Soldering copper to stainless steel

[Corn Cracker]

I finally got the right flux(thanks for the suggestions), it says it works with any solder to make a solid joint, it was 6 bucks at the a/c supply for a small bottle. I used the sterling solder which is a typical solder for copper. It held strong

Harris stay clean liquid flux and any plumbing solder

Pic turned,

MOD EDIT : I had to , it was hurting my neck

[Corn Cracker]

I made this post so that other folks can search it and get straight to the info, I dug around for a while looking

[acfixer69]

That solder is not a mgf recommended soldering for dissimilar metals SS /copper. I would advise you to do a leak check after a few boiler runs. After the different rate of expansion due to heat the metals and lack of proper wetting, it is likely to crack at the SS seam. I've seen this many times. A silver bearing solder is required per reliable mgfs.

[Corn Cracker]

Global mod, damn!
point taken.

I've been doing industrial plumbing for over 20 years, I've never heard that before although, it has been mentioned here at least twice since ive been trying to do this, that some folks here use that flux with regular plumbing solder with good results.

Sorry for the confusion, delete the post if you would

[acfixer69]

No need to delete that flux works with all solder I have used as you mentioned. However the solder is for typical plumbing joints, copper to copper or copper to brass. For copper to SS or carbon steel it needs some silver to wet proper. Been that way all my 50+years in the trade even the 10 years in Texas.

Posted as a member. Mod is for back room, out here all equal

[Corn Cracker]

I understand your point of the thermal expansion of different metals, thanks.

As far as structural strength of that butt joint, it's really strong, I tried to break it, it wouldnt.

[shadylane]

For copper to SS or carbon steel it needs some silver to wet proper.

Based on my limited experience, the higher the silver content the easier it is.

https://weldingproperty.com/brazing-cop ... ss%20steel.

[acfixer69]

For copper to SS or carbon steel it needs some silver to wet proper.

Based on my limited experience, the higher the silver content the easier it is.

https://weldingproperty.com/brazing-cop ... ss%20steel.

That's true for brazing but for soldering some 6%,7% is fine

[Corn Cracker]

I'm stopping back at the ac supply house today to get a roll of silver solder and some medium temp brazing rods. I can get stuff on a cash ticket through the company account and that drastically reduces pricing.

[Steve Broady]

That joint looks good to me. I’ve made several things using lead free plumbing solder and that flux, and so far the only joint that I’ve had fail was a butt joint between a stainless ferrule and a very thin stainless pot lid, where I’d hung way too much weight off the end and loaded the joint sideways. It finally cracked and broke on me, so I resoldered it with a copper flange to connect the two and it’s still going strong today. A thin layer of solder that’s in tension, has the absolute minimum surface area possible between parts, and subject to regular flexing is pretty much the worst case scenario and I’m not at all surprised that it failed. I find that flagged or overlapped joints where the solder is in sheer to be a lot more reliable - which is just good practice in general, to be honest.

Not trying to argue with an expert, but in my somewhat limited experience that solder will make a serviceable joint between copper and stainless as long as it’s done well in the first place, the joint has at least a little mechanical integrity of its own (I always flange thin parts now, or use copper rivets), and you don’t severely strain the joint while it’s in use. It’s not the strongest possible way to join two pieces of metal, but it seems more than strong enough for our purposes on 99% of the things we’d need it to do in this hobby. Maybe time will change that opinion.

And yeah, it can be a pain to get that stuff to wet out on stainless steel. Careful heat control, immaculate preparation, and brushing with flux while its molten all seem to help a lot.

[Rusty Ole Bucket]

I'm stopping back at the ac supply house today to get a roll of silver solder and some medium temp brazing rods. I can get stuff on a cash ticket through the company account and that drastically reduces pricing.

I just did a bunch of stainless ferrules to 2" copper and a 6" stainless ferrule to a stainless keg top. I used Harris Stay Clean flux and Harris #8 solder and it worked great. Not to mention the copper to copper stuff was effortless with a little heat management using Harris products. I did a bunch of research here and talking with some of the long time members and that's the magic combo, after doing it, I would have to agree. I used Oatey plumbing stuff for my initial build, but the Harris stuff is worth the extra bucks in my opinion.

Rusty

[Corn Cracker]

I'm finding whether soldering or brazing copper to stainless, the flame really doesn't need to be put directly on the stainless too much at all, start heating a couole of inches up on the copper and work it down to the stainless, it gets hot as the copper heats up and if brazing with higher temp rods, introduce the rod to the flame to heat it up before brazing