Soldering immersion flange to stainless tank

[Kev888]

Hi all,

Some time ago I got this ex-food industry stainless tank from George Beck - top bloke actually, I'd arranged to go up there for a smaller one but we discovered a fault with it so he upgraded me to the 113l/25gal one at no extra cost!!

Anyway its a nice thick tank and I'm wanting to install an immersion element in it. I used a mechanical flange in my hot water cylinder HLT, but I'd prefer a traditional brass solder-in one for the boiler due to it having fewer crevices. Trouble is I've never soldered to stainless before so thought I'd sound it out with you all. I've discovered a source of stainless steel flux and silver bearing soft solder (at a price) which should do the job but have no idea how easy this would be compared to say soldering a flange to a normal copper cylinder.

If it sounds too tricky I may consider gas instead, but I've never gone there and the idea of having to deal with another supply of gas cylinders puts me off, although the heating power is attractive so i haven't dismissed it.

Anyone soldered anything like this isn the past - was it much worse than soldering brass to copper?

Cheers
Kev

[Aleman]

It is straightforward to soft solder brass to stainless steel as long as you have the right flux The best I have found Is This 2207 acid based flux from Cup Alloys Of Chesterfield. It's aggressive enough to remove the chromium coating on the stainless and allow the soft silver solder to flow. . .. Temperature for soft silver solder is around the 205 range not really much more than standard lead free solder. . . . joint strength should be adequate as long as the flange is an engineers fit in the hole. The biggest issue I've found is that the pot acts as a great big heat sink . . . but that was using brazing solders at 450C

[Kev888]

Thanks for that Aleman - just what I was hoping. Also thats exactly the flux I'd been thinking of, which is excellent as it means I'm on the right track.

I've got a decent quality blow torch that I use propane with but it can also take mapp if necessary so 'hopefully' the heat won't be a problem for just soft soldering. I understand from t'internet that overheating some kinds of stainless can be a problem - not sure if 316 is one of those but perhaps the propane may be safer if it works.

Thanks again,
Kev

[bigdave]

Do you not fancy a burner for this one?

[Subsonic]

I've soldered stainless ok. The biggest problem is as per Alemans comments. It acts as a good heatsink and getting the temperature high enough is tricky, can be done though. Subsonic

[Kev888]

BigDave, yes in some ways a burner would be good - lots of power and no holes needed. In other ways not so good - mainly having to find and muck about with propane cylinders instead of just plugging it in, but also the extra noise and venting needed for inside use. All in all I felt electricity was just easier, but I agree its certainly not an easy choice - maybe I should look again.

Subsonic - thanks for that, also reassuring. Just to ball-park it, do you think a good quality hand torch like this which takes those professional propane or mapp disposable cylinders is enough or were you using the big torches used for cutting/welding and so on? Mine is a similar but older cheaper type of thing to that link.

Cheers
Kev

[bigdave]

Inside as in the house? Oh.... no I probably wouldn't use a gas burner in the house. Knowing my luck I'd burn the bloody thing down! In the garage then yes (concrete doesn't burn that easy) or outside but I can understand why you'd not be keen on a wacking great big burner blazing away in the front room! Although you could save a bit on heating in the winter!

[Kev888]

Inside as in the house? Oh.... no I probably wouldn't use a gas burner in the house. Knowing my luck I'd burn the bloody thing down! In the garage then yes (concrete doesn't burn that easy) or outside but I can understand why you'd not be keen on a wacking great big burner blazing away in the front room! Although you could save a bit on heating in the winter!

Yes it is a concern. I do boil outside at the mo, but was thinking of a more permanant setup in my conservatory when I get the up-scaled AG system going - mainly because its closer to the water supply than my shed/garage. Its not much of a concervatory to be fair but its got a wooden frame and plastic roof so not so inferno proof, and it is attached to the house. Its not much of a house to be fair, but... Anyway, guess I could relocate to the garage if I were to want gas, just means more lugging of water, but so far it looks like the immersion flange will be a goer if my torch is up to it.

Cheers
kev

[liddley]

Hi guys,
Just following your thread regards fitting and immersion style heating element to a stainless steel tank, I was considering this too, but wondered where I could get a boss from, with the right thread to accept the brass immersion element?
Or have you guys cut the boss from a copper cylinder or just solder the brass immersion element direct to the stainless tank??

[Kev888]

Hi,

tool station do two types of 2 1/4" threaded flange - a mechanical one and a solder-in one. My plan was to start with the solder in one - as it in theory offers fewer crevices to keep clean. But if that doesn't work I have the mechanical one to fall back on. That seems to be the best way around as the mechanical flange needs a bigger hole.

However, I since found people using the solder-in flange as a back nut, so they make a hole just big enough for the threads of the element to pass through and screw on the flange using a band type wrench. The only thing that puts me off about that is the force needed to create a seal is massive even with a mechanical flange thats designed for this, so with my thick walled tank I'm suspicious of getting enough grip on a slender ring. However, it needs the smallest hole of all the methods so could be worth a try as the first attempt. For info, Garth did this and it looked excellent - see a little way down this thread; think there's also a link somewhere in that thread to a long discussion about using elements re electrical safety.

I'm having a little trouble getting any flux thats suitable - I found some In B&Q that claims to be but I did a test and for me it seemed to be close to useless, and the chap selling the proper stuff mentioned above seems a little reluctant (apparently it can't be posted so the idea is you collect it at a craft exhibition; but in the absense of one of those I'm trying to arrange to visit him).
EDIT: though I'm now finding possible alternatives such as this


Cheers
Kev

[pantsmachine]

I'd be tempted to forget the soldering idea and get a s/s threaded female boss and weld it in place. I'd rather have the confidence of a welded fitting than a soldered one especially at those volumes and if your moving it about its asking to get twatted. Does crevice really matter in your boiler that much? Good luck whichever way you go.

[Kev888]

Thanks for the thoughts - and the good wishes!

Yes I'm sure you're right - welding could be the best solution all round, but it means I'd have to get someone else to weld it (as I only have soldering/plumbing type tools/skills), and I quite enjoy the satisfaction of doing it myself (foolish as that probably is ).

Of the DIY options, soft soldering just seems to be the simplest and cheapest way to get a good reliable seal against a rigid wall - the flanges are designed for soldering into domestic hot water cylinders where there's much more pressure/head than I have in the boiler, and they have enough of a surface area that it should be a 'reasonably' tough joint, so i'm fairly optimistic about it at the mo. I'm just being delayed by the scarcity of suitable flux.

Of course, it also helps that the mechanical flange is there as a fall-back - and I guess if all goes totally pear-shaped then there's nothing to stop me getting it welded as you say, so thanks for that idea. The key thing at this stage is I've hopefully thought through the options enough so that I'm not in any danger of wrecking my stainless tank - the biggest decision of all was to make such a hole in it, instead of moving to gas..

Thanks again,
Kev

[cockneyron]

Just a thought ,if your soldering fails and you take it to be welded you might find that any residual solder runs into the weld and ruins the weld or any gases given off by residual flux or solder interfer with the argon gas used in welding .

[Kev888]

Just a thought ,if your soldering fails and you take it to be welded you might find that any residual solder runs into the weld and ruins the weld or any gases given off by residual flux or solder interfer with the argon gas used in welding .

Yes thats true. I should be able to get rid of the solder relatively easily though - I have access to both sides anyway. Hopefully it won't come to that - even if the solder flange didn't work for some reason I should be able to get the mechanical flange sealed somehow - said the voice of ill-advised confidence

Cheers
kev

[Talisman]

Just out of interest why you putting in a brass piece to add an element. why not put in a Stainless piece and stainless weld it?