What are you going to do with the steam, at what pressure and at what rate? L
Man , if you are serious and cannot be dissuaded then I reccomend you check out www.lindsaybks.com for books on boiler construction ! Know this , if you have no experience with boilers they are deathly dangerous ! Let th' heat get a little too high or th' water level too low and they can explode ! If you are runnin' one at superheat , that high pressure , high temp steam is more deadly than an explosion if it developes a leak ! That steam from a leak will cut and cauterize at th' same time and you wont know you are hurt till you see parts of yer hand on th' deck ! Also know that a boiler on board a Navy ship is NEVER left unattended , there is a round th' clock watch done in 4 hr shifts to make sure it wont go "BOOM" !!!
Are they not fitted with decent pressure relief valves then ?
There might be dirt or rust clogging it up, or metal fatigue. A few years ago a vintage steam roller in Holland exploded for no apparent reason. Of course nobody has the instinctive understanding of these machines anymore... (which should be an incentive to build one!!!).
That's why they have to be very carefully inspected every year - there are still special insurance companies for that kind of risk. In the UK National Vulcan and British Engine still take steam boiler risks - and inspect annually. An old aquaintance was a metallurgist for them. Steve