# Copper boiler max size, how big?



## Amber (Jul 29, 2011)

This is just a question of curiosity, how big of a boiler can be made from copper before the material becomes a problem. For instance, if a person were to take 3 inch type L pipe and make sheet copper like you would for the end plates, could you safely combine several sheets to make a bigger boiler, and how big could you get away with before the strength of the material and the solder joints be came a safety factor. I suppose that if you could get some type K copper pipe, a larger boiler could be fabricated because of the thickness of the type K, but I assume there's a practical limit to the size at some point.


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## David Leech (Dec 9, 2008)

Amber, 
I believe that some early full size boilers were made of copper. 
Obviously as the volume of the boiler increases, so must the thickness of the walls. 
Likewise, there must be more stays involved for the fire box as size increases. 
I am sure that you are right though, as far as a 'practical' limit is concerned. 
Maybe it will depend on what thickness of copper is available. 
I wouldn't think that the solder joints would be a problem, as those joints are actually stronger than the material. 
All the best, 
David Leech, Delta, Canada


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## Michael Glavin (Jan 2, 2009)

Amber,

David’s comments ring true with me… 

The practical physical limit for a copper boiler more likely than not is a function of cost.

The copper boiler material will fail, rip and or rupture prior to a properly executed solder joint failing of either soft or hard solder types.

You can purchase small sheets of copper of various thickness for rolling your own boiler, albeit it probably is more expensive, but you are able to obtain thicker stock. That said a seamless copper tube is best suited for our boilers.

Keep in mind, round cylindrical boilers with conical ends are more structurally sound regardless of the material in play (more so with non-ferrous materials). We tend to use flat end plates in our small boilers with proper stays and reinforcement it works well of boilers comprised of copper construction. Thicker material would be preferred for the end plates if available.

There is a book written by Wagner that has tables or such that lists various materials-specifications and their respective feasibility for use in boiler construction. If I recall there is section in the ASME Code book with reference to materials and the limits thereof too.

Michael


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## Ray Cadd (Dec 30, 2008)

If I'm not mistaken, some of the small European locomotives used copper fireboxes.


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## Nutz-n-Bolts (Aug 12, 2010)

I have seen 7.5" gauge engines with copper boilers. Granted they were smaller size like an 4-4-0 style. David mentioned the full size locos, witch is new info for me. So it seams to me that Michael statement about cost is correct. Not only would steel material for a 7.5" gauge loco's boiler be cheaper but it would be stronger than copper. 

For our considerably smaller boilers it is more than strong enough, and easier to work with. One thing I would recommend is *only one seam *around the diameter of the boiler. None is better but it is an inherent necessity of rolling a boiler and fire box from flat stock.
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## David Leech (Dec 9, 2008)

Randy, 
I was thinking in terms of locomotives like Novelty at the 1829 trials. 
As Ray mentions, I think that they also continued to use copper tubes and fireboxes due to their better heat transfer with a steel boiler, for many years after, but eventually 'all steel' became the norm. 
All the best, 
David Leech, Delta, Canada


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## Amber (Jul 29, 2011)

If the silver braized seams are stronger than the metal itself, why would it matter if there were two seams? If a person wanted to build a 6 inch diameter boiler from readily available material, 2 seams would be necessary.


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## xo18thfa (Jan 2, 2008)

Practically speaking 6" diameter barrel, 1/8" thickness is the cut off between copper and steel. That's a cost factor more then anything. The biggest copper boiler I've seen is 8: diameter, 3/16" wall thickness on a Winton Mogul.

Kozo Hiraoka did a very in depth analysis of copper boilers in his "New Shay" book. With all his charts and formulas, you can build one up to about 10" diameter barrel running at 90 PSI.

The Australian Miniature Boiler Safety Committee (AMBSC) has two codes for copper boilers. The miniature boiler code allows up to 77mm dia and 75 PSI. They have a code for larger boiler too. I don't have a copy of that code so don't know what the limits are.


KN Harris' book has some calculations too.

3" "L" wall will make a very strong boiler. It's strength is off any chart I have. According to AMBSC flat endplates would be 2mm thickness (0.078") 


I've been told, but not seen in writing that 110 PSI is the maximum pressure limit for any copper boiler. At that temp, water boils at 334 degrees F. The strength of copper starts dropping dramatically.



Rolling boilers from flat has been done successfully for many years. AMBSC miniature code allows longitudinal joints, but the exact spec is in the Part 1 book I don't have. Kozo rolls everything from flat and straps them together. KN Harris talks in depth about coppersmith joints and other strap joints. LBSC rolled most of his boilers too.


It is "doable"


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## Amber (Jul 29, 2011)

So, a practical max pressure of 100 PSI is a good idea with copper boilers, just to be on the safe side. 
I wonder if a practical and safe boiler could be built by taking 2 sections of 2 inch type L or 3 inch type L copper pipe and splitting them long ways, and then reshaping them into a boiler with 2 long seams. You would get a bigger diameter boiler that way, using available pipe. I suppose it depends on the pressure that the boiler is intended for.


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## Phippsburg Eric (Jan 10, 2008)

What did you have in mind building Amber, if I may be so bold? 

I would think that on G-gauge track 3 to 3.5" is about the biggest you would need anyhow. Maine two foot gauge boilers topped out at 48" which is about 3.5" in 7/8" scale and that would be a big model engine. a 1:20.3 scale K36 boiler is in the 3" size range as is a 1:32 Big Boy. If you insulate the boiler the cladding is bigger than the boiler shell. Unless you need lots of power you can hide a smaller boiler in a larger outside shell and still have a respectable performer. 

Another way to make a larger diameter boiler from smaller pipe is to slit the pipe, flatten it then roll it the other way. cut the pipe 3.14 time the diameter of the cylinder you desire. it will make a cylinder 3.14 times as long as the pipe you start with. additional length can be added with a lap joint where one cylinder telescopes into the next. very strong and pretty straight forward to do.


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## Amber (Jul 29, 2011)

Oh, I wasn't planning on building a big boiler just yet, I was mostly just curious about what size boiler can be built with copper pipe and still be safe. Eventually I would like to build a boiler to power a 2 foot gauge engine such as an 18 ton Baldwin 0-4-0 in 1/6th scale for the mine tram. Since it will be on 4 inch gauge track, the boiler would be fairly large, but not so large as the boilers for 7-1/2 inch gauge. 
First, I have to build a couple of small boilers to see if I can do that successfully. My plan is to start with a vertical boiler using 2 inch type L pipe. If I can get that to steam properly, then I should be able to build a bigger boiler.


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## Amber (Jul 29, 2011)

Thinking about telescoping sections to make a longer boiler, what about using a "T" fitting for the firebox end of the boiler, and using the 3rd connection to form the body of the steam dome, either conventionally, or "boot boiler" style? Those fittings are made for type L pipe so they should be just as strong, and you can get them with the reduced size "center tap", for lack of a better way to describe it.


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