Sweating a Threaded Connection

Besides getting laughed at by your co-workers and cursed at by the person who tries to get it apart, what's wrong with soldering a threaded connection?
A co-worker was telling me about his first foray into the world of sweated plumbing connections.
He was a installing a new shower valve which involved a threaded connection at the valve and then sweated fittings after that.
He got everything installed and sweated but when he turned the water on, it leaked at one of the threaded fittings. He looked at the situation, realized he couldn't tighten the connection since everything else was soldered in place, so he took the easy way out.
He grabbed the torch and sweated the threaded connection.
Is he looking at problems down the road?
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Almost without a doubt. Let me rephrase that - yes.
Firstly the threaded connection should have had teflon tape or pipe dope. If neither was applied there's no surprise it leaked. A sweated connection, even using the correct fitting, needs to be cleaned with a wire brush or emory cloth, and flux must be used. Without those critical steps a sweated joint will likely fail. Without those steps on a threaded joint, well, it's basically hopeless.
The joint might not leak immediately, but a shower body usually has hot water running through it and the normal expansion and contraction and any other movement in the pipes or building will eventually create a pinhole leak.
The problem might not be noticed for a good long while, and by that time you're dealing with ripping open ceilings and tiled walls, and dealing with mold and rotted wood.
Covering up such a situation and hoping for the best is like holding your breath as a form of birth control.
R
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On 2/6/2011 4:56 PM, RicodJour wrote:

You assume he used pipe dope or Teflon tape? :-)
TDD
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Let's get up a pool on the date that it fails...first month,... second month,,,third month If there are teens in the house the odds go to the soonest. All bets are off if he goes on vacation without shutting off the water.
Joe
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I don't think he'll have any problems until the time comes to take it apart, but I sure am curious as to how he cleaned and fluxed that joint after it had been screwed together, and also how the flux reacted with the pipe dope or pipe tape.
--
Often wrong, never in doubt.

Larry Wasserman - Baltimore Maryland - lwasserm(a)sdf. lonestar. org
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?

Sounds like he did none of that. My guess is that he has solder holding just at the lip, not inside the joint. I doubt he'd have a catastrophic failure, but certainly could stat dripping soon.
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We have a winner here. In the situation as described, the threaded connection should have had teflon tape or joint compound and it was already made up and not taken apart again. If those are present, it can't be soldered properly. And if they aren't present, there is still no way to properly clean the connection or get flux in there without taking it apart.
Aside from all that, let's assume you tried to do this from scratch. First, you couldn't clean it well to remove oxide because of the threads being present. Second, in a slip fitting, meant to be soldered, the solder is drawn in by wicking action and gets sucked into the space through the whole slip fitting where the parts meet. With a threaded connection, at best it the solder would probably get in only a thread or two deep. Could it be enough so that it forms a seal and the rest of the threaded connection supplies the mechanical strentgh so that it works? Yes, but it isn't the right way to do things, particularly if it's a place behind a shower where access later could be a headache.
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I think it will be fine. Even in a normal install when the valve has to be replaced the pipes have to be cut. I always thought they should use flared fittings on those valves.
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Daniel Leonard wrote:

Only a moron would do that.
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Short. Direct. Accurate.
R
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If the guy who did the, err, plumbing work? got advice from Home Depot, it was from a guy standing outside and he didn't understand Spanish.
R
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Using one or the other is adequate, using both is just a waste of time and materials.
--
The best argument against democracy is a five-minute conversation
with the average voter. (Winston Churchill)
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On Thu, 10 Feb 2011 09:19:06 -0500, "Stormin Mormon"

One good rule of thumb - "don't sweat the small stuff"
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