0003-MI20-00S1-0230-0

MODEC International, Inc. FPSO

Design of Offshore Structures Specification 0003-MI20-00S1-0230, Rev. 0

TABLE OF CONTENTS 1.0

EXECUTIVE SUMMARY...................................................................................... 5

2.0

BACKGROUND ................................................................................................... 5

3.0

BASIS .................................................................................................................. 5 3.1 3.2

4.0

REFERENCES ...................................................................................................... 5 DEFINITIONS AND ACRONYMS ......................................................................... 6

GENERAL ............................................................................................................ 8 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10

DESIGN PHILOSOPHY ........................................................................................ 8 COMPANY PROVIDED DOCUMENTS ................................................................ 8 CONTRACTOR SUBMITTED DOCUMENTS ....................................................... 9 DOCUMENTATION............................................................................................. 11 DESIGN CRITERIA ............................................................................................. 15 STRUCTURAL MODELS .................................................................................... 15 MEMBER SIZE SELECTION .............................................................................. 19 CONNECTION DESIGN...................................................................................... 20 ACCESS.............................................................................................................. 20 OTHER CONSIDERATIONS............................................................................... 21

5.0

MATERIALS....................................................................................................... 21

6.0

LOADS ............................................................................................................... 21 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9

7.0

ACCEPTANCE CRITERIA................................................................................. 27 7.1 7.2 7.3 7.4

8.0

DEFORMATION CRITERIA ................................................................................ 27 ALLOWABLE STRESS ....................................................................................... 27 LOCATIONS FOR UNITY CHECKS ................................................................... 28 REACTION FORCE ............................................................................................ 28

IN-PLACE ANALYSIS ....................................................................................... 28 8.1 8.2 8.3

9.0

GRAVITY LOAD .................................................................................................. 21 ENVIRONMENTAL LOAD................................................................................... 24 DYNAMIC LOAD ................................................................................................. 26 DEFORMATION LOAD ....................................................................................... 26 PIPING LOAD ..................................................................................................... 26 CRANE LOAD ..................................................................................................... 26 CONSTRUCTION LOAD..................................................................................... 26 ACCIDENTAL LOAD ........................................................................................... 27 LOAD COMBINATION ........................................................................................ 27

GENERAL ........................................................................................................... 28 LOAD COMBINATION ........................................................................................ 29 LOCAL ANALYSIS .............................................................................................. 29

DYNAMIC ANALYSIS........................................................................................ 29 9.1 9.2 9.3 9.4

MODAL AND VIBRATION ANALYSIS ................................................................ 29 SEISMIC ANALYSIS ........................................................................................... 30 VORTEX SHEDDING.......................................................................................... 30 WAVE SLAM ....................................................................................................... 30

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10.0

FATIGUE ANALYSIS......................................................................................... 31 10.1 10.2 10.3 10.4 10.5

11.0

TRANSPORTATION ON FLOATER ................................................................... 43 TRANSPORTATIN ON BARGE OR SHIP .......................................................... 43

ACCIDENTAL ANALYSIS ................................................................................. 45 14.1 14.2 14.3

15.0

GENERAL ........................................................................................................... 38 COMPUTER MODEL .......................................................................................... 38 API APPROACH ................................................................................................. 39 DETAIL APPROACH........................................................................................... 39 LIFTING ITEMS DESIGN .................................................................................... 40

TRANSPORTATION ANALYSIS AND SEAFASTENING DESIGN................... 42 13.1 13.2

14.0

GENERAL ........................................................................................................... 36 ANALYSIS ........................................................................................................... 36

LIFTING ANALYSIS .......................................................................................... 38 12.1 12.2 12.3 12.4 12.5

13.0

GENERAL ........................................................................................................... 31 DESIGN PARAMETERS ..................................................................................... 31 SIMPLIFIED METHOD ........................................................................................ 34 DETAILED FATIGUE METHOD.......................................................................... 34 VIBRATION FATIGUE......................................................................................... 35

LOADOUT ANALYSIS....................................................................................... 36 11.1 11.2

12.0


DROP OBJECT ................................................................................................... 46 FIRE .................................................................................................................... 52 BLAST ................................................................................................................. 53

APPURTENANCE DESIGN ............................................................................... 54 15.1 15.2 15.3 15.4 15.5

EQUIPMENT SUPPORT DESIGN ...................................................................... 54 WALKWAYS, LADDERS, AND STAIRWAYS ..................................................... 55 ACCESS PLATFORMS....................................................................................... 56 LIFTING AND HANDLING STRUCTURES DESIGN .......................................... 56 CRANE SUPPORT STRUCTURES .................................................................... 57

Figures Figure 4-1 – Typical Module Structure Stool Layout ................................................................... 18 Figure 14-1 – Typical Drop Object Analysis Flowchart ............................................................... 47

Tables Table 4-1 – Steel Member Categories ........................................................................................ 15 Table 4-2 – Max Allowable UC ................................................................................................... 19 Table 6-1 – Live Load Carry-down Factor .................................................................................. 23 Table 7-1 – Allowable Deflection ................................................................................................ 27 Table 7-2 – Allowable Stress Increase ....................................................................................... 28 Table 10-1 – Applicable S-N Curves........................................................................................... 33 Table 10-2 – Design Fatigue Factor ........................................................................................... 33 Table 11-1 – Friction Coefficients ............................................................................................... 37 Table 12-1 – Dynamic Lifting Factor-I......................................................................................... 39 0003-MI20-00S1-0230-0.doc

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Table 12-2 – Dynamic Lifting Factor-II........................................................................................ 40 Table 12-3 – Consequence Factor ............................................................................................. 40 Table 13-1 – Default Motion........................................................................................................ 44 Table 14-1 – Temperature Deduction Factor.............................................................................. 52

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1.0


EXECUTIVE SUMMARY This document defines the minimum technical requirements for the structural design of offshore structures. Offshore structures include the structural system of topsides modules, skid supported equipment, or packaged supported equipment required for a Floating production Storage and Offloading facility (FPSO). This specification covers steel structures of topsides production / utility modules, pipe rack modules, turret support structure (TSS) pipe rack(s), skid mounted equipment, packaged structures, and vent/flare boom. It excludes the “hull” structures including the hull, living quarters, helideck, crane pedestals, turret support structure (TSS), module support stools, vent/flare boom foundation, turret mooring system, and other structural items attached to the ship’s hull. Special arrangements for each project are covered in particular specifications which supplement or amend this general specification.

2.0

BACKGROUND Company facilities must meet minimum Industry standards to ensure that Quality, Health, Safety, Environmental, and Operations goals are attained. Standard specifications are used to communicate the minimum standards within the Company as well as to Suppliers and Contractors.

3.0

BASIS Industry codes, standards, and practices, as well as Company experience and preferences are the basis for this document. The following references apply only as specified in the body of this document. If the reference is not mentioned within, it is not applicable. Latest reference editions, including addendums, in force at contract award apply. Reference requirement conflicts shall be brought to Company attention for resolution. The most stringent requirement of the following references applies unless otherwise specified in writing by the Company.

3.1

REFERENCES

3.1.1

Company

Number / Identification

Title

0003-MI20-00P1-0450

Weight Control Procedure

0003-MI20-00S1-0240

Materials for Offshore Structures

0003-MI20-00S1-0270

Marine Loadout and Transportation Specification

3.1.2

Client


Title

None

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3.1.3


Industry Codes, Standards, Rules, and Regulations


Title

ABS MODU

Rules for Building and Classing Mobile Offshore Drilling Units (2008)

AISC-ASD

American Institute of Steel Construction, Specification for the Design, Fabrication and Erection of Structural Steel for Buildings, Allowable Stress Design

AISC 360-05

Specification for Structural Steel Buildings

API RP 2A WSD

Recommended Practice for Planning, Designing and Constructing of Fixed Offshore Platforms-Working Stress Design

API RP 2C

Recommended Practice for Offshore Pedestal Mounted Cranes

DNV-RP-C203

Fatigue Design of Offshore Steel Structures

SCI-P-122

Guidance Notes for the Design and Protection of Topsides Structures against Explosion and Fire

0030/NDI

Noble Denton “Guidelines for Marine Transportations”

3.2

DEFINITIONS AND ACRONYMS The following definitions shall apply within the body of this document:

Term

Definition

ABS

American Bureau of Shipping

AISC

American Institute of Steel Construction

ANSI

American National Standards Institute

API

American Petroleum Institute

ASCE

American Society of Civil Engineers

ASME

American Society of Mechanical Engineers

ASTM

American Society for Testing and Materials

AWS

American Welding Society

BS

British Standard

BSI

British Standards Institution

Client

Company Client and/or its assigns

COG

Center of Gravity

Company

MODEC International, Inc. and/or its assigns

Contractor

Any entity or its assigns selected by Company to perform engineering design or procurement or fabrication or construction or loadout, transport and installation operations.

CA

Classification Authority

DNV

Det Norske Veritas

Engineering Contractor

Contractor responsible for engineering design of hull, topsides structures / modules, equipment and ancillary items, etc.

Fabricator

Group responsible for the fabrication of the structures

Facility

Supplier or Subcontractor shop and/or any property owned by a Supplier or Subcontractor where any portion of the work will be performed.

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MODEC International, Inc. FPSO Term

Design of Offshore Structures Specification 0003-MI20-00S1-0230, Rev. 0 Definition

FPSO

Floating, Production, Storage, and Offloading System

HSE

Health, Safety, and Environment

Hull Steel

The steel required for hull, living quarters, helideck, crane pedestals, module support stools, flare/vent tower foundation and any other structural items attached to the ship’s hull excluding Topsides Structural Steel.

Installation / Lifting Contractor

Contractor responsible for installing topsides structures / modules, equipment and ancillary items, etc. onto the FPSO hull structure. This could either be quayside or offshore.

Integration Shipyard

Company responsible for integration of all Topsides Modules on the FPSO

Marine Warranty Surveyor

Organization responsible for issuing of Certificates of Approval for the lifting, loadout, sea fastening, transportation, etc. as required by the Company and Builder’s Risk Insurance Company

NDI

Noble Denton International Ltd

Offshore Structures

A steel structural system for a Topsides Module, equipment skid, “packaged” equipment, and any other structural system to support loads applied to the FPSO.

Package Structure

A Production / Utility Structure supporting equipment that has more than 1 level and excludes Topsides Production/Utility modules. The “Packaged Structure” is supported by the Topsides Production/Utility module and/or ship’s hull.

SACS

Structural Analysis Computer System (Engineering Dynamics Inc.)

SCF

Stress Concentration Factor

SCI

Steel Construction Institute

SEI

Structures Engineering Institute, Affiliated with ASCE

Services

Any service or work performed by a Supplier that must comply with the requisition requirements or the contract to procure, design, manufacture, and deliver the work.

Shipyard Integration Contractor

Contractor responsible for integrating the Topsides Modules / Structures into a complete FPSO system

Standards

Industry Codes, Standards, Guides, and Recommended Practices referenced herein, meaning the latest issue or edition in force at the end of the Supplier bid validity date or the contract date.

Supplier

At quote stage: any entity invited to provide a quotation for the equipment and/or any Subcontractors thereto. At Purchase stage: any entity contracted for the supply of the equipment and/or any Subcontractors thereto. In all cases, the Supplier is responsible for performance of all Work and shall be the single point of contact for all Work related issues. The Company shall not receive information from nor respond directly to Subsuppliers.

Transportation Contractor responsible for furnishing transport vessels such as tugs, barges, and ancillary equipment Contractor to transport structures, etc. TSS

Turret Support Structure

Turret Mooring This system is defined as the turret head, chain table, swivel access structure, swivel, mooring lines, System mooring suction piles, etc. required to: maintain vessel on station, allow weathervaning, allow fluid transfer to production facilities and transfer of electrical, hydraulic, and other control signals. Vessel

Barge, Tug, or similar floating system used to tow, transport, or support structures, etc.

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MODEC International, Inc. FPSO Term Work

Design of Offshore Structures Specification 0003-MI20-00S1-0230, Rev. 0 Definition

Any material, item, or service listed in the requisition or contract as being in the Supplier’s Scope of Supply

4.0

GENERAL

4.1

DESIGN PHILOSOPHY Analysis shall demonstrate that all components of the offshore structures have been adequately designed for all of the loads the offshore structures shall be exposed to for the “life” of the structure including, but not limited to, environmental, accidental loads, fire, blast, heel from hull damage, lifting, fatigue, vibration, fabrication, assembly, hydrostatic / pneumatic test, transportation (land, sea, or air), skidding, ship / barge / vessel motions, hull deformation, operational, etc. and that all stresses shall be within allowable limits. Global design of the structural system and design of individual components shall consider direction of loads and appropriate loadings for all phases of the facility life. Abrupt changes in strength and stiffness shall be avoided, i.e. small components shall not restrain the deformation of large components. Alternative load paths shall be provided for environmental and functional loads whenever possible. When components are not redundant, special considerations shall be given to the consequences of component failure. There shall be increased quality control of the design, material, fabrication, and life cycle maintenance and inspection of components without redundancy. In general, deck structures shall provide lateral resistance in two orthogonal directions by truss action. Complete reliance on portal frame resistance should be avoided as much as possible. With written Company approval, the portal frame structure may be used in module structure for the convenience of equipment arrangement, material handling, etc. Inspection and maintenance of structures shall be easily accomplished. components and at all phases of platform life shall be considered.

Access to all

Unless due to safety or function consideration, unnecessary or duplicated weights (skids with flooring underneath, modules with flooring underneath, etc.) shall be avoided. Safety always has the priority and shall be taken into consideration from the start of the design, including temporary phases such as loadout, transport, and installation. Particular attention shall be paid to accessibility, circulation routes, escape routes, muster areas, partitions, fire resistance, finish materials, etc. The Supplier shall provide a Structural Design Basis document to the Company for approval prior to the start of the Supplier’s detail engineering work.

4.2

COMPANY PROVIDED DOCUMENTS Structures shall be designed in accordance with the Company provided project specific documentation such as Scope of Work, Design Premise, Environmental Reports, and Geotechnical Reports.

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The Company shall be notified of any errors, omissions, or recommended changes to the Company supplied documentation.

4.3

CONTRACTOR SUBMITTED DOCUMENTS Required Contractor provided documentation is dependent on the phases of project.

4.3.1

FEED FEED stage structural design documents include: • A detailed description of the concepts, including the main characteristics and features •

A review of the procedure for supply, fabrication, and installation

•

A list of calculations that shall be performed in a later stage

•

An estimated weight broken down over the main components with proper contingency

•

A schedule with breakdown of the main items

•

Drawings detailing important components and issues

•

Other documentation as specified by the project contract

The above mentioned documentation is insufficient for material ordering; thus, no materials shall be ordered at this stage.

4.3.2

Detailed Engineering Detailed engineering defines the main structures in detail and depicts the principles of the secondary structures. The corresponding documents include: • A Structural Design Basis and criteria particular specification •

A Design Brief summarizing the design methods and criteria to be used for basic engineering The Design Brief shall be approved by the Company prior to commencement of any basic design.

•

Complete Calculation Reports for the main structure, including the main connections and stiffeners, lifting padeyes, and foundations for all the phases and conditions of the structure life (i.e. lifting, transport, fatigue, vibration, blast and fire, etc.)

•

The Secondary Structure and its connections, not necessarily defined in detail, but specified in principle

•

Main Structure Design Drawings describing in detail the main structure, including detailed geometry, weld symbols, detailed definition of material grades and qualities, and itemized material list with weight indication The drawing areas not justified by calculations shall be clearly highlighted with the indication of the reason for the reserve.

•

Main Structure Connections Design Drawings, including detailed geometry, weld symbols, material grades, and itemized material list with weight indication

•

Principle Drawings for the Secondary Structure and their Connections

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•

Standard Structural Drawings

•

A Structural Weight Report covering Main and Secondary Structures

•

Main Structural Material Take-off itemized lists per drawing with recapture list per module/unit. This document shall enable steel ordering for the main structure.

4.3.3

•

Loading Diagrams for each Module, if required

•

Particular Technical Specifications, if required

Fabrication Engineering Fabrication Engineering is the shop drawing stage; the corresponding documents include: • Technical Specifications •

Structural Design Premises and Brief summarizing the structural design methods, criteria, and principles intended to be used throughout the detail design

•

The Contractor shall seek Company approval on this document prior to starting any detailed engineering.

•

A complete Calculation Report for the structure in its entirety, including each component and detail for all the phases and condition of the structure life (i.e. lifting, transport, fatigue, vibration, blast and fire, etc.), covering at minimum: -

The Main and Secondary Structural Members

-

The Main and Secondary Connections

-

Lifting Padeyes, Guides

-

Structural Details such as Stiffeners, Gussets, Penetrations, Equipment Supports

-

All Calculations related to the Foundations

-

All Calculations related to Loadout, Transport, Installation

-

All Calculations related to temporary phases such as panel Roll-up, Subassembly Lifting, Temporary Support Design, etc.

•

Main Structure Fabrication Drawings describing in detail the main structure, including detailed geometry, stiffeners, gussets, weld symbols, detailed definition of material grades and qualities, itemized material list with weight indication

•

Main Structure Connections Fabrication Drawings, including detailed geometry, stiffeners, gussets, weld symbols, detailed definition of material grades, itemized material list with weight indication

•

Detailed Fabrication Drawings for the Secondary Structure and Connections, including detailed geometry, stiffeners, gussets, weld symbols, detailed definition of material grades, itemized material list with weight indication

•

Standard Structural Drawings developed into Shop Drawing stage

•

Structural Material Take-off itemized lists per drawing, with recapture list per module/unit.

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This document shall enable steel ordering. •

Loadout, Sea Transportation, and Installation Drawings, Diagrams, Specifications, and Procedure.

•

Particular Specifications (i.e. shock absorbers for modules exposed to vibration)

•

A general Manufacture, Transport, and Installation Program

•

Shop Drawings

•

As Built Drawings

4.4

DOCUMENTATION

4.4.1

Design Brief The Contractor shall submit a structural Design Brief (Basis) for the Company’s review and approval prior to beginning analysis and design. The Design Brief should outline a specific plan for design and analysis. It shall provide the Company with an opportunity for early input and help serve as design documentation. The Design Brief shall be a means of summarizing agreement and clarification not covered in the specification, scope of work, data sheet, etc. and shall highlight any approved exceptions to the specifications. It should not repeat specification requirements, except where emphasis is thought to be important to the Contractor. The following items shall be included: • Intended Analysis Software

4.4.2

•

Approved Exceptions to Company specification, codes, and references

•

Description of Modeling Methodologies, Modeling Assumptions for various structural components and working conditions, Details for including or excluding Secondary Structures, etc.

•

Load Condition and Load Combination shall be adopted using the following analysis: -

In-place under operating and extreme conditions

-

Transportation

-

Lifting / Loadout

-

Fatigue

-

Miscellaneous loading such as accidental load, VIV, vibration, etc.

Reports The structural design documents shall include the following items: • Summary of the basis of the calculation and a list of the reference documents •

Summary of calculation philosophy and methodology

•

Summary of the conclusions of the calculation/analysis performed including any recommendation

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•

At the end, the results in the form of drawings or sketches with check on determinant conditions

•

Copy of the structural drawings showing the modeled structure

•

Copy of the platform plot plan drawings showing the modeled platform equipment location, identification, and weight

•

Copy of any document other than contractual reference documents used as a reference

•

Any hand calculation performed during the structural analysis at data input stage or as complementary verification or code check

•

The input electronic file of the computer model used for the analysis, including all output and code checks commands.

The above documents may be grouped in several appendices; however, the Company requires electronic formats in conjunction with the hard copies, i.e. in the form of a CD, uploaded to ProjecTools, etc. The calculation basis and methodology shall include the following items: • The environmental conditions: waves, currents, wind, snow, ice, temperatures, etc. •

Dead load and live load values used: level-by-level and load case-by-load case shall be in the form of drawings or data sheets.

•

Dimensions used for wind loads

•

Any element that needs special justification in the design report such as installed skidding of a heavy element on a floor, temporary bracings required during lifting, etc.

•

The theory, method, assumptions, and simplification adopted in the calculation presented clearly

The result of the calculation shall consist of: • Deflection of Structure, usually the max deflection on each controlling location •

The figured out deflection shall be checked against allowable deflection in terms of not only structural but also other disciplines such as piping.

•

Reaction/Supporting Force

•

The Unit Check in terms of strength and fatigue, where applicable

•

Other Output that is necessary to assess the calculation, such as the virtual spring force and sling load in lifting analysis

•

Any Modification on the Structural Member found necessary by the calculation shall be highlighted on the attached drawing.

The calculation report shall include, but not be limited to: • In-place (operating and extreme) •

Transportation

•

Lifting

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4.4.3


•

Modal analysis

•

Fatigue

•

Vibration (for rotating equipments support)

•

Loadout (if any)

•

Dropped object (if any)

•

Blast and Fire (if any)

•

Fatigue under transport conditions (if any)

•

Other studies depending of the structure type

Computer Models Complete and detailed computer outputs shall be submitted with the analysis report for any type of structural calculation or analysis performed on a computer. The electronic copy of computer structural models, including relevant calculation notes or analysis, shall be submitted to the Company together with the corresponding calculation report. Geometry and Load Data Sketches or Data Sheets done by computer reproducing in complete detail the modeled structure's geometry and topology, including the joint and member numbering, location and type of support points, member properties, member buckling parameters (effective length and buckling coefficient) Sketches shall precisely correspond to the modeled structure. Loading sketches or drawings showing the loads applied to the joints and the members shall correspond point by point with the computer input as well as the effective load magnitude and position on the platform. Computer Input/Output Presentation The inputs shall be explained by comments enabling the reader to find the instruction with ease and correlate any modeled item with the effective item pertaining to the platform. In particular, loading cases modeling equipment weights or loads shall be fully traceable and shall indicate equipment tag numbers on a case-by-case basis per the Project Equipment List and Platform Plot Plans. The load case combinations shall be given in the form of a table showing the different options and the coefficients used. Analysis results, including member forces, reactions, summary of loading cases, and loading combinations, shall be listed for each loading case. Joint displacements shall be printed for combined cases. The member code checking results shall be given in summary for each member group and shall include effective stresses, allowable stresses, summarized checking parameters, member geometrical characteristics, and critical load case identification.

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Summarized code checking results shall also be given in decreasing order for utilization factors exceeding a certain threshold value (approximately 0.75) in the form of plot on showing geometry, member number, and related ratio. Note checks shall be performed either automatically by computer (tubular joint) or manually by manual check (nontubular). The manual check may be performed on selective nodes considered to be most representative (i.e. with max forces of the same joint configuration and size). Code checking outputs shall also indicate the reference of the code formula for each printed utilization factor such as AISC, API RP 2A, or other Company approved standard.

4.4.4

Drawings The following items shall be provided for drawings during the detail engineering or fabrication stage: • Drawing List, including structural weight for each drawing on the list

4.4.5

•

This drawing list shall be updated at each new drawing revision issue. Structural General Arrangement Drawing (3D perspective)

•

General Note Drawing

•

Drawings representing all Plans and Elevations of the structures

•

Typical Connection and Welding Detail Drawings

Material Take-Off (MTO) The MTO responsible party shall be explicitly specified. The MTO shall be constructed drawing-by-drawing and element-by-element. Summaries shall be made for each subassembly and per element category (girders, flooring, columns, handrails, etc.). Lengths and areas taken into account shall be calculated from the drawings. The weight for bolts and welding beads may be taken grossly depending on the structure concerned. MTO summarization shall enable lift weight calculation.

4.4.6

Unit Unless the Company otherwise specifies, all calculations must be made with SI units throughout documents, reports, and drawings. Values not cited in SI units shall be converted into SI values prior to issuing to the Company. Upon receipt of Company approval, the use of inches shall be allowed for tubular sizes with the equivalent SI value attached as reference.

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4.5

DESIGN CRITERIA

4.5.1

Structural Member Category


Steel structural members are grouped as different categories according to the importance and consequence of the failure. Table 4-1 – Steel Member Categories Member Type

Required Usage

Example

1

Failure of any of these members would cause total or Padeyes and members connected to it, partial destruction of the module during its production or Main girders, Column, Critical node, installation, or they are members that cannot be repaired. Members that are critical during installation

2

Failure of any of these members would cause total or partial module shutdown, but no total or partial destruction of the module. Repair of these members requires stopping the production or installation.

Ordinary beam that is noncritical to overall structure, Bracing of truss, Gusset welded to first category member

3

Structural members other than those classified in first or second category.

Plating, Joisting, Stringer,

4

4.5.2

Stiffening elements

Nonstructural member of accessory or finishing elements, Handrails, Stairs, Ladders, Grating, False i.e. not participating in the overall strength of the platform Flooring, etc. structures

Corrosion Unless otherwise specified, no corrosion allowance shall be applied to structures.

4.5.3

Design Code Structural design shall be based on the Working Stress Design (WSD) method. Unless otherwise specified, with written approval from the Company, the Loading and Resistance Factor Design (LRFD) shall not be used. The API RP 2A WSD and AISC ASD shall be the followed primary design codes.

4.6

STRUCTURAL MODELS

4.6.1

General Structures shall be analyzed using proven and verified three-dimensional computer space frame analysis software, such as SACS®, STAAD. Pro®, or a Company approved equal. Computer models shall accurately represent the geometry, loads (magnitude, location, sequence, etc.), masses, stiffness, dynamic and/or hydrodynamic behavior and characteristics, and boundary conditions of the structure to be analyzed with regard to the kind of analysis to be executed. Any simplification, equivalence, submodel, or dummy member load cases resulting from subassemblies designed by others shall be documented in detail and shown to be acceptable for the type of analysis to be performed with regard to loads, mass, stiffness, displacements, boundary conditions, etc.

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An integrated model of the components making up the addressed structure shall be used for in-place analyses. Preservice analyses models shall include any preinstalled sections of the foundation and/or appurtenances. Corrosion allowance shall be used only for strength contribution in the installation analysis, but shall be unacceptable for the in-place analysis. However, the weight of the corrosion allowance should be considered in the most stringent way.

4.6.2

Members Computer models shall include all primary structural members and secondary structural members contributing to the overall stability and stiffness of the model. The stringer beams or equipment support beams shall be modeled when the significant loading that is greater than 5 MT is expected or the actual load path is expected to have an impact on the primary structure. If not explicitly modeled, plate stiffness could be simulated by dummy X bracing. Procedures for sizing simulated members shall be submitted to the Company for approval. Unless required for specific analysis, secondary members such as pump casing supports shall not be modeled as structural elements. Flare Tower or other structures exposed to elevated temperatures shall be designed in accordance with the methods, procedures, and data stated in API RP 2A and ANSI/AISC 360-05. The properties of steel at elevated temperatures in these documents shall apply when applicable.

4.6.3

Joints Tubular joint cans and brace stubs shall be considered primary members and be included in the global model. Primary brace centerline offsets at joints shall be modeled if the offset is greater than 1/4 of the chord diameter. The eccentric load on the joint shall be addressed appropriately by the member offset of manual added load.

4.6.4

Foundation and / or Supports Modules designed to be installed onto the deck of a floater subject to flexure due to global bending shall be analyzed for the effects of the foundation flexibility and stiffness for all load conditions the floater shall encounter. It shall be the Contractor’s responsibility to interface with the floating vessel Designers to define and obtain the engineering information required to assure the Topsides Modules / Structures are properly designed and the connection design meets the requirements of the floating vessel Designer’s requirements. This shall include providing the floating vessel Designer with the Topsides Module / Structure support reactions, deflections, center of gravity, etc. for the various load conditions. This process of result comparison and structural analysis shall be completed when the results are compatible and the data used by each produces an economical solution for floater hull and topsides structures.

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Support behavior of the foundation system shall be investigated under extreme environmental, operational, transit, and damaged condition. Stiffness Structural foundation support for modal and dynamic analyses may be modeled as springs or stiffness matrices with 6 degrees of freedom (super elements). Foundation linear stiffness values, if used, shall be calculated using loads that are most representative of the design conditions being considered. Locations Module Structure support stools shall be provided at each transverse frame of the FPSO. Module Structure shall be supported by a minimum of two rows of supports both in the longitudinal and transverse direction. By providing a large number of support stools, the transfer of load from the module Structure to the FPSO hull shall be sufficiently spread over the entirety of the hull. This is essential for existing tankers converted to FPSOs not originally designed to support heavy loads on the main deck. This also minimizes the amount of under hull deck steel that may be required to stiffen the FPSO ship frames at stool locations. Interfaces Support stools also cater to the inherent flexibility of the hull structure as well as the bending that occurs due to the sea state conditions and cargo loading. The connection between the support stools and the module structure shall be designed such that the impact of the hull flexibility on the stiff module structure shall be minimized. Connections vary depending upon the location. 1) Fixed The stools on the aft end of each module structure shall be fully fixed in all three translational directions. The module structure translations shall be restrained both in the vertical and horizontal directions at these stool positions. The design of these stools includes consideration of compression and tension in the vertical direction and horizontal loads, both in the transverse and longitudinal directions. 2) Sliding The nonanchor stools shall allow sliding between the hull structure and the topsides module framing to isolate the module structure for hull deflections. Center stools shall provide compression support and restraint against transverse movement. The modules shall be free to slide in the longitudinal direction to accommodate the hogging and sagging flexibility of the hull. The inboard and outboard row of stools shall provide compression support only with no fixities in either transverse or longitudinal directions. For cases of uplift, uplift restrains shall be applied on the support as precaution. It shall be properly designed to achieve the uplift restrain without extra restrain on horizontal direction. Any reaction force, no matter if it comes from fixed welding, uplift restrain, or friction shall be addressed explicitly in both the stool and topsides structure designs. The design of these sliding stools includes compression and tension (if uplift restrains is applied) in the vertical direction and horizontal loads, both in the transverse and longitudinal directions as either restrain force (for these with transverse restrain) or the

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friction force (for those with sliding design). The friction coefficient shall be set as 0.25~0.35 for steel-steel contact. See Figure below for a sample layout of the stool.

Figure 4-1 – Typical Module Structure Stool Layout 3)

Piperack and other full fixed modules The pipe rack structure shall be more flexible due to the need to coexist with existing FPSO piping down the center of the ship. The support “stools” for the pipe rack shall be welded to the bottom of the pipe rack columns; “fixity” shall depend on the stiffness of the “stools,” the hull structural system supporting the stools, and the details of the pipe rack column / stool connection. The open frame structure of the pipe rack shall be designed accordingly to handle the induced forces from the deformation of hull. Special stools shall accommodate module structures sensitive to vibration, such as support to the large reciprocating compressors. Each compressor shall be isolated from the adjacent compressor with its own supporting structure, and an additional set of stool locations shall be provided to further dampen the compressor vibrations. The full “fixed” boundary condition may be required for such stool design.

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4.7


MEMBER SIZE SELECTION Structural member sizes shall be selected on the basis of strength, stability, economy, availability, and constructability considering fabrication location. Where possible, the number of different sizes of members (tubulars, rolled shapes, and other structural steel shapes) and plate thicknesses shall be kept to a minimum. It is Contractor’s responsibility on the optimization of design to reduce the structural weight to a reasonable level without compromising strength, availability, constructability etc.

4.7.1

Minimum Thickness The minimum thickness shall be 8 mm (0.314 inches) for the first and second member type, 5 mm (0.196 inches) for other structural member (Type 3).

4.7.2

Maximum Slenderness The maximum slenderness ratio for ordinary members shall be limited to 120. For sensitive nonredundant members located in particular vibration active areas, the maximum slenderness ratio shall be 90.

4.7.3

Member Section Tubular members shall be selected from API (or ASTM) standards. If additional sizes of tubular members are required, the Company shall be notified to determine acceptability. Rolled sections (wide flange, angles, t-sections, etc.) shall be selected from AISC standards. Prior Company approval shall be required for the use of tubular members larger than 20 inches diameter with D/t ratios between 20 and 30. Unless otherwise approved by Company, the maximum D/t ratio for tubular members shall be 60. D/t ratios less than 20 shall not be used. Major rolled shapes shall be compact sections as defined by AISC. Sections with thickness greater than 50 mm (2.0 inches) shall be used only with prior written Company approval.

4.7.4

Max Allowable Interactive Ratio The following table defines the max allowable interactive ratio (UC) for different members under different design stage. Table 4-2 – Max Allowable UC Member Type

Conceptual & FEED

Detailed

1

0.80

0.95

2

0.90

1.00

3

1.00

1.00

4

N/A

N/A

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4.8

CONNECTION DESIGN

4.8.1

Welded Connection


The weld connection shall be designed for a direct and simple load transfer from one structural member to another, avoiding stress concentration and induced bending stresses as much as possible. Their fabrication shall be as simple as possible; constructability and welding access shall be particularly verified during design. All structural connections shall be justified by calculations. The minimum fillet weld leg size shall be 5 mm (0.196 inches). Wherever possible, tubular joints shall be designed and detailed as simple joints with no overlap. The theoretical gap (g) between braces shall be 75 mm (2.952 inches) minimum in order to account for fabrication tolerances and achieve a final 50 mm (1.968 inch) gap between weld toes. Use of ring stiffeners to resist the forces in connecting members shall require Company approval. If approximate closed ring solutions are used to design ring stiffeners, stiffener stresses shall include curved beam effects. All joints shall be designed to develop the strength required by the design load, but not less than 50% of the effective strength of the attached member as defined by API RP- 2A WSD. The joints designed for fatigue resistance shall follow instructions.

4.8.2

Bolt Connection Unless otherwise approved by the Company, bolt connection cannot be used for connections pertaining to type 1 and 2 structural member. Mechanical / locking devices of nuts shall be provided for bolted connections between structural members affected by vibrating equipment. In case bolted connections have to be implemented, they shall be designed according to AISC WSD. Bolting shall be zinc plated or galvanized and then painted or other effective protection.

4.9

ACCESS Skids / packages / modules shall be provided with means of passage sufficient for personnel to have at least 2 means of escape per level from the area and to be able to travel to a designated escape route in the event one were to be blocked due to a fire or other emergency. Access to operating equipment and valves shall be provided by means of stairs, walkways, and ladders with adequate handrails. Access to vessels, rotating equipment, valves, instruments and controls shall be sufficient for operation and maintenance. Sufficient access shall be provided by means of stairs, ladders, walkways or platforms with adequate handrails to safety devices to permit testing in-place.

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Instruments, valve control platforms, etc., shall not extend outside the skid / package / module or into designated access areas.

4.10

OTHER CONSIDERATIONS The following considerations shall be included in design of topsides structures • Corrosion protection system such as paint, coatings

5.0

•

Fire protection system (active and passive)

•

Access route, floors, and gratings

•

Supports for equipment including safety-critical communications, electrical, and firewater systems, etc.

•

Feasibility of welding and painting

•

Penetrations for piping, cabling, etc.

•

Difficult to inspect areas

•

Sequence of construction and any temporary erection

MATERIALS Materials for design shall conform to the Company’s Materials for Offshore Structures.1 Steels of higher strength than those defined in the Materials for Offshore Structures Specification shall be used in design only with Company written approval. The use of fiberglass grating requires written Company approval. Nominal yield strengths shall be used in design; mill certificate yield strengths shall not be used. Steel with “through thickness” properties shall be used where the structural member undertake through thickness load.

6.0

LOADS Loads that shall be addressed in the structural analysis are listed below.

6.1

GRAVITY LOAD Gravity loads shall include the load of all structures, equipment, bulks, appurtenances, variable supplies, vessel contents, entrapped water, grout, temporaries, etc. The contingency to apply at various stages of engineering design shall be as stated in the Company’s Weight Control Procedure document.2

1

Refer to Section 3.1.1

2


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Gravity loads included in the calculation model must correspond item-for-item to the target weight of the weight report. A weight and COG summary shall be provided. A topsides weight control report shall be maintained throughout the engineering / design phase. Any changes shall be incorporated in the weight control report.

6.1.1

Dead Load Dead loads are the weights of the structure, appurtenances, and any permanent equipment that does not change with the mode of operation. Steel include: Dead Loads structure, permanent equipment weight, permanent piping weight, electrical weight, etc. Structural dead load shall be increased by five percent (5%) in all analyses to account for mill and fabrication tolerances. Items not coded directly into the deck computer model shall have their weight input as a load based on the value taken from the weight control report. Examples of these types of loads are listed below: • Stairs •

Walkways

•

Access Platforms

•

Monorails (Heavy lift monorails, > 5 MT SWL, shall be taken into the model)

•

Handrails, etc.

During the early design stage, when the exact equipment load information is unavailable, a blanket dead load could be applied on the structure to represent the equipment weight. This dead blanket load is different from the live blanket load mentioned below. Appropriate contingency factor corresponding to the specific stage of design shall be used in analysis.

6.1.2

Live Load Live loads are the gravity loads that may change during the operation of the platform or from one mode of operation to another mode of operation. Live loads include, but shall not be limited to: weight of equipment that may be added or removed, weight of consumable supplies, weight of production/utilities equipment and piping contents, blanket live loads, forces exerted on the structure during operations such as material handling, vessel and helicopter landing, crane operation, etc.

6.1.2.1

Content Live load All the content should be applied as live load per the specific density and volumes. In the absence of accurate information concerning loads under normal operating conditions, the following loading shall be applied: • Vessels intended for liquids shall be full of the liquid they are intended to hold. •

Separators shall be half-filled with water.

•

Vessels for gas shall be 10% filled with water.

•

Gas lines plus weight of contained pressured gas

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MODEC International, Inc. FPSO • 6.1.2.2


Liquid lines shall be full of the liquid they are intended to hold.

Blanket Live load These loads shall apply to open areas of floors. Flooring (plating or grating with local stiffeners) of open areas on the modules shall be designed based on ABS MODU 3-1-2/1.11 for the following: • 4510 N/m² for walkways, general traffic areas •

9020 N/m² for work areas

•

13000 N/m² for storage areas

•

Skids supporting equipment shall be designed to provide a uniform deck loading of at lease 6000 N/m² (live load), but less than 14,400 N/m² (total load) based on wet or operating weight.

Dependant upon the element, carry-down factors for Topsides Production/Utility modules shall be used as tabulated below: Table 6-1 – Live Load Carry-down Factor Elements

Carry-down Factor

Plating & it supporting stringer (local analysis)

1.00

Primary module structure (global analysis)

0.50

Module support (global analysis)

0.25

For designated lay down areas and lay down modules, a design load of 20000 N/m² shall be used over the entire area to account for the variability of items brought on board the vessel. No carry down factor shall be applied on lay down module design. No blanket live load shall be applied on the area occupied by permanent equipment, skid, building, etc.

6.1.3

Load Locations The gravity loads of all steel, equipment, and variable loads shall be generated based on accurate representation of the locations, especially the actual COG and the load transfer paths. The COG shall impose significant influence on the inertial loads and dynamic properties of structures, despite the impact on static load which may not be so important. The mass of major equipment packages weighing more than 5 MT or that have a large vertical dimension relative to their width or length, living quarters, and other items which shall have significant local or global impacts on the structural design should be modeled as lumped masses with the proper vertical location to represent the actual COG. This could be implemented by either space load or via dummy load transfer member. When dummy members shall be used as a pyramid with lumped mass, special care should be exercised to ensure that no significant additional stiffness shall be added to the structure. Moment at each member ends should be released.

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6.2


ENVIRONMENTAL LOAD The environmental loads encompass all loads induced by actions of atmospheric and marine elements on the whole or part of the platform. These are essentially produced by: • Wind •

Waves

•

Currents

•

Ice

•

Snow

•

Temperature changes.

For topsides structures, the wave and current have no directly force acting on them, but play roles via motion of floater. The environmental loads shall be calculated based on the metocean conditions and criteria included in the particular project specification. Unless otherwise specified in the Project documentation or in local/national applicable regulation, environmental loads shall be calculated according to the requirements of API RP 2A. If available, the joint probability environmental conditions (of wind, wave, and current) shall be used following the criteria shown below: • Max wave within return period + associated current and wind •

Max current within return period + associated wave and wind

•

Max wind within return period + associated current and wave

If the above data is unavailable, upon receipt of written Company approval, the max wind, wave, and current could be combined together thus yielding a relative conservative result. Operating environmental conditions should represent a moderately severe condition at the platform location. Typically, a 1-year return period shall be used for operating environment, unless otherwise specified by National / Local regulations or the Company. Extreme environmental conditions shall be generated by the 100-year return period, unless otherwise specified by National / Local regulations or the Company.

6.2.1

Directions The environmental load shall be considered in 8 directions varying from 0˚ to 335˚. The wave, current, and wind loads shall be applied in the same direction. The most stringent directional combination of wind and acceleration shall be applied for ship motion.

6.2.2

Wave & Current The contribution of wave and current load shall be reflected by the motion of the floater for the topsides structure; therefore, the selection of wave and current shall be implemented via the selection of floater motion under designated wave and current conditions.

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6.2.3


Wind Wind load shall affect the motion of the floater as well as apply force directly on the topsides structures. Designs shall include wind loads on exposed areas of the modules. If appropriate, the effects of shielding may be considered. The wind load under quartering sea conditions shall be treated carefully. Wind loads in a diagonal direction shall be based on the projected area of the object perpendicular to the wind direction rather than a linearly combination of wind loads in the orthogonal directions. Without a verification based on model test or itemized calculations, the shape coefficient of 1.0 shall be used corresponding to the overall projected wind area of topsides module. Three second gust shall be considered in the design of individual members. Five second gust shall be used for the design of modules at in-place conditions. One minute wind shall be used in vortex shedding calculations and sea transportation conditions.

6.2.4

Motion Induced Load The load caused by the motion of the floater (heave, roll, pitch, etc.) contains two categories. One is the gravity component (g component), due to tilting of the floater; the other one is the load caused by the acceleration of the floater in both angular and tangent direction (inertial force). The analysis shall include both of them. The floater motion loads could be applied on the structures either by: a) Specifying the motion characteristics (motion center, location of module on floater/barge, pitch, roll, heave amplitude, periods, etc.) in special analysis software like “tow module” in SACS. The software shall automatically figure out the equivalent force in X, Y, and Z directions; then perform the structural strength analysis based on the derived motion induced forces. b) Figuring out the effective accelerations in each direction and converting the gravity load into equivalent force in corresponding directions by timing the derived acceleration with the gravity load thus applying these forces on the structure accordingly for analysis. All the gravity loads shall have their corresponding contribution in motion induced loads. Case A shall be achieved by specifying the mass converted from gravity load cases; for case B, the designer should apply those acceleration loads in X, Y, and Z directions manually. The motion induced load shall be combined together in load combination with phasing in consideration. Usually, the following combination should be taken. • Transverse force ± Heave (beam sea) •

Longitudinal force

•

α Transverse force

± ±

Heave (head sea)

β Longitudinal force ± Heave (quartering sea)

α and β coefficients reflect the phasing. Without detailed verification, it could be set corresponding to the attack angle of environment.

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6.3


DYNAMIC LOAD Dynamic loads are loads due to the response to an excitation of a cyclic nature, due to an impact, or due to the sudden application of a load (impulse type). Dynamic loads may be induced by waves, wind, current, crane (or lifting equipment operation), boat or helicopter landing, rotating equipment, blast, etc. The VIV loads acting on the slender member may also be a kind of dynamic load.

6.4

DEFORMATION LOAD Topsides are supported on a deformable hull structure (floater flexibility). Global deflection (hogging and sagging, deck transverse deflection, etc.) occurs due to the various tank loading conditions as well as wave loading. The way to consider these loads depends on the actual topsides structural support concept. The application of deformation load shall comply with the supporting conditions of the module. The approach to handle these deflections needs to be justified.

6.5

PIPING LOAD There are two resources contributing to piping loads: • Load acting on the support of piping anchoring points due to the fluid flowing inside the piping •

6.6

Load due to the thermal expansion of piping, which is also applied on the anchoring points of piping

CRANE LOAD Crane load is the load induced from the crane operation in terms of force + moment. The force and moment shall be applied in the same directions of environmental force to create the most onerous case. Two load conditions usually need to be considered: • The maximum vertical reaction combined with the associated overturning moment •

the maximum moment applied with the associated vertical reaction

In addition to the dead and operating weight, the loads shall account for the effects of platform accelerations and wind load associated with the operating environmental condition. The crane loads shall be applied in a minimum of eight directions to ensure the maximum load on the structure shall be identified.

6.7

CONSTRUCTION LOAD Construction loads are the loads resulting from fabrication, loadout, transport, and installation of a structure. All load conditions anticipated during construction of the structure shall be considered. Included are loads associated with fabrication tolerances and/or misalignment, differential support settlement, temporary support conditions, and component lifts and rollups.

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6.8


ACCIDENTAL LOAD The accidental loads such as fire, blast, impact, and drop object shall be dealt with properly in the designated analysis.

6.9

LOAD COMBINATION The basic load case defined above shall be combined to develop the appropriate load combinations, i.e. to produce the most severe effects on the structure under to different conditions that include both pre-service and in-service status. Temporary load conditions occurring during fabrication, loadout, transport, and installation shall consider combinations of dead loads, maximum temporary loads, and appropriate environmental loads (including motion induced loads if any). Load combinations proposed for structural analysis shall be submitted in table format to the Company for approval in the Design Brief prior to formal commencement of design.

7.0

ACCEPTANCE CRITERIA The acceptance criteria for the topsides structural designs are listed in subsections below.

7.1

DEFORMATION CRITERIA Primarily, deflections of primary beams and plate girders shall be limited to criteria based on equipment operating requirements specified by the equipment Suppliers. The horizontal deflections shall be limited to 1/300 of the topsides height under extreme environmental conditions. For vertical deflection, the following criteria shall be satisfied. Table 7-1 – Allowable Deflection Conditions

dmax

Cantilever beams

L/120

Supported beams

L/240

Static equipment supports

L/500

Rotating equipment supports

L/1000

Deck plate (thickness = t)

t (between stringers)

Wall flat plate (thickness = t)

t (between stiffeners)

7.2

ALLOWABLE STRESS Structural member and joint stresses shall not exceed the API RP 2A WAS and AISC ASD requirements. For each load condition, the allowable stress may include an appropriate increase over AISC ASD allowable. The table below lists the allowable stress increase factor for different load conditions.

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Table 7-2 – Allowable Stress Increase Load

Member Check

Joint Check

Conditions In-place operating

1.0

1.0

In-place extreme

11

11

Accidental load

12

Transportation

11

3

11

Lift

1.0

1.0

Loadout

1.0

1.0

7.3

3

3

12

6 3

6

LOCATIONS FOR UNITY CHECKS At minimum, internal member forces, stresses, and interaction ratios should be determined at both ends as well as at the midpoint of all members. Additional locations should also be considered for members that terminate at a highly stiffened joint, members that change cross sections along their length, or when the loading characteristics indicate that other locations may be more critical.

7.4

REACTION FORCE The reaction force of the topsides modules shall meet the requirement on the stool capacity given by the Marine Design Group.

8.0

IN-PLACE ANALYSIS

8.1

GENERAL A static three-dimensional computer analysis shall be performed for the topsides modules considering combinations of design loads, as defined in Section 6.0, including but not limited to the following: • Dead loads •

Live loads, including multiple positions of moveable equipments

•

Wind loads

•

Inertial loads

•

Deformation loads

•

Equipment induced load, such as unbalanced force of rotating machine

•

Piping load if any

•

Crane loads if any

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8.2


LOAD COMBINATION Operating in-place conditions are those conditions that are not severe enough to restrict normal operation. Storm in-place conditions are those resulting from the selected design events (i.e. extreme environmental conditions) that may induce a restriction of operation. The design of an offshore structure shall consider conditions combining environmental loads with appropriate dead and live loads in the following manner: • Operating environmental load conditions (including deformation load and other necessary loads if any) combined with dead loads and max live loads (including motion induced load and other necessary loads, if any) appropriate for normal operation of the platform •

Operating environmental load conditions (including deformation load and other necessary loads if any)combined with dead loads and minimum live loads (including motion induced load and other necessary loads if any) appropriate for normal operation of the platform

•

Extreme environmental load conditions (including deformation load and other necessary loads if any)combined with dead loads and max live loads (including motion induced load and other necessary loads if any) appropriate for combination with extreme environmental condition

•

Extreme environmental load conditions (including deformation load and other necessary loads if any)combined with dead loads and minimum live loads (including motion induced load and other necessary loads if any) appropriate for combination with extreme environmental condition

Environmental loads shall be combined in a manner consistent with the probability of their simultaneous occurrence during the loading condition being considered. The combination of motion induced load shall be consistent with the environmental load to create the most unfavorable situation.

8.3

LOCAL ANALYSIS Some loadings are local in nature and their impact to the global model may not be very severe. These loadings should be evaluated locally, such as the plating capacity under local concentrated load. For global analysis, rational load combinations should be developed for the global model and approved by the Company. One approach is to use proper carry down factors as specified in Section 6.

9.0

DYNAMIC ANALYSIS

9.1

MODAL AND VIBRATION ANALYSIS The natural frequency of each module structure shall be calculated in the analysis and summarized in a list for each independent module for Company review.

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The number of frequency shall be selected in such a way that the mass participation factor is above 95%. Fundamental periods of the structure in longitudinal, transverse, and torsional directions shall be determined. The natural frequency of the module structure shall be compared with the test and operation frequency of reciprocating or rotating components that may produce vibration resonance with the structure. Acceptance criterion shall show that the natural or combined frequencies should be at least 30% above or below the operating speed range of the equipment. If the results show that a resonance is possible, more detailed mass modeling or direct response-based analysis shall be performed. The response study should consist of a forced response and a time transient response analysis that may produce vibration levels due to drive train as a function of time. For the calculation, the modal damping ratio shall be less or equal to 0.04. Detailed methodology and procedures to perform dynamic response analysis shall be submitted to the Company for approval.

9.2

SEISMIC ANALYSIS Seismic analysis shall not be generally required for marine structures on floating units. If seismic action is determined to have an effect on the marine structure, including mooring system, then a detailed method and procedures for seismic analysis shall be submitted to Company for approval.

9.3

VORTEX SHEDDING All members shall be analyzed and designed to avoid flutter caused by vortex shedding from environment. Analysis shall include such members as vent / flare booms. All phases of fabrication, transportation, installation, and in-place conditions shall be investigated. The one minute mean wind velocity at the mid point of members shall be used for vortex shedding check. The degree of fixity could be set as 70% for most tubular members welded within frame. The critical damping ration could be set as 0.002 in lieu of a detailed analysis. Members susceptible to vortex-induced vibration shall be redesigned to prevent flow resonant shedding of the vortices. In special cases, other mitigation techniques may be considered. Detailed method and procedures for vortex analysis shall be submitted to the Company for approval.

9.4

WAVE SLAM The wave slamming check shall be performed per API RP 2A or other Company approved rules for all the members under potential wave impact load (such as green water). All phases (fabrication where wave slam is possible, transportation, installation, and in-place) shall be investigated in the design.

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10.0

FATIGUE ANALYSIS

10.1

GENERAL


If the structure is subject to cyclic loads from vessel response or flexure, rotating equipment, vortex induced vibration, etc., then a fatigue analysis shall be performed in accordance with the requirement of API/AWS codes or other Company approved rules. The fatigue damage shall be assessed considering the cumulative effect of the cyclic loading including: • Global loading causing overall hull girder deformation, including still water and dynamic wave effects •

Inertia loads caused by vessel motions, including high and low frequency components

•

Loading imposed at supports for topsides equipment, risers, and other attachments

•

Equipment vibration

•

Temperature effects

•

Local wind, wave, or current effects on slender structure

•

Load from live liquid

The written detailed fatigue procedure shall be provided in the Design Brief for approval by the CS and Company prior to commencing any work. As a minimum requirement, the following items should be included in the document: • Determination of the number of cycles •

Determination of fatigue stresses

•

Determination of stress concentration factors

•

Selection of S-N curves

•

Selection of wave energy spectra for tow and operation

•

Selection of the vessel heading in operation

•

Consideration of fabrication tolerances

•

Consideration of corrosion effects

•

Consideration of phase relationships between stress components

•

Inclusion of all relevant stress contributions

•

Determination of cumulative damage.

Fatigue damage shall be calculated for all primary joints. Explicit fatigue calculations shall not be required for secondary joints; however, good fatigue detailing should be used.

10.2

DESIGN PARAMETERS Some fatigue design parameters are specified in the following subsections.

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10.2.1


Stress Concentration Factors Stress concentration factors (SCF) shall be computed by an empirical formula, finite element analysis, or model test. Methodology to calculate SCFs for tubular joints shall include: • Empirical formulae or computational method proposed •

Joint classification methods

•

Procedures to evaluate connections outside the valid range of methods or parameters shall be defined

•

Modifications for ring stiffeners, grouted connections, etc.

Stress Concentration Factor (SCF) for all primary joints in the topsides shall be computed. Exceptions shall be approved by the Company. Individual SCFs for axial, in-plane bending and out-of-plane bending stress shall be applied to the associated nominal stresses to arrive to the hotspot stresses. When FEM analysis based SCFs are required, the Contractor shall either develop an FEA model or determine the appropriate SCFs per DnV-RP-C203, or other Company approved rules, or obtain the SCFs from previously analyzed joint of similar type. The following approach shall be used to compute the SCFs. • Tubular Joints - Efthymiou's equations with load path considerations •

WF-Beam to WF-Beam - Stress concentration factor of 2.0 may be used for well designed joints. This factor shall apply to hot rolled wide flange beams and plate girders of the same depth. FEA or other methods should be used to calculate SCFs for joints of beams with different depths.

•

Non-Tubular Joints - SCFs based on FEM analysis or Company approved SCF equations

•

Conical Transitions - SCFs based on FEM analysis or Company approved SCF equations

•

Ring Stiffeners - SCFs based on FEM analysis or Company approved SCF equations

•

Joints with Misalignment - SCFs based on FEM analysis or Company approved SCF equations (i.e. fabrication or installation tolerances greater than those defined in the fabrication specification).

Methodology and procedure to calculate stress concentration factors shall be submitted to the Company for approval.

10.2.2

S-N Curves Damage ratios for tubular members shall be calculated using API RP2A X S-N curve, or other Company approved standards. S-N curves and procedures for non-tubular members shall be as outlined by the AWS. The X curve shall be used only if weld profile control is incorporated into the fabrication process and if approved by Company. Fatigue lives of tubular members shall be checked at a minimum of 8 usage points corresponding to the crown, saddle, and quarter points of tubular joints. Both brace and chord side of tubular connections shall be checked.

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Basis for selection of the S-N curve shall be submitted to The Company for approval. The following curves could be used as default. Table 10-1 – Applicable S-N Curves Joint Type

S-N Curves

Tubular

API RP 2A - X’ / HSE T

Tubular to WF (Plate Girder)

ABS F / HSE P (1.34 factor)

WF (Plate Girder) to Tubular

ABS F / HSE P (1.34 factor)

WF (Plate Girder) to WF(Plate Girder)

ABS F2 / HSE P (1.52 factor)

Thickness Correction - Appropriate thickness corrections should be included in the fatigue calculations based on the latest edition of ABS / HSE specification. The allowable stress should be modified accordingly. Fillet Welds - For joints and details containing fillet welds, the weld toe should be checked with ABS F2 curve (HSE P curve with 1.52 classification factor). The weld root should also be checked using ABS W-curve (HSE P-curve with 2.54 classifications factor). The stress to be used with the W-curve should be the nominal shear stress on the effective throat of the weld metal.

10.2.3

DFF The value of the design fatigue factor (DFF) shall meet CA requirements or other Company approved standard. Unless otherwise approved by Company, the minimum safety factor for topsides structure is tabulated below. Table 10-2 – Design Fatigue Factor DFF

Joint (Member) Type

Inspectable

Non-inspectable

1 2 3 4

3 2 2 N/A

10 5 5 N/A

For the topsides module structures, only fire-proofed members shall be deemed non-inspectable. The Protective coating, typically paint with a thickness less than 2 mm (0.078 inch), is generally acceptable for non-destructive inspections without removing the coating.

10.2.4

DAF Dynamic Amplification Factor (DAF) shall be included properly in the determination of fatigue damage ratios.

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10.2.5


Weld Improvement Weld improvement techniques such as toe grinding or peening, which are performed to improve fatigue life, shall not be accounted in the initial fatigue analysis due to their uncertainty. Weld Improvement techniques could be utilized at the final design stage as a remedial measure. Any use of weld improvement techniques shall be detailed, shown on drawings, and Company approved.

10.2.6

Fatigue Lives Unless otherwise specified by the Company, the design shall be resistant to fatigue for a design service life of 20 years.

10.3

SIMPLIFIED METHOD A simple, deterministic fatigue analysis could be performed as a screening purpose in order to assess the need for a detailed fatigue analysis or verify the fatigue life of secondary structural components. Upon receipt of Company approval as well as a solid verification on the value of the Weibull shape factor, the simplified method could be used to assess the module structure fatigue life. A conservative value of 1.2 could be used if no more detailed verification is available at the stage of design. The largest stress range used for the simplified fatigue calculation shall be the maximum stress range happened in the design life of structure.

10.4

DETAILED FATIGUE METHOD

10.4.1

General A spectral fatigue analysis method shall be used for the detailed fatigue calculation on topsides structures.

10.4.2

Environmental Conditions Wave climate shall be represented by an aggregate of all sea states expected in the long term. Sea states shall be represented by the wave spectra. Unless otherwise specified on projectspecific data, the two-parameter ISSC spectrum shall be used. Wave scatter diagrams contained in project-specific data may be compressed into fewer data points only if the energy / frequency content are maintained. Methodology and procedures for wave selection and generation, generation of transfer functions or Response Amplitude Operators (RAOs), and compression of scatter diagrams shall be submitted for Company approval. Contribution from other environmental force such as wind shall also be addressed appropriately in the fatigue analysis.

10.4.3

Wave Frequency Fatigue The cumulative fatigue damage for the entire life of the structure shall be computed based on the probability of occurrence of each seastate as defined in the Metocean criteria.

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The floater should be analyzed using regular waves for a range of frequencies to define the motion Response Amplitude Operators (RAOs). The number of frequencies shall be selected to adequately define the transfer functions (both motion and stress transfer functions) over the range of periods for which there is significant energy in the wave spectrum, including peak frequencies from the floater RAOs. Structural loads generated from vessel motion analysis shall then be transferred (mapped) to a global structural model which shall include both the topsides structure (typically represented as a combination of beam and plate elements) and the hull (represented by a coarse mesh plate element model). In cases where it can be shown that the global forces in the topsides and hull are not coupled, the vessel motion RAOs can be used to generate the appropriate inertial loads in the structure similar to a module tow analysis. For this alternative, the effect of hull stiffness at the deck supports should be included.

10.4.4

Low and High Frequency Fatigue Some floating platforms experience significant motions due to wind and wave drift forces and the slowly varying changes in the gravity vector with pitch (the “g” component). This low frequency motion may cause low frequency fatigue damage. For some floating vessels such as FPSO, high frequency roll motion or ring and springing (TLP) may be experienced that may cause high frequency fatigue damage. A simplified analysis may be performed to quantify the relative importance of low/high frequency fatigue. If the resulting fatigue damage represents a significant portion of the total fatigue damage (say 10%), a more rigorous analysis shall be required; otherwise, it is sufficient to simply add the low or high frequency fatigue damage to the wave frequency fatigue damage. An alternate approach would be to increase the safety factor on the wave frequency fatigue to account for low or high frequency fatigue damage. However, if low or high frequency fatigue represents a significant portion of the total fatigue damage, a more rigorous analysis shall l be required. In this case, it would be necessary to combine the wave frequency and low or high frequency stresses using an appropriate combination method before computing the damage.

10.4.5

Tow Fatigue Tow fatigue analyses shall be required only for tow durations in excess of 14 days. Short distance tow in mild environment shall be excluded. If tow fatigue shall be evaluated, the design Contractor shall perform spectral fatigue analysis based on motion analyses of the combined topsides and transportation barge (or hull for FPSO) for the Metocean criteria provided by the Company or Tow Contractor. Fatigue damage calculations shall be the same as the in-place fatigue. The resulting fatigue damage from tow shall be added to fatigue damage from in-place conditions.

10.5

VIBRATION FATIGUE Fatigue due to the vibration of reciprocating or rotating machine shall be calculated in a deterministic way. Stress range could be derived directly from the unbalance force due to the vibrating machine. It is unnecessary to combine loads that do not vary in a comparable frequency level, such as gravity load, in the analysis.

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The calculated fatigue damage needs shall be added on the fatigue damage from in-place conditions using the superposition method per the Palmgren-Miner Rule.

11.0

LOADOUT ANALYSIS

11.1

GENERAL The loadout design shall conform to the Company’s Marine Loadout and Transportation Specification.3 The skid/wheel loadout is addressed in the present section. The lifting loadout is included in the section for lifting analysis (Section 12.0). A Preliminary Loadout Plan shall be developed as the basis of engineering analysis and design. The preliminary loadout plan shall include the following: • Loadout method and equipment •

Attachment points

•

Skidway and barge layout (if skidded)

•

Any other special characteristics of the loadout

•

Operational limits due to tides, currents, wind

The Final Loadout Plan prepared by the fabrication Contractor shall be reviewed to ensure consistency with the preliminary loadout plan. A review of the selected barge shall be performed to ensure that the barge has the structural strength to withstand the expected initial, intermediate, and final loading from the loadout operations.

11.2

ANALYSIS A preliminary three-dimensional structural model shall be developed based on the latest revision of the in-place model, including appropriate COG shift. Boundary conditions to model static/dynamic friction, lug pull force, and skid beam supports shall be modeled accurately. The structure shall be analyzed for the imposed forces during the loadout operation. Appropriate static/dynamic friction coefficients shall be determined based on the proposed skidding surfaces. The values listed in table below could be used if no supplier data is available. The static coefficient shall be used in analysis.

3


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Table 11-1 – Friction Coefficients Surface Sliding Steel/steel Steel/grease/steel Steel/Teflon Stainless steel/Teflon Teflon/grease/planed wood Teflon/grease/wood Steel/wood Steel/grease/wood Rubber tires (locked) Rolling Steel wheels/steel Rubber tire/steel Rubber tire/gravel

Static

Moving

Min. 0.15 0.10 0.10 0.08 0.08 0.10 0.20 0.15 0.20

Typ. 0.20 0.15 0.15 0.10 0.14 0.18 0.40 0.30 0.35

Max. 0.35 0.30 0.25 0.20 0.25 0.30 0.60 0.40 0.50

Min. 0.10 0.08 0.04 0.03 0.03 0.05 0.15 0.10 -

Typ. 0.15 0.12 0.05 0.04 0.06 0.10 0.30 0.15 -

Max. 0.25 0.20 0.10 0.07 0.08 0.15 0.40 0.20 -

0.01 0.02

0.01 -

0.02 0.06

0.01 0.02

0.01 -

0.02 0.04

The total pulling force shall be applied consistently with the proposed method of pulling and resisted by friction forces (static) on some skid shoes such that they create maximum impact to the structure, i.e. differential friction forces and differential pulling forces should be considered. For a skid shoe system fully braced horizontally, differential friction forces shall not be required. For most components with reasonable symmetry, differential pulling forces may be waived by the Company. The pulling force shall be applied on the proper location of the module structure for loadout analysis. If contact surface information is not known or cannot be easily determined at time of design, a minimum pulling force of 25% of module weight shall be used. The loadout analysis for skidding shall simulate racking conditions in terms of partial loss of one or more support points that the component may realistically experience. A minimum support settlement shall be developed based on the following information and shall be approved by the Company: • Incorrect trim of draft due to tidal fluctuation or wind •

Barge movement

•

Location, slope, or settlement of skidways

Differential support settlement of ± 25 mm per 15 m ( ± 0.984 inch per 49.212 ft) skid distance run shall be considered when: the fabrication yard and/or barge have not been selected, settlement prediction can not be determined, or the Company does not specify any support settlement values. For structures with 6 or more support points, load cases shall examine the structure for total loss of support at any 2 points. For structures with 4 support points, load cases shall examine the structure for total loss of support at any 1 point. A limiting deflection may be used if sufficient controls exist to prevent total loss of support.

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Loadout by dollies or heavy transports shall use differential settlement criteria specified by the dollies or heavy transport Manufacturer. Wind load should also be included in the load conditions. COG shift is another issue to be considered. The COG envelope could be taken as 7.5% of longitudinal and transverse dimension of structure at the FEED design stage and 2.5% for the detailed design and fabrication design stage. Local effect shall be avoided when applying COG shift via the additional force couple or moment. The detailed strength check on skid shoes shall be submitted to the Company for approval at the fabrication engineering stage. The loadout design shall also meet the requirement of Marine Warranty Surveyors.

12.0

LIFTING ANALYSIS

12.1

GENERAL The lifting design shall conform to the Company’s Marine Loadout and Transportation Specification. A lift analysis shall be performed for each module to be lifted. Results of the lift analysis shall be used to design the structure and lift related components, including but not limited to rigging (slings, spreader bars, shackles, and fitting connections), padeyes, trunnions, and installation aids.

12.2

COMPUTER MODEL A three-dimensional computer model shall be used for the lift analysis. The model should be similar to the loadout analyses but with the following issues accounted for: • Slings with the appropriate stiffness

12.2.1

•

Padeyes/trunnions/padears with proper offsets

•

Spreader bar/frame if any

•

Horizontal springs for the stabilization of structure

Sling Slings should be modeled using tubular members with the appropriate axial stiffness. The axial stiffness should be obtained from the sling supplier or approximated using the following properties: • The area of the tubular shall be 60% of the actual gross area of the sling based on the given sling diameter. •

The modulus of elasticity of the tubular shall be E=80,000 N/mm2.

•

The slings, as tension-only members, should not transfer end moments.

•

If rigging configuration is assumed and not known, then analyses shall be performed for 60o sling angle (angle between the sling and the horizontal).

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12.2.2


Offset The offset distance from padeye hole to padeye attachment to main framing should be accounted for to reflect any potential eccentric loads. Similarly, if a trunnion is used, the offset distance of the center of the trunnion to the main framing should be accounted for in the model.

12.2.3

Spreader Bar The spreader bar should be modeled as a prismatic member with a KL factor of 2.0. Eccentricity of sling lines at the ends, if any, should be accounted for to reflect any local bending.

12.2.4

Virtual Spring In most cases, additional horizontal springs shall be required to stabilize the structure and spreader bars (if any) during analysis. However, the generated reactions should be checked so as not to exceed 5.0 MT or 0.1% of module's total lifting weight, whichever is smaller.

12.3

API APPROACH For lifting a weight less than 1500 MT and only one crane lifting scheme adopted, the methodology described by API RP 2A shall be applicable.

12.3.1

Dynamic Factor The dynamic factors used for lifting analysis are listed below. Table 12-1 – Dynamic Lifting Factor-I Environment

Critical Component

Other Components

Open Water

2.0

1.35

Shielded Water

1.2

1.15

On Shore

1.00

1.00

12.3.2

Skew When rigging has been determined, skew effects must be assessed if sling lengths are outside of API tolerance, which is the total variation from the longest to the shortest sling should not be greater than 1/2 of 1% of the sling length or 75 mm (2.952 inches).

12.3.3

COG Shift Variation of the COG shall be accounted for by use of a COG envelope, which could be taken as 7.5% of longitudinal and transverse dimension of structure at FEED design stage and 2.5% for the detailed design and fabrication design stage. Local effect shall be avoided when applying COG shift via the additional force couple or moment.

12.4

DETAIL APPROACH For a lifting weight no less than 1500 MT or has more than one crane involved in lifting, a detailed lifting analysis method shall be deployed. In such an approach, each factor imposing

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influence on the structure would be explicitly addressed in terms of factors. The final factor shall be the product of all itemized factors and applied on the total lifting weight.

12.4.1

Dynamic Factor The dynamic factors used for the lifting analysis are listed below. Table 12-2 – Dynamic Lifting Factor-II

12.4.2

Onshore

Weight (MT)

Open Water

Shield Water

Moving

Static

<100 100~1000 1000~2500 >2500

1.30 1.20 1.15 1.10

1.15 1.10 1.05 1.05

1.15 1.10 1.05 1.05

1.00 1.00 1.00 1.00

Skew Factor Skew factor shall be 1.25 for indeterminate lift and 1.00 for determinate lift. There is another way to address the skew effect for 4 sling lifting. The two sets of diagonal slings may be supported by separate but coinciding hook points. An upward force shall be applied on one hook point to reflect the 45%-55% load split between diagonal opposite sling pairs.

12.4.3

Consequence Factor The consequence factors are listed in table below. Table 12-3 – Consequence Factor Item

Factor

Lifting Point and spreader bar

1.35

Attachment of lift point to structure

1.35

Member framing to lift point

1.15

Other member

1.00

12.4.4

COG Factor A COG factor of 1.03 shall be applied in addition to the COG envelop as mentioned in Section 12.3.3.

12.4.5

Tilt/Yaw Factor A tilt of 1.03 and yaw factor of 1.05 shall be applied for the two crane lift case.

12.5

LIFTING ITEMS DESIGN Some lifting items such as padeyes, trunnion, slings, and shackles need shall be designed appropriately per the loading from lifting analysis.

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12.5.1


Padeye Padeye design shall be based on the maximum sling load resulting from the lift analysis described in Section 12.3 and 12.4. Padeyes shall be oriented directly in line with the connecting slings. If different orientation is necessary, the associated out-of-plane moment shall be included in the design load. In addition to the expected out-of-plane moment, additional forces due to 5% of the maximum static sling tension load applied along the axis of the pin hole shall be included as per API RP 2A. Plate thickness, plate size, and pinhole diameter shall be proportioned to accommodate the selected shackle without excessive strain to the shackle and pin. Design calculations for padeyes shall include at minimum bearing, pull out, shear, axial, bending, and combined stress checks for the critical sections of the main plate, cheek plate, and all welding. The contact stress between padeye pinholes and pins shall be checked by Hertz pressure, which can be calculated as below: σ Hertz = 0.418 ⋅

DH DPin ) − 2 2 D ⋅D ⋅ H Pin 4

Fs lg ⋅ E ⋅ ( t pad

where Fs lg

=

Factored sling force

E

=

Young’s modulus

DH

=

Diameter of pinhole

DPin = t pad

=

Diameter of pin Thickness of padeye plate (main plate + cheek plates)

The allowable Hertz pressure is 2.5 times the yield strength.

12.5.2

Padear / Trunnion Padear / trunnion design shall be based on the maximum sling load resulting from the lift analysis described in Section 12.3 and 12.4. Padear / trunnion shall be oriented directly in line with the connecting slings. If different orientation is necessary, the associated out-of-plane moment shall be included in the design load. Design calculations for padear / trunnion should include the following checks: • Bearing of slings at the pin/tubular and cheek plate •

Shear/bending strength of pin/tubular

•

Shear/pull out through critical sections

•

Check for lowest tension failure load at critical sections

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12.5.3


•

Bending (in-plane and out-of-plane) at critical sections

•

Combined stresses (axial, shear and bending) at critical sections

•

Size of cheek plate welding

Sling and Shackle The breaking strength (as stated by Manufacturer) of slings, shackles, and fittings shall be selected based on the maximum static sling load (dynamic load factors = 1 and including other effect like COG shift and skew if applicable). The factor of safety for the breaking strength to the maximum static sling load shall be 4.0 for slings and 3.0 for shackles and other fittings. The safe working load (as stated by Manufacturer) of the slings, shackles, and other rigging connections shall be greater than or equal to the maximum static sling load.

12.5.4

Installation Aid If installation aids is applied in lifting, the following design impact factors (stated as a percentage of the maximum lift weight) shall be used: Primary guides (initial guides) Direct horizontal impact

-

10%

Transverse horizontal impact

-

2%

Vertical impact (pin and bucket only)

-

10%

Vertical friction force

-

1%

-

5%

-

10%

Secondary guides (final guides) Horizontal impact Vertical impact

The final guide engagement shall be 300 mm (11.811 inches) prior to module landing. Installation guides shall guide the lifted module to within a tolerance of +25 mm (0.984 inches).

13.0

TRANSPORTATION ANALYSIS AND SEAFASTENING DESIGN The transportation design shall conform to the Company’s Marine Loadout and Transportation Specification.4 Topsides Modules are subject to several transportation phases: from Fabricator to Integration site on a self-propelled ship or towed cargo vessel, from Integration site to floater Operational site on the floater, and from Fabricator to operational site on a self-propelled ship or towed cargo vessel). The transportation from Fabricator to Operational site of the floater may occur if a module becomes delayed or for installation of a module at a future date. The extent and detail of the transportation and sea fastening analysis shall depend on the environmental

4


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conditions, transit duration, transit route, dates of transportation, size of vessel / barge, size and weight of offshore structure being transported, etc. Transportation analysis and sea fastening design shall be based on API and criteria of an approved Marine Warranty Surveyor. The procedure and data used for the transportation and sea fastening design shall be approved by the Company in writing before proceeding with the work. The topsides structure shall be analyzed and designed for the condition of transportation in two scenarios as described in Section 13.1 and 13.2 respectively.

13.1

TRANSPORTATION ON FLOATER This scenario shall be applicable for the transportation from integration yard to the offshore site. The analysis would be as same as the analysis for the in-place condition with the following issues on attention: • The structural shall be identical to those used for in-place analysis. If some temporary modification is needed for the transpiration, then those modifications shall be reflected on the model.

13.2

•

The gravity load shall conform to the transit condition regarding to variable load, live load, piping / vessel content load, etc.

•

The boundary condition shall reflect the real situation, either same as the in-place condition, or with some temporary support or sea fastening if applicable.

•

The seastate shall comply with the transportation route.

•

The marine design group shall determine the motions of the floater for a range of sea states to ensure that most severe motions are taken into account. Wave spectra for different mean periods shall be used to evaluate potential dynamic amplification of motions near the natural periods of the barge / cargo system. Angular and linear accelerations shall be based on single amplitude responses for irregular spread seas.

•

The deformation of the hull under the design seastate shall be considered in the topsides structure analysis.

•

The 1 minute mean velocity at 10m above MSL shall be used in structural analysis. The 1 hour wind may also be used after receipt of Company approval.

•

A 1/3 increase in allowable stresses shall be permitted for transportation analysis and sea fastening design.

TRANSPORTATIN ON BARGE OR SHIP This analysis covers the transit from Fabricator to Integration Yard or from Fabricator to Offshore site if applicable. The topsides module shall be transported on a self-propelled ship or towed barge.

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The Noble Denton “General Guidelines for Marine Transportations” is applicable for such transportation analysis and design.5 A detailed transportation analysis shall be performed for each deck module or component after a Transportation Plan has been established. Transportation Plans shall include the selection of transport vessel, tow route, and environmental criteria. The following information shall be determined at the design stage: • Selection of barge/transport vessel and component layout •

Tiedown/seafastening

•

Transportation route to establish environmental criteria and loading

•

Motion analysis of the transport vessel with deck module

At an early stage, when the above information is not available, some default values could be used based on experience and the NDI suggestion shown in the following section.

13.2.1

Motion Derivation The motion response of the barge / ship shall be derived by a motion study (per section 7.7 of 0030/NDI) or model test (per section 7.8 of 0030/NDI) based on the barge condition, structure information, and environmental data (as per section 6 of 0030/NDI). In lieu of the motion study and model test, the default motion criteria could be applied per section 7.9.1 of 0030/NDI. Those default motion data is repeated in table below for information. Table 13-1 – Default Motion Vessel or transit nature Large vessels L>140 m LOA and B>30 m Medium vessels L>76 m and B>23 m Small vessels L<76 m or B <23 m Large cargo barges L>76 m LOA and B>23 m Small cargo barges L<76m or B<23 m Weather restricted operations in benign areas Inland and sheltered water transportations

Full cycle period

Single amplitude

Heave

Roll

Pitch

10 sec

20 deg

10 deg

0.2g

10 sec

20 deg

12.5 deg

0.2g

10 sec

30 deg

15 deg

0.2g

10 sec

20 deg

12.5 deg

0.2g

10 sec

25 deg

15 deg

0.2g

10 sec

5 deg

2.5 deg

0.1g

Static

Equal to 0.1g

Equal to 0.1g

0

Note: It needs to be highlighted that Noble Denton defines "benign” as; "An area that is free from tropical revolving storms and travelling depressions, (but excluding the North Indian Ocean during the Southwest monsoon season, and the South China Sea during the Northeast monsoon season).” "Weather restricted operation” is defined as; “An

5


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operation with an operational reference period generally less than 72 hours. The design environmental condition for such an operation may be set independent of extreme statistical data, subject to certain precaution.”6

13.2.2

Strength Analysis and Seafastening Design Transportation analysis and sea fastening design for a structure transported on a barge shall be performed as follows: • Three-dimensional stress analysis that combines gravity loads with inertial loads shall be performed. •

Head sea, quartering sea, and beam sea approaches shall be investigated as a minimum.

•

Linear and angular accelerations shall be applied simultaneously to the model.

•

“g” component of gravity load due to motion of barge shall be considered.

•

Barge flexibility shall not be taken into account except for under the following conditions: -

The cargo is longer than about 1/3 of the transport barge or vessel length.

-

The cargo is supported longitudinally on more than 2 groups of supports.

-

The seafastening design allows little or no flexibility between cargo and barge.

•

Structures and sea fastening shall be analyzed for transportation utilizing environmental criteria for transportation.

•

The structural analysis should reflect that gravity loads are not supported by tiedown and seafastening members, i.e. these members are subjected to environmental loading only. This may be achieved by proper modeling of the seafastening member or by running the analysis separately to address the gravity loads and environmental load respectively then combining the induced member force together for final checking.

•

The analysis should also take into consideration the vessel's longitudinal and torsional stiffness in conjunction with the proposed grillage and seafastening.

•

The following combination of motion induced force shall be taken: 1. Transverse force ± Heave (beam sea) 2. Longitudinal force

±

3. α Transverse force

±

Heave (head sea)

β Longitudinal force ± Heave (quartering sea)

The α and β coefficients reflect the phasing without detailed verification. Coefficients could be set corresponding to the attack angle of environment.

14.0

ACCIDENTAL ANALYSIS Accidental analysis pertains to the overall risk assessment of the project. The method given in section 18 of API RP 2A shall be followed. The risk assessment itself shall not be addressed here; however, the accidental analysis shall be introduced as an outcome.

6

“Guidelines for Marine Transportation,” Noble Denton; 0030/NDI. Refer to Section 3.1.3.

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In addition to the API RP 2A WSD, the DnV report “Design for Offshore Steel Structures Exposed to Accidental Loads” can be taken as primary guidance for the methodology of accidental analysis, unless the Company specifies some other document for the specific project.7

14.1

DROP OBJECT Dropped objects shall most likely result from crane operations where an object is dropped on to exposed surfaces of the topsides or swung laterally into structure, equipment, and/or piping. Loads are typically characterized in terms of impact energy. One approach for addressing dropped object scenarios is a materials handling study for the facility. This defines lift weights and frequencies for objects to be handled as well as where they shall be handled. Lifts typically include containers, tote tanks, food containers, equipment maintenance lifts, etc. Based on these evaluations, a number of drop object cases are defined, and the areas of the topsides subject to impact loads (drop zones) are identified. The drop object cases shall be selected from all the possible accident scenarios based on an evaluation of consequence and risk. The adequacy of the structure design shall be verified by demonstrating adequate strength and ductility against dropped objects that are selected from accident scenarios. The resulting dropped objects case shall serve as input to the structural discipline for dropped object analysis. A typical flowchart for the drop object analysis is listed in Figure 14-1.

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Detailed Risk Assessment

Material Handling Study

Topside Layout

Structural Engineering

Operation Procedure

Define accidental scenario and area needs protection

Define drop zone, equipment needs protection and protection device

Determine mass, height, energy, impact orientation, impact type for each object

Deck plate, stringer and beam

Laydown area

Equipment protection & bumper

Hatch cover

Redesign

Redesign Assess impact energy absorption

No

Operation Restrict?

No

Energy absorbed?

Yes

Serviceability OK?

Yes Define restriction

No

Yes Design OK

Figure 14-1 – Typical Drop Object Analysis Flowchart

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Accidents may result from other forms besides dropped objects. Possible side impact on equipment caused during material handling operations (particularly by cranes) should also be considered.

14.1.1

Case Identification For crane operations, and for each topsides area subject to impact, the number of objects, their size, configuration, and weight that shall be lifted over the area shall be identified. The average potential drop height for the different objects shall be assessed from the identified routings and lift heights. For local lift operations, gantry cranes, monorails, and others, the representative object for each area within the topsides shall be identified.

14.1.2

Impact Energy For each dropped object case, associated impact energy shall be computed. The impact energy, E, is related to the mass of the dropped object, M, and either the fall height, h, or the velocity at impact, VP as follows: E = M ⋅ g ⋅ h = 0.5 ⋅ M ⋅ VP2

It is acceptable to calculate an equivalent static load (impact load) for use in design calculations as long as it produces the same required impact energy. Impact orientations should be considered in defining the impact energy cases. For cubic shaped objects (i.e. container, tote tank), the design should consider corner, edge, and face impact. For tubular objects, side-on and end-on orientations should be considered.

14.1.3

Acceptance Criteria For extreme cases, the energy to be absorbed by the structure shall be at least equal to the impact energy. For cases more likely to occur, the energy absorption capability of the structure should be up to twice the impact energy. If a failure criterion is not achieved, then either the structure must be strengthened or steps must be taken to reduce the severity of the impact such as prescribing restricted operating procedures. The drop object analyses shall ensure that the structure satisfies the accidental load performance criteria; that is, the local damage shall be acceptable. The possible initiation of progressive collapse and damage to primary structure shall be avoided. The analyses should also prove that: • Acceptable damage limits are satisfied (deck penetration depths, deflection limits, dent size). •

Dropped object protection is cost-effective.

•

Damage from dropped objects does not lead to potential production shutdowns.

•

The structural component that can retard the dropped object sufficiently to prevent total penetration of the protection and thereby damage the underlying equipment and/or piping.

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14.1.4


Zones Vulnerable to Impact For design purposes, topsides areas are divided into three basic categories of exposure defined in terms of the effect of impact: Severe Areas These include any region of hazardous components where damage could threaten the integrity of the topsides or vessel (laydown areas and production areas, areas with vulnerable piping, etc.). Moderate Areas Includes zones in which dropped object impact would not threaten the integrity of the vessel or seriously impact its functionality. Many general deck areas often fall into this category. An example, frames are not normally provided over chemical injection skids, as it is reasonable to restrict crane operations over such an area even though it is physically possible to swing a load over the top of them. Non-critical Areas Limited structural damage is acceptable in these areas; therefore, the effect of accidental damage may not need to be directly considered. In such cases, protection is more for asset protection and maintenance than safety or protection of the integrity of critical components or services. Providing heavy bumpering around food container storage areas is an example of where nominal protection may be provided. No drop object case is rigorously defined.

14.1.5

Energy Absorption All of the impact energy shall normally be assumed to be absorbed by the resisting structure. If this assumption results in an unreasonable level of strengthening, then account may be taken of the amount of energy absorption by the impacting object. Factors that can influence and improve the energy absorption capability include: • Local punching or deformation of the resisting member(s) in the region of impact •

Material type (steel, wood) and pertinent material properties (i.e. for steel -yield strength, strain rate, strain hardening, ductility ratios, and toughness)

•

Resisting member section (compact, plastic section modulus, etc.)

The stiffness of the impacted structure is dependent upon the boundary conditions that influence deflection behavior, mode of vibration, and energy absorption mechanism. The structure capacity to develop membrane action is directly dependent on the structural detailing of the supports to the plate or beams. Supports to the impacted structure must be capable of sustaining the reaction loads caused by the dropped object.

14.1.6

Enhancement on Yield Stress Nominal yield strength shall be used; however, increased energy absorption under impact loading due to high strain rates and work hardening beyond the yield point can be considered. Account shall be taken of this in the design calculations by increasing the yield stress by 10 percent.

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14.1.7


Design Philosophy The post impact deflection of deck plate, stringers, or beams shall be limited to ensure that the underlying piping or equipment is not damaged; i.e., the energy absorption capacity shall be controlled by the limiting deflection. For some cases, the energy absorption may be limited by the capacity of the structure supporting the impact resisting structure. Where equipment or pipe-work containing hydrocarbons or other critical equipment located in a “drop zone” are not protected by a load bearing deck, a separate protection structure (frame) shall be considered. This may be an energy absorption frame or a separate load bearing deck. The impact resisting structure must behave in a ductile manner to provide energy absorption characteristics; hence, the design must provide a balance among strength, ductility, and flexibility. Design guidelines include: • Provide redundancy, where practical, in the supporting structure such that alternative load paths may be developed.

14.1.8

•

Where beam collapse is the failure mechanism, provide more than one plastic hinge (i.e. simply supported beams are less reliable than collapse mechanism because local damage at point of contact may prevent an effective plastic hinge from forming).

•

Avoid dependence on energy absorbing struts with a sharply decreasing post-buckling capacity.

•

Avoid pronounced weak sections and abrupt changes in strength or stiffness.

Design Procedures A general procedure for dropped object design is summarized as follows with an assumption that energy is not absorbed simply by a local mechanism such as denting of a tubular or damage to a flange or web:

1. Determine the likely collapse mechanism that may be initiated by the impact loading. 2. Check whether the impacting object has sufficient energy to trigger the collapse mechanism taking into account any barrier structure.

3. If the collapse mechanism is triggered, check that deflection limits are not exceeded. 4. Verify that the damaged structure can resist functional and environmental loads in its damaged state. The practice of designing members for local energy absorption is generally neglected. However, design conditions may need it in investigation. For tubulars, energy can be absorbed by denting. Wide flanges may absorb energy by the local bending of flanges as facilitated through web buckling or web crippling. Beams subject to high impact shall meet the provisions of AlSC minimum thickness for plastic design and for compact sections. If the section is not defined as compact, deck plate to flange welds shall be adequate to ensure lateral restraint of compression flange is maintained during deflections required to mobilize plastic hinges. Lateral buckling shall be checked. Beam connection welds shall be full penetration to ensure ductility.

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14.1.9


Design Methods General Design for dropped object protection shall follow the methods given below, which are conservative methods for sizing various structural components. Alternate methods of analysis may also be proposed for Company approval. In cases where approximate methods result in significant structural upgrades, more refined analysis methods may be appropriate. Such methods may incorporate membrane action of deck plate, impulse and vibration response theories, non-linear finite element analysis, etc. Deck Plate Deck plate shall be analyzed to demonstrate that its energy absorption meets the required impact energy. Energy absorbed in plastic deformation shall be due to plastic bending of the plate. A mechanism of failure using yield line theory shall be used. A number of simplifying assumptions could be applied to the analysis. Stringers, Beams and Girders Stringers, beams, and girders shall be analyzed to demonstrate that their energy absorption meets the required impact energy. The number of stringers or beams included in each dropped object analysis shall be consistent with the size of the dropped object. The effective width of deck plate shall be included with the stringer or beam cross section. Energy absorbed shall be based on plastic bending of the beam on the basis of plastic hinge rotation. Deck Hatches Design of hatches is typically governed by impact resistance. A simplified method based on conventional yield line theory is used to assess the impact energy absorption capacity of the hatch cover. Its energy absorption capacity is discussed above for deck plate; however, energy absorption for hatches should be half that for deck plate since there is insufficient edge restraint to develop plastic hinges at the edges. The supporting members must also be checked to ensure adequate strength to provide the assumed boundary constraints. Laydown Area Laydown area shall be plated and designed for specific dropped objects to minimize the potential for damage and maximize serviceability. Typically, they shall be designed for impact from a container or tote tank (or similar) on the same basis as decks. Supporting braces and connections shall be checked to ensure they can absorb the impact reaction loads. Where integrity critical components are situated underneath a laydown area, the design impact energy for the component shall be doubled. Laydown platforms shall also be checked elastically for placement of packages with applied impact factor of 2.0 (suddenly applied load with zero drop height).

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Bumpers Bumpers in the form of posts or frameworks typically comprised of tubulars or rolled sections shall be designed to absorb the defined impact energy in plastic deformation. In lieu of energy absorption methods, the bumper frame may be checked statically for 10% of the package weight applied laterally. Protection Frames In some cases, layout requirements will dictate the need for protection frames for exposed piping, valve stands, etc. In such cases, these may be designed to deflect an object (by providing a sloping surface) without excessive deformation rather than absorbing all the energy.

14.1.10

Other Considerations Other considerations may be identified during risk studies. Examples include impact of crane boom with other structural components, bumpering requirements for a forklift, and providing stops for conveyor trolleys. As appropriate, the structural design discipline shall propose criteria and assessment approach for such considerations.

14.2

FIRE Fire will not impose load directly on the structure, but it would significantly deteriorate the capacity of the structure. Hence, the structural analyses on fire are aimed at ensuring that sufficient capacity to support existing loads is maintained during an accidental fire event. Obviously, the fire analysis will determine if and where passive fire protection (PFP) is needed to avoid failure or collapse mechanisms, either local or global. Both the stiffness and strength of steel will reduce with the increase of temperature. If the specific information is not available at design stage, the following reduction factor corresponding to the strain level of 0.2% could be used. Table 14-1 – Temperature Deduction Factor Temperature (Co)

E (T ) / E (T20C o )

F (T ) / F (T20C o )

20

1.000

1.000

100

0.940

0.940

150

0.898

0.898

200

0.847

0.847

250

0.769

0.769

300

0.653

0.653

350

0.626

0.626

400

0.600

0.600

450

0.531

0.531

500

0.467

0.467

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Temperature (Co)


E (T ) / E (T20C o )

F (T ) / F (T20C o )

550

0.368

0.368

600

0.265

0.265

650

0.189

0.189

700

0.113

0.113

750

0.085

0.085

800

0.056

0.056

850

0.034

0.034

900

0.028

0.028

14.3

BLAST For accidental blast events, load information usually comes from blast simulation analyses of possible hydrocarbon explosion scenarios. Such analyses are typically conducted by the Process discipline, and the resulting blast loading parameters are typically provided to the Structural discipline. For the case of blast, loads are characterized by overpressure pulses for a short duration. Interaction between the Structural discipline and the blast simulation specialists is typically required to develop the input necessary for structural design. Normally, the overpressure of greatest emphasis is that on a blast wall that separates a safe area from process areas on a manned facility. Blast overpressure is characterized as a pulse, with pressure variation as a function of time. The pulse is typically modeled as a triangular shape with a peak overpressure and duration. The load definition needed for structural analysis includes: • Blast wall rating (usually peak overpressure) •

Idealized pulse duration for blast wall dynamic analysis

•

Representative pressure contours for determining average loading over the wall surface

•

Idealized pulse duration for average loading on the wall.

Items 1 and 2 are required input for wall design (or input to specifications for supplier walls). Items 3 and 4 are needed to develop loading on wall support systems. In addition to the blast overpressure pulse, a blast wall shall be designed for its self-weight and any induced gravity load from its supporting structure. Other load conditions include wind loads, installation loads, and thermal loads for associated firewall requirements; however, these shall not be combined with blast overpressure loads. Either elastic or plastic design methods may be used for the design of blast wall components; however, component designs shall avoid either brittle or buckling types of failure modes. If elastic design methods are used, the allowable stress can be increased by 2/3 to reach the full effective yield strength of the material, subject to limitations for buckling considerations.

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For plastically designed walls, maximum deformations of beam and plate elements during blast loading shall have a ductility level (factor) equal to or below those prescribed in Table 3.7 from the SCI guidance notes (SCI-P-122).8 The plastic strain limit shall be 0.05. To account for strain rate effects, the yield strength may be increased by 15 percent for mild grade steels and increased by 10 percent for high strength steels. The following items shall be considered for beams: • To ensure formation of plastic hinges under ductile behavior, symmetrical cross-sections shall be used. •

To ensure that the cross sections are able to develop plastic hinges and that local buckling does not occur, beams shall comply with the compact section requirements of AISC.

•

Flanges shall be supported laterally per AISC requirements. Blast wall plating shall be welded to flanges so as to provide lateral support.

15.0

APPURTENANCE DESIGN

15.1

EQUIPMENT SUPPORT DESIGN The design of equipment supports shall account for the dynamic effects of vessel motion. Support steel shall be designed to withstand the maximum forces from all load conditions experienced by the offshore structure. Supports should include diagonal braces to avoid moment connections to the main structure. Where moment connections cannot be avoided, the effect of the moment on the supporting structure should be accounted for in the calculations. Equipment and vessel supports should be checked locally for two conditions:

Hydrostatic Test Weights These weights shall be available from the Weight Control Report. Open area live loads will be applied in combination with the hydrostatic test weights, but environmental loads will not. Allowable stress will not be increased for this case.

In-place Operating Loads This condition will include the dead weight of the equipment plus contents under normal operating conditions. This will be combined with normal and extreme operating environmental conditions and open area live loads. Floor systems supporting heavy rotating equipment should be designed such that the natural frequency of the system is not between 0.7 and 1.3 times the operating frequency of the equipment.

8


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15.2


WALKWAYS, LADDERS, AND STAIRWAYS Handrails, ladders, walkways, and stairways shall comply with Company requirements and appropriate local regulatory agencies. Refer to the Company’s standard drawings for handrails, ladders, stairs, platforms, and walkways. Adequate handrails, ladders, walkways, and stairways in accordance with the requirements of this specification shall be provided for operating and maintenance access to all instruments, controls, and valves. Handrails must be continuous, uniform in height, safe to slide hand along, and should be made of piping or tubing without a structural angle. Handrail sockets shall be located so that the handrail may be installed and removed with ease with no section greater than 4.25m in length. Handrail sockets shall be exteriorly mounted to the structure. Handrail posts shall be spaced a maximum of 1.35m apart. Maximum gap between handrail posts shall not exceed 50 mm (1.968 inches). Handrails shall enclose all platforms and stairways. Handrails shall be fixed, except around the well bay areas, access hatches, and at crane laydown areas. These areas shall have removable handrails with handrail sockets fitted to removable handrail panels. Handrail design shall meet Company and local requirements. Except for helidecks, where safety nets or panels will be installed, handrails shall be installed on the perimeter of all open decks and walkways. Kick plates shall be provided on handrails located in areas without pollution curbs. Ladders shall conform to ANSI A14.3. Vertical ladders shall have non-corrosive, self-closing bars across the top handrail stanchion. Walkways, stairs, and landings shall be designed for live load specified in Section 6.0. These loads are for local design only and should be excluded in global design for stairways and landings and included for walkways with carry down factor as specified in Section 6.0. Walkways in high traffic areas and serving as primary means of egress will have a minimum clear width of 1.5 m (4.921 ft), exclusive of handrails. Survival craft muster areas shall be a minimum of 3 m wide. All other walkways, stairways, and landings shall have a minimum clear width of 900 mm (35.433 inches), exclusive of handrails. Gratings to cover the surface shall be of the same specifications as the stairways. Maximum angle for stairs shall be less than 40 degrees from horizontal, preferably 35 degrees. Stairways landings shall be designed to easily accommodate stretcher plus bearers. Stair width shall be a minimum of 0.9m wide and the treads shall be fixed, non-skid design with anti-slip stair nosing. Stairs shall be large enough not to present a trip hazard in an emergency. For plated deck areas, a 100 mm (3.937 inches) high perimeter coaming plate or a half round segment of 200 mm (7.874 inches) diameter shall be provided. Coaming shall meet Company and local requirements.

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15.3


ACCESS PLATFORMS Access ladders/service platforms shall be provided for main operating levels, main service levels, roof of buildings supporting major equipment, caissons, drain vessels, pumps, and other equipment which require frequent maintenance. Platforms shall be equipped with handrails, knee rails, and kick plates. Platforms and all stair tread shall be made from bar grating and have nosing unless otherwise specified. Access platform shall be designed for the same loading and carry-down factor as walkways. The supporting structures shall be designed using a three dimensional computer model and shall be subjected to environmental loading (accelerations and wind) specified for global analysis. The surface shall be covered with 25 x 5 mm (1 inch x 3/16 inch) galvanized serrated grating. Access to the platform can either be by ladder (equipment service platform) or stairway (routinely used service platform). Handrails shall enclose the access platform as specified in the previous section

15.4

LIFTING AND HANDLING STRUCTURES DESIGN Topsides lifting and handling appliances (chain blocks, travelling blocks, travelling beams, winches, pulleys, etc.) shall be characterized by their Safe Working Load (SWL), which is a function of the load to be handled. A specific layout drawing shall define in detail the type, location, and capacity (SWL) of each lifting and handling appliance. The design of the structural components supporting lifting and handling equipment shall be based on the safe working load (SWL) of the concerned piece of equipment, factored as required to take into consideration the induced dynamic effects when operating the lifting/handling appliance (to be documented after clarification with the equipment Supplier). Similarly, the loads induced by the operation of the lifting appliance such as horizontal transverse load and longitudinal acceleration or braking loads etc. shall also be taken into consideration (to be documented after clarification with the equipment Supplier). In case the Supplier data is incomplete or unavailable, the following shall be taken into consideration:

Vertical For the static calculations of the structural components supporting the lifting equipment, the following dynamic factors shall be applied to the vertical SWL: • Electric monorails, cranes, travelling crane: 1.25 •

Manual monorails, cranes, travelling cranes: 1.10

•

Lifting winches and pulleys, including. Life boats davits: 1.40

•

Fork lifts: 1.50

•

Belt conveyors: 1.20

•

Elevators and hoists: 2.00

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Horizontal The following horizontal loads shall be considered as acting simultaneously for the travelling cranes and monorails: • A transverse force equal to 10% of the load at each wheel, without dynamic factor, applied to the point of contact between the wheels and the support beam or rail

15.5

•

A longitudinal force applied to the same points, equal to two times the load defined above, for the drive wheels only

•

The force due to the impact on the stoppers of the gantry beam, calculated using the mass of the lifting equipment and the maximum translation speed (mass of the lifted load shall not be considered if the load is not rigidly connected to the lifting equipment).

CRANE SUPPORT STRUCTURES The crane supporting structure comprises the crane pedestal and its connections to the topsides primary steelworks. It does not include the slew ring, or its equivalent, or the connections between the slew ring and the pedestal. The supporting structure of the platform crane shall be designed according to the primary trusses and connected at the main deck elevation with minimal eccentricities. When located accordingly, their performance shall generally be governed by static loads with negligible dynamic amplification. They shall be subject to fatigue damage and always be checked to ensure that fatigue life is satisfactory for the required service conditions. Static design of crane pedestals shall be based on operating conditions. The static rated load of the crane shall be defined per API Spec 2C and given in the particular specification. The following requirements shall be particularly considered: • The crane pedestal, its connection node to the platform structure, and the structural members of the platform connected directly to the pedestal shall be designed against the dead load of the crane, plus a minimum of 2.0 times the static rated load of the crane. •

The structural members of the platform not connected directly to the pedestal shall be designed against the dead load of the crane plus a minimum of 1.33 times the static rated load of the crane.

•

With due consideration to the two points above, the following loading conditions shall be analyzed:

•

-

Maximum overturning moment with corresponding vertical load, plus a side load equal to 4% of the vertical load, applied simultaneously to the boom head sheave

-

Maximum vertical load with corresponding overturning moment, plus a side load equal to 4% of the vertical load, applied simultaneously to the boom head sheave

The fatigue design of the crane supporting structure, including the connection of the pedestal to the platform structure, shall be carried out considering the static rated load increased by a 1.33 factor. A minimum of 25,000 cycles shall be considered, unless otherwise noted in the particular specification.

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