Combining rupture disks with safety relief valves: Fid-Bau Portal

Combining rupture disks with safety relief valves

Brazier, Geof

Protecting process systems from overpressurisation is vital throughout the CPI (chemical process industries). Both safety relief valves and rupture disks are commonly used for this purpose. A rapture disk serves as a barrier and thus protects the safety relief valve from process media, extends the life of the relief valve and prevents leakage to the atmosphere. The advantages of combining the two devices are explored here, and suggestions are provided for the decision whether the combination of the two or a rupture disk alone might be better. Besides cost, a reason for the latter may be freezing liquids with the risk of safety valve blockage. Benefits under normal conditions are e.g. that the rupture disk not only prevents leakage, but also protects the safety relief valve from caustic and highly viscous process materials. Other considerations are also discussed including sizing based on capacity testing according to ASME (American Society of Mechanical Engineers) standards and/or on the CCF (combination capacity factor) for the flow capacity of the combination of rupture disk and pressure relief valve. A calculation example is given, together with considerations of pressure drop and differential pressure.