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Hazard Analysis of a TurretRECAPCore functions of a Turret System on an FSO:Maintaining the vessel on station through single point mooring;Allowing weathervaning or rotation of the vessel to adjust to climatic conditions;Fluid transfer from the risers to the process plant; andTransfer of electrical, hydraulic and other control signals.2The worlds leading sustainability consultancy
3Figure 1.0: Main components of a Internal Turret SystemGraphicsWhats this layout for?Plain slide without a text box used for inserting graphics e.g. pies, bars or images The worlds leading sustainability consultancyA series of swivel rings, or toroids, rotate on bearings about a central core. The production fluids flow up through pipes in the central core and round a toroidal shaped annulus between the swivel ring and the core, as illustrated in Figure 38. The fluids can exit through outlets in the swivel rings to reach the process plant on the vessel. Multiple dynamic seals prevent escape of hydrocarbon fluids to atmosphere. The central core rotates with the turret. The swivel rings rotate with the vessel as it weathervanes. Torque arms support the swivel stack and limit any sideways movement.34
Figure 2.0: Internal Passive Turret in Petrobras 31 FPSOGraphicsWhats this layout for?Plain slide without a text box used for inserting graphics e.g. pies, bars or images The worlds leading sustainability consultancyTurrets System and related Safety Concerns530 years of Operation in North Sea without major incident.Turret System equipment is designed for Zone 1 operation.Turret System is recognized to be a Safety Critical Element on an FPSO.
The worlds leading sustainability consultancySafety Critical Elements of a Turret SystemSwivel Stack Dynamic Seals in the SwivelsMain flexible riser connectionsMooring Lines and connectionMain Turret Bearings
6The worlds leading sustainability consultancyType of Turret and Its Safety ConcernsInternal Passive TurretPrime concerns are with turret bearings and ability to weathervane. Below are other damage mechanisms:Progressive degradation of bearingsExcessive friction of turretLeakage of flexible risers and connections in the turret and at the point of connection to the turntable manifolding.Cracking of elastomeric bend-stiffners
Figure xx: Overview of IPTFigure xx: Bearing ring for main Turret bearing of an IPTThe worlds leading sustainability consultancyType of Turret and Its Safety ConcernsInternal Active TurretOperational experience has indicated the following as the most safety critical areas:The upper bearings which takes all the loadsThe flexible riser hang-off connections to the turntableThe mooring line connection
Figure xx: Location of vertical and horizontal bearing pads and Flexible risersFigure xx: Bearing pads used for axial and vertical bearingsThe worlds leading sustainability consultancyType of Turret and Its Safety ConcernsExternal Cantilevered Turret (ECT)Areas of concern for the ECT system are as follows:Corrosion of the manifolding pipeworkDamage and failure of flexible risers and its associated connections.Progressive damage to mooring chains and connections.Integrity of cantilever support structureIntegrity of ESD valves on individual risers
Figure xx: Overview of the External Cantilevered TurretThe worlds leading sustainability consultancyType of Turret and Its Safety ConcernsSubmerged Turret Production (STP)Main concerns identified in the Safety Cases for STP buoys are:Anchor failureTurret SeizureHydrocarbon Leakage From flexible risers connections, top and bottom.
Figure xx: Overview of the External Cantilevered TurretFigure xx: Overview of the External Cantilevered TurretThe worlds leading sustainability consultancyThe Submerged Turret Production (STP) system is an elegant adaptation of the STL system toallow production as well as loading and is a much more compact design than conventionalturrets. The basis of the STP system is a conical buoy moored to the seabed. The buoy is pulledinto and secured in a mating cone in the bottom of the vessel and thus connecting the mooringsystem. Internal in the buoy is the turret with connections to the mooring and riser systems. Theouter buoy hull can rotate freely with the vessel around the turret by means of internal turretbearings. Oil is transferred through a compact multiple swivel via the loading manifold to theprocess system of the vessel. The turret is submerged and has water lubricated bearings. Whendisconnected, the buoy will float in an equilibrium position ready for new connection.10Type of Swivels and Its Safety ConcernsMultipath SwivelMain concerns regarding the above mentioned is:Failure of dynamic sealsCracking off bearing housings
Figure xx: Overview of the External Cantilevered TurretFigure xx: Overview of the External Cantilevered TurretThe worlds leading sustainability consultancyType of Swivels and Its Safety ConcernsCompact SwivelMain safety concerns for the above mentioned are integrity of dynamic seals, flexible risers and connections.
The worlds leading sustainability consultancyMonitoring of barrier oil pressure and torque and rotation on the torque arms isessential to ensure the swivel stack is functioning correctly.12
13Figure 1.0: Main components of a Internal Turret SystemGraphicsWhats this layout for?Plain slide without a text box used for inserting graphics e.g. pies, bars or images The worlds leading sustainability consultancyA series of swivel rings, or toroids, rotate on bearings about a central core. The production fluids flow up through pipes in the central core and round a toroidal shaped annulus between the swivel ring and the core, as illustrated in Figure 38. The fluids can exit through outlets in the swivel rings to reach the process plant on the vessel. Multiple dynamic seals prevent escape of hydrocarbon fluids to atmosphere. The central core rotates with the turret. The swivel rings rotate with the vessel as it weathervanes. Torque arms support the swivel stack and limit any sideways movement.13Potential Hazards and Its ConsequenceMarine Accidents on FPSOMooring FailureCritical failure of two or more mooring lines resulting in vessel drifting off stationRiser DamageRelease from risersThe worlds leading sustainability consultancyMarine Accident on FPSOs Mooring FailureCauses: Poor Design, Material failure, Severe weather, fouling of anchor lines, Turret seizure.Prevention:MaterialControl: Take vessel under towMitigation: Shutdown, Oil Spill response.
Frequency of Mooring Failure leading to loss of station keeping and damage to risers is 1.0 x 10-4 per year.
The worlds leading sustainability consultancyPotential Hazards and Its ConsequenceHydrocarbon Release on FPSOSwivel LeakDirect release of spilled oil to the sea, Fire at the Swivel, Explosion at SwivelDamage to cargo areaLoss of Some or all cargo to the seaThe worlds leading sustainability consultancyMarine Accident on FPSOs Mooring FailureCauses: Swivel seizure, Human Error, Rotating equipment failure, Excessive vessel motion, Process upsets, Poor maintenance, Helicopter crash.Prevention: Hydrocarbon boundary integrity, Impact protection, Natural ventilation, Operator competency, Passive fire protection, Pressure reliefControl: Emergency shutdown, blowdown, process segregationMitigation: PFP, Limited ignition sources, full flow drainage, ffire and blast walls, Inert gas in cargo tanks
The worlds leading sustainability consultancyAvailable Leak Frequency for SwivelsRelease SizeScenario DescriptionSize DistributionLeak Frequency (per year)Large (30kg/s)Production fluid or export gas release at swivel with potential resultsincluding spill to sea, fire or explosion, and escalation to cargo tanks or FPSO.1%1x10-3Medium (3-30kg/s)Hydrocarbon release at swivel with potential results including spill tosea, fire or explosion, and escalation to cargo tanks or FPSO.9%9x10-3Small (0.3-3 kg/s)
90%9x10-2Frequency of release of gas within Turret enclosure is estimated to be 2x10-2/year.Overall leak frequency for Swivel is 0.1 per year with hole size distribution that was suggested by SBM that was documented in Frequency Analysis of Accidental Oil Release from a generic FPSO Operations in GoM, Ref xx (dnv) :Table xx: Summary of Release Size, Scenario Description with respective leak frequencyThe worlds leading sustainability consultancyPotential Hazards and Its ConsequenceHydrocarbon Release on FPSOExplosion in turretDamage to the hullRelease from Cargo areaLoss of some or all cargo to the seaThe worlds leading sustainability consultancyMarine Accident on FPSOs Mooring FailureCauses: Material defects, dropped object, Excessive vessel motion, Various ignition sources, Poor maintenancePrevention: Impact protection, Operator competency, Passive fire protection, Corrosion protection, DO protection, Pressure reliefControl: Emergency shutdown, blowdown, process segregationMitigation: PFP, Limited ignition sources, full flow drainage, ffire and blast walls, Inert gas in cargo tanksFrequency of explosion in turret that may lead to leak in the cargo tank is 1x10-5 per year. HSE GOV UK provided a different frequency of turret explosion of approximately 2x10-4/year.The worlds leading sustainability consultancyConsequence of a Turret ExplosionStructural damage or plastic deformation of the turret. Missile generation is not considered credible. No potential for escalation to the gas injection manifoldFatality to all individuals involved in the initial blastSerious injury confined to turret and immediate surrounding area. High number of serious casualtiesLocal escape and evacuation routes potentially destroyed or damagedProcess area inventories potentially vulnerable to escalation but not envisaged21The worlds leading sustainability consultancyIncident ReportsGryphon FPSO, Aberdeen. (4th February 2011)Incident : Vessel lost control and went beam-on to the weather causing windward anchors to break and damage to the subsea infrastructure.Root Cause (Maersk Oil Investigation Report): Risk Management: The basis of design and FMEA did not include loss of heading.Competence: Personnel using the SDPM system had not refreshed or revalidated their initial training. ED did not routinely include Simrad Dynamic Positioning and Position Mooring system (SDPM) system malfunctions.Management of Change: The Performance Standard for the mooring system was too reliant on the anchor chains ability to maintain position.Operational Control: Lack of proceduralised mechanism22The worlds leading sustainability consultancyThe End23Questions?
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