Welding a copper boiler?

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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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this is a rhetorical question about a problem that should be answered with engineering data.
 
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.


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Should be de oxygenated copper, C106 here don't know what your code would be
 
Should be de oxygenated copper, C106 here don't know what your code would be

c122 plumbing copper is what we all use, about 99.9% pure, phosphorus de-oxidized high residual phosphorus. electrolytically purified fully de-oxidized copper, c101, is for electrical, more like 99.99% pure, c106 is in the later category so at least in the USA is what plumbing copper is made of.
 
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Sorry that should be de oxidized as you say not de oxygenated but the C106 is still the usually suggested grade.
 
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 ???
I have the same thought. A walk through a food processing plant will likely have all kinds of stainless unfired pressure vessels working at all kinds of pressures. And I have seen at least one commercial boiler size of about 30000 lbs per hour and maybe 300 psig in operation. It was a rare one but it exists. Now it could be only the drum was stainless but I do regret now not to have taken a closer look. Was busy at the time and wanted to get what I had to do done so left it alone.
 
Sorry that should be de oxidized as you say not de oxygenated but the C106 is still the usually suggested grade.

I believe there's some UK - USA nomenclature issues, looking at applegate.co.uk

your C101 ETP (electrolytic tough pitch) is what we call c110 ETP, and is about 99.95% pure

our c101 OFHC (oxygen free high conductivity) is 99.99% pure for electrical wire

but your C106 DHP (phosphorus deoxidized) doesn't exist here, we use c122 (phosphorus deoxidized) which as near as I can tell is the same thing, at applegate its listed as a related specification (whatever that means).

here in the USA if you're buying sheet metal its mostly c110 and some c101, but as far as I can tell phosphor deoxidized isn't available in sheet.

here in the USA if you're buying tube/pipe its all c122. we would have to saw it and unroll it to make our own sheet.
 
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.
If it was TIGged with the same material there would be no galvanic corrosion.
 
this is a rhetorical question about a problem that should be answered with engineering data.
for one thing, if it is a water tube type boiler, it woud NOT explode. At most, a tube wou;d split and blow out a line of steam which could cut you in half, or a line of water that turns to steam as it blows out. But explode? Naught.
 
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.
The model live steam locomotive hobby is bigger per capital in England and they use copper boilers.
 
I have the same thought. A walk through a food processing plant will likely have all kinds of stainless unfired pressure vessels working at all kinds of pressures. And I have seen at least one commercial boiler size of about 30000 lbs per hour and maybe 300 psig in operation. It was a rare one but it exists. Now it could be only the drum was stainless but I do regret now not to have taken a closer look. Was busy at the time and wanted to get what I had to do done so left it alone.
Yes, I also find it strange that quite a few people disagree with using stainless steel as a steam boiler
My goal is to make a steam train, and the boiler will definitely be stainless steel
 
Interesting to note a couple of comments in the paper:
https://www.materialwelding.com/stress-corrosion-cracking-scc/# "Even though SCC is a brittle kind of failure, the cracking hardly ever propagates rapidly enough to cause a catastrophic failure, even in the case of vessels which operate under pressure".
# "In austenitic stainless steels, SCC can occur in the unwelded parent material due to residual stresses from cold working or service stresses.
In the welded products where welding may add to the stresses, SCC can occur both in the parent plate and weld-metal. The most significant environment causing SCC is aqueous solutions of chlorides at elevated temperatures."
# "the preventive measure consists of avoiding the sensitization of the stainless steel by appropriate material selection or welding procedure control. Another effective measure is of course control of the environment." (I reckon many businesses capable of making certified pressure vessels in stainless steel will have suitable processes to minimise residual stresses in boilers and heat exchangers: But the "hobby" welder will probably not have such expertise and capability).
# "In the welded products where welding may add to the stresses, SCC can occur both in the parent plate and weld-metal. The most significant environment causing SCC is aqueous solutions of chlorides at elevated temperatures". - Thus, it would seem sensible practice to avoid TAP water that has been processed by the addition of Chlorine/chlorides and Fluorides. Natural rainwater should be OK in this respect.

"nuff said"?
K2
 
Peter 195:
Your statement "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"
A good guess, and I suspect nearly all true. But we Brits have a working standard for pressure vessel and boilers covering all materials, and as Model Engineers have a "special clause" permitting Silver Soldered Copper Boilers for our model use to be outside some of the regulations. Probably because our laws are based on "precedent": If we have done it successfully for a long time and no-one got killed or maimed, then we can carry-on doing it - for now.
But until the last few decades, stainless steel was expensive, (e.g. In the 1970s most public toilets were glazed ceramic, now (I.E. this century) they are stainless steel - due to cost!), so when "expensive", Brits don't use it for their hobbies. Hence such boilers would have to comply to latest regulations for design, materials, manufacture, etc. - which makes them expensive, thus not first choice for hobbies.

And many of us have "Old blow-lamps" - or modern ones - for heating so we do not need to invest in expensive welding equipment for our silver-soldering. - Just a few fire bricks and a bucket of sand. Some of us like to retain and practice the skills we learned in the 1960s (or whatever century) and thus do not need "modern technology" for a practical result. Many models are made to maintain the memory of technology from decades and centuries past. - They were not intended to be made by "modern methods with modern materials, etc.". And they are for hobby use, not commercial duty, as reflected in the legislative special clause and insurances.
K2
 
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.

.
Carbide precipitation comes to mind with stainless steels. Thats why many grades have an "L" suffix to there grade (ASTM austenetic grades). Having said that elevated temps for to long a period will cause carbide precip and the stainless will rust. Many guys weld either to hot or to cold and with a very slow travel speed inputting way to much heat and then continue welding without maintaining an interpass heat of about 300F.
Having said that I've tig welded type "k" copper pipe to copper fittings with argon and turned out visually acceptable.
 
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Having said that I've tig welded type "k" copper pipe to copper fittings with argon and turned out visually acceptable.

Does visually acceptable mean it looks good from the outside, but not so much from the inside? Were the welds structurally acceptable to you?
 
your solution is interesting as we did the same thing to weld some stainless project that could not be back purged there is also something call glove bags these are plastic bags with gloves built in You put the parts in then pull a vacuum on the bag then back fill with argon .

I use a double regulator so I can use back purge where possible I even use this when building race car chassis by drilling holes in joining tube joints then pull vacuum or at least put argon in from one end then pull the argon out with the vacuum pump you get a reasonably inert interior it’s surprising how nice welds on 413 look compared to non purged welds You get no sugaring inside I like the sand blaster cabinet idea but you realy have to clean it as any dust left in it offers huge surface area for plain air to stay on we pulled vacuum first as well as possible then introduce argon if you keep pulling vacuum you use huge amounts of argon but it just increases the charge cost. Most of the time customers don’t complain as very few shops will go to this much trouble to produce top quality welds . Almost all of what we did like this had certifications required that were don by customer inspectors. I worked in a battery r&d lab there were a number high vacuum glove boxes for TIG welding. The really high vac chambers were used for laser welding with the beam shot through special windows.
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.
 
Does visually acceptable mean it looks good from the outside, but not so much from the inside? Were the welds structurally acceptable to you?
As far as welds go the coupling to pipe joint would be classified as a lap joint or if it were carbon stainless or any other material it would be called a "socket weld" which uses a fillet weld to fuse the two together.
Being a pipewelder by trade and looking at the exterior and interior I would say that is an acceptable weld visually. However unless tested for mechanical qualities through destructive testing the visual means nothing
 
id avoid copper like plague the Tig heat gets it too hot even with heat sink this sneaks it each time the boiler gets up to pressure it stresses the material ultimately it will fail over heating would be very dangerous . There are lots of model copper boilers most secure to corrosion . They may look nice but that’s only on the surface . Now stainless also work hardens if you Schubert it you will see tools dull very quickly carbide works ok but you nee a ridged machine most China made small lathes are too flexible even mills suffer . Next few weld shops will mess with hobby stuff especially steel . I think most home TIG welders simply don’t have real working experience welding and selecting proper material I have a double argon regulator so I can back purge almost any weld condition . If you don’t know why I do this then you are not qualified to weld stainless Stainless is a nice expensive material . Next somehow you are going to have to hydraulic-test your new boiler you area may require an inspector to be present this process is relatively easy if you are equipped to do it. By now you have spent a fortune on material and testing

You can probably make a nice alloy steel boiler but to be really right you still should purge the unit alloy steel is not the cheapest material today don’t think you can easily mig weld it I do mug welding stainless too and I don’t like to as the shop is not really equipped I can use my TIG regulator and get good welds on stainless or alloy but it’s not my favorite I did both methods for a living for a while So bottom line purchase a commercial boiler and check it often for coorosion and don’t over pressurize it or over heat it I got a neat steam tables booklet on Amazon that is an eye opener if you haven’t had steam experience . Seems technical for models If you keep temps and pressures reasonable steam is fun. I run my models a lot to the point where I get wear and tear that many never see even my race car got run nearly every week end for 5 years sometimes we got double and triple headers. Even my body got hard work out playing sports untill I was 72 I’m broken and worn out now but as we used to say it was a good run .
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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As far as welds go the coupling to pipe joint would be classified as a lap joint or if it were carbon stainless or any other material it would be called a "socket weld" which uses a fillet weld to fuse the two together.
Being a pipewelder by trade and looking at the exterior and interior I would say that is an acceptable weld visually. However unless tested for mechanical qualities through destructive testing the visual means nothing
When I inspected a weld the visual look gave me an indication of the skill of the welder but did not confirm the weld was good. I would look for under cutting, spatter, weld pattern, and usually but not always it was the first indication of a good or bad weld. I also knew I would not be able to check the porosity or penetration of the weld without testing. Now I have also seen ugly looking welds that passed with flying colors. But more often then not a weld with defects on the surface also has defects underneath. But unless you know and understand what you are looking at the visual can mean nothing. As one old welder told me once " I can make this look pretty or make it to hold I made it to hold."
 
A strange experience:
I experienced a weld - from a factory process, with speed controlled and jig held MIG torch, so gas, feeds and speeds, etc. all calibrated and set, and batch recorded.... but of thousands of welds joining structural end fittings to steel tubes, one single end casting had some "contamination" so the weld that looked as perfect as the rest had zero penetration into the casting. Sent to the Welding Institute for a report on "Why? and what went wrong?" they were completely bamboozled. This was not a pressure weld, but a tension member: When the load was applied as the structure was assembled, a ring of unwelded steel casting appeared as the end piece pulled-out of the tube. Micrograph sections showed perfect penetration and welding to the tube and a non-welded friction joint between the weld and the end casting. The report suggested the end casting may have been simply VERY cold, or had some insulating pollution (Oxide?) on the surface that prevented the arc from "hitting" real metal so the feed metal "spray" simply sat on the surface of the end casting. Further metallurgical lab studies had failed to find any contamination, so the Welding Institute report had "no conclusion" for the failure. - Had this been a pressure vessel shell, pipe-joint or whatever, the pressure test would have definitely exposed the faulty weld. The Company had stringent checks in place, so all welded and bolted joints were examined for movement as the structure was built and during loading up to completion. These checks had identified the failure part way through construction of the building. No other faults were found.
Conclusion. A visually externally perfect weld can have a total failure within. But if it "holds the load without failure", then it can be deemed OK. - Except the "Factor of Safety" may be compromised.
For Boilers in service, the equivalent loading "to ensure safety" is the periodic Hydraulic test at an excess well above the Safety valve release pressure. (ASME and UK regs require different pressures, but both have "Excess" pressure applied hydraulically).
I personally feel that there can be many boilers "in service" where joint integrity is "Imperfect", even by design, such that an over-pressure of the boiler could fail a joint at well below the "design expectation". The Safety valve must therefore be suitably respected and checked against the gauge at every steaming to be sure that boilers cannot experience adverse conditions. ALL Boiler operators MUST also be well trained and "compos mentis" when operating boilers to prevent operation outside the correct operating limits.
(compos mentis: = (law) Of sound mind, sane; thus criminally responsible for one's eventual wrongdoing).
K2
 
HMEL: Your comments are probably the most pertinent of all - and should be read slowly and carefully by all weld inspectors... "When I inspected a weld the visual look gave me an indication of the skill of the welder but did not confirm the weld was good. I would look for under cutting, spatter, weld pattern, and usually but not always it was the first indication of a good or bad weld. I also knew I would not be able to check the porosity or penetration of the weld without testing."
Thanks,
K2
 

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