John,

Richard's link gives the best there is. No regulations as such but a code of practise that satisfies the insurers. It really just seems to boil down to this extract from the code:

“…Design Verification

5.1

The constructor of a boiler to other than a recognised design available through the model engineering trade and/or press shall produce design drawings and demonstrate to the satisfaction of the inspector, either by calculation or by well-proven example, that the design and materials used have adequate strength.

5.2

If no working pressure is stated on the drawings, or published accompanying text, the boiler shall be treated as a new design and calculations shall be produced and validated…”

A safety factor of about 8x seems to be acceptable for the calculations, if you are starting from scratch then Martin Evan's "Model locomotive Boilers" steers you through the design calculations. A boiler inspector will look at the quality of the joints and witness an hydraulic test to twice working pressure and a steam test to 1.5 times working pressure.

As far as I can make out, that's pretty much it.

HTH,

Rod

Edited By Roderick Jenkins on 15/09/2016 12:14:27