Boiler certification in a launch

[John OlsenParticipant @johnolsen79199]

Not being based in the UK I have no idea what the law is there, but I know that here in New Zealand the situation is ambiguous to some degree. Apparently the marine people have responsibility for boilers in vessels, but they are apparently not interested in small steam boats. So people generally get their steam launch boilers tested and certified as if they were a stationary boiler, or if they are small enough to qualify, under the model engineering club system, which is OK for boilers up to a cubic foot and 100 psi if I recall correctly.

My own 30 foot launch has a boiler much bigger than that. and the intended working pressure is 170 psi, or about 11 Bars if you go that way. So it has so far had a hydraulic test from SGS M&I and will have a steam test with them once I get the burner operating reliably and with enough power to make such a test meaningful. So it will actually have the same certification it would have if it was bolted to the floor in some factory. It was also built with fully traceable materials, and the welder was done by a firm certified for pressure vessel work. The safety valve was set and sealed for me by the supplier. The boiler design is actually certified for a working pressure of 250psi, but I don't feel that the white metal bearings in my engine would be very happy with the sort of loads that would lead to so plan to operate at the more moderate pressure.

If I was in the UK, I would approach the Steam Boat Association and get my boiler certified through their system. They are accustomed to the types of boilers used in amateur steam launches, and it will be possible to get insurance and all that.

Even if there was really no official scheme available, I would want to make sure that any boiler I had anything to do with was inspected and OKed by someone other than myself, and with no emotional ties to the project. If you can't find an independent inspector who thinks it is OK then maybe it isn't!

It is also important to bear in mind that the real danger with steel boilers, provided they are reasonably competently made in the first place, is corrosion due to neglect. A boiler that is not used often can corrode just as fast and maybe even faster than one that is in regular use.

John

[Brian HParticipant @brianh50089]

I suspect t hat rusting inside a small compressor air tank wold not result in an explosion, just a small leak at the most rusted point that would prevent the pressure from rising.

Brian

[John OlsenParticipant @johnolsen79199]

You are right, when a compressed air container fails there is likely to be a bit of a bang but not the kind of disaster that a boiler can create. This is because the water in a boiler is at an elevated temperature, so that as the pressure drops due to a rupture, more of it flashes into steam. I've read somewhere about domestic radiators being tested with compressed air just by putting them into a bit of a cage and putting the pressure on. They would go with a bit of a bang if they failed, but not break out of the cage. With water and steam, the water flashing into steam will keep the pressure up long after the air would have dissipated.

John

[Clive IndiaParticipant @cliveindia]

Small boilers are covered in the 2018 Boiler Regulations

They are really easy to test.

Why not just test them?

[Tony Wright 1Participant @tonywright1]

Just be sensible.

[Harry WilkesParticipant @harrywilkes58467]

Here is a link to the SFMES current small boiler regs link

H

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