Copyright 2012, Brazilian Petroleum, Gas and Biofuels Institute - IBP This Technical Paper was prepared for presentation at the Rio Oi & Gas Expo and Conference 2012, held between September, 17-20, 2012, in Rio de Janeiro. This Technical Paper was selected for presentation by the Technical Committee of the event according to the information contained in the final paper submitted by the author(s). The organizers are not supposed to translate or correct the submitted papers. The material as it is presented, does not necessarily represent Brazilian Petroleum, Gas and Biofuels Institute’ opinion, or that of its Members or Representatives. Authors consent to the publication of this Technical Paper in the Rio Oil & Gas Expo and Conference 2012 Proceedings.

______________________________ 1 BSc EDEE, Business Development Manager - Aker Pusnes AS

IBP1267_12 MOVABLE CHAIN JACKS AND WINCHES,

CASE STUDY OF PETROBRAS’ P58/P62 AND ENI’S GOLIAT Reidar Grindheim1

Abstract Recently, Aker Solutions delivered a movable chain jack system to Petrobras’s P58/P62 FPSOs and a movable windlass system to ENI’s Goliat FPSO. This paper highlights the main differences between the two systems and when it is beneficial to employ movable systems. There are many parameters to consider in determining which system to use – also a traditional system involving a single winch or chain jack per mooring line may in many cases be preferred. The movable chain jack concept is designed to operate multiple mooring lines within the same cluster. A single chain jack is lifted by a skidding gantry and moved to the next mooring line and so forth. Installation and messenger chains are moved using a large sliding chain locker allowing for later offloading of the surplus chain. The movable windlass system is also designed to operate multiple mooring lines within the same cluster. However, in this case the winch is rotary and can operate via electric or hydraulic power. One of the main considerations is to move the windlass and keep the mooring lines intact without cutting them. 1. Introduction The primary purpose of an offshore mooring system is to maintain a floating unit on station within specified tolerances. These tolerances are often based on offset limits determined from the configuration of the riser system. The mooring system provides restoring forces that act against environmental forces (wind, waves and currents) that are trying to move the unit off station. Most mooring systems for offshore application are spread moored or single point moored (including turret systems). Spread mooring is the conventional mooring approach and is widely used for both drilling and production units. Spread mooring keeps the unit in position at an optimal heading but does not allow weathervaning. Single point mooring (internal/external turrets) is used primarily for ship-shaped vessels allowing the vessel to weathervane. However, a spread moored system can also be applied to ship-shaped vessels and we see many of this type off the coast of West Africa and Brazil. Traditionally, on-vessel mooring equipment has consisted of individual winches, fairleads and chain stoppers located at each mooring line. The mooring lines can be chain, wire rope, fiber rope or a combination. This paper discusses movable chain jacks and winches recently supplied for spread mooring systems on both ship-shaped and cylindrical-shaped FPSOs. 2. Traditional Spread-Moored Platform Designs Position moored production and drilling units come in various shapes and sizes. Traditionally, we have seen semisubmersible, spar and ship-shaped units. All these units have applied winch or chain jack systems. Figure 1 shows typical designs that have been in use for several decades.

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Figure 1. Traditional spread moored designs 3. Recent Spread-Moored Platform Designs The last few years have brought several other designs to the attention of potential operators. Figure 2 shows the variety of these more recent designs. Of these recent designs, we know that the Sevan Platform, MinDOC and Octabuoy have all been built and deployed (Octabuoy delayed). All these new designs will need some type of spread moored system. In some cases this may include a movable tensioning system.

Figure 2. Recent spread moored designs

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4. Traditional Tensioning Equipment In the early days of winches, the power source was steam. Aker Pusnes’ first steam winch was manufactured in 1891. Spare parts for steam winches on merchant ships are still being supplied. Today, however, hydraulic or electric motors power offshore winches. There are various types of tensioning equipment used on offshore platforms. Some of the main types of offshore winches are described below and depicted in Figure 3: 4.1. Traction Winches The traction winch is a sophisticated design, offering high pulling force over the whole length of rope (synthetic or steel). It is mainly used for long lengths of rope. The rope is pulled in by grooved, twin drums (frictional holding created by several parallel wraps) and the free end stored on a separate storage drum. Synthetic ropes can also be stored in a bin. 4.2. Rope Drum Winches Rope (synthetic or steel) drum winches are used when all the rope can be hauled in or reeled out and stored on the same drum. They can normally operate at faster speeds than chain winches. The pulling force will normally decrease as the number of layers of wire/rope increases on the drum. Spooling equipment or grooved drums can be used with the winch to provide improved spooling. 4.3. Chain Winches/Windlasses Offshore chain winches normally comprise a cable lifter with minimum 5 pockets and a drive unit consisting of a gearbox with electric or hydraulic motor(s). Special compact winches of this type have been developed for turret mooring on FPSOs and spread moored production rigs. The extreme compact size is possible because band/disc brakes and hydrodynamic brakes are replaced by pawl stoppers on the cable lifter unit itself. This is acceptable for most production units where there is no requirement for emergency release of the chain. Chain winches with emergency release properties (band brakes, water brakes, disc brakes) are also common for offshore applications where drilling is involved but are comparatively larger and heavier. 4.4. Continuous CWMS Combined chain wire mooring systems (CWMS) is an old product range from Pusnes. Originally designed in the early 1970s, these winches are advanced, even today. The continuous CWMS means that the chain section of the mooring line (before the anchor) can be pulled in without disconnecting the chain/wire. CWMS winches are mainly for semisubmersible oil drilling rigs and can be electrically or hydraulically driven. They are designed for use in deep water below 1000 m and can release the wire/chain at loads equal to the breaking load (emergency release). 4.5. Rotating Jacking Winches The rotating jacking winch is a novel concept, but only competitive for a particular set of requirements; high pulling force, slow speed, controlled emergency release. The rotating jacking winch can be used for rope or chain and comprises a drum unit (or chain wheel) which is powered into a continuous rotating motion by 2 hydraulic cylinders. The cylinder rods are linked to band brakes at each end of the drum. These band brakes clamp onto the flange during the push and retracting movement of the cylinders (in a synchronized mode) enabling constant rotation of the drum. 4.5. Chain Jacks The chain jack (e.g. Aker Pusnes RamWinch) is aimed at production type vessels such as FPSOs, semisubmersibles, spar platforms, etc. Since many floating production units are designed for 20-30 years life at one location, the need for large complex winches with emergency release is in many cases unnecessary. These facts lead to the development of a hydraulic chain jack - a straight forward design for pulling in, lowering and locking a chain mooring line. A chain jack’s main features comprise:

• Simplified hydraulics, with only one or two lifting cylinders • Cheaper installation and maintenance costs • Integrates chain jack with chain stopper • Compact size and low weight

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Figure 3. Types of offshore mooring winches 5. Petrobras P58/P62 FPSO In 2010, Petrobras signed contracts to convert the MT Roncador and MT Suva to spread moored FPSOs. MT Roncador was a 280 000 dwt tanker built in 1991 and would during the conversion be named P-58 FPSO. The P-58 is destined for the Baleia Azul field, in the Parque das Baleias complex in the northern portion of the Campos basin. MT Suva was a 280 000 dwt tanker built in 1993 and would during the conversion be named P-62 FPSO. The P-62 is destined for the Roncador field in the Campos basin. Both FPSOs are planned for installation in 2013. Figure 4 is a photo of P-58 at the pre-conversion shipyard Keppel FELS in Singapore. In the center of the photo you see the balcony structure that will support the movable chain jack system and the fairlead support structure directly below.

Figure 4. P-58 pre-conversion at yard in Singapore

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5.1. Project Description Petrobras, together with FEED partner Technip, opted for a movable chain jack system for both FPSOs. The FPSOs will be spread moored with 22 mooring lines for the P-58 and 21 mooring lines for P-62. Spread moored systems are ideally suited for the benign coast offshore Brazil and also West Africa. Movable tensioning systems means that infrequent re-tensioning/positioning of the FPSO is envisaged during station keeping. It is obvious that a movable system requires more handling and execution time compared to systems with tensioning devices at each mooring line. However, when little re-tensioning/positioning is needed, the movable system provides considerable weight and space benefits, especially in this case where Petrobras will be offloading excess chain (i.e. no permanent chain lockers). 5.2. Movable Chain Jacks Aker Pusnes (part of the Aker Solutions group) was selected as supplier to provide the movable chain jack system and fairleads for both FPSOs. The supplier had vast experience with all types of offshore mooring systems but never before delivered a movable winch system. A new design based on experience with a single cylinder chain jack (RamWinch) was quickly developed. The main task of the chain jack system is to pull the mooring chain through the fairlead to the main deck of the FPSO and perform top tensioning of the mooring line. The top chain (120mm R4) is then secured to the deck using a chain stopper. Figure 5 depicts an artist’s view of the mooring arrangement at one cluster along the deck of the FPSO.

Figure 5. Aker Pusnes movable chain jack system at one cluster

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The movable chain jack concept was designed to operate multiple mooring lines within the same cluster. A single chain jack is lifted by a skidding gantry and moved to the next mooring line and so forth. Installation and messenger chains are moved using a large sliding chain locker allowing for later offloading of the surplus chain. Typical operating speed is between 1-1.5 m/min. It is currently envisaged that a fully trained crew can perform the repositioning of the chain jack, chain locker and installation chain ready for tensioning the next line in approximately 2 hours. 5.3. Lessons Learned Testing always proves to be an invaluable activity to ensure that equipment fulfills all predefined requirements. Rigorous testing was performed according to well defined test plans. One chain jack was set up under a mockup skidding frame with the movable gantry and motorized turn down sheave above. Chain handling, pull in, pay out, lifting of chain jack and skidding were all performed to simulate actual operations onboard. Figure 6 shows the test facilities with equipment mounted on and under mockup skidding frame.

Figure 6. Testing at Aker Pusnes Valuable experience was gained through testing and project execution. The following can be highlighted as the main lessons learned:

• The overall chain handling and tensioning scenario should be more thoroughly discussed during early stages of the project. A better understanding of the whole installation phase can lead to improved designs etc. How will the chain be cut and handled on deck? How to connect to installed chain etc? A thorough review is mutually beneficial for both client and supplier.

• Client expressed an opinion of not being too keen on the structural pedestals needed to support the chain jack at all mooring line locations. These were necessary to keep the chain jacks vertically supported. Perhaps in the future, something similar could be an integral part of the chain jack.

• Interface between components with respect to cables, hydraulic hoses etc need early attention. Is the layout of cables/hoses on the platform detailed enough to enable suppliers to procure lengths as part of the equipment packages or should they be supplied at a later stage when the layout is more complete and by who?

• Lifting of the chain jack under the gantry proved to be slightly off center compared to chain access opening in the gantry. A spreader bar was designed to attach on top of the chain jack for lifting.

6. ENI Goliat FPSO Eni Norge selected the Sevan 1000 FPSO for the floating production platform to be installed at the Goliat field in the Barents Sea. Goliat is the first oil field to be developed in the Barents Sea and first floating cylindrical FPSO to be used on the Norwegian Continental Shelf. Hyundai Heavy Industries was awarded the engineering, procurement, construction onshore commissioning and transportation contract for the Goliat FPSO. Production is planned to start at end of 2013. The platform is designed for challenging arctic conditions and introduces new winterization systems.

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Contracted suppliers needed to meet strict environmental requirements with respect to equipment and components. Aker Pusnes (part of Aker Solutions) was contracted to supply the on-vessel mooring equipment for the 14-point spread moored system. Figure 7 shows an artistic view of the platform.

Figure 7. Artist’s view of Goliat FPSO 6.1. Project Description The FPSO will have a diameter of approximately 90m and be located in 380m of water depth. Reducing the amount and weight of equipment on deck is often a priority. Fewer windlasses can be considered if they can be easily moved from one mooring line to another without cutting the chain. Eni, together with platform designer Sevan Marine, opted for a movable windlass system for the FPSO. Three movable windlasses will perform tensioning of the 14 mooring lines. The mooring system is divided in 3 clusters, all with different distance to the suction anchors. The lines are different for each cluster - two clusters will have 4 lines and one cluster will have 6 lines. Two clusters have a buoyancy element in the mooring lines and therefore the length of the line segments varies as well. The mooring chain has a diameter of 165mm (R5) and the fiber rope segments a diameter of 295mm. Total length of chains is approximately 8500m and fiber ropes approximately 12000m. 6.2. Movable Windlasses Focus on environmentally friendly equipment and reduced possibility of hydraulic oil leakage lead to the choice of electric drives for the windlasses. These electric windlasses were designed from scratch but based on years of experience with mooring winch designs. The windlasses have a pulling capacity of 450t, and the pre-tension in the mooring system after installation will be in a range of 140t to 280t. The MBL (minimum braking load) of the mooring line segments are 2680t (Chain R5) and 2530t (Rope). Figure 8 shows one of the movable windlasses with integrated chain handling frame. Main components of the movable windlass are; 1 cable lifter, 1 main gear wheel, 4 planetary gears, 4 transmission brakes and 4 frequency controlled electric motors. The transmission brakes are hydraulically powered by a separate HPU (hydraulic power unit). There is no clutch mechanism in the driving unit. Although the top mooring chain is 165mm the windlasses are designed to handle 84mm chain. The 84mm chain is used to pull the 165mm chain up to the platform were it is locked into eccentric fairlead chain stoppers (EFCS). These EFCSs are briefly described in item 6.3. Using a smaller chain to pull in and tension the mooring lines greatly reduced the size of the windlass and also weight. This also meant that chain handling on deck was much easier with 84mm instead of 165mm. Total deck weight was dramatically reduced using the movable windlass concept. In addition, the choice of eccentric fairlead chain stoppers also contributed to deck weight reduction as this meant the chain stoppers could be located on the hull below the waterline. Further weight reduction was achieved due to the fact that the windlass need only be designed for 84mm installation chain and not the 165mm mooring chain. It is estimated that total deck weight reduction compared to the originally proposed system (early bid phase) was approximately 250 tonnes.

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Figure 8. CAD drawing and actual windlass at test facilities 6.3. Eccentric Fairlead Chain Stopper (EFCS) and Chain Tensioner Unit (CTU) Although movable windlasses reduce the number of windlasses required onboard, there will always be a need for individual chain stoppers at each mooring line in order to secure the tensioned lines to the platform. Chain stoppers can be of various types and sizes and even an integrated part of a chain jack (e.g. RamWinch™). In recent years, an underwater fairlead and chain stopper have been combined to create a fairlead chain stopper and further development has rendered an eccentric fairlead chain stopper (EFCS). Eni, together with platform designer Sevan Marine, chose the EFCS for their Goliat FPSO. Figure 9 displays the EFCS design and factory testing. The EFCS combines the flexibility of a flag type fairlead with the holding ability of a chain stopper. The compact design, low weight and hull mounted location contributes to lower topside weight and thus improved platform stability. The chain is locked in a long pivoting arm below the waterline. This constrains the maximum loads to a small area on the lower part of the hull. Chain wear and static/fatigue stress are greatly reduced. However, the main benefit of the EFCS is the reduced risk of out of plane bending (OPB). The long stopper/arm ensures that motion between the chain and platform is mainly taken out at the horizontal pivot point thereby avoiding potential OPB in a chain link. In order to keep the chain between the windlass and EFCS from becoming too slack, a chain tensioner unit (CTU) was designed. The CTU is located at the top end of the 84mm portion of the chain. A chain with too much slack could allow excessive movement between links which could lead to accelerated chain wear. On the other hand, too much tension in this section could inhibit free movement of the stopper/arm.

Figure 9. Eccentric Fairlead Chain Stopper, 3D drawing and factory testing

Chain stopper

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6.4. Lessons Learned Again, as with the P58/P62 project, valuable experience was gained through testing and project execution. The following can be summarized as main lessons learned:

• Design of the Sevan 1000 FPSO had not progressed sufficiently at the time of contract signing for the mooring system to be fully configured. Several changes to the proposed windlass design needed to be carried out in order to fulfill the revised mooring requirements. One such major revision was the chain size to be handled by the windlass. Originally, a 60mm installation chain was to pull the 165mm chain up through the EFCS and around the windlass. Our proposed windlass included a dual chain size cable lifter unit. The cable lifter would first pull in the 60mm installation chain using a smaller pocketed wheel and then transfer the 165mm chain over to a larger pocketed wheel. This procedure was changed so that the top end of the 165mm chain would extend to just below the windlass (between EFCS and windlass) and the installation chain was changed to 84mm. This change required additional engineering to redesign the windlass. We stress the importance of having the mooring system as fully configured as possible before contract awards in order to avoid major equipment redesign during project execution.

• The overall chain handling and tensioning scenario should be more thoroughly discussed during early stages of the project. It seems there should be a better mutual understanding and who is responsible for what.

• During project execution, the platform designer saw the need to relocate the attachment point of the ECFSs to

a point 10m lower than proposed location. This resulted in a redesign of the CTU. The new location of the EFCSs meant that the additional weight of 10m of chain needed to be taken into consideration for the CTU design.

• During internal testing of the chain handling operation, one motor transmitted a faulty shaft encoder signal. A

shaft encoder is an electro-mechanical device that converts the angular position or motion of a shaft to an analog or digital code. The faulty signal caused one electric motor to freeze while three others tried to rotate. The combination of insufficient program logic in the control system and faulty mounting of the encoder allowed the motors to act differently. The control system and motors were supplied by different vendors. The main cause to this incident was found in the interface between the different vendors. This incident emphasizes the importance of having one defined system integrator that is involved throughout the entire design process. Scenarios like this are often caused by lack of continuity in the interface between vendors. Figure 10 shows the normal encoder position and figure 11 the incorrect position. (Note that a plastic splined coupling that transmits rotational movement between the motor and encoder has been removed in order to view motor shaft end and encoder shaft.)

Figure 10. Normal encoder position Figure 11. Incorrect encoder position

End of encoder

End of encoder

End of motor shaft

End of motor shaft

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7. Conclusions Movable tensioning systems can be an interesting choice for offshore production platforms where the frequency of necessary re-tensioning/positioning is low enough to justify the additional work required to move the tensioning devices from mooring line to mooring line. It may also be a concept of choice when deck weight is a critical factor and one tensioning device per cluster helps lower the overall weight. The movable tensioning device can be provided as either a movable chain jack or rotary winch. This paper presented both movable types recently developed for an FPSO and semisubmersible design. Several lessons were learned during execution of both projects. One of the most important lessons was the value of testing as this gives both supplier and customer the confidence that the equipment actually works the way it was designed – especially if the design is new. Interface between component suppliers of a system needs greater focus with one designated as overall integrator. As in most cases, completed projects of this type can bring about new ideas and improvements. Figure 12 shows a possible new movable concept based on experience with these recent projects.

Figure 12. Future movable chain jack with integrated chain locker 8. References GRINDHEIM, R. Development of Innovative Mooring Winch and Experience from First Use on Floating Production

Vessels, INTSOK Conference, London 2001. HØVIK, J. Moor sense than luck, Oil & Gas Agenda, 2011. ANTONSEN, B.T., Report – Damage on Windlass, 4947-01-PUS-R-KA-0007, 2012 NOBLE DENTON EUROPE LTD FOR HEALTH AND SAFETY EXECUTIVE. Floating production system, JIP FPS

mooring integrity. Her Majesty’s Stationary Office, 2006.