Well, the Stanley boilers NEVER had an explosive failure. When they do come to the end of their service life, they typically leak so badly that pressure can't be maintained, and people had to get a new one or pull the current one for repair.
What you might want to do is join the "Steam Automobile Club of America" and buy a set of plans for a Stanley boiler. They came in different horsepower ratings (steam generating capacity) for 10 hp, 20 hp, 30 hp, and 40 hp. Stanley engines, mostly having to do with the diameter of the drum and the length of the tubes. It would be fairly easy to tailor one to your requirements.