steam boilers

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steamboat_bruce

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I am just starting to build a fire tube steam boiler for a model steamboat that I am building. Does anyone have experience rolling brass tubes in a brass tube sheet?
 
Bruce, how big is the boiler?
Buy a copper tube.
Hilmar
 
Bruce,
Be careful if you are going to use any brass in a boiler, especially if you are going to gas fire it. It has a few bad properties that makes it not the ideal material for high pressure use.
I would take Hilmars advice and source copper tube. Plus all cross tubes and stays should be of copper, and all your tapped connections on the boiler should be of phos. bronze.

John
 
Bruce,
The problem with using brass on a boiler, especially if it is run with a gas burner is that the brass de-zincs (running on gas accelerates it) and starts to break down and corrode, usually on the inside where it can't be seen. It also hardens and goes more brittle with the constant flexing that the pressure causes.
The reason for the phosphor bronze boiler fittings is for the same reason, it is less susceptible to corrosion and a lot stronger, so preventing the fittings from 'blowing out'.
Also, seeing as to how you are going to make the boiler from a sheet, how are the ends going to be joined together. There are two accepted methods for this, one is to butt joint the ends, then fit a reinforcing strap on the inside that is rivetted either side of the joint, then silver soldered over the whole area including rivets. The other, and more difficult method is to dovetail the joining ends so they fit precisely together and 'lock' the joint, again this would most probably be fitted with a backing strip and fully silver soldered
Here in the UK a brass boiler wouldn't even be thought about, let alone considered, unless it was one of the 'toy' steam engines, that are usually soft soldered and run at very low pressures.
Even at your designed running pressure of 20psi, and a rough guesstimate of 150 sq. ins. suface area (excluding the boiler tubes), this gives a rough total of 3,000 lbs of surface area pressure, and the total improbability of it ever happening, if a fitting was to blow out, or the boiler split, it could cause a major injury either from flying shrapnel or scalding water.
Also your boiler testing seems a bit excessive. We usually take ours to twice working pressure for the initial commision, plus the safety valve is tested to ensure that it is releasing enough steam to prevent the boiler going above the designed working pressure (in some cases people fit two to be on the safe side, just in case one siezes up). In your testing case, again a guesstimation, 150sq ins surface area times 150psi works out to 22,500lbs.(10 tons approx.) surface pressure, I personally wouldn't like to be in the area when you are carrying out your testing, even though being done hydrostatically.
I am not trying to put you off making your boiler, but please be aware of the facts and figures.

John
 
Bruce( I like that name) I suggest that you call Village Press at 800 773-7798 and ask for Live Steam & Outdoor Railroadings magazine Nov/Dec 06 issue. They have an article on The Safety of Copper Boilers by Kozo Hiraoka . If you do a google search for his name you will find he has authored many books on steam engine construction.You may also want to order the Jan/Feb 07 issue as they have an article about safety valves.I wish you the best on your build and I am in no way connected with Village Press.
 
Sorry Bruce,
Misunderstood your first post, it came across to me that you were rolling the main shell from brass. So I hope you see what direction I was coming from with regards to safety.
We in the UK seem to build our boilers to totally different specifications to yourselves in the US.
Do you have to have a certified boiler certificate before you run in public? We have to have ours certified by a 'competant' person (engineer designated as a steam tester) before it can be used in public, then every year it has to have a steam test even if it hasn't been steamed, then every four years a pressure test. Getting insurance for third party is dependant on this certification.
These rules have been relaxed slightly for boilers under the 3bar/litre rule.
Just out of general interest, if you want to know a bit more go to here
http://www.paddleducks.co.uk/forum/viewtopic.php?t=2792
There is a dowloadable pdf file that lists what is required.

John
 
Bruce,
Sorry I didn't answer your question about what bronze to use.
We use three different types generally.
Our codes are pb102 or pb1 for general use including boiler bushes and stays and I think 606 is the leaded free cutting variety.

John
 
""I thought about boiler certification some time ago. I contacted the State of Missouri boiler inspector. The boiler does not need it to be certificated if I run privately. ""

Bruce
This is different from State to State as fare as I know.
Hilmar
 
Hi Bruce,
It now comes over to me that you are experienced in boiler making, it worried me on your first post that you were a newbie who didn't know what he was getting into so hence all the safety issues.
I am aware of hydrostatic testing of boilers, but I have seen a chap testing an article that he called a boiler by having it weighted down in a bucket of water, and connected directly to his compressor, he was standing over it looking for air leaks, you couldn't see my a*** for dust.
How are you gas firing it? Are you going for a blowtorch type burner or for what we are all using in the UK now, that is ceramic radiant heat?
If I can be of help, I don't know everything, but if I can I will try to get the info you require.

John
 
Hi John,
would you use flue tubes with Radiant Heat?
Hilmar
 
Hi Hilmar.
With radiant heat the flames are very small but intense so usually they are for use where the water is in very close proximity to this heat.
In a vertical boiler with vertical flue tubes this is a perfect solution as the boiler can be heated directly at the bottom and due to convection the heat then passes up the vertical tubes still having a lot of heat to turn the water into steam and if the main chimney also has cross tubes so much the better.
With horizontal fire tube boilers a 'blowtorch' method is in my opinion better because the flames can travel into the firetubes and heat the water that way, and as Bruce was saying, to get the flames and heat to penetrate better a draught is required.
There are many ways to run a horizontal boiler from radiant heat but the boiler is designed slightly differently. The standard for a horizontal is a centre flue with cross tubes running across the flue, another method is to have the burner underneath and the tubes are arranged vertically with the 'smokebox' collector on top of the boiler rather than at the opposite end of the boiler. the other methods are tubes hanging from the bottom of the boiler or copper 'hedgehog' spikes hanging down, all designed to get the water as close to this very powerful radiant heat.
The last vertical boiler I made would heat up 1.5 pints of cold water to working steam pressure of 30psi in 5 to 6 minutes. So it is a very good heat source, coupled to the fact it is virtually silent compared to a blowtorch.
If you look at the title page from this website it shows a radiant burner ( they are fairly easy to make) and the method used to heat the boiler.
http://www.modelsteamenginesuk.com/boilers.asp
Hope this has explained it enough, it has totally confused me.

John
 

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