silversolder question

[Steve W.]

Like the others have said, Silver Solder is a pain to work with even after you get used to it. All of the copper air lines in my shop were done with a propane torch and old school plumbing solder. My compressor is set at 160 lbs and they have been fine for 25 years of daily use.

You are overthinking it.

I don't know enough about soldering vs brazing to present a plausible argument against any of the previous posters.

What I DO know is that when I soldered up the copper lines for my shop, I grabbed the same solder and flux that I have used for some plumbing repairs in the house. Because I did not have to purchase it, I paid no attention to its composition or brand. Cleaned up the joints, applied a bit of flux, heated, then applied the solder. Never did any purging (did not even know it was a 'thing'), just cut everything to fit, painted the lines so they looked better and hung them on the ceiling. 10 years later, it's all still there.

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[LopezBart]

What I DO know is that when I soldered up the copper lines for my shop, I grabbed the same solder and flux that I have used for some plumbing repairs in the house. Because I did not have to purchase it, I paid no attention to its composition or brand. Cleaned up the joints, applied a bit of flux, heated, then applied the solder. Never did any purging (did not even know it was a 'thing'), just cut everything to fit, painted the lines so they looked better and hung them on the ceiling. 10 years later, it's all still there.

"soft solders" - e.g. household plumbing solders - melt at temperatures that do not cause copper oxide to form. Silver-brazing alloys, however, melt at higher temperatures where oxidation can be an issue.

https://www.technic.com/sites/default/files/resources/Solder%20Alloy%20Melting%20Temperature.pdf

More data than most people ever need: https://en.wikipedia.org/wiki/Solder_alloys

 

[Steve W.]

^^^ Like I said, I don't know enough to know ALL the details, I just know what worked for me.

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[ching0n]

^^^ Like I said, I don't know enough to know ALL the details, I just know what worked for me.

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just know that tap water head pressure is 40-70psi and pex is rated to like 160psi at room.

 

[Fabtechprerunner]

We seem to have forgotten that the OP is sticking together air compressor piping, not medical gas, a rocket engine, potable water piping, a Mars rover, a nuclear reactor, a commercial freezer, a hazardous chemical plant, an aircraft carrier, or a steam boiler.

This is all very educational, though.

I do understand. However, if he is using any air tools with this air compressor, nailer, impact wrench etc I would be flowing nitrogen no matter what. You dont want flaky oxidation scale mixing with good air took..

 

[Fixr]

I do understand. However, if he is using any air tools with this air compressor, nailer, impact wrench etc I would be flowing nitrogen no matter what. You dont want flaky oxidation scale mixing with good air took..

From previous posts, i have the impression that plumbing solder with a propane torch doesn't get copper pipe hot enough to form oxides. Is that correct?

 

[LopezBart]

From previous posts, i have the impression that plumbing solder with a propane torch doesn't get copper pipe hot enough to form oxides. Is that correct?

This is correct unless one completely overheats the joint. Traditional 60/40 lead/tin solder melts at 361-374F; modern lead-free solder melts at the mid 400s depending on the alloy. Copper oxide formation typically isn't an issue below 500F, apparently.

An hour spent w/ some scrap copper tubing, an infrared non-contact thermometer and a propane torch would be informative.

 

[oldmachinenut]

I did the copper air lines (200 feet of 1/2” L copper, 15 drops) in my shop with a Prestolite air/acetylene torch and lead-free solder and flux I had from numerous plumbing jobs. I did it over 20 years ago, it has been constantly pressurized at 140psi and there are absolutely no leaks.

 

[rlitman]

This is correct unless one completely overheats the joint. Traditional 60/40 lead/tin solder melts at 361-374F; modern lead-free solder melts at the mid 400s depending on the alloy. Copper oxide formation typically isn't an issue below 500F, apparently.

An hour spent w/ some scrap copper tubing, an infrared non-contact thermometer and a propane torch would be informative.

Forget the non-contact thermometer. They are very misleading on metal. Copper's emissivity can be as low as 0.03 when shiny and over 0.9 when badly oxidized and crusty, so an infrared thermometer assuming emissivity is 0.95 will under-read the actual temperature by almost random amounts. If you have a thermal camera, you could stick a piece of Kapton tape onto the pipe and take your readings off of that (that's how I get good thermal readings from aluminum).

OTOH, a long-stem thermometer from a turkey fryer inserted into a copper tube could give a good (though a bit delayed) reading if the tip is more than a hand's width from either end. I'm not sure how much any of this matters though.

Oxidation prevents solder from adhering. Try soldering without flux.

You can SEE copper oxide formation, and it's pretty easy to see when it runs the spectrum from "pretty colors" to "mill scale". We're all familiar with how pennies oxidize over the years from their minting, and that's happening in people's pockets, but it takes just about incandescent heat before it rapidly builds up a layer that wants to flake off. A you're getting the metal to glow (in a darkened room) while soldering, you've already burned off all your flux and won't get solder to stick.

 

[ching0n]

From previous posts, i have the impression that plumbing solder with a propane torch doesn't get copper pipe hot enough to form oxides. Is that correct?

oxides are an issue in refrigeration cycles because the compressor ends up cycling the contaminants. The layer's small and I'd venture to say not structurally compromising...just filter your airline so it doesn't end in your tools (though doubt it'd be catastrophic).