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Im not really sure how to join some pieces of copper pipe together because I fear the joining material may melt when the project is tested. Without revealing anything, the project will involve heating a section of copper pipe to rather high temperatures (350C+) and I think that solder & epoxy will both fail under those kind of temperatures. What other options do I have? Unfortunately I don't have a welder, but I have a powerful blowtorch on hand.

As a small side question, how much will this kind of heat affect the safe working pressure of the pipe?

thanks

braze it together or use silver solder...

seem to be good options , but id like a bit more headroom, for safety and if I want to increase the heat. Would aluminium work?

I believe you can tig weld copper with the correct shielding gases and filler rods.

thanks that might be the way to go. This guy explains how to do it.

My blowtorch can melt copper surprisingly so I might be able to weld it.
Any thoughts on my second question? Thanks

The problem with heating the copper with a blow torch is the excess air drawn through the flame. This oxidises the copper and makes porous leaky filler. The industry standard for refrigeration work is silver brazing solder with an oxy torch with the oxygen set neutral to low (carborizing flame) with a small feather inside the flame envelope. The area inside the feather is oxygen deficient and provides shielding gas to protect the joint from oxidisation. It will actually remove the oxide from the pipe. When silver brazing you can see the pipe start to glow then the oxide burn off leaving shiny copper ready for a good braze job without using flux. Since you need temperature resistance to 350 C and the silver brazing is done at about 600C, you should be OK.

I would highly recommend finding someone with the proper torch. Trying to use air will result in oxidised copper that the filler will not stick to, but roll off instead.

A typical alloy contains 45% Ag, 15% Cu., 16% Zn and 24% Cd and it has melting point and flow point 607°C and 618°C respectively.

Reference http://www.welding-technology ... razing.htm

Don't use the low temperature plumbing solder or silver bearing solder. Use the high temp silver brazing solder.

I would make the "tank" or whatever this is for out of threaded steel fittings. Unless that in impractical....which I don't see why it would be....

What in gods name are you doing that it is going to be that hot?? How long of a period will it be that hot??? a second, a few seconds????

It's probably a steam cannon, in which case copper would be a better option then thick steel or iron. Keep in mind solder melts at a higher temperature the second time, so you may be ok

Higher pressure steam boilers run at higher temperatures. Boiling point is dependent on pressure. Model steam enthusiasts build copper boilers so they don't rust out. Water at 350C would be at about 100 Bar pressure.

braze it up, can hold higher pressures

Alster370 wrote:Im not really sure how to join some pieces of copper pipe together because I fear the joining material may melt when the project is tested. Without revealing anything, the project will involve heating a section of copper pipe to rather high temperatures (350C+) and I think that solder & epoxy will both fail under those kind of temperatures. What other options do I have? Unfortunately I don't have a welder, but I have a powerful blowtorch on hand.

As a small side question, how much will this kind of heat affect the safe working pressure of the pipe?

thanks

JB weld or devcon plastic steel

Copper melts at about 1,000C, so the usual safety factor in a pressure rating may not be enough, if the pipe is going to reach that temperature.

I suggest getting this done properly by a professional if you're going to be pushing the safety factor.

Some reading for ya. (BIG file...have patience...save a copy for reference)

http://www.google.ca/url?sa=t&source=we ... wB3yLmPGBQ

None of the ratings go to 350C , but should give some useful information.

Tube ratings at temp on ~pg 26.

Joint ratings at temp on pg 28.

Be aware that brazing temps will anneal the copper (assuming it's drawn)...lowering the rating of the tube.

The problem with heating the copper with a blow torch is the excess air drawn through the flame. This oxidises the copper and makes porous leaky filler. The industry standard for refrigeration work is silver brazing solder with an oxy torch with the oxygen set neutral to low (carborizing flame) with a small feather inside the flame envelope. The area inside the feather is oxygen deficient and provides shielding gas to protect the joint from oxidisation. It will actually remove the oxide from the pipe. When silver brazing you can see the pipe start to glow then the oxide burn off leaving shiny copper ready for a good braze job without using flux. Since you need temperature resistance to 350 C and the silver brazing is done at about 600C, you should be OK.

I would highly recommend finding someone with the proper torch. Trying to use air will result in oxidised copper that the filler will not stick to, but roll off instead.

I thought this might be a problem. Thankfully I know where I can get some work done with a proper torch.

What in gods name are you doing that it is going to be that hot?? How long of a period will it be that hot??? a second, a few seconds????

Miniature steam cannon, just as a side project until I have finished my planning for my upcoming coaxial. Probably not too long, im hoping high temperature will boil the water fairly quickly. It will be small because I want a relatively short firing time and the only way to do that easily is with a small chamber. Steam takes up ~1700 times more volume than water, so even a small chamber of 20ml can produce half decent pressures.

Water at 350C would be at about 100 Bar pressure.

This particular setup will have a burst disk, mainly to make sure the pressure doesn't build up too high, But also to maximize the performance.

Be aware that brazing temps will anneal the copper (assuming it's drawn)...lowering the rating of the tube.

So ideally I need my copper to be type K (446psi rating at 400f W 1/2D)
I wasn't planning on huge pressures anyway, 100psi would be fine.