In Summary

• Generally, burst pressure varies inversely with temperature so the specified burst temperature must be carefully considered.
  - Specify the lowest temperature at the time the disk is expected to burst.
  - Different materials and different types of rupture disks have different sensitivities to temperature effects.
  
  
• The rupture disk is a differential pressure device.
  - The specified burst pressure is a value equal to the vessel relief pressure minus the backpressure.
                                                                   Or
  - The vessel relief pressure equals the specified burst pressure plus the backpressure.
  
• There are three types of backpressure to consider, these being constant, built-up and superimposed.
  - Constant backpressure is the pressure in the system that does not vary. It is generally a predictable component of the superimposed backpressure.
  - Built-up backpressure is the pressure created in the system as a result of fluid flow. It is a varying component of the superimposed backpressure.
  - Superimposed backpressure is the total pressure exerted (imposed) on the rupture disk by other sources. It is a variable that directly increases or decreases a vessel's relief pressure. It can also interfere with the expected operating ratio of the disk.
  
• Do not pipe multiple vessel relief systems into a common header; keep the piping separate. However, the individual piping may go to a common disposal system.
  
• Along with the Manufacturing Range (MR), Operating Ratio (OR) and Burst Tolerance (BT), the process design engineer must also consider backpressure when specifying the rupture disk.

References

1. API (www.api.org) Recommended Practice 520, "Sizing, Selection, and Installation of Pressure-Relieving Device in Refineries, Part 1-Sizing and Selection", 7^th Edition (January 2000)
2. API (www.api.org) Recommended Practice 521, "Guide for Pressure-Relieving and Depressuring Systems", 4^th Edition (March 1997)
3. ASME (www.asme.org) "Boiler and Pressure Vessel Code, Section VIII, Division 1" (1998)
4. Nazario, F. N., "Rupture Discs, A Primer", Chemical Engineering Magazine, June 20, 1988.