Soldering brass fittings to copper

[Stephen Tashi]

TL;DR

When a heavy brass fitting is soldered to copper pipe, how can I be sure the brass is hot enough? Does the visual appearance of flux indicate when a joint is hot enough to apply solder?

When soldering a brass fitting (e.g. https://www.pexuniverse.com/1-pex-x-3-4-pex-brass-pex-copper-fitting-adapter-lead-free-brass ) to copper (e.g. a 3/4 inch copper coupling) I think there is a danger that copper gets hot enough to melt the solder, but the brass fitting (being more massive) isn't hot enough. Can I use the visual appearance of flux (e.g. Oatey H-20@5) on the brass as a clue? Should the flux liquify or bubble? Should I apply the torch mainly to the brass instead of at the middle of the joint?

Another question, on the above example is whether the raised lip on the brass fitting should be set snug against the end of the coupling - or should I leave a small gap for the solder to flow into.

I ask the general question, because I soldered the particular example and even though the solder flowed around the joint, the joint leaked.

 

[Averagesupernova]

I have soldered a lot of copper pipe and a fair amount of copper pipe to brass valves. If you had a leak the reason could be poor application (incomplete) of flux or you did not have the solder flowing how you thought you did. You may also have poor luck with a dented fitting. I have had that happen. It has become so second nature to me that it is hard for me to imagine screwing one up. What I have found is that once the solder starts to flow easily into the joint, it is hot enough. As long as you have adequate flux it should hold.
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I have soldered some seemingly impossible to get at joints tucked up in between ceiling joists/ductwork/etc. and have had good luck as long as the work was clean, well coated with flux and enough heat to easily flow the solder. It is easy to assume the work needs to be heated all the way around but this is not necessarily the case. I always solder brass to copper on a bench if possible and then solder the assembly into place just to be safe. A heavy brass fitting definitely takes more heat and I prefer doing that work where I can see all the way around the fitting.
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As to where to heat the joint, heat the outer part. I assume the fitting you linked to fits around the copper pipe and not inside a copper fitting.

 

[Baluncore]

What type and grade of solder are you using, silver solder?

 

[essenmein]

If you are soldering that pex fitting to Cu pipe, then if I was doing it i'd run the torch over both, that brass fitting isn't that big, so should heat fairly quickly, if the brass fitting was larger eg a valve or something (with the valve taken out), then I almost eyeball the differences in mass and apply heat proportionally more to the larger mass.

I always clean both surfaces with plumbers sand paper (even if new fittings), apply flux to both, bottom the pipe out in the fitting heat with torch, you'll see the flux start to boil off, I then repeatedly touch the fitting and/or pipe with the solder wire (hold the flame away while doing this) to check if the temp is there, once it is it will wick in there nicely. Just be careful not to let any solder run onto the pex side of things or that will never seal!

Regarding leaks, I had one annoying one which looked like it was soldered properly, but after about and hr under pressure the thing sprung a pin hole leak, seems the flux somehow bubbled or something in the solder, allowing water out. Pain because the pipe was full of water and closed off so figuring out how to get the water out again and reflow it was the challenge. But once that was figured out, I just re applied flux, reflowed the solder and voila, leak gone.

 

[Stephen Tashi]

I always solder brass to copper on a bench if possible and then solder the assembly into place just to be safe.

That's what I did on my second try. Working at a bench, I soldered the brass adapater from 3/4 inch copper to 1 inch PEX onto a copper couping. Then I soldered the coupling on the copper line, working in a trench. So far, no leaks.

 

[marcusl]

Flux should bubble, but not turn black, burn and dry out. Use a hotter torch to reach temperature more quickly if that’s happening. Always heat the fitting. Bottom pipes fully into fittings.

One more thing that helps—clean the soldered joint with a small wire brush dipped in water and wipe with a rag after the joint cools. That will prevent ugly green corrosion later.

 

[hutchphd]

TL;DR Summary: When a heavy brass fitting is soldered to copper pipe, how can I be sure the brass is hot enough? Does the visual appearance of flux indicate when a joint is hot enough to apply solder?

I think there is a danger that copper gets hot enough to melt the solder, but the brass fitting (being more massive) isn't hot enough.

Flux should bubble, but not turn black, burn and dry out. Use a hotter torch to reach temperature more quickly if that’s happening. Always heat the fitting. Bottom pipes fully into fittings.

I know this is an old post but it seems to me that @marcusl "buried the headline" in this reply: always heat the heavy fitting not the pipe, and only hot enough to just make the solder flow into the (fluxed) joint , testing it all the while.

 

[Baluncore]

If you avoid the sunlight, and work in the dark, you can see the surface heat changing, as the solder flows into the joint.

 

[sophiecentaur]

If you avoid the sunlight, and work in the dark, you can see the surface heat changing, as the solder flows into the joint.

This is great advice for brazing with silver solder (easyflow) but a pipe in a hole, joining to a chunky brass fitting would be best soldered with regular plumbing solder. Nothing should get even dull red-hot with lead type solder. Only for very special shapes of brass and copper plumbing should you need silver solder.
Experience has shown me that the water pipe must not have any water in it so a wick of tissue poked into the pipe can detect / cure that. if you get steam out of the end of the pipe then you'll never get the solder to stick to the copper. Steel wool works well for me when cleaning both surfaces and plenty of flux. I still have some lead based solder and that works best, even if it's a bit naughty.
A large flame should be moved over both sides of the joint and plenty of flux applied inside and out. When the joint is hot enough, the solder will melt and be drawn into the gap. I nice fillet should form round the total circumference. Enough is enough and you don't want to block the pipe inside with solder beads.

 

[Averagesupernova]

Experience has shown me that the water pipe must not have any water in it....

Yeah, any water will kill the job for sure. Sometimes it's impossible to stop it. If you're working where a valve seeps upstream and continues to flood where you are trying to solder, dry ice contained around the pipe upstream will freeze the water preventing it from flooding your work.

 

[hutchphd]

so a wick of tissue poked into the pipe can detect / cure that.

I've always used a plug of "wonder" bread to hold any (low pressure) water at bay. Rapidly expelled under "mains" pressure.

 

[Baluncore]

This is great advice for brazing with silver solder

What type and grade of solder are you using, silver solder?

To which there was no reply.

 

[berkeman]

Thread paused for a bit...

 

[berkeman]

An off-topic subthread has been deleted. Since the OP @Stephen Tashi has not been at PF for several months, I'll leave this thread closed for now. If he comes back and wants' this thread re-opened, he can just send me a PM. Thanks folks for some interesting tips.