Rupture Disc Reliefs in Liquid Service

For liquid reliefs through rupture discs without significant lengths of downstream piping the flow is represented by Equation 9-2 or by Equation 9-3 for flow through a sharp-edged orifice. No corrections are suggested. 

Equations 9-2 and 9-3 apply to rupture discs discharging directly to the atmosphere. For rupture discs discharging into a relief system (which might include knockout drums, scrubbers, or flares), the rupture disc is considered a flow restriction, and the flow through the entire pipe system must be considered. The calculation is performed identically to regular pipe flow (see chapter 4). The calculation to determine the rupture disc area is iterative for this case. Isaacs5 recommended assuming that the rupture disc is equivalent to 50 pipe diameters in the calculation. 

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