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FPSOs are well suited to deep water applications, while their large storage capacity makes
them particularly effective as early production systems, where there is no oil pipeline.
Figure 1: SBM Offshore’s FPSO Cidade de Paraty, sailing away from the shipyard.
1.2
Abbreviations
FPSO
Floating Production Storage & Offloading
HFT
Hardware Fault Tolerance
HMI
Human Machine Interface
IPL
Independent Protection Layers
LO/LC
Mechanically Locked Open / Locked Closed valve
PST
Process Safety Time
SIF
Safety Instrumented Function
SIL
Safety Integrity Level
SIS
Safety Instrumented System
SRS
Safety Requirements Specification
1.3
Fast developing hazards
This paper particularly focuses on the Riser Depacking overpressure hazard, but also draws
on experience from other hazards such as the incorrect line-up of an Oil Cargo pump
resulting in a suction-side overpressure.
In these cases, the initiating event is a human error, which includes:
•
Opening a manual on/off valve out of sequence
•
Opening a manual choke valve too quickly
•
Opening a remote operated on/off valve out of sequence
1.3.1 Riser de-packing
FPSOs are usually connected to the oil reservoir via risers which interconnect the Subsea
systems to the FPSO hydrocarbon separation and processing systems. When the FPSO
riser valves are closed, pressure builds up behind the riser valve and a gas cap may
develop. If Subsea valves are closed, or subsea pumps are tripped, the hazard potential
comes from this high pressure gas cap. However, if the Subsea valves remain open