Page 491 - APPLIED PROCESS DESIGN FOR CHEMICAL AND PETROCHEMICAL PLANTS, Volume 1, 3rd Edition

Process Safety and Pressure-Relieving Devices 457

Rupture Discs As Sole Relieving Devices Rupture Discs Used in Multiple Or For
Additional Hazard Due To External Heat

Max. Possible B.P. 105 PSI 110 PSI Max. Possible B.P. 116 PSI
<· 5% Rupture Toi. l +5% '" {
Max. Stamped B.P. 100 PSI J + 5%
MAWP <., Max. Stamped B.P. 110 PSI
105 PSI
+ Mfg. Range - + 10% MAWP 110% MAWP/
91 PSI J + 10% + 10%
Specified B.P. .......____MAWP �
}-5%
- Mfg. Range
Min. Stamped B.P. 86 PSI 95 PSI Specified B.P. 100 PSI
}-5% }
- 5% Rupture Toi.
-5% S%
Min. Possible EI.P. 82 PSI
91 PSI Min. Stamped B.P. 95 PSI
} "
-5%
Operating Pressure 86 PSI Min. Possible B.P. 90 PSI
to B.P. Percentage

Multiple Devices Additional Hazards
Max. Operating Pressure Due To External
Heat

Example Example
Mfg. Range O + 10%, - 5% Mfg. Range O + 10%, - 5%
MAWP O 100 PSI MAWP c 100 PSI

Figure 7-31A. Rupture disks as sole relieving devices. By permis- Figure 7-318. Rupture disks used in multiple or for additional haz-
sion, Fike Metal Products Div., Fike Corporation. ard due to external heat. By permission, Fike Metal Products Div.,
Fike Corporation.

(MR) discussed earlier applied to the burst pressure wi!l thus: 105 = 0.7 Pb
establish the most probable maximum Pb. Pb-min = 105/0.7 = 150 psig min rupture disk burst
The burst pressure maximum cannot exceed the pressure
l\11AWP of the vessel. Depending on the situation, it may
be necessary to work backward to the operating pressure From manufacturing range table for this type of disk, MR
maximum to see if this is usable. Table 7-9 summarizes = + 10/-5%@ 150 psig rupture pressure minimum. The
typical rupture disk characteristics noting that the maxi- maximum rupture pressure = 150 + 10% = 165 psig,
mum normal operating pressure of the system is shown as plus/minus the disk tolerance of 5%, allowing a final
a function of the rupture disk bursting pressure, Pb. maximum burst pressure of 173.2 psig.
The minimum stamped bursting pressure of the disk
Example 7-3: Rupture Disk Selection would be 150 psig + 5% tolerance = 157.5 psig.
With a -5% MR, the specified burst pressure would be
Examination of the temperature control ranges of a 157.5 + 5% = 165.4 psig.
process reactor reveals that the normal controls are to With a + 10% upper MR, the maximum stamped burst
maintain a pressure of the reacting mixture of 80 psig, pressure of the disk could be 165.4 + 10% = 181.9 psig.
while the upper extreme could be 105 psig, which would Using the code allowed tolerance for burst, the disk
be defined as the normal maximum operating pressure. could burst al 181.9 + 5% = 190.9 psig. The maximum
Select a conventional rupture disk, then from Table 7-9; allowable working pressure for the vessel cannot be less than
Pmaxop = 0.7 P1, 181.9 psig.