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 Nevada Administrative Code (Last Updated: January 6, 2015)
 Chapter455C Boilers, Elevators and Pressure Vessels
  BOILERS AND PRESSURE VESSELS
  Pressure Vessels

  NAC455C.294. Maximum allowable working pressure and minimum factor of safety.  

Latest version.

  •      1. The maximum allowable working pressure for standard pressure vessels must be determined in accordance with the applicable provisions of the edition of the code under which they were constructed and stamped.

         2. The maximum allowable working pressure on the shell of a nonstandard pressure vessel must be determined by the following formula:

    TStE

    ——

    =

    maximum allowable working pressure, in PSIG

    RFS

    where:

    TS            =

    ultimate tensile strength of shell plate, in PSIG. If the tensile strength of a carbon steel plate is not known, it shall be deemed to be 55,000 PSIG for temperatures not exceeding 650 degrees Fahrenheit. For all other materials, the lowest stress values for that material designated in division 1 of section VIII of the ASME Boiler and Pressure Vessel Code, as adopted by reference in NAC 455C.108, must be used.

    t                =

    minimum thickness of shell plate of weakest course, in inches.

    E              =

    efficiency of longitudinal joint, depending upon construction. The following values must be used:

    For riveted joints, calculated riveted efficiency.

    For fusion-welded and brazed joints:

    Single lap weld                                                40 percent

    Double lap weld                                              50 percent

    Single butt weld                                              60 percent

    Double butt weld                                             70 percent

    Forge weld                                                       70 percent

    Brazed steel                                                     80 percent

    R              =

    inside radius of weakest course of shell, in inches, if the thickness does not exceed 10 percent of the radius. If the thickness is more than 10 percent of the radius, the outer radius must be used.

    FS            =

    factor of safety.

         3. The maximum allowable working pressure for nonstandard pressure vessels subjected to external pressure will be determined by the applicable provisions in division 1 of section VIII of the ASME Boiler and Pressure Vessel Code, as adopted by reference in NAC 455C.108.

         4. The minimum factor of safety may not be less than the factor set forth in the edition of the code that was applicable at the time of construction. The maximum allowable working pressure may be decreased if deemed necessary by the inspector or special inspector to ensure the operation of the vessel within safe limits. The inspector or special inspector shall consider the condition of the vessel and the particular service to which it is subjected.

         5. The maximum allowable working pressure permitted for formed heads under pressure will be determined by using the appropriate formulas set forth in:

         (a) Division 1 of section VIII of the ASME Boiler and Pressure Vessel Code, as adopted by reference in NAC 455C.108; and

         (b) Subsections 3 and 4.

     (Added to NAC by Div. of Industrial Relations by R101-02, eff. 12-15-2004)