A stationary floating vessel used to store crude oil or petroleum products at offshore fields pending transfer to shuttle tankers.
Quick facts
Regulation
MARPOL Annex I
In practice
From a marine engineering perspective, an FSO must maintain the reliability of its mooring system, hull integrity, cargo pump systems, inert gas plant, crude oil washing capability, and the oil discharge monitoring and control system, all of which are subject to MARPOL Annex I requirements. Because the vessel is continuously in a production environment with little opportunity for normal drydocking, class societies have developed in-water survey programmes for FPSOs and FSOs. Engineers must execute a rigorous planned maintenance schedule to prevent structural corrosion, mooring fatigue failure, and cargo system degradation in the absence of the normal port-call maintenance opportunities available to trading tankers.
Regulatory detail & full definition
A floating storage and offloading vessel is a permanently moored or semi-permanently stationed vessel used to store crude oil, condensate, or liquid petroleum gas produced from nearby subsea or fixed platform wells, holding the product until it can be periodically transferred to a shuttle tanker for transport to shore. Unlike an FPSO, an FSO carries no production processing equipment: it receives already processed hydrocarbons directly from a pipeline or production platform. The hull may be a purpose-built vessel or a converted tanker, and it is typically moored on a single-point buoy or spread mooring.
From a marine engineering perspective, an FSO must maintain the reliability of its mooring system, hull integrity, cargo pump systems, inert gas plant, crude oil washing capability, and the oil discharge monitoring and control system, all of which are subject to MARPOL Annex I requirements. Because the vessel is continuously in a production environment with little opportunity for normal drydocking, class societies have developed in-water survey programmes for FPSOs and FSOs. Engineers must execute a rigorous planned maintenance schedule to prevent structural corrosion, mooring fatigue failure, and cargo system degradation in the absence of the normal port-call maintenance opportunities available to trading tankers.