Cause & Consequence
- Failure of vessels or pipework
Floating production/storage unit
Specific Incident Equipment
The spill originated from a filter on a cargo (crude oil) export line located upstream of the export metering skid. The filter is comprised of a main housing, door and filter basket. The housing door is sealed using a bandlock closure mark 1 with an energised seal.
1. Design- failure related to design
The Bandlock closure mark 1 uses energised seals to create a seal on the filter housing door. This requires application of fluid pressure on the seal in order to push the seal out against the seal face. In the event that there is no pressure applied to the seal, it will relax back to its normal profile. In this condition and in the event there is a backwash (i.e. when pumps are shutdown quickly as occurred in this situation) , this can result in debris being washed up into the bandlock seal area. With debris in contact with the seal or seal face, the seal can be compromised resulting in leak path. Following system shutdown and spill containment, the filter housing was opened for inspection of the seal. Pieces of plastic, polythene and perspex material were found between the seal and seal face.
2. Equipment- No failure in the equipment itself
Operation –ESDV trip and immediate shutdown of the cargo discharge pumps allowed fall in pressure within the line and the resulting backwash flushed debris into the relaxed seals.
3. Procedural – Deficient procedure
Standard Operating Procedure did not require standby person for restart after shutdown as it was assumed that the pre discharge pressure testing and uneventful discharge demonstrated export line integrity. The effects of shutdown on the integrity of the seals were not known.
4. Operational mode in area at time of release - Cargo discharge
- Review the adequacy of bandlock closure for use on the filter enclosure and identify alternative closure devices.
- Review the design of the filter arrangement to avoid debris getting to the sealing area with the installation of a screen between the filter and the seals.
- Provide CCTV coverage to allow monitoring of the metering skid during offloading operations.
- Review and update Standard Operating Procedure to ensure that clear guidance is provided for startup, shutdown and on actions to be taken following a trip of export operations including requirement to have standby person at metering skid.