Welding a copper boiler?

[GreenTwin]

I have a copper boiler design going, and have contemplated TIG welding it.

Steamchick and I had a lengthy discussion about this.
As I recall, you don't need a special copper for welding boilers, but check me on that.
I did not buy special copper.

And it would seem that you need a lot of amperage to weld copper.

It seems one way to circumvent needing a high amperage TIG machine is to preheat the copper in a kiln.

I have seen several TIG welded copper boilers online, and it seems to be a successful and fully accepted method, if done correctly.
One would have to be well versed with TIG welding.

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[ianjkirby]

There was a discussion about someone building a stainless steel boiler a few years ago, and they all but beheaded the guy for suggesting such a thing.
They rattled off a laundry list of reasons why stainless won't work for a boiler, and how that would be extremely dangerous.

I do recall that the folks "in the know" about boilers were admant about never building a boiler from stainless.
And I seem to recall it was against code around here too.

I was contemplating a stainless boiler build until I read the thread about stainless and boilers.
I wish I would have saved that thread so I could mention the specifics of it.

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The Australian code mentioned above for miniature boilers made of Duplex Steel is not stainless steel as such. It is a special alloy (2205 rings a bell; its a while since I was involved; Sandvik produce it) which avoids the major issues with "ordinary" stainless steels, primarily "chloride stress corrosion cracking". There are several existing boilers in NZ and Australia which have given good service, and none have yet shown any concerns.

 

[peterl95124]

its hard to believe that stainless can't make a good boiler, look at all those Jensen, Mamod, Wilesco, etc, commercially made model steam plants that all seem to have stainless boilers ???

 

[Mechanicboy]

its hard to believe that stainless can't make a good boiler, look at all those Jensen, Mamod, Wilesco, etc, commercially made model steam plants that all seem to have stainless boilers ???

These boilers in toy steam engines is made of brass with nickle plating. Stuart steam is produce the copper boilers.

 

[Shopgeezer]

My dalliance with turbojet models has shown me the difficulties of welding the stainless steel combustion chamber for a model. Best done in a vacuum chamber. My plan was to buy a sandblasting cabinet and rig the Argon tank on the tig welder to trickle into the cabinet. Cover the rubber gloves built into the cabinet with welding gloves. Run the tig cables in through a rubber grommet, put the burner cage setup on a rotating table, and take the auto darkening lens from a welding helmet and fasten it over the window in the sandblast cabinet.

If only I had enough lifetimes to get that all done.

 

[peterl95124]

I've been scouring the internet for why stainless should be avoided for boilers, and its very hard to find reliable information, and there are commercially made stainless steel boilers available today. the only thing that stands out is the experience of the nuclear industry where some stainless experienced chloride induced corrosion and stress fracturing, but I dare say we don't operate at the pressures and temperatures of nuclear and we don't plan on operating 24/7 for a hundred years, and we could use distilled water like they do if it came down to it.

My guess is the Brits simply don't want to go through the time and effort to establish a safety record with stainless for the necessary insurance, which is entirely understandable, but in other countries it seems no stainless model boiler has ever failed?

 

[Weldsol]

I've been scouring the internet for why stainless should be avoided for boilers, and its very hard to find reliable information, and there are commercially made stainless steel boilers available today. the only thing that stands out is the experience of the nuclear industry where some stainless experienced chloride induced corrosion and stress fracturing, but I dare say we don't operate at the pressures and temperatures of nuclear and we don't plan on operating 24/7 for a hundred years, and we could use distilled water like they do if it came down to it.

My guess is the Brits simply don't want to go through the time and effort to establish a safety record with stainless for the necessary insurance, which is entirely understandable, but in other countries it seems no stainless model boiler has ever failed?

Hi Peter yes I never got an answer around 15yrs ago I put the same question to a UK model forum and got loads of you can't do that, so I questioned their reasoning as to why and got the following responses
1. Chloride attack at the water line
2. When a copper boiler lets go it bursts a stainless one will shrapnel
3. Nobody uses stainless for boilers
4. I would not get an approval on it
5 We have always used copper or carbon steel
I explained how I would overcome these problems.
1. Use Duplex / Super Duplex to overcome the chloride attack
2. Fit a bursting disc ( a disc which will burst a determined pressure)
3. They were already allowing stainless steel boilers on scale models in Belgium
4. We were in the EU then so in theory and weld procedure was transferable for use in UK
5. Without researching on different materials and methods we would still be living in caves
After toing and froing the final killer was No one would insure it therefore it would not be allowed for use in UK
I'm sure if I had pursued this and thrown a lot money and with tests etc, it might have got through.
It was cheaper to just do a carbon steel boiler
Paul

 

[plipoma]

I think stainless steel suffers from stress crack corrosion, it doesn't do well under stress.

 

[peterl95124]

I think stainless steel suffers from stress crack corrosion, it doesn't do well under stress.

And copper work hardens under cyclic stress and then breaks, that's why brake tubing is steel not copper. The problem with this discussion is there are no facts relevant to model engine boilers only thoughts.

 

[Mechanicboy]

... that's why brake tubing is steel not copper.

It's not true, we are using copper tube when we are replacing the old brake corroded steel tube with the new brake copper tube. Greetings from car mechanic.

 

[peterl95124]

It's not true, we are using copper tube when we are replacing the old brake corroded steel tube with the new brake copper tube. Greetings from car mechanic.View attachment 141527

You are probably mistaken, that is most likely a copper-nickel alloy, or copper plated steel, the following is off the internet --->

What is Copper-Nickel Brake Lines?​

In the olden days, copper brake lines were a hazard waiting to happen. In 1965, brake lines were the cause of 251,000 car accidents. The Society of Automotive Engineers determined the corrosive deterioration of the steel brake line was at fault.

The industry switched to brake lines made from 100% copper. These lines burst from the pressure causing even more accidents. People demonized the copper brake lines.

Fast forward into the new millennium. Then came the invention of a new alloy that was 90% copper and 10% nickel. This was superior to steel and could handle far more pressure than a 100% copper line.


<--- but we don't use cupronickel for boilers, IIRC because of galvanic corrosion between the silver we braze with and nickel leading to stress cracking, which is a shame because cupronickel is so much stronger than pure copper.

 

[Mechanicboy]

You are probably mistaken, that is most likely a copper-nickel alloy, or copper plated steel, the following is off the internet --->

What is Copper-Nickel Brake Lines?​

In the olden days, copper brake lines were a hazard waiting to happen. In 1965, brake lines were the cause of 251,000 car accidents. The Society of Automotive Engineers determined the corrosive deterioration of the steel brake line was at fault.

The industry switched to brake lines made from 100% copper. These lines burst from the pressure causing even more accidents. People demonized the copper brake lines.

Fast forward into the new millennium. Then came the invention of a new alloy that was 90% copper and 10% nickel. This was superior to steel and could handle far more pressure than a 100% copper line.


<--- but we don't use cupronickel for boilers, IIRC because of galvanic corrosion between the silver we braze with and nickel leading to stress cracking, which is a shame because cupronickel is so much stronger than pure copper.

We has both copper and cupronickel who are darker and more stiff to form in curves than copper tubes for brake in the cars when we're replace the corroded steel tube.
I have never seen a cracked copper tube caused by the brake pressure since I have worked and still work for 30 years as a car mechanic.

 

[Steamchick]

Original equipment brake lines on modern cars are steel, but very cleverly protected from corrosion by the corrosion-resistant coatings applied, and care in the factory to prevent damage of that coating. (Well legislated, so brake systems MUST be serviceable for a long time). So, they last well in excess of 10 years, unless stone chipping or road grit abrasion deteriorates the anti-corrosion coating. On top of that, the stringent MOT rules in UK, Europe, Japan and other countries ensure that the car will not be permitted on the road unless the brake pipes are corrosion-free (on visible outside surfaces). That system seems to work and permit the copper-nickel brake lines for after-market use. Bin there, dunnit! (14 year old Peugot, 15 year old Saab, 13 year old GM, etc.). Same applies to the fuel lines securely fixed to the car body. The car testing includes 1200 hours in a salt-spray chamber - after which no corrosion is permitted on brake lines. The stainless steel "corrosion-resistant" fluorescent lamps lasted much longer - but were rusty after 60000 hours and needed replacement. And these were NOT stressed by pressure.
Incidentally, I use "Copper" car brake tube for the steam lines on my static models, as it is relatively cheap and easily available "from the car shop", and (I think?) adequate strength and serviceability. - Am I wrong to use that pipe?
Back to model boilers: They are also examined and tested annually, then certified by an inspector so the Insurance covers the club member. The (correct) use of means they are not exposed to "industrial" service, but usually much less than 500 hours per year - like a family car's usage. If there is corrosion in a silver-soldered copper boiler, then it usually shows itself as a steam leak at a joint, but not a catastrophic failure. (Possibly from bi-metallic electrolytic corrosion of the silver solder? Or Scale build-up and consequential local overheating? Or a short-term low water level leading to local overheating? etc.). Therefore, the combined materials, manufacture, regular checks, service life, and due diligence of the Modelling community keeps us safe, not just the correct material choice. - IMHO.
K2

 

[Steamchick]

And here is a Gas fired Stainless Steel boiler in use - 5in Pacific loco, home design by Joan Lluch (Spain):

Ken

 

[GreenTwin]

You would not catch me within 1000 feet of any stainless steel boiler.
Maybe they are safe, but not according to what I have heard.
Better safe than sorry.

.

 

[Weldsol]

I think stainless steel suffers from stress crack corrosion, it doesn't do well under stress.

That is another reason for using the correct grade of stainless material and filler material and the correct weld procedure, I'm afraid a lot of people see stainless as a one off shiny material and do not realise how many grades there are, the same applies for machining such as 303 is a free cutting stainless but try and do it with say 304 which work hardens then wonder why tools blunt or taps break.
Every stainless type is made for specific applications
paul

 

[Steamchick]

Joan Lluch was a professional chemical plant engineer, designing equipment to do chemical stuff without being dissolved by the stuff. He used his expertise to design the boiler for efficient steam generation from a wire gauze gas radiant of around 30kW. Complete with economiser, superheater, etc.
I understand he got the boiler made professionally by a certified company. To satisfy Spanish rules...
I am not advocating "home build " of this.
K2

 

[plipoma]

Here is a good article about stress crack corrosion in SS, Stress Corrosion Cracking- SCC: In Depth Guide

 

[peterl95124]

Here is a good article about stress crack corrosion in SS, Stress Corrosion Cracking- SCC: In Depth Guide

Plipoma, AHHA !!!, that's the kind of factual engineering information I've been looking for. THANKS !!!

so its not just the nuclear industry, but also the chemical, petro-chemical, pharmaceutical, and food industries. This still leave the question, is the chlorine in tap water sufficient for SCC (at boiler operating temperatures), which I don't find answered.

and there's still some confusion, some sites say SCC results in catastrophic failure, others say the problem results in leakage that's impossible to repair and instead the entire thing has to be replaced.

it sounds like if you want to use stainless it should be duplex-stainless (like SAF 2205) and be professionally TIG welded using back-fill and approved filler rod, and then professionally inspected, that might be a tall order for a home shop model builder.

meanwhile you can buy commercially made 100psi steam generators made out of 316L. And there's the ubiquitous cappuccino and espresso makers which I'll guess are made of stainless(?) and obviously use tap water.

so the truth is still evasive...

 

[GreenTwin]

Can anyone really afford to find out the hard way that their stainless boiler stress cracked, and it explodes at a show or something?
This is not a liabilty I can or would accept; way too risky.

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