otc14099-tandem mooring lng offloading system

7/18/2019 OTC14099-Tandem Mooring LNG Offloading System

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Copyright 2002, Offshore Technology Conference

This paper was prepared for presentation at the 2002 Offshore Technology Conference held in

Houston, Texas U.S.A., 6–9 May 2002.

This paper was selected for presentation by the OTC Program Committee following review of information contained in an abstract submitted by the author(s). Contents of the paper, aspresented, have not been reviewed by the Offshore Technology Conference and are subject tocorrection by the author(s). The material, as presented, does not necessarily reflect anyposition of the Offshore Technology Conference or its officers. Electronic reproduction,distribution, or storage of any part of this paper for commercial purposes without the writtenconsent of the Offshore Technology Conference is prohibited. Permission to reproduce in printis restricted to an abstract of not more than 300 words; illustrations may not be copied. The

abstract must contain conspicuous acknowledgment of where and by whom the paper waspresented.

AbstractThe attractiveness of placing a natural gas liquefaction planton a vessel moored at or close to an offshore field is known.This vessel can either be part of an oil development in which itliquefies associated gas or a stand alone development of a gasfield. In the associated gas case, the Floating LNG (FLNG)

unit makes certain oil developments feasible by turning theassociated gas disposal into a moneymaking opportunity. Inthe gas field case, the FLNG makes remote offshore field production economic. The safe reliable transfer of this LNG in

open sea, possibly harsh, environment has however not been possible. The proposed LNG Offloading Arm (LOA)

effectively combines proven technology and operatingexperience to effect the safe and reliable transfer of LNG between tandem moored vessels or between a fixed tower andLNG carrier in up to 5 meter significant seas. The concept is based on the experience of mooring systems surviving 100years storms, dis-connectable mooring systems in typhoon

areas and work performed on cryogenic swivels. The LOAstructure consists of “vertical” and “horizontal” arm section

with swivels to provide articulations required to follow therelative motions between the FLNG and the tandem mooredLNG carrier. The vertical section is supported from a

cantilevered rotating structure on the back of the FLNG vesselor on a fixed tower. The horizontal section connects the LNGcarrier to the lower end of the vertical section. Each section is

composed of a central pipe for LNG transfer and a largediameter outer pipe structure also used as the vapor returnfrom the LNG carrier. The LNG carrier can be passivelymoored using gravity restoration by weights located in the

horizontal section of the loading arm or DP assisted using boththe arm and the LNG carrier thruster system.

IntroductionThe technology for cryogenic liquefaction and storage of LNGon an offshore floating vessel is known. The safe reliable ship

to ship transfer of this LNG in an open sea, possibly harsh,environment has however not been possible. SBM havingexperience in both the supply and operation of mooringsystems put this experience to work in the development of aTandem LNG Offloading system. The philosophy adopted for this development was to keep the design simple and whenever

possible stick to components that had a known track record.Having over 40 years experience in the design, supply, and

operation of Single Point Mooring (SPM) systems andFloating Production Storage and Offloading (FPSO) systemsthe value of simple robust design was well understood andapplied to this LNG Arm development. Known technology

and operational experience either directly or indirectly appliedto the Arm include soft yoke or gravity moorings (Fig. l),articulated fluid transfer arms (Fig. 2), cryogenic swivels (Fig.3a and b) and tandem mooring systems (Fig. 4). Additionallyexperience from designs that must disconnect and reconnect intyphoon or ice areas has led to the understanding of structures

and mechanical systems exposed to dynamic forces andmotions, as well as the physics of making connection under these conditions. The LNG Offloading Arm detailed hereineffectively combines this technology and operating experienceto enable the offshore industry to effect the safe and reliable

offshore transfer of LNG.

Loading arm descriptionThe offloading Arm shown in operation and stored position(Fig. 5 and 6), is designed for tandem offloading in a harshenvironment (up to 5m significant wave height). The Arm is

supported from a cantilevered rotating structure on the back of

a turret moored LNG - FSO or FPSO. The shuttle carrier can be passively moored using the gravity restoration of theweighted arm or can also be DP assisted using both the Armand a shuttle carrier thruster system. When connected, theArm provides for a continuous flow path between the LNG

FPSO and the shuttle carrier.The Arm is composed of a central pipe for LNG transfer

(up to 32 inch) and a 2-m diameter pipe arm structure, whichis also used as the vapor return from the shuttle carrier. TheArm support structure and outer structural shell are fabricatedfrom stainless steels compatible with LNG. The inner LNG

OTC 14099

Tandem Mooring LNG Offloading SystemL. Poldervaart, J.P. Queau, Single Buoy Moorings, Inc.; Wim Van Wyngaarden, Gusto Engineering



2 L. POLDERVAART, J.P. QUEAU, WIM VAN WYNGAARDEN OTC 14099

piping is also made of stainless steel to minimize the relativethermal deformation between the Arm structure andthe piping.

The offloading Arm consists of two long arms, a counter weight, one short arm with connector and seven swivels. The

swivel locations are depicted by the color changes on the arm(Fig. 5). The Arm has been configured in a way that all

swivels lie in the same plane. This swivel arrangementminimizes moments and eliminates secondary bending acting

on the articulations. The swivels in the Arm provide for alllinear and angular movements required for the Arm to follow

both the FPSO and carrier relative wave and slow driftmotions. The lifting of the counterweight at the Arm elbow provides for the mooring restoration of the shuttle carrier andaids the connection/disconnection procedure.

Each of the loading Arm articulations (Fig. 7) consists of alarge diameter roller bearing with a sealing system for the

vapor return, and a cryogenic swivel having a sealed LNGchamber and bearing. The cryogenic swivel and piping iscentrally supported to the outer pipe through insulated web

structures. Relative axial motions resulting from inner andouter pipe differential thermal or structural strain are taken by

slip joints placed along the inner pipe. The LNG vapor returnsthrough the large diameter structural pipe on the outside of thecentral LNG pipe. Heat transfer between the Arm vapor spaceand outer structural components is controlled by the useof insulation.

LNG loading arm componentsThe loading Arm described in the previous sections is under development. An elevation view shows the Arm overallexternal arrangement in Figure 8. Components used in thisarm, be they mechanical or structural are well known. The use

and combination of some of these components at temperaturesranging from ambient to cryogenic is however new. Details of these components will be briefly described. The maincomponents of the LNG Offloading Arm are as follows:1. Arm FPSO support structure2. Arm inner and outer pipe3. Arm counterweight

4. LNG swivel bearing and sealing system5. Large diameter LNG vapor return swivel bearing and

sealing system6. LNG pipe slip joints7. Arm outer to inner pipe supports8. Arm to shuttle carrier connector and regulating valves

9. Insulation Note: A pick-up line is shown between the FPSO and the

LNG carrier. This is only required for the connection betweenthe arm and the LNG shuttle carrier.

Arm FPSO support structure. The main LNG Arm support

member consists of a fixed vertical column placed at the stemof the FPSO. A short distance below the top of this column a

diagonal support takes longitudinal mooring loads from thecolumn into the FPSO. The column houses a centrally located

24 inch (max 32 inch) LNG line for loading and provides for vapor return within its outer shell. The LNG line in thecolumn is fitted with a slip joint at the base and a swivel at the

top. Fitted to the top of the column is a bearing and a 2-mdiameter horizontal vapor return pipe with a central 24 inch

LNG pipe that extends outward to the first articulation of theLNG loading arm. A diagonal support member at this

articulation carries the bulk of the Arm vertical loads and alsoserves as the Arm rotation member. Rotation of the Arm is

effected by a motorized rotating structure located near the bottom of the fixed vertical column. This rotating structure is

fixed to the vertical column by way of a large diameter slewing bearing, which is geared and driven by two hydraulicmotors. These motors are used to deploy the Arm from itsstorage position to its operating condition when a LNG carrier

is moored.Lateral mooring loads from the Arm are resisted by a dual

cable arrangement fitted on either side of the loading arm onthe stern of the LNG FPSO. These cables attach to the fixedside of the first Arm articulation and pass downward to the

corners of the FPSO stern. One of these cables is detachableto allow the rotation of the Arm when moved to itsstored position.

Arm inner and outer pipe. The inner pipe of the LNG armcarries the LNG being transferred. The present design uses upto a 24-inch diameter, stainless steel pipe (Fig. 9). The pipe isfitted with swivels at each Arm articulation (see Figure 11)and slip joints handle differential motions with respect to the

outer pipe. Fixed and sliding guides keep the LNG pipecentrally positioned in the outer pipe. Short pipe spools or elbows with flanges are located next to swivels and slip jointsto allow for removal or servicing of these components.

Hatches through the outer pipe shell at articulations provideaccess to these components.

The outer pipe of the LNG Arm is the structural member that transmits all loads and carries the weight of the Arm as itspans between articulations. The pipe has a nominal diameter of 2 m with a stainless steel shell. At all articulations the pipetransitions into heavy stainless steel rings which are used tohouse large diameter bearings. At pitch articulations the bearing housings extend as re-enforcement along the shell.

This re-enforcement carries the primarily axial pipe load toeither the adjoining fixed outer shell, or to an adjoining bearing ring.

Arm counterweight. The loading Arm counterweight performs two functions in the offloading system. The primary

role of the counterweight is to provide sufficient weight at theArm elbow to affect the mooring of the shuttle carrier. Asecondary function is to use this weight in the lower horizontal pipe to counterbalance the shuttle connector

causing it to rise when disconnected (figures 10a, b, c, d,and e).

The articulated vertical pipe member of the Arm and thecounterweight form a mechanism whereby mooring loads are



OTC 14099 TANDEM MOORING LNG OFFLOADING SYSTEM 3

resisted by the horizontal component of this pipe tension as itarticulates from vertical. The required size of counterweightlargely depends on the length of the vertical pipe, size of

shuttle carrier and environment in which this offloadingoperation is performed.

The counterweight has been positioned behind the Armelbow to affect the lifting of the arm shuttle connector when it

is not connected. To stop this pipe and connector from fullupward rotation, the elbow articulation is placed in the

vertical pipe just above the horizontal pipe. When rotating,this placement causes a forward shift in the center of gravity

of the lower horizontal pipe, which results in a stableintermediate position. This position allows the connectingcarrier to connect by pulling the Arm to the connector, whichcontrols the connection relative motions.

LNG swivel bearing and sealing system. The LNG swivel is

housed in the vapor return or structural arm support member.Its function is to rotate, seal and sustain applied loads while passing LNG. The swivel has redundant pressure seals (a

primary and secondary) and three bushings, which align andconnect the LNG pipe as it articulates. The bushing clearance

is designed to keep the relative movements of the swivel partswithin limits that result in seal deflections, which will alwaysresult in proper sealing.

SBM has successfully tested seals for cryogenic LNG usefor over 10 years. In 1999 in-house studies and testing of newmaterials suitable for seal and bushing use at cryogenic

temperature were completed. Based on this work new sealshave been designed and are under test. Upon completion of this testing, the best seals, old or new, will be designed intothe 24-inch LNG Arm prototype swivel, which will then be tested.

The material used for the swivel bushing will be similar tothat used for the sealing material. The material testingdiscussed above included materials suitable for this duty. Dueto the Arm pipe-in-pipe design, the load carried by the LNGswivel bushings will only be due to pressure, gravity and flowmomentum. The use of pressure balanced slip joints in theLNG piping eliminates any large shear or bending moment

loads acting on these swivels. The bushing material friction,stress and wear properties will therefore give a very long life.

Based on testing and past experience, the swivel willrequire no maintenance for a period of at least 5 years. In theunlikely event repair or maintenance is required, there is in-situ access for this and even for swivel replacement.

Large diameter vapor return swivel bearing and sealing

system. This large diameter swivel system has a multitude of functions. The bearings must provide for rotation, alignmentand structural loading resulting from thermal, gravity,dynamic, pressure and mooring loads. This swivel consists of

four seals and three sets of rollers. Two of the seals will provide for the containment of the LNG vapor and two seals

will close in the bearing cavity. A leak detection systemisused to monitor the integrity of the vapor seals. The roller

bearing is configured as a normal three-race roller bearing andhas sufficient strength to take the required loading whilemaintaining an alignment, which will insure proper sealing.

The seals used in this large diameter swivel will be of similar construction to those used in the inner cryogenic

swivel. The seals will also be capable of sealing cryogenicLNG liquid should the inner pipe sealing system fail. The

three-race roller bearing will have the geometry of normal bearings used at ambient temperatures; it will however be

modified to be able to operate at lower temperatures. Use of insulation on the inside of the outer shell will however insure

that the bearing operating temperatures always remain closeto ambient.

Maintenance of this swivel would only involve bearinglubrication at specified intervals. This will be automated and

designed once the bearing selection is finalized. Servicing of these articulations would involve the disassembly and

separation of the inner piping and outer bearing flange. This isregarded to be an unlikely occurrence, however this can becarried out on board the LNG FPSO.

LNG pipe slip joints. The LNG loading Arm uses the outer structural pipe to support the inner LNG pipe. Thermal

differences between these pipes can approach 200 degrees C.Differential elongation of these pipes due to thermalexpansion would result in high loads and stresses should they be rigidly tied together. To account for this relative elongationslip joints are placed along the inner cryogenic pipe.

The slip joints used are axially pressure balanced to

maintain the longitudinal pipe tension due to pressure effects.A non-pressure balanced slip joint would induce compressiveloads in the piping system. These loads would be taken bysupports and swivel bushings complicating the overall design.

To minimize bending across the slip joints they are placednear pipe supports. This helps to ensure minimal eccentricity

and wear. The slip joints do not require any maintenance for the life of the arm. Should service be required, the joint can beremoved by disconnecting the adjacent flanges and pulling the joint out of the piping for disassembly.

Arm outer to inner pipe supports. The inner LNG piping isentirely supported from the outer structural pipe. Supports are

fixed to the outer shell wall and have an open radial webterminating in a central ring that surrounds the inner LNG pipe. This central ring is fitted with segmented blocks havinggood insulating and friction properties. These blocks will

either have a close sliding fit to the inner LNG pipe, or theywill be grooved to engage a flange from the inner piping or

swivel. The open radial web in these supports allows for LNGvapor return flow and manned access should servicing be required.

The supports are located throughout the arm to both secure

the inner pipe and minimize thermally induced stresses. Thesupport arrangement that best accomplishes this is shown in

figure 11. The working principle of this arrangement is that allsupports and slip joints lie in the same plane when the Arm is




in its equilibrium position. Three key supports are those at theArm pitch articulations as these articulations are orthogonal tothe plane and thus arrest both the axial and rotational

movement with respect to the outer pipe. Swivels havingarticulations within the plane are fixed to the outer shell and

are turned by the inner piping as it articulates with the Arm.The rotating pipe sides of these swivels pass to a slip joint,

which minimizes swivel loading.

Arm to shuttle carrier connector and regulating valves.

The connector of the LNG arm to the shuttle carrier is a mated

unit, half of which is permanently installed on the carrier bow.The connector design incorporates the following functions:

• 1) - Connector winch, alignment and locking system

• 2) - LNG pipe connector and valve system

• 3) - LNG vapor connector and valve system

• 4) - Arm purging system

These functions are further elaborated below:1) - A single shaft, double drum, 50 tons winch is used for the

pull-in of the LNG arm to the shuttle carrier bowconnector. The connector’s central and azimuthalalignment is obtained through the use of two stabguides. Pull-in cables attach to Arm mounted male stabs

that are pulled through and into carrier mounted femalestab guides. Once the connectors have been pulled intocontact, a hydraulic latching system locks and seals theconnector and outer vapor barrier from the atmosphere.The rate of connection and the differential motion between shuttle and arm is controlled by the speed of

the shuttle pull-in winch.2) - Once the arm has been secured to the carrier and the

mooring is established, the LNG pipe connection is

made by hydraulic actuation of closure rods, which lift acarrier based flange and seal against the Arm LNG

flange. Lowering of these closure rods opens this flangeconnection. Should this occur without draining of theArm during an emergency disconnect, LNG betweenflange connection and Arm valve spills into carrier plenum. This avoids LNG spill when Arm disconnects.

Prior to startup of LNG transfer valves on both sides of this connection flange are opened, which allows flow

from the LNG FPSO to commence.3) - The LNG vapor path is sealed by a seal carried in the

flange on the LNG shuttle carrier side of the connector.The vapor return flow from carrier to LNG FPSO passes

through two large diameter spring-loaded valves locatedin the sealed bottom deck of the LNG arm. Opening of

these valves is effected by the action of the same closurerods that lift and close the LNG flow connection. Oncethese valves are opened, the LNG vapor path to the plenum under the arm connector is established. The

carrier vapor return piping also connects to this plenum.A valve on the carrier outside the plenum is opened

prior to commencing LNG loading.4 ) - After offloading is completed the Arm is LNG gas freed

by purging with nitrogen. This purging can be carried

out from the FPSO with use of a cross over between theLNG piping and vapor return at the carrier end of thearm. This cross over consists of a small diameter pipe

and valve, which allows nitrogen to flow from theLNG piping into the vapor return path by way of a

ring manifold.

Insulation. A study has been carried out on the Arm heattransfer. This study indicated that for the rate of LNG liquid

and vapor flow, heat gain was not a problem and insulationwas not required. This study also indicated that with normal

sort of ambient air movements the outer uninsulated shellremained at near ambient conditions. Without air movementthe outer shell however remains at near vapor returntemperature. These temperature differentials require the Arm

inner to outer piping design to handle almost 200 degrees C of thermal deformation. Having the capability to handle these

deformations, it was found beneficial to insulate the inside of the outer pipe as it eliminates thermal cycling of the outer shell and its mechanical components.

Arm safety systemsThe LNG loading arm has two functions:- To transfer the mooring loads between the LNG carrier and

the FPSO- To transfer the LNG and the vapor return between these

vesselsThe safety system monitoring and controlling these function

will be detailed below.

Mooring safety systems. The Arm mooring function isdesigned for a 5-meter significant wave height threshold. Thisweather condition will result in a certain maximum excursion

for the moored LNG carrier. Should this excursion be reachedthe load monitoring system on this will signal the EmergencyShut Down (ESD) system of the arm. When this signal isreceived, the following procedure is initiated:1 . Start ESD 1 procedure2 . Wait a certain time continuing to monitor the tension

- Should loads remain at normal level, the mooring

master may choose to resume loading.- If the loads continue to increase, the mooring master

can initiate the arm disconnection- Should mooring loads reach a higher predetermined

level triggering ESD 2, theArm is automatically disconnected.

3. Disconnection procedure- Open the main connector

- Disconnect the mooring line.Fluid transfer safety systems. The fluid transfer system isdesigned in accordance with the requirements of the OCIMF(Design and construction specification for Marine Loading

Arms). The fluid transfer safety system monitors and controlsvalves, Arm sealing systems and flow pressure.

The safety system is composed of:

• 1 ESD valve for the LNG before the loading Arm




• 1 ESD valve for the vapor return on the carrier beforethe connector

• 2 SD hydraulically activated LNG valves; one at the end

of the loading Arm and one after the connector onthe carrier

• 1 LNG flow connector and vapor return self-closing

system at the end of the Arm, which will automaticallyoperate when the Arm to carrier connector is activated.

• LNG pipe and vapor return pressure detection sensors.

• Leak detection system for vapor passing the Arm outer vapor seals.

• LNG liquid detection in the carrier plenum chamber.The fluid transfer safety system continuously monitors the

above valves and sensors. Should any faults be detected thesystem will automatically go to an ESD 1 or ESD 2 condition.When an ESD condition is triggered, the safety systemautomatically starts a sequence of actions.

Loading arm analysis

The components described above when assembled andconnected to LNG vessels will moor and transfer LNG. Tofacilitate sizing of this system a fully dynamic computer simulation tool was developed. To demonstrate this capability

a sample analysis is shown. Results of this analysis will provide values for the motions and reaction forces at each

articulation during a design storm.Environment conditions for the simulation are:

• Waves: Pierson-Moskowitz spectrum, Hs=5m, T p=12s,

• Wind: Mean velocity U10=25 m/s,

• Surface current: Uc=1.3 m/s.For directionality, two cases have been considered:

• All parallel: wind, waves and current come from the

same direction,• Transverse: wind and waves parallel while current is

at 60°.The LNG FPSO and shuttle tanker hulls are modeled as

finite element meshes, which are input and run usingdiffraction software.

As variations of draught are very small for both the FPSOand the shuttle, the models use the average draught for bothvessels. The main particulars are listed in the table below:

Units FPSO Shuttle

L.O.A. m 328 290

Lbp m 320 275Beam m 58 48.1

Depth m 30 27

Draught m 15 11.3

Displacement t 288 000 124 500

Area exposed to longitudinal wind m² 2 320 1 700

Area exposed to transverse wind m² 11 200 8 500

Position of the turret (from bow) m 68 N/A

The overall model of the loading arm, FPSO and shuttletanker is shown in figures 13a and b. The FPSO has a turretmooring near the vessel bow, and the shuttle tanker is tandem

moored to the FPSO using the LNG loading arm. The arm inthis model consists of 6 tubular sections of 2.0-m diameter.Each section is connected to the next via a hinge articulation

allowing only one rotational motion. The masses, centers of gravity and moments of inertia have been derived from the

detailed design and entered in the model. The articulated Armhas a 150-ton counterweight, which gives the required

restoring properties to the mooring system. The armequilibrium position is at 51.8 m. and positive load values

indicate tension when the carrier is pulling away from theLNG FPSO.

Parallel Storm Analysis. A 3-hour time domain simulationwas performed for the parallel storm. The statistics of therelative surge and heave motion between the LNG arm

attachment points on the deck of the two vessels arelisted below:

Mean Max Min

Relative surge (m) 61.4 69.9 52.9

Relative heave (m) -0.6 6.2 -4.8

This table shows the range of excursion of the vesselsrelative motions are 17 m in surge and 11 m in heave and that

the minimum surge always stays above 51.8 m that shows thecarrier always pulls on the FPSO. The statistics of the pitchangle for the long vertical and horizontal LNG Armcomponents are listed below:

Mean Max

Vertical (°) 20.2 43.7Horizontal (°) 0.4 14.2

The basic physics of the Arm is such that the pitch of the

vertical leg accommodates surge while the horizontal leg pitchaccommodates heave. The most loaded articulation of thisloading arm is the first articulation between the FPSO and theArm. This articulation is one that allows for relative roll while

supporting the bulk of the LNG arm weight. For the in-lineenvironment, the reaction at this articulation is:

Mean Max Min

Surge (kN) 932 3,511 87Heave (kN) 2,856 4,087 2,663

Pitch (kN.m) 11,710 16,757 10,918

Transverse Storm Analysis. A 3-hour time domainsimulation was also performed for this storm. The statistics of

the relative motion of the Arm connector attachment on theFPSO and shuttle vessel are given below:

Mean Max Min

Relative surge (m) 50.7 62.3 39.4

Relative sway (m) 31.9 43.7 16.4

Relative heave (m) -0.6 5.9 -4.8




As a combination of sway and surge determine theseparation between vessels. This run again shows the Arm notto go into compression, meaning the vessels never come

closer than their equilibrium position. The statistics of the pitch angle for the Arm vertical and horizontal legs is listed

below:

Mean 2←RMS Max MinVertical (¡) 17.7 11.3 41.8 0.8

Horizontal (¡) 1.2 8.6 14.6 -17.6

The transverse environment causes all Arm articulations to beloaded. The most loaded articulation is again the first at thetop. The statistical and extreme values of the loads in thisarticulation during the 3-hour storm are given in below:

Mean 2←RMS Max Min

Surge (kN) 655 557 2,671 -5Sway (kN) 487 410 1,741 -49

Heave (kN) 2,827 202 3,867 2,602

Pitch (kN.m) 11,590 828 15,855 10,668

The above bearing loads and rotations found in the Armanalysis do not present any problem for the Arm components.

SummaryThe LNG Offloading Arm described has been developed tocarry out the transfer of LNG in sea states up to 5 meters. Thecomponents and the particular arrangement thereof have beenchosen to create a passive transfer system as experienceindicates automation in these systems leads to down time. The

Arm mooring is based on a well-proven gravity principle, andthe design of the Arm mechanical components is robust for a

long life. The use of a pipe-in-pipe arrangement for transferring LNG liquid protects the liquid line from externalshock and provides a secondary containment should this pipehave a containment problem. The sealing of LNG liquid and

vapor is known and is based on seals that have been tested for a long operational life. Access for maintenance, service or repair is provided to all mechanical components to assureminimal down time. The Arm connect/disconnect system can perform in seastates giving quick carrier turnaround and iscontrolled by safety systems assuring quick disconnect in the

event of emergencies.




Figure 1 – Soft yoke sytems

Figure 2 - Articulated transfer arm




Figure 3a - Cryogenic swivel

Main characteristics of the prototype swivel are:

• Fluid passage diameter : 16” (400 mm)

• Temperature range ambient to -200°C

• Pressure range : 0.50 bar to 30 bar

• Double sealing arrangement

• Main body is made of stainless steel, with high resilience at low temperature

Standard bearing materials

Figure 3b – Laboratory Cryogenic Swivel Figure 4 – FSO XV – Elf Nigeria - 1991




Figure 5 Figure 6

The LNG loading Arm shown here (in stored position) is being developed to The LNG loading Arm shown here (in stored position) is being developed to

ensure reliable LNG transfer to or from a storage facility ensure reliable LNG transfer to or from a storage facility.

Figure 7 - LNG arm swivel articulation




Figure 8 – LNG offloading arm arrangement

Figure 9 – Inner and outer pipe arrangement




10 a – Offloading model systems Figure 10b

The Vertical arm tension produced by the weight causes a horizontal To ease system connection and disconnection the weight and elbow pivot are

component that passively creates the mooring restoration of the LNG arranged to give the Arm connector an equilibrium position well above the

carrier. carrier bow.

Figure 10c Figure 10d

The weight placement behind the elbow gives the stable lower arm This means the arm is pulled down to connect.

position shown.

Figure 10e

And self pivots up when released for emergency or disconnected




Figure 11 – Arm support arrangement

Figure 12 – Loading Arm Articulation Figure 13a

Dynamic Analytic capabilities have been developed to fully model and

assess the Arm mooring capability

Figure 13b – Offloading system model

b d

A B D Er

Sliding pipe

Swivel anchored to outer

Slip joint

Tension/compression rod to outer

otc14099-tandem mooring lng offloading system

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