Mich. Admin. Code R. 408.4207 - Factors of safety

Rule 207.

(1) The lowest factor of safety that will be permissible on existing installations under any conditions is 4.5. Secondhand boilers shall have a minimum factor of safety of 5 when the longitudinal joints are of butt- and double-strap construction, and a minimum factor of safety of 6 when the longitudinal joints are of lap-riveted construction.

Horizontal-return tubular boilers having continuous lap-riveted joints of more than 12 feet in length shall have a factor of safety of not less than 8.

(2) The factors of safety for all standard boilers having longitudinal joints other than lap-riveted construction shall be increased at the end of its specified age limit by not less than 5/10, except that after a thorough internal and external inspection and a hydrostatic pressure test of 1 1/2 times the pressure allowed and held for a period of at least 30 minutes, during which no distress or leakage develops, the pressure may be continued at a factor of 5.5. These factors may be increased by the inspector as the condition and safety of the boiler may dictate, and in no case shall the factor of safety be less than called for by the rules for new construction.
(3) In no case shall the maximum allowable working pressure on old boilers be increased, unless they are being operated at a lesser pressure than would be allowable for new boilers, in which case the changed pressure shall not exceed that allowable for new boilers of the same construction.


Mich. Admin. Code R. 408.4207
1979 AC

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