2021/8/8 16:52:19
Sizing for Rupture Disk Devices
General
Rupture disk devices may be used as the primary relief device for gas, vapor, liquid or multiphase service. The rupture disk size, when used as the sole relieving device shall be determined as specified, may only be used when a rupture disk device discharges directly to the atmosphere, is installed within eight pipe diameters from the vessel nozzle entry, has a length of discharge not greater than five pipe diameters, and has nominal diameters of the inlet and outlet discharge piping equal to or greater than the nominal pipe size of the device. Section 5.11.1.3 applies in all other cases.
The nominal size of the rupture disk device selected shall have a minimum net flow area, MNFA, equal to or greater than the required calculated discharge area. Consult the manufacturer for the minimum net flow area of the rupture disk device.
Rupture Disk Sizing Using Flow Resistance Method
The calculated size of a pressure relief system containing a rupture disk device may also be determined by analyzing the total system resistance to flow. This analysis shall take into consideration the flow resistance of the rupture disk device, piping and other piping components, entrance and exit losses, elbows, tees, reducers, and valves. The calculation shall be made using accepted engineering practices for determining fluid flow through piping systems. The calculated relieving capacity shall be multiplied by a factor of 0.90 or less to allow for uncertainties inherent with this method. In these calculations, flow resistance for rupture disk devices can be obtained from the manufacturer. The flow resistance is expressed in terms of velocity head loss (KR). ASME Code certified values should be used where available.
Rupture Disk Devices Used in Combination with PRVs
The capacity of a rupture disk device in combination with a PRV, where the rupture disk device is located at the valve inlet may be determined by multiplying the ASME stamped valve capacity by the combination capacity factor, Kc. Kc values are certified and published by the National Board of Boiler and Pressure Vessel Inspectors for specific disk/ valve combinations. When a disk/valve combination does not have a certified Kc then a Kc value of 0.90 shall be used provided the flow area is equal to or greater than the inlet of the PRV.
