The Steamboating Forum

Gee Mike. Now my eyes hurt...
RussN

Hi Mike

What a wonderful site but as Russ said, it gets to your eyes.

Coming back to the issue of safety valves or relief vales there is an article in SteamBoating Magazine (Issue 17-6) by Tony Anderson which includes them. The the photos and diagrams are still on the website and can be downloaded. His schematic is shown below:
Tony has moved the design of his plant along a bit further now and I may yet be able to twist his arm to write about it for the Mono-Tube website

Regards

Pete

"Quick question about your steam separator;
Is it considered part of your boiler pressure vessel or considered 'plumbing'?"

The separator vessel (6 inch diameter pipe, about 20 inches long, is considered an integral part of the boiler proper, and thus must NOT have any valve between the fired monotube coil (more than 100 feet of coil tube) and the separator. The boiler relief valve is mounted on the separator. This entire assembly falls under the ASME Code, Section I, Power Boilers.

The separator could have been considered as an "unfired pressure vessel", but then the pressure relief valve for the "Power Boiler" would have been required upstream of the separator. Then the separator would come under another set of rules, ASME Code, Section VIII, Unfired Pressure Vessels, and would still need its own pressure relief valve.

Years ago I built a small monotube steam generator, with no separator. When I shutoff the steam to the engine (without shutoff of the fire), that unit would have the safety valve lift and re-seat very quickly, and immediately repeat this process, at about 600 times per minute. How do I know 600 times a minute? Because I have been around military machine guns, the US M60 in particular, so I have some idea about this rate. Obviously this punishes the relief valve, and situations like this need to be avoided.

Fred, thank you for the explanation regarding the steam separator and where it falls in the ASME code. I suppose making one out of schedule 80 nipples, caps, bell reducers, Tees, etc might disqualify it from adhering to 'code'?

Sorry for the late reply. ASME Code rules do allow pipe sections, caps, reducers, etc to form a pressure vessel. To meet code there are many detailed rules, and to have a code stamped pressure vessel the fabrication must be performed by a "Code Shop", with calculations, material certifications, etc.

You mention using schedule 80 nipples welded to a vessel. This process, while apparently strong enough for our typical pressures, is prohibited by the code. Proper A-105 welded steel nipples, generally called "weld-o-lets" or "thread-o-lets" are needed as they have enough metal to structurally reinforce the hole in the vessel. These require full penetration welds, and generally a welding rod is placed between the vessel shell and the weld-o-let to make a gap before welding. Stick welding is OK, MIG is not OK.

The photo shows a "Thread-o-let" about to be welded into a boiler shell, with an alignment fixture that temporarily passes through a drilled hole in the vessel shell. Note how heavy this connector piece is, compared to schedule 80 pipe.

Piping components can be A-53 ERW (Electric Resistance Welded) pipe, but sometimes this pipe seam needs to be radiographed for code requirements. I always use seamless pipe for pressure vessels, so no radiographs are required. A-106 pipe is all seamless, and sometimes A-53 pipe can be had as seamless too.

Thank you again Fred for the explanation. My thoughts were a separator completely outside of the casing and pressure vessel. Made strictly of threaded fittings with zero welding if possible. Something like this, albeit much more complex (see attached)

Hi Fred, just wondering how your bigger, faster, meaner, rougher, tougher project is coming along?

Progress has been slow lately, as I have taken on a bit too much consulting work, building a 75,000,000 Watt geothermal plant in California, plus new design work for a new 100,000,000 Watt Sodium cooled nuclear reactor. The plan is to build a lightweight hull (similar to Margaret S lines) with an oil fired monotube boiler driving a 1000 cc three cylinder uniflow engine. Design is going to drive the hull (with a propeller) at about 15 MPH, far faster than other steamers I have seen. But I need to get a round tuit.

Short film of the monotube plant with a small (350 cc) engine on test:

https://youtu.be/9RIk7G01ngg

Hydrostatic test of steam/water separaror which receives 400F mixture from monotube coil. Steam to engine, hot water to counterflow heat exchanger that heats incoming feedwater.

Hi Fred,

What part of California is the concern you're consulting for located? Make it out that way much?

What kind of square footage of heating surface and hp figures are you looking at getting out of that plant? Room to force it and turn it up to eleven?

15mph is well past the contemporary hobby steamboat realm. Certainly in the US. It amazes me how many fast steamboats there were in their heyday, and how few there are today. Round Toits are hard to come by though.

I would love to see more footage of your plant and the development of the 3-cylinder uniflow in the future