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OLF FPSO Lessons Learned Project 2002Summary of Key Issues, Lessons Learned & Challenges Database of Norwegian FPSO Key Issues & Lessons Learned Norwegian FPSO successes Most widely reported issues/problems relating to UKCS FPSOs UK FPSO Checklist

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OLF FPSO Project 2002

Table 1: Summary of Key Issues, Lessons learned and ChallengesHome

CATEGORIES OF FPSO ISSUES

Overall Level of Importance

Underlying cause Issues/Problems Green water has affected 4 of 5 FPSOs. Waves over the bows have damaged structure and broken accommodation windows. Waves along the side have damaged ancillary equipment including fire stations, cable trays and pipework. Model testing and environmental predictions appear to have been inadequate to allow designers to eliminate these green water effects. 3 of 5 FPSOs have experienced internal cracks between tanks. Cracks were detected through minor leaks. No leakage has occurred outside the hull. In each case a programme of inspection and repair has been initiated. This involves taking the tanks and adjacent tanks out of service, making a manned entry and after cleaning, fitting appropriate stiffeners. The turret location is a key design issue. With the turret at greater than 75% of overall hull length from the stern, the vessel weathervanes free. At around 65% (4 of 5 FPSOs), thrusters are required to maintain/control heading. The controlled heading FPSOs have the advantage of being able to lock the turret and thereby reduce bearing and swivel wear. However this places a demand on the thrusters (which are safety critical) and the crew to mange turret repositioning. 3 types of turret bearings are used by the 5 FPSOs. 2 of 3 types have been troublesome. The wheel and rail type have proven unsatisfactory due to high point loading from the wheels, excess construction tolerances, vessel deflection, poor rail heat treatment leading to surface cracking and inadequate wheel lubrication. The hydraulic turret bearings have suffered from pad wear, high starting friction, gripper failures, hydraulic imbalance and difficulty to access and repair components. The layout of equipment on an FPSO is a critical design phase. Concerns noted include placing main generators too close to the accommodation, poor mechanical handling solutions, exhaust and flare radiation problems, module overcrowding when others are very spacious, poorly placed vents, access and escape routes restricted by cable and pipework, poor workshop and store locations.Design (D), Construction (CN), Commissioning (CM), Operational (O)

Remedial Actions / Lessons Learned Retroactive repairs/redesign including the fitting of side panels, raising bow walls and moving sensitive equipment appear to have reduced the problem. In some cases cargo limits have been imposed. A joint North Sea workgroup including the authorities and classification societies has now led to a greater understanding of green water design requirements. Conventional hull design and basic fatigue analysis has been unable to eliminate FPSO hull cracking in service. While this is not unusual for trading vessels the operational problems and costs of offshore repair make this situation undesirable. Future hull designs should make use of fatigue analysis in all critical and high risk areas with construction detail subject to high levels of control Experience to date from the single Norwegian FPSO with a free turret indicates lower maintenance and crew involvement than with the other FPSOs. In addition that FPSO has managed to achieve adequate safety of the accommodation forward of the turret, by using a firewall. Current experience suggests that a free turret with swivel and thrusters used for offloading only, results in the lowest Opex. Turret bearing design has evolved over time. While simple rails and wheels have proven inadequate, heavy duty rails and multiple bogies with rubber pads to spread the load have proven an effective solution. Hydraulic pads were selected to deal with high mooring loads on a large turret. While this has been effective leading to no downtime, maintenance has been excessive. A key learning from all designs is the need to make all components easily serviceable and replaceable. It is recommended that when a basic FPSO layout is outlined more time is spent with all interested parties both informally and through formal design reviews to ensure the best compromises are achieved. Capex, Opex and Safety issues must all be carefully considered by relevant specialists.

Green water SUMMARY

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D

Hull - Strength SUMMARY

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D

Turret Location SUMMARY

4

D

Turret Design SUMMARY

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D

Layout

SUMMARY

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D

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The Offshore Management Centre, RGU

77015022.xls.ms_office Summary

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OLF FPSO Project 2002

CATEGORIES OF FPSO ISSUES

Overall Level of Importance

Underlying cause Issues/Problems On only one FPSO capex over-runs were avoided. In this case contract terms were followed with minimum change. This kept costs under control, however the Operator admits quality was poorer than expected and opportunities to improve the design at low cost were missed. On the remaining projects costs over-ran significantly but the quality was higher than the original specification and design improvements implemented. 3 of 5 FPSOs had serious compression problems (gas seal failures, repeated bundle change-outs and cracked pistons) due to undersized scrubbers and liquid carry-over. Problems were solved by upgrades, improved instrumentation and online equipment monitoring. The cost of these failures which includes; service costs, spares, CO2 tax, substitute diesel fuel, and lost gas export income was substantial. The FPSO accommodation has insufficient beds (4 of 5 FPSOs). The situation is worsened by recent proposals from the unions that two people should not sleep in the same cabin simultaneously. This lack of beds seriously hampers summer maintenance programmes and delays major repairs or upgrades. Overall performance has been excellent. 4 of 5 FPSOs are delivering 95% or more of available volumetric production. While these figures were lower in the first 18 months production, regularity has generally exceeded industry expectations. There is no evidence that FPSOs are less safe than other installations. A number of FPSOs reported that with a smaller crew than a platform, relationships, communication and morale are better. FPSOs are placed on location for the duration of field life typically 720 years. This means that all major repairs, inspections and maintenance must be carried out in situ. Marine standards and codes assume periodic visits to port and occasional dry-docking.Design (D), Construction (CN), Commissioning (CM), Operational (O)

Remedial Actions / Lessons Learned

Capex Over Runs SUMMARY

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D

Almost all FPSO projects in the 90s were underbid by the main contractor. The Operator can either participate actively implementing upgrades when poor quality or low cost solutions are offered, or impose the contractual terms. In general an optimum balance can be struck by working with the contractor to maintain quality and provide assistance to improve efficiency. A number of factors contributed to these problems, poor instrumentation, vessel movement reducing efficiency of separation train, liquid hold up in pipes and slugging and poor performance of internals. It would seem a good investment to install larger scrubbers than normal to provide a safety factor for unknowns. The economic impact of limited accommodation on operations and project(start-up and upgrades) is likely to be significantly greater than the cost of the extra beds and facilities. Future FPSOs should have 100+ usable beds and/or have provision for temporary expansion. There is a lack of fully objective data and it is too early to fully evaluate the success or failure of different FPSO designs and operating strategies. To date high performances have been achieved but often at the expense of major modification and/or ongoing repair programmes. Opex data was not available for the review. There is evidence that active attention to and reporting of hazards improves safety awareness and thereby performance. The challenge is to revise all aspects of marine standards incl. quality control, material specifications, coatings, fatigue analysis, subcontractor management, and mechanical handling to take account of the need for minimum maintenance and in field repair.

Compression SUMMARY 1

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D

SUMMARY Accommodation

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D

Uptime Performance SUMMARY

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O

Safety - General SUMMARY In Situ Repairs and Modifications CHALLENGE

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O

4

D

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The Offshore Management Centre, RGU

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OLF FPSO Project 2002

CATEGORIES OF FPSO ISSUESCrew SUMMARY

Overall Level of Importance

Underlying cause Issues/Problems All FPSOs operate with a base crew of 35-40. This required a number of staff particularly crane operators and mariners to be multi skilled. However most FPSOs carry typical POB levels of 5570. This can cause significant problems for major maintenance or upgrade projects. A means is required to increase FPSO accommodation for short periods (say 2-6 months) for project or major repair/remedial work. The upgrade would have to meet all applicable safety requirements including the provision of recreation space, lifeboat, refuge and escape facilities. Construction standards for cargo and ballast pipework have proven inadequate for FPSOs. Problems have included weld failures, leaks and corrosion. GRE pipework has had to be reinforced due to inadequate jointing Place