PS7-3.1

INDIA’S FIRST LNG IMPORT TERMINAL ANDTHE CHALLENGES OF LNG TANK DESIGN

LA PREMIER TERMINAL D’IMPORTATION DE GNL EN INDE ETLES DIFFICULTES DE CONCEPTION DES RESERVOIRS

Ing Paul Sullivan BE, CEng, MIEI, MIWEMDirector of Sales & Marketing

Ing Keith Mash BEng MEng CEng MICEDesign Manager

Whessoe International

ABSTRACT

Dabhol Power Corporation (DPC) appointed Enron, as lead shareholder, to developan LNG Importation Terminal adjacent to their power plant, in order to provide naturalgas as a fuel, in place of naptha. DPC/Enron bid out a base scheme for the project to themarket in 1997.

In bidding the project, Whessoe International proposed to DPC/Enron an alternativescheme. This proved to be the most attractive offer, based on lifetime cost, safety andoperability considerations.

Enron and Whessoe spent the following 8 months in Front End and ValueEngineering studies, optimising the scheme. The final design was for a 5MTPA plantwith half a million cubic metres of storage in 3x160,000m3 full containment LNG tanks,and dual regassification streams at high and intermediate pressures, for the trunkpipelines and the power plant respectively.

This paper will outline the pivotal influence of the LNG Tanks in the development ofthe Whessoe alternative scheme. This influence extends to offloading line sizes, boil-offgas handling, venting systems, in-tank pump selection, and regassification plantoperation.

The paper will also deal with the technical and logistical challenges of designing andconstructing the world’s largest full containment PC/9% Ni LNG tanks, outside Japan.

PS7-3.2

INDIA’S FIRST LNG IMPORT TERMINAL ANDTHE CHALLENGES OF LNG TANK DESIGN

INTRODUCTION

In 1997 Dabhol Power Corporation (DPC) decided to press forward with the DabholLNG Import Terminal, in support of their Power Plant expansion. In doing this theyembarked upon an historic undertaking, to engineer and construct India's first LNGterminal facility.

The first LNG facility in any country is pioneering and ground breaking for allparties, including the developer, the contractor and the statutory authorities. In every casewhether for Importation or for Export Terminals, the parties are faced with an essentiallynew technology for that country. Although the existence of international standards hashelped to ease concerns, there is still a tendency to marginally revisit, if not reinvent thewheel.

In order to develop comfort with the technology it has not been uncommon forcomparisons to other equivalent industries to be used. Historically the LNG industry hasbeen compared to either the nuclear, refining, gas plant or LPG industries. In India, whichhas come into the LNG market rather later than many of the major energy importingnations, there appears to have been a great degree of comfort elicited from their extensiverecent experience with other low temperature and cryogenic gas processes. It was hardlysurprising therefore that Whessoe International with their major experience in the Indiangas terminal market were an obvious choice for prequalification.

Whessoe, together with their existing in-country construction and erection partnerPunj Lloyd, were eventually selected by DPC/Enron as EPC contractors for the plant.Whessoe subsequently invited Skanska Cementation International (formerly Kvaerner) tojoin the team as lead contractor and overall project manager, due to their unparalledreputation in delivering major projects in the Indian market.

The terminal presented many technical and logistical challenges, particularly given aclient as informed and demanding as DPC/Enron. In it’s finally developed form, thisproject has created a new benchmark, not just for India, but for all future world class,stand alone, privately financed LNG import projects. Dabhol has not succeeded incommoditising the LNG import business, but it has most certainly, put the possibility inplay.

PS7-3.3

DISCUSSION

Site Description and Location

The site is located approximately 360 km south of Bombay on the southwest coast ofIndia’s Maharashtra State. Figure 1 indicates the location of the site with in peninsularIndia.

Dabhol Site

Figure 1 - Site Location in Peninsular India

Access to the site can be gained via the H17 ‘Bombay to Goa Highway’, along theChiplun to Guhaga road. The site is approximately 50 km west of the town of Chiplun. Atpresent, road access is slow and travel to the site is commonly via chartered helicopterfrom Bombay, flight time approximately one hour. Figure 2 indicates the general sitelocation.

PS7-3.4

Figure 2 – General Site Location

Dabhol Site

PS7-3.5

Topography

The majority of the site is located within a valley, approximately 1km long, whichleads directly into the Arabian Sea. The nature of the ground can be assessed from co-ordination layout presented in Figure 3.

Figure 3 – Co-ordination Layout

The centre of the valley is flat, generally at a level of 10m, reducing to 5m near thesea. The valley forms a cove adjacent to the coast known locally as Smugglers Cove. Theslopes with residual soil cover around the central cove are steep, (up to 1 vertical to 2horizontal), and rise to approximately 115m. Slopes predominantly in weathered andfresh rock are steeper, particularly where exposed as sea cliffs. In the vicinity of theProcess Area, the site slopes downwards in an easterly direction, in very general termsfrom approximately 50m in the west to 25m in the east. Two tanks, T500 and T600 arelocated on higher ground, in an area locally referred to as the Meadowlands, at a level ofapproximately 110m. The slopes of the cove are undulating from the effect of streams,which have cut into the valley sides.

Geology of the Area

This southern Maharashtra region of India has a continental crust composed ofPrecambrian rocks (Archaen age gneisses and schists, igneous rocks and Precambrian agesediments) older than 3 billion years. The West Coast is affected by a series of north-north west to south-south east trending faults, incurred during a period of tectonic activitywithin the Cretaceous period. This tectonic activity caused a West Coast rift. This rift wasthe source of the Deccan continental basalt vulcanism. This vulcanism has producedmany basaltic lava flows which have buried the Precambrian rocks at great depths (1300-

PS7-3.6

1400m) below the earth’s surface. This volcanic region is known as the Deccan Trap andconsists of massive basalts, vesicular and amygdaloidal basalts, tuff breccia and redbaked paleosols. The flows dip gently, at 3° to 4° to the west. Individual flow thicknessescan vary from one metre up to 40 metres.

There are a few recent deposits throughout the region. Some localised alluvialdeposits exist. General cover throughout the region comprises of tropical weatheredbasalts which have produced red/brown laterite soils and hard indurated laterites.

Soil Conditions & Site Geology

The geology is relatively simple, consisting of near horizontal lava flows. Theweathering of individual lava flows has resulted, generally, in a stepped profile of thehillsides. Each layer comprises basalt with secondary quartz and calcite. The separateflows can be easily identified, becoming stronger and more massive towards the base ofeach.

Weathering of the basalt has resulted in the formation of an indurated laterite and aresidual laterite soil, underlain by highly weathered rock. During Phase I of theearthworks for the power station above Smuggler’s Cove, these deposits were observed toreach considerable thicknesses. Most of the work has been performed within them, ratherthan in the fresh basalt. These soils can give rise to low CBR values (California BearingRatio), when the weathering has resulted in a clay rich material.

At Smuggler’s Cove there does not appear to be any indurated laterite. At thislocation, there is a relatively thin cover of laterite soil over a similar thickness ofweathered rock. Below this weathered zone, are generally strong fresh grey basalts, withthe exception of the weathered upper surface of individual lava flows.

In the base of the valley the depth of weathering is somewhat deeper than on the sideslopes, particularly on approaching the sea. In the vicinity of the shoreline, marine sandsalso overlie weathered rock. Away from the marine sands, trial pits revealed moderatelydense clayey sands and firm silty clays.

The geology around Tanks T500 and T600 is slightly more complex than for thoselocated at Smuggler’s Cove. There are few exposures of rock in the locality, because ofthe presence of dense vegetation. The boreholes, also, indicate a considerable thickness oflaterite soil (up to 10m), overlying up to 2m of weathered rock before encountering freshbasalt.

Proposed Scheme

The scheme comprises the construction of 3 x 160,000 m3 gas storage tanks togetherwith associated process plant.

A combination of excavation and bulk filling were required to form a number ofplateaux at various locations. Some plateaux had structural loads applied from the gasstorage tanks and items of plant from the processing facility, whilst others were formed toprovide access and circulation areas where levels and gradients were unsuitable. Thedesign of these areas required consideration of the suitability and compactioncharacteristics of fill materials, together with long term consolidation settlements.

Associated with the principal excavations and fill areas for the plant, works were alsorequired to construct infrastructure in the form of roads and drainage works. The drainage

PS7-3.7

works were required to cater for run-off from the construction areas together with passingexisting drainage flows from the surrounding area.

Highways were required to form access to the site as well as around the Process Areaand the Tanks.

LNG Tank Main Features

Tank Design Data- Design Type Full Containment- Gross Liquid Capacity 160,000 m3

- Normal Working Capacity 153,800 m3

- Design Temperature of Product -168 Deg C- Specific Gravity 0.47- Design Pressure 210mbarg - Depth of LNG in Service 36.44m- Hydrotest Level 21.409m- Heat Leak 0.05%/day

Concrete Secondary Containment Features- Inside Diameter 77.4m- Height to Top of Ring Beam 39.55m- Number of Buttresses 4- Horizontal Post Tensioning Size 19K15- Vertical Post Tensioning Size 19K15- Wall Thickness 0.6m- Stem Thickness 1.2m

9 Percent Nickel (Ni) Steel Primary Container Features- Diameter at Ambient Temperature 75.0m- Shell Height 37.3m- Minimum Shell Course Thickness 10.0mm- Maximum Shell Course Thickness 27.5mm

Initial Scheme

The initial scheme as contained in the invitation to bid required 3 number 160,000m3

single containment LNG storage tanks. As described the topography was particularlydifficult due to the steep escarpments in the area. The findings of a site reconnaissancecarried out by Whessoe’s Front End Engineering Team revealed that there was scope forlayout optimisation initially with respect to containment type, tank and process areaelevations.

After detailed engineering studies Whessoe were able to offer the client fullcontainment prestressed concrete LNG storage tanks. The immediate benefit to the clientwas the heightened safety classification of full containment vs single containment tanks,and the savings in earthworks due to the smaller footprint.

In addition the tanks were positioned so as to found directly on bedrock ensuring thatall tanks were identical and soil structure interaction effects could be minimised/negated.The process area was lowered to avoid rotating machinery/ vaporisers being constructedon excessive depths of fill that would be prone to settlements.

PS7-3.8

At the contract negotiation stage the Whessoe team worked in conjunction with theClients engineers to further develop and optimise the process design. This was facilitatedby Whessoe deploying experienced process designers within the Client team. Theformation of this joint team enabled Whessoe to understand and achieve the Clientsobjectives.

In particular the Client was concerned with design; selection and optimisation ofprocess related items, which presented Whessoe with numerous challenges.

Process-Related Challenges

These main features of the terminal’s location provided the following key designissues to be addressed and optimised;

1) Very long jetty into deep water for the LNG carriers.(1.7 km long, 2.8 km to thetanks.)

2) Large long unloading line/s to the tanks (2 - 32”dia. 2.8km. long.)

3) Development of design philosophy and loading concept for future tanks atelevations of 110 m.

4) The building line was 500metres minimum back from the shore and within thecurtilage of the cove.

5) The location and elevation (+25m) of the three initial large LNG storage tanks(160,000m³ capacity.)

6) Maximum ship unloading rate to the unusually elevated tanks (12,000m³/hr.)

7) Sizing of major equipment, layout, and location of the process area and controlbuilding, to optimise energy consumption and lifetime cost.

8) Location of the fire protection system firewater storage and pump station.

9) Gas transmission lines up the cliff to the power station and future gas grid.

10) Electrical and utility supplies and DCS/ESD communication between the LNGTerminal and the power station.

11) Environmental aspects to comply with local and national codes and TACregulations (Tariff Advisory Committee.)

Process Optimisation

The following process orientated optimisation studies were carried out:

a) In order to minimise the size, number and cost of the 2.8km unloading lines anexhaustive study was carried out with respect to unloading rates and pressuredrops from LNG carriers ranging in size from 85,000m3 to 135,000m³.

b) To minimise the line pressure drop, a study of jetty line expansion loops versusdouble bellows was carried out. Although expansion loops were cheaper, theywould have increased the overall pressure drop in the system, which was critical

PS7-3.9

to the design. In addition they would also have consumed a significant space andrequired piled supports. Forty number double bellows, were selected in order toprovide an in-line solution with minimal pressure drop.

c) The piled jetty design and jetty head layout were optimised to accommodate LNGcarriers up to 135,000M³ capacity and 50 ft. loading arms were used (3 liquid and1 vapour). The operating envelopes for the loading arms had to cover a range ofLNG carrier sizes and could have caused an increase in loading arm size. Byappropriate controls they were maintained at the 50ft size.

d) A detailed surge analysis of the jetty lines was necessary due to the highunloading rates, large volumes of LNG and the distance to the tanks

e) The vapour return system to the ship warranted a very detailed cost/design study,to identify whether a cold return line or shipside LNG injection was the mosteconomical.

f) With the initial process parameters outlined on the material balance, a HYSYSmodel was developed for the entire plant and optimised for the bestthermodynamic and energy efficiency to meet the power station requirements.

g) One of the key features at an early stage was to optimise the LNG tanks; operatingpressure and Boiloff Gas Condenser presssure so that the electrical power forsendout, compressors, boosters and vaporisation could be minimised. Savings ofin excess of 20% of total power requirements for the LNG Terminal were realised.

h) Specific cases of tank design pressure and size were analysed to optimise theoverall tank performance. This included filling rates through line sizes up to 40”.

i) The in-tank LNG pumps, LP booster pumps and HP booster pumps wereoptimised in support of power station and gas grid pressures. It is noteworthy thatthe selected pumps are the largest in the world of their type. The number of pumpsper tank for operational flexibility and sparing was also carefully analysed.Because the tanks were all at different levels around the cove, in-tank flow controlsystems were required to balance the discharge flows and pressures to thedownstream equipment. The L.P. booster pumps provide LNG at 44 Barg. for thevaporisers feeding the power station while the H.P. booster pumps provide LNGat 100Barg. for the gas grid.

j) The benefits, sizes and costs of reciprocating compressors versus centrifugalcompressors for the steady tank boiloff duty and weekly peak ship unloading dutywere determined.

k) The Boiloff Gas (BOG) Condenser is a critical item for size, residence time andcost. In order to finalise the design a detailed parametric study was carried outusing HYSYS.

l) The types of vaporisers reviewed included horizontal double bank shell and tube,sea water open rack vaporisers(ORVs), submerged combustion vaporisers(SCVs), and vertical shell and tube. The latter was chosen in this instance becausea heating medium was already available from low grade power station waste heat.

PS7-3.10

Additionally they offered easier operation, good control of outlet gas temperature,excellent turndown of about 10/1 and most importantly an established trackrecord.

m) The heating medium for the vaporisers was stipulated as 40% methanol/water.This medium comes warmed from the power station gas turbine air inlet coolersand returns chilled after the vaporisation back to the turbine air coolers. However,on the advice of the gas turbine suppliers, the power station had to alter themedium at the turbines to ethylene glycol/water owing to safety considerations(flammability.) Consequently the cooling of the gas turbine air is achieved with aglycol/water circuit which then interchanges it’s heat with a methanol/watercircuit. This in turn provides the heating medium for the vaporisers. Because ofthe poorer heat transfer properties of the glycol solution compared to methanol,more vaporisers would have been needed if glycol had been used as the primaryheating medium.

n) Because of the distance from the power station, it was necessary to have aseparate firewater protection system for the LNG Terminal. This comprised a firewater storage tank and firewater pumphouse, with diesel and electric drivenpumps. The makeup water to the tank was provided by the power station. Thefirewater tank capacity and firewater coverage rates for equipment had to complywith TAC requirements. The economics of extending the fire protection system tothe jetty head was considered in detail but it was found more economic and securefor the jetty area and jetty head to have its own system fed by sea water pumps,with a fresh water flush capability. This system included water fog curtains for theships’ side, elevated monitors and fixed monitors plus hydrants.

o) Owing to the topography of the cove and the large tanks, the maximum vapourrates and the prevailing wind , a flare stack was selected over venting. The flarestack height, maximum radiant heat flux and sterilisation area required wasconsidered carefully for the area and elevation. At the jetty head a small ventstack was provided in a remote area for minor spillages. The plant was designedso that any minor pressure reliefs are held within the system or may be adjustedby the operator. In the event of an equipment malfunction the flare could beneeded for the process and the storage tank boiloff. The tanks themselves are alsoprotected by large pilot operated safety relief valves.

p) Four locations were considered for the control building before fixing on alocation near the perimeter of the process area adjacent to the approach road.This enabled the operators to be the ‘eyes and ears’ of the plant while having asafe building location with good access. The blast proof design ensured theintegrity of the building and occupants in the unlikely event of a significantemergency. The building dimensions were kept to a minimum, as required bycode, for manning level requirements.

q) It was important to define the physical terminations (battery limits) for all of theutilities, power supplies, metering and process lines coming from the powerstation as most were routed down the steep side of the cove. Anchoring andmonsoon water diversion was critical issues and influenced much of the routing.

PS7-3.11

The next significant area for design consideration was the seismic design of the tankand tank related items.

Seismic Related Challenges

The majority of the seismic activity in India is located along the mountain range ofthe Himalayas, in particularly Nepal, Kashmir and Pakistan. By comparison, the Dabholsite is located some 1500km south of this region in Peninsular India, a region of low tomoderate seismic activity.

Indian Standard, IS1893, criteria for earthquake resistant design of structuresclassifies the Dabhol area as a Zone IV.

In accordance with the requirements of NFPA59A a detailed Seismic HazardAssessment (SHA) was carried out to determine the Operating Basis Earthquake OBEand Safe Shutdown Earthquake SSE.

The OBE represents the maximum earthquake intensity that may occur during the lifeof the structures, during and after which the structures are required to remain fullyoperational without repair. It is allocated the statistical return period of 475 years.

The SSE is an extreme event representing the most severe conditions for which it isconsidered necessary to cater. This level corresponds to the seismic intensity with a 1%probability of occurrence during the lifetime of the structures. It is allocated the statisticalreturn period of 10,000 years. The structures may accept damage, but are required tofulfil their containment functions during and following a Safe Shutdown Earthquake. Inaddition the outer tanks are designed so as to withstand the effects of an OBE earthquakewhilst holding the product.

In accordance with NFPA59A 5% damped SSE and OBE design spectrums wereconstructed based on the 10,000 and 475 year recurrence periods. Effective PeakAccelerations (EPA) for the OBE and SSE event were defined as 0.075g and 0.22grespectively. Tripartite plots for both earthquake levels are presented in Figure 4.

PS7-3.12

Figure 4 – Tripartite Plots for OBE and SSE Design Spectrum

Seismic Analysis of Pipework, Roof Mounted Structures and Appurtenances

Within Client specifications, national and international building codes there is anabsence of guidance with respect to the seismic design of pipework, roof mountedstructures and appurtenances. In this instance appurtenances constitute non-structuralcomponents and equipment as dry chemical units, electrical control panels, cranes.

Whessoe’s (WIL) experience with both tank and terminal design in moderate to highseismic zones indicates that caution should be exercised when designing roof mountedstructures and pipework. Specifically, magnifications of ground motion between 2.5 and4.5 have been observed for tankage related items. The 1997 version of the UniformBuilding Code (UBC) states that a maximum increase of 1.8 should be allowed, whichclearly underestimates the design lateral force.

If the appurtenances respond at a frequency greater than or equal to the Zero PeriodAcceleration (ZPA) then dynamic coupling should not occur and the approach will yieldsafer designs.

This however is not the case for roof mounted structures and pipework where thefundamental frequencies of structural systems are close to one another or are coincident.This is normally always the case since the roof; roof-mounted structures and pipeworkhave fundamental frequencies between 5 to 10 Hertz.

Natural Frequency In Hertz

Spec

tral

Vel

ocit

y

OBE and SSE Design Spectra

0.01 0.1 1 10 1000.0001

0.001

0.01

0.1

1

1 m

0.1 m

0.01 m

0.001

m

0.000

1 m

1E-5 m

1E-6 m

1 g

0.1 g

0.01 g

0.001 g

0.0001 g1E-5 g

OBE Design SpectraSSE Design Spectra

PS7-3.13

Prior to the commencement of the seismic analysis Whessoe conducted a detailedreview of international and national standards with respect to the seismic analysis of LNGtanks. A seismic philosophy was developed to ensure that the safety envelope waspreserved under the extreme events.

For this reason recourse was taken to ASCE 4-86 (Seismic Analysis for SafetyRelated Nuclear Structures), for guidance on the effect of coupling between the primaryand secondary structures.

At the highest level the Seismic Strategy focused on the accurate prediction ofsecondary floor spectra and raft displacements whereby enabling the design of thepipework using multi-point spectra techniques.

To facilitate this Whessoe developed a detailed finite element model of the outer tank(walls and roof), access tower, roof mounted structures, crane handling structures anddominant pipework.

Finite Element Model Statistics

The model comprises 3d shell and beam elements to model the behaviour of the tankand structures. Connections between the key structures, namely the main platform to roof;pump handling structure to main platform; access tower to tank and dominant pipeworkto main platform was provided by three dimensional joint elements. Figure 5 illustratesthe finite element model used for the determination of seismic effects.

Figure 5 – 3D Finite Element model of combined Tank/Structural System.

PS7-3.14

The Dabhol tanks are located on bedrock with a shear wave velocity (Vs) greater thanor equal to 1100ms-1. Soil structure interaction effects were therefore ignored and fixedbase models were considered valid for the dynamic analysis of the tank fluid system.

The model comprises 30,000 elements with approximately 180,000 degrees offreedom. Due to the size of the problem it was impracticable to use conventionalsubspace iteration techniques for the extraction of the modes. To overcome this problemrecently developed state of the art Lanczos block solvers were used, enabling all modesup to the zero period frequency, approximately 1300 modes, to be extracted in less than 5hours.

This was essential since it enabled the design team to alter the geometricconfiguration of the platforms and smooth undesirable spiking of the floor spectra. Thisfast tracking enabled sufficient confidence to be gained in a relatively small time frame toenable the procurement of critical items.

Pipework Analysis

The key driver behind the pipestress analysis was to ensure that the tanks couldwithstand an SSE event enabling the tank to be emptied for inspection purposes. Thetechniques adopted for the pipework are similar to those embodied within ASME III.Where floor spectra and raft displacements appropriate to each group of supports areapplied to a 3 dimensional finite element model of the pipework system.

The computer program PSA5, a commercial program developed in house by WILover the last 30years, with an established track record in the nuclear industry, was usedfor the pipe stress design.

The mass participation factors, eigenvalues and eigen displacements wereautomatically extracted from the 3d FE model. Bespoke programs were used to calculatethe Secondary Floor spectra for each relevant node for 3% damping.

Amplification of the spectra was observed of up to 5.7 times the input motion, this issignificantly more than the 1.8 predicted by UBC. Secondary spectra for the platformcolumn, and upper platform are included in Figure 6. For reference purposes the inputspectra is plotted.

PS7-3.15

Frequency In Hertz

Rela

tive

Vel

ocit

y

0.01 0.1 1 10 1000.001

0.01

0.1

1

10

10 m

1 m

0.1 m

0.01 m

0.001

m

0.000

1 m

1E-5 m

10 g

1 g

0.1 g

0.01 g

0.001 g

0.0001 g

Upper PlatformPlatform Column PositionsSSE Input Spectra

Figure 6 – Secondary Floor Spectra At Platform Column and Upper Platform Locations

At design review meetings concerns were raised regarding the effect of the 40-inchfill line on the dynamic behaviour of the support structures. Smaller bore was modelledby including the mass secondary systems into the FE model. However it was felt that thestiffness contribution of the 40-inch line could adversely effect the floor spectra either byfrequency shifting or spiking.

To investigate this phenomenon the 40-inch line was explicitly modelled using thinshells, which accurately represented the stiffness distribution at bend and bifurcationpositions.

Prior to inclusion into the model proper, sub models of the pipework were created andbench marked against the pipestress results, Figure 7 illustrates the finite element modelat the heatbreak position.

PS7-3.16

Figure 4 – Local View Of 40 inch Fill Line

Excellent correlation was found between the pipe stress and finite element modelparticularly with respect to fundamental frequencies, mode shapes and participatingmasses.

For certain support locations the effect of the inclusion of the pipe was to shift thedominant frequencies of the floor spectra. In numerous instances the significantamplification or spiking of the spectra was observed, which was not previously exhibited,In other areas attenuation or frequency shifting of the floor spectra occurred.

It became apparent that there was no reliable method for determining the resultingeffects of the inclusion of the line other than explicitly modelling the same. By adoptingthis approach we could ensure that the safety criteria of NFPA59A were met.

Roof Mounted Structure Design

A similar level of caution must be exercised when determining the seismic forces forthe platform structures, as any underestimate in response may lead to an unsafe design.

The 3d finite element model was prohibitively large to directly calculate the designmoments and forces for the supporting structures. To determine the seismic accelerationson the platform bespoke spreadsheets were written to calculate the modal coefficients andwhen combined with the eigenforces determine the spatial forces in each joint. Thedesign level acceleration for the each platform was determined by dividing the sum of thejoint forces (base shear) by the mass of the platform.

Due to the separation between the modes the Square Root Sum of Squares methodwas considered appropriate for the modal combination. In accordance with ASCE 4-86the 40% rule was used for the spatial combination.

PS7-3.17

The resulting accelerations were significantly larger than the design accelerationssuggested by UBC. Adoption of the 1.8 magnification factor in this instance is clearlyinappropriate and would lead to a potentially unsafe design.

CONCLUSION

The central influence of LNG tank design know-how, on Import Terminal projectdevelopment is very clearly demonstrated. It is no accident that the new generation ofImport Terminal EPC contractors have primarily evolved from the ranks of what werepreviously specialist LNG tank contractors. These companies have the inherent skill baseand track record in all aspects of cryogenic design, procurement and construction. Theyalso have a broader hands-on experience of delivering economic bespoke solutions forintermediate size projects.

The broadening profile of client background has also stimulated some change in theindustry perception. Newer clients entering the market are frequently from different sidesof the energy industry, such as power generators. They also come from a much morecommoditised background, with a high degree of proficiency in packaged projects andfinancing. These clients offer a major opportunity to the new generation Terminalcontractors, such as Whessoe, as they are prepared to enter into an early day relationshipand share some risk and reward in the front end development.

LNG terminal contractors are highly proficient specialists in a relatively niche market.When this is realised, the benefits of early co-operative studies should not beunderestimated. The final scheme at Dabhol with full containment LNG tanks operatingat a significantly higher pressure, proved to be both more economic and more buildablethan the scheme originally conceived. This all came about as a result of the earlycombination of the skill bases of the client, DPC/Enron and Whessoe as contractor.