Suitable Boiler for a LocoMobile Twin Simple (6hp)

[DetroiTug]

Jon,

Will do on the boiler. (PM Sent)

Not sure on the HP ratings.

-Ron

[marinesteam]

Ron,

Very well stated.

Would like to add that any boiler built should meet ASME code as this is the time tested determination of the minumum requirements needed to build a safe boiler. I understand the desire to do-it-yourself but this isn't a place were anyone should be testing there skills out.

I would also assume that if you have a non-code boiler that it would be nearly impossible to get insurance in order to be able to operate in public. Even if you have insurance, having a non-code boiler would be the first place that the insurance companies look in order to get out of making any payouts if an incident were to happen.

I am planning on designing my watertube boiler and running the initial calcs, but will be having the design verified and built by a stamp holding shop.

Ken

[barts]

The price of Code boilers is such that many of us could not justify or even afford the hobby if they were required. I've got a couple of degrees in Mechanical Engineering, and felt comfortable designing and building Otter's new boiler myself in 1996, using commercial components (end caps, reducers, thread-o-lets, etc) for the pressure drum. I did the fabrication, welding and silver brazed in the copper tubes. Others may come to different conclusions for their own projects. The majority of boats on the West Coast do not have Code boilers; those that do are generally firetube boilers.

I hyro-test my boiler once a year to 150% (275 psi) of maximum working pressure, and store it full (no frost here) of water w/ tsp when not in use. I did manage to unsilver-solder a tube once when I let the water level get too low (the gauge glass was re-done to prevent a re-occurrence); the small size of the copper tube limited damage to wet soot getting everywhere.

- Bart

[Johnlanark]

Perhaps you may not be aware that The Steamboat Association of GB has a library of boiler designs.
http://www.steamboat.org.uk/sbas_boiler_designs.htm

[russkey]

... how do you know what RPMs you should be turning ? ...

Based on the things I've seen on this forum, as well as my reading of Steam-Engine Design, it seems that the only really practical way is to estimate and interpolate the RPM based on existing data on documented engines of similar configuration. It appears that RPM depends on things like the torque that the piston is able to generate in conjunction with the load that it is subjected to and the various internal frictional effects. Perhaps there is some way of figuring out the "maximum safe RPM" based on materials and geometry, but your average runtime RPM is a tough one. I've encountered this problem while trying to design my rotary engine (exacerbated by the fact that there isn't any reference that I can use, as far as existing engines go). At this point, my plan is to simply construct an engine with what I thing are oversized steam passages and valves, as these seem to be the parts that are actually sensitive to RPM, or steam flow rate (which are closely related). Other parts, such as the flywheel, need careful RPM calculation for larger engines, but this unlikely to be a problem with our smaller steamboat target sizes. I would love to see a contradiction to this, since it would make my life easier!

[marinesteam]

Bart,

Some very good points.

I too have a mechanical engineering degree so I feel comfortable designing a pressure vessel. But since it's not my area of expertise I know that it's prudent to have someone who is qualified check the work. I also know that I'm not qualified to be welding a pressure vessel. Hopefully, I can find a shop that is willing to let me do some of the work, bending and machining parts before they do the welding, I would like to roll in the tubes as well, hopefully saving some money but I know my limitations.

I also think there needs to be a clarification for those who may not know (not you) in that a non code boiler still needs to be built to code. The code is the minimum design standard that should be used when designing a boiler. The boiler still won't be a code boiler even if built to this standard if it wasn't built by a "S" stamp holding shop. Part of this is that the design firm is taking the some of liability in that they have certified that the design is suitable for the intended service. Obviously, this only covers the design of the boiler not any faults due to operational issues. As a sidenote: The boiler code came into existance because of the high rate of failures and death caused by theses failures due to the inadequate construction used on early steamboats.

The point to be made is that I have seen newbies come into the forums (not only this one) saying "I love steam all I need to do buy an engine and build myself a boiler" but it's not that easy. Luckily our hobby (and small scale live steam) has been free of any incidents but it only takes one "Medina" to change all of that. In Colorado it's also a crime to operated a boiler without inspection and Colorado cites the ASME code as it's standard for design.

As for the SBA's boiler design library, that's a very good reference and starting point but for those of us in the US one would still need to have the design reviewed and built by a stamp carrying shop for it to be a "code" boiler.

Saving some money is all and good, I try to do so when I can. But a power boiler is no place to find out what you don't know.

This is a good conversation to have but perhaps if it continues it should be it's own thread as not to hijack this one. Sorry if I have.

Ken

[JonRiley56]

Gents,

By all means keep the dialog going, it is worthwhile. Where or how I find a boiler for my boat is of secondary importance. I do have a couple of observations/questions on this subject:

1. If one acquires a used boiler, what kinds of "provenance" or proof do you need as to the integrity of the design and the quality of the build ? How does one know if there have been any modifications, repairs etc ? Could you in fact face a greater liability with a "tired" code boiler than with a fresh home built ? If the only in service test for biolers is hydro pressure testing and they both pass............how could you predict one might fail sooner than the other ?

2. Is there a difference between public and private use ? If it is not for hire etc are the regulations different. I believe in some activities there is a difference between "hobby" and "commercial".

3. Could one make the argument that the need for code assemply is directly proportional to the potential for injury/damage resulting from a malfunction and that therefore in decreasing need would be Fire Tube, Water Tube, and Monotube Flash ?

3. Is the code approved construction requirement just for the rpessure vessel or the entire assembly ? Is it conceivable to have someone build the pressure vessel part with the appropriate outlets etc and then finish the rest yourself ?

4. As an aside, I havent seen any talk in the marine boiler world of "fusible" plugs as sagety devices. Are they used and I have not noticed them, or are they particularly related to stationay steam like traction engines.

[DetroiTug]

"1. If one acquires a used boiler, what kinds of "provenance" or proof do you need as to the integrity of the design and the quality of the build ? How does one know if there have been any modifications, repairs etc ? Could you in fact face a greater liability with a "tired" code boiler than with a fresh home built ? If the only in service test for biolers is hydro pressure testing and they both pass............how could you predict one might fail sooner than the other ?"

Ans: When purchasing a used boiler, if the buyer is not qualified to assess it's worthiness, then they should consult a professional. If that is not possible, then they should just buy a new boiler. I bought my boiler used and the seller said it was only fired up once. After checking it over inside and out and there was nothing more than very light surface rusting, Inside the firetubes, top to bottom the mill shale was still present indicating the boiler had not seen any considerable use. Then I had some knowledgeable steamfolk in the area take a look, and they agreed with my amateur assessment. After a 300 pound hydro test, I felt comfortable operating it at 100 psi. There is a guy here in the area that has an ultrasound for checking shell thickness, I'm going to get that done along with the hydrotest in the spring. Age on a boiler, code or not, is really not conclusive at all, a new boiler if abused can be rendered unsafe in a span as little as 5 years. And on the other end of the spectrum, there are several 100 year old boilers around that are still safe to run. Riveted boilers, if I remember correctly, single lap, single row rivets can only be certified to 100 psi and butt jointed double row rivet boilers are good to 150 or 200 psi working pressure. Getting back to the failure question: If there is any indication the boiler might fail, obviously discard it. Has nothing to do with probability. If there is any probability, discard it. Pick a boiler type for the application and then go through the proper testing etc to ascertain it is 100% safe. Design the steam system safely, operate it safely, and it will be safe... Regardless the type of boiler. If one wanted to get technical, I guess it would be the monotube is the safest due to the low volume of water. However, monotubes are not very practical to use in a steamboat. There must be some sort reservoir/steam dome for any sort of operating stability. And of course that reintroduces increased volume.

"2. Is there a difference between public and private use ? If it is not for hire etc are the regulations different. I believe in some activities there is a difference between "hobby" and "commercial"."

Ans: In most states, a code boiler is required if you are going to carry paying passengers. Other than that, the boiler does not have to be certified, each state varies though. And this is also dictated by the size of the fire grate.

"3. Could one make the argument that the need for code assemply is directly proportional to the potential for injury/damage resulting from a malfunction and that therefore in decreasing need would be Fire Tube, Water Tube, and Monotube Flash ?"

Ans:Again, Buy, build, have built a boiler in a safe condition for the application, set it up safely and operate it safely, and there won't be any problem.

"3. Is the code approved construction requirement just for the pressure vessel or the entire assembly ? Is it conceivable to have someone build the pressure vessel part with the appropriate outlets etc and then finish the rest yourself ?"

Ans: Sure, that's what most people do, they buy a professionally made boiler and then set up the rest of their system themselves. Definitely, come here to the forum, start a thread on your project and post pics a long the way. I don't know where you'd get any more professional advice. That's what I did, and the input and coaching I received saved a lot of trial and error.

"4. As an aside, I havent seen any talk in the marine boiler world of "fusible" plugs as safety devices. Are they used and I have not noticed them, or are they particularly related to stationary steam like traction engines."

Ans: I think fusible plugs are mainly for locomotive/traction type boilers where the crown sheet is easily exposed. Most marine boiler designs like the VFT, the boiler would have to be empty to expose the crown sheet.

[87gn@tahoe]

This video shows that even annually inspected code boilers are not infallible when age and improper operation are factors:

http://www.youtube.com/watch?v=PsSVfAg1 ... 16F52EB07E

[barts]

Most steamboats out this way definitely don't have Code boilers...

Scotch boilers have fusible plugs.

A monotube boiler built along the "flash overfeed principle" has been successfully used in steamboat w/ fancy controls....
http://www.thesteamboatingforum.net/for ... ?f=8&t=237

- Bart