Sweating copper pipe.

Ryudo · Sat Jul 18, 2009 6:17 am

Hi, I guess I can firstly use this topic as an introduction for myself, I'm a new user (though I've been lurking unregistered for a few months, soaking up information). I thought I'd finally register as this site has helped me out quite a bit in the past with projects.

I'm planning on making a coaxial airgun, I've already got most of the parts and completed some of it, but I'm a little concerned about the working pressure of soldered joints. I've looked around for some estimates but opinions on this seem very divided and varied. Does anyone know the safe working PSI I could use in an airgun using sweated/soldered joints?

I'm a little concerned about it giving out while there's air in the chamber, I want to shoot BBs/bearings at my targets, not the guts of my airgun.

At least 200 PSI would be outstanding, but if I could get 500 out of it I'd be laughing.

Thanks in advance,
-Paul.

inonickname · Sat Jul 18, 2009 6:43 am

Standard solder is fine (using a blowtorch). Sweating with silver solder/oxy fuel will actually reduce the working pressure of the pipe due to annealing.

You're way in the clear as long as you use flux and do good joints. Try get an antitomy solder if you can. I believe gippeto did some calculations and testing on a dead weight tester and found the shear strength of a lead-antitomy solder joint to be around 17500 psi, so you're well in the clear as long as your joints are good.

Ryudo · Sat Jul 18, 2009 7:23 am

Holy hell! Unfortunately my compressor doesn't pump 17.5k PSI, much as I'd like it to.

Sounds like I've been worrying about nothing, and will be able to go to town with it. I've seen some of gippeto's posts, and I'm happy to trust his judgement as he seems quite experienced on the subject.

I believe my joints will be fine, I'm no expert but I've done it before. Thanks inonickname.

frozebyte · Sat Jul 18, 2009 10:46 am

Will the pipes even hold 17500psi?!
You can trust Gippeto alright, hes really experienced

Make sure those joints are good

EDIT: Good luck with your project, mind filling us in on the progress?

inonickname · Sat Jul 18, 2009 10:54 am

There's a lot of different wall thicknesses of copper, and diameter plays a huge role. The copper tube handbook has information on everything.

Average burst pressure for mid wall thickness mid size copper is around 8000 psi. Larger diameter, lower burst pressure, thinner walls, lower burst pressure. And vise versa.

The Copper Tube Handbook (warning, PDF)

frozebyte · Sat Jul 18, 2009 10:59 am

Wow inonickname im impressed, a copper tubing handbook... right... gosh spudguns are driving me crazy! My friend has joined in the fun on spudfiles

Ryudo, we will be waiting for a thread on your project!

Ryudo · Sat Jul 18, 2009 6:37 pm

Thanks frozebyte, I'll post some images when it's closer to being finished, maybe a damage video too if I feel amorous.

inonickname · Sat Jul 18, 2009 6:40 pm

Frozebyte, just out of interest, which one is your friend? Ryudo?

Edit: wow, I've already exceeded the amount of spudbux I can earn in a day. Limit = bad

Technician1002 · Sat Jul 18, 2009 6:53 pm

For stuff over 500 PSI, a hard solder is recommended. A/C refrigeration is mostly soldered with silver brazing solder. Get training before attempting this.

Without an oxy torch, silver bearing solder is best.

inonickname · Sat Jul 18, 2009 6:57 pm

If you go into oxy-fuel soldering pipes you will most likely anneal the living $%^# out of the pipe, so you definitely need to know what you're doing.

By the way, silver solder is indeed over 9000 times as strong as lead solder.