HEAVY LIFT INSTALLATION STUDY OF OFFSHORE STRUCTURES. LI LIANG (MS. Eng, NUS)

Transcription

1 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 004

2 HEAVY LIFT INSTALLATION STUDY OF OFFSHORE STRUCTURES LI LIANG (MS. Eng, NUS) A THESIS SUBMITTED FOR THE DEGREE OF MASTER OF ENGINEERING DEPARTMENT OF CIVIL ENGINEERING NATIOANL UNIVERSITY OF SINGAPORE ii

3 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.

4 TABLE OF CONTENTS CHAPTER 1 INTRODUCTION Background 1. Objectives and Scope of Present Study 1.3 Organisation of Thesis CHAPTER REVIEW OF LIFTING DESIGN CRITERIA Review of Various Lifting Criteria. Practical Considerations for Standard Rigging Design..1 Sling Design Loads (SDL).. Shackle Design Loads..3 Lift Point Design Loads..4 Shackle Sizing..5 Tilt during Lifting..6 COG Shift Factor.3 Summary CHAPTER 3 HEAVY LIFTING EQUIPMENT AND COMPONENTS Introduction 3. Heavy Lift Cranes 3..1 Crane Vessel Types 3.. Frequently Used Crane Vessels 3.3 Heavy Lift Shackles 3.4 Heavy Lift Slings Sling properties 3.4. Grommets versus Slings Sling and Grommet Properties 3.5 Lift Points 3.6 Summary CHAPTER 4 RIGGING THEORY AND FORMULATION Introduction 4. Rigging Sling System with Four Lift Points 4..1 Using Main or Jib Hook without Spreader Structure 4.. Using Main or Jib Hook with Spreader Structure 4..3 Using Main and Jib Hooks at the Same Time 4.3 Rigging Sling System with Six Lift Points Using Main or Jib Hook with Spreader Frame 4.3. Using Main and Jib Hooks without Spreader Structure 4.4 Rigging Sling System with Eight Lift Points Using Main or Jib Hook with/without Spreader Structure 4.4. Using Main and Jib Hooks without Spreader Structure 4.5 Summary i

5 CHAPTER 5 JACKET LIFTING Introduction 5. Vertical Lift of Jackets 5.3 Horizontal Lift of Jackets 5.4 Summary CHAPTER 6 MODULE LIFTING Introduction 6. Vertical Module Lift and Installation 6.3 Deck Panel Flip-Over 6.4 Summary CHAPTER 7 FPSO STRUCTURE LIFTING Introduction 7. Lift Procedures and Considerations for FPSO Modules 7.3 Rigging Systems with Multiple Spreader Bars 7.4 Lifting of Lower Turret 7.5 Lifting of Gas Recompression Module 7.6 Lifting of Flare Tower 7.7 Summary CHAPTER 8 SPECIAL LIFTING FRAME DESIGN General Discussion 8. Effect of the Shift of the Centre of Gravity 8.3 Lift Point Forces 8.4 Padeye Checking 8.5 Trunnion Checking 8.6 Summary CHAPTER 9 FINITE ELEMET ANALYSIS FOR LIFTING DESIGN Introduction 9. Finite Element Analysis for Module Lifts 9..1 Structural and Material Details 9.. Finite Element Modelling and Analysis 9..3 Discussions 9.3 Finite Element Analysis for Lifting Padeye Connection Structural Details 9.3. Loading Cases Finite Element Modelling Result Analysis 9.4 Summary CHAPTER 10 CONCLUSIONS AND FUTURE WORKS Conclusions 10. Recommendation for Future Work BIOBLIOGRAPHY APPENDIX A FEM ANALYSIS FOR JACKET UPENDING PADEYE ii

6 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

7 Nomenclature/Abbreviation A - Cross Sectional Area AISC - American Institute Steel Construction API - American Petroleum Institute CoG - Centre of Gravity CRBL - CGBL - Calculated Rope Breaking Load 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

8 H 4 - height of hook block above module (without spreader structure), or height of spreader above module (with spreader) H 5 - 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 L i - length of ith sling MBL - MWS - Minimum Breaking Load 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 - Sx, Sy - SWL - Semi-Submersible Crane Vessels Sectional Modulars 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 W h, L h - the width and length of hook block W m, L m, H m - the width, length and height of module, respectively W sp, L sp - width and length of spreader v

9 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 x c, y c - location of the centre of gravity of module in local coordinate system θ i - angle of sling with respect to the horizontal plane τ g - Punching strength vi

10 List of Tables Table.1 Table. Table.3 Table 3.1 Table 3. Table 4.1 Table 4. Table 4.3 Table 4.4 Table 4.5 Table 4.6 Table 4.7 Table 7.1 Table 7. Table 7.3 Table 7.4 Table 7.5 Table 8.1 Table 8. Lifting Criteria comparison - Single Crane Lift Lifting Criteria comparison - Double hook Lift Dynamic Amplification Factors Some of Heavy Lifting Crane Vessels in the World Shackle Side Loading Reduction For Screw Pin and Safety Shackles Only Formulations for rigging configurations with four lift points (using main or jib hook block without spreader) Formulations for rigging configurations with four lift points (using main or jib hook block with spreader structure) Formulations for rigging configurations with four lift points (using main and jib hook blocks at the same time ) Formulations for rigging configurations with six lift points (using main or jib hook block ) Formulations for rigging configurations with six lift points (using main and jib hook blocks at the same time) Formulations for the rigging configurations with eight lift points (using main or jib hook block at a time ) Formulations for rigging configurations with eight lift points (using main and jib hook blocks at the same time ) Lifting Operation Summary for Laminaria FPSO Contingency Actions Plan / Procedure Preparation Check List Loadout Check List Installation Check List Weight and COG data Total Weight and COG vii

11 Table 8.3 Table 9.1 Table 9. Table 9.3 Table 9.4 Table 9.5 Table 9.6 Table 9.7 Table 9.8 Table 9.9 Table 9.10 Table 9.11 Table 9.1 Table 9.13 Table 9.14 Table 9.15 Table 9.16 Table 9.17 Table 9.18 Table 9.19 Table 9.0 Table A.1 Member Analysis Result Summary Load factor used for lifting analysis Design value of material parameter Sample of Member Group Properties Sample of SACS Section Properties Sample of SACS Plate Group Properties Sample of SACS Plate Stiffener Properties SACS Loading Summary Sample of SACS Loading ID and Description Type of Support Constraints and Member Releases SACS Load Combinations Sample of 75% Lifting Weight Factor SACS Combined Load Summation Support Reactions Spring Reaction Sample of SACS Member Stress Listing Joint Stress Ratio Listing Sling Force Summary Dimensions and length of each tubular member Maximum stress (MPa) of each case Maximum stress (MPa) for braces Member forces coming out from SACS analysis viii

12 List of Figures Figure 1.1 Figure.1 Figure 3.1 Figure 3. Figure 3.3 Figure 3.4 Figure 3.5 Figure 3.6 Figure 3.7 Figure 3.8 Figure 3.9 Figure 3.10 Figure 3.11 Figure 3.1 Figure 3.13 Figure 4.1 Thesis Organizations Vs Contents of Study Centre of gravity (COG) shift Lifting Equipment and Components Saipem S7000 SSCV ton Capacity Sheerleg Crane Vessel Asian Hercules II : 300 ton Capacity Derrick Barge Crane Thialf : 1400 ton Capacity Derrick Lifting Barge DB101: 3150 ton Capacity Samples of Some Shackles (Green Pin and Crosby) Sling Forming & Cross Section Sling Configuration Actual usage of Slings Lift point connections- Padeye and Trunnion Fabricated Lifting Padeye Actual fabricated Lifting Trunnion Details of a Typical Padeye Determination of rigging configuration: tasks, inputs and outputs Figure 4. 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 ix

13 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 Figure 5.a Figure 5.b Figure 5.c Figure 5.3 Figure 6.1 Figure 6. Figure 6.3 Figure 6.4 Figure 6.5 Figure 6.6 Figure 6.7 Vertical Lifting of Jacket Horizontal Lifting of Jacket Loadout operation at Fabrication Yard (800ton) Horizontal Lifting of Jacket Dual Crane Lifting a Tripod Jacket (600 ton) Horizontal Lifting of Jacket Dual lift of a Jacket from transportation barge ISO View of lifting horizontal Jacket (3150ton) Deck Panel Stacking in progress Computer Model for Deck Panel Flip-over Deck Panel 180 Degree Flip Over Module Lifting Four Sling Arrangement Module Installation One Lifting Bar Arrangement Module Lifting Two Bars System Module Lifting Three Bars System x

14 Figure 6.8 Figure 6.9 Figure 6.10 Figure 7.1 Figure 7. Lifting with a spreader frame Multi-Tier Rigging System Tendem Lift of a Module Rigging arrangement for lifting FPSO modules with spreader bars Lifting of Lower Turret (680 ton) Figure 7.3 Lifting of Upper Turret - Manifold Deck Structure with Three Spreader Bars Figure 7.4 Figure 7.5 Figure 7.6 Figure 7.7 Figure 8.1 Figure 9.1 Figure 9. Figure 9.3 Figure 9.4 Figure 9.5 Lifting of Upper Turret Gantry Structure Lifting of Swivel Stack Bottom Assembly Lifting of Gas Recompression Module Upending and Lifting of 9-metre Flare Tower Lifting Frame Details Computer Lifting Model Plot COG Shift of Module during Lifting Jacket Loadout arrangement Upending process of Jacket Jacket positions for the four load cases Figure 9.6 Configuration of Joint 164 Figure 9.7 Figure 9.8 Figure 9.9 Figure 9.10 Boundary conditions for the FE model Finite element mesh 1 st -principal stress contour of load case D Local view of Von Mises stress contour of load case D xi

15 Figure A.1 Figure A. Figure A.3 Figure A.4 Figure A.5 Load conditions Stress distribution for the braces of load case A Stress distribution for the braces of load case B Stress distribution for the braces of load case C Stress distribution for the braces of load case D xii

16 CHAPTER 1 INTRODUCTION 1.1 Background Heavy lifts are frequently carried out during the fabrication and/or installation of major offshore components and structures, such as welded girder beams, tubular columns, deck panels, sub-assemblies, flares, bridges and completed jackets / modules. Without heavy lifting equipment, offshore steel platforms cannot be built effectively. For an offshore platform, the issue of final installation of the completed jacket / topside is considered as early as the conceptual study stage. The major determining factor is availability of heavy lift crane vessel around the region. Heavier structures can be fabricated if a lager crane vessel is selected for the project. Many topside structures are split into several modules instead of an integrated deck structure due to non-availability of sufficient lifting capacity of heavy offshore crane barge in the region or at required time window schedule. Offshore hook-up and commissioning costs are very high as compared to those for the same work performed onshore. This has led to the fabrication of very large modules, where the intention is to minimize hook-up associated with connecting modules together offshore. The great advancement of offshore technology during the last 30 years was largely due to the development of very heavy lift equipment. Thirty years ago, a 1000 ton module would be considered a very heavy lift, while the biggest crane barge in the world at that time could hardly lift 000 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. 1

17 Nowadays, a semi-submersible derrick barge can lift a structure up to 1,000 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

18 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 00 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 3

19 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 0 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. 4

20 1. 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

21 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

22 1.3 Organisation of Thesis Figure 1.1 summarises the organisation and contents of the thesis. Following the introduction, Chapter 1 and Chapter 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 - RPA (000), DNV Marine Operations Part - Recommended Practice RP5 Lifting (1996), Phillips Petroleum (1989), Heerema (1991), Noble Denton & Associates (NDA) (1996), Health and Safety Executive (HSE) (199) 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

23 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. 8

24 Finally, conclusions and general discussions are given in Chapter 10. Evaluation of Design Criteria (Chapter ) Equipment Selection and Component Design (Chapter 3) Rigging Theory and Formulations (Chapter 4) Theory and Knowledge Structures to Be Lifted Rigging System Lift Points Lift Operation Scopes for Design and Analysis Jacket Lifting (Chapter 5) Lifting Frame Design (Chapter 8) Module Lifting (Chapter 6) FPSO Structure Lifting (Chapter 7) Applications FEM Analysis for Lifting System (Chapter 9) Special Case Considerations Figure 1.1 Thesis organization and contents of the thesis 9

25 CHAPTER LIFTING CRITERIA.1 Review of Various Lifting Criteria There are several lifting criteria and specifications written specifically for offshore heavy lift, including API-RPA (000), DNV Marine Operation Part Recommended Practice RP5 (1996), Phillips Petroleum (1989), Heerema (1991), Noble Denton & Associates (NDA) (1996), Health and Safety Executive UK (HSE) (199) 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-RPA (000) with a number of modifications to cater for weight inaccuracy etc. The original lifting criterion in the API RPA (000) 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. 10

26 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. 11

27 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. 1

28 . 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...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 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 0, Health and Safety Executive - see Table.3. d) Further increase each individual lifting point load by the skew load distribution factor of 1.5 as recommended in DNV RP5, which primarily accounts for different sling stiffness and lengths than theoretically assumed. 13

29 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 = = 38. tonnes (.1) 4 sin60.. 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...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

30 Individual Slings (Single Slings) a) At the sling eye, Minimum Calculated Rope Breaking Load, CRBL = SDL E b (.) 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). E b = the sling bend efficiency (reduction) factor = (.a) ( D/d ) 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. 5 E t (.3) Where, E t = 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

31 c) At the sling eye, SDL Minimum CRBL = E b (.4) d) At the sling termination, SDL Minimum CRBL = E t (.5) e) At the sling bend, SDL Minimum CRBL = E t (.6) Individual Grommets Grommets sling may be sized as follows: f) Minimum Calculated Grommet Breaking Load, SDL Minimum CGBL = E b (.7) Doubled Grommets g) Minimum Calculated Grommet Breaking Load, SDL Minimum CGBL = xe b (.8) 16

32 ..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 00 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 00 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 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

33 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...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 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

34 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...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

35 fcog factor shall be calculated as follows: d x + a d y + b f cog = 1.05 (.9) b b where, as shown in Figure.1, a and b are the distances between analysis COG and nearest footing in x and y directions and d x and d y are the distances between the position of maximum shifted COG and analysis COG in x and y direction, respectively. 0

36 .3 Summary Lifting criteria and sling specifications in practice are first reviewed in this chapter. These codes include API-RPA (000), 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. 1

37 Table.1 Lifting Criteria comparison - Single Crane Lift Noble DnV Heerama Shell BP Oxy Amoco Chevron Denton Range of Module Weight >500 >500 >500 >1000 >500 >500 >500 >500 1 A. Weight Factor (Pre-AFC) B. DAF (Slings) C. Skew load factor D. CG Shift factor E. Tilt factor F = A x B x C x D x E G. Rigging weight factor H. Lift point design factor I. Load member design factor J. Sling Design = (F x G) K. Lift point Design = (F x H) L. Load member design = (F x I) The overall lift point design factor (K) from API RP A (000) is.00. Table. Lifting Criteria comparison - Double hook Lift Noble LOC Heerema Chevron BP Amoco Denton Range of Module Weight >500 >1000 >500 >500 >8000 >500 1 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 = A x B x C x D x E x F x G I. Rigging weight factor J. Lift point design factor K. Load member design factor L. Sling Design = (H x I) M. Lift point Design = (H x J) N. Load member design = (H x K) The overall lift point design factor (K) from API RP A (000) is.00. Table.3 Dynamic Amplification Factors (DAF) Design (factored) < to 1000 >1000 Lift Weight (tonne) DAF Offshore DAF Inshore

38 Y Support location Analysis COG Max. COG shift dy X b Design envelope a dx Figure.1 : Centre of Gravity (COG) Shift 3

39 CHAPTER 3 HEAVY LIFTING EQUIPMENT AND COMPONENTS 3.1 Introduction As shown in Figure 3.1, crane vessel, rigging components including shackles, slings and grommets and lift point connections (including padeyes and trunnions) are basic considerations in heavy lift design. The crane barge is the most expensive piece of equipment and the most important member in lift operation as well. The safety of the crane barge during lift operations is the first consideration for both crane barge owner and client. The characteristics of the crane barge also constrain the rigging arrangement and necessary reinforcement of the module structure. To safely pick up and install the module is the ultimate objective of carrying out a lift operation. The module cannot be damaged or overstressed or distorted during lift. Reinforcement is needed when the module is too flexible to withstand the load during lift. The rigging system is the only connection of module to crane vessel. The rigging components include slings, spreader structure, shackles, padeyes (or trunnions) and their arrangement. The selection or design of a rigging arrangement is dependent on the barge characteristics, module structural pattern and behaviour during lift, and the site parameters. 4

40 3. 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 ton capacity) in Figure 3. and DB10 (with up to 1000 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 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 DB10 (1000 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 5

41 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. 6

42 3..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. & 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 7

43 3.. 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 300 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. m from forward of vessel Position : 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) : m Breadth moulded : m Depth moulded : 8.50 m Max. /Min draft : 5.00/.40 m Gross tonnage : tons Net tonnage : 3168 tons Displacement : tons (even keel) Speed : 7 knots (1.97 km/hr) Deck loading : 15 ton/m² The crane structure has been designed based on the following criteria: Harbour condition: Wind speed : 0 m/s Current : 3 Knots Offshore condition: Wind speed : 0 m/s Current : 5 Knots Max. sig. wave height : Hs = 1m 8

44 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 14,00 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 01.6m Length of vessel 165.3m Breadth 88.4m Depth to work deck 49.5m Draught m GRT 136,709 ton NRT 41,01 ton Deck load capacity 15 mt/square metre Total deck load capacity 1,000 mt Transit speed with 1,000 tons deck load 6 knots at 1.5 metres (43.6 ft) draft. Ballast pump capacity 0,800 cubic metre/hour PORTSIDE or STARBOARD CRANE Main hoist revolving Auxiliary hoist Whip hoist 7,043 ton up to 31. m (10 ft) 900 ton at m (10-60 ft) 198 ton at m ( ft) 9

45 Derrick Barge DB101 DB101, as shown in Figure 3.5, has the following details: Main Dimensions: LOA m (480 ft) Beam 51.9 m (170.3 ft) Depth 36.6 m (10 ft) Working Draft Min. 7.5m (4.6 ft), 3.5m (Max. 77 ft) Clear Deck: 43,000 sq. ft. Tonnage: Gross 5,313, Net 15,693 Cranes Main Crane: IHC E-3500 Boom Length: Main 67.0m (19.75 ft) Aux m ( ft) Whip 104.m ( ft) Hook Capacity: Main,430 ton (, ft. (Revolving), 3,150 ton (3, ft. (Tied Back), 540 ton ( ft. (Aux.) & 135 ton ( ft. (Whip) Deck Cranes: 83 ton (9 5 ft. 30

46 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 100 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