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Author Topic: Why did my pipe fail to unsolder?  (Read 13526 times)

Offline Atomic-S

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Why did my pipe fail to unsolder?
« on: 07/03/2011 03:47:16 »
Because of frost damage, I had to repair a half-inch (12 mm) inside-diameter domestic water pipeline. There was a broken 90 degree elbow. It was soldered to two other pipe sections. I was able to get a torch on it and release it from the two pipe sections. I then put on a new elbow, soldering it with paste flux and Sn-Sb alloy, plus whatever solder was still on the joint I do not know what type of alloy it is, except that it obviously had a low melting point. Turned on the water and it leaked. I then tried removing the new elbow. It came off of one side but absolutely would not release from the other. I eventually heated it up to the point that another joint about 5 inches (127 mm) away let loose, but the joint in question refused to budge. The solder was seen to melt around the edge of it, at least in some places. Any idea what the problem is?


 

Offline Geezer

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Why did my pipe fail to unsolder?
« Reply #1 on: 07/03/2011 03:58:23 »
Is there any possibility there was still some water near the joint? A very small amount will absorb enough heat to prevent some of the solder melting. That might also explain why the joint failed initially.
 

Offline RD

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Why did my pipe fail to unsolder?
« Reply #2 on: 07/03/2011 04:54:50 »
Some white bread may be of use ...

Quote
none of the joints I fixed were ever found to be dripping, except on a rare occasion where I was working on a pipe that wasn't totally drained of water, which brings me to the next topic - water and sweat soldering don't get along, unless you have enough bread to make the difference.

Bread? Did he say bread? Yep, not dough, er money kinda bread. Real white bread, ...

http://www.misterfixit.com/nosweat.htm
« Last Edit: 07/03/2011 05:12:25 by RD »
 

Offline Bored chemist

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Why did my pipe fail to unsolder?
« Reply #3 on: 07/03/2011 07:18:16 »
If the bit 5 inches away melted then t's not because the water was keeping the joint cool.
My guess is that the pipe or fitting had become misshapen (possibly by the pressure of the ice) and jammed the metal together.
 

Offline Geezer

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Why did my pipe fail to unsolder?
« Reply #4 on: 07/03/2011 07:24:46 »
My guess is that the pipe or fitting had become misshapen (possibly by the pressure of the ice) and jammed the metal together.

Interesting guess, but if that were the case, how did he manage to reassemble the joint?
 

Offline graham.d

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Why did my pipe fail to unsolder?
« Reply #5 on: 07/03/2011 17:34:56 »
It's very hard to know without actually being there. If the elbow fitted easily and now won't come off, it does rather seem like the solder is not melting because water is present, and this may well be why it did not solder wholly in the first place. Try pushing a cloth down and then withdrawing it to see if it's wet. If it's dry, then heating the joint should release it. If it's wet, you have to get it completely dry or it won't solder. If you thought it a tight fit when you assembled it, then maybe it was distorted and it didn't seal because you did not get enough overlap or the gap was too wide somewhere to allow the capiliary action to get the solder to seal the joint.

If it's wet and you can't prevent water flowing to it whilst trying to solder it, use a compression joint.
 

Offline Geezer

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Why did my pipe fail to unsolder?
« Reply #6 on: 07/03/2011 18:57:26 »
I wonder if it's possible that the old solder and new solder combined to produce an alloy with a rather high melting point? I've seen something like that happen when using a soldering iron, but I would have thought the temperature produced by the torch would still be high enough to melt the alloy. Still, if some of the antimony de-alloyed (is that possible?) it could be a problem, because antimony melts at 630°C

BTW, according to Wiki (Soldering) -

"For environmental reasons, 'no-lead' solders are becoming more widely used. Unfortunately most 'no-lead' solders are not eutectic formulations, making it more difficult to create reliable joints with them."

 

Offline Bored chemist

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Why did my pipe fail to unsolder?
« Reply #7 on: 07/03/2011 19:37:17 »
If any of the solder melted then the pipe is a good deal hotter than the boiling point of water so there's no liquid water there.

Another possibility is that the copper has diffused into the solder while it was hot creating a sort of bronze joint which would be hard to get apart.
 

Offline Geezer

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Why did my pipe fail to unsolder?
« Reply #8 on: 08/03/2011 01:49:25 »
Of course, if the problem is caused by water, you could always do what plumbers sometimes do to shut it off. They clamp a freezer on the pipe. No kidding! Here's an example.

http://www.ridgid.com/Tools/SF2500-Pipe-Freezer
 

Offline graham.d

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Why did my pipe fail to unsolder?
« Reply #9 on: 08/03/2011 13:06:42 »
If any of the solder melted then the pipe is a good deal hotter than the boiling point of water so there's no liquid water there.

What can sometimes happen (and I have experienced this) is that you can get the occasional water drip falling on the the joint from some distance away. This may be somewhat unlucky, but it can render a joint only partially soldered. I had this problem soldering a joint near the bottom of my central heating system. I also had a problem removing the part soldered joint. I could tell it was not right because the solder had not flowed out of the (Yorkshire) joint evenly. I used a compression joint in the end.

Another thought occurred to me. It is possible to overdo the heating on a solder joint. Heating too long can cause too much solder to escape and leave voids. The heat should be removed a few seconds after you se it run out of the joint. Also a word on the preparation. The copper, and the inside of the elbow, should be cleaned all round with wire wool and then coated with a thin layer of flux, before assembly. It is importent to ensure the pipes have gone into the elbow far enough too.
 

Offline CliffordK

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Why did my pipe fail to unsolder?
« Reply #10 on: 08/03/2011 14:52:12 »
It seems as if it is always easiest for me to get the temps I want with my oxy-acetylene torch.  The handheld propane units are always a pain.

Sometimes it is best to just cut everything off and get a good clean joint to start with. 

As far as the joint not coming loose...  were you using pliers on it?  It is easy to deform once hot & you're reefing on it. 

Can overheating solder change its properties? 
 

Offline graham.d

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Why did my pipe fail to unsolder?
« Reply #11 on: 08/03/2011 17:44:01 »
I'm not sure whether overheating the solder is too much of a problem (except for it running out of the joint) but overheating the copper oxidises it and stops the solder from adhering to it.
 

Offline Geezer

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Why did my pipe fail to unsolder?
« Reply #12 on: 08/03/2011 19:01:44 »
Where has Atomic gone? We need more data!!

Graham mentioned Yorkshires. I don't think he's referring to pudding.

In the UK, copper pipe fittings can come with solder already loaded in a groove inside the fitting (at least they used to). All you do is clean everything properly, apply flux, assemble, and heat the joint until you see a small fillet of solder emerge between the fitting and the pipe.

For reasons unknown, I don't think anything similar is available in the US, so you have to feed solder into the joint once it's hot enough. In tight situations, that can be a lot more difficult.
 

Offline graham.d

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Why did my pipe fail to unsolder?
« Reply #13 on: 09/03/2011 09:04:52 »
It never occurred to me that Yorkshire couplings may not be available in the US. Actually a lot of plumbers in the UK also feed solder in rather than use Yorkshire couplings because they cost a few pennies more. It makes very little difference to the overall cost of a job of work but using the Yorkshire couplings is much easier and makes neater joints.
 

Offline SeanB

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Why did my pipe fail to unsolder?
« Reply #14 on: 09/03/2011 19:38:12 »
Soft soldering leads to problems as the solder ages, and mixing different types of solder also can create odd alloys ( though most alloys tend to have a lower melting point, Woods metal being an extreme example of this) that can behave strangely. Most likely is that the pipe deformed, and wedged itself inside the fitting, either by the end turning up or by the fitting becoming deformed and creating a lock.

Overheating the solder also will cause the solder to dissolve copper from the pipe, and this makes an alloy that has both a higher melting point than solder, and welds the 2 pipes together.

I use compression fitting preferably on old pipe, as it is hard to ensure proper cleaning if the pipe is close to a wall, and the compression fitting can easily be undone in case of leaks. Solder fittings are good for new pipe that is clean and dry, though I do cheat at times and use a silver loaded rod that I use for airconditioning, as this works very well, and the joints are stronger than the pipe. They can be done with MAPP gas, but are better with the oxy-acetylene torch.
 

Offline grizelda

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Why did my pipe fail to unsolder?
« Reply #15 on: 13/03/2011 02:29:57 »
Possibly the pipe was cold and shrunken and the elbow was warm and expanded so when they equalized in temperature they formed an interference fit. Another possibility is that the pipe had small cracks (splits) near the end and they expanded during soldering. They would have been prevented from shrinking and closing when the solder hardened in the cracks before the copper cooled.
« Last Edit: 13/03/2011 02:44:11 by grizelda »
 

Offline Atomic-S

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Why did my pipe fail to unsolder?
« Reply #16 on: 20/03/2011 01:37:34 »
Thanks for all the opinions; they tell me more than I knew before. I finally fixed the problem by ripping out the bad section of the line and replacing it. When I replaced it, I thoroughly sanded and then fluxed the surfaces, and then used lead-tin solder applied first at the opposite side from where the flame was, and then all around generously. It went together pretty easily, and that section of the repair ended up not leaking. (I had another leak at the valve, but that is another question). As to why the problem: I don't think water was the issue. Any water would have had to come up from a lower altitude. The most likely cause, having read your posts, was some kind of an alloying problem involving the solders and possibly the copper from the pipe. It could have gotten overheated. I did find that when I was putting in the new fittings and pipe, the tin-lead solder melted quite readily. I was using an air-acetylene torch. Inasmuch as the line does not convey drinking water, the toxicity issues associated with lead should not be a problem for this installation. The tin-antimony solder that I had initially used melts at a higher temperature, and that could possibly have been the beginning of problems. Also, I do not know how it reacts metallurgically with copper, compared with the lead-tin solder.
 

Offline Geezer

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Why did my pipe fail to unsolder?
« Reply #17 on: 20/03/2011 21:50:56 »
Air-acetylene gets pretty toasty. You may have overheated the joint, in which case the flux could have burned off and allowed the copper to oxidise before it tinned properly.

The trick is to apply a lot of heat over a large area so that the heat conducts through the copper into the spot where you want to apply the solder. You should not apply too much heat right at the joint. I've found a propane torch that produces a wide flat flame works very well.
« Last Edit: 21/03/2011 05:46:13 by Geezer »
 

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Why did my pipe fail to unsolder?
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