Building a steam engine boiler question?

Hi I'm new to this. I'm wanting to build a small steam locomotive perhaps 5" or 7-1/4" gauge.

I have a steel fire extinguisher (powder) that I can use as a boiler and that's about 5" diameter.

What kind of thickness should the boiler walls be if I want a reasonable operating pressure?

Is steel suitable for boilers with the concern of corrosion?

Second. I'm using the marine style boiler design with a cylindrical fire box, is 4" cast iron drain pipe suitable? The only concerns I know is that cast iron is hard to stick weld and I want to weld the tube plate to it.

hi simon,

join a club if you are in the UK and discuss with your club boiler inspector.

im far too polite on here to comment on your proposal, your club boiler inspector might be somewhat more forthright!

cheers,

julian

Creating own boiler without the knowledge and approval of the boiler inspector is a bomb without knowing when it will explode.

Hi Simon,

Julian's suggestion to join a boiler club is the best way to start your project. Your loco will have to be certified by a club inspector before it can run on their tracks. The 5" and 7 1/4" gauge for locos normally refers to the width of the rails, not the diameter of the boiler a 7 1/4" gauge loco has a boiler about 10" diameter, similar to that on my 6" Ruston Proctor TE.

Steel is a suitable material. Anti-rust treatment and storage procedures are used to prevent corrosion. Copper is better but more expensive.

I am in Australia and have to build the boiler to the AMBSC Boiler Code – Part 2 – Steel Boilers. A summary of the requirements are:

250-700 kPa (36-101 psi), Fire tube boiler – 50 litres max., Water tube boiler – 25 litres max.

Barrel diameter 4” – 14” Dia., Barrel thickness not less than 6mm

AS 1074 pipe fittings are not suitable (standard pipe fittings from hardware shop)

Good luck with your engine, Paul.

Edited By Paul Lousick on 12/05/2015 00:43:07

Add a couple of dozen old golf club shafts as boiler tubes and you'll be good to go

Edited By Ady1 on 12/05/2015 00:44:09

I think a propane cylinder would be better or consult Rainbows for the more technical aspects of the design.

Unless you are building the boiler to engineering certified drawings and have it checked by a boiler inspector, I can only say one word:- BOOM !!!!

Assuming you want to run the loco on a public track then any steel you use will have to have the correct paperwork from the supplier so you can basically forget about using any form of recycled materials.

5-6" Boiler would typically need to be in the region of 6mm thick steel for the barrel and plates. This allows a cetrain amount for wastage (rusting) but the use of a boiler treatment will slow the process but still not allow you to use thinner material.

Forget the Cast iron

What is your welding like? it will need to be tested which means sending it off for non destructive testing. Are you able to specify the correct weld prep to get a strong enough joint for the design pressures?

As said talk to your local club boiler inspector where you intend to run the loco.

Edited By JasonB on 12/05/2015 07:56:57

Great post Simon! Reminds me of when I was a lad many years ago intending to build a steam engine from a knackered Atco lawnmower engine using a five gallon oil drum for a boiler fired by my dads paraffin "flame thrower" weed burner. Fortunately it never got beyond the design stage as I lacked the resources to actually join the "boiler" to the engine!

Seriously though, 40 odd years later I have finally started building my dream steam engine in the form of a 4" traction engine. With 45 years of hindsight and a health & safety act in place to protect the rest of the population from my bodgery, I decided to get a professional to build my boiler. It cost me the thick end of 2 grand but when finally up and running will be safe and insurable to run in public (subject to regular testing) for years to come.

By all means have a go at making your own boiler but acquire the appropriate skills first and obtain the appropriate, traceable materials. Building a loco will entail a great deal of time and expense which will largely be wasted if your boiler doesn't comply with regulations since without a pressure test certificate and public liability insurance you won't be able to run it on any public track.

Good luck & stay safe! Martin.

Simon, get some books on model boiles(some one will recomend which is best}, and subscribe to "Model Engineer" or similar publication, and learn about boilers and the science, and engineering that goes with them. These although small are not toys (Mamod etc), they are in them selves full size boilers. Join a club if possable. Best wishes.

Ian S C

Edited By Ian S C on 12/05/2015 12:53:49

Simon - my advice is to say nay to the armchair pundits and go ahead and build it!! Trust me, it wil never go bang, not in a million years!

I agree fizzy, but is a good idea to understand a bit about what your letting yourself in for.

Ian S C

Bang

Hi Simon,

My advice is to read a couple of books or articles on boiler making and get a feel for what is possible and safe. Steel boilers can be fine, but to be insured they must meet stringent standards. If you make one from scrap, no-one is going to give you an insurance ticket for it.

Neil

nigel/fizzy,

you cant be serious in your comment to simon to 'go ahead' with 4" dia cast iron drain pipe surely?

my advice to anyone going down the boiler route as a beginner is to build a loco from a well known and excellent design (there are quite a few that are well known but not excellent that have boiler problems in the design department). later on if you want to explore designing your own boiler you will at least have the construction experience under your belt so to speak. designing your own boiler is not something i would ever advise a beginner to do as a first attempt, as simon has clearly shown by his wish to use 'odds and ends' of material.

cheers,

julian

New poster.

First post and comes up with more dangerous stunts than even Rainbow can come up with ?

Give over someone is having a laugh at your expense.

Personally I think he's be better with 6" drainpipe.

Julian....I know you well enough to know that you understand that it is impossible to effect a home made weld good enough between cast iron and steel to endure even low pressure, let alone boiler pressure. I can only presume the original question is a wind up, if not then by all means go ahead and attempt the impossible, trust me, it wont blow up! Sorry if the irony in my reply was lost, but if I struggle to get pressure tight welds using top materials and years of coded experience this one is a complete non starter. Indeed, you are correct, I am not serious. No offence intended.

No its not a wind up. I'm genuinely a beginner( this is the beginners section) maybe I have not done sufficient research but from all the replies I now see the importance of doing the job properly with instruction, the correct materials and material pressure tolerances etc. I will contact a local club and search for more information. I now know that apart from the impossibility of welding cast iron as a pressure critical material its a no no. Thanks anyway for the replies I'm much more better prepared and will do more more research.

Simon, have a read of the test code for starters it will give you some idea of what is required though does not give indications of suitable materials.

Fizzy has shown elsewhere that a steel boiler can be made at home for a very reasonable cost but you must use the correct materials and be able to weld to a high standard. On the larger engines the performance difference between steel and copper will be less of an issue.

Simon, good onya for taking the comments constructively. As all have advised, read up everything you can.