Mont. Code Ann. § 50-74-216
Hydrostatic pressure test
50-74-216 . Hydrostatic pressure test. When necessary, the boiler inspector shall subject boilers, except those exempted by 50-74-103 , to hydrostatic pressure, which hydrostatic pressure shall not exceed 150% of the steam pressure allowed on the boilers, providing there are no such leaks on such boilers which prevent the inspector from applying such hydrostatic pressure.