ABS has published industry best practices to address the challenges posed by an aging global Floating Production Storage and Offloading (FPSO) fleet.
Enhancing Safety on FPSOs: Operations and Maintenance is the output from an ABS-led working group consisting of Chevron, Shell Trading (U.S.) Company, Petrobras, MODEC and SBM as well as The Bahamas Maritime Authority (BMA), the Republic of the Marshall Islands (RMI) Registry, and the U.S. Coast Guard 8th District.
The FPSO safety guidance focuses on areas such as tank design and arrangement, cleaning and inspection, risk-based inspection of hull structures, composite repair tracking and carrying out repairs while operating. “Operations and maintenance challenges vary widely across the global fleet of FPSOs. With many assets well over 40 years old, hull integrity and maintenance require a large portion of resources,” says Matt Tremblay, ABS Vice President, Global Offshore.
Tank design for cleaning and remote inspection
– Stiffener profiles should be changed to minimize the deposit of sediments and to facilitate COW.
– Tank suctions are to be preferably located at the center line of the tank. Alternatively, consideration may be given to a suitable list within the acceptable hull girder strength and stability parameters to facilitate flow towards the tank suctions or suctions in tank sumps if allowed for by double hull construction.
– Large sized limber holes through transverse and longitudinal framing so as to allow efficient cargo drainage to pump suction.
– MARPOL requirements for COW systems require a minimum of 85 percent vertical and 90 percent horizontal surface coverage. Consideration for additional COW machines during the design phase by a thorough shadow analysis is recommended to maximize the coverage, especially in way of bottom areas.
– Consideration of a COP system arrangement to run dedicated COP for COW during offloading
– Hydraulic pumps, in lieu of the conventional steam turbine pumps, with deep suction wells may enable better offtake of the crude oil with sludge at the bottom. Alternatively, the use of in-tank eductor stripping systems
– Cargo pump used for COW may have direct suction from clean slop tank, with the suction capacity large enough to not cause abnormal vibration due to cavitation.
– Consider remote control valves on COW branch lines to simultaneously control COP from Cargo Control Room (CCR) during offloading.
– It is recommended that adequate means of positively isolating the COW machines servicing one tank from the rest of the system be provided to enable maintenance and positive isolation for confined space entry.
– Arrangement of topsides should allow for the entire machine to be pulled and laid down. Approved temporary lifting arrangement may also be considered as an alternative. Another option to consider would be COW machines that can be removed in sections.
To prevent bottlenecks, ABS is also implementing a requirement to include a tank to serve as an additional slop tank or take the place of any tank other than a cargo tank that is necessary to continue production in 2022. Tanks in current designs may have one or more of the following specialty designations:
– Slop tank
– Off-spec produced oil tank
– Produced water tank
– Flow assurance tank
– Tanks designated for use with chemicals designed to prevent hydrate formation
To promote normal operation of the production system and allow offloads to continue while tanks are being examined, all specialty tanks such as the ones listed above should be arranged and piped to be interchangeable whenever possible when they are fitted, subject to restrictions related to fiscal metering and environmental regulations for managing oily water mixes.
Conducting repairs while operating
Executing FPSO structural repairs while operating is a situation all operators typically face during the lifecycle of the FPSO, even under the most rigid asset integrity management regimes. To overcome some of the challenges previously discussed, owners and operators must find solutions that will produce the expected results while having the following key expectations in mind:
– Safety of personnel, environment and asset
– Reduced impact to production
– Achieving effective results
– Compliance with classification and statutory requirements