Wipe Solder Joint?

Sometimes in soldering copper pipe and fittings, it's difficult to wipe a joint giving it a "nice" finished appearance. This is especially true for the backside of some work.
Is there some quality, durability or other reason for the wipe? Or, is it just cosmetic, and essentially unnecessary?
Thanks,
Dick
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Mainly cosmetic and also sometimes the drip will form a sharp point, which can later cut you if you don't see it coming.
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Prof Reid wrote:

I've seen reports that wiped joints are stronger than unwiped joints, but strength is relative. If the joint is properly done (cleaned, fluxed, adequate heat, etc.) it is going to be plenty strong. Dave
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Mainly cosmetic. I noticed that a lot of pro plumbers wipe the joint with flux and a brush so I adopted it.
Steve Manes Brooklyn, NY http://www.magpie.com/house
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Actually, if you have a "bad" joint with a pinhole leak, wiping can form a fillet against the fitting and seal up the pinhole. Sort of last chance to have a leakproof joint, plus make it look good.
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Prof Reid wrote:

A good wipe can remove traces of flux, some types of which may over time cause an unsightly greenish corrosion on the pipe and fittings.
Anyway, its just cosmetic, 'cause when talking about sweated copper plumbing joints, "The solder you can see isn't doing anything useful."
Jeff
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Been told that union plumbers wipe the joint to remove the flux you applied before soldering. Don't know if the flux is destructive over time to the copper or if it is just cosmetic. IMO keep a wet rag handy and wipe the joint.

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Prof Reid writes:

It can't possibly help the joint, only disturb it when it is freezing. But it does look more workmanlike.
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On Sun, 01 May 2005 22:42:23 -0500, Richard J Kinch

Can't say for sure, but logically a joint is better (stronger) when it cures slowly. Wiping it with a damp rag, cools the solder quickly. I'd have to agree that wiping looks cleaner.
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Mostly cosmetic, however...
Plumbing flux is corrosive to copper. Generally speaking it won't cause a problem (because the quantities are small), but it does leave you with greenish stains.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.
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