1112.12 Discharge Piping.

The piping used for pressurerelief device discharge shall be in accordance with Section 1112.12.1 through Section 1112.12.5. [ASHRAE 15:9.7.9] 1112.12.1 Piping Connection. Piping connected to the discharge side of a fusible plug or rupture member shall have provisions to prevent plugging of the pipe upon operation of a fusible plug or rupture member.

[ASHRAE 15:9.7.9.1] 1112.12.2 Pipe Size. The size of the discharge pipe from the pressure-relief device or fusible plug shall be not less than the outlet size of the pressure-relief device or fusible plug. [ASHRAE 15:9.7.9.2]

(3) The design pressure of the body of the relief valve

used on the higher-pressure vessel shall be rated for operation at the design pressure of the higher-pressure vessel in both pressure-containing areas of the valve. [ASHRAE 15:9.7.8.3] 1112.11.4 Discharge Location, Special Require-ments. Additional requirements for relief device discharge location and allowances shall apply for specific refrigerants in accordance with Section 1112.11.4.1.

[ASHRAE 15:9.7.8.4]

1112.11.4.1 Water (R-718). Where water is the refrigerant, discharge to a floor drain shall be permitted where the following conditions are met: (1) The pressure-relief device set pressure shall not

exceed 15 psig (103 kPa).

(1) The pressure-relief device set pressure shall not

exceed 15 psig (103 kPa). (2) The floor drain shall be sized to handle the flow

rate from a single broken tube in a refrigerant

(2) The floor drain shall be sized to handle the flow

rate from a single broken tube in a refrigerantcontaining heat exchanger. (3) The Authority Having Jurisdiction finds it

acceptable that the working fluid, corrosion

1112.12.4 Design Back Pressure. The design back pressure due to flow in the discharge piping at the outlet of pressure-relief devices and fusible plugs, discharging to atmosphere, shall be limited by the allowable equivalent length of piping determined in accordance with Equation 1112.12.4(1).

« «

Where: L = Equivalent length of discharge piping, feet. Cr = Rated capacity as stamped on the relief device in pounds per minute (lb/min), or in SCFM multiplied by 0.0764, or as calculated in Section 1112.14 for a rupture member or fusible plug, or as adjusted for reduced capacity due to piping in accordance with the manufacturer of the device, or as adjusted for reduced capacity due to piping as estimated by an approved method.

[Equa

22 ) d • ln ( 6 • f

[Equa tio n 1112.12.4(1)]

0.2146 • d ⁵ ( P 0 ² P

P0 )

( P 0 ² P 22 ) d • ln ~~(P2~~

f • C r ² 6 • f

222 2019 CALIFORNIA MECHANICAL CODE

REFRIGERATION

f = Moody friction factor in fully turbulent flow. d = Inside diameter of pipe or tube, inches. ln = Natural logarithm. P2 = Absolute pressure at outlet of discharge piping, psia. P0 = Allowed back pressure (absolute) at the outlet of pressure relief device, (psia).

Where: C = Rated discharge capacity of air, pounds per minute. d = Smallest internal diameter of the inlet pipe, retaining flanges, fusible plug, or rupture member ; inches.

For rupture members:

[Equation 1112.14(3)] P1 = (rated pressure in psig x 1.1) + 14.7 For fusible plugs: P1 = Absolute saturation pressure, corresponding to the

stamped temperature melting point of the fusible plug