Soldering stainless with plumbing solder... it is possible

[newerbrewer]

Just wanted to let everyone know that it is possible, and pretty easy to solder stainless with plumbing solder and propane. You will not get the strength of a weld, or anywhere close but it will fasten 2 pieces of metal together leak free if done right. Here is what I did:

Materials - Auto body sandpaper (or any other i suppose) fine grit, Harris Stay-Clean Liquid Flux - important that you buy the liquid not the paste, regular lead free plumbing solder (I use oateys).

1) Get your surfaces impeccably clean. Clean, then lightly sand
2) Apply flux to areas you want solder. I use a q-tip
3) Heat with propane torch
4) Re-Apply some more flux
5) Solder like you would copper

Note, be very careful with this flux. Use in a well ventilated area... you don't want to breath in the fumes. Works like a hot-damn. Good luck.

[newerbrewer]

Almost forgot... always read the MSDS (available on the Harris site), avoid contact with skin and all that stuff... Also to clean (from the harris site):

What is the procedure for removing Stay Clean® Flux residue?

Soak soldered parts in two ounces tri-sodium phosphate or bicarbonate soda added to one gallon of water heated to 120ºF.
Rinse in detergent treated water, heated to 120ºF.
Rinse in clean water heated to 120ºF.

[MuleKicker]

So I take it you are using an acid based flux? Im glad to here the success story, I have some soldering to do.

[newerbrewer]

I've tried lots of fluxes... only this specific one ever worked for me. Again, no paste... only liquid. Get it clean and lightly sanded. Good luck. And yes.... acid.

[LWTCS]

Agreed that proper acid flux is key to not wanting to stick an ice pick in your ear while soldering copper and stainless.

I have had success using paste flux however (but it sucks).
A commercial grade iron would be an excellant tool also.

It is doable.

Great tips brew.

[newerbrewer]

Not just doable, its pretty easy once you find the right flux. I knew it was possible using very high silver content solder but that was way out of my budget. The plumbing solder works perfect, its cheap, we all have lots... propane heats'er up well too. Good luck.

[rednose]

Do someone know a good online supplier for Stay-Clean?

The ebay suckers ask 25$ for shipping a 5$ four ounce flask.

Just bought some absinthe spoons with almost the same weight and paid 5$ for shipping to EC.

[squidd]

Well, here's my contrarian experience.

I have used paste flux exclusively, with an electric soldering iron (275 watts IIRC) to join SS frying pan to SS stockpot to SS stockpot to SS bucket. The latter is a water seal.

The flux is Lenox Sterling and is water soluble. It contains zinc chloride (no acid that I know of) and washes off with a damp rag. I've used it with both Sterling and Oatey lead-free solders.

These combinations also work a treat for joining SS to copper.
Available at Lowe's.

squidd

[ozone39]

I'm very curious as to how this joint will respond to continuous heating and cooling cycles.....

[squidd]

Good point Ozone, and I don't know the definitive answer.

Are your referring to soldered joints in general, or to my particular methodology ?

It will be a while before I can find the time to complete the head and subject the whole still to a number of cycles.
So far, the boiler has had one cycle to test for leaks and it's tight.

Your concern probably relates to the different expansion coefficients of tin and SS.
This would certainly be less of an issue than it would be with tin and copper.

Also the heating and cooling cycles are relatively gradual rather than abrupt; that should help mitigate the concerns.
In any case, I will report in due time.

squidd

[squidd]

Arrgh,

Just realized you were probably referring to a copper/SS joint.
Don't have the answer to that either.

squidd

[newerbrewer]

Squid... that's a pretty big soldering iron, I don't have anything like that around here. Glad you have things working for you. I was not speaking of what doesn't work, just what does for me, good to have other contributors on the forum... many minds make short work of difficult problems.

Brew

[squidd]

Hi Brew,

The reason I like using an iron is the elimination of potentially (for me anyway) overheating and discoloring the thin stockpot material.

Like you I thoroughly clean the surfaces to be joined, after which I scrub them with a Stainless Steel brush.
The fluxed surfaces are then easy to tin with the iron as the solder wets quite well.

squidd

[WalkingWolf]

Soldering Stainless and Copper has frustrated the shit out of me. I've tried it and was unsuccessful more the than once (and more than twice) so I elected to go with the easy-flange construction. I really like how the flanges turned out but am still frustrated by the fact that I was unsuccessful. I think I'll give this another go just to see if I can get-r-dun.

[LWTCS]

I would definitely recommend brazing anything that had to supply any kind of load bearing capacity.

I sprung an ugly leak on the dog dish so I figured to bump the solder withj a bit of heat. Try to get the solder hot enough to collaps and fill,,,,,,,,,NOT.
Soon as the torch flame made contact with the very thin dog dish material,I could hear the metal buckle and pucker. It opened up the remainder of the joint. Had to have an iron fix that big ole leak as the torch was just too hot

Good stout stainless would be much better. My dog dish application is just too thin.

[ScottishBoy]

I used Zinc Chloride to mount my 1.5 inch copper to my SS drain with no problems other than the solder wanting to slip out the gap in the joint. Woked and treat and it seems to a fairly stable solder. I tinned the copper with regular flux and then sanded, cold fluxed, heat from the opposite side until dry, the hot fluxed and soldered. Held pretty well.

That being said, now I have the awful feeling that I will break it on my next run...because thats seems to be the way this week is going.

[WalkingWolf]

I gave this process a go this afternoon. Works really well. Bought the Harris Stay-Clean Liquid Flux as directed and sanded the pieces to be joined. Cleaned well with alcohol. Applied flux and heated up (not up to solder temp) as it cooled down I applied more flux. Fluxed the copper well. Applied the heat to the copper and the joint soldered up well. Of my previous attempts, of which there were several, I never got anything remotely serviceable as a soldered joint . This process worked really well for me and I want to thank you NewerBrewer for the heads up on what worked for you (and now me)

[newerbrewer]

WW: Glad to help. I've learned so much here, just happy to have something to contribute. I know many members have struggled with SS in the past. Glad it worked for you as it did me.

Brew

[Stilly]

I was wondering if several months later there were any updates on how this soldering technique for joining SS to copper holds up after numerous use cycles.

Thank you

[still crazy]

Actually I hadn't noted this post earlier and I also discovered the "Stay-Clean" flux.
This stuff is the balls!!!!
I clean my joint by mechanical means, plumbers roll on copper, Dremial grinder for about a 1/4 " on stainless.
Fit up my joint
Heat the stainless letting the copper which is more conductive draw its heat from the stainless
THEN I drip the stay-clean to the join <<<<<< DO NOT BREATHE THE VAPORS
Hit the join with solder and the solder flows in nice and smooth.

I used it to join a 1" copper female to copper pipe fitting to a 1/32" stainless fire extinguisher.
I could literally stand on the wrench (263lbs) and not break the joint.

Link here to that post. page 2 near the end

http://homedistiller.org/forum/viewtopi ... tinguisher

I am going to be adding some outlets to a few beer kegs later. If anyone wants I will document.<<<<pics

[myles]

I built the hydrid copper stainless inner pot for my double boiler with a very thin stainless stock pot and a copper dome. Soldered using a 56% silver hard solder and borax based flux. It worked a treat altough heat control was an issue with such thin stainless and MAP gas.

However, a word of caution. A few months down the line I had to bin it. The thin stock pot cracked - right along the boundary line between the solder and the stainless. Different expansion coeficients possibly.

I didnt notice at first until I observed that my propylene glycol bath wasn't heating as expected. Rum wash had leaked into the glycol bath and burnt, discolouring and affecting the glycol.

Check your boiler occasionally, I hardly ever took the inner boiler out of the glycol bath. Your boier could be fine to start with but develop a leak later.

[BakerBoy]

I'm building my first still - I've successfully soldered copper to copper and stainless to copper using a butane torch and plumbing solder... but have failed a couple times soldering stainless to stainless...

Reading up on several posts here and it seems more control/success can be had using a soldering iron than a torch (less chance of oxidizing the flux + you can push the pooling solder around)... some have successfully used a 175watt, 250watt and even a whopping 600watt soldering iron... seeing as i'm only really going to be making 4 or 5 stainless solder joins in my lifetime, im looking at a cheap 100watt iron for $20

Is 100watt soldering iron going to get hot enough to solder stainless to stainless?

[maheel]

i am no expert but i reckon if you buy that 100w iron your going to need to do the below pretty quick, i dont think it will be anyway hot enough. (but could easily be wrong)

Is 100watt soldering iron going to get hot enough to solder stainless to stainless?

is key to wanting to stick an ice pick in your ear while soldering copper and stainless.

[rad14701]

For something like soldering SS to SS I'd probably use a true soldering iron that is heated with a flame and then held at the work site... I've done SS to SS with a 225W soldering gun but prefer the soldering iron method... THIS is what I am referring to...

[jake_leg]

I just had some apparent success using a MAP torch, 4% silver bearing lead free solder, and neat muriatic acid flux to seal the join between a thin SS dog dish from the pound store and a brass tank connector. All relatively cheap materials.

First I tinned the tank connector with regular flux. Scrubbed hell out of the dish with sand paper and applied a few drops of acid. Screwed the tank connector together, blasted the inside of the fitting away from the join until hot, then applied solder in a ring around the join. The first time I did it I didn't put it down flat after I had finished and the solder flowed out. I had to repeat the whole process but it worked second time around. Having the joint clamped in the tank connector probably prevented the dog dish buckling too much. After it had cooled down I gave it a good wash to get the acid off. Time will tell if it leaks, falls apart or corrodes but I was pretty pleased with it as a first attempt. The solder definitely stuck to the the SS.

The liquid SS fluxes are generally a mixture of zinc chloride, ammonium chloride, and hydrochloric acid. On heating they all release HCl. Neat pool acid works the same way but requires more care in handling. Safety goggles and protective gloves are a good idea, and do it outside to vent the HCl fumes. Next time I might try 5-10% phosphoric acid as a flux (hydroponics pH down, diluted). It's supposed to be less corrosive if you don't succeed in washing it all off.

[BakerBoy]

You nailed the problem i had... Heating the metal before applying flux is the key - I don't bother applying liquid flux while the SS is cold - heat it up just until the flux sizzles when applied (avoid breathing those vapours)- if you heat the SS too hot, the flux wont flow around to cover more metal, it'll just evaporate.

I'm no expert - but this is what worked best for me...
1) heat metal slightly until the flux sizzles when applied
2) apply flux all over the metal parts to be joined
3) heat metal fully until at solder melting point
4) solder that bad boy

I use a cheap $35 propane torch and plumbing solder

In NZ & AUS... Bunnings sells a liquid flux called "Weldwell - Duzall" (green bottle) - its 'hydrochrolic acid' based liquid flux and works great - i could never find that "stay-clean' brand the US guys talk about

[jake_leg]

Glad it worked for you! Sounds like we both got the solder to stick OK.

I should say that I am lousy at plumbing and have no technical expertise to speak of.

I have read some advice to flux, heat, and then reflux the SS. I suspect that heating before fluxing will tend to reoxidize the SS. Maybe not if you heat gently. I chose not to flux twice because I had clamped the tank connector on before heating. I figured that the fitting was covering up the SS and preventing it oxidizing. Also I didn't want to be adding neat HCl to a hot bit of metal without lots of protection. The fumes were pretty hairy as it was.

I have also heard that if you are heating SS directly you should use a carburizing flame i.e. a bit yellow and sooty. Same reason I think, to avoid excessive oxidation. Again I didn't do that. I gave it full blast because was aiming the flame at the tank connector.

Harris Stay-Clean is ZnCl, NH4Cl, and HCl according to the datasheet. I'm sure there are equivalent brands.