Joining stainless tube to steel pipe

I'm making a steel-post-and-stainless-cable railing for my deck. The
posts are standard 1-1/2 inch pipe. The cable will be attached with
swaged fittings at the end and corner posts, but will simply pass
through holes in the intermediate posts. I want to keep water from
getting inside the posts where the cable passes through, so I plan to
drill through the posts, and insert a short stainless tube across the
dimeter of the pipe. I've experimented with both brazing and soft
soldering the stainless tube in, and both appear to work, but the
soldering is much easier. Also, the heat needed for brazing tends to
melt the end of the stainless tube (5/16 OD, 1/4 ID), so the soldered
job looks better, too. The posts will be painted.
So here are the questions:
1. Will the soft soldered joint take normal outdoor Nebraska thermal
cycles (-20 F to 105 F) without cracking over time and allowing rust to
get a foothold? There is no real mechanical stress to the joint other
than from temperature changes.
2. Are there soft solders that are stronger than those for plumbing?
3. Should I consider something else, like hard solder (I think this
takes a temp as high as brass brazing, doesn't it?) or epoxy?
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Silver solder, which requires a temperature much lower than brazing. It is much stronger than soft solder, and easier to apply. Check with your local welding supply house, and be certain to purchase the proper flux. There's a black one on the market that is reputed to be superior to the ordinary borax product, a white paste that is applied to the joint before soldering. It is much easier to overheat than the black one, and is highly recommended for joining dissimilar metals.
Reply to
Harold and Susan Vordos
A tin-silver solder works great on stainless, provides good color match, is considerably stronger than plumbing solder and works at low temperature -- about 430F. Harris Staybrite is one such material. Flux can be Harris Staykleen or ordinary tinner's fluid.
It will handle thermal cycles. It's used in refrigeration and in food & beverage applications. Joints must fit well; it is quite fluid and doesn't "bridge" gaps well. Staybrite 8 is a similar material with higher silver content, will bridge gaps better because it has a plastic range. It's harder to find, though.
A stronger material would be a silverbrazing material. It may not be a good color match because most silversolders contain some copper, and you'll get some discoloration of the stainless from heat. It runs at about 1200 to 1400F. It'd be stronger than you need here; I'd go with the Staybrite.
Reply to
Don Foreman
Look at this. Four reasoned, polite, and helpful responses in less than 24 hours. Maybe there is something to this Internet thing after all.
Reply to
Thanks for the lead. I researched Stay Brite. It is a little hard to find, but is available mail order, anywhere from $50-$90 for a one pound spool. However, McMaster carries a silver/tin solder with just about exactly the same composition (from the MSDS sheets) for about $35. If anything, it has slightly higher silver content. It doesn't list a brand, but I wouldn't be surprised to see that it is Stay Brite when I get it. They also have a flux that appears to be very close to Harris Stay Clean (again from the MSDS sheets). Thanks for the advice.
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