resoldering a joint: conflicting advice

When a leaky (yorkshire type with in-built solder ring) fitting is replaced the advice is to use a new fitting (of course), but do you need to remove the old solder from the pipe ends?
a) Some people say you must clean the pipe back to bare copper leaving no trace of the old solder .
b) Others say you heat it and wipe the old solder smooth with steel wool and that the rpesence of solder on the pipe will actually help.
Any thoughts?
Robert
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RobertL laid this down on his screen :

If it has been burn or overheated then yes, remove it back to bare copper.
Otherwise get it molten and wipe the solder off, then take a good look all the way round to make sure the solder has flowed properly all the way around. If it has then use some abrasive to just flatten it down enough to make a new fitting go on easily, flux then solder as normal with a new fitting.
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The above has always worked for me.
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On Sat, 3 Jan 2009 00:49:58 -0800 (PST), RobertL

That isn't easy to do.

"Tinning" (coating parts to be joined with a thin solder film before joining them) is a normal technique when soldering and used to achieve the best quality joints. You can wipe the joint with steel wool although a quick wipe with dry wool or cotton rag is often better at removing the solder evenly.
The only problem you are likely to encounter is difficulty fitting the new coupling if a blob of old solder remains after wiping in which case reheat the joint gently and re-wipe. The most common error is overheating.
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What is the result of overheating?
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wrote:

The flux is designed to work within a set temperature range, if you exceed it the flux will burn and foul up the joint. Burnt flux is just dirt, and you'll need to dismantle the joint and clean it up.
If you get much hotter the solder will burn. This forms a hard crust which is difficult to remove and doesn't take well to being resoldered.
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Thanks. Good to know the science behind the mess I made in the past.
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When I've been teaching people and watching what they do wrong, I would say the most common error is heating for too long. That can include over-heating, but also includes not heating properly so joint isn't getting hot enough quickly enough.
Following up in a close second place is not cleaning up the mating copper surfaces well enough in the first place.
With regards to cleaning up prior to resoldering, then I would say if you disassembled a working joint, then it must have been properly tinned in the first place. If you disassembled a leaking joint, then it wasn't properly tinned, and unless you can work out where the failure was and fix it, you might end up with the same problem again. You don't need to take all the solder off, but you need to ensure the exposed solder and copper are clean, bright and shiney, and reflux in the case of exposed copper. Because of the difficulty in inspecting and cleaning up internal surfaces in fittings, it's usually easier to use a new fitting.
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Andrew Gabriel
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Yup - only thing to add is I've occasionally seem a fitting with a pin hole in it. Some say it can happen on tube too - but I've only ever seen it on ancient stuff.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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In article

If it was leaking it could mean the original wasn't clean (or not enough flux/heat was used) so the solder didn't 'tin' properly. However this should be obvious after removal by examining the pipe. If the solder coating is continuous then simply apply flux, heat, push on the new fitting etc and solder as normal. But that's for end feed. With solder ring you'll need to be able to assemble things before applying heat.
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*Heart attacks... God's revenge for eating his animal friends

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Remove burned or oxidised copper or solder, and all flux traces. Otherwise clean, shiny solder traces count as tinning and are helpful. Remember that tin oxides are transparent, so may still be present when you can't see them. Generally a good scratch at it all over with #1 wire wool is enough. Use a strip of rucksack webbing (1" flexy nylon) or similar with a snippet of wire wool trapped underneath it to "towel" around the back of the pipe.
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On Sat, 3 Jan 2009 00:49:58 -0800 (PST), RobertL wrote:

Rubbish, you want the pipe "tinned", this will make the making the new joint much easier.

Heat the pipe so that the solder flows and wipe any excess away/off with a slightly damp rag. This should leave nothing more than the tinned pipe nice and clean ready for a dab of flux and new joint.
Steel wool is for cleaning pipe before a first joint is made, personally I don't like it for that purpose it leaves lots of bits about. One of the proper pipe cleaner tools is easier and less messy.
--
Cheers
Dave.




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Steel wool's an excellent way to screw up a joint if you don't remove all the bits, cheap nasty pan scourers or a scotch abrasive pad are best IMHO but my father in law swore by wire wool (he was a plumber for 40+ years).

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It also has a nasty habit of getting into the skin.
Best I've found are those black cleaning strips available in the sheds and Screwfix, etc. Ideal for cleaning round the back of an awkward pipe.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On Sun, 04 Jan 2009 14:09:27 +0000 (GMT), Dave Plowman (News) wrote:

I just use a bit of ali oxide 120 or 80 grit "sand" paper. Cut an inch wide strip off the end of the roll, marginally cheaper than the 25mm wide strip but not worth worrying about. One less thing to carry though.
--
Cheers
Dave.




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thank you all for your advice on this.
Robert
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