I am looking at a couple copper pipe joints where a temporary copper cap was
soft soldered in the normal way over hard copper water line. From the
coloration the joints have obviously been overheated in the process of
trying to desolder them. They swear that they used ordinary plumbing solder
to solder them together and a third joint they had soldered at the same time
with the same solder but did not do anything in the way of desoldering to,
desoldered very easily with only moderate heat when I tried. It slid right
apart as soon as it got hot enough for the solder to flow just like it's
supposed to, but the other two (the overheated ones) will NOT come apart. I
have tried grabbing the very end of the cap with pliers and pulling twisting
etc and it will not budge. I am positive they have been heated enough that
there is no way that soft solder by itself is capable of holding them
together. Solder touched to the pipe next to the joint readily flows but the
joint stays rock solid. The pipe is not distorted so it is not a crimp type
effect jamming them together. It is obviously plain copper pipe there are no
threads. The only thing around the joints is soft plumbing solder residue,
which easily melted when the joints were heated. No sign at all of any hard
solder/brazing and they say they just used ordinary plumbing solder. Could
they have been over heated enough with MAPP gas to effectively weld the
copper? I don't want to heat them much beyond the flow point of plumbing
solder if I can help it because they are pretty close to the wall, and I
don't want a fire or destroyed solder joint in the wall. Anybody seen this
To make sure you are not fighting water/steam, use a nail or screw
and put a hole in the cap. Sometimes fittings get a tenacious
hold, it is almost more like they are in a physical bind than the
solder holding them, that might require a swat with a hammer while
it is hot. I know you don't have enough hands and this will
require some creativity or an assistant.
Keep the whole world singing . . . .
DanG (remove the sevens)
On Mar 27, 9:03?am, email@example.com wrote:
its easier to start new but desoldering is possible and the trace
solder if cleaned well helps adhesion of new solder. some new fittings
come pre soldered, a form of this.
some bozo hammered the cap on:(
No, they aren't welded. Somebody probably drove the cap on over a burr formed
tube was cut, or the fitting was on the tight side.
I've seen larger sizes (1-1/2, 2") that have been in service for a while
that's a case of not enough solder to fill the joint and corrosion setting in...
It finally came apart but the caps had to be cut lengthwise with a die
grinder and then pried away with a screwdriver while hot. Even at that there
were several small spots where copper adhered and would not come off no
matter how much direct heat was applied. It just tore away as the rest of
the cap was forced off and stayed stuck to the pipe. Even red hot (wet
towels wrapped around the pipes at the wall to heat sink heat away from the
joints in the wall). Those places had to be filed down. A few small test
holes in the wall verified that the joints in the wall were still intact and
not leaking so I guess that's the good news. Thanks for the responses.
A common occurrence when soldered joints are overheated or heated for a long
time is that the molten solder actually dissolves some of the copper. This
alloy has a higher melting point than the solder and each time it is heated
more copper will dissolve, raising the melting point even more. This
dissolving is also what causes copper soldering tips to pit and erode away.
I heard of someone who used copper to make a soldering pot and the bottom
dissolved out of it. Your experience is normal and quite common. Working
quickly with a minimum of heat will reduce the problem.
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