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:
- A dynamic simulation study of uncontrolled de-packing should be conducted to analyze the potential impact on the system.
- Interlocks and inhibits could be installed to reduce the probability of a hazardous situation arising.
- Affected pipe work (Inlet piping, manifolds, etc.) and equipment (e.g. inlet separator) can be rated at higher pressures than normally required to with stand the pressure incursions.
- HIPS can be an alternative option as well.