Soldering vs. Brazing

Mike F · Jan 24, 2006

I am setting up a compressed air system in my garage. The max pressure of the compressor is 175 psi. I am planning to run 3/4" type L copper. I have been to the copper.org site and researched the search function here and get conflicting advice. Now, I realize there may be liability issues on the copper.org site, but I wanted to get some "practical" advice. They say to braze- which I have never done. I was planning to solder. Does anyone have experience with this? I was able to find 1 poster here who soldered and didn't report any problems. If I do braze, I was unsure of the brazing rod material and flux required. Any suggestions? Thanks
Mike

Bob NH · Jan 24, 2006

If I were installing a compressed air system I would use 1/2" steel with black or galvanized fittings. It's not that big a deal and you need a few lengths of 1/2" pipe. At HD you can probably buy various lengths already threaded. You can use threaded ball valves without adapters.

You will need to put a flexible connection between compressor and hard pipe or the vibration will break something.

Sponsor · 2022-01-29T12:20:58-0800

Chassis · Jan 24, 2006

Agree with Bob. I've never seen copper air lines, and I spend a fair amount of time in manufacturing plants where there is lots and lots of compressed air piping.

Mike F · Jan 24, 2006

The only problem is that I live on a small barrier island in Long Island, which is only 3 blocks wide (= lots!! of humidity) and I was worried about rusting inside the pipes and subsequently the tools.

Chassis · Jan 24, 2006

If you want to braze, I don't see an issue with it. Brazing is not a big deal, I enjoy it. I needs a hotter flame and different filler rods. It's in between soldering and welding. Heat both pieces to be joined until the filler material starts to flow freely, then feed the rod into the joint. Very much like soldering in this way.

For a torch you need mapp gas, map/oxy or oxy/acetylene. Propane isn't going to handle it. For rods you might find them at HD/Lowe's, or a welding supply would have them for sure.

Seems to me like black gas pipe would be the way to go. After all, it's buried in the ground and is installed in wet/moist environments. You will need a threader though, so there is no free lunch either way. Only hope would be that if you can design your pipe runs so that you use standard lengths, you can screw it together without cutting/threading. I would think you could do that.

You need a drier in your compessed air system. Stop by the local auto service station and see what they are using for air piping. I'll bet it's not copper.

Bob NH · Jan 24, 2006

Drier, Oiler, and Filter

Most industrial air systems include a drier, filter, and oiler. The filter and oiler are often sold as a package with a regulator, but you don't want oil if you are using it for painting. The idea is to protect the tools. Should be no rust in the pipes.

Plumber1 · Jan 24, 2006

We ran steel pipe too.
From 1/4" up to 3" black pipe.

Gary Swart · Jan 24, 2006

We're not talking industrial plant usage here. For a home shop, copper works very well, it's much easier to install than iron pipe because of the cutting and threading issues, but black iron is OK to use. Regular galvanized pipe and PVC should never be used. PVC especially has a tendency to shatter after it gets old. As far as solder vs brazing, I believe solder will work just fine. My home shop is plumbed with soldered copper and is under constant 125 psi, I never turn the compressor off. All of the checking I did indicated this was acceptable and safe.

Mike F · Jan 24, 2006

Thanks all. I was just out in the garage measuring things up. Earlier today I was at HD to price out both systems. Pretty much equal. I realize, however, that copper would be much easier to work with due to measuring and fitment issues. If I am off by 1" on galvanized I would be stuck, and copper could just be cut. Of note, copper.org says it's okay to use type L copper for compressor apps. Solder is alright, but brazing is stronger. I have some extra copper lying around. I may just solder a small piece and see if it holds.

Dubldare · Jan 24, 2006

Average burst pressure of a regularly 'soft' (95/5 or lead-free) is around 1000 psi, at room temperature.

I'd solder it, unless you're running very high pressures and poor at soldering.

http://www.copper.org/applications/plumbing/techref/cth/tables/cth_table4.htm

Mike F · Jan 24, 2006

great info, thanks. Looks like solder it is.

Jimbo · Jan 24, 2006

Copper in a compressed gas system should use flare fittings, not soft solder.

Dubldare · Jan 24, 2006

Actually, annealed pipe is weaker than drawn pipe.

While the premise of a 'heartier' fitting can be argued with flare fittings (less apt to completely rupture/ blow apart), I know of no code which specifically states flare only. Copper.org recommends brazing for compressed air systems.

All that being said, I know of miles of compressed air piping which utilizes type L drawn pipe and lead-free solder, working at 100# day and night. This system has been up and running for over 20 years without failure.

Gary Swart · Jan 25, 2006

My solder fitting have held perfectly for over 5 years without a problem, and I never turn the compressor off. The system is under 125 psi 24/7. Perhaps it can be proven that flared joints are less prone to fail, but I doubt if the difference is more than academic. Sweating is much easier in my opinion than flaring.

Mike F · Jan 25, 2006

I have also heard from others over the past day or so who have soldered without any problems. Since the system will only be dealing with pressure rather than temperatures the strength should be adequate. I guess I will find out and report back after all is done ( I am still waiting for delivery on the compressor and also have to run a subpanel for extra circuits for this and a scissor lift ). It's been good to find another forum like the one you guys have here. Very helpful!

Gary Swart · Jan 25, 2006

When you install the tank, use a length of hydralic hose to connect the compressor to the air line. This absorbs any vibration from the compressor. You can get a hose made up for just a few bucks. Also, put the compressor legs on pads. You find a place in the phone book. Put a cut off valve before the hose.

Spaceman Spiff · Jan 25, 2006

In all of the commercial buildings I have helped designed all of the mechanical engineers designed soldered copper lines. They said you can get a bunch of air through a 1/2" copper line. We were running 600 CFM a few thousand feet from a central plant compressor set through 2" and all of the branches with 3 or less point of use FRL's (filter-regulator-lubricator) or FR's (filter-regulator) were on 1/2" Cu. These installations are in four of the largest hotels in Las Vegas, if that means anyhting... Every installation I have seen uses a braided stainless steel covered rubber hose to connect the compressor to the house air pipe to isolate vibration. If you plan on painting, use oil free air like they said; to do this use a FRL or FR at the end of the line so you can select oiled or oil free at the point of use, instead of using a whole system oiler at the compressor.

I have had 1/2" Cu compressed air lines in the last two houses I owned with no problems. I used a short 3/4" dia compressed air hose to connect the house air pipe to the compressor to isolate vibration.

Mike F · Jan 25, 2006

I am planning on the flexible line off the compressor until the hard lines begin. I am looking around for vibration pads. I was told to get as thick as possible, but they seem to be standard around 1" thick rubber sandwiched around cork. I will use wedge anchor bolts into the concrete so the unit won't walk.

hj · Jan 25, 2006

air

I cannot find a recommended air pressure for copper tubing, but 175 psi sounds like a bit beyond what would be recommended. Brazing requires that the fitting and tubing be heated to a cherry red temperature. That temperature detempers the tubing and fitting thus weakening it.

Spaceman Spiff · Jan 25, 2006

I checked at Cerro Tube and they specify their type L for compressed air applications. They don't give a working pressure, though. I bet a call to them would tell us or if anyone has a copy of ASTM B88.

Soldering vs. Brazing

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