ARSD 61:08:05:17.04. Factors of safety

The working pressure shall be decreased by the inspector if the condition and safety of the boiler warrants it. The following factors of safety represent minimum values to be used. The lowest factor of safety permissible on existing installations is 4.5, except for horizontal-return-tubular boilers with continuous longitudinal lap seams more than 12 feet in length, for which the factor of safety is 8. When the latter type of boiler is removed from its existing setting, it shall not be reinstalled for pressures in excess of 15 psig.