Page 497 - APPLIED PROCESS DESIGN FOR CHEMICAL AND PETROCHEMICAL PLANTS, Volume 1, 3rd Edition

Process Safety and Pressure-Relieving Devices 463

Pb = stamped bursting disk pressure plus accumulation using a 1)4..inch disc with Mone! metal. Other disk and
of 10% plus atmospheric pressure, psia valve manufacturers have their 0\'111 combination data,
P 2 = pressure on outlet side of rupture disk, psia which when available, avoids the requirement of derating
the capacity to 80% of the rated capacity of the pressure
Wt � Sp Gr relief valve. Disks (metal or graphite) that fragment
Volumetric flow : A= , sq in. (7 - 46) should neoer be used because these may become potential
38Kd � Pb-P 2
problems for the safety valve performance. Therefore, a
non-fragmenting disk should be selected, such as a
where Sp Gr = fluid specific gravity relative to water = 1.0 @ reverse acting/reverse buckling preferably pre-scored
60°F
\,Vt = liquid flow, gallons per minute design, but knife blades are a viable alternate.

Sizing for Combination of Rupture Disk and Pressure Relief Example 7-4: Safety Relief Valve for Process
Valve in Series Combination
Overpressure
When the rupture disk is installed on the inlet side of The conditions set forth on the Operational Checklist,
the pressure relief valve (see Figures 7-10, 7-11 and 7-12), Figure 7-14, are used in the example specified on the
the ASME code requires that for untested disk-valve com- specification form (Figure 7-33).
binations that the relieving capacity of the combination
be reduced to 80% of the rated relieving capacity of the
pressure relief valve [ l]. Example 7-5: Rupture Disk External Fire Condition
For flow tested combinations, see a few typical data in
Table 7-12. Note, for example, that using a Continental An uninsulated 12-ft X 36-ft horizontal storage tank
disk reverse acting knife blade rupture disc with a Crosby containing CC1 4 is to be protected from overpressure due
JOS/JBS pressure relief valve that the combined effect is to external fire by means of a rupture disk. The tank does
to multiply the rated capacity of the Crosby valve by a mul- not have a sprinkler system. Storage pressure is 5 psig and
tiplier of 0.985 for a set pressure in the 60-74 psig rauge should not exceed 10 psig. Tank is assumed to be full. k =

Table 7-12
Rupture Disk/Relief Valve Combination Capacity Factors
I TELEDYNE DRESSER KUNKLE
I DISC DISC DISC PRESSURE FERRIS 1900-30 CROSBY CROSBY CROSBY THRU LONERGAN
SET
5000
1900
2600&
TYPE SIZE MATERIAL PSIG 4500 1900-35 JOSI JBS JB JO 5999 D&OB
ZAP 1.5 Mone I 60-74 0.982 - 0.985 0.983 0.980 - -
(contd)
1.5 Mone I 75 PLUS 0.982 - 0.985 0.990 0.986 - -
1.5 Nickel 30-49 - - 0.965 - 0.975 - -
I 1.5 Nickel 50-59 0.989 0.984 0.965 - 0.975 0.988 0.966

1.5 Nickel 60 PLUS 0.985 0.984 0.992 - 0.994 0.988 0.996

ZAP 3.0 Stainless Steel 15-29 0.963 0.966 - - - - -
]o Stainless Steel 30-34 0.993 0.966 0.955 - I - -
- I
-
-
-
0.970
0.966
0.993
35-49
3.0 Stainless Steel
3.0 Stainless Steel 50-59 0.993 0.966 0.970 0.976 0.981 I - -
Extracted by permission: Continental Disc Corp., Bul. #1-1111, pg. 4. Only portion of original tables presented for illustration.
Nole: Zap is a reverse-acting rupture disk using replaceable knife blades. Patented. Other disk and valve manufacturers have tested their own combi-
nations to obtain combination capacity factors.