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I have a threaded cast iron flange that I'm going to use a brass nipple join a copper connector. I'll be using Teflon tape for the NPT connections, and my instinct is to solder the threaded copper adapter to the copper pipe before I "snug and grunt" the copper connection in. However it may not always be possible to solder connections before hand.

Is it safe to solder near a Teflon'ed joint?

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Soldering close to Teflon tape can cause flu-like symptoms, I have worked with Teflon pipe and tubing.

When we had to heat it, to weld it or stretch it for fittings, caution was needed and had to be careful to keep it below 500f , if higher temps were needed we did the work in a fume hood and one spring there were a lot of birds outside (mud swallows) that died because of the fumes when we were welding a bunch of segments. Birds are quite susceptible to the fumes.

If outside there is normally enough air flow but a fan above the area to push or pull the vapor away is usually enough.

Especially now I would not want flu like symptoms sad some of the guys would get careless and breathe the fumes then complain the entire next day. So use caution plenty of fresh air and you should be fine. I usually wrap a wet towel around areas I want to prevent heat transfer to. .....

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  • I thought this was a joke, but then I googled it and I guess it's a thing with birds. Guessing it's really toxic, since fluorides are the base for some nerve agents, but people have a larger biomas so we are less effected. Nov 10, 2020 at 15:05
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If you don't vastly overheat the joint (which tends to make soldering unsuccessful anyway as flux burns off and the surface oxidizes) most solder melts below the upper working temperature of PTFE (such as Teflon®)

Following normal practice and wrapping a damp rag around adjacent joints helps to limit heating beyond the joint of interest, as well.

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    The solders I use are above the vapor point of PFTE it’s not normally hazardous for humans but can cause flu like symptoms (perfluropneumonia is what they call it or did when we were modifying chem benches with Teflon pipe) but I agree with the wet rag to reduce the heat transfer.
    – Ed Beal
    Nov 2, 2020 at 18:38

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