Bending StiffenersEngineered Systems

Trelleborg Offshore

Contents Page

Introduction 1

Company Profile 1

Bending Stiffeners 2

Dynamic bending stiffeners

Static bending stiffeners

Steel interface structure

Diverless bending stiffener connector

Specification & Analyis 3

Design & Engineering 3

Materials & Manufacture 4

Quality & Testing 5

1

Introduction

Trelleborg CRP bending stiffeners havebeen in service for over 15 yearsprotecting and supporting all types ofdynamic risers (flexible risers, umbilicals,mooring lines and cables), adding localstiffness to the riser adjacent to a rigidconnection to limit bending stresses andcurvature to acceptable levels.

Each bending stiffener manufactured byTrelleborg CRP is individually designed

to meet the load cases of each individualapplication. Over the last 15 yearsTrelleborg CRP have built up a track recordin service and in dynamic testing which isunrivalled for the production of bendingstiffeners.

Trelleborg CRP are Proven to Perform.

Company Profile

In January 2006, all CRP group companieswere acquired by Trelleborg AB, a companywith over 23,000 employees operating inmore than 45 countries. Trelleborg’smarket leading positions are based onadvanced polymer technologies and indepth applications know how.

Trelleborg CRP is a member of theTrelleborg Offshore group of companies,

all with a shared interest in the provision

of solutions for the offshore industry.

As part of Trelleborg Offshore, TrelleborgCRP benefits from a number of synergieswith other group companies includingcombined research and developmentprogrammes, materials technology, costefficiency initiatives, production andlogistical flexibility and a sound financialplatform.

Despite being part of a large global networkof companies, Trelleborg CRP has remainedtrue to the principles of customer serviceand product innovation that launched thecompany over 30 years ago, continuing tooffer engineered solutions that assist itsclients to increase the efficiency, costeffectiveness and onsite safety of all theirprojects, no matter where in the world.

Customer Service

All Trelleborg Offshore companies pridethemselves on customer focus andTrelleborg CRP’s global team of dedicatedprofessionals are committed to helpingensure that all clients’ projects arecompleted on time and within budget.

As a result, Trelleborg CRP provides acomprehensive range of premium servicesand support.

Trelleborg Offshore Global Network and Markets

Trelleborg Offshore group companiesemploy more than 1250 highly trained staffin strategically located manufacturing andoffice facilities across the globe. Thesefacilities are complemented by a number ofpolyurethane processing and dispensingplants servicing global subsea requirements.

Companies currently within TrelleborgOffshore are:

• Trelleborg CRP Ltd., Skelmersdale, UK (two facilities).

• Trelleborg Offshore, France.

• Trelleborg Offshore, Norway.

• Trelleborg CRP Inc., Houston, USA(two facilities).

• Trelleborg Emerson & Cuming, Inc., Boston (two facilities).

• Trelleborg OCP Ltd., Barrow-in-Furness, UK.

• Trelleborg Viking AS. Mjöndalen, Norway.

• Trelleborg Fillite, UK & USA.

The companies service the following core sectors:

• Cable & Flowline Protection.

• Engineered Products.

• Drilling.

• Thermal Insulation.

• Subsea.

• Marine.

• Glass Microspheres.

• Seismic.

• Defence.

• Industrial.

• Fire Protection.

• Downhole Products.

2

Bending Stiffeners

Dynamic flexible risers, power cables andumbilicals may be connected to a rigidstructure such as a subsea riser base or the turret exit of a floating productionvessel. The presence of environmentalloads subsequently causes the riser to flexabout this fixed location. This movement,in combination with large axial loads maycause damage to the riser structure due to overbending and fatigue.

Trelleborg CRP produce individuallydesigned integral bending stiffeners forrigid riser end fittings. These conicallyshaped polyurethane mouldings add localstiffness to a riser, flowline, cable orumbilical to limit bending stresses andcurvature to acceptable levels.

The bending stiffener has a conicalexternal profile and a central hollowcylindrical section allowing it to slide over the end of the riser.

Each bending stiffener is designedindividually to protect the riser minimumbend radius (MBR) under the definedtension and angle combinations, meetingthe loadcases (tension vs angle) of eachapplication, and are specified as eitherdynamic or static depending on theirintended use.

Dynamic Bending Stiffeners

Dynamic Bending Stiffeners are a fullyengineered solution to protect flexiblerisers or umbilicals in demandingapplications where a long service life is required. The bending stiffener ismanufactured from moulded polyurethaneelastomers specifically developed, qualifiedand tested over many years.

The dynamic bending stiffener protects theriser/umbilical MBR under defined tension/angle combinations. The local stiffnessadded to the riser/umbilical limits bendingstresses and curvature to acceptablelevels. Each dynamic bending stiffener isspecifically tailored to individualrequirements using specifically writtendesign software and manufacturedincorporating integral steelwork designed to interface with the client’s connectingstructure.

Static Bending Stiffeners

Static Bending Stiffeners are used primarilyfor overbend protection during installationand overboarding.

Static bending stiffeners are manufacturedfrom moulded polyurethane elastomers andhave been specifically developed, qualifiedand tested over many years. Protecting thepower cable/mooring line, static bendingstiffeners are typically 1-2m long withvarious interfaces available to suit specificrequirements such as at subsea terminations,by adding local stiffness to the powercable/umbilical adjacent to the rigidconnection, limiting bending stresses and curvature to acceptable levels.

Interface Structure

In order to transfer loads out of thepolyurethane section of the bendingstiffener a steel interface structure ismoulded into the base of conical section.Trelleborg CRP have the in-house capabilityto design and manufacture a wide range ofsteel interface structures to enable thebending stiffener to be connected to theadjacent rigid connection. Often requiringcomplex interface engineering TrelleborgCRP work closely with clients to ensureease of construction, installation andintegrity in service are considered duringthe design.

Trelleborg CRP have extensive experienceof designing and building such structuresfrom simple adaptor plates to highlyengineered diverless connectors,generating detailed structural design andfatigue analyses of the complete bendingstiffener system.

Diverless Bending StiffenerConnector

For applications where the bendingstiffener is prefitted to the riser prior todeployment and reeled off the laybargebefore being pulled into the I Tube,Trelleborg CRP developed the DiverlessBending Stiffener Connector System(DBSC).

The DBSC assembly normally consists ofthe following components:

• Female Interface – the main interface for the connection of the bending stiffener connecto.

• Diverless Bending Stiffener Connector – self activating and diverless.

• Bending Stiffener

• ROV Removable Clamp – required during installation of the DBSC then removed.

• Fixed Clamp/Back-up Clamp – required during installation of the DBSC, remaining in place during normal service life then used to facilitate the removal of the DBSC should it be required.

The Trelleborg CRP DBSC is secured withinthe bore of the female interface.

via a fatigue resistant locking arrangement.

The process is quick and reliable withminimal ROV assistance required duringinstallation.

Diverless Bending Stiffener Connector System

3

Specification & Analysis

The crucial pieces of information requiredfor the design of a bending stiffenerinclude the following:

• Umbilical/flowline/cable/riser diameter, MBR and stiffness.

• Loadcases (tensions vs angle) – a complex process requiring careful liaison with both pipe supplier and system designer to ensure that the true worst case conditions are used in the design.

• Operating temperature of both pipe contents and ambient environment.

• Operational environment – water or air.

• Interface requirements with load bearing steelwork/end termination.

• Fatigue loads and cycles. (for dynamic bend stiffener design)

• Tension and angle combination. (for dynamic bend stiffener design)

Once this information has been obtained,the preliminary and detailed design of thebending stiffener is assisted by TrelleborgCRP’s proprietary finite element softwarepackages – Stiffener and Orcabend.

These programs were developed andcustomised by MCS and Orcina specificallyfor Trelleborg CRP, based on their Flexcom3-D and Orcaflex software packages, whichare recognised as market leading dynamicanalysis software packages throughout theoffshore industry.

The software packages generate a 2-DFinite Element Model of a bending stiffenerto suit a given set of design conditionsusing a specified set of properties for thestiffener body material. The softwarepredicts the performance of the bendingstiffener when subjected to a range ofloadcases, temperatures and also thestress and strain being exerted within the stiffener.

Another important output produced by theprogram is the bending moments andshear loads generated within the stiffenerwhich need to be transferred into the rigidinterfacing structure.

A further software package known asSPOST.R is used to address the design ofthe metallic load transfer structure and anyother interface structure required toconnect the stiffener.

The satisfactory performance of all thecomputer software packages used byTrelleborg CRP has been extensivelyverified by the use of the following:

• 3-D Finite element analysis.

• Static bend tests.

• Dynamic bending testing installation.

Design & Engineering

Trelleborg CRP have assembled a designand engineering team with significanttechnical knowledge and experience gainedover many years in the offshore andoceanographic industries designing andinstalling flexible pipes, cables andumbilicals.

This experience is important when workingin close cooperation with clients tounderstand in detail the functionalrequirements such as:

• Operating conditions.

• Installation constraints.

• Interface requirements.

In particular, the accurate definition of theoperating conditions is necessary prior tothe commencement of detailedengineering.

Having captured all the required designinformation it is then necessary to analysethe data, interpret the results and consider

any particular mechanical interfacingrequirements in order to produce a bendingstiffener design to suit the clientsspecification and installation requirementsin the most cost effective way.

Materials & Manufacture

4

Materials

The bending stiffener body is manufacturedfrom moulded polyurethane elastomersspecifically developed, qualified and testedover many years.

Trelleborg CRP has a range of materials tosuit different applications, all of which areextremely tough, durable and suitable forextended service in arduous subsea andtopside applications.

The choice of polyurethane elastomer isbased upon its low modulus and highelongation at break. A comparison betweenthe stress vs strain properties of steel anda typical polyurethane elastomer isillustrated in the graph below.

Trelleborg CRP has invested significantly inthe development of new materials and theconduct of qualification programmes todemonstrate their suitability for use in suchan application. Typical test requirements

are listed below:

• Fatigue resistance.

• Creep resistance.

• Tensile strength.

• Tear resistance.

• Temperature dependency.

• Ageing in air and seawater.

• UV resistance.

If an adjacent cathodic protection systemis present, the steel interface componentof a bending stiffener is usually fabricatedfrom high strength structural grade carbonsteel. Alternatively it can be produced usingmore exotic corrosion resistant materials.

Manufacture

Trelleborg CRP has built up over 20 yearsof experience in the manufacture ofpolyurethane products for the oil, gas andmarine markets, and has harnessed thiswealth of knowledge to ensure its place at theforefront of bending stiffener manufacture.

The manufacturing process for bendingstiffeners can be broken down into anumber of key stages:

• Mould tool production.

• Steel insert component production.

• Assembly of mould tool and steel insert.

• Pre-heat tooling.

• Inject polyurethane into mould.

• Cure cycle.

• Demould and finish.

This apparently simple process includes a number of complex and demandingrequirements, for example, the world’slargest bending stiffener, produced byTrelleborg CRP for the Banff Field requiredan oven 12m long to house the assembledmould tool for the pre-heating process.

From the final design, the production of thestiffener takes place in Trelleborg CRP'smodern moulding facility, utilising state ofthe art polyurethane processing equipment,giant ovens and a tightly controlled factoryenvironment. Trelleborg CRP has withoutdoubt the world's largest and mosttechnically sophisticated productionequipment anywhere in the world, enablingTrelleborg CRP to meet the ever increasingdemands of the oil and gas industry.

0%0 0

10 1300

1% 2% 3%

Strain (%)

Polyurethane Properties – Stress Strain Curve

PolyurethaneAlloy Steel

Str

ess

(Allo

y S

teel

)

Str

ess

(Pol

yure

than

e)

4% 5% 6% 7%

Quality & Testing

5

Over the last 15 years Trelleborg CRP hasbuilt up a track record in service and indynamic testing which is unrivalled for theproduction of bending stiffeners and thegroup has produced thousands of units.

The testing of bending stiffeners can bedivided into three main categories:

• Material testing –to verify that the polyurethane materials used in manufacture have properties that match those used to model the bending stiffeners in the design software.

• Static bend testing –to verify that the actual bending stiffener deflects to the same shape predicted by the design software, under a given tension/angle loadcase.

• Dynamic testing – to verify the performance of the bending stiffener in simulated in-service conditions, and demonstrate fatigue life, etc.

Trelleborg CRP has an extensive trackrecord for supplying large dynamic bendingstiffeners and conducting full-scale dynamictest programmes to demonstrate theirfatigue performance.

Trelleborg CRP Bending Stiffenersundergoing dynamic testing

Client Project End User

Dunlop Armaline Emerald Sovereign Oil & Gas

Wellstream Blenheim Arco-British

Alcatel Mars Shell Offshore

Wellstream JIP Joint Industry Project

Alcatel Norn Statoil

Alcatel Deepstar Texaco-Deepwater Research Programme

Kvaerner Asgard A Statoil

Alcatel Macaroni Shell Offshore

Wellstream Asgard B Statoil

Wellstream Roncador Petrobras

Alcatel Fram Norsk Hydro

Alcatel Roncador Petrobras

Pirelli Roncador Petrobras

Alcatel Europa Shell Offshore

NKT Deepwater JIP Joint Industry Project

Coflexip Stena Offshore Qualification Coflexip Stena Offshore

Duco Inc Typhoon Chevron

Duco Inc Serrano Shell US

Duco Inc Nile BP Amoco

Wellstream Inc Barracuda/Caratinga Petrobras

Wellstream Inc Barracuda/Caratinga Petrobras

Wellstream Inc Barracuda/Caratinga Petrobras

Nexans Nakika Shell

Wellstream Albacora Lest

Wellstream ASAP

Nexans Thunder Horse TH-EOH2 Shell

Nexans Thunder HorseTH-ST1 Shell

Nexans Atlantic AT-ST2 Shell

Nexans Atlantic AT-EO1 Shell

Wellstream RO33

Nexans King BP

Test programs undertaken using Trelleborg CRP Bending Stiffeners

EUROPE

Trelleborg Offshore

Stanley Way, SkelmersdaleLancashire WN8 8EA, UK

Tel: +44 (0)1695 712000Fax: +44 (0)1695 712111

114 rue Saint Lazare - BP2060960476 - Compiègne cedex 2, France

Tel: +33 (0)3 44 23 03 50Fax: +33 (0)3 44 23 03 49

Sothammargeilen 9, DusavikbasenBygg 1, 4029 Stavanger, Norway

Tel: +47 51 54 38 00Fax: +47 51 54 35 00

Email: offshoresales@trelleborg.comWebsite: www.trelleborg.com/offshore

Trelleborg Viking AS

PO Box A, 3051 Mjöndalen, Norway

Tel: +47 32 23 20 00Fax: +47 32 23 22 00

Email: viking@trelleborg.comWebsite: www.trelleborg.com/viking

Trelleborg CRP Ltd.

Paxton Place, West Pimbo, Skelmersdale,Lancashire WN8 9QH, UK

Tel: +44 (0)1695 714300Fax: +44 (0)1695 555586

Stanley Way, SkelmersdaleLancashire WN8 8EA, UK

Tel: +44 (0)1695 712000Fax: +44 (0)1695 712111

Email: crpsales@trelleborg.comWebsite: www.trelleborg.com/crp

Trelleborg OCP Ltd.

3 Peter Green Way, Barrow-in-FurnessCumbria LA14 2PE, UK

Tel: +44 (0)1229 842070Fax: +44 (0)1229 842071

Email: ocpsales@trelleborg.comWebsite: www.trelleborg.com/ocp

Trelleborg Fillite Ltd.

Goddard Road, Astmoor Industrial Estate,Runcorn, Cheshire WA7 1QF, UK

Tel: +44 (0)1928 566661Fax: +44 (0)1928 572380

Email: fillite@trelleborg.comWebsite: www.trelleborg.com/fillite

NORTH AMERICA

Trelleborg CRP Inc.

519 N Sam Houston Pkwy E, Suite 200,Houston, TX 77060, USA

Tel: +1 (832) 456 8300Fax: +1 (832) 456 8385

1902 Rankin Road, HoustonTX 77073, USA

Tel: +1 (281) 774 2600Fax: +1 (281) 774 2626

Email: crpsales@trelleborg.comWebsite: www.trelleborg.com/crp

Trelleborg Emerson & Cuming, Inc.

209 Forbes Boulevard, MansfieldMA 02048, USA

Tel: +1 (774) 719 1400Fax: +1 (774) 719 1410

24 Teed Drive, RandolphMA 02368, USA

Tel: +1 (781) 963 6794Fax: +1 (781) 963 6788

Email: emerson@trelleborg.comWebsite: www.trelleborg.com/emerson

Trelleborg Fillite Ltd.

1856 Corporate Drive, Suite 135,Norcross, Georgia 30093-2925, USA

Tel: +1 (770) 729 8030Fax: +1 (770) 729 9639

Email: fillite@trelleborg.comWebsite: www.trelleborg.com/fillite

REF: B

S 0

3/0

9

The information contained in this publication is for guidance only and does not constitute a specification. All figures are nominal. This documentdiscloses subject matter in which Trelleborg CRP Limited has proprietary rights. Neither receipt nor possession thereof confers or transfers anyright to reproduce or disclose the documents, any information contained therein, or any physical article or device, or to practice any method or process except by written agreement with Trelleborg CRP Limited.

Trelleborg CRP Limited is committed to further development of all its products. The right is reserved to alter this specification without prior notice.