THE SANDWICH PLATE SYSTEM (SPS)Author: Denis WelchDirector, SPS Overlay

Intelligent Engineering (UK) LtdUK

welch@ie-sps.comSYNOPSIS

SPS is the first new materials-based construction technology in maritime and civil engineeringsince the introduction of iron and steel 150 years ago. Over ten years of research and developmenthave been invested in the technology for these conservative markets, to the satisfaction of the keyplayers: owners, operators, manufacturers and classification societies.

The composite structure, of metal faceplates separated and continuously supported by theelastomer core, gives SPS the required strength and stiffness without the need for secondarystiffening. These inherent material properties of SPS give rise to significant benefits in fabrication,performance, safety and economics.

In addition, SPS plates behave globally as a diaphragm, eliminating the conventional problem of‘local buckling’. This characteristic allows optimisation of engineering designs and dramaticsimplification of structures, eliminating fatigue and corrosion prone details, resulting in betterperformance and extended service life.

The combination of the inherent properties of the two materials provides a wide variety of otherbenefits. These include superior impact performance, reduced weight and through-thickness andbuilt-in damping of vibration and structure borne noise. SPS is approved as providing a 60-minutefire barrier and is additionally a very effective blast barrier.

SPS Overlay is the ship repair application of the SPS technology used as an alternative to crop-and-replace. The existing corroded or worn plating forms one side of a steel composite panel witha new top plate and an elastomer core. The resulting composite fully restores and enhances thestrength of the original structure and provides a surface that is permanently flat. The process isextremely quick and uses a fraction of man-hours required for a conventional crop-and-replacerepair.

This paper will trace the development of the technology and discuss a range of repair applicationscarried out using SPS Overlay.

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1. INTRODUCTION

The theme of this year’s conference is “New Environment, New Technology,New Capability”. Lloyd’s Register says of SPS “[The] revolutionary SandwichPlate System is superior in every practical way to conventional, stiffened steelplate. SPS is a new generation building material bringing shipbuilding and civilengineering industries to the threshold of a new era…” I hope therefore that thispaper will align with the objectives of the conference in discussing the newopportunities that SPS offers in the design, construction and maintenance of navalvessels.

2. BACKGROUND

2.1 Shipbuilding

One hundred and fifty years ago ships were built from wood before iron andsubsequently steel became the norm. The other main metallic material used isaluminium because of its lighter weight when compared with steel. To achieve

the strength to resist loads, the “panel-stiffened” concept was adopted whichinvolved more elaborate production process [4], [5]. Non-metallic materials arealso now in common use and these include fibreglass and generic glass re-enforced plastics.

Assembling methods have evolved from the original woodwork skills ofshipwrights to riveting plates together and now a wide range of cutting andthermal welding techniques from oxyacetylene to plasma are in common use.

Sandwich plate ship structures integrate SPS plates with steel primary structureenabling Naval Architects to design lightweight, greatly simplified, higherperformance ships. SPS plates comprising two metal plates bonded to acontinuous elastomer core, form a much stiffer and stronger system than a singlestiffened metal plate, preclude local buckling, and eliminate the need for closelyspaced discrete stiffeners (Figure 1). In flexure, the plates act as flanges and thecore as the web. The thicknesses of the sandwich elements and metals used forthe face plates can be tailored to meet particular structural and performancerequirements. (A designation xx-yy-zz (e.g. 5-30-5) is used to denote thethicknesses of the three sandwich components, steel-elastomer-steel, in

millimetres.)

Figure 1 – SPS Newbuild Panels vs. Conventional Stiffened Steel Plate

2.2 Ship Repair

Whilst there have been advances in materials and methods in shipbuilding, theship repair technique for addressing damaged or corroded structure remains thatof cropping out the old steelwork and replacing it with new, which is inevitably atime and labour consuming process that is inherently dangerous and results instructures with various degrees of locked-in stress concentrations that compromisestructure integrity.

SPS Overlay is the ship repair application of SPS technology. It repairs severelycorroded or worn structural steelwork by incorporating existing plating in a thincomposite formed by a new top plate and an elastomer core which is injected in-

SPS Structure

ConventionalStructure

situ. The technology can be applied to any surface, vertical as well as horizontal,(e.g. bulkheads as well as decks and tank tops) and the thicknesses of the core andthe new top plate can be designed to reinstate to the original designed strength, orto significantly increase the load bearing capacity of the structure – withoutadditional stiffening.

Figure 2 – Section Through and Overlay Deck

3. SANDWICH PLATES

Lloyd’s Register describes SPS as “revolutionary”. Certainly the technologyoffers those responsible for the design and construction and maintenance of shipsa new set of options, which, after more than ten years of research anddevelopment with Intelligent Engineering’s industrial partners BASF, is now anestablished product in the marine industry. SPS has been endorsed byClassification Societies and embraced by a growing number of licensees;Singapore based Keppel Shipyards being an early adopter.

SPS construction has a number of benefits over conventional steel construction,including simplified structure from the elimination of secondary stiffeners,reduced weight, increased fatigue resistance and reduced susceptibility tocorrosion, leading to less maintenance and easier inspection. SPS also has anumber of other benefits, which offer unique advantages in Naval construction,such as built-in fire protection; enhanced resistance to puncture, impact, blast andballistic rounds. SPS construction also dampens structural-borne noise andvibration and can feature different faceplate materials e.g. aluminium, stainlesssteel and mild steel combinations.

All of the above contribute to performance optimisation reductions in productioncosts and to a longer and safer service life.

SPS was initially developed to provide impact resistant plating for offshorestructures in the Canadian Beaufort Sea. Research and development over the lastten years has focused on material characterisation, structural behaviour andperformance. This covers design principles, fire resistance and engineering,energy absorption design philosophies and the development of connection detailsspecific to sandwich plate structures. A growing portfolio of marine and civil

Perimeter BarNew Top Plate Elastomer

Existing deck plate

projects has stimulated the development of applications for both new constructionand repair of existing structures.

SPS has approvals from the major ship classification societies and regulatoryauthorities for use in newbuilds and the ship repair, with 80,000m² of decks, tanktops, bulkheads and other structures having already benefited from the applicationof the technology since the first commercial project in November 1999 .

A summary of the technology development undertaken to date is given inAppendix A.

4. BENEFITS IN NAVAL SHIP CONSTRUCTION

From the point of view of hull design, the ideal ship:

Has a hull form that optimises its role in carrying cargo or as an operationalplatform

Is economic to build

Is safe and efficient to operate

Requires minimal maintenance

Retains its value

SPS goes some way to addressing these challenges and ship operators are keen totake advantage of the benefits in structural simplicity, reduced maintenance andimproved lifetime performance. IE’s approach to the newbuilding opportunities isto work closely with our industry partners and to introduce the technologygradually through several no-risk applications. The SPS based design of achemical carrier for use on the Rhine River has been approved by GermanischerLloyd and by ZKR, the multi-national body that regulates traffic on the river(Figure 3). Production engineering work is underway at Krupp Stahlbau inHannover and construction will take plate late 2007. The experience will moveIntelligent Engineering further up the learning curve towards building a full oceangoing vessel, which is already the subject of intense interest from owners and shipbuilders.

In 2003 Flensburger Schiffbau Gesellschaft (FSG) commenced the fitting of SPSpanels in the funnel casings of a series of six new RoRo vessels for DFDSTorLine (Figure 4). The casings could be made much thinner using SPS platesbecause of the elimination of secondary stiffening and fire insulation. Exhaust gasuptakes and generators could still be accommodated with A60 fire protectionbuilt-in to the SPS plates. As a result, the space saved enabled additional trafficlanes to be incorporated into the design. Assembly of the unstiffened involvedstraight forward plate to plate butt welds with of course no stiffener connectionsto align and connect.

Figure 3 –Midship Section of Rhine Figure 4- Newbuild RoRo Ferry Funnel

Chemical Carrier Casings

The immediate advantages of SPS over conventional stiffened steel plates are asfollows:

Simplifying fabrication: In SPS fabrication, there are fewer parts, fewerintersections, less welding, and a reduced surface area. A study has shown thatalmost 9km of stiffeners and some 3000 connections can be eliminated in theconstruction of a 10,000DWT product Oil Tanker by substituting conventionalpanels with SPS plates.

More efficient operations: the permanently flat and impact resistant surfaceprovided by SPS can aid cargo loading/unloading efficiencies.

Better design features: The SPS design removes the principal sources ofstress concentrations and reduces the effects of crack initiations and fatigue,which directly impacts the future cost of maintenance and through-lifeownership.

Improved production engineering: SPS plates are extremely flat anddimensionally accurate which together with the elimination of brackets andstiffener connections makes the assembly process less skill dependant inassembly and more easily inspected for quality assurance.

Weight: For newbuilds, the weight of an SPS arrangement is less than that ofa conventional structural arrangement.

Cost: The overall SPS arrangement has lower build and operational costs thanthe equivalent conventional stiffened plate arrangement for reasons mentionedpreviously.

Features that are of specific interest to Naval ship designers in comparison withtraditional materials are likely to be; performance in respect of fatigue andcorrosion resistance and weight reduction and survivability; arising from thematerial’s ability both to withstand extreme load events such as grounding andblast resistance and also to resist ballistic puncture from bullets or shrapnel. Thisin addition to built-in fire protection and vibration dampening.

Performance

Fatigue and corrosion

Weight reduction

Vibration dampening

Survivability

Extreme loads

Blast / ballistic

Fire proofing

4.1 Impact Resistance

Composite structures such as SPS are extremely efficient in their ability to absorbextreme operational and accidental loads by dissipating the strain fields over alarge area and by avoiding the hard spots associated with the panel stiffening inconventional panel construction. Intelligent Engineering has demonstrated thevastly superior capabilities of SPS construction through a number of impact testscarried out at the BASF laboratories at Ludwigshaven in Germany. Groundingconditions have been simulated using large-scale sections representing a40,000Dwt product oil tanker and a Juniper class icebreaker that were acted on by4 x 500tonne capacity actuators. Applied loads, strains and displacements werecontinuously measured during the test and a close correlation established betweenthe predicted failure conditions for both the conventional structure and the SPSequivalent which demonstrated a significant improvement in energy absorbsionand maintenance of structural integrity.

(a) Test specimen and reaction blocks (b) 100-mm diameter hemispherical impactor

(c) pendulum apparatus and 2083 kg mass (d) corner impactor - close up

Figure 5 - Impact Specimen and Test Set-up(The tests involved impact loads being applied to specimens via 100mm hemispherical or a diamond shaped impactor mounted on a pendulum

that had a mass of 2083kg and an effective velocity of 20km/hr)

In addition to controlled laboratory tests, Intelligent Engineering has conducted apractical demonstration of the suitability of the material for use in deckconstruction for rock carrying vessels. In this case the customer repeatedlydropped rocks weighing up to 2100kg onto a 3m x 3.5m test sample thatsimulated a corroded deck reinstated by SPS Overlay (Figure 6). The deckabsorbed the severe test without debonding and with relatively little damage to theimpacted surface. The tests resulted in an order being placed for the reinstatementof corroded deck plating on a rock carrying vessel which has since carried over

Impactor

Reaction Blocks

SPS TestSpecimen

2083 kg

one million tonnes of quartz rock with only minimal evidence of wear and tear tothe deck surface.

4.2 Blast

Tests carried out by the US Navy at the Naval Warfare Surface Centre havedemonstrated the ability of SPS plates to out-perform the equivalent steelstructure. Intelligent Engineering’s specification was to provide an SPS plate noheavier than a ½" DH36 steel plate.

Although details of the test conditions are confidential, the resulting photographcomparing the ½" plate with the SPS 5-30-5 equivalent speaks for itself(Figure 7).

Figure 6 – Rock Drop Test

Figure 7 –Blast Test Comparison

SPS 5-30-5 vs ½" DH36 steel plate(50" diameter) - NWSC Carderock

4.3 Ballistic Protection

Intelligent Engineering has commissioned a series of ballistic tests that wereconducted in the UK by QinetiQ (formerly the Defence Evaluation and ResearchAssociation - DERA). These involved firing standard NATO 7.62mm rounds atSPS and equivalent stiffened steel plates from different range and angle. Thesedemonstrated that SPS stops projectiles at shorter strike ranges (higher velocities)

steel platemild steel SPS

bi-metal SPS

above line = Win

below line = Defeat

0

50

100

150

200

250

300

350

400

450

90 75 60 45 30 15

angle, 0

range,

metres

with 75% less chance of structure penetration (Figure 8).Figure 8 – Ballistics Tests Comparison

4.4 Fire Resistance

SPS has exceptional resistance to fire and can eliminate the need for theinstallation of thermal insulation. It is an extremely effective barrier to heat,flame, smoke and toxic gases. It will contain a fire and prevent it spreading toadjacent compartments, greatly limiting the growth of a fire throughout astructure. The elastomer core has excellent insulation properties. Full-scale deckpanel and bulkhead tests conducted in laboratories under International MaritimeOrganisation (IMO) A60 specified conditions have shown that the temperatureincrease at the unexposed surface of SPS was +5C with insulation (Figure 9) and+38C without insulation. The comparable temperature changes for steelstiffened plate are +192C and +710C respectively.

Figure 9 – SPS Plate after Fire Test Remains Cool and Retains Strength

4.5 Noise and Vibration Attenuation

An attractive feature of elastomer is its damping property and its presence in SPShas enhanced its damping response. Vibration and impact tests carried out at theIntersonar Laboratories in Holland have shown the response amplitude functionfor SPS is much less than steel, with the damping coefficient of being 4 to 5 timesgreater than steel (Figure 10). The effect of these SPS damping characteristics isthat there would be less vibration on the deck of a ship constructed from SPS orrepaired using the SPS concept. In addition, slamming loads would be less likelyto be transmitted thereby allowing high speed craft to maintain their speed inhigher sea states.0

10

20

30

40

50

60

70

80

20 25 30

Frequency, Hz

Tran

sfer

Func

tion Steel

SPS

-8

-6

-4

-2

0

2

4

6

8

0 200 400 600 800 1000 1200 1400

Time, ms

Disp

lace

men

t,m

m

Steel

SPS

Figure 10 – Graphs Showing Noise Vibration Attenuation

5. SPS OVERLAY (Ship Repair)

SPS Overlay is the repair application of SPS and works by incorporating theplating of the existing structure into a composite formed by a new top plate and anelastomer core that is injected in-situ.

The first application of SPS Overlay was the reinstatement of an area of deck onthe 1975 built P&O RoRo Ferry Pride of Cherbourg in November 1999. Sincethat date, Intelligent Engineering has undertaken 78 Overlay projects in 45shipyards worldwide, 11 in Singapore alone. Applications have ranged fromRoRo’s to Bulk Carriers to Offshore Oil and Gas Rigs.

5.1 Conventional Repair (Crop and Replace)

One of the most disruptive and risk laden activities in a repair or conversionproject is structural modifications using crop and replace methods. This requiresthe original structure to be taken out and replaced by new plating. The mainsteps, as applied to the repair to a deck of a ship, are illustrated in Figure 11.

Piped and electrical services and insulation in the vicinity of the repair aredisconnected and removed.

The existing plates are removed from the stiffeners in small sections byoxyacetylene cutting.

The new plates are installed and welded to the existing stiffening.

Insulation, pipe racks and cable trays are re-installed and service runs re-connected and tested.

Regardless of the circumstances, this is a disruptive, time consuming, uncertain,and inherently dangerous operation.

Disruptive: because it obviates parallel working in the area and can leave sectionsof the ship exposed to the elements.

Time consuming: because traditional crop and replace methods requireplating to be removed and replaced in small sections in consideration of liftingcapabilities and because the adjacent structure may not be capable of absorbingthe transferred static loads.

Uncertain: because attached insulation, piped and electrical services anddecorative finishes must all be removed and replaced with the risk of damage andunforeseen reinstatement problems.

Dangerous: because the demolition and removal process necessitates extensiveoxyacetylene cutting, and the creation of temporary access openings that representfire and injury hazards.

5 Weld stiffeners to plating2 Remove insulation and services

4 Fit new plate

3 Cut plating from stiffeners

1 Existing deck

6 Replace insulation and services

Figure 11 – Conventional ‘Crop and Replace’

5.2 SPS Overlay

SPS Overlay overcomes the operational difficulties of conventional repairtechniques by retaining the existing structure. As a consequence, an SPS Overlayrepair is extremely fast, safe, non-disruptive, and from a scheduling perspective,predictable. Although deck reinstatement is taken to illustrate the process, SPSOverlay is applicable to any flat surface whether it is horizontal or vertical. Thetechnology can be used to reinstate the structure to its original load bearingcapability or to accommodate heavier loading conditions. Intelligent Engineeringhas also developed non-welded solutions using advanced adhesives to create thesteel cavities in circumstances where hot work is a problem.

An example of this is the reinstatement of the bottom shell plating on the FPSOIndependence operated by Conoco-Phillips, which Intelligent Engineeringundertook in-situ off the coast of West Africa whilst the vessel continuedoperations. Traditional repair would have required expensive and disruptiveunderwater work. Low heat or no-heat solutions have since been applied in theSPS Overlay repair of an LNG Carrier adjacent to the cryogenic insulationmembrane and in voyage repairs to plating above engine room oil tanks on acruise ship.

The Process

The customer provides Intelligent Engineering with the relevant drawings andthickness measurement results for the area to be reinstated. IE’s designers usedirect calculation and FE modelling to determine the required thickness of theelastomer core and new top plate necessary to return the structure to its originalstrength, or better. This means that plating that has corroded below conventionaldiminution limits can be considered in the SPS Overlay Solution.

Drawings are prepared showing the layout of the cavities and steelwork details forthe specific applications and a design is submitted for approval by the relevantClassification Society. The drawings form part of a comprehensive specificationfor the SPS Overlay project, which defines the steelwork requirements that areusually carried out by a repair yard chosen by the customer in competitive tender.Alternatively, IE can provide a turnkey package to include the steelwork. The shipdoes not need to be docked for an SPS Overlay application and, since the existingstructure remains intact, there is no danger of misalignment, which is presentwhen large sections of steel work are removed in conventional repair.

Design details have now been developed for a wide range of SPS Overlayconfigurations, which are familiar to Class and help minimise the design andapproval lead-time (Figure 13).

1. ALL DIMENSIONS IN mm AND TO BECONFIRMED AT SHIP PRIOR TOWORK COMENCING.

2. STEEL - CLASS GRADE AOR EQUIVALENT.

3. ALL STEEL ON INTERIOR OF SURFACESOF SPS CAVITIES ARE TO BE GRITBLASTED TO A SURFACE ROUGHNESSOF 60+MICRONS, AND BE CLEAN, FREE OFGRIT, GREASE AND WATER.

4. SPS CAVITY MUST BE AIR TIGHT.5. THERE SHALL BE NO SUBSTITUTIONS OF

MATERIALS WITHOUT PRIOR WRITTENAPPROVAL OF INTELLIGENT ENGINEERING.

6. STEEL SPACERS 50mm DIA WITH THKEQUAL TO THE ELASTOMER CORE, TOBE TACK WELDED TO EXISTING DKPLATING BETWEEN PERIMETER BARS ANDDIRECTLY ABOVE TRANSVERSE OR LONGLSTIFFENERS, AT INTERVALS OFAPPROXIMATELY 750mm IN ANY DIRECTION.

7. WELDING TO CLASS STANDARDS.8. ALL WELDING TO BE COMPLETE PRIOR

TO ELASTOMER INJECTION.

CJO

JB11

CR-02-10-003

MAY 2002

MAY 2002

NTS A3

RO-RO SPS OVERLAY

SPS CAR/TRUCK FERRY DECK

SHEET SIZE:

DRN:

Proprietary and ConfidentialCopyright Intelligent Engineering 2002

CHK:MOD:

OFSHEET

Inte llig ent Eng inee ring (Cana da) Limited72 Ch amberla in AvenueOttawa, OntarioCa nadaTel: +1-613-5 69-311 1Fax: +1-6 13-569 -3222

DRAWING No.:DATE:REV. No.:

TITLE:

FILE NAME:

DATE:

SCALE:

PROJECT:

CHECKED:

DATE:DRAWN BY:

NOTES

ELAS TOM ER

STRUCTUREEXISTING

PLATESP S TOP

BA RPE RIMETER

PLATESPS TOP

PERIMETERBAR

ELASTOMER

EXISTINGSTRUCTURE

EDGE PREPARA TIONDEP TH AS REQUIRE D TOGIV E A 3MM ROOT DEPTH

12mm CHAMFER345°

PLATES PS TOP

ELASTOMER

STRU CTU REEXISTIN G

ELASTOMERSPS TOP

PLATE

PLATESPS TOP

60°3

RECTAN GUL ARPERIMETER BAR

RAMPEXISTIN G

EXISTINGRAMP

360°

EXISTINGCURB

PERIMETERBAR

SPS TO PPLATE

ELASTOMEREXISTING

S TRUCTURE

PERIMETERBAR

SPS TOPPLATE

EXISTINGDEC K

PERIMETERBARSPS TOP

PL ATE

EXISTINGPIPE PENETR ATION

ELASTOMER

PLA TESPS TOP

ELASTOMER

SUM PDRAIN

PE RIMETERBAR

STRUCTUREEXISTING

ELASTO MER

TRANSVEXISTING

PLATESPS TOPBAR

PERIMETER

DECKEXISTING

AND WELDED TO PERIMETER BAREXISTING FRAME BKT TRIMMED BACK

10mm CHAMFER60°

SPS TOPPLATE

EXISTINGDECK

TACKWELD 50

DIA

ELASTOMERCORE THK

EXISTINGSTIFFR

Figure 12 – Finite Element Analysis Figure 13 – Standard Details

SPS Overlay is carried out by grit blasting the existing plating then welding (or insome cases where hot work is to be avoided, gluing) steel perimeter bars to theplating to form a grid onto which a new top plate is welded to form a an airtightcavity into which IE’s engineers inject the two chemicals that react exothermallyto form the elastomer core.

A typical panel of 20m² is filled in eight minutes and sets in fifteen minutes. Thecore is fully cured in about 3 hours. The stages of an SPS Overlay Process areillustrated in Figure 14.

a. The existing structure is retained. The example shown is the tank top of a bulkcarrier before reinstatement by SPS Overlay. The combined effects of grabdamage and the hydraulic effect of loading powdered cargoes had deflectedthe existing plating by up to 65mm severely impacting unloading efficiencies.Operational comparison of the subsequent SPS Overlay reinstatement withconventional repairs has led to repeat business from the owner.

b. Shows the fitting of perimeter bars and spacers prior to installing the new topplate.

c. Fitting of new top plate that forms the shallow airtight box into whichIntelligent Engineering’s field staff injects the core.

d. During the curing process, the top plate is maintained flat by fitting temporaryrestraint beams, which are held in position by magnets supplied by IntelligentEngineering.

e. The injection head is attached and pumps chemicals into the cavity.

f. The finished surface is extremely flat and capable of absorbing severe impactloads without distortion.

(a) (b) (c)

(d) (e) (f)Figure 14 – SPS Overlay Process

5.3 Summary of Benefits

The process is safer by virtue of the structure remaining intact and because ofthe convenient access and reduced hot work (thermal cutting and welding).

The resulting repaired structure will not have any misalignments and thepotential build-up of locked-in stresses and fatigue concentrations is avoided.

SPS Overlay embodies the same characteristics of the newbuild compositestructure, e.g. high impact resistance, built-in fire protection, noise andvibration attenuation and reduced fatigue stresses.

Plating that has corroded significantly beyond conventional limits can berepaired by the SPS Overlay concept to the satisfaction of the ClassificationSocieties.

The process is very straightforward and no special skills are required for thesteelwork, which IE can provide as a turnkey package.

The reduced manual labour content of SPS Overlay effectively reduces theprice difference between Europe and the Far East.

The time taken to repair is typically four or five times faster than crop andreplace and time savings are further enhanced as there is no need to detach andre-attach piping and electrical services and insulation. Steelwork man hoursare typically 80-90% less than crop and replace.

5.4 SPS Overlay Case Studies

Isle of Arran

The Isle of Arran is a passenger/vehicle ferry owned by Caledonian MacBrayneand was built in 1984 by Ferguson’s in Port Glasgow. The vehicle deck was

designed to carry a combination of cars and trucks, with the axle load of the truckslimited to 11 tonnes and parking restricted to specified lanes.

Life extension plans for the vessel included a requirement to fit a Hi Fog fireprotection system in the engine room, located directly below the vehicle deck, andto strengthen the deck to take 2 axle trucks with 14 tonnes per axle across the full760m² of deck area.

The steel work was carried out by Garvel Clyde at their yard near Glasgow. A thinOverlay satisfied the new wheel loading criteria, with work below deck limited tothe fitting of six brackets at existing pillar locations. The work was completedinside 3 weeks and the effect was to take the deck strengthening off the criticaltime path by allowing work on the fire protection installation to proceed inparallel.

Figure 15 – Isle of Arran Figure 16 – SEDCO 600 Helideck

SEDCO 600 Helideck

Transocean required the helideck on their drilling rig to be upgraded to meet newlegislation, under which landing loads are taken as a greater multiplier of the

aircraft deadweight. Approximately two-thirds of the 445m² helideck was integralwith accommodation spaces and a conventional crop and replace solutiontherefore required extensive and time-consuming removals of ceilings, insulation,air conditioning, piping and electrical services. The strengthening was carried outwithout disruption to the accommodation spaces in a little over two weeks at thePPL shipyard in Singapore.

6. CONCLUSIONS

The unique characteristics of SPS provides new and exciting options in the designand maintenance of Naval vessels. The technology is robust and SPS is approvedby the major Classification Societies and Lloyd’s Register issued guidelines forthe construction of ships in SPS in March 2006.

REFERENCES

1. Kuo, C, “Managing Ship Safety”, LLP Ltd London, 1998, ISBN 1-85978-841-6.

2. “The Public Inquiry Into The Piper Alpha Disaster”, The Cullen Report,HSMO Cm 1310, Nov 1990.

3. “M.V. Herald of Free Enterprise – Fatal Accident Investigation” (SheenReport), Report of Court No 8074, UK Dept of Transport, 1987.

4. Eyres, “Ship Construction”

5. Chambers, D W., “Design of Ship Structures”, HMSO, 1993, ISBN0117727172

6. Smith, C S, “Design of Marine Structures in Composite Materials”, Elsevier,1990.

7. Proceedings from a series of International Conferences on ComputerApplication in Shipbuilding called (ICCAS), starting from 1973 in Japan toMalmo in 2002.

8. “A New Concept for New Age – The Sandwich Plate System (SPS) forShipbuilding”, Lloyds Register Marine Bulletin, September 2000.

9. Kennedy, S J, “Strength, Performance and Safety of SPS (Sandwich PlateSystem)”, Schiffbautag, Hamburg, October 2003.

10. Brooking, M A Kennedy, S J, “The Performance, Safety and ProductionBenefits of SPS Structures for Double Hull Tankers”, RINA Int. Conf. OnDouble Hull Tankers, London Feb 2004-09-02.

11. Kuo, C., Sukovoy, O., Little, N., Sharp, A., “The Generic ManagementSystem (GMS) Approach to Fire Safety of Composite Materials”, Interfram2004, Edinburgh, July 2004.

12. Kuo, C., Welch D W., “Sandwich Plate System and its use in EffectiveShiprepair”, European Shipbuilding Repair and Conversion – The Future,London , November 2004.

13. Sukovoy, O., Kuo, C., Little, N., Kennedy, S., J., “SPS – Satisfying SOLASFire Safety Requirements”, Design for Safety Conference, Osaka, Oct 2004.

14. “Guidelines on Alternative Design and Arrangements for Fire Safety”, IMOMSc/Circular 1002, Annex FP45/16 2001.

15. Welch, D W., “The Sandwich Plate System”, IMarEST/IESIS, Glasgow,2005.

16. Kennedy, D.J.L et al., “The Sandwich Plate System for Bridge Decks”,Proceedings 19th Ann. Int. Bridge Conf, Engineers Society of WesternPennsylvania, Pittsburgh, June 2002.

17. Kennedy, S.J., “Innovative use of Sandwich Plate System for Civil andMarine Applications”, Int. Symposium Innovation and Advances in SteelStructures, Singapore, August 2004.

Author’s Biography

Denis Welch joined Intelligent Engineering in January 2002 as DirectorSPS Overlay. He trained as a Naval Architect at Swan Hunter and was asenior consultant with A&P Appledore before joining BritishShipbuilders as Director of Ship Production Technology. Since then hehas held several senior management positions in engineering-ledmanufacturing industries, including spells as Deputy Managing Directorof Cleveland ridge and Engineers, Plant Manager at Cummins Diesel andManaging Director of GEC Marconi’s Electro Optic Systems Division.

Appendix A

SPS Technology Development

Material Characterisation

The polyurethane elastomer core is an engineered plastic that has been developedby Elastogran GmbH in accordance with Intelligent Engineering’s materialcharacterisation specification for the anticipated extremes of the full range ofoperating temperatures between -45ºC and +100ºC. Mechanical properties of theelastomer, including density, tensile strength (as illustrated in Figure A.1(a)),compressive strength, shear modulus and Poisson’s ratio were verified inaccordance with the appropriate ASTM or DIN standards and are summarised inTable A.1.

Table A.1 Characteristic Elastomer Material Properties

Test ResultsDensity

e= 1150 kg/m 3

Tensile BehaviourProperty -80 oC -60 oC -40 oC -20 oC 23 oC 60 oC 80 oCE (MPa) 3859 2924 1765 1164 874 436 248

y(MPa) 38.9 29.5 28.4 23.0 16.1 8.1 6.2

u () 7.2 11.1 13.2 15.1 32.1 43.1 47.4

Compressive BehaviourProperty -80oC -60 oC -40 oC -20 oC 23 oC 60 oC 80 oC

E (MPa) 3878 2813 1347 1166 765 501 336

y(MPa) 52.1 33.5 30.9 21.4 18.0 10.2 7.9

Shear Modulus (Torsion Pendulum Test)Property -

80oC -60 oC -40 oC -20 oC 23 oC 60oC 80 oC

G(MPa)

1386 955 559 429 285 180 135

Poisson Ratio

Mec

han

ical

Pro

per

ties

0.36Thermal Expansion Coefficient

Property -30 oC -10 oC 10 oC 30oC

50 oC 70 oC

x10-6m/m· oC) 96.1 120.1 133.6 148.7

162.5 184.7

Specific HeatProperty -20 oC 23 oC 60 oC 80 oC

c (J/kg·oC) 1217 1414 1588 1687Thermal ConductivityT

her

mal

Prop

ertie

s

k = 0.1774 W/m•oC (R-value/mm thickness = 0.032 oF·ft2·h/Btu)

Structural Behaviour And Performance

Classification rules commonly specify minimum plate slenderness parameters topreclude local failures because such failures prevent the flexural and compressionmembers (stiffened steel plates, girders, transverses) from reaching theirmaximum strength. For the SPS system, in a parallel manner, a minimum bondstrength and a modulus of elasticity of the core material are required to precludelocal failures and to limit shear deformations in the core that reduce this strength.These values have been determined analytically and verified by tests.

Bond at the interface between the core and face plates is required for compositeaction under normal operating loads, which may include dynamic loading events

like wave action or impact loads (grab or heavy cargo) that occur frequently; andmust be maintained for the full range of normal operating temperatures. Morethan one thousand tests have been conducted in shear and direct tension (directionof load transfer across the interface) on bond strength test specimens, as illustratedin Figure A.1(b), with a variety of surface preparations (primed surface,commercial bonding agents, surface roughness, casting conditions, elastomerproperties, ambient temperatures, base metals, and on samples subject toadvanced corrosion, seawater and chemicals to determine the bond strength foranticipated fabrication and operating conditions. Based on the results of thesetests, specifications for surface preparation and design values have beenestablished.

The characteristic flexural and compressive strength of SPS plates was establishedby tests as illustrated in Figures A.1(c) and (e). Compression tests includedstocky columns, which gives cross sectional compressive strength (no buckling)and more slender columns that failed by either inelastic or elastic global buckling.The tests verify that SPS plates with a core modulus of elasticity greater than theminimum specified can obtain the flexural (plastic moment capacity) orcompressive strength without local buckling, de-lamination of the face plates orany other local failure modes generally associated with laminates. Analyticalpredictions of strength calculated from commercially available finite elementprograms, verified against the test results, were in close correspondence withmean test-to-predicted ratios of 0.98 and 1.05 and coefficients of variation lessthan 5% for flexure and compression respectively. Additional full-scale ultimate(proof) load tests, like the lashing pot test shown in Figure A.1(d), are conductedas required.

The same finite element programs are being used for parametric model studies todevelop design equations for Classification Rules for determining the scantlingsfor SPS ships and SPS ship components. Intelligent Engineering is currentlyworking with Lloyd’s Register on developing a set of rules and regulations forsandwich plate ship structures. Until these rules are available, SPS ships can bedesigned and assessed by direct design calculations, which establish equivalencyto comparative steel ships. Intelligent Engineering has received approvals frommajor ship classification societies for the use of SPS in new builds and therehabilitation of ships with over 26,000 m² of SPS decks, hulls, tank tops,bulkheads, bow fingers and funnel casings in service on 30 projects.

0

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0 100000 200000 300000 400000 500000

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(a) elastomer tension coupon test (b) bond strength

(c) flexural strength

(d) lashing pot pull-out test (e) compressive strength

Figure A 1 - Global and Local Strength

(a) fatigue resistance of a block connection (b) salt water and chemical resistance

(c) inherent vibration damping provided byvisco-elastic core

(d) ballistic resistance

Figure A.2 - Improved Resistance

Other performance characteristics that have been established and quantifiedinclude:

Fatigue resistance (S-N curves) of the interface bond and welded connectiondetails specifically developed to join prefabricated SPS plates (refer to FigureA.2(a)).

Salt water and chemical resistance of the elastomer core should it becomeexposed during the life of the structure. Figure A.2(b) shows test samplesfrom one of four test series where sets of 30mm elastomer cubes werecompletely immersed in typical chemical species.

Vibration damping and structural borne noise transmission Figure A.2(c)illustrates typical displacement attenuation curves for SPS and steel platessubject to a single pulse. The inset picture illustrates a standard vibrationcharacterisation test conducted at BASF laboratories in Ludwigshafen.

Ballistic resistance limits for stiffened steel and SPS plates (all-steel and bi-metal) subject to standard 7.62mm rounds are illustrated in Figure A.2(d).These tests were conducted by QINETIQ (formally DERA).

Fire Resistance and Engineering

SPS has exceptional resistance to fire. It is an extremely effective barrier to heat,flame, smoke and toxic gases. It will contain a fire and prevent it spreading toadjacent compartments, greatly limiting the growth of a fire throughout astructure. This has been demonstrated by an extensive series of full-scale deckpanel and bulkhead tests, conducted in accordance with IMO (SOLAS) standardsat independent fire laboratories. The Maritime Coastguard Agency (MCA) co-developed the fire safety test programme and has witnessed SPS fire tests. FigureA.3(a) shows the standard SOLAS stiffened steel deck panel without structuralfire protection. The plate is severely distorted and the maximum surfacetemperature increase on the unexposed surface is +713ºC. The surfacetemperature on SPS plate with structural fire protection, shown in Figure A.3(b),is +5ºC. The corresponding temperature on an insulated steel plate was +192ºC.

a) Stiffened Steel Plate b) SPS 8-40 8 deck plate

Figure A3 - Safety of Life at Sea – Enhanced Fire Resistance

The steel faceplates present a fully non-combustible barrier to a fire that mayoccur from either side and the elastomer core provides an extremely effectiveinsulator against heat from fires. If an SPS panel is directly exposed to fire for anextended period then the elastomer core acts as sacrificial layer on the fire side(ablation) and gases from the elastomer surface vent into the fire side throughtemperature controlled pressure release valves. Only the exposed elastomersurface layer is affected, the remaining elastomer and the elastomer-steel bondedsurface on the unexposed surface are unaffected.

SPS can provide greater insulation than conventional arrangements. After thestandard 60-minute fire test (945ºC at one hour), the average temperature increaseon the unexposed surface of a SPS 4-25-4 plate without structural fire protectionwas 96ºC. The corresponding increase for a SPS 8-40-8 plate was 24ºC. For anA-60 barrier, SOLAS requires this increase to be no greater than 140ºC. WithSPS plates the unexposed surface remains cooler longer, extending containmentof the fire, and allowing more time for people to escape and fire fighters to fightthe fire. Based on the experimental evidence and fire engineering analysesconducted with the University of Strathclyde, the MCA has submitted thefollowing information papers to the IMO on the performance and behaviour ofSPS when subjected to fire loads.

Equivalence of a New Composite Structural Material to Steel in MaritimeStructures SPS (Sandwich Plate System), Maritime Safety Committee 74th

session, 2001

Fire Equivalence of SOLAS Chapter II-2 for the Sandwich Plate System (SPS),Sub-committee on Fire Protection 47 th session, 2002

(a) corner impact test, punctured steel plate (b) corner impact test, SPS plate - no rupture

(c) deformed shape of large-scale stiffened steelicebreaker hull test specimen

(d) deformed shape of large-scale SPS double hullproduct oil tanker test specimen

(e) stiffened steel hull- terrorist bomb (f) blast test specimens

Figure A.4 - Environmental and Asset Protection – Impact and Blast Resistance

SPS platesteel

Lloyd’s Register, together with the University of Strathclyde, are conducting aseries of Fire Engineering Analyses for a number of SPS designs in accordancewith recently introduced IMO guidelines (SOLAS Chapter II-2 Regulation 17).Based on the analysis of the DFDS Tor Line funnel casing constructed withprefabricated SPS plates, Lloyd’s Register presented the following conclusion inthe submission, which was submitted to the Danish Maritime Authority and isnow approved.

“From review of the extensive research and development and the fire engineeringanalysis carried out by Intelligent Engineering Limited and StrathclydeUniversity, some of which is reproduced in this report, it is concluded that for itsintended use, SPS meets all the relevant safety objectives and functionalrequirements of the revised SOLAS Chapter II-2 and should be considered as atleast equivalent to a conventional insulated stiffened steel plate of A-60 firerating.”

Energy Absorption

To increase its energy absorption capacity, a structure must be simplified anddesigned to allow localized progressive plastic membrane action in the hull or sideshell plating to occur. Simplification is achieved by eliminating stiffeners and byintroducing a plate structure with equivalent in-plane buckling capacity andstiffness to the stiffened plate, and flexural capacity to sustain transverse loads.This is uniquely achieved with the SPS plate section. Furthermore, the ductilecore eliminates hard spots over primary supports and provides continuous supportto the faceplates, dissipating localized bending strains. The net effect is anincrease to the puncture resistance and blast resistance. A further benefit is thatthe polyurethane elastomer provides an effective crack arrest layer. In the case ofdouble hull product oil tankers, the inner cargo tank lining can be effectivelyisolated from cracks that propagate from tears (sheared plating which mayeventually occur under high energy impacts) in the outer hull through the framingmembers into the inner hull, thus preventing oil outflow.

Figures A.4(a) and (b) graphically illustrate the local impact resistance of astiffened steel plate and a SPS plate when subjected to a corner shaped impactor,simulating the impacts of ship hulls with floating semi-submerged containers ordead heads or grazing off wharfs or from grabs for tank tops in bulk carriers. Theimpactor was mounted on a pendulum swing with a mass of 2 tonnes that wasraised two metres and released. The impactor struck the plate at approximately 20km/hr. The stiffeners of the steel plate were buckled where they framed intotransverses and the plating was holed or punctured. The impacted faceplate of theSPS plate was plastically deformed in the shape of the impactor and embeddedinto the elastomer core in the shape, but not penetrated.

Figure A.4(c) shows a plastically deformed stiffened steel plate icebreaker hullsection. At the load points the hull plating was bent sharply (hard spot withconcentrated bending strains) and ruptured. Figure A.4(d) shows the outer hull ofa 40,000 dwt SPS product oil tanker loaded with four 500T actuators. The hullplates, and longitudinal and transverse girders, were designed for both normaloperating loads and to maximize the energy absorption capacity for extreme loads

events. The hull plating developed plastic membrane action between longitudinalgirders, which extended into adjacent cells as the longitudinal buckled. Ruptureof the outer SPS plating did not occur as the elastomer core effectively distributedthe load and dissipated the bending strains.

Figures A.4(e) and (f) show a stiffened steel hull section that was subject to aterrorist bomb attack and two structurally equivalent plates that were subjected tounderwater blast loads. In both cases the steel plates shear, tear and open. Notonly is the hull ruptured but also a significant portion of the blast energy wastransmitted to the structure or contents behind the hull plate causing secondarydamage. The SPS plate effectively contained the blast load through plasticmembrane action.

The use of SPS plates coupled with the appropriate energy absorption designphilosophy improves the crash worthiness of the hull structure (maximizes thetotal energy absorption of the structure), provides a decreased risk ofenvironmental pollution and asset protection.