Modifications to API RP 520
Applications of Rupture Disks
1. Soft seated PR valves may be considered as an alternative to rupture disk (RD)/PR valve combinations for services operating below 450?F (232?C) when control of fugitive emissions is required to meet environmental regulations. The use of soft seated PR valves shall be approved by the Owner’s Engineer.
2. If installed upstream of a PR valve, rupture disks (RD) shall be installed as shown in Figure A–5.
3. The rated temperature at which the RDs are specified to function is the minimum temperature of the disk itself before it relieves. This may be lower than the normal process temperature due to ambient cooling of the non-flowing piping, RD, and disk holder, and is strongly affected by the geometry of the inlet piping.
The inlet piping must be designed and evaluated before the rated rupture temperature of the RDs is finalized.
Rupture Disk Selection and Specification
1) Rupture disks (RD) may be used in conjunction with or as a substitute for PR valves only with the approval of the Owner’s Engineer. Acceptable types of RDs are:
a) Pre-scored tension loaded conventional (forward acting) for both liquid and gas/two-phase service.
b) Pre-scored (cross-scored) reverse buckling for gas/two-phase only service.
c) Pre-scored (semi-circular) reverse buckling for gas/two-phase or liquid service. Pre-scored (semi-circular) may not be used under PRVs due to possible fragmentation.
2) The manufacturing range for all RDs shall be the lowest available from the manufacturer. The manufacturing range shall be applied below the design pressure of the equipment. Use of other types of RDs with larger manufacturing ranges shall be approved by the Owner’s Engineer.
