, the reaction on the pipe and fitting was all too reminiscent of the leaky jobs from the past - the solder was not flowing quite right, in some places bigger bubbles, others barely had any. not the seamless touch where it flows momentarily 360 degrees around in a matter of a millisecond after touching it up.

when i was done, i was 75% sure that it would leak when i turned the water on. however, it did not.

my question is: what are the chances that the successful job is only temporary and that it will burst 2, 3, 10 days down the road ? has anyone seen weak joint break after the fact.

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Old 12-11-2008, 02:04 PM   #2
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do soldered joints ever break after ?


Ama; without seeing it very difficult to anser, however from your description it sure sounds like a "cold" joint to me. Only suggestion I can give is, be sure pipe is empty, clean the heck outta the outside with emerypaper,Heat it back up, flux the living heck outta the joint, re solder it may flow. Remember DO NOT heat the joint, heat behind it and let the heat build at the joint.

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Old 12-11-2008, 10:49 PM   #3
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do soldered joints ever break after ?


Amakarevic:

I have only seen two solder joints in my whole life that held for a long time and started leaking later. Generally, if the joint holds for the first minute under pressure, it'll hold for the next 500 years.

Bending copper pipes a little to get an elbow to fit, in my view, wouldn't compromise the quality of the solder joint you get. As long as the pipes and fitting were sanded, brushed and fluxed properly, and the soldering was done properly, I'd have no concerns about it.

But, I have a question:

People always attribute poor solder joints to insufficient heat or water in the piping, but they ignore the most common cause of bad solder joints, and that is air pressure building up inside the pipe due to heating. It's surprisingly common for people not to realize that unless they provide a way for the air pressure inside the pipe to escape, then the increased air pressure inside the piping is going to be wanting to push the liquified flux out of the joint at the same time that capillary pressure is trying to draw the molten solder into that joint, and that capillary pressure is not very strong.

Do you recall whether or not there was a way for the increased pressure in the hot piping to escape at the time you were soldering?

You describe "bubbles" in your post. Was this just the soldering flux boiling off, or did it appear to you that the joint was "blowing bubbles in the flux". I can't help thinking that what you may have been dealing with was just air pressure inside the piping. If so, then the joint is probably good.

The reason why is that the PRIMARY purpose of using soldering flux is to form a physical barrier between the oxygen in the air and the bare metal. It's that brown oxide film that makes old pennies and copper piping brown that also prevents solder from sticking. That oxide layer forms slowly at room temperatures, but almost instantaneously at soldering temperatures. The flux coats the bare metal even when the flux is liquified until the force of capillary pressure pulling the molten solder in forces the flux out of the joint.

I'm just guessing, but I don't believe an air bubble escaping through the flux would remove the flux completely from the bare metal. It seems to me that there would still be a thin film of flux over the metal even with the passage of an air bubble out of the joint. So, as long as O2 from the air never came into contact with the bare metal, that joint SHOULD be OK.

Maybe buy a small inspection mirror and a flash light. After soldering, wait for the piping to cool down some, and then clean all the joints with a paper towel damp with mineral spirits to remove any residual flux, especially the black burned flux right where pipe enters fitting. This will allow you to inspect the joints carefully, and you should be able to see a thin silver ring around every soldered joint, just as you described their formation in your post. Those rings are the proof of the pudding.

To answer your question, I would turn off the water at your water meter and give that elbow a good shake to show it who's boss. If it don't leak then, it prolly won't.

But, my building has copper piping and was built in 1960. I had one solder joint inside a kitchen cupboard that let go when the water was shut off and the pipe was empty. I was sanding the end of the pipe about 3 or 4 feet away, and the pipe started to move more than normal. A 35 year old solder joint had loosened up and let go. In another case, I had to cut a hole in a closet wall to get at a solder joint that had started to leak 40 years after the building was built. In both cases you could tell from looking at the pipe that it hadn't been properly soldered because the solder band at the end of the pipe wasn't all the way around the pipe.

Last edited by Nestor_Kelebay; 12-11-2008 at 11:15 PM.
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Old 12-12-2008, 11:20 AM   #4
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do soldered joints ever break after ?


nestor, i am not sure i am understanding you right but i would expect that the increased pressure would always escape through the open end of the pipe. who would ever be working with a pipe that is sealed on all ends ???
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Old 12-12-2008, 03:19 PM   #5
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do soldered joints ever break after ?


Quote:
Originally Posted by amakarevic View Post
nestor, i am not sure i am understanding you right but i would expect that the increased pressure would always escape through the open end of the pipe. who would ever be working with a pipe that is sealed on all ends ???
It would escape through the open end, if you had one. Sometimes people will be working the middle of a run and not open a faucet. This will cause a closed system with pressure build up when you start heating.
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Old 12-12-2008, 03:53 PM   #6
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do soldered joints ever break after ?


Quote:
Originally Posted by amakarevic View Post
nestor, i am not sure i am understanding you right but i would expect that the increased pressure would always escape through the open end of the pipe. who would ever be working with a pipe that is sealed on all ends ???
Amakarevic: It's just as Joed said. Although I might not be able to think of a specific example right now, you'll find that there will be times that there won't be any way for air pressure inside the pipe to escape except through the joint you're trying to solder. If you have trouble soldering a joint (as you say you had), then not providing an alternate path for the air pressure to escape is the prime suspect.
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Old 12-12-2008, 04:05 PM   #7
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do soldered joints ever break after ?


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Originally Posted by Nestor_Kelebay View Post
you'll find that there will be times that there won't be any way for air pressure inside the pipe to escape except through the joint you're trying to solder.
hmmm - why not just turn one of the valves somewhere ? hard to think of a system w/out valves here and there.
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Old 12-12-2008, 04:26 PM   #8
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do soldered joints ever break after ?


If in doubt, redo the connection.

Marginal connections can fail if they are moved forcefully as you say you did.

When you said you saw bubbles this could be from overheating and boiling the solder away and make a marginal connection.

Connections in tough places are worth redoing if you don't think it is right.

I pressure test all my connections with 40psi of air if I have some that are going to be very hard to fix if I have a leak. At my vacation home I just buried 80 feet of pipe and did a 24 hour pressure test since I wanted to make sure there were no leaks before I buried the pipe. It passed and I buried it.
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Old 12-12-2008, 11:16 PM   #9
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do soldered joints ever break after ?


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Originally Posted by amakarevic View Post
hmmm - why not just turn one of the valves somewhere ? hard to think of a system w/out valves here and there.
The problem in most cases is not that there isn't a valve to open. The problem in most cases is that the person doing the soldering doesn't realize that unless they open that valve, they're preventing air pressure inside the pipe from escaping.

If Bill is working on the hot water supply piping in his home, he may only shut the hot water off at the water heater so that wife Jane or junior can still use cold water. If Bill opens a hot water faucet to allow the hot supply pipe to drain, and some time later Jane or junior decides to pour a glass of water from that faucet, then cold water goes rushing into the hot water piping through that faucet body. So, Bill realizes what the problem is and does the logical thing... he closes the hot water faucet so that Jane and junior can still use cold water but prevent cold water from getting into the hot water piping he's working on.

It doesn't occur to Bill that by preventing cold water from getting into the hot water piping, he's also preventing air in the hot water piping from escaping. If Bill now finds that his solder joints are uncooperative, he SHOULD be asking himself about how the air in that pipe can get out.

If he did, he would realize he's trapped the air in that pipe by closing the hot water faucet. If he doesn't ask that question, then he probably won't have any idea why the soldering didn't go well until someone explains it to him. And then, of course, it'll be blindingly obvious what the problem was.

Quote:
Why not just turn one of the valves...
Exactly, but you make it sound like I'm telling you to do something that's already blindingly obvious. Tell us something... when you were having trouble with your copper fitting not taking solder yesterday, did you ask yourself if air pressure inside the piping could be the problem? It seems to me that IF (big if there) you did, you would have stated that the piping was open in your original post so that we would have ruled out that possibility and focused on other possible causes. If you didn't say anything about the piping being open in your post, it wasn't an important point at the time you typed your post, and so it wouldn't have been an important point at the time you were doing the soldering.

So, perhaps the best answer to your question might be: "Cuz we rely so much on our eyesight for information that if we can't SEE what the problem is, then we give up on trying to solve it and put it in the same bag as the crop circles, UFO's and the Burmuda Triangle. That is, we give up on trying to solve it and just add it to all the other mysteries of life.

The solution to a problem only becomes blindingly obvious once you figure out what's causing the problem, and that's only easily done when you can SEE what's causing it. When your eyes don't give you any hint at the solution, it becomes a more difficult problem to solve. We are almost completely dependant on our eyes to answer all our questions for us.

Quote:
hard to think of a system w/out valves here and there.
How about the 3/4 inch copper piping and 3/4 inch finned copper tube radiators in a hot water heating system?

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Last edited by Nestor_Kelebay; 12-13-2008 at 09:12 AM.
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