Joining Copper and Stainless Steel

[KS2K]

I am working on a prototype concept, but I need some help.

Think of a stainless steel open top box 30" long x 24" wide x 10" deep. I need to run (8) 2.00" copper pipes, evenly spaced, thru the box, 5 inches off the bottom of the box. The pipes will run in the 30" long dimension. No problem punching the holes for the copper pipes. Heres the question. The copper pipe, where it penetrates each side of the Stainless box must be water tight as the box will be filled with water. The copper pipes will pass steam raising from a container of boiling water. The steam will not have any pressure, as the opposite end will be open to the air.

Can Copper/Stainless be welded, brazed, soldered ? How do I make that water tight joint ?

Thanks
KS2K

[W Welding]

I've solders lots of copper pipe fittings to Stainless for maple sugaring pans.
What thickness is your stainless?

[KS2K]

I've solders lots of copper pipe fittings to Stainless for maple sugaring pans.
What thickness is your stainless?

Stainless is 20 gauge, type 304.
What method do you use to solder copper to stainless, must be lead free solder, what flux, any special tricks in soldering them ?

Thanks
KS2K

[Mark Lindquist]

Mark Lindquist

In refrigeration we use a 45% silver brazing alloy. It melts at around 1100 degrees. A white paste flux is used. This would be better than soft solder. You heat both parts until the flux starts to turn clear and add the alloy. Very strong connections.

[redintn]

In refrigeration we use a 45% silver brazing alloy. It melts at around 1100 degrees. A white paste flux is used. This would be better than soft solder. You heat both parts until the flux starts to turn clear and add the alloy. Very strong connections.

DITTO, works very well, kinda of pricie, but you pay for works well.

[Bodybagger]

I also recommend silver brazing. I like Safety-Silv 56. You can get it in a 5 pack of uncoated, or 3 pack of flux coated. I use paste flux but I keep both around. I think they are running about 10-12 dollars per rod. Some refrigeration places will sell you one rod at a time.

These things will braze darn near anything and are a must for brazing dissimilar metals. Steel to copper is a very common joint in refrigeration (steel tubing on hermetic compressors joined to copper refrigeration lines).

I'm going out on a limb here but I think 45% silver is adequate for mild steel to copper but you want to step up to 56% when doing stainless to copper for best wetting of the stainless steel.

[kcstott]

+1 For safety silv 56 Used this stuff many time works great I would only choose something else if I needed something that melted cooler.

[KS2K]

Thanks to everyone for your help. Silver Brazing it is.

KS2K