boiler tube

[Julian]

Hi Guys,

At a recent steam fair Rich and I each picked up a piece of copper tube that both just shouted-
"Make me into a boiler....pay the man the tenner!"

Its 107mm diameter by 300mm long and the copper is 1.68mm thick. In the chaos that is currently my workshop I cannot find a book that tells me the formula for working out the permissible pressure it can take. Can someone please remind me and if feeling helpful tell me the max pressure. I hope to run it between 50 and a hundred psi but preferable the higher end of the range. It will need a test cert as it will be over the three bar litres and I want it to run a multi-cylinder engine so need steam and pressure available in good quantities.


Also any suggestions for type or style of boiler? It will be static.


Julian

 

[Maryak]

Julian,

Here is a link to Rich's question on boiler shell/tube thickness. http://www.homemodelenginemachinist.com/index.php?topic=2699.msg24083#msg24083

I hope this helps.

Best Regards
Bob

 

[tel]

Just off the cuff that bit of tube sounds a bit light for a 100psi shell. Been a while since I worked one out tho'.

Some good info HERE

 

[hammers-n-nails]

this link doesnt contain a answer to your question but its got alot of other info on the subject
http://books.google.com/books?id=DO4OAAAAYAAJ&printsec=frontcover&dq=steam+boiler#PPR10,M1

 

[SandyC]

;D

Hi Guy's,


Julian,

That piece of tube calculates out to be capable of a maximum working pressure of 97.92psi.
I would not use this above 75psi (5 bar).... 60psi (4bar) would be much better.

This is assuming it is a pure C106 grade of copper.
If you do not know the grade then err towards the lower value.... or less.

As for the type of boiler... well this will largely be determined by the steaming rate required, which is governed by the size/rpm etc of your engine/s.

Only by knowing this you will be able to determine the amount of heated surface you require in order to evaporate the water @ the designed pressure for any given design (they vary so much in evaporation rate) and from this you can then determine the size of burner you need in order to meet the steam rate.

Given more specific details I am sure we can get you pointed in the right direction.

Hope this is of some help.

Best regards.

SandyC

 

[Jasonb]

Are you sure it's 107mm as 108mm is a standard plumbing size and plumbing copper is not suitable for boilers.

Jason

 

[vlmarshall]

... plumbing copper is not suitable for boilers.

Ouch, really? Why not?

 

[shred]

Ouch, really? Why not?

Under 120 PSI, plumbing pipe is fine, according to the Copper Development Association (using the ASME Boiler and Pressure Vessel Code): http://www.copper.org/applications/plumbing/techcorner/cu_tube_steam_systems.html

 

[vlmarshall]

Oh good. Lacking any other source for "non-plumbing copper pipe", I was having visions of tossing out my Cracker boilers and, well, I don't know... rolling a boiler from sheet... or turning it from solid stock! ;D

Thanks, Shred.

 

[Jasonb]

Plumbing copper can become brittle due to the heat of silver soldering/brazing, due to the oxygen and lead that it may contain, more so if using Oxy-acetylene, have a look at the bottom couple of paragraphs on this page

http://www.cupalloys.co.uk/brazing-of-copper-c99.html

As you say your boiler will be getting tested have a word with your boiler inspector before you start work.

 

[steamboatmodel]

This is what it says
"Avoid the use of plumbing grade copper that can contain lead. Lead is added to improve machinability and is present mainly as discrete insoluble particles throughout the metal structure. The particles are fully molten well before brazing temperatures are reached and this means that that under the inevitable thermal stressing conditions during the brazing cycle, parent material cracking can occur because of general structural weakness. Any lead being dissolved into the brazing alloy may also result in a brittle joint. "
I think you will only run into this problem with old pipe as most contries have something similar to the US Safe Drinking Water Act, which require everything lead free.
Regards,
Gerald.

 

[Jasonb]

I think its more the oxygen in the copper that is the reason for not using it

"The solution is to use only phosphor de-oxidized copper or oxygen free grades of copper. These are designated C103 and C106."

Jason

 

[tmuir]

Under 120 PSI, plumbing pipe is fine,

Thanks you had me worried for a moment and as any boilers I plan to make in the near future will have an operating pressure of 20PSI or less it will be fine for me.