Several pressure relief valve installation guidelines are peculiar to the case of a rupture disk in the inlet line. Each of these is required by Section VIII of the ASME Boiler and Pressure Vessel Code.
a. The rupture disk should be of a nonfragmenting design. Fragments may interfere with the operation of the pressure relief valve.
b. The rupture disk, when burst, should have a net flow area equal to or greater than the inlet connection area of the pressure relief valve.
c. The space between the rupture disk and the pressure relief valve must be equipped with a free vent, a bleed valve, an excess-flow valve, a pressure indicator, or some other means of detecting rupture disk leakage. Build-up of pressure in this space would increase the burst pressure of the rupture disk, which operates on the pressure differential across it.
d. When evaluating the nonrecoverable pressure drop across the inlet line, the rupture disk device should be represented in the list of fittings with its certified flow resistance factor (KR). If no certified value is available, a value of 2.4 should be used.
Figure 1200-18 shows a typical installation of a rupture disk in the inlet line of a pressure relief valve.