What is Riser depacking or depressurization?
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Offshore oil and gas facilities often have long production risers; the uncontrolled de-pressuring or de-packing of these risers could result in flow excursions in excess of the set capacity of the flare system and could consequently over-pressurize the topsides pipe work and equipment.
Although the inlet separator PSVs are sized for blocked outlet scenarios (full flow), there are other cases, namely inadvertent opening of choke valves (mechanical failure) or uncontrolled riser de-packing into topsides pipework (resulting from an operator error) that could cause the PSV capacities to be exceeded, thereby endangering the personnel on board and the integrity of the topside facility.
Following are the some of the system design strategy to mitigate the risk: