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faulttree·NUREG-0492 / IEC 61025·engineering, energy, manufacturing·complexity 3/3·since v0.6.5

Pressure vessel rupture (full vocabulary)

Voting, inhibit, house and undeveloped events in one tree — a 2-of-2 relief group, an over-pressure inhibited by a heater condition, and an order-3 minimal cut set with the tighter MCUB probability.

For the process-safety / HAZOP engineer

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Vessel ruptures Fault tree for "Pressure vessel ruptures": 1 top, 2 intermediate, 3 basic, 1 house, 1 undeveloped. 1 minimal cut set: {PRV_A, PRV_B, PUMP}. P(top) = 1.60e-6 (mcub). Event "EXT" is declared but referenced by no gate (unconnected). Vessel ruptures Heaterenergised 2/2 Pressure vesselruptures Sustainedover-pressure PUMP Pump runaway p=0.004 Both reliefs fail PRV_A Relief A stuck p=0.02 PRV_B Relief B stuck p=0.02 P(top) = 1.60e-6 (mcub)
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What this shows

The full NUREG-0492 vocabulary in one tree. INHIBIT renders as a hexagon with the HEATER conditioning event as an ellipse on its side; because HEATER is a house event forced to state: 1, it is absorbed as a constant TRUE and OVP reduces to {PUMP}. VOTING 2/2 is a redundant relief group that fails only when both valves stick.

The single minimal cut set is {PUMP, PRV_A, PRV_B} (order 3), and prob: mcub reports the minimal-cut-set upper bound — tighter than the rare-event default. EXT is an undeveloped event (diamond) that is declared but referenced by no gate, so it is noted as unconnected in the diagram description. Switching the heater to state: 0 would prune the over-pressure branch entirely and make the top event unsatisfiable.

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