Page 443 - APPLIED PROCESS DESIGN FOR CHEMICAL AND PETROCHEMICAL PLANTS, Volume 1, 3rd Edition

Process Safety and Pressure-Relieving Devices 409

Pressure Vassel Requirements Vessel Typical Characteristics of
Pressure Pressure Rellel Valves

Maximum allowable Maximum relieving
accumulated pressure 121 pressure for
(fire exposure only) - 120- fire sizing
- -
- -
Maximum allowable - - Multiple valves
accumulated pressure 116 Maximum relieving
for multiple-valve installation pressure for
(other than lire exposure) - 115- process sizing
,- - - Single valve
...... - Maximum relieving
,- - pressure for process sizing
Maximum allowable -� - Maximum allowable set pressure
::,
accumulated pressure ccs ' for supplemental valves
for single-valve installation � 110 (fire exposure)
(other than fire exposure) ,- Q) - '
:i
,- "' -
"' �
c. - t � Overpressure (maximum)
c:
- c:
� :i: -
5
...... 3: 105 Maximum allowable set pressure
Q) for additional valves (process)
�� -
3:
- .Q -
<ii
...... E -
::,
E
Maximum allowable - ·;. -
working pressure ccs 100 t Maximum allowable set pressure
E
or design pressure - 0 - Simmer for single valve
(ty
E - pical)
Start to open
...... Q) t
-� - Slowdown (typical)
�
- - (see Note 6)
- 95-
- -
- - Closing pressure
- - for a slngle valve
- -
Maximum expected
operating pressure 90 Leak test pressure (typical)
(see Notes 5 and 6) - -
- -
-
...... -
-
- 85-
Notes:
I. This figure conforms with the requirements of Section VIII of the 4. The maximum allowable working pressure is equal to or greater
ASME Boiler and Pressure Vessel Code. than the design pressure for a coincident design temperature.
2. The pressure conditions shown are for pressure relief valves in- 5. The operating pressure may be higher or lower than 90.
stalled on a pressure vessel. 6. Section VIII, Division 1, Appendix M, of the ASME Code should
3. Allowable set-pressure tolerances will be in accordance with the be referred to for guidance on blowdown and pressure differentials.
applicable cedes.
Figure 7-7A. Pressure level relationship conditions for pressure relief valve installed on a pressure vessel (vapor phase). Single valves (or more)
used for process or supplemental valves for external fire (see labeling on chart). Reprinted by permission, Sizing, Selection and Installation of
Pressure Relieving Devices in Refineries, Part 1 "Sizing and Selection," API RP-520, 5th Ed., July 1990, American Petroleum Institute.