[astroball]

I am trying to weld or braze a thin, hollow stainless steel coil to a large hollow stainless steel pipe.

Should I add guides along the large pipe to help the welder align the coil?

Will the welder bend the pipe (used for the coil) or does the coil need to be pre-formed?

Is there a way to increase the size of the weld between the two pipes (e.g. by adding a half-pipe guide along the surface of the large pipe)? I'm also trying to increase heat transfer between the pipes.

Thanks

[Poland308]

Wow loaded question! What are your heat transfer materials in each pipe? Concider silver soldering the pipe to pipe surface. 45% silver brazing rod or higher silver content will give you a solid connection. What is the temp difference between your two heat transfer fluids/ gasses?

[Coldman]

I can't visualise what you're trying to do with your brief description, so I don't know if you are talking about a serpentine coil, or circular coil to fit inside a cylinder or something else. A sketch, pic or drawing would help heaps.

Generally: a welder won't be bending any pipes above 1/2" and even then he would have to have benders of the required radius which is doubtful. Mostly they will weld on supplied elbows or return bends. Mostly coils are mandrel bent in a tube works and welded together afterwards. You would have to organise the mandrel bending and have a drawing or sketch to give the tube works.
Hope this helps.

[astroball]

Thanks all for the advice ao far. Here's a link to the picture: http://bit.do/erWEV

[Poland308]

http://www.hossfeldbender.com/wp-conten ... endNo2.pdf

Call the factory. They can set you up with the bender and dies to bend up to 2 inch sch 40 pipe. You can bend serpentine coils with it.

[Coldman]

Thanks all for the advice ao far. Here's a link to the picture: http://bit.do/erWEV

You still haven’t told us the pipe sizes.
We’ll keep squeezing.


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[astroball]

6.3 mm OD, 6.0 ID for the coil
180 OD, 160 ID for the pipe

[Coldman]

Finally.
Welder can bend this 1/4” tube around the the pipe no problem. I suggest you supply annealed tube and he won’t have to heat it. He’ll just wrap it around the pipe into a coil and then spread it to the right spacing. My suggestion is to tig silicon bronze or aluminium bronze to get a good contact bead. Silver solder is good to but for staino needs to be 55% to take and it will run like water so difficult to built up a good contact bead plus expensive.
If you want to go bionic you can supply a notched sheet metal strap to space the coil to the exact pitch.


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[astroball]

Thanks for the feedback! Is there a minimum thickness for the annealed tube (for the coil) or the large pipe if bronze tig is used?

How high would you recommend the walls of the notch be, and is it better to extrude out of the pipe or cut into the pipe? I imagine the notch would have a semi-circular profile if cut into the pipe.

[Poland308]

The thinner the wall the better the heat transfer.

[tweake]

I imagine the notch would have a semi-circular profile if cut into the pipe.

if you machined a helix into the big pipe and made a good fit, you could do away with welding and just use thermal epoxy.
or braze/solder it into place. ie wick metal in between the two pipes. if you just weld out on the edges you will not get much metal to metal contact in the grove.
if you need to weld it then don't grove the big pipe. simply wrap the small pipe around. that way you can get weld in under the small pipe and provide more contact area.