Help: Looking for a steam engine forum

[ajoeiam]

Please tell us the size of bore and stroke, and max running speed. What power do you need from the engine? (E.G. Equivalent electric motor size and power).
We can recommend the size of boiler and burner needed.
Calculations are essy, but we need the data to input...
K2

Hmmm - - - so you have some kind of formulas.
Please - - - - where would I get such formulas?

My thinking tends to be in both directions - - - - like - - - I play with my desired
numbers to fine tune results. So sometimes I might want to start with a set boiler size
and then work backward from that.
(Then there are the variables for heat input and material burned and the draft for variables in the boiler itself and then one is really finding a lot of spots on one's head for the required head scratching!!!!)

TIA

 

[abby]

There are several good books on model boiler making available but bear in mind that if you intend to run the engine in public you will need to comply with your relevant local regulations which may even require you to have liability insurance.
Boilers holding a couple of litres or more and running at as much as 100 psi require more than beginners skill during manufacture.
It is normal to use heavy gauge copper for construction and silver solder (silver braze in USA) for joining , this requires a large heat source such as a big propane burner or oxy acetylene.
If you just want to see it run use compressed air.
Dan.

 

[ajoeiam]

There are several good books on model boiler making available but bear in mind that if you intend to run the engine in public you will need to comply with your relevant local regulations which may even require you to have liability insurance.
Boilers holding a couple of litres or more and running at as much as 100 psi require more than beginners skill during manufacture.
It is normal to use heavy gauge copper for construction and silver solder (silver braze in USA) for joining , this requires a large heat source such as a big propane burner or oxy acetylene.
If you just want to see it run use compressed air.
Dan.

Any way of getting a list of said references?

(I've worked on boilers of up to some 160 MW so I think I've at the very least have some connections that are fully certified for the welding.)

 

[abby]

Model Boilers with the exception of very large models , are made from copper , even TIG welded copper is questioned in the UK.
The copper must be of the "oxygen free" variety and special rods are required for TIG.
The world of model steam is marred by the regulators nowadays.
For very low pressures such as in Mamod engines , soft soldered brass is used but these are just toys
I will qualify this by saying that you can do what you like for private use but for sale or use in public areas the regulations apply.
A simple google search for "model boiler books" will turn up loads.
"Model Boilers and Boilermaking" by K.N.Harris is as good as any.
Dan.

 

[animal12]

Richard , when you get your sweet looking engine running please post a video of it operating . That is a real work of art you have there
animal

 

[Steamchick]

Just a word of caution, "A Joe, I am" (Please correct me if I misunderstand your name?). As you are is the US of A, the boiler you purchase or make MUST comply with ASME Boiler regulations. I recommend you buy a back-copy of Live Steam and outdoor railroading, Nov/Dec 2006, Volume 40 no. 6. This has an excellent article about boiler design and manufacture, and the ASME regulations and what you must do and not do, to comply with regulations. e.g. if you buy a boiler from (say) the UK, or otherwise from outside the US, you need a certificate of compliance to ASME, or some other declaration from the seller, that your insurance will accept, otherwise the insurance will wriggle-out of any payment, in the event of any claim following a failure. (That is, if you want to be covered by insurance).
But for "public display" - which could even qualify as you showing your brother's kids, or the bloke next door - you must be insured...
Joining a club, may entitle you to being covered by the club's insurance for public display, while within their premises, and as certified by their "techinical appointed person". (Which is what I do).
Any second-hand boiler is classed as "uncertified" and must be certified as if it is new. I.E. a set of calculations for the various tubes, end-plates, stays etc. A full visual examination for corrosion, scaling, or "poor soldering" or other poor design or workmanship. An hydraulic test to prove the design, a steam test to prove the safety valve and gauge performance, etc. etc. against the specified firing method at "maximum fire". And confirmation of the boiler water feed pumps (minimum 2) in their final installation and operation (allows for engine driven pumps, axle pumps, electric or steam pumps and hand pumps. etc.).
As a native, you'll know better than I what the Federal laws can do....
I have been looking at all the different rules and regs, and I think that complying with ASME will cover almost everyone else's requirements, but just complying with another country's regs may not meet ASME. e.g. ASME uses a very technical way of defining the hydraulic test pressure, which can be higher than other counties' requirements. Also ASME limits silver-soldered-copper-boilers" to 100psi. And ASME has no scope for exceptions.
But don't be daunted by ASME, it is no different from understanding what you can and can't do when driving. Buying a boiler in the US should "automatically" get you ASME approval, if from a "proper" boiler making company/distributor.
I hope this helps answer some of you question #21?
I can provide some odd papers I have written to help others decide "what boiler?", "what burner?", etc... Just let me know exactly what you need and I'll dig out something suitable?
Enjoy,
K2

 

[Steamchick]

Hmmm - - - so you have some kind of formulas.
Please - - - - where would I get such formulas?

My thinking tends to be in both directions - - - - like - - - I play with my desired
numbers to fine tune results. So sometimes I might want to start with a set boiler size
and then work backward from that.
(Then there are the variables for heat input and material burned and the draft for variables in the boiler itself and then one is really finding a lot of spots on one's head for the required head scratching!!!!)

TIA

As you are is the US of A, the boiler you purchase or make MUST comply with ASME Boiler regulations. I recommend you buy a back-copy of Live Steam and outdoor railroading, Nov/Dec 2006, Volume 40 no. 6. This has an excellent article about boiler design and manufacture, and the ASME regulations and what you must do and not do, to comply with regulations.
I have attached a couple of files that I use for boiler design stuff... I also use K.N. Harris as a bible!
They may give you some clues?
K2

 

[ajoeiam]

As you are is the US of A, the boiler you purchase or make MUST comply with ASME Boiler regulations. I recommend you buy a back-copy of Live Steam and outdoor railroading, Nov/Dec 2006, Volume 40 no. 6. This has an excellent article about boiler design and manufacture, and the ASME regulations and what you must do and not do, to comply with regulations.
I have attached a couple of files that I use for boiler design stuff... I also use K.N. Harris as a bible!
They may give you some clues?
K2

Thank you very much for this set of docs!
Any further questions will most likely be in private unless you specifically refuse such.

Deepest regards

 

[comstock-friend]

As you are is the US of A, the boiler you purchase or make MUST comply with ASME Boiler regulations

This is incorrect. Very few of the model steam engines in the United States have ASME certified boilers. In fact code requirements make it almost impossible to build a certified boiler in a 'hobby' environment. All material must be code certified materials from certified suppliers, any welding must be done by code certified welders. The certifying inspectors will have manufacturing holds at various points in the assembly and test. Note that boilers 6" nominal diameter and less are exempt from mandatory certification. Note also in the USA that the individual states have ultimate control as to what constitutes an acceptable boiler. Some state may require ASME for hobby boilers. Where I live, California, most boilers operated at my home club track, the Los Angeles Live Steamers are not certified and never could be. When a state tries to mandate ASME compliance, a exemption will usually be carved out for hobby use. Commercial operations such a park railroads will usually be required to have certified boilers. For ten years I designed ASME Section 1 power boilers and Section 8, Div 1 and 2 pressure vessels. My job interfaced with our in house QC and the State of California Department of Industrial Safety pressure vessel inspector. We also carried National Board certification for those customers that required NB registration. A complete set of the current code will set you back about $18,000. No not a hobby item...

John

 

[Steamchick]

Thanks John, I thank you for the correction, as you have the expertise I do not have. I had picked up that model boilers had to satisfy the ASME regulations from an article in Model Steam and Railroading, which did not explain exceptions, just how to comply with ASME when designing model boilers... I shall now read that as a recommendation, not requirement.
Certainly, in the UK there are regulations and exceptions. And when we were subjected to EU regulations those were applied. But the simple UK exception is the "bar-litre" stored energy product. Of course, all the main manufacturers of boilers comply with regs and provide certification accordingly. Usually "home-made" boilers are certified by "local testers" being made to standard designs, examined and hydraulically tested. I am sure full sized boilers are examined and tested by Lloyds approved inspectors, as has been the practice since my Great-Grandfather was one.
I have been recently re-calculating my own designs - and de-rating the NWP of some - based on ASME principles, as given in the magazine article. Would you mind if I send you a mail directly as I do have some points that I have not been able to define or confirm from my research on the web? As a design engineer (30 years ago) my expertise is well below yours for this subject, but is more general.
Thanks again. I think it important to "be sure" of facts in this issue.
K2

 

[Arcus47]

Whats your opinion about the operational difference between 3mm copper sheet and the 1/8th copper sheet requirement for a NWP of 100 psi. Is this the de-rating you were referring to?

 

[Steamchick]

Hi Arcus:
Ha! - You have opened a can-of-worms asking for "my opinion"...
Putting it simply: It really depends on where the change from 1/8" to 3mm applies. In the barrel of a boiler:
# Hoop stress - related to cross-sectional area = 4xt ... so stress increased by 4.1% = or Normal Working Pressure decreased accordingly by 4%.
# End plate STIFFNESS = related to the cube of thickness - so NWP for 3mm derated to 88% of NWP for 1/8" end plates.
BUT:
The biggest "error" I have seen in some text books is that they use the TENSILE strength of Copper (210MPa) for FLUE tubes and firebox inner walls (Cylindrical fireboxes) whereas the Annealed strength of Copper in compression is quoted as 45MPa. I.E. The flue tubes can only take 20% of the boiler pressure that Water tubes of the same size can withstand.
What I mean is that if some components are calculated for a certain NWP using the Tensile strength of copper, then they should ONLY have a rating of 20% of that NWP if those components are subjected to "external pressure.
Many of the text books appear to have omitted this fact completely, and size their flue tube, etc. ("external pressure" components) using the Tensile strength of copper.
So please beware of the application of pressure on each and every surface that is stressed by the pressure, and use the appropriate limiting "Strength" value for your calculations.

Does this help or confuse?
K2

 

[Arcus47]

That definitely helps - the reason I asked the question is that my club boiler inspector passed my plans for a 6 inch diameter vertical boiler at 100 psi using 3mm thick copper plate. This was in 2018 (you can view the build in and it was certificated against AMBSC code Part 1 Issue 5 1984 to have a NWP of 100psi. It will be coming up for it's certificate renewal in May 2023 and I was wondering if the NWP will be reduced in light of the stricter requirements.

 

[Steamchick]

Hi Arcus,
Sorry to be tardy getting back to this, but I have been away on holiday in Scotland for Hogmanay. (Hic!).
Sober now....
Simply, a previously certified boiler design need not be re-certified as a design. JUST annual/biennial testing, depending on the certifying authority's requirements. So the calculations you presented that have been accepted will still be OK. That's why there are so many "old" boilers in service that maybe would not be re-certified as a NEW DESIGN nowadays.
The reality is that if a boiler has a factor of safety of 3 or more on the NWP then the DESIGN test at 2 x the NWP will be not fail. And in service the boiler should not exceed 1/3rd of the stress at the "calculated" failure pressure. A higher safety factor means more metal/cost/mass and less stress on the boiler. But Copper gets stronger as it "work hardens" with age, so in effect the real safety factor has improved through ageing, but that is outside the scope of the calculations.
E.g. A boiler with a flue tube designed "to fail" at just over 300psi when calculated for hoop stress versus the ANNEALED copper strength in compression, has a calculated safety factor of 3 against a NWP = 100psi. BUT as the copper gets "stronger" with age and work hardening, the safety factor may develop "naturally" up to 5, 6, 7 or more? WHO knows? - I don't. As the compressive strength can vary from 45MPa (Fully Annealed) to ~330MPa (Increased by a factor of over 7 times!), it is my guess that over time a FOS of >8 is possible from an initial "FOS of >3".
BUT - and here is the risk... The initial hydraulic test at 2 x NWP (to prove the manufacture is "sound"?) may collapse a newly assembled and fully annealed flue tube - hence a failed test! - as there may well be Ovality factors, non-linear factors (out-of-straight), distortion factors (dents, etc. other than ovality) and Stress Concentration factors affecting the real tube in compression.
IF the Accredited (Approved) Certifying Tester is happy, then I am happy. I can only warn of potential risks affecting boiler design and manufacture.
But your 3mm plate has been used for the inner wall of a cylindrical surface of the firebox...
I'll send you a direct message about this, and other "observations" about your set-up.
I enjoyed the video, especially the accompanying Dvorak! I guess NZ qualifies as a New World in its own right?
Regards,
K2