ABS Procedure for Analyzing Fixed PlatformGeometric &

Structural Data

RIGGIN

RIGPLOT

Loading DataWave, Current,

Wind,Dead Loads

RIGLOAD

Resultant Forces and Moments

Soil Characteristics

BMCOL

Boundary Conditions

Data Library for Structural Analysis

Evaluation and Analysis of Results

Deflections, Rotations, Forces, Moments and

Stresses

Finite Element Analysis

Miscellaneous Loads and

additional Data

Fatigue Analysis

Fine mesh analysis of Local Structure

Dynamic Analysis

API RAP 2ASection 1

Planning

1.1General1.1.1Planning: Adequate planning should be done before actual design is started and the initial planning should include the determination of all criteria upon which the design of the platform will be based.1.1.2Design Criteria:Design criteria include all operational requirements and environmental data, which could affect the detailed design of the platform.1.1.3Codes and Standards: Codes and standards acceptable for engineering design and practices from the standpoint of public safety.

1.2Operational Data

1.2.1Function

1.2.2Location

1.2.3Orientation

1.2.4Water Depth

1.2.5Access & Auxiliary Systems

1.2.6Fire Protection

1.2.7Deck Elevation

1.2.8Wells

1.2.9Equipment & Material Layouts

1.2.10Personnel & Material Handling

1.2.11Spillage & Contamination

1.2.12Exposure

1.3Environmental Data

1.3.1General Meteorological & Oceanographical Considerations

1.3.2Winds

1.3.3Waves

1.3.4Tides

1.3.5Currents

1.3.6Ice

1.3.7Earthquakes

1.3.8Sea-floor Instability

1.3.9Scour

1.3.10Marine Fouling

1.3.11Other Environmental Information

1.4Site Investigation

1.4.1Foundations soil Properties

1.4.2Sea-Bottom Survey

1.4.3Soil Investigation & Testing

1.6 Fixed Platform TypeAfter considering all factors, the following fixed platform types are available.1.6.1Template, consisting of the jacket or welded tubular frame; Piles, which is permanently anchored to the sea-floor; and a superstructure providing the deck space and supporting operational and other loads.

1.8 RegulationsEach country has its own set of regulations concerning offshore operations. When designing, installing and operating offshore platforms in any coastal waters of any country, the appropriate rules and regulations must be adhered to.

1.7 Safety ConsiderationsGuidance may also be obtained from the latest edition of the Manual of Safe Practices in Offshore Operations published by the Offshore Operators Committee.

1.5 Selecting the Design Environmental ConditionsFactors to be considered include the following:• Probability of personnel to be quartered on the platform and the

sufficiency of the available transportation systems to remove personnel from the platform on short notice.

• Prevention of possible pollution.• Intended use of the platform.• Planned life of the platform.• Cost of the platform, giving consideration to both initial cost and

estimated losses if the design criteria are exceeded.

Selection of Structure Type General RequirementsFixed platforms come in many shapes and. Offshore structures must provide suitable space and characteristics compatible with operational requirements. Operational requirements consist of many factors.

1 Geographical Locations:Environmental conditions probably have the greatest impact upon the required strength and minimum space of a fixed platform. Wind, storms, and ice not only impose large lateral loads on a platform, but also complicate the logistical support of supplies and consumable materials used thereon, generally resulting in increased storage requirements and significantly increase payload.

Earthquakes also impose severe dynamic loading, and since the timing of their occurrence can not be accurately predicted, evacuation of personnel is impractical and safety considerations require critical attention.

Rough weather also affects and usually prolongs marine construction activities, underwater operations, inspection, and repairs.

2 Function:The influence of intended function on the basic configuration of a platform must not be unrecognized, for ultimately the only purpose of an offshore platform is to provide a dry work area and to hold equipment up out of the waves.

3 Water Depth:Water depth is the yardstick with which the challenge of an offshore venture is measured. No matter which environmental criterion (earthquake, ice, wave, or current) controls the design, its effect on a fixed offshore platform increases with water depth.

The depth of water also sets the height of the below-water structure, and the size, shape, and weight of this space frame will influence the selection of platform type and affect fabrication yard and derrick barge requirements.

4 Seabed Characteristics:Regardless of the creditability of the basis for the assumed seabed conditions, a detailed foundation investigation program should be carried out as early as possible to confirm basic assumptions, identify local stratigraphic anomalies, and quantify engineering parameters.

Pile capacity requirements, both lateral and axial, and the ability to install the piles are the most significant factors to be considered.

Soil characteristics near the seabed also affect the design. Platforms in weak soil may have intolerable lateral deflections that may be limited only by using more or larger piling than otherwise would be required to sustain the gravity loads and overturning moments. These platforms may also require very large mudmats at the bottom of the jacket to support the weight of jacket and the pile segments temporarily until pile installation is complete and the connections to the jacket are made.

Soil resistance to leg penetration may affect elevation control, especially if leg closures required for jacket buoyancy or floatation control are located at the bottom of the leg.

5 Well Slots:The number of wells to be accommodated on a platform affects the structural requirements in a number of ways. Wave forces on the wells may account for as much as 40% of total lateral load on a platform and depending on their location within the structure, may introduce a significant amount of torsion into the analysis.

As the platform deflects at the mudline, it pulls the wells along with it, introducing shear and moments into them.

6 Types of Development Rigs:A number of basic rig types have evolved over the years in support of offshore development drilling operations. Variations in characteristics, requirements, and details are common and the platform designer should obtain as much detailed information as is available on the specific rig to be used or on all the potential rigs being considered for use on the platform. Some rig types are named as follows:

Tender Rigs; Standard self-contained Rigs; Mini-self-contained Rigs; Completion/Workover Rigs; Cantilevered Jack-up Rigs.

7 Production Facilities:Space allocation and load distribution is an integral part of preliminary development of the structural configuration of a platform.

Economics dictate that, wherever possible, all or a large portion of the process equipment and systems should be installed on the deck section and hooked up in the fabrication yard.

Preinstalled systems should be confined to the lower deck(s) to avoid conflicts with the drilling rig. Equipment should be located toward the interior of the production area, leaving the more accessible perimeter of the lower deck open for future components or those which by necessity, must be field installed.

Pipe and wiring should be preinstalled under the decks to eliminate the significant problems of access to these areas in the field, and to keep as much space clear for equipment as possible.

In-service maintenance requirements for valves, clean-outs, junction boxes, etc., should not be overlooked.

8 General Styles:There are no formulae or fixed rules that determine the optimum style of platform that fulfill all of the requirements of the development plan.

Not recognizing the impact of a factor or its potential variation may impose a serious economic penalty on the owner of the platform or jeopardize the safety of the employees.

Traditional styles have evolved over the years of intense offshore development. Variations are numerous, recognizing specific circumstances and designer perception.

9 Constraints:There are many identified constraints that impose limitations on the design of platforms. Historically, platform builders have tried to anticipate future platform requirements. It has not been uncommon for a frontier platform project to be constrained by the limitations of existing yards and equipment. Other constraints are:Installation Constraints; Weight Constraints;Length Constraints;Size Constraints; and Fabrication Constraints.

10 Preliminary ProportioningGeneral:The configuration of an offshore platform may be determined and/or constrained by any or all of the factors discussed above. Recognizing which factors influence a particular project requires perception developed through experience on previous projects. A better alternative as used here may be defined as one that results in either:

)An overall increase in the utility or life of a structure for the same cost, or

)An overall reduction in its cost without an increase in risk or loss of function.

The following items in an offshore platform must be optimized during the proportioning process and appropriate number of iteration steps must be taken in order to produce the most satisfactory design.

Piling Jacket Leg Spacing &

Batter

Horizontal Framing Levels

Framing Styles

Tubular Braces