Heavy Lift Installation Study of Offshore Structure 2004
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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 ii
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 1.1 1.2 1.3
INTRODUCTION ...................................................................................... 1 Background Objectives and Scope of Present Study Organisation of Thesis
CHAPTER 2 2.1 2.2 2.2.1 2.2.2 2.2.3 2.2.4 2.2.5 2.2.6 2.3
REVIEW OF LIFTING DESIGN CRITERIA .......................................... 10 Review of Various Lifting Criteria Practical Considerations for Standard Rigging Design Sling Design Loads (SDL) Shackle Design Loads Lift Point Design Loads Shackle Sizing Tilt during Lifting COG Shift Factor Summary
CHAPTER 3 3.1 3.2 3.2.1 3.2.2 3.3 3.4 3.4.1 3.4.2 3.4.3 3.5 3.6
HEAVY LIFTING EQUIPMENT AND COMPONENTS....................... 24 Introduction Heavy Lift Cranes Crane Vessel Types Frequently Used Crane Vessels Heavy Lift Shackles Heavy Lift Slings Sling properties Grommets versus Slings Sling and Grommet Properties Lift Points Summary
CHAPTER 4 4.1 4.2 4.2.1 4.2.2 4.2.3 4.3 4.3.1 4.3.2 4.4 4.4.1 4.4.2 4.5
RIGGING THEORY AND FORMULATION ......................................... 57 Introduction Rigging Sling System with Four Lift Points Using Main or Jib Hook without Spreader Structure Using Main or Jib Hook with Spreader Structure Using Main and Jib Hooks at the Same Time Rigging Sling System with Six Lift Points Using Main or Jib Hook with Spreader Frame Using Main and Jib Hooks without Spreader Structure Rigging Sling System with Eight Lift Points Using Main or Jib Hook with/without Spreader Structure Using Main and Jib Hooks without Spreader Structure Summary
i
CHAPTER 5 5.1 5.2 5.3 5.4
JACKET LIFTING.................................................................................... 78 Introduction Vertical Lift of Jackets Horizontal Lift of Jackets Summary
CHAPTER 6 6.1 6.2 6.3 6.4
MODULE LIFTING.................................................................................. 88 Introduction Vertical Module Lift and Installation Deck Panel Flip-Over Summary
CHAPTER 7 7.1 7.2 7.3 7.4 7.5 7.6 7.7
FPSO STRUCTURE LIFTING............................................................... 102 Introduction Lift Procedures and Considerations for FPSO Modules Rigging Systems with Multiple Spreader Bars Lifting of Lower Turret Lifting of Gas Recompression Module Lifting of Flare Tower Summary
CHAPTER 8 8.1 8.2 8.3 8.4 8.5 8.6
SPECIAL LIFTING FRAME DESIGN .................................................. 121 General Discussion Effect of the Shift of the Centre of Gravity Lift Point Forces Padeye Checking Trunnion Checking Summary
CHAPTER 9 FINITE ELEMET ANALYSIS FOR LIFTING DESIGN ....................... 139 9.1 Introduction 9.2 Finite Element Analysis for Module Lifts 9.2.1 Structural and Material Details 9.2.2 Finite Element Modelling and Analysis 9.2.3 Discussions 9.3 Finite Element Analysis for Lifting Padeye Connection 9.3.1 Structural Details 9.3.2 Loading Cases 9.3.3 Finite Element Modelling 9.3.4 Result Analysis 9.4 Summary CHAPTER 10 CONCLUSIONS AND FUTURE WORKS.......................................... 170 10.1 Conclusions 10.2 Recommendation for Future Work BIOBLIOGRAPHY ....................................................................................................... 174 APPENDIX A FEM ANALYSIS FOR JACKET UPENDING PADEYE .................... 181
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Summary 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. iii
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
iv
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
v
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
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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
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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
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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
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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
x
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
xi
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
xii
CHAPTER 1 1.1
INTRODUCTION
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.
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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 semisubmersible 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
2
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
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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.
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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
5
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.
6
1.3
Organisation of Thesis
Figure 1.1 summarises the organisation and contents of the thesis.
Following the introduction, Chapter 1 and Chapter 2 provide a thorough review and discussion of current design codes and standards used in heavy lift. The discussion covers the codes and recommendations from API - RP2A (2000), DNV Marine Operations Part 2 - Recommended Practice RP5 Lifting (1996), Phillips Petroleum (1989), Heerema (1991), Noble Denton & Associates (NDA) (1996), Health and Safety Executive (HSE) (1992) and Shell (1990).
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
7
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.
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Finally, conclusions and general discussions are given in Chapter 10.
Evaluation of Design Criteria
Equipment Selection and Component Design
Rigging Theory and Formulations
(Chapter 2)
(Chapter 3)
(Chapter 4)
Theory and Knowledge
Structures to Be Lifted
Rigging System
Lift Points
Lift Operation
Scopes for Design and Analysis
Jacket Lifting
Lifting Frame Design
(Chapter 5)
(Chapter 8)
Module Lifting
(Chapter 6)
FEM Analysis for Lifting System
(Chapter 9) FPSO Structure Lifting
(Chapter 7) Applications
Figure 1.1
Special Case Considerations
Thesis organization and contents of the thesis
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CHAPTER 2
2.1
LIFTING CRITERIA
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 inhouse 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.
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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.
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•
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.
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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.
13
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:
SDL =
500 × 1.1 × 1.2 × 1.25 = 238.2 tonnes 4 × sin 60°
(2.1)
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.
14
Individual Slings (Single Slings) a)
At the sling eye,
Minimum Calculated Rope Breaking Load,
SDL × 2 .25 × 0 .55 Eb
CRBL =
(2.2)
Note: the 0.55 factor allows for uneven distribution of the sling load to each leg of the sling eye due to friction.
CRBL = the sum of the individual minimum breaking loads of the core and outer unit ropes of the sling multiplied by a 0.85 spinning loss factor (HSE). Eb
= the sling bend efficiency (reduction) factor = 1- 0 . 5
(2.2a)
( D/d ) 0 . 5
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, Minimum CRBL =
SDL ×2 . 25 Et
(2.3)
Where, Et = Efficiency of termination method = 0.75 for hand splices, 0.95 for mechanical, or swaged splices and 1.0 for resin poured sockets.
Doubled slings Where slings are doubled around the shackle and/or the lifting hook of the crane, effectively halving the sling length, the equations given in a), b), are modified as follows: 15
c) At the sling eye,
Minimum CRBL =
SDL × 2 . 25 × 0 . 55 Eb
(2.4)
SDL × 2 . 25 × 0 . 55 Et
(2.5)
SDL × 2 . 25 × 0 . 55 Et
(2.6)
d) At the sling termination,
Minimum CRBL =
e) At the sling bend, Minimum CRBL =
Individual Grommets Grommets sling may be sized as follows:
f) Minimum Calculated Grommet Breaking Load, Minimum CGBL =
SDL × 2 . 25 × 1 . 1 Eb
(2.7)
Doubled Grommets
g) Minimum Calculated Grommet Breaking Load, Minimum CGBL =
SDL × 2 . 25 × 1 . 1 2 xE b
(2.8)
16
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
17
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
18
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 touchdown 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.
19
fcog factor shall be calculated as follows: f cog =
dx + a dy + b × ≥ 1 . 05 b b
(2.9)
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.
20
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.
21
Table 2.1 Lifting Criteria comparison - Single Crane Lift
Range of Module Weight 1 2 3 4 5 6
Noble Denton
DnV
Heerama
Shell
BP
Oxy
Amoco
Chevron
>2500
>2500
>2500
>1000
>2500
>2500
>2500
>2500
A. Weight Factor (Pre-AFC) B. DAF (Slings) C. Skew load factor D. CG Shift factor E. Tilt factor F=AxBxCxDxE
1.125 1.10 1.25 1.05 1.00 1.62
1.10 1.10 1.25 1.00 1.00 1.51
1.15 1.10 1.50 1.00 1.00 1.90
1.15 1.10 1.50 1.05 1.00 1.99
1.15 1.10 1.50 1.00 1.00 1.90
1.15 1.10 1.50 1.00 1.00 1.90
1.15 1.10 1.25 1.05 1.00 1.66
1.15 1.10 1.50 1.00 1.05 1.99
7 G. Rigging weight factor 8 H. Lift point design factor 9 I. Load member design factor
1.03 1.35 1.15
1.03 1.35 1.15
1.03 1.00 1.00
1.03 1.00 1.00
1.03 1.25 1.10
1.03 1.30 1.15
1.03 1.30 1.15
1.03 1.30 1.15
10 J. Sling Design = (F x G) 11 K. Lift point Design = (F x H) 12 L. Load member design = (F x I)
1.67 2.19 1.87
1.56 2.04 1.74
1.95 1.90 1.90
2.05 1.99 1.99
1.95 2.37 2.09
1.95 2.47 2.18
1.71 2.16 1.91
2.05 2.59 2.29
The overall lift point design factor (K) from API RP 2A (2000) is 2.00.
Table 2.2 Lifting Criteria comparison - Double hook Lift
Range of Module Weight 1 2 3 4 5 6 7 8
Noble Denton
LOC
>2500
>1000
A. Weight Factor (Pre-AFC) B. DAF (Slings) C. CG Shift factor D. Tilt factor E. Yaw factor F. Torsion factor G. Skew factor H=AxBxCxDxExFxG
Heerema Chevron
>2500
>2500
BP
Amoco
>8000
>2500
1.125 1.10 1.03 1.03 1.05 1.00 1.00 1.38
1.15 1.10 1.05 1.03 1.05 1.00 1.10 1.58
1.15 1.10 1.05 1.03 1.05 1.00 1.00 1.44
1.25 1.10 1.05 1.03 1.00 1.00 1.10 1.64
1.15 1.10 1.08 1.03 1.00 1.00 1.10 1.55
1.15 1.10 1.05 1.03 1.05 1.10 1.00 1.58
9 I. Rigging weight factor 10 J. Lift point design factor 11 K. Load member design factor
1.03 1.35 1.15
1.03 1.00 1.00
1.03 1.10 1.10
1.03 1.30 1.15
1.03 1.25 1.10
1.00 1.35 1.15
12 L. Sling Design = (H x I) 13 M. Lift point Design = (H x J) 14 N. Load member design = (H x K)
1.42 1.86 1.59
1.63 1.58 1.58
1.48 1.58 1.58
1.68 2.13 1.88
1.59 1.93 1.70
1.58 2.13 1.82
The overall lift point design factor (K) from API RP 2A (2000) is 2.00.
Table 2.3 Dynamic Amplification Factors (DAF) Design (factored) Lift Weight (tonne) DAF Offshore DAF Inshore
1000
1.30 1.15
1.20 1.10
1.10 1.05 22
Y Support location
Analysis COG
dy
Max. COG shift
X
b
Design envelope
a
dx
Figure 2.1 : Centre of Gravity (COG) Shift
23
CHAPTER 3
3.1
HEAVY LIFTING EQUIPMENT AND COMPONENTS
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.
24
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 25
requirements between the jacket legs and the crane booms. In addition it has become apparent that the dynamic aspects of large offshore installations should not be ignored as these may seriously impact the feasibility, safety and schedule of lift operations.
In recognition of these tendencies, many experts has been active from an early stage onwards in promoting the theoretical and practical development of offshore heavy lift analyses as an integral consideration in the design of large liftable offshore structures. The objectives of such analyses are three folds: firstly, given the large weights and sizes of present day integrated topsides and liftable jackets, the extrapolation on the basis of past experience is often not possible and unreliable, and therefore one wants to be reassured beforehand that a proposed lift installation is technically feasible. Secondly, it should be verified that a lift operation can be performed in a safe manner without unacceptable risk to personnel involved or to the structure or the crane vessel. Thirdly, an assessment of the workability (or weather downtime) of a lift operation is required by project management when deciding on the installation time in relation to the fabrication schedule. Moreover it may be of interest to establish whether the workability is determined by factors under the control of the engineering design project team or of the installation contractor.
In an actual project, the choice between an integrated deck or split modules can be difficult.
The split module concept is to separate the integrated deck into smaller
pieces called modules, by splitting the integrated deck in vertical or horizontal directions, which can be easily lifted by smaller crane vessel (with lower cost), but result in higher offshore hook-up cost.
Besides using a larger crane vessel to install
the integrated deck, “Float-over” method is also used for installation of heavy deck without weight limitation. The float-over method will not be discussed in this thesis. 26
3.2.1 Crane Vessel Types In general, the floating crane lift vessel can be classified into two main groups: A) Sheer Leg Crane, like Asian Hercules II in Figure 3.3. Advantages - Less draft for access in-shore shallow water area - Smaller in barge size, easy maneuvers - Economic saving Disadvantages - Non swivel of crane boom - Offshore lifting limitation B) Derrick Crane Barge (or SSCVs) This group can be further classified into two types: Type I – Facilitated with dual crane booms, such as S7000 in Figure 3.2 & Thialf in Figure 3.4. Type II – Single crane boom, like DB30, DB50 & DB101 as shown in Figure 3.5 Advantages of Derrick Barge - Swivel of crane boom, more lifting flexibility - More suitable to offshore lifting operation - Bigger barge size, more stability Disadvantages - Deep draft for not able to access in-shore shallow water area - Big barge size, not easy maneuvers
27
3.2.2 Frequently Used Crane Vessels Sheer Leg Floating Crane – Asian Hercules II Asian Hercules II, as shown in Figure 3.3, is a self-propelled lifting vessel that has a maximum hoisting capacity of 3200 ton. The crane structure comprises mainly an A-frame and jib.
The A-Frame can be skidded along fixed tracks on deck into three different working positions: Position 1
:
Located at 5.2 m from forward of vessel
Position 2
:
Located at 33.0 m from forward of vessel
Position 3
:
Located at 59.0 m from forward of vessel
The general specifications are as below: Length (overall)
:
91.00 m
Breadth moulded
:
43.00 m
Depth moulded
:
8.50 m
Max. /Min draft
:
5.00/2.40 m
Gross tonnage
:
10560 tons
Net tonnage
:
3168 tons
Displacement
:
16500 tons (even keel)
Speed
:
7 knots (12.97 km/hr)
Deck loading
:
15 ton/m²
The crane structure has been designed based on the following criteria: Harbour condition: •
Wind speed
:
20 m/s
•
Current
:
3 Knots
Offshore condition: •
Wind speed
:
20 m/s
•
Current
:
5 Knots
•
Max. sig. wave height
:
Hs = 1m 28
Derrick Barge – Thialf Thialf, as shown in Figure 3.4, is the largest Deepwater Construction Vessel (DCV) operated by Heerema Marine Contractors and is capable of a tandem lift of 14,200 ton. The dual cranes provide for depth reach lowering capability as well as heavy lift capacity to set topsides. This multi-functional dynamic positioned DCV is tailored for the installation of foundations, moorings, SPAR's, Tension Leg Platforms (TLPs) and integrated topsides, as well as pipelines and flowlines. Main dimensions as below, Length overall
201.6m
Length of vessel
165.3m
Breadth
88.4m
Depth to work deck
49.5m
Draught
11.8-31.6m
GRT
136,709 ton
NRT
41,012 ton
Deck load capacity
15 mT/square metre
Total deck load capacity
12,000 mT
Transit speed with 12,000 tons deck load 6 knots at 12.5 metres (43.6 ft) draft. Ballast pump capacity 20,800 cubic metre/hour
PORTSIDE or STARBOARD CRANE Main hoist revolving
7,043 ton up to 31.2 m (102 ft)
Auxiliary hoist
900 ton at 36.0 - 79.2 m (120 - 260 ft)
Whip hoist
198 ton at 41.0 - 129.5 m (134 - 425 ft)
29
Derrick Barge – DB101 DB101, as shown in Figure 3.5, has the following details: Main Dimensions: LOA
146.3 m (480 ft)
Beam
51.9 m (170.3 ft)
Depth
36.6 m (120 ft)
Working Draft
Min. 7.5m (24.6 ft), 23.5m (Max. 77 ft)
Clear Deck:
43,000 sq. ft.
Tonnage:
Gross 52,313, Net 15,693
Cranes Main Crane: IHC E-3500 Boom Length: Main
67.0m (219.75 ft)
Aux.
97.33m (319.33 ft)
Whip
104.2m (341.75 ft)
Hook Capacity: Main 2,430 ton (2,700 stons) @ 66 - 78 ft. (Revolving), 3,150 ton (3,500 stons)
@ 66 - 78 ft. (Tied Back),
540 ton (600 stons)
@ 115 - 279 ft. (Aux.) &
135 ton (150 stons)
@ 350.0 ft. (Whip)
Deck Cranes: 83 ton (92 stons)
@ 25 ft.
30
3.3
Heavy Lift Shackles
Shackles are used in lifting and static systems as removable links to connect wire rope, chain and other fittings. The shackles used most commonly in industry are manufactured by two groups, namely Green Pin and Crosby as shown in Figure 3.6.
The wide range of shackle sizes provides choices to designer, with the working load limit from 0.5 ton to 1200 ton. The shackles are mostly used to connect sling to padeye on the lifting components. However, the shackles can also be utilized to adjust (increase) a particular sling length in a set of slings.
Design The theoretical reserve capability of carbon / alloy shackles should be as a minimum 5 to 1. Known as the DESIGN FACTOR, it is usually computed by dividing the catalog ultimate load by the working load limit. The ultimate load is the average load or force at which the product fails or no longer supports the load. The working load limit is the maximum force which the product is authorized to support in general service. The design factor is generally expressed as a ratio such as 5 to 1. Also important to the design of shackles is the selection of proper steel to support fatigue, ductility and impact properties.
Type & Applications -
Screw pin shackles are mainly used for non-permanent applications.
-
Bolt-type shackles are preferably used for long term or permanent applications and in circumstances where the pin of the shackle may rotate during loading. 31
-
Chain shackles are used mainly on one-leg systems.
-
Anchor shackles on multi-leg systems.
Shackle Material The following are the common materials used for shackle manufacturing: Mild steel, untreated, which is comparable to ISO Grade 3; High tensile steel, untreated or normalized, which is comparable to ISO Grade 4; High tensile steel, quenched and tempered, which is comparable to ISO Grade 6; Alloy steel, quenched and tempered, which is comparable to ISO Grade 8;
All shackles are upset-forged, on special requirement drop-forged shackles can be obtained.
The proper performance of premium shackles depends on good manufacturing techniques that include proper forging and accurate machining. Closed die forging of shackles assures clear lettering, superior grain flow, and consistent dimensional accuracy. A closed die forged bow allows for an increased cross section that, when coupled with quench and tempering, enhances strength and ductility. Closed forging combined with close tolerance pin hole assures good fatigue life, particularly with screw pin shackle.
Quench and tempering assures the uniformity of performance and maximizes the properties of the steel. This means that each shackle meets its rated strength and has required ductility, toughness, impact and fatigue properties. The job requirements demand this reliability and consistency.
32
The quench and tempering process develops a tough material that reduces the risk of brittle, catastrophic failure. The shackle bow will deform if overloading occurs, giving warning before ultimate failure.
The proper application of shackles requires that the correct type and size of shackle be used. The shackle's working load limit, its size, a traceability code and the manufacturer’s name should be clearly and boldly marked in the bow. Traceability of the material chemistry and properties is essential for confidence in the product. Material chemistry should be independently verified prior to manufacturing.
For example, a Green Pin standard shackle has following technical indications: WLL 125 T - Working Load Limit 125 tons Bs
- the manufacturer's symbol
H
- Traceability code
6
- Grade
CE
- Conformity European.
Documentation Shackles can be supplied from vendors with the following documents: •
a work certificate;
•
a certificate of basic raw material;
•
an inspection certificate DIN 50049 - 3.1.B or 3.1.C.;
•
a proof-load test certificate;
•
a certificate with the actual breaking load found on the tested samples;
•
a test report of Magnetic Particle Examination and
•
a test report of Ultrasonic Examination. 33
Usage The correct type of shackle should be selected for a particular application. The Working Load Limit (WLL) should be applied in a straight pull and overloads must not be made. Side-loads should be avoided as the products are not designed for this purpose.
If side-loads are required, as shown in Table 3.2, shackles should be fitted to the load in a manner that allows the shackle body to take the load in a true line along its centreline; and not in such a way that bending loads are induced, other than those for which the shackle is designed.
When using shackles in conjunction with multi-leg slings, due consideration should be given to the effect of the angle between the legs of the sling. As the angle increases so does the load in the sling leg and consequently in any shackle attached to that leg.
To avoid eccentric loading of the shackle, a loose spacer may be used on either end of the shackle pin or a shackle with a smaller jaw width should be used. Welding washers or spacers to the inside faces of shackles or closing shackle jaws shall not be used to reduce the width between the shackle jaws, as this will have adverse effects on the mechanical properties of shackles. Extreme circumstances or shock loadings must be well taken into account on selecting the products.
The applications, where the shackle pin can rotate and possibly be unscrewed due to movement (e.g. of the load or rope), must be avoided.
34
Finished shackles may not be heat-treated because this may affect the Working Load Limit and the material structure.
Shackles in use should be subject to thorough examination by a competent person at least every 6 months. In practice, re-certificate is carried out by mechanical Professional Engineer. This is necessary because the product in use may be affected by wear, misuse, overloading with consequent deformation of the steel structure.
Shackles should be inspected before use to ensure that: •
the body of the shackle and pin are both identifiable as being of the same quality grade;
•
all markings are readable;
•
the pin is of the correct type;
•
the threads of the pin and the body are undamaged;
•
the body and pin are not distorted and unduly worn;
•
the body and pin are free from nicks, gouges and cracks.
Also, the pin should be correctly screwed into the shackle eye, i.e. tighten finger tight, then lock using a small tommy bar or suitable tool so that the collar of the pin is fully seated on the shackle eye. The pin needs to be the correct length so that it penetrates the full depth of the screwed eye and allows the collar of the pin to bed on the surface of the shackle eye. Incorrect seating of the pin may be due to a bent pin, too tight fitting thread or misalignment of pin holes.
35
It is important not to replace a shackle pin with a bolt, other than one designed for the purpose, as it may not be suitable for the loads imposed.
It is important in the case of shackles fitted with a bolt, nut and split cotter pin that the length of the plain portion of the bolt is such that the nut will jam on the inner end of the thread or on the eyes of the shackle, and that the rivet on the bolt is cross drilled for a split cotter pin. A bolt type shackle in operation without using a split cotter pin should not be used.
36
3.4
Heavy Lift Slings
As an important lifting component, the sling is limited in design not only by the lifted weight and also by the factors listed below: •
Being pre-rigged on the structure;
•
Diameter - the largest slings to date have been about 400 mm, though currently available machinery can build slings 475 mm in diameter;
•
Weight of the slings - the sling making machinery has an upper weight limit, about 80 ton, for any individual sling. Thus large diameter slings are restricted by the length in which they can be manufactured;
•
An installation contractor may wish to lay the slings down on the module after lifting so that they can be removed individually. This is to avoid the slings moving towards each other, hence limiting possible damage on the module.
In actual lift projects, sling retention devices (keepers plates) must be fitted to the trunnions to keep the slings in place during transportation and sling connection. Slings need to be tied down to the lay-down platform using soft ropes, to prevent movement during transportation. For a module, sling slashing may be required to prevent damage to module equipment.
3.4.1 Sling properties
The cable laid slings and grommets are most commonly used in heavy lift operation. The term "cable laid" indicates wire rope constructed from six smaller diameter ropes laid up in a helical manner about a single core rope. A hand-spliced soft eye is placed at each end of the rope section to form a "cable laid sling". The term "grommet" refers 37
to a continuous sling made up in the form of a rubber band. Eyes are formed by securing the two parts of the grommet together with seizing to produce a loop at each end.
A common trait of these systems is that they require an element with high tensile stiffness and relatively low bending stiffness. Selection rules for wire ropes are rooted in history, of which the purpose or derivation is not easily traced. Most implementations are the result of the design engineers' biases and experiences, based on many years of practical use of cables and wire ropes.
The task of designing a wire-rope-based system follows the basic description of the design process. In addition, each step may be decomposed into several inter-related subtasks. For instance, system definition subtasks include the selection of a drum, selection of the appropriate number and sizes of sheaves, selection of wire rope end fittings, and design of the wire rope itself.
The design of a typical wire rope involves the selection of the following geometrical and material parameters as shown in Figure 3.7. •
Numbers of wire lays in each strand, wires in each wire lay, and strand lays in the rope
•
Diameters of the individual wires and strands as well as the total rope diameter
•
Lay lengths (pitches) of the wire lays within the strands and the strands within the rope
•
Configuration of the strands and total rope (i.e., lay directions, etc.)
•
Individual wire cross sections
38
•
Core type
•
Wire and core materials (including treatment, etc.).
Conventional wire rope slings are limited to diameters of about 4 inches. Braided slings and several other types of multipart slings have also been used for heavy lifts, but cable laid slings have proven their superiority and are presently the standard for the industry. The generally recognized authority for the design and construction of cable laid slings and grommets is Guidance Note PM 20, “Cable Laid Slings and Grommets” issued by U.K. Health and Safety Executive. The guidance note was prepared by a working group of experts primarily from the offshore construction and wire rope manufacturing industries. The note covers construction procedures and prescribes how safe working loads are to be established.
One of the problems encountered in the construction of cable laid or any large diameter slings is the maintenance of an acceptable tolerance on differential length. Three factors involved in the minimization of the tolerances are: •
Control of the production of the unit ropes from which the slings are constructed.
•
Accurate measurement and marking of rope during construction.
•
Mechanical control of splicing tensions to achieve a balanced termination.
Some measurable length differential will be present at the end of construction and the magnitude can be expected to increase due to differential permanent elongation under load. A reasonable tolerance on length for the life of the slings is ±0.25 percent of the length. The length differential for a matched set of 100 foot slings constructed under ideal conditions may be as much as 6 inches.
39
Heavy lift slings are made of machine spun cable laid rope and usually terminated by hand made eyes and splices. The eye and splice sections are softer than the cable section. These are up to 40 rope diameters in length and significantly affect the overall sling characteristics. Sling splices can slip during load take up and some allowance should be made in the sling load calculations for this effect. The characteristics become stiffer and more linear with repeated use.
Grommets are made out of a single length of wire rope which is spun into a continuous multi-strand loop of wire. They generally have softer characteristics than slings of similar minimum breaking load (MBL). The single grommet is softer than the equivalent double sling with two spliced eyes. No slippage allowance is necessary in grommet design.
3.4.2. Grommets versus Slings
In one major offshore lift project, dual crane lifts with doubled grommets were used to provide four parts per lifting point. These proved to be lighter as a percentage of the module weight than doubled slings and resulted in rigging weights approximating to 2% of the lift weight. For the single crane lifts doubled slings were used and resulted in rigging weights between 3 and 3.5% of the lifted weight.
The grommet lengths were adjusted to permit the centre of lift to be matched to the centre of gravity. This was achieved by means of intentionally scheduled late manufacture of a pair of grommets. However, this resulted in potential for late delivery
40
of rigging and therefore careful integration of grommet and module fabrication scheduling was required. In spite of the rigging being a low percentage of overall module weight, the individual rigging components still weighed approximately 50 ton each and rigging installation in the module fabrication yard, at the lift height required, presented some difficulty and necessitated the preparation of detailed handling procedures.
An allowance should be made in the design for differential tension across the hook or padeye. This is due to friction preventing the full load equalization in the rope or spliced eyes. The tension ratio between the two parts is usually taken as 45:55. This corresponds to a coefficient of friction of 6.4% around a 180 degree bend.
Slings apply a torque to the crane hook and lifting padeyes. This causes a 2% increase in sling loads for single hook lifts, increasing to 4% in long and slender modules. Sling torque has a negligibly small effect on sling loads in double hook lifts.
3.4.3. Sling and Grommet Properties A.
Properties of rope and splice
A1.
New rope (1st load cycle) T =
Cr × Lo d mr
nr
(3.1)
Where, T = Load in % MBL Lo = Extension in % of original length d = Sling rope diameter (mm) Cr = 132.8 ± 25% nr = 1.75 mr = 0.3807 41
Used rope (2nd cycle onwards) Elastic modulus E = 2533 ± 25% kg/mm² A2.
New eye/splice (1st load cycle) T=
Ce × Lo ne d me
(3.2)
Where, Ce = 16.48 ± 30% ne = 3.5 me = 0.6286 Used eye/splice (2nd load cycle onwards) Elastic modulus E = 1357 ± 25% kg/mm²
B.
Grommet properties
These properties are for a simple continuous two-part grommet, i.e. having two ropes connecting the padeye to the hook. B1.
New grommet (1st load cycle)
T=
C g × Lo ng d mg
(3.3)
Where, T = Load in % MBL of tow ropes Lo = Extension in % of original length between hook and padeye d = grommet rope diameter (mm) Cg = 69.0 ± 25% ng = 1.80 mg = 0.4618
42
3.5
Lift Points
Lift points are the locations where intensive sling tensions meet with module structure. Lift points should be properly designed to allow sling tensions smoothly transfer to other strong structural members. Depending on the factored lift loads, slings and shackles can be selected from available sling and shackle lists (inventories) or ordered from suppliers. How to get safe enough and yet reasonably factored lift point loads has been the focus of all industry design codes. There are basically two types of lift points which connect rigging systems to module structures: Padeye and trunnion, as shown in Figure 3.10.
Padeyes are important lift components, which link module structure and shackles. In lift arrangement, a shackle locks up a padeye by inserting shackle pin through padeye hole, while the shackle bow connects to a sling.
The design of padeye requires special attention and detailing. It is recommended that padeyes to be designed with the main connections in shear rather than in tension. High tension loads in the thickness direction of steel material should be avoided. Padeyes should be also dimensioned to properly fit up with shackles and avoid uneven contact areas, which is usually resolved by using cheek plate and spacer plates.
Although the padeyes themselves are usually adequately designed for vertical and horizontal loads, the structure to which the padeyes connect must be able to accept and transmit the total vertical and horizontal forces back into structure.
Trunnions are normally used to lift very heavy modules. The advantages of trunnions
43
are their simplicity in rigging connections where slings or grommets are looped over the braces without the use of shackles, and the freedom for a sling or a grommet to rotate around the trunnion brace. The latter may be beneficial for module upending, overturning or rotating.
Trunnions can be either cast or fabricated. Ideally the diameter of the trunnion should be four times the sling diameter. The use of cast trunnions means that early design is required because castings have a long lead time. The fabricated trunnions are frequently used in the offshore industry.
44
3.6
Summary
Crane barges, rigging components including shackles, slings and grommets, and lift point connections (including padeyes and trunnions) are discussed based on practical considerations in heavy lift design.
The barge is the most expensive piece of equipment and the most important member in lift operation as well. The safety of the barge during a lift operation is the first consideration for both barge owner and client. The characteristics of the barge also constrain the rigging arrangement and necessary reinforcement of the module structure.
The rigging system is the only connection for the module to the crane barge. 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.
Sling retention devices (keepers plates) must be fitted to the trunnions to keep the slings in place during transportation and sling connection. Slings need to be lashed down to the lay-down platform using soft ropes, to prevent movement during transportation. For a module, sling slashing may be required to prevent damage to module equipment.
45
Table 3.1 Some of Heavy Lifting Crane Vessels in the World
Contractor
Crane Vessel Name
Nominal Lift Capacity (Ton)
Vessel Type
Location
Asian Hercules II
Asian Lift
3200
Sheer Leg
Singapore
Asian Hercules
Asian lift
1600
Sheer Leg
Singapore
Semco L1501
Semco Salvage
1500
Sheer Leg
Singapore
Crane 5000
McDermott
4500
Sheer Leg
Gulf of Mexico
DB 50
McDermott
3960
Derrick
Gulf of Mexico
DB 101
McDermott
3150
Derrick
Gulf of Mexico
DB 102
McDermott
12000
Derrick
Gulf of Mexico
DB 30
McDermott
2790
Derrick
South Asia
DB 27
McDermott
2160
Derrick
Arabian Gulf
Muashi-3600
Fukada Salvage & Marine
3600
Suruga-2200
Fukada
2200
Derrick
Japan
Kongo
Fukada
2050
Derrick
Hiroshima,Japan
Rambiz 3000
-
3300
Derrick
Europe
Samsung 3000
Samsung Heavy Industry
3000
Thialf
Heerema
14200
Derrick
North Sea
Hermod
Heerema
8100
Derrick
Gulf of Mexico
Balder
Heerema
5670
Derrick
Gulf of Mexico
M7000
Saipem
14000
Derrick
North Sea
Castoro Otto
Saipem
2160
Derrick
W. Hemisphere
S 3000
Saipem
2250
Derrick
South Asia
Kurushio
Nippon Steel
2250
Derrick
South Asia
HD2500
Hyundai
2250
Derrick
Arabian Gulf
Stanislav Yudin
Seaway Heavy Lift
2250
Derrick
Dubai
HLS 2000
NPCC
2160
Derrick
Arabian Gulf.
Lan Jiang Hao
COOEC
3420
Derrick
China
Da Li Hao
Shanghai Salvage
2500
Derrick
China
Nian Tian Long
Guangzhou Salvage
1500
Derrick
China
Derrick
Derrick
Tokyo Bay
Korea
46
Table 3.2 Shackle Side Loading Reduction For Screw Pin and Safety Shackles Only Angle of Side Load from Vertical In-Use of Shackle 0° In-line* 45° from In-line 90° from In-line
Adjusted Working Load Limit 100% of Rated Working Load Limit 70% of Rated Working Load Limit
50% of Rated Working Load Limit * In-Line load is applied vertical to the pin.
Spreader bar
Rigging
Lift point
Module
Site
Crane Vessel
Figure 3.1
Lifting Equipment and Components
47
Figure 3.2 Saipem S7000 SSCV with maximum of 14000 ton Capacity
48
Figure 3.3 Capacity
Sheerleg Crane Vessel – Asian Herlues II : with maximum of 3200 ton
49
Figure 3.4
Derrick Barge Crane – Thialf : 14200 ton Capacity
50
Figure 3.5
Derrick Lifting Barge DB101: 3150 ton Capacity
51
Figure 3.6
Samples of Some Shackles (GreenPin and Crosby) 52
Figure 3.7 Sling Forming & Cross Section
53
Figure 3.8
Figure 3.9 Left:
Sling Configuration
Actual Usage of Slings
Sling being attached to Crane hook
Right: Sling being laid on platform and ready to sail for offshore hook-up
54
Sling Plate Trunnion
Shackle
Padeye
Figure 3.10
Pipe Trunnion
Lift point connections- Padeye and Trunnion
55
Figure 3.11
Fabricated Lifting Padeye
Figure 3.12 Left:
Actual fabricated Lifting Trunnion
Plate Type – Trunnion joining to Centre plate
Right: Tubular Type – Trunnion joining to Centre Tubular
Figure 3.13
Details of A Typical Padeye 56
CHAPTER 4 4.1.
RIGGING THEORY AND FORMULATION
Introduction
The design of rigging sling systems involves the available lift points (strong points in module), the available slings in inventory, the spreader structure and the hook blocks of the barge. In other words, all the components from the lift points at the module to the hook block should be considered. In actual rigging arrangement, the sling system can be with four, six, eight or more lift points, and spreader bar or frame may be used to protect the module from extensive compressive forces or any possible clashing/damage to other equipment. Rigging sling systems with more than eight lift points are used to lift large and flexible modules. It can be seen that the configuration of the rigging sling system determines the forces in all the components of the rigging system including padeyes, shackles, slings and spreader structures (if any), and thus affects the selection and design of these members. Moreover, the configuration of the rigging sling system is one of the most critical factors that should be considered in the analysis of stresses in the module and in the determination of the barge gesture including the angles of crane boom and jib.
The objective of this section is, as shown in Figure 4.1, to investigate the algorithms and formulations to determine the configurations of rigging sling systems, which are affected by the location of lift points, length of rigging 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 hooks) at a time. Emphasis is placed on the determination of the critical geometrical quantities of the rigging sling system including the sling angles with respect to the horizontal plane and the distances between the module, spreader structure and hook blocks. 57
Accurate sling tensions can be computed using the methods presented in Chapters 2 and 3. Some practical methods, however, are also presented in this chapter due to the specific nature of individual problems.
In this chapter, useful formulations and procedures for determining sling angles, hook height above module, spreader height above module, and hook height above spreader are derived based on the selected slings from the sling inventory and the geometrical dimensions of spreader structures. The established formulations can also be used to design new slings and spreaders by applying them appropriately.
For the convenience of discussion, the geometrical parameters are defined as follows: 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)
Li -
length of ith sling,
θi -
angle of sling with respect to the horizontal plane,
(xc, yc) - location of the centre of gravity of module in local coordinate system, Wm, Lm, Hm - the width, length and height of module, respectively, Wh, Lh - the width and length of hook block, and Wsp, Lsp - width and length of spreader.
The superscripts (B) and (J) used in this chapter denote parameters related to the boom (main frame) and jib hook, respectively, while the subscripts m and h are related to
58
module and hook. For example, L(B) and L(J) represent the lengths of boom and jib, while Wh and Wm the widths of hook block and module, respectively.
4.2
Rigging Sling System with Four Lift Points
Rigging sling systems with four lift points are frequently used in offshore and marine module installation where lift points can be located at the legs of the jacket or strong structural components.
4.2.1. Using Main or Jib Hook without Spreader Structure Three typical rigging arrangements in terms of the hook position with respect to the Centre of Gravity (CG) are shown in Figure 4.2. These are configurations with (1) four-equal slings, (2) two-matched-pair slings and (3) four-unequal slings. The formulations for the geometrical parameters of the three rigging configurations are summarised in Table 4.1.
4.2.2. Using Main or Jib Hook with Spreader Structure As mentioned in the above section, spreaders are used to avoid extensive compressive forces in modules to protect modules or equipment from damage. In actual applications, a spreader structure can consist of simple spreader bar or a spreader frame. Figure 4.3 shows three typical rigging arrangements with spreader structures: (i) one spreader bar, (ii) two parallel spreader bars, and (iii) a spreader frame. To simplify the discussion, module geometry, lift points, spreaders are assumed to be symmetric about geometrical axes.
The formulations for the geometrical parameters of the three rigging configurations are 59
summarised in Table 4.2, where θ and γ are the angles of the sling below and above the spreader with respect to the horizontal plane, respectively, φ is the angle between the real plane of the slings and the horizontal plane, Dsp is the distance between two spreader bars and L′ and L" are the lengths of the slings below and above the spreader, respectively.
4.2.3 Using Main and Jib Hooks at the Same Time In the case of using both main and jib hook blocks at the same time as shown in Figure 4.4a, the distance between the main and jib hook is normally made equal to the distance Dx between lift points, and the real planes of the main hook slings and jib hook slings are thus perpendicular to the horizontal plane. The formulations to determine the geometrical parameters of rigging configurations are given in Table 4.3. The loads taken by the main hook and jib hook are dependent on the lift points and CG positions as shown in Figure 4.4b.
4.3
Rigging Sling System with Six Lift Points
Due to the constraint of structural patterns of modules, rigging systems with six lift points may be used in certain cases. Modules with six lift points can be lifted up by single (main or jib) hook block or by two (both main and jib) hook blocks due to various practical considerations.
4.3.1 Using Main or Jib Hook with Spreader Frame If only the main or jib hook block is used, a spreader structure is normally needed to accommodate the force distribution in the slings above and below it. Figure 4.5a shows a typical rigging arrangement for using a single hook block to lift up a module with six
60
lift points, where a planar frame is used to protect the module from intensive compression and to effectively transfer the forces from the lower slings to the upper slings. The span of the spreader frame can be designed equal to the distance Dx between lift points to minimise the horizontal compressive forces (in the x-direction) on the module. The formulations for determining the geometrical parameters of this rigging configuration are summarised in Table 4.4.
Attention should be paid to the tensions of individual slings as well as the forces at individual lift points, as the forces may be significantly unevenly distributed depending on the global stiffness of the module structure and sling system, as discussed in Chapter 2. It is known from Chapter 2 that the sling tensions are evenly distributed if the module is very stiff compared to the slings. However, if the module structure is very flexible, or, in other words, the slings are comparatively very stiff, the tensions of the two middle slings can be much larger than the tensions of other slings. In this case, two big slings are required for the middle positions. Since the sling tensions are transferred to the lift points, the corresponding lift point loads at the two middle positions are also much larger than those at the two ends. Thus, bigger shackles and stronger padeyes or trunnions should be designed for the lift points at the middle locations. Furthermore, as the forces finally find their paths in the structure, local overstressing and excessive deformation of the module may occur since the forces during the lifting operation may be significantly different from the actual working loads assumed during the design of the module.
To obtain accurate sling tensions and structural performance during the lift, a comprehensive structural analysis, as proposed in Chapter 3 should be conducted on the rigging configuration including the actual stiffness of the slings and the module. 61
The design of the spreader frame should be also based on the consistent load condition of the rigging system.
4.3.2 Using Main and Jib Hooks without Spreader Structure If both the main and jib hook blocks are used at the same time as shown in Figure 4.6a, the distance between the main and jib hook is normally designed to be equal to the distance Dx between lift points, as discussed in the previous section. The formulations for determining the geometrical parameters of this rigging configuration are summarised in Table 4.5. Figure 4.6b gives the loads taken by the main and jib hooks which depend on the lift points and CoG positions.
If two doubled slings, instead of four single slings, are used for those slings at the main hook block, the formulations provided in Table 4.5 are still valid except that the length of the slings L(B) should be changed to half the length of the corresponding doubled slings.
4.4
Rigging Sling System with Eight Lift Points
Rigging sling systems with eight lift points are often used in shipbuilding and offshore structural installations. The lift points in a ship block may be the cross points of bulkheads or strong points at hull structures. In this section, some practical rigging configurations are discussed. In the case of doubled slings, the force split ratio of the two arms of a doubled sling (α), as discussed in Chapters 3, should be applied appropriately.
62
4.4.1 Using Main or Jib Hook with/without Spreader Structure Figure 4.7a shows an eight-point rigging sling configuration without any spreader structure where four doubled slings with the same length L are used. Figures 4.7b and 4.7c show rigging sling systems with two parallel spreader bars and a spreader frame, and the lengths of the doubled slings below the spreader structures and single sling above the spreader structures are denoted Ld and Ls, respectively.
The formulations for determining the geometrical parameters of the rigging configurations are summarised in Table 4.6.
4.4.2 Using Main and Jib Hooks without Spreader Structure As will be discussed in Sections 6.2.3 and 6.3.2, when both the main and jib hook blocks are used at the same time as shown in Figure 4.8a, the distance between the main and jib hook is normally made equal to the distance Dx between the lift points. The formulations for determining the geometrical parameters of this rigging configuration are summarised in Table 4.7. Figure 4.8b gives the loads taken by the main and jib hooks, which depend on the locations of lift points and CoG positions.
4.5
Summary
The determination of the configuration of rigging sling systems is an important step in heavy lift design, since the configuration affects the tensions in rigging slings, loads in lift points and forces in shackles and link plates, and thus affects the design of those lift components. Furthermore, it also affects the selection of the boom and jib angles of a barge to fulfil lift requirements.
63
The geometrical configurations of rigging sling systems are dependent on the location of lift points, available rigging slings and the details of the spreader geometry and hook blocks. The algorithms and formulations for the determination of configurations of rigging sling systems with four, six and eight lift points, which cover the majority of heavy lifts in offshore and marine industries, are presented in this chapter. The sling arrangements can be with single slings, doubled slings or doubled make-up slings. The type of spreader structures included in the discussion can be a simple spreader bar, two parallel spreader bars or a spreader frame. The hook block(s) involved in a particular rigging system can be one (main or jib hook) or two (both main and jib hooks) at a time. Emphasis is placed on the determination of the critical geometrical quantities of the rigging sling systems. These include the sling angles with respect to the horizontal plane, hook height above the module or spreader structure, and spreader structure above lift points. The algorithms and formulations presented in this chapter can be applied both for selecting slings from the inventory and for ordering new slings.
64
Table 4.1 Formulations for rigging configurations with four lift points (using main or jib hook block without spreader)
Type of
Parameters and formulations
Approximate
rigging
tilt angle
configuration four-equal slings L 1 = L2 = L3 =L4 2-matchedpair slings L1 = L 2 , L3 =L4
four-unequal
θ1=θ2=θ3=θ4 = cos ( −1
( D x / 2 − Wh / 2) 2 + (D y / 2 − L h / 2) 2 L1
tg −1 (
(x c ) 2 + (y c ) 2 H4
H 4 = ( L 1 ) 2 − (D x / 2 − Wh / 2) 2 − (D y / 2 − L h / 2)
θ1=θ2= cos −1 ( θ3=θ4= cos −1 (
( D x / 2 − Wh / 2 − x c ) 2 + (D y / 2 − L h / 2) 2 L1 ( D x / 2 − W h / 2 + x c ) 2 + ( D y / 2 − L h / 2) 2 L3
γ ≈ tg −1 (
yc ) H4
H 4 = ( L 1 ) 2 − (D x / 2 − Wh / 2 − x c ) 2 − ( D y / 2 − L h / 2) 2
θi= cos −1 (
( D x / 2 − Wh / 2 + x i ) 2 + ( D y / 2 − L h / 2 + y i ) 2 Li
slings
(i=1,2,3,4)
L1≠L2≠
where x 1 = x 2 = x c , x 3 = x 4 = − x c
L3≠L4
γ≈
γ≈0
y1 = y 4 = − y c , x 2 = x 3 = y c H 4 = (L1 ) 2 − ( D x / 2 − Wh / 2 − x c ) 2 − (D y / 2 − L h / 2 + y c ) 2
65
)
Table 4.2 Formulations for rigging configurations with four lift points (using main or jib hook block with spreader structure)
Type of rigging configuration
Parameters and formulations
θ = cos −1 (
One spreader bar γ = cos −1 (
φ = cos −1 (
Two parallel spreader bars
( D x / 2) 2 + (D y / 2 − L sp / 2) 2 L′
( L sp / 2 − L h / 2) 2 L ′′
)
H 4 = ( L ′) 2 − (D x / 2) 2 − (D y / 2 − L sp / 2) 2
) H 5 = (L ′′) 2 − (L sp / 2 − L h / 2) 2 (D y − L h ) / 2
( L ′) − ( D x / 2 − Wsp / 2) 2 + ( L ′′) 2 − ( Wsp / 2 − Wh / 2) 2 2
H 4 = ( L ′) 2 − (D x / 2 − Wsp / 2) 2 sin(φ)
)
H 5 = (L ′′) 2 − ( Wsp / 2 − Wh / 2) 2 sin(φ)
D sp = D x − 2 ( L ′) 2 − (D x / 2 − Wsp / 2) 2 cos(φ) −1
θ = cos ( γ = cos −1 (
θ = cos −1 (
Spreader frame
( D x / 2 − Wsp / 2) 2 + (D y / 2 − D sp / 2) 2 L′ ( Wsp / 2 − Wh / 2) 2 + (D sp / 2 − L h / 2) 2 L ′′ ( D x / 2 − Wsp / 2) 2 + ( D y / 2 − L sp / 2) 2 L′
) )
)
H 4 = (L ′) 2 − ( D x / 2 − Wsp / 2) 2 − ( D y / 2 − L sp / 2) 2
γ = cos −1 (
( Wsp / 2 − Wh / 2) 2 + (L sp / 2 − L h / 2) 2 L ′′
)
H 5 = (L ′′) 2 − ( Wsp / 2 − Wh / 2) 2 − ( L sp / 2 − L h / 2) 2
66
Table 4.3 Formulations for rigging configurations with four lift points (using main and jib hook blocks at the same time )
Type of rigging configuration
Without Spreader bars
Parameters and formulations
θ( B) = cos −1 (
D (yB) − L(hB) 2L
)
H (4B) = L2 − (D (yB) / 2 − L(hB) / 2) 2
(similar for θ ( J ) and H (4J ) )
With spreader bars
θ ( B) = cos −1 (
D (yB) − L(spB) ) 2 L′
H (4B) = (L′) 2 − (D (yB) / 2 − L(spB) / 2) 2
γ ( B) = cos −1 (
L(spB) − L(hB) ) 2L′′
H 5( B) = (L′′) 2 − (L(spB) / 2 − L(hB) / 2) 2
(similar for θ ( J ) , H (4J ) , γ (J) and H 5(J) )
Table 4.4 Formulations for rigging configurations with six lift points (using main or jib hook block )
Parameters and formulations
Type of rigging configuration
With spreader frame
θ = cos −1 (
γ = cos −1 (
Dy 2L ′
H 4 = (L ′) 2 − (D (yB) / 2) 2
)
Wsp − Wh 2L ′′
)
H 5 = (L ′′) 2 − ( Wsp / 2 − Wh / 2) 2
67
Table 4.5 Formulations for rigging configurations with six lift points (using main and jib hook blocks at the same time) Type of rigging configuration
Parameters and formulations
θ
Without
( B)
−1
= cos (
L( B)
)
H (4B) = [L( B) ]2 − [D (xB) / 2]2 − [D (yB) / 2 + L(hB) ]2
spreader frame
[D (xB) / 2]2 + [D (yB) / 2 − L(hB) / 2]2
θ ( J ) = cos −1 (
D (yJ ) − L(hJ ) 2L( J )
)
H (4J ) = [L( J ) ]2 − [D (yJ ) / 2 + L(hJ ) ]2
68
Table 4.6 Formulations for the rigging configurations with eight lift points (using main or jib hook block at a time )
Type of rigging configuration
Parameters and formulations
1 L4 + a 4 + b 4 − 2( L2 a 2 + L2 b 2 + a 2 b 2 ) 2L H H θ1 = tg −1 ( 4 ) , θ 2 = tg −1 ( 4 ) a b where L is the length of doubled slings, H4 =
Without Spreader Structure
a= [
Dy Lh 2 D (x1) Wh 2 D y L h 2 D ( 2) W − ] +[ − ] and b = [ x − h ] 2 + [ − ] 2 2 2 2 2 2 2 2
φ = cos −1 (
Dy / 2 − Lh / 2 d1 + d 2
)
H 4 = d 1 sin(φ) , H 5 = d 2 sin(φ)
H H4 H ) , θ 2 = tg −1 ( 4 ) , γ = tg −1 ( 5 ) a b c where φ is the angle between the real plane of sling and horizontal plane. θ1 = tg −1 (
With Two Parallel Spreader Bars
d1 =
1 2L d
a= [
L4d + p 4 + q 4 − 2(L2d p 2 + L2d q 2 + p 2 q 2 ) ,
d 2 = L2s − (
Wsp 2
−
Wh 2 ) , 2
Wsp 2 D y D sp 2 Wsp 2 D y D sp 2 D D − ] +[ − − ] +[ − ] , b= [ ] , 2 2 2 2 2 2 2 2 (1) x
D sp L h 2 Wh 2 ) +( − ) 2 2 2 2 with Ld being the length of doubled slings below spreader, Ls being the length of single D (1) Wsp D ( 2 ) Wsp sling above the spreader, p = x − and q = x − 2 2 2 2 c= (
H4 =
Wsp
( 2) x
−
1 2L d
L4d + a 4 + b 4 − 2(L2d a 2 + L2d b 2 + a 2 b 2 ) , H 5 = ( L s ) 2 − c 2
H H4 H ) , θ 2 = tg −1 ( 4 ) , γ = tg −1 ( 5 ) a b c where Ld is the length of doubled slings below spreader, Ls is the length of single sling above the spreader, θ 1 = tg −1 (
With Spreader Frame
a= [ c= (
D (x1) Wsp 2 D y L sp 2 D ( 2 ) Wsp 2 D y L sp 2 − ] +[ − ] , b= [ x − ] +[ − ] and 2 2 2 2 2 2 2 2 Wsp 2
−
L sp L h 2 Wh 2 ) +( − ) 2 2 2
69
Table 4.7 Formulations for rigging configurations with eight lift points (using main and jib hook blocks at the same time )
Type of rigging configuration
Parameters and formulations θ
Without spreader frame
( B)
−1
= cos (
[D (xB) / 2 − Wh( B) ] 2 + [D (yB) / 2 − L(hB) / 2] 2 L( B)
)
H (4B) = [L( B) ] 2 − [D (xB) / 2 − Wh( B) ] 2 − [D (yB) / 2 + L(hB) ] 2
θ ( J ) = cos −1 (
[D (xJ ) / 2 − Wh( J ) ] 2 + [D (yJ ) / 2 − L(hJ ) / 2] 2 L( J )
)
H (4J ) = [L( J ) ] 2 − [D (xJ ) / 2 − Wh( J ) ] 2 − [D (yJ ) / 2 + L(hJ ) ] 2
70
Inputs Hook block info. Sling info. (from inventory) Lift point info. Spreader info.
• • • •
TASKS
Outputs
Determination of rigging configuration
•
Sling angles
• 1. 2. 3.
Heights of
•
Algorithms
•
Formulations
hook above module hook above spreader spreader above module
Figure 4.1 Determination of rigging configuration: tasks, inputs and outputs
ISO View
Wm Dx L4
L3
θ3 θ4
z
L1
H4 L 2
θ2
y
y
LPT 3
CG (x c , y c )
Lh
x
Dy
x Wh
LPT 4
Hm (H3)
LPT 2
Lm
LPT 1
θ1 Rigging configuration with four equal slings
x Barge Direction
LPT 3
Wm
Wm
Dx
Dx
CG (x c , y c )
LPT 3
LPT 2
Dy LPT 4
LPT 1
Rigging configuration with matched-pair slings
CG (x c , y c ) LPT 2
Dy
Lm LPT 4
Lm
LPT 1
Rigging configuration with unequal slings
Figure 4.2 Rigging configuration for four-lift-point sling systems using main or jib hook block without spreader
71
L''
H5
γ
Wm
γ
Dx
L'
H4 θ
y
θ z
Lm
x θ
θ
Dy
Lh
Lsp
Hm
Rigging configuration with one transverse spreader bar
γ
Wm
H5
L''
Dx
φ
z
Wsp
x
θ
H4
y
'
L
Wh Lm
Dsp
Lh
Dy
φ
Hm Rigging configuration with two parallel spreader bars
Wm ''
L
'
L
z
y x
Dx
H5
γ
Wsp θ
Wh
H4 Lm
Dy
Lh
Lsp
Hm Rigging configuration with a spreader frame
Figure 4.3 Rigging configurations for four-lift-point sling systems using main or jib hook block and spreaders 72
jib hook main hook
L'' γ
( B)
γ (J)
H 5( B)
H
'
L
H 5( J )
H (4J )
( B) 4
z
θ ( B)
D (yB)
y
x
L(spJ ) L(hJ )
L(hB) L(spB)
D (yJ ) L m
θ(J)
Dx Hm
Wm
Figure 4.4a Rigging configuration for four-lift-point sling systems using main and jib hook blocks and spreader bars
W
W (J)
( B)
D (x1)
W ( B) =
D(x2 ) W D(x1) + D (x2 )
W (J) =
D (x1) W D (x1) + D (x2)
D (x2 )
CG
W Figure 4.4b Hook load distribution for four-lift-point sling systems using both main and jib hook blocks
73
Wh
L''
Wsp′′
γ
H5
Wsp′
H sp
Wm Dx
L'
H4
z
y
θ
Wh
x
θ
θ
Lm
Dy
Hm
Figure 4.5a Rigging configuration for six-lift-point sling system using main or jib hook block with spreader frame T′
T′
W
T′
T1 T1
T2 T2
T1 T1
T1
T′ =
T′ 1 W 2 sin( γ )
T1
T2 T2
T1
T1 T2 = αT1
θ
θ
θ
where α is dependent on the stiffness of module structure and sling system
W Figure 4.5b Sling tensions for six-lift-point sling system using main or jib hook block with spreader frame
74
jib hook
main hook
H (4B)
L( J )
L( B) z
θ
D (xB)
( B)
y
H (4J ) θ (J)
x
D (yB)
L(spJ ) L(HJ )
L(HB)
Hm
D (yJ ) L m
Dx Wm
Figure 4.6a Rigging configuration for six-lift-point sling system using both main and jib hook blocks W (J)
W ( B)
D (x1)
W ( B) =
D (x2 ) W D (x1) + D (x2)
W (J) =
D (x1) W D (x1) + D (x2 )
D (x2)
CG
W Figure 4.6b Hook load distribution for six-lift-point sling systems using both main and jib hook blocks
75
L
Wm D (x2)
D (x1)
H4
Wh
θ2
θ1
Lm
Dy
Lh
Hm
Figure 4.7a Rigging configuration for eight-lift-point sling system using main or jib hook block without spreader frame
Wm
D (x2)
H5
D (x1)
Wh H4
θ2
Lm
θ1
Dy
Lh
Hm
D sp
Wsp
Figure 4.7b Rigging configuration for eight-lift-point sling system using main or jib hook block with two parallel spreader bars
Wm
Ls
H5
D (x2)
γ
D (x1) Ld
Wh
H4
θ2
Lm
Dy
Lh
L sp
θ1
Hm
Wsp
Figure 4.7c Rigging configuration for eight-lift-point sling system using main or jib hook block with spreader frame
76
Dx L( J )
L( B )
H (4B)
z y
θ
( B)
H (4J )
D (yB)
L(hB)
x θ(J)
Hm
D (yJ ) L m
L(hB)
Wh( B)
Wh( J )
D (xB)
D (xJ )
Wm
Figure 4.8a Rigging configuration for eight-lift-point sling system using both main and jib hook blocks
W
W (J)
( B)
D (x1)
W ( B) =
D (x2 ) W D (x1) + D (x2)
W (J) =
D (x1) W D (x1) + D (x2 )
D (x2 )
CG
W Figure 4.8b Hook load distribution for eight-lift-point sling systems using both main and jib hook blocks
77
CHAPTER 5
5.1
JACKET LIFTING
Introduction
The fixed steel jacket is the most common type of structure used for supporting facilities for the offshore production of oil and gas. A few of jackets have been built with sufficient buoyancy to enable them to self-float, but the majorities have been transported from fabrication yard to offshore site on aboard of an ocean-going cargo barge.
The following steps should be taken during the conceptual design of a jacket.
The capacity of the lift cranes falls off dramatically with increasing radius. It is, therefore, essential to take all possible steps to minimize the operating radius. The smaller the cross section of the jacket is, the smaller the crane radius is. Therefore limiting both top and bottom plan dimensions of a horizontally lifted jacket, will give improved liftability. Smaller plan dimensions cause more piles and higher dynamic amplification in the inplace condition.
If the jacket is not square in plan then a clearance and radius study should be carried out to determine which way round the jacket should be on the barge to give maximum hook capacity. Selection of barge width may also be critical in determining the optimum crane radius.
78
In determining the crane radius, the clearance between the barge and the crane vessel hull, the jacket and the hull, and the jacket and the crane boom or crane cabs must not be less than 3m during lifting.
The common offshore installation method of barge transported jackets is directly by lifting, using a heavy lift vessel (HLV) or a semi-submersible crane vessel (SSCV). While another method is to lunch jacket from cargo barge and then upending by using crane vessel. The main differences between lifted and launched jackets are that the latter have launch frames and auxiliary buoyancy tanker. Launch frames have also another function, serving as supporting framework during jacket construction and for skidding the jacket onto the launch barge during loadout. Some form of auxiliary buoyancy is necessary on launched jackets to arrest the jacket during launch, and as an aid during upending and installing the jacket on the seabed.
Lifted jackets without the requirement for launch frames and the auxiliary buoyancy tankers needed to achieve a safe launch, which will give quite saving of steel materials. Lifting slings and lifting trunnions (installed on the jacket) are required to lift the jacket from the cargo barge into the water.
There are a variety of ways by which a jacket may be lifted and installed into position on the seabed. Each depends on the characteristics of the jacket. The first method is the vertical lift whereby the jacket is vertically transported on and lifted vertically off the barge and placed on the seabed.
79
In the situations where the jacket is too tall for vertical lifting it can be lifted horizontally from the barge using slings attached close to the top and base of the jacket. Installation follows by lowering the jacket base and raising the top of the jacket. This method is inappropriate for longer jackets as the lifting capacities of the cranes reduce with increasing crane boom radius. Such circumstances will probably result in a two-stage installation. Firstly the jacket is lifted from the barge and lowered into the water until it floats. This requires the use of auxiliary buoyancy. The main lifting slings are then removed and the prerigged upending slings attached to the crane hook. The jacket is then upended and positioned on the seabed.
It is relevant to point out that the configuration and sling tensions for lifting jackets vertically or horizontally are discussed in the previous chapter.
5.2
Vertical Lift of Jackets
The majority of shallow water jackets are constructed, loaded out and transported with the jacket in its vertical position. The jacket is installed by lifting it clear of the cargo barge by either a single or dual lift, removing the barge, and then lowering the jacket into place on the seabed as shown in Figure 5.1.
The advantages of this method of lifted jacket installation with respect to other methods are: the jacket is vertical during all phases of installation: no re-rigging of lift slings is required during installation (which means that offshore installation time/cost is reduced significantly); and only a minimum ballasting system (if any) is necessary. The 80
disadvantages are that the jacket height is limited by the available boom height capacity of the crane vessel and the vertical construction of the jacket. For jacket installation of this sort a submersible cargo barge is required to meet hook height requirement.
However, the influence of the new generation SSCVs is illustrated by the comparatively large weight of the 8400t Gyda jacket in North Sea, which was installed in a water depth of approximately 65m in 1989 by Saipem S7000.
5.3
Horizontal Lift of Jackets
In the case of jackets in greater water depth, the height of the jacket prohibits vertical lifting. Consequently, the jacket is constructed horizontally at the fabrication yard and loaded out onto the cargo barge in a similar manner to the launched jackets. For horizontal jacket, there will involve number of lifting operations: 1)
Lifted
loadout
horizontally
onto the transportation barge in fabrication yard, see Figure 5.2a , 2) Lifted up from transportation barge offshore, see Figure 5.2b, 3) upending jacket from horizontal position into vertical position, 4) Lift jacket vertically for final installation. Also refer to Chapter 9.3 for more details.
Two upending methods are used for installation of horizontal jackets:
•
Upending in air, which requires a larger SSCV with two hooks working independently, like S7000. Refer to Figure 5.3 and Figure 9.4. This can also be achieved by two Crane vessels, see Figure 5.2. 81
•
Upending in water, which is commonly used as less SSCV requirement. This may further be divided into two categories: those installed with the rigging always attached (these jackets invariably have no auxiliary buoyancy) and those installed using a re-rigging method while the jacket is free floating (such jackets may require auxiliary buoyancy).
The former category of installation is best suited to medium water depth jackets. When partially supported by buoyancy, the load was transferred to the auxiliary hook. The main hook was re-rigged at the top of the jacket, which was then upended.
For short jackets the lifting points are close to the top and the base of the jacket. Such positioning facilitates the upending of the jacket, where one crane is used to hold the top of the jacket vertical while the other lowers the base.
The jacket size is restricted by the various factors. At the lower lift point, the main crane hook typically only has enough wire to go to the same level as the SSCV pontoons. The vessel operator prefers that the crane hooks do not go underwater. The upper lift slings need to pass over the top of the jacket. Both this and the restrictions on lowering the crane hooks result in long slings attached to the jacket. But the length of these slings is limited by the maximum allowable hook heights when lifting the jacket off the barge. The crane vessel draught may be limited to only a few positions because of stability and motions restrictions.
82
The typical sequence for the lifting of deep water jackets is as following:
Step 1: Jacket lifted horizontally from the cargo barge after removing seafastening, Jacket lowered into the water, where it floats horizontally. The jacket may require auxiliary buoyancy.
Step 2: Slings and spreader beams are removed. The derigging of the jacket included: •
lay down of slings on the rigging platforms;
•
release and removal of slings one at a time;
•
removal of end shims on the spreader beam;
•
removal of the spreader beams.
This operation took usually about 24hrs.
Step 3: The pre-rigged upending rigging, at the top of the jacket is attached to the crane
Step 4: The jacket is upended by a combination of ballasting and raising the crane hook
It should be noted that the large jackets have required substantial loadout frames. If they had been built as launched jackets, the equivalent weight would have been built into the structure as launch frames and load out rails. This in turn would have attracted higher wave loadings in the in-place condition. Additional anodes and/or painting would have been needed. These extra weights on a launched jacket hence require temporary buoyancy to be fitted.
83
5.4
Summary
Jackets which are built and transported vertically offer significant savings over jackets built on their side. These include:
•
Loadout and transportation forces are carried efficiently by the legs and vertical face braces. Plan bracing sizes reduce and there is a minimum of temporary steel that becomes redundant when the jacket is in place;
•
No ballasting/upending system is required and the legs are free flooding;
•
The jacket is not required to float or to have submerged, remote, sling release systems;
•
The same slings are used for lift and placement. No separate upend slings are required;
•
The water depth for this type of lift installation is limited by the available hook height of the SSCV to around 65-70m. If built vertically, jackets are limited by the height of the cranes in the fabrication yard.
84
Considerations for lift jacket structures horizontally and vertically are discussed in this chapter. Lifting large jackets have required substantial loadout frames.
Figure 5.1
Vertical Lifting of Jacket
85
Figure 5.2a
Figure 5.2b
Horizontal Lifting of Jacket-Loadout operation at Fabrication Yard (2800ton)
Horizontal Lifting of Jacket-Dual Crane Lifting a Tripod Jacket (6200 ton) 86
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) 87
CHAPTER 6 MODULE LIFTING 6.1
Introduction
Normally, deck structures are broken to several modules and fabricated on the ground block by block. After fabrication, they will be assembled together by lifting. If the deck is a truss deck, the obvious problem is that during fabrication, we do not have truss action in the deck, so the deflection of the deck may be very large such that final fit-up could pose major problem. For opened deck, the deflection will not pose a problem, but we have to make sure the deck leg work points do not shift during assembly. It is obvious that opened deck is cheaper to fabricate than a truss deck provided the plate girders in the opened deck are not too expensive. When a deck is fabricated, we usually turn it upside down to facilitate downhand welding position. After the deck plate is welded to all the deck beams. It will be turned over 180 degrees to a correct position. For this operation, simple temporary padeyes will be provided at the edge of the deck. The only difficulty in this operation is that the deck is halffinished, so it is still very flexible.
With the DB102 and the S7000, modules of up to 10 000t can be lifted using cranes in tandem. The full capacity of the crane vessels is not available as they normally operate at radii greater than that which gives the maximum lift capacity. In addition, allowances need to be made for weight growth, COG shift and module tilt. Lifts of up to 8 000t can be lifted using a single crane. Chapter 9.2 presents the detailed analysis for the completed module.
88
6.2
Vertical Module Lift and Installation
For the design of the deck padeyes, there are few problems that we should be aware of. First, the confirmation of the deck lift weight and the exact centre of gravity location will usually come very late during fabrication. So an economic design should be such that it will not have major impact on the fabrication schedule even though they may be the last item to be fabricated and installed. The padeye together with the pipe can be fabricated separately, it then can be easily installed after the centre of gravity is confirmed. Installation only involves one girth weld. This type of detail will have least impact on the fabrication schedule if the equipment vendor data is late. For a deck with a lot of equipment on the main deck, a spreader frame or a spreader bar may be needed. In this case, the padeye main plate should line up with the adjacent webs of the primary girders.
In terms of fabrication cost, the cost for fabricating a padeye is extremely small compared with the overall project cost. It is therefore unwise not to be conservative in the design, after all, the weight and centre of gravity information would normally not be available until the end of the job. After fabrication, all primary welds in a padeye should be l00% NDT (Non Destructive Test). In certain critical locations, a simple MPI (Magnet Particle Inspection or DPI (Dye Penetrant Inspection) is unlikely to yield meaningful result, So Ultrasonic Test (UT), Radiography Test (RT) or other NDT technique may be required.
The choice of material and the design of bumper guide are also very important to heavy lift. However, these items are the outside scope of this paper. 89
The advantages of lifting the modules in one piece are: •
Increased hook-up, in particular all piping, electrical, instrumentation and telecommunications cables can be run without spliced connections;
•
Higher percentage of commissioning the module onshore;
•
No need for bumpers and guides for offshore lifting of individual modules and
•
Offshore hook-up rates are approximately five times onshore rates.
The disadvantages of very large modules are: •
Modules have a high concentration of weight over a small area. This may result in fabrication pads and loadout quay walls needing substantial strengthening of their foundations;
•
Cargo barges and perhaps even the large launch barges may require strengthening to take the concentrated loads, during transportation;
•
If large launch barges are used, then their depth may require substantial dredging to be carried out at the fabrication yard;
•
If the module is built with the drilling derrick or flare, the module may be higher than overhead obstructions between the yard and sea. Obstructions include power cables. Thus the module would need to be completed down river from the main construction yard;
•
The preferred load out method for modules is by using trailers. With the very large modules, there may not be enough trailers available. For a 10 000t module, the trailers from all owners needed to be combined to perform the loadout. Joint venturing of trailer owner is quite common and, for example,
90
80% of Europe's trailers were needed for loading out the recent integrated deck for Gannet;
A most important aspect of the design of large lifts is the control of weight and its CoG. The typical sequence of weight control includes: 1.
During detailed design, a monthly weight report is produced by the designer.
2.
During fabrication the responsibility for the detailed weight report passes to the fabricator.
3.
The designer produces an independent weight report less frequently during this period.
4.
Two weighings are usually required, the first of a partially complete module and the second just before loadout (normally one week).
5.
The installation contractor is able to reduce the lift tolerances on the basis of the weighing, which in turn gave greater confidence to the offshore lift
To handle a big sling, such as one with 150mm in diameter, is not an easy task. Doing it onshore is much easier than offshore. For this reason, all the rigging equipment should be rigged up in the yard before loadout. One of the common mistakes in deck padeye design is the failure of the design engineer to appreciate the difficulty in installing the slings and shackles. In many instances, the eye of the padeye is located below deck. This will make it difficult for the workers to line up the padeye and the shackle to push in the pin, because there is no platform for them to stand on. In some cases, the design engineer forgot to cater for the need for link plates to do a level lift. A good design will make sure that the shackle can be installed on top of the deck where people can have space to work. Another common mistake is that there must be enough 91
space to physically position the pin and push it through the pin hole. There have been many cases that an access hole has to be cut in the web of the intersecting girder in order to install the pin. When a spreader frame is used, it too has to be rigged up in the yard. Design engineers should remember that the weight of the rigging is heavy. It could be 100 tons or more. This weight has to be supported on the deck and enough protection bumpers will have to be installed to keep the sling from damaging any deck equipment.
When we lift a deck, the maximum out-of-level across a diagonal should be limited to 300mm to 600mm. This means that if we want to achieve almost level lift, we have to use link plate to bring the CoG directly under the hook. If the sling capacity is not big enough, we may have to use double slings. This can be accomplished by using sister plates.
In certain lifting arrangement, contractor uses trunnion or padeye details. This is to remove the requirement for very large shackles for the lift and allow the sling to turn. For sling or cable laid sling, the sling capacity may be de-rated if it is bent around a small object, etc. If the cable laid sling is already 300mmφ, say, we may not be able to find a big enough wide-body shackle to go with the sling without derating the sling capacity. In this case, a trunnion detail is an attractive alternative. For very heavy lift, some engineers specify precast lifting eye. This is not a cheap solution. Since this is a proprietary detail, it will not be discussed here.
Before we do the lift, we should also check the strength as well as the eccentricity on the prongs of the hook. Using double slings at the deck level is acceptable, but at the
92
prong location, one sling will take more load than the other, because the first sling will have already taken up a lot of space. This eccentric load may cause eccentricity moment at the prong which may not have been designed for. If this moment causes the prong to twist or rotate, we have to make sure the lines on the crane hook will not jump out of the sheave. This will have to rely on the experience of the barge superintendent.
Before the deck is lifted, the derrick barge is set up some distance away from the platform with perhaps 8 point mooring arrangement. When the deck is picked up from the material barge, we have to walk the barge forward for setting the deck. However, enough bumper guides will have to be provided to make sure the package will not be damaged during setting. For dual barge or dual crane lift, we have to pay attention to the relatively crane tip movement. This may change the load distribution of the structure. It will be very critical if it is a marginal lift.
93
6.3
Deck Panel Flip-Over
To fabricate a topside module structure, the most common method is to sub-assembly each deck panel on ground level, and stack them one level by another. Most of topside modules are consist of three, or four deck levels. The lifting weight of a single deck panel structure can go as heavy as 1,200 ton, like Malampaya project shown Figure 6.1.
To ease the fabrication work, some of deck panels are built upside down. A typical erection sequence is as below: •
Lay the completed flat steel deck plate on temporary support,
•
Weld main beams onto the deck plate,
•
Secondary beams join to the main beams and
•
Fit-up vertical column and braces.
The great advantage for the above fabrication method is to change welding process from top welding into bottom welding, which leads into the benefit for welders and time saving for the project.
It is required lots of detailed engineering to flip over the completed deck panel. As it is involved many different steps, engineers must perform structural stress analysis for each step as shown Figure 6.2. Temporary strengthening may be required for certain area in case of over stress occurred. Spreader bars are utilized to facilitate the rotation. Two or three lifting cranes may be mobilized to complete the flip-over operation as shown in Figure 6.3.
94
6.4
Summary
Practical considerations for module lifts, which include vertical lifts and flip-over are discussed in this chapter.
One of the most important aspects of the design of large lifts is the control of weight and the CoG of the module. This requires a proper sequence of weighing scheme to ensure the accuracy of these parameters. The locations of padeyes and arrangement of slings are also to be considered properly. Link-plates or additional shackles are frequently used in lift design to ensure level installations.
For deck panel flip-over operation, force distribution between two cranes or two hooks should be calculated precisely. The forces at two hooks vary with the change of the module incline angle during flip-over.
95
Figure 6.1
Deck Panel Stacking in progress (Panel lifting weight: 1,200 ton)
96
Figure 6.2
Computer Model for Deck Panel Flip-over
97
Figure 6.3
Deck Panel – 180 Degree Flip-Over
98
Figure 6.4
Module Lifting – Four Sling Arrangement
99
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
100
Figure 6.8 lifting with a spreader frame
Figure 6.10
Figure 6.9 Multi-Tier Rigging System
Tendem Lift of a Module
101
CHAPTER 7 FPSO STRUCTURE LIFTING 7.1
Introduction
The lifting operation for FPSO (Floating Production Storage and Offloading) project involves the loadout from fabrication site, transportation to integration yard and installation onto FPSO Hull deck. The topside modules can be fabricated in various locations. The module size and weight are engineered to the certain lifting vessel during the detailed design stage. The followings are the lifting operation carried out in Sembawang Yard for Laminaria & Corallina Development Project.
The sheerleg crane vessel namely Asian Hercules II was used for the operation. Most of modules were directly lifted up at the Erection yard, transported to the Hookup yard on crane hook for a distance of approximately 2.2km, and then installed onto FPSO. In General, it took one day to complete one module lifting operation from preparation, loadout and installation. However, there were cases that two modules were installed onto FPSO within a day.
7.2
Lift Procedures and Considerations for FPSO Modules
GENERAL •
The communication channels were set-up for all the parties, such as Owner (WOS), Lifting contactor (ALPL), fabricator (SME), Marine Warranty Surveyor (LOC) etc, for different stages as below:
•
during the preparation works
•
during the Loadout
•
during the Transportation
•
during the installation operation:
102
•
A flowchart showing the relationship of all parties along with responsibilities for the operation covered under the operation.
•
The estimated operating schedule for the lifting operation must be agreed prior to the operation
•
For each module, a specific procedure was prepared with all the necessary calculation and detailed drawings.
PREPARATION FOR LOADOUT General Preparation The Erection site of module must be cleared from all obstructions such as temporary supports, construction equipment, movement of crane etc. Temporary scaffolds or other facilities shall be in place at the designated lifting padeyes to facilitate installation and remove of rigging system. It is crane operator’s responsibility to provide and handle the tag lines. Four tag lines will be attached to each of modules during lifting. The minimum length shall be 15 meters.
Environmental Criteria The module lifting/installation was carried out in sheltered water.
Wave and Swell No relative movements of the vessel anticipated due to lifting/installation carried out in sheltered harbour. Any vessel movement was monitored closely.
Water depth The water depth charts for the quay of both loadout and installation yard were surveyed prior to crane vessel arrival to ensure sufficient water depth.
103
Wind Hercules II can be operated at wind speed of 20 m/s during hoisting in harbour condition. However for lifting operation, a wind speed of 5m/s is the limitation. If higher wind occurs, a decision shall be made by agreement of all parties both prior to the commencement of lifting and during the operation itself.
Consensus Lifting operation was not initiated unless the Mater of Asian Hercules II Crane vessel and representatives from all parties (owner, SME and LOC) agreed that the lifting conditions were safe. Information regarding to wind, wave and swell of Singapore at the time of the operation was obtained from the weather station.
Lifting Crane For the detail of Lifting crane Asian Hercules II, refer to Chapter 3.2.1a. LOADOUT •
On the day of the lifting operation, the floating crane was moored into position. Lower the hook and connect to rigging system as shown on detailed drawing.
•
Hook blocks were then raised until the slings are just taut. At this point, slings/shackles and spreader bar was inspected. Prior to the lifting, the LOC certificate shall be provided and checked off on the checklist.
•
Lift-up the module until it is well clear from temporary support and other obstacle. At the point of lifting clear of temporary support, checks should be carried out to allow the two fixed points touching footing pads on hull deck first, otherwise adjustment shall be made. 104
•
Hercules II then raise boom to the maximum, i.e., enough gap between crane boom and module.
•
De-mooring all the mooring lines.
•
Hercules II is ready for sail to Berth 8 – Installation yard.
TRANSFER OF Module The module will be transported to Berth 8 for installation on the Hook of Hercules II for a distance of approximately 2.2km per the transportation routine drawing.
INSTALLATION Asian Hercules II will lay two stern anchors. Hercules II will be moored perpendicular to FPSO. The port and starboard forward moorings are to be tied with bollards on the FPSO. Two fenders (1.2m OD x 1.5m in length) will be utilized in front of Hercules II.
FPSO shall be moored at Berth 8 with adequate mooring lines. The mooring calculation shall be approved by Client & surveyor. For installation of module, the FPSO will be trimmed to even keel position. The pre-installed footing on hull deck should be checked for their condition and dimensions.
The
temporary scaffoldings shall be provided to access module for derigging purpose.
Two pre-slings for mooring of the lift vessel to the Hull, will be attached to the hull own bollards rigged down along the hull side and the ends with soft eyes are located approximately 1m above sea water line.
105
•
Final check on the mooring conditions of Hercules II.
•
Hercules II manoeuver herself to slowly lower the module slowly onto Hull deck to match with pre-installed footings. Prior to lowering, a check shall be completed of barge/vessel moorings to confirm the continuation of operation.
•
Client (WOS) /Marine Warranty surveyor (LOC) to check, confirm and accept that module is properly installed.
•
Starting minimum bolting with the approval of LOC prior derigging.
•
The crane barge is ready for de-mooring for next lifting.
SAFETY ANALYSIS The Job Safety Analysis (JSA) was conducted together with Client, Marine warranty surveyor, Lifting contractor. The critical points and caution area during the operation will be highlighted. CHECK LIST Prior to each lift, the check lists in Table 7.3 to 7.5 were checked and signed by all three parties. 7.3
Rigging Systems with Multiple Spreader Bars Rigging systems with one, two and spreader bars, as shown in Figure 7.1, are extensively use in the lifting and installation of FPSO modules. The configuration and force distribution in the rigging system have been discussed in Chapter 4.
7.4
Lifting of Lower Turret The 680ton Turret shown in Figure 7.2 was built at Noell Imac’s yard in Mussafah, Abu Dhabi. The turret was transported to Singapore on Ocean going heavy lift ship “Happy Buccaneer”. The turret was offloaded by Asian Hercules and stored at Berth 8 of Sembawang yard until installation onto FPSO for a period of three months.
106
For installation of the Lower Turrent into FPSO Moon pool, the following challenges were faced: Crane Selection Choose a right crane which is able to lift the Turret across over FPSO (50m wide and 22 m height above sea water). Or else to shift FPSO is a costly operation. Crane selected: ASIAN HERCULES II 3200Mton Floating Crane Crane Boom : A-Frame And JIB in 0 degree Max. dry weight of Turret Weight of lifting rigging system
= =
680.0 Mton 24.0 Mton
( Sling 19mton + Shackle 5mton = 24Mton )
______________________________ Total Lifting Loadings: 704.0 Mton Considering Dynamic Factor of 1.05, lifting weight: 739.2 Mton Lifting Requirement: Minimum out-reach
=
Turret to Ship: Ship width: Clearance
87.00M 20.35 m 50.00 m 16.65 m
Minimum hook height
=
From crane chart: At out reach of Hook height Lifting capacity
= = =
62.5 M 87.0m 70.0 m > 62.5 m Ok! 900 Mton > 739.2 Mton Ok!
Sling Selection Due to a small clearance (169mm) between turret and moonpool, the tilt angle must be as minimum as possible. As only three padeyes are installed, two grommet slings were used as the balance slings to crane hook via single Shackle. Turret Installation For installation of Lower Turret, the FPSO was trimmed to even keel position, and the watertight moon pool closing plate was in place with the lugs on the closing plate welded. Three vertical support jacks installed on the moon pool
107
closing plate and set to the theoretical elevation. Three horizontal jacks were also in position. Pumps necessary to activate the jacks was ready and tested.
Video Cameras installed inside moon pool and working properly. Gear for rotating chain guides was in place. All the scaffoldings and other temporary equipment inside the moon pool shall be removed to avoid any clashing with turret during lowering operation.
Due to a small clearance (169mm) between turret and moonpool, six nos of old ropes or cables (appr. φ50mm) as guide protections were evenly installed inside the moon pool (against the moon pool circular wall) to protect the paint during the turret lowering operation. Three nos of spot lights were installed in the Turret to illuminate area where the video cameras are looking at. These lights were facilitated with cables and end sockets for connecting the power lines at hull deck.
The closing plate seal pressurization system as installed earlier must be disconnected and the water filled seals must be drained and inflated with compressed air to a pressure of 2.5 bars one by one such that one seal system remains active at any time.
The floating crane was moored into its position. Lower the hook and connect to the turret rigging system. Raise Hook block until the slings are just taut. At this point, slings and shackles were thoroughly inspected. Lift-up to well clear any obstacle, i.e. two meters between lowest point of the Turret and highest point of
108
obstacles on berth site. Rotate the Turret 90 degree clockwise by using folk lift. Hercules II continues raise A-Frame to a boom angle of 61 degree. Retrieve forward anchor. Move backward with the assistance of anchor lines until the center line of turret is in line of moon pool. Release the mooring line on starboard side. Hercules II moves sideward until the turret is on top of moon pool. Drop the forward anchor. Tie the starboard mooring line onto a new bollard of Hull.
Start to lower the Turret slowly into the moon pool. When chain cable is at the level of the vessel deck, connect the chain stopper rotating slings to the main deck. Check alignment at this stage and make adjustment when necessary.
Stop at the level where the guide wires start being functioning to check equal activating. Video cameras will be used to monitor clearance between the chainstoppers and the closing plate. The clearance will be adjusted by means of the hoists fitted on vessel deck. Continue to lower the turret into the moon pool until it is in contact with the 3 supporting jacks. WOS/Marine Warranty surveyor (LOC) to check, confirm and accept that turret is properly supported by the 3 jacks prior to derigging - completion of lifting operation.
Figures 7.3, 7.4 and 7.5 show design details of lifting and installation of other parts of the turret.
109
7.5
Lifting of Gas Recompression Module For each lifting, lifting crane capacity was studied. The following is the details of lifting of Module PX04, the gas recompression module, as shown in Figure 7.6. The estimated lifting weight for each PX04 is 1001.0 ton The lifting weight of PX04:
1001.0 Mton
Adding the weight of slings, shackles and Spreader bars: Total: Considering Dynamic Factor of 1.05, lifting weight: Crane Type:
78.0 Mton 1079.0 Mton 1133.0 Mton
ASIAN HERCULES II, 3200Mton Floating Sheerleg Crane
Crane Boom: A-Frame in Position I with JIB (0°) Lifting Requirement: Minimum out-reach =
70.0m
Minimum hook height =
86.0m (5m clearance)
From crane chart: At out reach of
=
70.0m
Hook height
=
87.4m > 86.0m ok!
Lifting capacity
=
1500Mton > 1133.0Mton Ok!
110
7.6
Lifting of Flare Tower
The installation of the 92m of Flare Tower onto FPSO, as shown in Figure 7.7 was studied during detailed design stage of Flare Tower. In general, two methods were discussed as below: Method A:
To install the Flare Tower in two pieces, ie, to cut flare tower at mid section.
Method B:
To install the Flare Tower in one complete piece.
Advantages: Method A: -
The Flare Tower weight can be reduced
-
No any technical issue during lifting/installation
Method B: -
Time saving for both heavy lifting crane and fabrication
Disadvantages: Method A: -
Required two separate lifts
-
As the lifting height limitation of Hercules II JibII, the fly Jib is required for installation the upper part. This would lead into time/money costing for the boom changing.
-
Safety issue. To connect the upper part onto the lower part, the welding must be carried out up the height of 62m above the sea level. This must be avoided to reduce any potential risk.
Method B: -
The steel weight increased slightly
111
-
Required lot of detailed engineering study to ensure safety, clashing free and cost saving
Method A was not chosen due to high risk up in the air.
For method B, following critical issues were studied carefully: a)
The flare Tower was fabricated on ground. Both main hook and Jib hook were utilized to upbend as shown in Figure 7.6. Additional padeye was designed. Updending structural analysis was performed with the modification of upper leg.
b)
After releasing the main hook, the flare tower was lifted by Jib hook only. Hercules then carried the flare for about 2.2 km from fabrication site to integration site. Dynamic analysis was done to ensure the completed system is safe.
c)
Prior to installation, the dimension of stab-in guide and Flare leg was checked. Special guide system was designed to receive the tower.
d)
The upper leg of Flare was protected with the mooring rope.
112
7.7
Summary
Design and operation for lifting FPSO modules are discussed in this chapter. Lift procedures and considerations for FPSO modules are indicated and rigging systems with multiple spreader bars are highlighted. Practical design and analysis considerations for lifting lower turret, gas recompression module and flare tower, which are unique for stingy requirement of installation accuracy, heavy load and geometry, are discussed based on real projects.
113
Table 7.1 LIFT AREA NO. CODE
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
HU10 PF00 PX20 PX19 PR05 PR03 PR04 PR01 PX18 PX01 PX02 PX04 PX03 PM05/ HD20 HD70 TX00 TX00 TX00 PX12 PX14 PX16 PX17 PX09 PX11 PX13 PX15 HU90
Lifting Operation Summary for Laminaria FPSO M O B
AREA DESCRIPTION
TURRET ( LOWER ) FLARE TOWER LAYDOWN AREA FWD TURRET FLARE EQUIPMENT SUPPORT PROCESS PIPERACK 5 PROCESS PIPERACK 3 PROCESS PIPERACK 4 PROCESS PIPERACK 1 CHEMICAL INJECTION LAYDOWN AND STORAGE AREA UTILITY AREA POWER GENERATION POWER GENERATION ACCESS / TRANSPORT ROUTE PEDESTAL CRANE X-1402 PEDESTAL CRANE X-1401 TURRET – MANIFOLD STRUCTURE TURRET – GANTRY STRUCTURE TURRET – SWIVEL STACK PRODUCED WATER CORALLINA SEPARATION LAMINARIA SEPARATION DEBUTANIZER GAS RECOMPRESSION GAS LIFT GAS LIFT GAS INJECTION DEBUTANIZER COLUMN
Table 7.2 SCENARIO Breaking/parting of either shear leg or FPSO mooring line Failure of shear leg to lower load Power failure on shear leg crane Bad weather
1ST 1ST ST 1 ST 1 ST 1 1ST 1ST 1ST ST 1 ST 1 ST 1 1ST 1ST 1ST ST 1 ND 2 ND 2 2ND 2ND 2ND ND 2 ND 2 ND 2 3RD 3RD 3RD RD 3 RD 3
LIFT WT (TON)
680 228 46 70 71 26 25 76 154 212 345 1,120 589 45 92 92 697 372 50 411 780 700 307 875 906 967 1,066 95
WEIGHING
SPREADER BAR LENGTH (M) (Eye to Eye)
1ST
Final BOTTOM
Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes -
Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes -
2 NOS
TOP 1 NOS
11.565 13.545 13.545 13.545 19.775 19.775 11.565 19.775 19.775 19.775 19.775 -
14.080 2.92 4.72 4.72 2.92 16.720 15.840 18.480 18.480 18.480 4.72 4.100 18.480 18.480 18.480 16.720 18.480 18.480 18.480 18.480 -
NOS OF SLINGS REQ’D 3 2 4 6 6 6 6 6 10 6 6 10 10 6 4 4 6 4 4 10 10 10 10 10 10 10 10 4
Contingency Actions Plan / Procedure PRIMARY CONTINGENCY
SECONDARY CONTINGENCY
Standby mooring rope
Tug's assist
Lower boom
Maintain crew to repair None
start emergency generator automatically The lifting operation will be postponed
114
Table 7.3 Preparation Check List DESCRIPTION WOS
LOC
SME
Asian Hercules vessel in position at Erection yard, ready for lifting operation. Slings, shackles and spreader bar are ready Certificate for sling, shackle and cranes LOC to have checked the lifting gears Certificate for Spreader bars Qualified rigging supervisor and safety officer are present Shiploosed items removed from module and list prepared Bearing Pads and connecting bolts are ready Erection area cleared of temporary equipment and obstructions. Temporary access way to the lifting trunnions Movable crane standby
Table 7.4 DESCRIPTION
Loadout Check List WOS
LOC
SME
Hercules II is proper anchored and moored in its lifting position Check mooring line conditions Shackle and slings are in good condition and attached on module loadout area is clear of any obstruction This procedure reviewed by all the parties Agreement to commence lifting operations. Certificate of Approval for Lift issued by LOC.
Table 7.5 Installation Check List DESCRIPTION WOS
LOC
SME
Hercules II mooring its designed position with two mooring lines tie on FPSO, two aft anchors dropped Set-down area on FPSO is clear of obstacles, ready to receive it. Footing level/location survey done, trimmed if necessary Bearing Pads and connecting bolts are ready on FPSO Hull deck LOC certificate provided to commence lifting Agreement to lower down module Module leveled and proper installed Minimum bolt connection approved by LOC Agreement to release crane hook
115
One spreader bar Two spreader bars
θ2
θ1 θ1
θ2
θ4 θ3
θ3
CG
CG
θ
3 spreader Bars θ1 θ2 θ θ3
CG
Fig. 7.1 Rigging arrangement for lifting FPSO modules with spreader bars
116
Figure 7.2
Lifting of Lower Turret (680 ton)
Figure 7.3 Lifting of Upper Turret – Manifold Deck Structure with Three Spreader Bars
117
• •
As the Gantry Structure is transported to installation yard on Barge “Sea Prosper”, proper seafastening removal procedure was established prior to lifting; The four slings are also very carefully selected due to COG eccentricity
Figure 7.4
Lifting of Upper Turret – Gantry Structure
Single sling is attached to Swivel Stack with the balanced system to crane hook.
Figure 7.5
Lifting of Swivel Stack – Bottom Assembly
118
Figure 7.6 Lifting of Gas Recompression Module
119
Figure 7.7
Upending and Lifting of 92-metre Flare Tower
120
CHAPTER 8 SPECIAL LIFTING FRAME DESIGN 8.1
Introduction
A versatile lifting frame is designed for the loadout / installation of six pallets (topside structures) onto Shell EA FPSO at Sembawang Yard.
The weight and COG of six pallets used for the lifting frame design is listed in Table 8.1. As we can see from Table 10.1, the COG for each pallet is different from other. Also, the lifting point distances in Y-direction for Separation Pallet port and Power Generation port are not the same as others. It is a challenge to make an uni-frame used for 6 lifts.
The final design weight is based on the pallet self-weight with 15% contingency plus lifting frame weight and rigging weight. Dynamic factor of 1.5 is considered at the same time. The design is performed in accordance with API RP2A and AISC (American Institute Steel Construction) Allowable Stress Design 9th Edition. The lifting frame analysis is performed by the software SACS (Structural Analysis Computer System).
With the lifting frame weight and rigging weight, the total weight used in analysis is listed in table 8.2.
The hook point is 26 meters high from the lifting frame for all pallets except the pallet Power Generation Port, in which the hook point is 16 meters considered due to hook height limitation. Tube check and joint/overlapping check against API RP 2A are made and the dynamic factor of 1.50 is considered. It is found that all members and joints are sufficient. The maximum stress ratio for member check is 0.86 on the member 2-4 when pallet Power Generation Port is lifted in Table 8.3. 121
8.2.
Effect of the Shift of the Centre of Gravity
Lifting Point Location Coordinates (MM) Point No X Y 1 0.0 18480 2 18060 18480 3 0 0 4 18060 0 Reaction loads without COG shifting Pallet WT COG (mm) (ton) X Y Cooler Utility Separation (Port) Separation (Starboard) Compression (Port) Compression (Starboard) Power (Port) Power (Starboard)
y 1
2
x 3
4
Base Reaction (ton) 1 2 3
4
998.0 1088.8 860.0
9465 8120 9830
8640 9340 10710
222.1 302.9 227.2
244.5 247.4 271.3
252.9 296.4 164.8
278.5 242.1 196.8
680.4
9330
9240
164.4
175.8
164.4
175.8
594.7
9840
6740
98.7
118.2
172.0
205.8
618.7
8840
9240
158.0
151.4
158.0
151.4
1063.4 780.2
13040 12640
9073 9840
145.1 124.7
376.9 290.8
150.5 109.5
390.8 255.3
Reaction loads with COG 500mm shifted towards –ve X-direction Pallet WT COG (mm) Reaction (ton) (ton) X Y 1 2 3 4 Cooler Utility Separation (Port) Separation (Starboard) Compression (Port) Compression (Starboard) Power (Port) Power (Starboard)
998.0 1088.8 860.0
8965 7620 9330
8640 9340 10710
235.0 318.1 240.9
231.6 232.2 257.5
267.6 311.3 174.8
263.8 227.2 186.8
680.4
8830
9240
173.9
166.3
173.9
166.3
594.7
9340
6740
104.7
112.2
182.4
195.4
618.7
8340
9240
166.5
142.9
166.5
142.9
1063.4 780.2
12540 12140
9073 9840
159.6 136.2
362.5 279.3
165.5 119.6
375.9 245.2
122
Reaction loads with COG 500mm shifted towards +ve X-direction WT COG (mm) Reaction (ton) Pallet (ton) X Y 1 2 3 Cooler Utility Separation (Port) Separation (Starboard) Compression (Port) Compression (Starboard) Power (Port) Power (Starboard)
998.0 1088.8 860.0
9965 8620 10330
8640 9340 10710
209.1 287.6 213.3
257.5 262.6 285.1
238.2 281.5 154.8
293.2 257.0 206.8
680.4
9830
9240
155.0
185.2
155.0
185.2
594.7
10340
6740
92.7
124.2
161.5
216.3
618.7
9340
9240
149.4
159.9
149.4
159.9
1063.4 780.2
13540 13140
9073 9840
130.7 113.2
391.4 302.3
135.5 99.4
405.9 265.4
Reaction loads with COG 500mm shifted towards –ve Y-direction WT COG (mm) Reaction (ton) Pallet (ton) X Y 1 2 3 Cooler Utility Separation (Port) Separation (Starboard) Compression (Port) Compression (Starboard) Power (Port) Power (Starboard)
4
4
998.0 1088.8 860.0
9465 8120 9830
8140 8840 10210
209.2 286.7 216.5
230.4 234.2 258.6
265.8 312.6 175.4
292.7 255.4 209.5
680.4
9330
8740
155.6
166.2
173.3
185.3
594.7
9840
6240
91.4
109.4
179.3
214.6
618.7
8840
8740
149.4
143.2
166.5
159.6
1063.4 780.2
13040 12640
8573 9340
137.1 118.3
356.2 275.9
158.5 115.8
411.6 270.1
123
Reaction loads with COG 500mm shifted towards +ve Y-direction Pallet WT COG (mm) Reaction (ton) (ton) X Y 1 2 3 998.0 9465 Cooler 1088.8 8120 Utility 860.0 9830 Separation (Port) 680.4 9330 Separation (Starboard) Compression 594.7 9840 (Port) Compression 618.7 8840 (Starboard) Power (Port) 1063.4 13040 780.2 12640 Power (Starboard)
4
9140 9840 11210
234.9 319.1 237.7
258.7 260.7 283.9
240.1 280.2 154.2
264.3 228.9 184.1
9740
173.3
185.3
155.6
166.2
7240
106.1
126.9
164.6
197.1
9740
166.5
159.6
149.4
143.2
9573 10340
153.1 131.0
397.7 305.5
142.5 103.1
370.9 240.5
124
8.3.
Sling Forces Unit : kN SACS MEMBER NO. 18-22 17-22 20-22 19-22 16-22 15-22 13-22 14-22
Power Generation Starboard
869.00
957.68 2145.91 1649.33 1525.19 1844.42
833.53
Separation Pallet Starboard
1276.90 1028.62 1596.13
Separation Pallet Port
1560.66 1525.19 2358.72 1241.43 1046.35 1667.07
993.15 1347.84
Compression Pallet Starboard
1259.17
957.68 1436.52
709.39
709.39 1436.52
957.66 1259.17
904.47
602.98 1064.08
656.19
904.47 1879.88 1223.70 1152.76
Compression Pallet Port Power Generation Port
851.27
815.80
851.27 1596.13 1028.62 1294.64
1294.64 1294.64 2908.50 2553.81 2571.54 3032.64 1365.58 1294.64
125
8.4
Padeye Checking Also refer to the typical padeye in Figure 3.13. SHACKLE SELECTION Required SWL (SWL = SLt)
SWL
PROPOSED SHACKLE PROPERTIES Type Shackle I.D. Safe Working Load Safety Factor for Shackle Minimum Breaking Strength Factor of Safety Pin Diameter Jaw Width Inside Length
480.00
tons
( As per lifting analysis ref: section 2)
500 M.T. Green Pin Anchor Shackle (model P-6036)
PADEYE GEOMETRY Main Plate : No. Thickness Radius Cheek Plate 1 : No. Thickness Radius Cheek Plate 2 : No. Thickness Radius 1. Check Pin Hole Diameter : Pin Dia. + 6mm Allowance Pin Hole Dia. Provided
SWLh SF MBS MBS/SWL Dh Wh Lh
= = = = = = =
500 4 2000 4.17 185.00 250.00 700.00
tons
Nm Tm Rm Nc1 Tc1 Ra1 Nc2 Tc2 Ra2
= = = = = = = = =
1 80.00 381.00 2 50.00 305.00 0 0.00 0.00
nos mm mm nos mm mm nos mm mm
tons > 4.0. O.K! mm mm mm
= Dh + 6 mm
= =
191.00 mm 190.000 mm
= 1.25*D = D/2 + 3"
= = =
237.50 171.20 381.00
D
2. Check Main Plate Radius : Minimum Radius or Rm
Radius Provided 3. Check Shackle Inside Length : Minimum Inside Length Inside Length Provided
mm mm mm
= (Ds + Rm- D/2+6mm)
4. Check Shackle Jaw Clearance : Minimum Clearance Required Centraliser plate thickness
Lh
= 407.00 mm = 700.00 mm ( where assuming sling diameter Ds = 115mm )
Clr
mm
O.K!
= 6.00 = (Wh-Nm*Tm-Nc1*Tc1-Nc2*Tc2-2*Clr)/2 = 29.000 Provide Centraliser Plate = 25.000
O.K!
mm mm
126
PADEYE STRENGTH CHECKS Padeye Des. Load (Dynamic Fac. = 1.5)
Pd
= SWL * 1.50 ( where SWL = SLt )
MATERIAL : Type Yield Strength
GRADE -50 Fy
1. CHECK BEARING Allow. Bearing Stress Bearing Area
Fp Ap
Actual Bearing Stress
fp
Fv
= 0.4 * Fy
Lm Lc1 Lc2 Av
= = = =
Actual Shear Stress
fv
Actual Tensile Stress
Ft At ft
720.00
tons
=
345.00
MPa
= 0.9 * Fy = 310.50 MPa = Dh*(Nm*Tm+Nc1*Tc1+Nc2*Tc2) = 33300.00 mm^2 = Pd / Ap = 212.11 MPa Stress Ratio = 0.68
2. CHECK PULLOUT SHEAR Allow. Shear Stress Shear Area : Length : Main Plate Cheek Plate 1 Cheek Plate 2 Area :
3. CHECK TENSION FAILURE AT 3.1 SECTION THROUGH PINHOLE Allow Tensile Stress Tensile Failure Area
=
=
138.00
O.K!
MPa
Rm - D/2 = 286.000 mm Ra1 - D/2 = 210.000 mm Ra2 - D/2 = 0.000 mm (Nm*Tm*Lm +Nc1*Tc1*Lc1+Nc2*Tc2*Lc2)*2 = 87760.00 mm^2 = Pd / Av = 80.48 MPa Stress Ratio = 0.58
O.K!
= 0.45 * Fy = 155.25 MPa = Nm*Tm*(2*Rm-D)+Nc1*Tc1*(2*Ra1-D)+Nc2*Tc2*(2*Ra2-D) = 87760.00 mm^2 O.K! = Pd / At = 80.48 MPa Stress Ratio = 0.52
3.2 SECTION AROUND UNDERSIDE OF CHEEK PLATE 1 Allow Tensile Stress Ft = 0.60 * Fy Length of Section Lt = approx 1.5*pi*Ra1 Area of Section At = Tm*Lt Actual Tensile Stress ft = Pd / At Stress Ratio
= 207.00 MPa = 1437.28 mm = 114982.29 mm^2 = 61.43 MPa = 0.30
O.K!
4. CHECK ATTACHMENT FOR CHEEK PLATES CHECK CIRCUMFERENTIAL WELD BETWEEN CHEEK PLATE & MAIN PLATE E70XX Electrode Weld Strength Ftw = 70 ksi = 483.00 Allow. Shear Stress Fsw = 0.3 * Ftw = 144.90 Load in Cheek Plate Pcd = Pd*(Tc1)/(Nm*Tm+Nc1*Tc1) = 1962.00 = Weld Size Req'd Lg = Pcd / (Fsw*Ra*π*0.707) 19.99 Minimum (AISC) : For Main Plate thk. > 3/4" = 8.000 Weld Size Provided : Fillet Weld = = 35.00
MPa MPa kN mm mm mm
O.K!
127
CHECK ATTACHMENTS OF PADEYES A. SECTION PROPERTIES
Y
'a' 'b'
5 'a'
Location 1 'b'
'a'
'a'
2
3 'b'
4
Location 2 'b'
1 'a'
--- bottom flange
X
128
CHECK ATTACHMENTS OF PADEYES (CONT'D) A. SECTION PROPERTIES About X-X axis S/no
Description of Elements
1 NIL 2 NIL 3 NIL 4 80 x 1312 5 NIL 2a NIL 3a NIL Summation
Dimension 'a' (mm) 0.00 0.00 0.00 80.00 0.00 0.00 0.00
Dimension 'b' (mm) 0.00 0.00 0.00 1312.00 0.00 0.00 0.00
Y (mm)
Area A (mm^2)
0.000 0.000 0.000 656.000 1312.000 0.000 0.000
0.00 0.00 0.00 104960.00 0.00 0.00 0.00 104960.00
AY (mm^3)
AY*Y (mm^4)
0.000E+0 0.000E+0 0.000E+0 6.885E+7 0.000E+0 0.000E+0 0.000E+0 6.885E+7
0.00E+00 0.00E+00 0.00E+00 4.52E+10 0.00E+00 0.00E+00 0.00E+00 4.52E+10
I x-x own (mm^4)
0.000E+0 0.000E+0 0.000E+0 1.506E+10 0.000E+0 0.000E+0 0.000E+0 1.506E+10
Yc , Distance to centroid of section measured from bottom flange = summation(AY)/summation(A) Yc = 656.00 mm I x-x = summation(I x-x own) + summation(AY*Y) - [{summation(AY)}^2/summation(A)] I x-x = 1.506E+10 mm^4 Sxx = 2.295E+7 mm^3 Height of main plate Thickness of main plate Area of Main plate,
Aweb
= 1312.00 mm = 80.00 mm = Height x Thickness
= 104960.00 mm^2
About Y-Y axis S/no
Description of Elements
1 NIL 2 NIL 3 NIL 4 80 x 1312 5 NIL 2a NIL 3a NIL Summation
Dimension 'a' (mm) 0.00 0.00 0.00 80.00 0.00 0.00 0.00
Dimension 'b' (mm) 0.00 0.00 0.00 1312.00 0.00 0.00 0.00
X (mm)
0.00 0.00 0.00 0.00 0.00 0.00 0.00
Area A (mm^2) 0.00 0.00 0.00 104960.00 0.00 0.00 0.00 104960.00
AX (mm^3)
AX*X (mm^4)
0.00 0.0E+00 0.00E+0 0.0E+00 0.00E+0 0.0E+00 0.00 0.0E+00 0.00 0.0E+00 0.00E+0 0.0E+00 0.00E+0 0.0E+00 0.000E+0 0.000E+0
I y-y own (mm^4)
0.000E+0 0.000E+0 0.000E+0 5.598E+7 0.000E+0 0.000E+0 0.000E+0 5.598E+7
Xc , Distance to centroid of section measured from middle of main plate = summation(AX)/summation(A) Xc = 0.00 mm I y-y = summation(I y-y own) + summation(AX*X) - [{summation(AX)}^2/summation(A)] I y-y = 5.598E+7 mm^4 Syy = 1.399E+6 mm^3
129
CHECK ATTACHMENTS OF PADEYES (CONT'D) Sling Angle (w.r.t Horizontal) Tensile Force = SWL * SIN (theta) Shear Force = SWL* COS (theta) Out-of-Plane Force = SWL*0.05 (5% of actual force) Dynamic Factor = Design Tensile Force = Design Shear Force = Design Out-of-Plane Force =
1.50 (Td = T* 1.50) (SHFd = SHF* 1.50) (OPFd = OPF*1.50)
Height of Centerline of Hole Distance from bottom flange to centreline of hole Mxx = SHFd x H - Td x (Hm -Yc) Myy = OPFd x H
theta T SHF OPF
= = = =
60.00 415.69 240.00 24.00
Degree tons tons tons
Td = SHFd = OPFd =
6116.91 3531.60 353.16
kN kN kN
H = Hm = = =
0.306 1.025 1176.47 108.07
m m kN-m kN-m
1. CHECK SHEAR STRESS Allow. Shear Stress In-plane : Actual Shear Stress
Fv
= 0.4 * Fy
=
138.00
MPa
fvx
= SHFd/Aweb Stress Ratio
= =
33.65 0.24
MPa
O.K!
2. CHECK TENSILE STRESS Allow. Tensile Stress Actual Tensile Stress
Ft ft
= 0.6 * Fy = Td/Summation(A) Stress Ratio
= = =
207.00 58.28 0.28
MPa MPa
O.K!
Fb
= 0.6 * Fy
=
207.00
MPa
fbx
= Mxx/Sxx Stress Ratio
= =
51.26 0.25
MPa
O.K!
fby
= Myy/Syy Stress Ratio
= =
77.22 0.37
MPa
O.K!
= ft/Ft + (fbx+fby)/Fb
=
0.90
= 0.66 * Fy
=
227.70
MPa
= = =
109.54 77.22 33.65
MPa MPa MPa
3. CHECK BENDING STRESS Allow. Bending Stress In-plane : Actual Bending Stress Out-of-plane : Actual Bending Stress
4. CHECK COMBINED STRESS Combined Stress Ratio 5. CHECK VON MISES YIELDING CRITERIA Allow. Combined Stress Fc
5.1 Check maximum combined stresses at main plate location. Sum of Stresses in X-Plane fx = ft + fbx Sum of Stresses in Y-Plane fy = Ave. Shear Stress txy = (SHFd/Aweb) Actual Combined Stress Stress Ratio
fc
= (fx^2+fy^2-fx*fy+3*txy^2)^0.5 MPa = 113.58 = 0.50
O.K!
O.K!
130
8.5
Trunnion Checking Max. Static sling force, Ps Ps = 480 x 0.5 x 1.1 ÷ (Sin60°) = 305 Mton Trunnion Cross Section Area, At At = (914 – 38) x 38 x π = 1004577 mm² Shear Stress, fv = 1.5 x (305 x 9.81 x 1000) ÷ (104577 x 0.5) = 85.83 N/mm² < Fv = 0.4 Fy = 0.4 x 345 = 138 N/mm² OK! Where, 1.5 = Dynamic factor
C
Fy = 345, Material Yielding stress Ring Stress
8”
As per Roak Formulas, Cross sectional Area, A= 8 x 1.5 + 16.5 x 1.5 = 36.75 in²
18”
Plate thickness = 1.5”
C = 6.811 in Moment Inertia, I = 1 /12 x 16.5 3 x 1.5 + 16.5 x 1.5 x (9.75 – 6.811)² + 8 x 1.5 x (6.811 – 0.75)² = 1216 in4 Sectional Modulars, S = 1216 / (18 – 6.811) = 108.68 in3 131
ROARK CLOSED RING ANALYSIS EQUATIONS FROM 6th ED
SEMBAWANG SHELL EA PROJECT-LIFTING FRAME TRUNN 01-Mar-01 (AS OF 20 JUNE 1992: MULTIPLE CASES AVAILABLE) THE FOLLOWING ARE ASSUMED CO (ONLY THE FIRST 4 CASES OF EACH CATAGORY) 1) CROSS SECTION 2) MODULUS OF ELASTICITY 3) POISSON'S RATIO 4) RADIUS
CASE NUMBPARAMETERS: TOTAL W SHIFT ANGLE (kN) (DEG)
O
O
o
(DEG)
(DEG)
(mm)
25 25 25 25 25 25
0.0000 0.0000 0.0000 0.0000 0.0000 0.0000
0.00 0.00 0.00 0.00 0.00 0.00
0.0000 0.0000 0.0000 0.0000 0.0000 0.0000
N.A. N.A. N.A. N.A. N.A. N.A.
N.A. N.A. N.A. N.A. N.A. N.A.
16 16 16 16 16 16
0.0000 0.0000 0.0000 0.0000 0.0000 0.0000
0.00 0.00 0.00 0.00 0.00 0.00
12.5000 25.7000 40.5000 60.0000 0.0000 0.0000
12.5000 25.7000 40.5000 60.0000 0.0000 0.0000
N.A. N.A. N.A. N.A. N.A. N.A.
2984.6080 0.0000 0.0000 0.0000 0.0000 0.0000
0.00 0.00 0.00 0.00 0.00 0.00
N.A. N.A. N.A. N.A. N.A. N.A.
N.A. N.A. N.A. N.A. N.A. N.A.
558.8000 0.0000 0.0000 0.0000 0.0000 0.0000
25S 25S 25S 25S 25S 25S
RADIUS TO RING NEUTRAL AXIS (mm)=
284.2006
YIELD STR. CROSS SECT. PROPERTIES MPa AREA (mm^2) SECT (mm^3) 344.72 23709.6 1780946.1
132
RESU LT S:
M AX. C H EC K SEM BAW AN G SH ELL EA PR O JEC T-LIFTIN G FR AM E TC IR C U M . TEN C IR C U M . TEN M O M EN T + BEN D IN G D EG R EES M O M EN T C IR C U M .TENAD IAL SH EA STR ESS R ATIOSTR ESS R ATIO S TR ESS R ATIO (kN -m ) (kN ) (kN ) 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 135 140 145 150 155 160 165 170 175 180 185 190 195 200 205 210 215 220 225 230 235 240 245 250 255
60.678 59.644 56.579 51.594 44.869 36.648 27.226 16.943 6.170 -4.708 -15.301 -25.235 -34.162 -41.779 -47.834 -52.146 -54.605 -55.152 -53.896 -51.027 -46.744 -41.259 -34.787 -27.550 -19.767 -11.656 -3.431 4.704 12.554 19.940 26.696 32.673 37.745 41.803 44.763 46.564 47.168 46.564 44.763 41.803 37.745 32.673 26.696 19.940 12.554 4.704 -3.431 -11.656 -19.767 -27.550 -34.787 -41.259
-559.488 -565.277 -582.364 -609.921 -646.602 -690.589 -739.659 -791.260 -842.608 -890.786 -932.851 -965.947 -987.411 -994.882 -986.393 -960.461 -913.617 -833.370 -746.152 -653.255 -556.016 -455.800 -353.985 -251.948 -151.047 -52.609 42.085 131.813 215.430 291.871 360.172 419.475 469.036 508.238 536.592 553.746 559.488 553.746 536.592 508.238 469.036 419.475 360.172 291.871 215.430 131.813 42.085 -52.609 -151.047 -251.948 -353.985 -455.800
0.000 83.137 163.269 237.502 303.155 357.861 399.657 427.055 439.105 435.436 416.278 382.464 335.416 277.104 209.991 136.959 60.775 -15.507 -84.473 -145.570 -198.361 -242.527 -277.867 -304.302 -321.873 -330.737 -331.164 -323.536 -308.336 -286.145 -257.632 -223.545 -184.703 -141.985 -96.315 -48.657 0.000 -48.657 -96.315 -141.985 -184.703 -223.545 -257.632 -286.145 -308.336 -323.536 -331.164 -330.737 -321.873 -304.302 -277.867 -242.527
0.114 0.115 0.119 0.124 0.132 0.141 0.151 0.161 0.172 0.182 0.190 0.197 0.201 0.203 0.201 0.196 0.186 0.170 0.152 0.133 0.113 0.093 0.072 0.051 0.031 0.011 0.009 0.027 0.044 0.060 0.073 0.086 0.096 0.104 0.109 0.113 0.114 0.113 0.109 0.104 0.096 0.086 0.073 0.060 0.044 0.027 0.009 0.011 0.031 0.051 0.072 0.093
0.165 0.162 0.154 0.140 0.122 0.099 0.074 0.046 0.017 0.013 0.042 0.069 0.093 0.113 0.130 0.142 0.148 0.150 0.146 0.139 0.127 0.112 0.094 0.075 0.054 0.032 0.009 0.013 0.034 0.054 0.072 0.089 0.102 0.113 0.122 0.126 0.128 0.126 0.122 0.113 0.102 0.089 0.072 0.054 0.034 0.013 0.009 0.032 0.054 0.075 0.094 0.112
0.279 0.277 0.272 0.264 0.254 0.240 0.225 0.207 0.189 0.194 0.232 0.265 0.294 0.316 0.331 0.337 0.335 0.320 0.298 0.272 0.240 0.205 0.167 0.126 0.084 0.042 0.018 0.040 0.078 0.114 0.146 0.174 0.198 0.217 0.231 0.239 0.242 0.239 0.231 0.217 0.198 0.174 0.146 0.114 0.078 0.040 0.018 0.042 0.084 0.126 0.167 0.205
133
DEGREES 260 265 270 275 280 285 290 295 300 305 310 315 320 325 330 335 340 345 350 355 360
CIRCUM. TEN CIRCUM. TEN MOMENT + BENDING MOMENT CIRCUM. TENADIAL SHEA STRESS RATIOSTRESS RATIO S TRESS RATIO (kN-m) (kN) (kN) -46.744 -51.027 -53.896 -55.152 -54.605 -52.146 -47.834 -41.779 -34.162 -25.235 -15.301 -4.708 6.170 16.943 27.226 36.648 44.869 51.594 56.579 59.644 60.678
-556.016 -653.255 -746.152 -833.370 -913.617 -960.461 -986.393 -994.882 -987.411 -965.947 -932.851 -890.786 -842.608 -791.260 -739.659 -690.589 -646.602 -609.921 -582.364 -565.277 -559.488
-198.361 -145.570 -84.473 -15.507 60.775 136.959 209.991 277.104 335.416 382.464 416.278 435.436 439.105 427.055 399.657 357.861 303.155 237.502 163.269 83.137 0.000
0.113 0.133 0.152 0.170 0.186 0.196 0.201 0.203 0.201 0.197 0.190 0.182 0.172 0.161 0.151 0.141 0.132 0.124 0.119 0.115 0.114
0.127 0.139 0.146 0.150 0.148 0.142 0.130 0.113 0.093 0.069 0.042 0.013 0.017 0.046 0.074 0.099 0.122 0.140 0.154 0.162 0.165
0.240 0.272 0.298 0.320 0.335 0.337 0.331 0.316 0.294 0.265 0.232 0.194 0.189 0.207 0.225 0.240 0.254 0.264 0.272 0.277 0.279
134
8.6
Summary
The final design of the lifting frame is shown in Figure 8.1.
The lifting devices of the above spreader frame are the combination of padeye and lifting trunnions. Padeyes are designed underneath of spreader frame, while the lower slings remain un-changed, these save lots of rigging changing time during actual lifting operation. The trunnions above the spreader frame make operator much easier for rerigging of slings for next lift. The trunnions are also catered for different COG. The concept of X-Brace at centre and introduction of thicker joint-can eventually lead into a lighter frame, 69 ton only. Other concept, four braces at corner, was studied and found not cost saving. A 50mm thick of the main plate of padeye/trunnions per design are good enough for the lifting. The above analysis was based on the fabricator stock of main plate 80 mm thick.
135
Table 8.1
Weight and COG data C.O.G (See Note) X Y (mm) (mm)
Lifting Point Dist X Y (mm) (mm)
780
12640
9840
18060
18480
Separation Pallet Starboard
680
9330
9240
18060
18480
3
Separation Pallet Port
860
9830
9840
18060
16740
4
Compression Pallet Starboard
619
8840
9240
18060
18480
5
Compression Pallet Port
595
9840
6740
18060
18480
6
Power Generation Port
1063
13040
10840
18060
22015
S/No .
PALLET DESCRIPTION
Pallet Weight (ton)
1
Power Generation Starboard
2
y
Note: Origin is located at the lower left lifting point, shown on the left. x
Table 8.2
Total Weight and COG Revised C.O.G (based on frame)
Lifting Weight (m.ton) Pallet 15% contin.
Computer Model Frame 5% contin
Misc. Load Rigging & Padeye
X (mm)
Y (mm)
Power Generation Starboard
897
58
29
12325
9788
Separation Pallet Starboard
782
58
29
9301
9240
Separation Pallet Port
989
58
29
9766
10592
Compression Pallet Starboard
712
58
29
8861
9240
Compression Pallet Port
684
58
29
9750
7020
Power Generation Port
1222
58
29
12777
9084
DESCRIPTION
136
TABLE 8.3
MEMBER ANALYSIS RESULT SUMMARY
SACS Group ID PALLET NAME
1
2
3
4
Criti.
Max. Criti. Max. Criti. Max. Criti. Max.
Memb
UC* Memb
UC
Memb
UC
Memb
UC
Power Generation Starboard
4-12
0.48
4-21
0.35
2-21
0.28
2-4
0.37
Separation Pallet Starboard
12-20
0.33
1-21
0.20
3-21
0.19
2-4
0.16
Separation Pallet Port
12-20
0.49
4-21
0.31
3-21
0.20
2-4
0.33
Compression Pallet Starboard
12-20
0.29
1-21
0.20
3-21
0.19
1-3
0.13
Compression Pallet Port
15-10
0.39
1-21
0.18
2-21
0.26
2-4
0.27
Power Generation Port
15-10
0.63
4-21
0.64
2-21
0.64
2-4
0.86
* UC: Unity Check = Actual Stress over Allowable stress
137
Figure 8.1
Lifting Frame Details
138
B
A
B
1
1
SIM. DETAIL 1
DETAIL 1
SIM. DETAIL 2
DETAIL 2
2
2
B
DETAIL 3
R020
CHAPTER 9
9.1
FINITE ELEMENT ANALYSIS FOR LIFTING DESIGN
Introduction
Finite Element Analysis (FEA) is a computer based method to simulate and analyse the behaviour of engineering structures and components under a variety of conditions. It is an advanced tool that is used in engineering design. The method is comprised of three stages: (A) pre-processing, in which the analyst develops a finite element mesh of the geometry and applies material properties, boundary conditions and loads; (B) solution, during which the program derives the governing matrix equations (stiffness x displacement = load) from the model and solves for the displacements, strains and stresses and (C) post-processing, in which the analyst obtains results usually in the form of deformed shapes and contour plots which help to check the validity of the solution.
FEA is widely accepted in almost all engineering disciplines. The technique is based on the premise that an approximate solution to any complex engineering problem can be reached by subdividing the structural component into smaller and more manageable (finite) elements. The Finite Element Model (FEM) is analysed with an inherently greater precision than would otherwise be possible using manual calculations, since the actual shape, load and constraints, as well as material property combinations can be specified with much greater accuracy than that used in manual calculations.
It is possible to perform a simulation of a design concept and to determine its real world behaviour under envisaged environments to enable the concept to be refined prior to the creation of drawings, when minor cost expenditure is committed and 139
changes are inexpensive. Once a model has been developed, the analysis helps in evaluating the feasibility of the new design as well as trouble shooting failed components to refine the design.
This chapter discusses FEM structural analysis in heavy lift design and analysis. Two critical lift applications, namely, living quarter module lifting and lifting padeye joints, will be investigated using different finite element models.
9.2
Finite Element Analysis for Module Lifts
9.2.1 Structural and Material Details A typical living quarter module in North Sea field development project consists of the following structural components: •
Utility Area,
•
Living Quarter Area,
•
Cellar deck,
•
Helicopter deck,
•
Bridge,
•
Drain caisson,
•
Deluge caisson,
•
Sewage caisson,
•
Seawater caisson and
•
Fire water caisson.
All decks except the cellar deck are plated decks. As for the cellar deck, there is an open frame structure for free ventilation. The utility area and the living quarter area are closed and airtight. The deck structure is made to fit the jacket and supported on three 140
points. The interface point is at elevation LAT (Low Astronomical Tide) +20.0m. The helideck is an octagon of 22.8m internal diameter and is located approximately 4.0m above the roof. The helicopter deck is designed for landing of a Westland EH101 helicopter.
The lifting analysis is performed using the SACS software. The computer model of the module consists of eight levels, including the roof and helideck level, from EL.+22.0m to EL.+50.5m. The module is to be lifted offshore using single hook with a lifting spreader frame.
The analysis consists of 92 load combinations. They are two for basic load combinations of two diagonally opposite lifting points carrying 75% of the lift weight; two combinations with the basic loads and factors; eight combinations with the basic loads, the factors and couples which simulate CoG (centre of gravity) shift of one meter towards each frame corner and eighty combinations with horizontal force of 5% lift weight incorporated in eight directions each to check lifting spreader frame.
The maximum expected lift weight of 1556 ton, which includes module weight of 1391 ton, rigging weight of 65 ton and grillage and sea-fastening weight of 100 ton, is used as per the design requirements. The consequence factor of 1.15 is added for members connecting directly to the padeye as per code requirement.
All the members and the joints were checked against the DANISH code as per project requirement. The load factor used in lifting analysis is tabulated in Table 9.1.
It was considered at the same time that the lift design weight was distributed over the 141
lifting points on the spreader frame such that the two diagonally opposite lift points carried 75% of the lift weight. In addition, CoG shift of 1m towards each corner of the frame was considered instead of CoG Shift (fcog) factor of 1.05 in load case 210, 220, 230, 240, 310, 320, 330 and 340. Design Load Factor = (γc)*(γf)*(DAF)*( fcog)*(SKLt)
(9.1)
= 1.368 (for load case 200 and 300)
Design Load Factor = (γc)*(γf)*(DAF)* (SKLt)
(9.2)
= 1.303 (for load case 210, 220, 230, 240, 310, 320, 330 and 340)
Material for secondary beam, external cladding except in Row A and Row B in accommodation area, internal cladding and deck plate of level one, level three, level four, level five and level six will be mild steel with yielding stress of 248 MPa.
Material for main beam, plates to be used as part of main steel, external cladding in Row A and Row B in accommodation area and deck plate of level two, roof and mezzanine deck, as well as lifting spreader frame will be high strength steel with yielding stress of 345 MPa.
Deck plate thickness is 6mm except for lay-down area where 15mm is used. External cladding in Row A and Row B in accommodation area is 6.0mm corrugated plate, in Row 1 and Row 2, while the others in 4.5mm. Rib pattern dimensions are 230mm length with 68mm depth and 45° bevel.
The design value of material parameter will be determined by dividing characteristic value by the partial coefficients γm as given in Table 9.2.
142
The module is designed to be lifted offshore using spreader frame with one hook point. The frame was connected with the module on the top of helideck at the point A2 (joint 8220) and B2 (joint 8120) as well as on the roof at the point A3 (joint 7230) and B3 (joint 7130). Temporary braces between the roof and helideck level on Row A and Row B, as well as on Row 2 and Row 3 were provided.
9.2.2 Finite Element Modelling and Analysis The sling was modelled as weightless tubular with moments at the two ends released. The minimum sling angle considered was 70 degree as per the information provided by the installation contractor, Heerema Marine Contractors. Since the system with four slings connecting a hook is structurally under-constrained, two springs were required to ensure numerical stability by the SACS program. The two artificial springs were applied onto joints 1220(A2) and 1130(B3) at EL (+) 17.187. To simulate the uneven distribution of lift weight at two diagonal opposite lifting points, the elastic modulus of slings was adjusted proportionally, which was achieved by several SACS runs and using an iterative method.
Deck plates and external corrugated wall in accommodation area were modelled as shear plate and corrugated plate respectively.
Members with the same properties are grouped by the computer. A sample list of member group properties generated by the computer and section properties are extracted and shown in Table 9.3 and Table 9.4.
Plates with the same properties are
grouped by the computer. A list of ‘plate group’ properties generated by the computer and section properties is extracted and shown in Table 9.5 and Table 9.6.
143
The weight of main steel was generated by SACS program. Other gravity loadings, which included rigging, secondary and miscellaneous steel, architectural components, mechanical, piping, and electrical & instrument were manually calculated and added to the model. The summary of loads is shown in Table 9.7, while Table 9.8 gives sample of loading description.
Structural Loads It consists of two groups of loading. One is the computer generated self-weight of the model. The other is the structural weight derived from manual calculation which includes leg stabbing guide, secondary beam, plating & grating, corrugated wall, handrail, staircase and miscellaneous steel.
Architectural Loads It consists of deck and wall insulation, floor finishes, partition, cladding, ceiling, furniture, etc.
Mechanical Loads This consists of dry and operating load from mechanical equipment, HVAC ducting and fire safety equipment. The loading is separated to three groups.
Piping Loads It consists of the dry weight of pipes and ducts etc.
Electrical and Instrument Loads
144
This consists of electrical bulk weight and electrical and communication equipment weight.
Rigging Weight and Grillage & Sea-fastening This consists of rigging weight of 65 ton and grillage & sea-fastening weight.
Couples to simulate CoG shift of one meter Couples to simulate CoG shift of one meter towards spreader frame corners.
Horizontal Force of 5% of Lift Weight 5% of lift weight acted on lifting spreader frame horizontally to check the frame.
Structural Analysis Computer System (SACS) suite of software was used to perform the lifting analysis. A total of ninety-two (92) load-cases were considered in the analysis. These combinations covered module basic weight combination (2), lifting case without CoG shift (2), lifting cases with CoG. shift (8) and lifting case with horizontal force (80), see Table 9.10 for the example. Table 9.11 gives the sample of 75% lifting weight factor of point B2 and A3 at different loading conditions.
Analysis results, such as combined load summation, support reactions and spring reactions, are given in Table 9.12 to 9.14. All members are found to have stress ratios less than unity. Members with stress ratios greater than 0.9 are listed in Table 9.15. All joints are found to have stress ratios less than unity shown in Table 9.16. The summary of the four sling forces is given in Table 9.17.
145
9.2.3
Discussions
Support condition The hook point is treated as a fixed point. Slings attached to module are treated as moment free members. Artificial spring supports must be added for the numerical stability in computations. Spring stiffness factors should be small to minimise significant horizontal forces as Table 9.9.
CoG shifting/Load distribution The above analysis has taken into account of CoG shift of 1.0m, with 75% and 25% of load distribution on two diagonally opposite lifting points. This is normally not considered if API RP 2A method is chosen as design code.
Early Weight Control Weight control report for accurate lifting weight and CoG is still not ready; therefore, the computer analysis results are good enough for the selection of rigging and lifting crane vessel.
Rigging system modelling The requirement of spreader bar/frame per module layout of top level needs to be identified. The correct sling property (weight less), sling length and offset at padeye points need to be assessed, and proper releases of all slings need to be specified. Joint displacement Designer often tends to make mistake of misalignment of CoG and hook, which leads the joint displacements to be very large. To overcome this, a few computer runs are required to find out CoG location and to adjust hook point accordingly.
146
9.3
Finite Element Analysis for Lifting Padeye Connection
9.3.1 Structural Details The Dan FG jacket is a conventional space frame structure, consisting of 4 legs with the top of the jacket work points arranged in a grid with a transverse spacing of 20 metres at EL(+) 13.5m. 2 pile sleeves will be attached to each leg of the jacket. The four legs are double battered at 1:9.4 in both transverse and longitudinal directions. The top of the jacket cut-off elevation for all four legs of the jacket are at EL(+) 15.000m. Jacket horizontal bracing levels are at EL(-) 39.5m, EL(-) 29.8m and EL(+) 12.6m. The jacket is designed for 42.9m water depth. The height of jacket is 58.4m. The estimated possible lifting weight for Jacket is 3038 tons, based on the weight control report.
The jacket will be fabricated in a horizontal position. The fabricated jacket will be loaded out by lifting it off using ‘Asian Hercules II’ from quayside onto the barge. The lifting arrangement for loadout is shown in Figure 9.3. Loadout analyses were carried out to simulate the lifting operation to evaluate the adequacy of the jacket together with appurtenances & rigging gear during loadout lift.
On reaching its tow destination in the Danish sector of the North Sea, SAIPEM will carry out the upending with SSCV S7000, see Figure 3.5. The S7000, operating in dynamic mode at a heavy lift draught of 27.5m, in 43m of water depth, will lift the jacket off the vessel and upend it using the cranes in tandem. The upending process is explained in Figure 9.4. 11 steps of upending analyses were performed to simulate different orientations of the jacket from the initial horizontal position to the final vertical position of the jacket. 147
During the above analysis, the lifting points were found essentially important. The critical padeye, hereafter called Joint 164 (from SACS), on Jacket pile sleeve is analysed using the finite element method (FEM) with the computer program of MSC/NASTRAN. The purpose is to compute the stress distribution in the four loading cases during load out and upending as shown in Figure 9.5. As illustrated in Figure 9.6, the joint 164 consists of two chord members, three bracing members and a pad-eye member. To simulate the actual loading conditions, loads subjected to lifting by the sling are applied at the centre of the pad-eye while the other end of each chord or brace, where the member is strongly supported by other members, is fixed. The fixed boundaries for all the chords and braces are shown in Figure 9.7. What is concerned in the analysis is the stress distribution in the adjacent areas around the joint. If the stress level was found too high, the structure will be improved and re-analyzed till satisfying results are achieved.
Except the pad-eye member, dimensions and length of members 2 to 6 are listed in Table 9.18. For the pad-eye, the main plate is 100mm thick and the two cheek plates are 100mm thick also. In addition, the joint is reinforced with three 100mm thick full ring plates.
9.3.2 Loading Cases The forces of each member from one load out analysis and three upending analysis by SACS IV have been listed in Table A.1 in Appendix A. The joint is modelled with all braces members (members 2, 3, 4 and 6) being extended to the locations where supports are provided by other strong braces. The other ends (away from joint 164) of these four members are fixed. Since there is no support at the other end of chord 148
member 5, no constraints are applied over there. The sling forces being applied on the pad-eye for cases A, B, C & D are shown in Figure A.1 in Appendix A. Thus the force will distribute mainly based on the stiffness of members automatically, which is the most reasonable way.
9.3.3 Finite Element Modelling The FE model for the structure is illustrated in Figure 9.8. The four-sided solid element (labelled as CTETRA in NASTRAN) with ten nodes and five-sided solid elements (labelled CPENTA in NASTRAN) are employed to model the structure. They are 2ndorder isoparametric elements.
Particularly fine mesh is generated in the welding-line area to ensure computation accuracy; 128 elements are used around the circumference. The pad-eye and stiffeners are also modelled with element size of 20~50 millimetres. Other parts of the structure are modelled with relatively coarse mesh with an element size of 100 millimetres. The model consists of 211,113 elements with 376,104 nodes. 9.3.4 Result Analysis Stress of the structure under one load out and three upending conditions is computed for the above FEM model using MSC/NASTAN. The 1st-principal stress distributions and Von Mises stress distributions of the Case D only are shown from Figure 9.9 to Figure 9.10 respectively. The maximum stress values are summarised and listed in Table 9.19.
More detailed results of the maximum stresses on the braces are given in Appendix A. The maximum stress values are summarised and listed in Table 9.20.
149
Stress analysis of the pad-eye Joint 164 under the loadout (1 case) and upending (3 cases) conditions was conducted. The Von Mises stress and 1st-principal stress results are presented for each case. Since the maximum stresses (both 1st-principal stress and Von Mises stress) are less than or close to the yield strength of the steel material used for the structure, the structure should globally be safe under the four aforementioned load conditions. Since the maximum 1st-principal stress of case D is a little bit larger than the yield strength, it would be better if small side-stiffeners can be added at the bottom connection of main plate to the pile sleeve.
150
9.4
Summary
Finite element analyses have been performed on a living quarters module and detailed behaviour of a padeye connection. In the numerical modelling, the hook point is treated as fixed. Spring support must be input for structural stability. The spring stiffness factor should be small to minimise the horizontal reaction force. It is important to identify the requirement of spreader bar/frame according to the module layout at the top level and to model correct sling property (weight less), sling length and offset at padeye locations. Finite element analysis can also provide important information for detailed stress evaluation and safety check at the padeye connection.
151
Table 9.1
Load factor used for lifting analysis Factor Single Crane Lift 1.15 Load Contingency Factor (γf) Dynamic Amplification Factor (DAF) 1.10 C of G Shift (fcog) 1.05 Tilt Factor (SKLt) 1.03 Yaw Factor (for local design of trunions) N/A Consequence Factor (γc) N/A Trunion attachment joint 1.15 Members local to lift point 1.00 Other structural steel members Table 9.2 Design Value of Material Parameter Material Parameters
Safety Class Safety Class Safety Class normal high and Strict high and Normal Material Control Material Control (Secondary steel (Primary steel (Primary steel members) members) members)
Yield stress
Fy
1.28
1.21
1.15
Tensile strength
Fu
1.56
1.48
1.41
Punching strength
τg
1.41
1.34
1.28
Modulus of elasticity E
1.48
1.48
1.34
Note:
The material parameters, Fy of 1.21, E of 1.48 and τg of 1.34, were used in computer analysis
by SACS software .
152
Table 9.3 Sample of Member Group Properties SACS SACS Group ID SECT ID
Outside Wall Diameter Thick
E
G
(units: cm, kN) FY
KY
KZ
SPC DEN SAM
34.5 34.5 34.5 34.5 34.5 34.5 34.5 34.5 34.5 34.5 24.8 24.8
1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1 1
0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5
LEN
*1000 *1000 0B1 0B2 1H3 1H4 1H5 1I5 2B5 2B5 2C1 2C5 SL1 SL2
21.9 27.3
1.27 1.27
HEB300 HEB400 HEB500 IPE500 2B5 IPE500 2C1 2I5C 27.3 27.3
7.5 7.5
20 20 20 20 20 20 20 20 20 20 4 4
8 8 8 8 8 8 8 8 8 8 8 8
7.849 7.849 7.849 7.849 7.849 7.849 7.849 7.849 7.849 7.849 0.001 0.001
0.5
Where: * data in column SPC for tubular shear checking only ** data in column LEN for segment length *** data in column E for ID SL1 & SL2 will be variable: E for SL2 = 20000kN/cm2 E for SL1 = 4000kN/cm2 Table 9.4 Sample of SACS Section Properties SACS Section ID 0D5 2I5C HS2 PG2 TP2 TP3
Type
A
WF WF BOX BOX CON CON
30 20 30 70 45.7 145
B 2.8 2.0 1.2 4.0 3.175 2.5
(unit: cm)
C
D
70 50 30 85 76.2 76.2
1.45 1.5 1.2 5.0
Note: A -- depth for Box section, flange width for WF section, one end diameter for CON section B -- side wall thickness for Box section, flange thickness for WF section, thickness for CON section C -- width for Box section, depth for WF section, one end diameter for CON section D -- top and bottom wall thickness for Box section, web thickness for WF section
153
Table 9.5
Sample of SACS Plate Group Properties
(units: cm, kN)
ID
THIC K
M
E
U
FY
PLZO SECT
AV.SP L
T
DEN
1F1 2F1 2W1 2W4 2WA 2WB 6F1 7F1
0.6 0.6 0.42 0.42 0.503 0.503 0.6 1
S S Y Y Y Y S S
20 20 20 20 20 20 20 20
0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25
24.8 24.8 24.8 24.8 34.5 34.5 24.8 34.5
25 25 3.0 3.0 3.0 3.0 18 20
35 80 33 33 33 33 50 35
B B T T T T B B
0.001 0.001 0.001 0.001 0.001 0.001 0.001 0.001
TROUGH HP100X8 CORR CORR CORR6 CORR6 HP120X8 TROUGH
X X Y Y Y Y X Y
Note: Column M S -- Shear plate Y -- Corrugated in local Y direction I -- Isotropic plate (used for deflection checking only for plate group 1F1, 2F1, 3F1, 4F1, 5F1 and 6F1) Table 9.6
Sample of SACS Plate Stiffener Properties
Type
Label
IBM BOX BOX IBM BOX
HP120X8 CORR CORR6 HP100X8 TROUGH
Table 9.7 Item Structural (a) Model (b) Misc Loading Architectural Mechanical HVAC Fire and Safety Electrical Piping Rigging Grillage & seafatener Total
(unit: cm)
A
B
C
D
E
F
12 6.0 6.0 10 27.5
0.8 23 23 0.8 35
2.3 10 10 2.17 15
0.8 0.5 0.6 0.8 0.5
1.4 0 0 1.27 0.001
1.4 0 0 1.27 0.5
SACS Loading Summary Lift Wt (Mton) 399.14 373.05 183.50 102.09 35.95 51.24 95.07 59.28 65.00 100.00 1464.32
Contingency 1.05 1.05 1.10 1.10 1.10 1.10 1.10 1.10 1.00 1.00
Final Lift WT (mton) 419.10 391.70 201.85 112.30 39.55 56.36 104.58 65.21 65.00 100.00 1555.64
154
Table 9.8 Loading D01 D02
Sample of SACS Loading ID and Description Description
D21 D22 D23 D41 D51
Main Steel Weight (created by computer) Miscellaneous Weight (leg stabbing guide, secondary steel, plating & grating, corrugated wall, handrail, staircase, louver and wind shield) Architectural Weight (wall insulation, partition, floor, ceiling, door, window, furniture) Mechanical Equipment Lift Weight HVAC Bulk Weight and Equipment Dry Weight Fire and Safety Bulk Weight and Equipment Dry Weight Piping Dry Weight Electrical and Instrument Bulk Weight and Equipment Dry Weight
X01 XA2 XA3 XB2 XB3
Lifting rigging Weight and Grillage & Seafastener Weight Couples to simulate CoG shift of one meter towards A2 Couples to simulate CoG shift of one meter towards A3 Couples to simulate CoG shift of one meter towards B2 Couples to simulate CoG shift of one meter towards B3
X000 X090
Horizontal force induced by 5% of lift weight (at 0 degree) Horizontal force induced by 5% of lift weight (at 90 degree)
D03
155
Table 9.9
Type of Support Constraints and Member Releases
TYPE
LOCATION
JOINT NO.
Fixed Support
EL(+)69m
hook
XY-Spring
EL(+)21.8m
1220, 1130
Sling
Lifting Frame
Horizontal Brace
Member 8.625”ø x 0.5”
Table 9.10 Loading Number D01 D02 D03 D21 D22 D23 D41 D51 X01 XA2 XA3 XB2 XB3 100
RELEASES
Stiffness = 1kN/mm Mx, My, Mz, Fz One end: Mx, My, Mz The other end: My, Mz One end: Mx, My, Mz The other end: My, Mz
Level 1
SACS Load Combinations 75% of lift weight at point B2 & A3 100
200
210
220
230
240
75% of lift weight at point A2 & B3 110
-1.05
-1.05
-1.05
-1.05
-1.1
-1.1
-1.1
-1.1
-1.1
-1.1
-1.1
-1.1
-1.1
-1.1
-1.1
-1.1
-1.0
-1.0 1.303
300
310
320
330
340
1.303 1.303
1.303 1.303
1.303 1.303
-1.368 -1.303 -1.303
-1.303
-1.303
1.303 -1.368 -1.303
-1.303 -1.303 -1.303
156
Table 9.11 Loading Number 220 X000 X090 Loading Number 230 X000 X090 Loading Number 240 X000 X090
221 1.15 2.052
Sample of 75% Lifting Weight Factor 75% of lift weight at point B2 & A3 222 1.15 1.451 1.451
223 1.15 2.052
224 225 1.15 1.15 -1.451 -2.052 1.451
226 1.15 -1.451 -1.451
227 1.15
228 1.15 1.451 -2.052 -1.451
75% of lift weight at point B2 & A3 231 1.15 2.052
232 1.15 1.451 1.451
233 1.15 2.052
234 235 1.15 1.15 -1.451 -2.052 1.451
236 1.15 -1.451 -1.451
237 1.15
238 1.15 1.451 -2.052 -1.451
75% of lift weight at point B2 & A3 241 1.15 2.052
242 1.15 1.451 1.451
243 1.15 2.052
244 245 1.15 1.15 -1.451 -2.052 1.451
246 1.15 -1.451 -1.451
247 1.15
248 1.15 1.451 -2.052 -1.451
Note: Factor 2.052 = 1.368*1.5 (where 1.5 = sling force 75%/25% distribution) Factor 1.451 = 2.052*sin(45) Factor 1.15 = Consequence factor for member connecting to padeye Table 9.12 SACS Combined Load Summation LOAD CASE Fx (kN) Fy (kN) Fz (kN) 100 -0.25 -2.50 15241.50 200 -0.33 -3.42 20850.39 210 202.49 -281.38 19859.67 220 -242.24 -248.09 19859.70 230 204.75 273.19 19859.65 240 -244.32 239.49 19859.69 110 -0.25 -2.50 15241.50 300 -0.33 -3.41 20850.39 310 202.49 -281.38 19859.67 320 -242.24 -248.09 19859.70 330 204.75 273.19 19859.65 340 -244.32 239.49 19859.69
157
Table 9.13 LOAD 100 200 210 220 230 240 110 300 310 320 330 340
Support Reactions Joint HKA2 Fx Fy 447.62 612.35 678.87 577.38 575.31 485.45 1171.37 1602.44 1621.15 1521.50 1517.42 1429.44
-611.74 -836.86 -927.77 -789.06 -786.24 -663.43 -1600.83 -2189.94 -2215.51 -2079.32 -2073.76 -1953.52
(UNIT: kN) Joint HKA3 Fx Fy
Fz 2400.16 3283.43 3640.12 3095.90 3084.82 2602.99 6280.89 8592.26 8692.60 8158.25 8136.42 7664.65
-1296.20 -1773.20 -1698.38 -1818.55 -1562.25 -1700.04 -321.39 -439.66 -429.25 -546.93 -293.33 -428.59
Table 9.14 Spring Reaction LOAD Joint 1220 CASE Fx Fy Fz 100 -1.25 -5.52 0.00 200 -1.71 -7.55 0.00 210 89.18 -155.58 0.00 220 -130.86 -136.94 0.00 230 110.42 139.46 0.00 240 -114.22 122.47 0.00 110 -1.73 -4.96 0.00 300 -2.37 -6.79 0.00 310 88.56 -154.86 0.00 320 -131.49 -136.22 0.00 330 109.80 140.18 0.00 340 -114.85 123.19 0.00 Table 9.15
-1315.20 -1799.19 -1723.28 -1845.21 -1585.15 -1724.96 -326.10 -446.11 -435.54 -554.95 -297.63 -434.87
(Unit: kN) Joint 1130 Fx Fy 1.13 1.55 113.47 -111.20 94.50 -129.93 1.61 2.21 114.09 -110.58 95.12 -129.30
-2.82 -3.85 -133.40 -118.75 126.13 109.42 -3.37 -4.61 -134.12 -119.47 125.41 108.69
Fz 5160.21 7059.17 6761.33 7239.71 6219.37 6767.90 1279.48 1750.33 1708.85 2177.36 1167.77 1706.23
Fz 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Sample of SACS Member Stress Listing
MAX LOAD DIST AXIAL BEND STRESS SHEARFORCE GROUP COMB COND FROM STRES Y Z FY FZ KLY/ KLZ/ UNITY NO. END RY RZ MEMBER ID KN KN (N/MM²) CK
7267-8220 7167-8120 H231-H230 H131-H130 7120-7121 7110-8120
LFD
0.95
325
3.6
176.5
8.6
0.0
0.0
0.0 64.5
64.5
LFD
0.95
205
3.6
175.3
9.1
0.0
0.0
0.0 64.5
64.5
LF4
0.92
201
3.0
186.2
-29.0
-71.3 -161.5
-21.7 32.9
32.9
LF4
0.91
301
2.9
181.1
27.9
-73.4 -182.4
11.4 32.3
32.3
4I3
0.91
200
0.0
LFD
0.90
218
3.2
60.1 -167.3 169.1
6.4
-37.1
11.1
151.1 40.5
31.1
0.0
0.0
0.0 57.1
57.1
158
Table 9.16 JOINT H000 H120 H130 H131 H220 H230 H231 H330
DIAMETER (CM) 76.2 76.2 76.2 45.72 76.2 76.2 45.72 76.2
Joint Stress Ratio Listing THICKNESS (CM) 2.54 2.54 2.54 3.175 2.54 2.54 3.175 1.9
YLD STRSS (KN/CM2) 34.5 34.5 34.5 34.5 34.5 34.5 34.5 34.5
UC 0.527 0.81 0.654 0.148 0.747 0.685 0.165 0.331
Load Case
Table 9.17 Sling Force Summary: (unit: kN) Member ID H130-HKB3 H220-HKA2 H120-HKB2 H230-HKA3 Section SL1 SL1 SL2 SL2 100 1416.28 2517.13 6649.08 5480.92 200 1937.47 3443.43 9095.96 7497.90 210 1313.86 3817.52 8612.04 7181.54 220 1884.43 3246.77 8117.72 7689.66 230 1883.43 3235.14 9199.25 6605.91 240 2390.11 2729.83 8629.15 7188.53 110 5534.20 6586.99 2583.27 1358.99 300 7570.79 9011.01 3533.93 1859.10 310 6675.16 9116.24 3318.60 1815.04 320 7256.20 8555.85 2813.93 2312.67 330 7243.80 8532.95 3906.73 1240.33 340 7761.16 8038.19 3326.07 1812.26
159
Table 9.18 Member No.
Dimensions and length of each tubular member
Outer diameter (mm)
Thickness (mm) Length in the model (m)
2
700
30
4.91
3
1200
70
5.36
4
1200
40
4.16
5
2522
70
3.86
6
2522
70
7.00
Table 9.19 Maximum stress (MPa) of each case Case No. Von Mises
1st-Principal
Corresponding Location
A
305
350
Connection of central ring plate to main plate
B
242
300
Bottom connection of main plate to p-sleeve
C
328
356
Connection of central ring plate to main plate
D
358
431
Bottom connection of main plate to p-sleeve
Table 9.20 Maximum stress (MPa) for braces Case No. Von Mises
1st-Principal
Corresponding Location
A
147
165
Weld for braces 3 and 4
B
98.9
59.5
Weld for brace 3
C
300
306
Connection of central ring plate to brace 2
D
76.3
60.6
Bottom ring plate
160
Hook Point
Figure 9.1
Computer Lifting Model Plot
161
HALFDAN PHASE III HDB C.O.G. SHIFT OF MODULE DURING LIFTING 2
3
H230 H220
A
y x
a b
C.
Envelope of C.O.G.
H120
H130
COORDINATES OF JOINTS
B
H220 H230 H120 H130
X 5.06 17.19 5.06 17.19
Coordinates (m) Y 7 7 -7 -7
Z 51.2 51.2 51.2 51.2
DIMENSIONS OF MODULE Span between A2 and A3 = 12.13 m Span between A2 and B2 = 14.00 m SELFWT AND MISCELLANEOUS WT. OF MODULE (WITH CONTIGENCY) Total Weight = -15242.32 kN Centre of Gravity C.O.G. x = 10.230 m y = -0.059 m Envelope of C.O.G Shift Shift of 1m towards each leg: A2 (H220)
(H230)
A3
α = 53.779 x ecc. = -0.591 y ecc. = 0.807 α New C.O.G., (x, y)= (9.639, 0.748)
α = 45.406 x ecc. = 0.702 y ecc. = 0.712 α New C.O.G., (x, y)= (10.932, 0.653) COG = (10.23, -0.059) New C.O.G., (x, y)= (9.633, -0.861) New C.O.G., (x, y)= (10.938, -0.765) α α = -53.318 α = -44.923 α x ecc. = -0.597 x ecc. = 0.708 y ecc. = -0.802 y ecc. = -0.706
B2 (H120)
(H130)
B3
APPLIED FORCE TO MAINTAIN EQUILIBRIUM DUE TO C.O.G. SHIFT Horizontal span to distributed My across Row A2 and Row A3 = 12.13 m Horizontal span to distributed Mx across Row A2 and Row B2 = 14.00 m Description Eccentricity (m) M Induced (kN.m) Force To Counter Induced Moment (kN) y-dir My Mx A2 A3 B2 B3 x-dir 1. Loadcase 201 -0.59 0.81 -9006.73 -12296.63 -810.42 -67.91 67.91 810.42 2. Loadcase 202 0.70 0.71 10701.37 -10853.98 53.47 -828.75 828.75 -53.47 3. Loadcase 203 -0.60 -0.80 -9105.36 12223.78 61.24 811.89 -811.89 -61.24 4. Loadcase 204 0.71 -0.71 10792.34 10763.53 829.27 -60.45 60.45 -829.27
Figure 9.2
COG Shift of Module During Lifting
162
Figure 9.3
Jacket Loadout arrangement
163
Figure 9.4
Upending process of Jacket
164
CASE A CASE B
CASE C CASE D
Figure 9.5
Jacket positions for the four load cases
165
Figure 9.6
Configuration of Joint 164
Figure 9.7 Boundary conditions for the FE model
166
(a) Side view in xy-plane
(c) Local view
(d) Local view for pad-eye Figure 9.8 Finite element mesh
167
(a) Global view
(b) Local view st
Figure 9.9 1 -principal stress contour of load case D
168
Figure 9.10 Local view of Von Mises stress contour of load case D
169
CHAPTER 10
CONCLUSIONS AND RECOMMENDATIONS
FOR FUTURE WORK
10.1
Conclusions
Lifting criteria and sling specifications in practice are reviewed and discussed in this thesis. Relevant justification is made based on the lift projects in construction yard. The practical and dominating considerations in rigging are sling design loads, shackle design loads, lift point design loads, shackle sizing, tilt control and CoG (centre of gravity) shift factor.
Crane barges, rigging components including shackles, slings and grommets and lift point connections (including padeyes and trunnions) are discussed based on practical consideration in heavy lift design. The rigging system is the only connection of module to barge. Lifting plays a very important role in major offshore engineering construction. The selection or design of a rigging arrangement is dependent on the crane barge characteristics, module structural pattern and behaviour during lift, and the site parameters.
Rigging configuration affects the tensions in rigging slings, loads in lift points and forces in shackles and link plates, and thus affects the design of those lift components. Furthermore, it also affects the selection of the boom and jib angles of a crane barge to fulfil lift requirements. The algorithms and formulations for the determination of configurations of rigging sling systems with four, six and eight lift points, which cover the majority of heavy lifts in offshore and marine industries, are presented in this thesis. The sling arrangements can be with single slings, doubled slings or doubled
170
make-up slings. The type of spreader structures included in the discussion can be a simple spreader bar, two parallel spreader bars or a spreader frame.
Jackets which are built and transported vertically offer significant savings over jackets built on their side. Considerations for lift jacket structures horizontally and vertically are discussed. Lifting a large jacket may require substantial loadout frame which needs proper design.
Practical considerations for module lifts, which include vertical lifts and flip-over, are investigated. One of the most important aspects of the design of large lifts is the control of weight and the centre of gravity (CoG) of the module. This requires a proper sequence of weighing scheme to ensure the accuracy of these parameters. For deck panel flip-over operation, force distribution between two cranes or two hooks should be calculated precisely since they vary with the change of the module incline angle during flip-over.
Lift procedures and considerations for FPSO modules are discussed and rigging systems with multiple spreader bars are highlighted. Practical design and analysis considerations for lifting lower turret, gas recompression module and flare tower, which are unique for stringent requirement of installation accuracy, heavy load and geometry, are discussed based on real projects.
A versatile spreader frame is designed that includes the combination of padeye and lifting trunnions. Padeyes are designed underneath of spreader frame, while the lower slings remain un-changed, these save significant rigging changing time during actual
171
lifting operations. The trunnions above the spreader frame enable the riggers easier access for re-rigging of slings for subsequent lift.
Finite element methods are used for lifting module and padeye connection analysis. In the modelling, the hook point is considered fixed. Spring supports needs to be input to prevent numerical problems with regards to rigid body modes and the specified spring stiffness should be significantly smaller than the structural stiffness. It has been illustrated that detailed finite element analysis can provide important information for the stress design and safety check for padeye connections.
10.2
Recommendation for Future Work
Based on the detailed investigations by the author, the thesis has reported some findings which will be useful for future reference. In view of the important nature of installation engineering for offshore structures, the following areas may be recommended for further investigation:
-
Structural steel optimization of offshore platforms due to lifting considerations. As most of structural members connected to the lift points are normally governed by lifting operation, structural optimisation can result in significant cost saving.
-
Investigation of padeye configuration with ring stiffeners. The FEM results in Section 9.3 show that some stiffeners are not fully utilized, more optimized configuration with regards to number and location of ring stiffeners is recommended for further study.
172
-
Study of the impact of accidental loadings on rigging system. Accidental loadings, such as gust wind load, wave surge load, etc., have significant effect on the safety of lifting operation and thus studies on these aspects are crucial to lifting design.
173
BIBLIOGRAPHY
•
American Petroleum Institute (API). Recommended Practice for Planning, Designing and Constructing Fixed Offshore Platforms – Working Stress Design, API-RP 2A WSD, 21st edition, December 2000.
• American Institute Steel Construction (AISC), Allowable Stress Design, 9th Edition, 1991.
• Structural Analysis Computer System (SACS) Release 5.1, 2003, by EDI, USA.
• DNV Marine Operation Part 2 Recommended Practice RP5 Lifting, 1996
•
Baar, A. and Feigenbaum, E. A. (eds) The Handbook of Artificial Intelligence, William Kaufmann, USA, 1981.
•
Baar, J. J. M. Developments in The Analysis of Offshore Heavy Lift Operations. In Proc. of 1st International Offshore and Polar Engineering Conference, August 1991, Edinburgh, UK, pp 15-22.
•
Baar, J. J. M., Pijfers, J. G. L. and van Santen, J. A. Hydrodynamically Coupled motions of a Crane Vessel and a Transport Barge. In Proc. 12th Offshore Technology Conference (OTC), 1992, Houston, USA.
•
Black, W. J. Intelligent Knowledge-based System: An Introduction. Van NostrandReihold, UK. 1986.
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APPENDIX A FEM ANALYSIS FOR JACKET UPENDING PADEYE
Additional FFM results for Jacket upending padeye with various loading cases are summarized in this section. •
Summary of load cases and member forces Table A.1 Member forces coming out from SACS analysis
181
182
•
Summary of loading applied to padeye
(A.1) Load out (wire-frame view)
(B.1) Upending in vertical position (wire-frame view)
(C.1) Upending in horizontal position (wire-frame view)
(A.2) Load out (solid view)
(B.2) Upending in vertical position (solid view)
(C.2) Upending in horizontal position (solid view)
Figure A.1 Load conditions (to be continued) 183
(D.1) Upending in tilted
(D.2) Upending in tilted
position (wire-frame view)
position (solid view)
Figure A.1 Load conditions
184
•
Stress distribution of upending padeye
(a) 1st- Principal stress
(b) Von Mises stress Figure A.2 Stress distribution for the braces of load case A 185
(a) 1st- Principal stress
(b) Von Mises stress Figure A.3 Stress distribution for the braces of load case B 186
(a) 1st- Principal stress
(b) Von Mises stress Figure A.4 Stress distribution for the braces of load case C 187
(a) 1st- Principal stress
(b) Von Mises stress Figure A.5 Stress distribution for the braces of load case D 188
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