Heavy lift installation study of offshore structures

10 2.1 Review of Various Lifting Criteria 2.2 Practical Considerations for Standard Rigging Design 2.2.1 Sling Design Loads SDL 2.2.2 Shackle Design Loads 2.2.3 Lift Point Design Loads 2

HEAVY LIFT INSTALLATION STUDY

OF OFFSHORE STRUCTURES

LI LIANG (MS Eng, NUS)

A THESIS SUBMITTED FOR THE DEGREE OF MASTER OF ENGINEERING

DEPARTMENT OF CIVIL ENGINEERING NATIOANL UNIVERSITY OF SINGAPORE

2004

HEAVY LIFT INSTALLATION STUDY

OF

OFFSHORE STRUCTURES

LI LIANG (MS Eng, NUS)

A THESIS SUBMITTED FOR THE DEGREE OF MASTER OF ENGINEERING

DEPARTMENT OF CIVIL ENGINEERING NATIOANL UNIVERSITY OF SINGAPORE

ACKNOWLEDGMENTS

The author would like to express his sincere appreciation to his supervisor Associate Professor Choo Yoo Sang The author is deeply indebted to his most valuable guidance, constructive criticism and kind understanding Appreciation is extended to Associate Professor Richard Liew and Dr Ju Feng for their assistance and encouragement

In addition, the author would like to thank the National University of Singapore for offering the opportunity for this research project

Finally, the author is grateful to his family, the one he loves, and all his friends, whose encouragement, love and friendship have always been the major motivation for his study

TABLE OF CONTENTS

CHAPTER 1 INTRODUCTION 1 1.1 Background

1.2 Objectives and Scope of Present Study

1.3 Organisation of Thesis

CHAPTER 2 REVIEW OF LIFTING DESIGN CRITERIA 10 2.1 Review of Various Lifting Criteria

2.2 Practical Considerations for Standard Rigging Design

2.2.1 Sling Design Loads (SDL)

2.2.2 Shackle Design Loads

2.2.3 Lift Point Design Loads

2.2.4 Shackle Sizing

2.2.5 Tilt during Lifting

2.2.6 COG Shift Factor

2.3 Summary

CHAPTER 3 HEAVY LIFTING EQUIPMENT AND COMPONENTS 24 3.1 Introduction

3.2 Heavy Lift Cranes

3.2.1 Crane Vessel Types

3.2.2 Frequently Used Crane Vessels

3.3 Heavy Lift Shackles

3.4 Heavy Lift Slings

3.4.1 Sling properties

3.4.2 Grommets versus Slings

3.4.3 Sling and Grommet Properties

3.5 Lift Points

3.6 Summary

CHAPTER 4 RIGGING THEORY AND FORMULATION 57 4.1 Introduction

4.2 Rigging Sling System with Four Lift Points

4.2.1 Using Main or Jib Hook without Spreader Structure

4.2.2 Using Main or Jib Hook with Spreader Structure

4.2.3 Using Main and Jib Hooks at the Same Time

4.3 Rigging Sling System with Six Lift Points

4.3.1 Using Main or Jib Hook with Spreader Frame

4.3.2 Using Main and Jib Hooks without Spreader Structure

4.4 Rigging Sling System with Eight Lift Points

4.4.1 Using Main or Jib Hook with/without Spreader Structure

4.4.2 Using Main and Jib Hooks without Spreader Structure

4.5 Summary

CHAPTER 5 JACKET LIFTING 78 5.1 Introduction

5.2 Vertical Lift of Jackets

5.3 Horizontal Lift of Jackets

5.4 Summary

CHAPTER 6 MODULE LIFTING 88 6.1 Introduction

6.2 Vertical Module Lift and Installation

6.3 Deck Panel Flip-Over

6.4 Summary

CHAPTER 7 FPSO STRUCTURE LIFTING 102 7.1 Introduction

7.2 Lift Procedures and Considerations for FPSO Modules

7.3 Rigging Systems with Multiple Spreader Bars

7.4 Lifting of Lower Turret

7.5 Lifting of Gas Recompression Module

7.6 Lifting of Flare Tower

7.7 Summary

CHAPTER 8 SPECIAL LIFTING FRAME DESIGN 121 8.1 General Discussion

8.2 Effect of the Shift of the Centre of Gravity

8.3 Lift Point Forces

9.2 Finite Element Analysis for Module Lifts

9.2.1 Structural and Material Details

9.2.2 Finite Element Modelling and Analysis

Successful lift installations of heavy offshore structures require comprehensive and detailed studies involving many engineering and geometrical constraints including geometric configuration of the structure, its weight and centre of gravity, member strength, rigging details, lifting crane vessel and other construction constraints These constraints need to be resolved efficiently in order to arrive at a cost-effective solution

This thesis summarises the results of detailed investigations by the author involving actual offshore engineering projects The thesis first reviews the lift criteria adopted in the offshore industry The key practical considerations for selection of appropriate crane barges, rigging components are discussed The algorithms and formulations for rigging systems with various number of lift points are then presented

Practical considerations for module and jacket lifts are investigated For deck panel flip-over operation, the force distribution between two hooks which varies with changing module inclined angle, is calculated consistently Lifting procedures and rigging systems with multiple spreader bars for Floating Production Storage & Offloading (FPSO) modules are also studied Emphasis is given to the design and analysis of lifting unique components to meet the stringent installation requirements

The thesis is reports on a versatile spreader frame design which incorporates a combination of padeye and lifting trunnions Detailed finite element modelling and analysis are conducted to analyze the lifting module and padeye connection It is found that finite element analysis can provide important detailed stress distributions and limits for safety verification of lift components

Nomenclature/Abbreviation

A - Cross Sectional Area

AISC - American Institute Steel Construction

API - American Petroleum Institute

CoG - Centre of Gravity

CRBL - Calculated Rope Breaking Load

CGBL - Calculated Grommet Breaking Load

D - Pin Hole Diameter of Padeye

DAF - Dynamic Amplification Factors

DB - Derrick crane Barge

Dh - Pin Diameter of Shackle

DNV - Det Norske Veritas

E - Modulus of elasticity of Steel

Eb - the sling bend efficiency (reduction) factor

Et - Efficiency of termination method

FEM - Finite Element Method

FEA - Finite Element Analysis

FPSO - Floating Production Storage and Offloading

Fb - Allowable bending stress

Ft - Allowable Tensile stress

Fy - Material Yield stress

Fu - Steel Tensile strength

Fv - Allowable shear Stress

G - Shear Modulus of elasticity of Steel

H4 - height of hook block above module (without spreader structure), or

height of spreader above module (with spreader)

H5 - height of hook block above spreader (with spreader), or,

=0 (without spreader) HSE - Health and Safety Executive

Ix, Iy - Moment of Inertia

Lh - Inside Length of Shackle

Li - length of ith sling

MBL - Minimum Breaking Load

MWS - Marine Warranty Surveyor

Rai - ith Cheek plate Radius of Padeye

Rm - Main plate Radius of Padeye

SACS - Structural Analysis Computer System

SDL - Sling Design Load

SSCVs - Semi-Submersible Crane Vessels

Sx, Sy - Sectional Modulars

SWL - Safe Working Load

T - Static Sling Load

Tci - ith Cheek plate thichness of Padeye

Th - Crane Hook Load

Tm - Main plate thichness of Padeye

Wh - Jaw width of shackle

Wh, Lh - the width and length of hook block

Wm, Lm, Hm - the width, length and height of module, respectively

Wsp, Lsp - width and length of spreader

WLL - Shackle Working Load Limit

d - Sling rope diameter

fb - Actual bending stress

fc - Actual Combined stress

fcog - COG shift factor

ft - Actual Tensile stress

fv - Actual shear Stress

xc, yc - location of the centre of gravity of module in local coordinate system

θi - angle of sling with respect to the horizontal plane

τg - Punching strength

List of Tables

Table 2.1 Lifting Criteria comparison - Single Crane Lift

Table 2.2 Lifting Criteria comparison - Double hook Lift

Table 2.3 Dynamic Amplification Factors

Table 3.1 Some of Heavy Lifting Crane Vessels in the World

Table 3.2 Shackle Side Loading Reduction

For Screw Pin and Safety Shackles Only Table 4.1 Formulations for rigging configurations with four lift points

(using main or jib hook block without spreader) Table 4.2 Formulations for rigging configurations with four lift points

(using main or jib hook block with spreader structure) Table 4.3 Formulations for rigging configurations with four lift points

(using main and jib hook blocks at the same time ) Table 4.4 Formulations for rigging configurations with six lift points

(using main or jib hook block ) Table 4.5 Formulations for rigging configurations with six lift points

(using main and jib hook blocks at the same time) Table 4.6 Formulations for the rigging configurations with eight lift points

(using main or jib hook block at a time ) Table 4.7 Formulations for rigging configurations with eight lift points

(using main and jib hook blocks at the same time ) Table 7.1 Lifting Operation Summary for Laminaria FPSO

Table 7.2 Contingency Actions Plan / Procedure

Table 7.3 Preparation Check List

Table 7.4 Loadout Check List

Table 7.5 Installation Check List

Table 8.1 Weight and COG data

Table 8.2 Total Weight and COG

Table 8.3 Member Analysis Result Summary

Table 9.1 Load factor used for lifting analysis

Table 9.2 Design value of material parameter

Table 9.3 Sample of Member Group Properties

Table 9.4 Sample of SACS Section Properties

Table 9.5 Sample of SACS Plate Group Properties

Table 9.6 Sample of SACS Plate Stiffener Properties

Table 9.7 SACS Loading Summary

Table 9.8 Sample of SACS Loading ID and Description

Table 9.9 Type of Support Constraints and Member Releases

Table 9.10 SACS Load Combinations

Table 9.11 Sample of 75% Lifting Weight Factor

Table 9.12 SACS Combined Load Summation

Table 9.13 Support Reactions

Table 9.14 Spring Reaction

Table 9.15 Sample of SACS Member Stress Listing

Table 9.16 Joint Stress Ratio Listing

Table 9.17 Sling Force Summary

Table 9.18 Dimensions and length of each tubular member

Table 9.19 Maximum stress (MPa) of each case

Table 9.20 Maximum stress (MPa) for braces

Table A.1 Member forces coming out from SACS analysis

List of Figures

Figure 1.1 Thesis Organizations Vs Contents of Study

Figure 2.1 Centre of gravity (COG) shift

Figure 3.1 Lifting Equipment and Components

Figure 3.2 Saipem S7000 SSCV 14000 ton Capacity

Figure 3.3 Sheerleg Crane Vessel – Asian Hercules II : 3200 ton Capacity

Figure 3.4 Derrick Barge Crane – Thialf : 14200 ton Capacity

Figure 3.5 Derrick Lifting Barge DB101: 3150 ton Capacity

Figure 3.6 Samples of Some Shackles (Green Pin and Crosby)

Figure 3.7 Sling Forming & Cross Section

Figure 3.8 Sling Configuration

Figure 3.9 Actual usage of Slings

Figure 3.10 Lift point connections- Padeye and Trunnion

Figure 3.11 Fabricated Lifting Padeye

Figure 3.12 Actual fabricated Lifting Trunnion

Figure 3.13 Details of a Typical Padeye

Figure 4.1 Determination of rigging configuration: tasks, inputs and outputs Figure 4.2 Rigging configuration for four-lift-point sling systems -

using main or jib hook block without spreader Figure 4.3 Rigging configurations for four-lift-point sling systems -

using main or jib hook block and spreaders Figure 4.4a Rigging configuration for four-lift-point sling systems -

using main and jib hook blocks and spreader bars Figure 4.4b Hook load distribution for four-lift-point sling systems -

using both main and jib hook blocks Figure 4.5a Rigging configuration for six-lift-point sling system -

using main or jib hook block with spreader frame

Figure 4.5b Sling tensions for six-lift-point sling system -

using main or jib hook block with spreader frame Figure 4.6a Rigging configuration for six-lift-point sling system -

using both main and jib hook blocks Figure 4.6b Hook load distribution for six-lift-point sling systems -

using both main and jib hook blocks Figure 4.7a Rigging configuration for eight-lift-point sling system -

using main or jib hook block without spreader frame Figure 4.7b Rigging configuration for eight-lift-point sling system -

using main or jib hook block with two parallel spreader bars Figure 4.7c Rigging configuration for eight-lift-point sling system -

using main or jib hook block with spreader frame Figure 4.8a Rigging configuration for eight-lift-point sling system -

using both main and jib hook blocks Figure 4.8b Hook load distribution for eight-lift-point sling systems -

using both main and jib hook blocks Figure 5.1 Vertical Lifting of Jacket

Figure 5.2a Horizontal Lifting of Jacket

Loadout operation at Fabrication Yard (2800ton) Figure 5.2b Horizontal Lifting of Jacket

Dual Crane Lifting a Tripod Jacket (6200 ton) Figure 5.2c Horizontal Lifting of Jacket

Dual lift of a Jacket from transportation barge Figure 5.3 ISO View of lifting horizontal Jacket (3150ton)

Figure 6.1 Deck Panel Stacking in progress

Figure 6.2 Computer Model for Deck Panel Flip-over

Figure 6.3 Deck Panel – 180 Degree Flip Over

Figure 6.4 Module Lifting – Four Sling Arrangement

Figure 6.5 Module Installation – One Lifting Bar Arrangement

Figure 6.6 Module Lifting – Two Bars System

Figure 6.7 Module Lifting – Three Bars System

Figure 6.8 Lifting with a spreader frame

Figure 6.9 Multi-Tier Rigging System

Figure 6.10 Tendem Lift of a Module

Figure 7.1 Rigging arrangement for lifting FPSO modules with spreader bars Figure 7.2 Lifting of Lower Turret (680 ton)

Figure 7.3 Lifting of Upper Turret -

Manifold Deck Structure with Three Spreader Bars Figure 7.4 Lifting of Upper Turret – Gantry Structure

Figure 7.5 Lifting of Swivel Stack – Bottom Assembly

Figure 7.6 Lifting of Gas Recompression Module

Figure 7.7 Upending and Lifting of 92-metre Flare Tower

Figure 8.1 Lifting Frame Details

Figure 9.1 Computer Lifting Model Plot

Figure 9.2 COG Shift of Module during Lifting

Figure 9.3 Jacket Loadout arrangement

Figure 9.4 Upending process of Jacket

Figure 9.5 Jacket positions for the four load cases

Figure 9.6 Configuration of Joint 164

Figure 9.7 Boundary conditions for the FE model

Figure 9.8 Finite element mesh

Figure 9.9 1st-principal stress contour of load case D

Figure 9.10 Local view of Von Mises stress contour of load case D

Figure A.1 Load conditions

Figure A.2 Stress distribution for the braces of load case A

Figure A.3 Stress distribution for the braces of load case B

Figure A.4 Stress distribution for the braces of load case C

Figure A.5 Stress distribution for the braces of load case D

CHAPTER 1 INTRODUCTION

1.1 Background

Heavy lifts are frequently carried out during the fabrication and/or installation of major offshore components and structures, such as welded girder beams, tubular columns, deck panels, sub-assemblies, flares, bridges and completed jackets / modules Without heavy lifting equipment, offshore steel platforms cannot be built effectively

For an offshore platform, the issue of final installation of the completed jacket / topside is considered as early as the conceptual study stage The major determining factor is availability of heavy lift crane vessel around the region Heavier structures can be fabricated if a lager crane vessel is selected for the project Many topside structures are split into several modules instead of an integrated deck structure due to non-availability of sufficient lifting capacity of heavy offshore crane barge in the region or at required time window schedule

Offshore hook-up and commissioning costs are very high as compared to those for the same work performed onshore This has led to the fabrication of very large modules, where the intention is to minimize hook-up associated with connecting modules together offshore

The great advancement of offshore technology during the last 30 years was largely due

to the development of very heavy lift equipment Thirty years ago, a 1000 ton module would be considered a very heavy lift, while the biggest crane barge in the world at that time could hardly lift 2000 tons at the required lifting radius In South East Asia, the biggest crane barge available in the region at the time was only around 600 tons

Nowadays, a semi-submersible derrick barge can lift a structure up to 12,000 tons

In the recent past, a 10,000 ton jacket in the North Sea would have to be launched Using present day equipment, the same jacket can now be lift-installed by a semi-submersible crane barge which has two cranes In most cases, lift-installed jacket is more cost-effective In South East Asia, jackets and decks are getting larger and heavier, with the largest jacket to-date around 10,000 tons and the largest deck around 11,500 tons Single lift installation can be a very attractive cost alternative For platform decommissioning or removal, it may be possible to use a crane barge to pick

up the old deck and old jacket It may be appropriate to mention that the Offshore Industry would not have developed to what it is today without all the heavy lift equipment developed over the last 30 years

For fabrication of offshore structures, the method which was first developed in the United States more than 40 year ago is quite different from other industries Offshore structures are usually first fabricated in small units After fabrication, these will be moved to an open area for assembly Offshore contractors tend to do as much work as possible on the ground to minimize work in the air This method is productivity driven

In fabrication, one can do a much better and faster job on the ground and in a weather protected workshop This fabrication technique means that there are a lot of heavy lifting operations in the yard as compared to typical onshore building construction Before all the sub-units are assembled, these may need to go through many lifting operations, such as, roll up, stacking, flipping, etc Each lift by itself could be more than one thousand tons In this type of fabrication technique, there are a lot of

opportunities for errors Safety and accident prevention should thus be considered in the design stage

For offshore installation, major cost savings can be achieved if the structure can be installed in one piece For integration of topside modules, it can save significant offshore hook-up time For jacket, the cost of fabricating launch trusses can be eliminated A heavier lift requires a larger crane barge It is a very high premium to pay for the rental of a big derrick barge, especially if none is available in the area and it has to be mobilized from elsewhere A large capacity crane is an expensive equipment and crane usage is normally considered as part of the overhead cost for fabrication yards Usually the cost is included in the fabrication tonnage rate It will normally involve fewer people to operate a crane onshore For offshore installation, a crane barge usually has only one big crane, except for larger semi-submersible derrick barges which can accommodate two cranes side-by-side When a derrick crane barge is mobilized for an offshore installation project which includes hook-up and commissioning, it will have 200 to 300 workers/engineers on board The cost is extremely high Some of the semi-submersible derrick barges have accommodation capacity for more than 700 men In addition, the client will also need to pay for mobilization and demobilization costs Depending on location, these costs could be millions of dollars To design a structure to suit the installation contractor is certainly

an excellent way to minimise cost

For a typical project, the offshore portion accounts for around 30% of the total project cost The question that comes to everyone's mind is how to reduce this number and be more competitive One of the solutions is to reduce offshore hook-up time This means

that one should make the lift of a structure as heavy as possible and with few lifts as necessary However, one should be extremely careful in interpreting this statement The project may not be cheap if one has to mobilize a big derrick barge from far away supply base It could also be expensive if it requires two barges to do the lift and the other barge has to be mobilized from elsewhere Making a single heavy lift to minimize hook up time or to eliminate the launch trusses is an excellent idea provided

we have the right equipment at a reasonable price and at the right time

For FPSO module installation, there are normally 20 to 30 heavy lifts The need to design a common rigging system to suit different configurations, weights and centres

of gravity is a challenge to all designers Since it is usually impossible to have a common rigging system for all lifts, the designer needs to minimize the number of rigging changes to reduce the schedule associated with heavy lifts for the planned installation sequence

1.2 Objectives and Scope of Present Study

As indicated in Section 1.1, heavy lifts in major offshore projects are required to be conducted safely and cost-effectively It is always a challenge for a structural design engineer to produce an optimized design for both the lifted structure and lifting rigging system for use with the selected crane barge that will lead to cost savings The author has been involved in some major offshore projects which required considerations for alternative designs and detailed analysis for different structural schemes for heavy lift The author is thus motivated to investigate the inter-related engineering and fabrication issues and to document the findings in this thesis

The two key objectives of the research study are:

• Investigate lifting schemes which can provide cost-effective solutions and safe operations for heavy lift installation of structures, and

• Evaluate selected rigging systems with different spreader and lift point arrangements to provide guidelines for heavy lift design

The scope of the present study can be summarized as follows:

• To study the current design codes for lift design and highlight key considerations for heavy lift;

• To evaluate heavy lift rigging systems which involve different crane barges and lifted structures with associated spreader arrangement and consistent lift point combinations Practical issues involved in actual projects, especially for lift installation of jackets, offshore decks and modules for FPSO (Floating Production Storage and Offloading) vessel will be investigated

• To investigate global structural responses of lifted structures and detailed stress

conditions of the lift point through finite element analyses

• To document the findings on heavy lift in the thesis for future reference by designers and engineers

Lifting equipment and components, including details on crane vessel/barge, slings, shackles and lift points are discussed in Chapter 3 Lift points are the locations where large sling tensions are transmitted to the lifted module structure Lift points should be properly selected to allow sling tensions to smoothly transfer to strong structural members Two common types of lift points which connect rigging systems to module structures are padeyes and trunnions With appropriate factored sling tensions, slings and shackles can be selected from available sling and shackle lists (inventories) or ordered from suppliers It has always been the focus of the design codes to provide consistent safety factors for the lift components within a rigging system for heavy lift

An appropriate rigging system includes available lift points (strong points in the module structure), available slings in inventory, spreader structure (bar or frame) and hook block(s) of the crane barge In actual rigging arrangement, the sling system can involve four, six, eight or more lift points, and spreader bar or frame may be used to

protect the module from significant compressive forces or possible damage Chapter 4 summarises the investigation into the algorithms and formulations to determine the configurations of rigging sling systems, which are affected by the location of lift points, length of slings and geometry of spreader and hook block The hook block(s) involved in a particular rigging system can be one (main or jib hook) or two (both main and jib) at a time Emphasis is placed on the determination of the critical geometrical quantities of the rigging system including the sling angles with respect to the horizontal plane and the distances between the module, spreader structure and hook blocks This chapter also serves as a theoretical basis of the following three chapters which focus on practical issues in lift design of real projects, of which author was involved as project manager or engineer

Chapters 5, 6, and 7 discuss the practical considerations in lift design and operations for jacket, modules and modules for FPSO (Floating Production Storage and Offloading) A special design for a lifting frame is proposed and analyzed in Chapter

8

Finite Element Analysis (FEA) is widely accepted in almost all engineering disciplines A finite element model can represent and analyse a detailed structural component with greater precision than conventional simplified hand calculations This

is because the actual shape, load and constraints, as well as material property can be specified with much greater accuracy than that used in hand calculations Chapter 9 discusses finite element approaches in heavy lift design and analysis Two important lift applications, for living quarter module lifting and padeye connection for heavy lift, are investigated and reported in this chapter

Finally, conclusions and general discussions are given in Chapter 10

Theory and Knowledge

Scopes for Design and Analysis

Rigging System Lift Points Lift Operation

Figure 1.1 Thesis organization and contents of the thesis

CHAPTER 2 LIFTING CRITERIA

2.1 Review of Various Lifting Criteria

There are several lifting criteria and specifications written specifically for offshore heavy lift, including API-RP2A (2000), DNV Marine Operation Part 2 Recommended Practice RP5 (1996), Phillips Petroleum (1989), Heerema (1991), Noble Denton & Associates (NDA) (1996), Health and Safety Executive UK (HSE) (1992) and Shell (1990) Amongst these criteria, some of these are either not updated or strictly for in-house use Only the API, DNV and HSE codes are easily available to the general public The API codes are the oldest and the most well established in the Offshore Industry The HSE recommendation deals with cable laid slings and grommets in detail, but it does not address other lifting system or factors such as dynamic amplification, weight growth, etc This recommendation should be used in conjunction with other codes The DNV code is the most comprehensive and is widely used in the North Sea

For South-East Asia, the most commonly accepted criterion is still the API-RP2A (2000) with a number of modifications to cater for weight inaccuracy etc The original lifting criterion in the API RP2A (2000) was written mostly by engineers working in the Gulf of Mexico The document was intended for those lifts performed in the area Over the years, the code expanded and received acceptance as a worldwide standard Although these criteria are written primarily for offshore lift, they can also be adopted for onshore lift with minor modifications In fact, this has been done for many years

During the performance of the lift, there will be dynamic loads induced by the action

of the waves on the crane vessel and the cargo barge These loads are conventionally allowed for by the application of Dynamic Amplification Factors (DAF) to the static load in the hooks and slings Typical value of DAF, as used at present in relation to Semi-Submersible Crane Vessels (SSCVs), is about 1.10 for slings in offshore operations This will be in addition to any quasi-static changes in the hook and sling loads associated with the load transfer

A second category of dynamic loads exists This is associated with the action of slewing the crane or of starting or stopping the hook as it is being raised or lowered These loads are normally allowed for in the specification of the safe working load (SWL) of the crane It should be recognized that the skill of the crane operator can have a significant effect in reducing these forces Also, but to a lesser extent, his expertise will help to prevent the build-up of dynamic oscillations induced by the waves

Some extensive analyses of the dynamics of the lift have been carried out by using SSCVs In most cases, actual SSCV /module/ cargo barge combinations and rigging geometries with predicted COG (Centre of Gravity) positions have been used The dynamic analyses drew attention to a number of interesting results as follows:

• It was found that increasing the barge draught tended to decrease the DAF in short period sea states

• When the module was on the barge with the slings tensioned, there was a spread of natural periods from 3-8 s Hence, there were both significant dynamic effects and considerable scatter in the results

• The DAFs were generally worse in beam seas (i.e., beam onto the barge)

• The DAFs were less for the heavier modules

• The sling load DAFs were in general larger than the hook load DAFs

• The DAFs were quite low, while the module was freely suspended There would be some advantage in picking a module off the crane vessel's own deck rather than off a cargo barge

The distinction between beam and head sea DAF was sufficiently marked to allow recommended DAFs for head seas to be significantly less than for beam seas

2.2 Practical Considerations for Standard Rigging Design

This section discusses the design requirements for the selection and design of heavy lift rigging as given by Shell

2.2.1 Sling Design Loads (SDL)

Standard 4 point Lifts for the Jacket or Deck

The sling design load (SDL) is based on the factored lift weight, with the individual sling loads being determined from DNV Marine Operation, Part 2 Recommended Practice RP5 Lifting The procedure to be used is summarized below:

a) Distribute the lift weight to the lifting points, adopting the factored lift weight

based on the factors presented in the weight control engineering

b) Increase each individual lifting point load by 10% to account for inaccuracy in

the calculation of the centre of gravity

c) Further increase each individual lifting point load to account for the Dynamic

Amplification Factors given in “Cable Laid and grommets” Guidance Note PM

20, Health and Safety Executive - see Table 2.3

d) Further increase each individual lifting point load by the skew load distribution

factor of 1.25 as recommended in DNV RP5, which primarily accounts for different sling stiffness and lengths than theoretically assumed

e) Calculate the sling load accounting for the angle the sling makes with the

horizontal, including allowance for component tilt This sling angle should not

be below 55° at any point for level lifts

As an example, the SDL for a 500 tonne (factored) lift, evenly distributed to 4 points, offshore, with a 60° sling angle would be:

tonnes

60sin4

25.12.11.1

2.2.2 Shackle Design Loads

These loads may be calculated as for the slings, but can be decreased by the sling factored weight above the shackle point

2.2.3 Lift Point Design Loads

This is primarily to determine adequate rigging sizes For the design of the structure and lift points (padeyes), design loads should be based on the structural analysis requirements

SDL is used to determine the sling, or grommet size The governing design criteria is given in HSE, which sets out the basis for the design criteria listed below and has been developed for heavy lift slings of diameter 100mm and above, where the rope is not usually tested to destruction, and which would normally be required for deck, module and jacket lifts

Individual Slings (Single Slings)

a) At the sling eye,

Minimum Calculated Rope Breaking Load,

D = minimum diameter around which the sling is bent

d = cable laid rope diameter

Note: D should preferably always exceed d to avoid sling load de-rating

b) At the sling termination,

c) At the sling eye,

Grommets sling may be sized as follows:

f) Minimum Calculated Grommet Breaking Load,

×

(2.8)

2.2.4 Shackle Sizing

The sizing of shackles is much simpler than slings and can be based on the following:

Minimum Shackle Working Load Limit, WLL = Sling Design Load, SDL

Note: The WLL is usually quoted by the major shackle Manufacturers, e.g Crosby Group, and should be taken as analogous to the safe working load The WLL is usually based on a ratio of ultimate strength to WLL of not less than 4 for shackles above 200 tonnes WLL Should any Manufacturer quote WLL's based on a lower factor, the WLL should be derated accordingly Higher ratios between ultimate strength and WLL are normally adopted for shackles below 200 tonnes capacity, however in these cases the WLL must not be increased above the Manufacturer's quoted values

Shackle to Shackle Connection

It is often necessary to make up long sling lengths using 2 slings joined together with a shackle/shackle connection, usually by joining pin/pin This is acceptable and no derating of the shackle is required

Side Loads on Shackles

Shackle WLL's are quoted for sling loads in line with the shackle i.e at right angles to the pin Should the lift configuration result in side loading, not perpendicular to the pin shackle, de-rating as recommended by the Manufacturer is necessary To avoid side

loading during the lifting, it is necessary to ensure a close fit-up between the inside of the shackle jaws and the padeye main, or cheek plates The width of the main/cheek plate combination should preferably exceed 0.8 times of the jaw width

In certain circumstances, the shackle available far exceeds the design requirement for the width of the main/cheek plate combination In such cases, this width can be reduced to one half of the jaw width by adopting non-load bearing centralisers between the padeye and shackle jaw to ensure an in-line lift

2.2.5 Tilt during Lifting

Decks and modules

Matched sling pairs should be used to limit the tilt of the module, or deck, to less than 2° in either the transverse or longitudinal direction, or less than 3° in diagonal direction, whichever is less Where, due to excessive eccentricity of the package centroid, the tilt exceeds this value, the lengths of the sling pairs should be altered accordingly

Lifting of the jacket off the barge

Sling lengths for side lifting of the jacket off the barge deck, at the offshore location, should preferably be selected so that the barge deck and the jacket framing interface remain parallel during the lift off This avoids possible damage due to the jacket being

impacted as it is raised off the barge sea-fastenings and it also provides more clearance between the hook and the boom sheave

FPSO Module Lifts

For installation of fabricated modules onto FPSO, in most cases, there will be a specific requirement in which one of the support legs is required to be settled down first This will require the detailed sling calculation to ensure module tilt to the touch-down corner

Other Lifts

For certain operations, specific tilt angles may be required to allow safe lifting/installation as would apply when installing a bridge between two platforms

2.2.6 COG Shift Factor

Possible Centre of Gravity (COG) shift shall be accounted for by applying a COG shift factor (fcog) to all assigned weights in the load combinations fcog is calculated for the support point most sensitive to shift in COG, and applied equally for the whole structure

The COG from the analyses shall be used in the calculations of the COG shift

fcog factor shall be calculated as follows:

05.1

a d

where, as shown in Figure 2.1, a and b are the distances between analysis COG and nearest footing in x and y directions and dx and dy are the distances between the position of maximum shifted COG and analysis COG in x and y direction, respectively

2.3 Summary

Lifting criteria and sling specifications in practice are first reviewed in this chapter These codes include API-RP2A (2000), Det Norske Veritas (DNV) RP-5, Phillips Petroleum, Heerema, Noble Denton & Associates (NDA), HSE and Shell API, DNV and HSE codes are easily available to the general public The API codes are the oldest and the most well established in the offshore industry

Practical considerations for standard rigging design are discussed in detail The

practical and important considerations in rigging design are

• Sling Design Loads (SDL),

• Shackle Design Loads,

• Lift Point Design Loads,

• Shackle Sizing,

• Tilt during Lifting and

• COG Shift Factor

Table 2.2 Lifting Criteria comparison - Double hook Lift

Noble LOC Heerema Chevron BP Amoco Denton

Range of Module Weight >2500 >1000 >2500 >2500 >8000 >2500

1 A Weight Factor (Pre-AFC) 1.125 1.15 1.15 1.25 1.15 1.15

9 I Rigging weight factor 1.03 1.03 1.03 1.03 1.03 1.00

10 J Lift point design factor 1.35 1.00 1.10 1.30 1.25 1.35

11 K Load member design factor 1.15 1.00 1.10 1.15 1.10 1.15

12 L Sling Design = (H x I) 1.42 1.63 1.48 1.68 1.59 1.58

13 M Lift point Design = (H x J) 1.86 1.58 1.58 2.13 1.93 2.13

14 N Load member design = (H x K) 1.59 1.58 1.58 1.88 1.70 1.82

The overall lift point design factor (K) from API RP 2A (2000) is 2.00.

Table 2.1 Lifting Criteria comparison - Single Crane Lift

Denton Range of Module Weight >2500 >2500 >2500 >1000 >2500 >2500 >2500 >2500

11 K Lift point Design = (F x H) 2.19 2.04 1.90 1.99 2.37 2.47 2.16 2.59

12 L Load member design = (F x I) 1.87 1.74 1.90 1.99 2.09 2.18 1.91 2.29

The overall lift point design factor (K) from API RP 2A (2000) is 2.00.

Table 2.3 Dynamic Amplification Factors (DAF)

X Y

CHAPTER 3 HEAVY LIFTING EQUIPMENT AND

COMPONENTS

3.1 Introduction

As shown in Figure 3.1, crane vessel, rigging components including shackles, slings and grommets and lift point connections (including padeyes and trunnions) are basic considerations in heavy lift design

The crane barge is the most expensive piece of equipment and the most important member in lift operation as well The safety of the crane barge during lift operations is the first consideration for both crane barge owner and client The characteristics of the crane barge also constrain the rigging arrangement and necessary reinforcement of the module structure

To safely pick up and install the module is the ultimate objective of carrying out a lift operation The module cannot be damaged or overstressed or distorted during lift Reinforcement is needed when the module is too flexible to withstand the load during lift

The rigging system is the only connection of module to crane vessel The rigging components include slings, spreader structure, shackles, padeyes (or trunnions) and their arrangement The selection or design of a rigging arrangement is dependent on the barge characteristics, module structural pattern and behaviour during lift, and the site parameters

3.2 Heavy Lift Cranes

In the mid 1980s, the available lifting capacity was increased dramatically with the introduction of the latest generation of Semi Submersible Crane Vessels (SSCVs): S7000 (with up to 14000 ton capacity) in Figure 3.2 and DB102 (with up to 12000 ton capacity) Coupled with the upgrading of the Heerema SSCVs, Balder and Hermod, the availability of these vessels has led to development of lifted jacket concepts for medium and deeper water and modules over 10000 ton in weight Table 3.1 lists some

of heavy lifting crane vessels in the world

Nowadays it is generally recognized that the application of large SSCVs, such as McDermott's DB102 (12000 ton capacity) and Saipem’s S7000 (14000 ton capacity), may reduce the costs of offshore installation work significantly, especially for large integrated topsides and liftable jacket structures The dynamic aspects of heavy lift installations are to some extent yet unknown However, the knowledge of these aspects

is essential to properly assess the feasibility and safety of heavy lift operations

Both the lifting capacity and the installed lift weights have increased dramatically during the past two decades For a long time the available offshore crane capacity used

to be well ahead of the demand and did not impose any significant restrictions on the weight and dimensions of lift-installed offshore platforms In recent years, however, the maximum available crane capacity of large SSCV's has become a limiting factor in the design of integrated topsides and liftable jackets

For example, the maximum dimensions of liftable jackets are effectively constrained

by the crane capacity and outreach of large SSCV's, as well as by minimum clearance