Opt 2008 Advanced Deepwater Spool Analysis Paper 27-02-08

7/30/2019 Opt 2008 Advanced Deepwater Spool Analysis Paper 27-02-08

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Advanced Deepwater Spool Piece Design

IBCs 31st

annualOffshore Pipeline Technology Conference & ExhibitionHung Hing Chan, Lenas Mylonas & Colin McKinnon Page 1


Hung Hing Chan Senior Consultant J P KennyLenas Mylonas- Subsea Construction Engineer J P KennyColin McKinnon - Technical Director J P Kenny

Abst ract

Deepwater pipelines are connected to manifolds/trees/FTA/ITA by utilising diverless rigid spoolsand mechanical connectors. Deepwater rigid spools have to be designed to accommodateexpansion movements resulting from high product temperatures, low strength soils andphenomena such as pipe walking. They also have to accommodate spool fabrication andinstallation tolerances. These requirements drive the spool geometry and can lead to complex

spool geometries that are difficult to install.

This paper summarises the technical challenges associated with deepwater spool piece designand proposes methods for reducing the size and complexity of tie-in spools, including:

Review of the pros and cons of vertical and horizontal connection systems

Review of typical connector loads and capacities

Review the impact the various types of tolerances have on spool design includinginstallation and, metrology

Review of loads induced in the spools and connectors while the running tools operateduring levelling and stroking

Discussion of installation issues that should be considered during spool design. Examplesof good and bad spool designs are presented.

Description of finite element modelling techniques that can be used to reduce the loadingson the spools and connectors

Review of structure settlements after installation

Review of typical stress and strain results from a spool analysis

Use of DNV-OS-F101 limit state approach to reduce spool sizes.

Use of pipeline design changes to reduce spool sizes and connector loads.


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1. Why are Tie-in Spools Important?

A typical deepwater development may consist of 1 export pipeline, 6 infield lines, 12 flowlines, 11structures and 18 well. Each of these elements has to be connected by means of tie-in spoolscarrying oil or gas product, injection water, injection chemicals, riser lift gas, etc. The tie-inprocess is performed diverless at great depth, which requires the use of subsea constructionvessels and ROVs that are costly and time consuming. The connections must be highly reliable.Each element must be recoverable. The spools connection flowlines to manifolds may have toaccommodate large expansion movements, which can lead to large spool sizes that are difficultto fabricate and install.

2. Review of the Pros and Cons of the Horizontal and Vertical Connectors

There are 2 main types of connector used in deepwater projects. The following photos showtypical horizontal and vertical connectors and spool configurations.

The picture below show a horizontal multi bore connector with chemical injection lines ridingpiggyback on the main spool. The stab-in guide on the connector mates with a receptacle on theconnecting structures. A running tool is deployed to make up the connector. Doghouse insulationis fitted after the connection is made. A single spreader bar is used to support the spool.

Horizontal Spool


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The picture below shows a vertical mono bore connector. The running tools used to make up theconnector are deployed with the spool. Doghouse insulation is fitted after the connection is made.

A single spreader bar is used to support the spool.

Vertical Spool and Connector

The following table lists some of the criteria that should be considered when selecting connectortype for a deepwater project. In many cases the decision can be quite subjective, as both types ofconnector have been used successfully in deepwater.

A colour code is used to help assess the strength and weaknesses of each system against eachcriterion.

Risk Description

High may limit the application of this system in some cases.

Medium risk needs to be assessed on a project basis

Low proven reliable service


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IBCs 31stannualOffshore Pipeline Technology Conference & ExhibitionHung Hing Chan, Lenas Mylonas & Colin McKinnon Page 4

Analysis Criteria Vertical Connector Horizontal

Ease of Installation Vertical connectors are gravity deployed directly over the hub,connection tooling is simpler, lighter & cheaper, allows shorthub-to-hub spacing, vertical connections can allow compactreceiver assemblies, large rotation of hubs is not allowed.

Horizontal sthen controtooling,dockstroking is deflection, sexpansion capull-in loadsaccommodat

Controls Multibore and umbilicalinstallation (e.g. tree jumpers)

Difficult / industry very little experience Simple / lotsconnectors designs easibetter-controvertical connspecific orienkeys on the systems. If awould be admain connealike. There Multibore on Horizontals hGirassol and

Landing and locking loads. The vertical connector running tool has to control the landingloads and ensure they are not transferred into the lockingfunction.

The horizonlanding and high level of

Seal replacement Vertical connector has to be completely removed in order toreplace a seal. With the vertical connector greater care isrequired to ensure the connector is not separated too far.

Seals (or seastroking back


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Torsional Load capacityVertical connectors are generally exposed to higher torsionalloads as a result of the connector orientation.

Horizontal cominimised by

Turning Moment Because the Vertical Connector is fitted to taller structuresthere is an increase in the turning moment on the structure.

Simple

Impact on Structure Design Vertical connector spool configurations can result in significantloading of seabed structures.

Horizontal coof receiver smore compvertical conn

Hydrate avoidance Vertical configured spool hampers free drainage of water. The horizoaccommodatform of dogeffectively dconnectors.

Complexity Simpler connection on trees and manifold Requires mosystem

Maintenance No difference No difference

Flow assurance Gas is more likely to collect within the jumper enabling hydrateto form in the jumper if hydrate mitigation procedure fail.

Hydrate formation may become an issue at the top of thehairpin U bends in vertical connectors, which is less of anissue with horizontal connection system

Pipework is that cause hy


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Size and Weight Large, Heavy Larger, Heav

Anti-Snagging Capability Pipe runs vertically out of the connector Pipe runs ho

Proven Technology Yes Yes

Emergency DisconnectionFeature

Yes Yes

Soft Landing SystemLanding and locking loads - The vertical connector runningtool has to control the landing loads and ensure they are nottransferred into the locking function.

System has soft landing system or controlled descent during

final alignment of critical components

Landing andsystem has locking opercontrol over t

Soft landing

stroked into c

Tolerance to HydrodynamicsInduce Loads

Low High

Controls Multibore and umbilicalinstallation (e.g. tree jumpers)

Difficult / industry very little experience Simple / lots

Controlled connector landing andmakeup

Greater risk of seal damage or problems with connectormakeup

Lesser risk oconnector ma

Decouple Schedule for spoolhandling and makeup

Difficult Simple

Retrieval of tree/manifoldDifficult Simple


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Connector stroking distance Neutral on Spool design Can be use

spool)

Pigging The complexity (and risk) is increased in the verticalconnection system because of the extra 5D bends that have tobe fitted to the Pigging loop. The Pig launcher receiver has tohave a 90 degree bend fitted so that it doesnt interfere withthe connector installation tooling.

Less risk of orientation of

Loads on Horizontal vs. Verticalaxis connections

Advantage for riser base Advantage fo

Insulation For the vertical system there is a limit on the thickness ofinsulation so that the tool can still be placed on and taken offthe connector. If additional insulation is

required this would make the insulation doghouse large anddifficult to install. A further consideration is plane of deployingthe insulation doghouse, for verticals it has to be wrappedaround the connector whereas for Horizontals it is lowered

onto the connector and hence is easier.

Horizontal corequirementsdue to the p

system.

Metrology Higher requirementVertical connectors require more accurate metrology in orderto accurately install both ends of a flowline spool. This isbecause the vertical connector is placed directly on the finalalignment structure whereas the horizontal connector islowered into a receptacle that gives both coarse and finalalignment as well as allowing an additional tolerance during

the connector final make up.

Lower require


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Multibore design The vertical connector does not generally have a specific

orientation whereas the receptacle and keys on the connectororientate the horizontal systems. If a multibore system isutilised there would be advantages in using it throughout onmain connections and process connections alike. There hasbeen very littleutilisation of Multibore on vertical systems whereas multiboreHorizontals have been used on Greater Plutonio, Girassol andDalia projects amongst others.

Horizontal

multibore connectors dsystems.

Equipment Retrieval DifficultThe requirement to recover flowline / umbilical jumper in orderto retrieve subsea production equipment, such as tree ormanifold horizontal connectors may be disconnected andstroked away from the equipment and left in the receptacle.

Vertical connectors require to be lifted away from theequipment and either wet parked or retrieved to surfaceincreasing total vessel time.

Horizontal connectors only require one end of a flowline spoolto be disconnected in order to retrieve an item of subseaequipment, whereas vertical connectors require both ends tobe disconnected.

Requirement for additional structure vertical connectorsrequire a secondary receptacle in order to wet park theflowline spool after retrieval of the subsea equipment.Alternatively a secondary connection system such as a

flowbase could be utilised. A horizontal connector does notrequire any secondary equipment for wet parking but doesrequire some form of structure to accommodate the guidanceand/or pull in system.

Simple


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Analysis Criteria Vertical Connector Horizontal Conn

Deploy to place system Not affected by seabed condition

Buoyancy application Buoyancy in some cases is required in order to reduceconnector and spool stresses where nominal spoolsare particularly long, loads are particularly high due tostructure movements and equipment are installedoutwith installation tolerances necessitating the designof special jumpers.

Structural Requirements The vertical structure has a slightly smaller footprintthan the horizontal connector and this may result in aslightly reduced weight and footprint for structuresusing a vertical connector but they are slightly taller.

Taller Structures however will mean higher momentsthat are acting to turn over the structures.

Maintenance No difference


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3. Review of Connection Systems Capacit ies

3.1. Typical Connector Capaciti es

The spool designer needs to know the design capacities for each size of connector.

Typical limiting capacity of different connector sizes is given in the table below. The data is basedon a study of connectors from FMC Aker Kvaerner and Cameron. The data can be used forhorizontal and vertical connectors, as the capacities are similar.

It should be noted that the capacity of the spool, the manifold/FTA piping and foundations maynot be as great as the capacity of the connector and needs to be checked by the designer.

Typical Connector Capacities

Forces (kN) Moments (kNm)Diameter /

Location

Connector

LocationLoad Case

Fz (Fy2+Fx

2) Mz (My

2+Mx

2)

Manifold 40 30 60 20010Manifold - FTA

FTA

Operation

40 30 60 200Manifold 120 70 40 150

6Manifold-Well Well

Operation120 70 40 150

Manifold 40 30 60 20010Manifold ITA ITA Operation 40 30 60 200

FTA 70 50 60 25012FTA FTA FTA

Operation70 50 60 250

Note that these are estimated maximum capacities and there may be a trade off between forcesand moments.


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4. Tolerances

4.1. Introduction

The following sections describe the tolerances that need to be considered during a spool design,namely:

Structure installation tolerances

Metrology tolerances

Fabrication tolerances

Hub to connector tolerances

Connector stroking tolerances.

4.2. Structure Installation Tolerances

Typical installation tolerances for wellhead guide bases, manifolds, flowline termination units andin-line tees are given below:

Wellhead Guide-bases: Verticality 2 degAzimuth 15 deg

Manifolds Verticality 3 degAzimuth 5 deg

FTAs/in-line tees Verticality 5 deg

Distance between pairs of Christmas tree connection tie-in points:

25 10 metres

Distance between production manifold and flowline connection:

35 5 metres

The spool piece geometry must have sufficient length and angular capacity to accommodatethese tolerances during fabrication. If pre-fabricated spool elements are used they must havesufficient green material to accommodate these tolerances.

4.3. Metrology and Fabrication Tolerances

Once the subsea structures have been installed the distance between the connectors and theangular alignment of the hubs will be established by survey.

These measurements will then be used to fabricate the spools.

Typical metrology and fabrication tolerances are:

+150mm in any three axes

+2 degrees in any three axes


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4.4. Hub to Connector Tolerances

Hub to connector tolerances arise from a number of sources including fabrication tolerances forthe inboard structures, stack-up tolerances for two-part structures such as MSS/Manifold andPGB/Tree and also the requirement that production jumpers shall be re-usable after treeinterventions. The tolerance stack-up reports will be required during the project execution. Theseshall be considered in the stress analyses of spools.

4.5. Connector Stroking

Connector stroking (closure of the hub and connector) induces stresses in the tie-in spool whichshould be included in the stress analysis. A typical stroke length is 500mm. In some casesstroking will reduce the stresses in the tie-in spool. It may be possible to change the localarchitecture to take advantage of this fact.

The following pictures show the stroking of a horizontal connector. The running tool would thenbe removed and the doghouse fitted, if needed.


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Before Stroking

After Stroking


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4.6. Tolerance Types

A distinction should be made between the structure installation tolerances, which will bequantified during offshore metrology, and the other tolerances resulting from metrology,fabrication and stroking.

The structure installation tolerance shall be accommodated within the design of prefabricatedspool kits that will have angular and length adjustment on closing welds during spool fabrication.

All other tolerances have to be accommodated in the design flexibility of the spools. The spooldesigner needs to check the spool can accommodate all the possible combinations of angular &linear tolerances and misalignments.

4.7. Spool Fit-up

A spool fit up test performed onshore prior to shipping the spool offshore is an important part ofthe process of ensuring the spool can be installed offshore without the need for modification.Significant cost and time penalties can result if the spool has to be shipped back to the fabricationyard to be adjusted to fit correctly.


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5. Spool Installation Considerations

5.1. Introduction

The following section provides guidance on the installation issues that should be consideredwhen developing the spool configuration.

5.2. Spool Installation Guidance

The following installation guidance should be considered when developing spool piece layouts.

Spool can be installed based on 60-meter accumulative length (pipe length) and 45-meterdistance between connector to connector.

Installation is feasible with appropriate engineering input based on 60- meter accumulative

length and 45-meter distance between connector to connector

Spool will be hard too install when over length 70-meter accumulative length and 50-meterdistance between connector to connector.

Installation is feasible with 60 metre cumulative length (pipelength) and 45 metre envelope(connector to connector).

The width of the spool should be kept to the minimum.

The centre of gravity of the spool should be kept close to the main axis of the spool.

Lift capacity of the vessel crane must be adequate at the required radius

A common rigid spool installation practice is that the rigid spool gets to be lifted off the deckof the installation vessel or barge/supply vessel and deployed to depth by using the vessel

crane or a & r winch.


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5.3. Spool Installation Difficu lties

The picture below shows a very large spool that was a result of subsea structures (manifold andwell) being placed on the seabed outside of installation tolerances. As a consequence the spoolload could not be accommodated by the connector capacities and the SPS contractor had to re-visit its connector engineering specifications and engineer & manufacture new designedconnectors that would accommodate the load of the spool.

In addition the installation vessel could not load the spool on its deck or the rental barge it hadavailable and the installation contractor had to hire a longer and wider barge in order to load outthe spool. Three spreader bars were utilised for the load out and installation of this spool a quiterare practice in comparison to a viable spool common practice, which is one spreader bar/maximum two spreader bars. The whole saga had a major financial impact to thecontractor/operator and a severe schedule delay. In summary after metrology was received thespool was installed after 170 days.

Complex Spool Li ft


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6. Optimised Spool Design

6.1. Introduction

The original and revised spool configurations presented over leaf have been analysed using thenon-linear, large deflection finite element software ABAQUS. The results of the analysis arediscussed below.

6.2. Stress Analysis Results

The stress distributions and connector loads for the straight spool and the M spool are presentedover leaf. The analysis includes the effect of pipeline expansion, metrology tolerance, fabricationtolerance and connector stroking.

The connector loads for the M spool are reduced by a factor of 10. The bending stresses in the Mspool are reduced and are moved away from the connector location.

Stress Analysis Results Summary

Connector Loads

Item descriptionSpoolStress(Mpa)

AxialForce(KN)

ShearForce(KN)

Torsion(KN*m)

Moment(KN*m)

Original Spool Design 442 67.7 142.1 39 692.8

Optimised Spool Design 248 28.2 37.39 4.7 68

Spool and Connector Capacity 423 70 50 60 250


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Spool geometry before optimisation

Spool geometry after optimisation


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Finite Element Results before Optimisation(In-plane bending moment contour plot )

Finite Element Results after Optimisation(In-plane bending moment contour plot )


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7. The fini te element modelling techniques that can be used to reduce the

calculated loadings on the tie-in spoolsBy employing sophisticated Finite element program such as Abaqus, it is possible to obtain amore detail solution, hence reduction in unnecessary conservatism. There two major featureswithin Abaqus that we could take advantage are described as below.

7.1. Analys is mode

A spoolpiece is a relatively small structure designed to accommodate large end displacementsimposed by pipeline expansion, hence the geometric nonlinear effects must be considered infinite element analysis. The advantages of employing nonlinear analysis techniques

Provider higher accuracy solution to the problem

Render lower stress and load results within the structure because of load redistribution asthe geometry of the structure deforming

7.2. Boundary condition

Metrology and spool fabrication tolerances can lead to misalignment at the connector hub face.As a result, residual loads can arise from spool deformation due to installation forces induced tomatch-up the connector faces. The magnitude of these residual loads are depending of thestiffness of the system at the region close to the connectors.

The finite element technique to reduce the loading are as follow:

The stiffness of the load path from the connector into the inboard hub, its mountingstructure and the steel framework of the inboard structures shall be included, this would

allows for flexibility, hence reduction in connector loads Modelling the misalignments tolerances with kinematics constraints, this would provide

certain flexibilities within the system, hence lower the localised bending moments at theconnector supporting system.


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8. Structure Settlements after Installation

Subsea structures can experience immediate and consolidation settlement through their field life.The prediction and qualification of these settlements is important to ensure the structure remainsstable and serviceable. The settlement experienced by a structure is not only dependant on thegeotechnical properties of the soil but also the stress distribution across and down the structurefoundation and is considered under serviceability limit state conditions.

Installation Contractor should to carry out a detailed finite element analysis for the RMM(Removable Manifold Modules) caisson settlement. An axisymmetric Plaxis finite element modelhas to be developed. The caisson settlement shall be then computed for the following load cases:

Caisson and grillage installation;

Manifold installation;

Spool installation and other line loads.

It should be noted that although the grillage and caisson will be installed as a single structure theloads cases were separated here for computational reasons.

The development of settlement with time was computed as well as the limiting cases of drainedand undrained conditions. Parametric studies were carried out to evaluate the influence of thefollowing parameters:

Soil compressibility;

Permeability;

Mobilised soil / caisson interface friction;

Effect of a gap between the top plate and the soil plug.

Below you can see indicative analysis results of field life settlements that have been carried outfor a 7 m outside diameter by 9.5 m deep RMM caissons:

Immediate settlement after manifold installation =0.14 m;

Immediate settlement after jumper installation =0.23 m;

Total settlement after 25 years =0.48 m;

Total long term settlement (400 years) =0.64 m;

Differential total settlement after manifold installation = 0.34 m.


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9. Use of limi t state criteria to reduce spool sizes.

The traditional Allowable stress Design is normally provide us more conservitive solution howeverit is over simplistic and often overlooking the influence of the integrity of the structure undercombinations of loads. The limit state criteria provide us a rigorous and economical solutiondesign by considering various relevant fail mode consideration for spoolpiece. It methodology isprimary based on statistics to determine the level of safety required by or during the designprocess. The following example shows that for a type case where the spool is subjected to thepipeline displacement loads from both ends, the results based on allowable stress check and theresults from limit state criteria( load based and strain based ) are showing form Fig 5-7, it is clearfrom Fig 8 that both the limit state design and alloweable stress approach predict the similaruntilisation distribution along the spool but the limit state criteria give lower utilisation ratio, hencereduction in spool size requirement.

Al lowable stress ut il isation contour plot


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Utilisation contour p lot(Limit State Criteria assumed load control cond ition)


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Utilisation contour plot(Limit State Criteria assumed displacement control condi tion

Utilisation ratio along the spoo l length

Utilisation under different Design Criteria

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

0 50 100 150 200 250 300 350

Element Number

Utilis

ationRatio

DNV -ALLOWABLE STRESS UTILISATION

DNV-DISPLACEMENT CONTROL UTILISATION

DNV-LOAD CONTROL UTILISATION


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10. Loading Conditions for spoolpieces.

The spoolpiece is primary under displacement-control by having imposing displacements from thepipeline ends and mislignment tolerance,however if the spoolpiece is designed to rest on theseabed, then the frictional force between the spool and seabed would induce a significant degreeof load control.

11. Design Code and capacity, design criteria

The design code usually used for spool analysis is DNV-OS-101[1] which is a primary designcode for pipeline design. Nevertheless it can be used for the straight part of the spool withcareful considerations because the bends tend to behave different from a straight pipe,especially the ovality response under in-plane bending which in this case a separated designcriteria is required to be performed. The most convenient way to establish this design capacity isby utilising a 3-D non-linear finite element analysis. The displacement at failure should becompared with the corresponding displacement under design conditions. The safety factor shouldbe set at 3.0 or above as approve by classification society such as DNV

What DNV says about bends and spools:

The local buckling criteria, see D300-D600, are only applicable to pipelines that are straight instress-free condition and are not applicable to e.g. bends

Another intermediate case is an expansion spool in contact with the seabed. Pipeline expansioninduced by temperature and pressure imposes a displacement at the end of the spool. Thestructural response of the spool itself has little effect on the imposed expansion displacement,and the response is primarily displacementcontrolled. However, the lateral resistance to

movement of the spool across the seabed also plays a significant part and induces a degree ofload control. The answer to the question on if a condition is load controlled or displacementcontrolled is impossible since the questions in wrong, the question should be; how can one takepartial benefit of that a condition is partially displacement controlled element? On a general basisthis needs sensitivity analyses. A load controlled criterion can, however, always be applied.

Bends exposed to bending moments behave differently from straight pipes. Ovalisation becomesthe first order of deformation and changes the stress pattern considerably compared to straightpipes.

The ovalisation of the bend has typically to be determined by finite element calculation. Theacceptable distortion will typically governed by the bullet points in D900.

12. Use of pipeline design changes to reduce spool sizes and the need for twoconnectors per tie-in spool.

Uncontrolled Pipeline end expansion could lead to severe challenge for spools design. TheDesign option to reduce the end expansion can be listed as below:

By introducing route bends close to the pipeline ends to initiate the controlled buckles to absorbthe pipeline expansion, however the feasibility of this option would depending of the soil frictionbetween the pipeline the seabed.


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By introducing a sleeper close the pipeline end to initiate buckle formation, hence reduction inpipeline expansion at the end

13. Conclusions

13.1. Summary

Connection system must satisfy where applicable the following functional and designrequirements:

A design with a proven long term integrity of 20 years

Suitability for Design water depth 2500 m and qualified and proven for this depth

High insulation requirements on some areas of the fields requiring a cooldown time of up to12 hours (6 hours for SPS equipment and 12 hours for flowlines and risers). As well as thisrequirement, a system that avoids cold spots will help to reduce hydrate problems duringshutdown periods.

Controlled connector landing and make-up. In deep water operations the accuracy ofplacing and making up a connector is a challenge and a connection system that minimiserisks associated with tooling and makeup is required

Ability to replace seal subsea. In the event of a seal leak this would be required and simplemethod would be advantageous.

Ability to retrieve subsea equipment (e.g. Christmas Tree or a Manifold) without having toretrieve or wet park the spool Assembly

Have the ability to wet park long term prior to connection or installation of equipment.

Preferred Functional Requirements:

A capability to incorporate multiple connection points (multibore) within one connectorbody.

Common tooling throughout the field. This would reduce the complexity and logisticalproblems with supporting the installation operations and providing tool spares and technicalexpertise.

Rapid Installation. This would reduce the amount of vessel time and could also reduce therisk if the connectors are easy to make up with few operations.

Reduced structure height and size. A smaller, lighter structure will be easier to handle forthe installation contractors and a lower structure will be more stable on the sea-bed whenloaded.

Suitability for a maximum pipeline expansion movement of up to 4.50m at the FTAconnections and capable of withstanding the loads associated with this (should wetinsulation be considered).

Ability to use the same connection system for the main/extension umbilicals as well asprocess connections.

Ability to use the same connection system for rigid and flexible spools/jumpers.


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A horizontal deploy to place connection system is preferred and recommended for the followingreasons: Controlled connector landing and makeup.

Decouple spool Handling and makeup Added schedule flexibility

Retrieval of equipment (can pull Tree / Manifold).

More suited to multibore design

Tolerance to forces due to flowline movement (including bending and torsion)

A Vertical deploy to place connection system is preferred and recommended for the followingreasons:

Connection tooling is simpler, lighter & cheaper

Allows short hub-to-hub spacing

Vertical connections can allow compact receiver assemblies

Large rotation of hubs is not allowed

Thermal expansion can be accommodated via known pull-in loads

Stroking generates deflection, so short jumpers difficult

Docking of hub on porch is vertical, stroking is horizontal

Relative hub twist can be accommodated

13.2. Conclusion

Horizontal connections are advantageous where there is considerable relative hub movement(perhaps on long flowlines and some risers) and where rotation around the horizontal axis is likely(e.g. at the ends of long flowlines and in-line tees on gas/water injection lines). Verticalconnection systems are faster and simpler on manifold-tree connections and elsewhere wherethere is little hub movement. Different tooling is generally used for each. As a single connectionsystem is favoured and significant relative hub movements expected, horizontal connections arelikely to be favoured on deepwater operations.

In addition overall having a vertical connector/spool which is cheaper, simpler and faster

(installation wise) is a preference for every operator and contractor but the a vertical spool isrestricted to a standard geometrical M shape that is often needed to incorporate angular offset tothe line of the pipeline to fit the subsea field layout, and this would introduce high torsional load atthe connection system.

Unlike the horizontal spool which has the flexibility to more geometrical configurations andshapes in order to optimized for any given field layout arrangement.

The average elevation of the vertical spool is much higher than that of horizontal one, hencesubjected to higher current and wave induce water particle velocity, as the result the verticalspool is more susceptible to vortex induces vibration.


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Both Horizontal and Vertical Connectors have advantages and disadvantages. Choice is field andoperator specific.

Integrated working between systems engineers, design flowline engineers, subsea productionengineers and installation engineers is a necessity to produce fully optimised spool designs.

Typical connector capacities, installation, metrology and fabrication tolerances, stroke length andsettlements are presented.

A spool optimisation example is presented.

The use of advanced FE analysis and limit state criteria can result in significant in spool lengthsaving.

Pipeline buckling initiation technique and Pipe-in-pipe flowlines can be employed to reduce end

expansion, hence reduction in spool sizes.

14. Acknowledgement

The Authors would like to thank the support of Paul Linfoot and Andrew Whitehead in thepreparation of this paper.

15. Reference

[1] DNV-OS-F101 Submarine Flowline Systems, DNV Offshore Standard 2007

Documents

Opt 2008 Advanced Deepwater Spool Analysis Paper 27-02-08