GUIDELINES FOR MARINE OPERATIONS
MARINE LIFTING
February 1998
London Offshore Consultants GUIDELINES FOR MARINE OPERATIONS LIFTING
TABLE OF CONTENTS 1.
INTRODUCTION................................................................................................................... 4 1.1 1.2 1.3 1.4
2.
PLANNING OF MARINE LIFTS ........................................................................................ 7 2.1 2.2 2.3 2.4 2.5 2.6
3.
General Site Survey Lifting Manual Documentation Design Calculations Operational Aspects
LOADS AND ANALYSIS...................................................................................................... 9 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10
4.
Scope of Guidelines Definitions Reference Documents Certificates of Approval
General Module Design Weight Rigging Weight Centre of Gravity and Tilt of Module - Single Crane Static Hook Load - Single Crane Lift Static Hook Load - Dual Crane Lift Dynamic Lift Load Derivation of Lifting Point Loads - Single Crane Lifts Derivation of Lifting Point Loads - Dual Crane Lifts Lifting Through Water
STRUCTURES ...................................................................................................................... 16 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10
General Consequence Factors Method of Analysis of Module Strength of Module Padeye Design Padears and Trunnions Cast Lifting Points Fabrication and Installation of Lifting Points Seafastening Bumpers and Guides
London Offshore Consultants GUIDELINES FOR MARINE OPERATIONS LIFTING
5.
REQUIREMENTS FOR LIFTING EQUIPMENT ......................................................... 21 5.1 5.2 5.3 5.4 5.5
6.
General Sling Force Distribution Shackles Spreader Beams Hydraulic Lifting Devices
CRANE AND CRANE VESSELS ...................................................................................... 24 6.1 6.2 6.3 6.4 6.5
General Allowable Load Crane Radius Curve Minimum Clearances Crane Vessel Stability
APPENDICES Appendix A1: Summary of Stages in Design/Analysis of Single Crane Lift Appendix A2: Summary of Stages in Design/Analysis of Dual Crane Lift
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1.
INTRODUCTION
1.1
SCOPE OF GUIDELINES These guidelines are a basis for the planning, design and operational aspects of marine lifting. Guidelines for loadout and transportation are covered in the two preceding chapters. The purpose of them is to specify appropriate standards, based on sound engineering and good marine practice in order to ensure that lifting operations maintain an acceptable level of safety at all times. These guidelines are intended to cover any lifting operations which are subject to approval by the Marine Warranty Surveyor. For example:C C C
Topsides Module Lifting Subsea Structure Lifting Jacket Lifting
Other considerations may apply for other categories of lift. These guidelines are based on experience over a large number of lifting operations. However, as knowledge advances in specific areas, Marine Warranty Surveyors should recognise that lifting operations may use alternative or new methods. The fundamental principle to be followed by the introduction of novel or alternative methods is that the overall level of safety of a lifting operation should not be reduced. The Marine Warranty Surveyor for a project will require to review the following for any lifting operation requiring approval:C C C C
Design specifications Proposed lifting procedure Rigging design Crane vessel details
This information should be made available to the MWS in sufficient time to enable completion of these reviews well before the planned operations.
1.2
DEFINITIONS Company: Warranted Company or representatives acting on their behalf.
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MWS: Marine Warranty Surveyor and/or Marine Warranty Survey Company. Installation Contractor: Shall mean the contractor who is responsible for the installation and marine lifting operations. Module: A structure or parts thereof subject to lifting. Sling: Steel ropes spun together with a spliced eye in each end. Grommet: Steel report spun together and spliced such that there is no end. Dynamic Amplification Factor (DAF): A factor accounting for the global dynamic effects which may be experienced during lifting. Consequence Factor: An additional factor to be applied in assessing the structural strength of lifting points and primary structure. Module Design Weight (MDW): The maximum weight of the module including all relevant contingencies. Rigging Weight: The weight of all rigging which will be lifted by the crane.
1.3
REFERENCE DOCUMENTS MWS review of technical documents will include checks to current editions of relevant codes and standards.
1.4
CERTIFICATES OF APPROVAL The lifting design calculations and operations manuals shall be prepared well before the planned start of operations and require approval by the MWS prior to the lifting operation commencing.
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A MWS Certificate of Approval for Lift shall be issued to the attending Surveyor immediately prior to the lift when all preparations and checks are completed to his satisfaction, and environmental conditions/weather forecast are suitable for the planned duration of the operation.
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2.
PLANNING OF MARINE LIFTS
2.1
GENERAL The Installation Contractor shall prepare and issue a comprehensive lifting manual for approval by the MWS. This manual may form part of an installation manual for the Module. All planning for marine operations is based, where possible, on the principle that it may be necessary to interrupt or reverse the operation. This is generally impractical for lifting operations. Therefore points of `no return', or thresholds, shall be defined during planning and in the operations manual. Checklists should be drawn up detailing the required status to be achieved before the operation proceeds to the next stage. Operational planning shall be based on the use of well proven principles, techniques, systems and equipment to ensure acceptable health and safety levels are met and to prevent the loss or injury to human life and major economic losses.
2.2
SITE SURVEY Drawings shall be prepared to document that the lifting site is suitable for the planned lifting operation. A drawing shall be prepared clearly showing existing pipelines and seabed obstructions. The drawing shall also show the areas where mooring anchors cannot be placed.
2.3
LIFTING MANUAL A lifting manual shall be prepared and shall include, as a minimum, details of the following:C C C C C C C C C
Time schedule Module dimensions Module weight and COG information Module buoyancy and COB information Organisation and communication Site information Crane vessel tugs and barges Clearances module/crane/vessel/barge Crane vessel mooring and/or DP arrangement
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C C C C C C C C
C C C
2.4
Crane radius curve Lifting equipment Vessel handling procedures Mooring arrangement Pre-lift checklist Description of operation Limiting environmental criteria Specific operations: Barge/crane vessel ballasting ROV Survey and positioning Suction and ventilation systems Recording Procedure Drawings Safety and contingency plans
DOCUMENTATION The MWS requires to sight all relevant documentation related to the crane vessel including but not limited to Classification and Statutory records and details of crane tests. The MWS requires to be satisfied that all certificates for component parts of the rigging, particularly slings, grommets and shackles, are valid. All slings and grommets shall meet the requirement of Guidance Note PM 20 from the Health and Safety Executive - `Cable laid slings and grommets' (October 1987). Documentation which confirms that suitable tests of the welds on the lifting points have been satisfactorily carried out shall be available for inspection by the attending Surveyor. If a Module is lifted more than once, then a close visual inspection of the lifting point welds shall, where access is possible, be carried out by a competent person before the second and subsequent lifts.
2.5
DESIGN CALCULATIONS Calculations prepared by the designers of the Module, lifting points and rigging arrangements shall be submitted for review. Generally, the calculations will be reviewed and checked against the criteria contained herein. Where computer analyses form the basis of the designers' submission, details of the program and the basis of the input should be made available to assist the MWS in their reviews and approval.
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2.6
OPERATIONAL ASPECTS Before approving the lifting operation the MWS will require detailed descriptions and specifications of the equipment involved and a comprehensive procedure for the lifting operation. Where the limiting criteria for a lift have been derived by dynamic analysis resulting in a limiting criteria based on an allowable significant waveheight, Hs, and associated wave period it is recommended that a wave buoy or similar device is deployed at the lifting site to allow accurate determination of the existing seastate.
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3.
LOADS AND ANALYSIS
3.1
GENERAL This section gives guidelines concerning the derivation of the loads for which the lifting equipment, structure and crane vessels should be assessed. The stages in the design or analysis of a lift are summarised in a flow chart in Appendix 1. The text of these guidelines should be read in conjunction with this chart.
3.2
MODULE DESIGN WEIGHT The Module Design Weight (MDW) shall include adequate contingency factors to allow for the module being heavier than intended. The MWS will require to review the designers' proposed overweight allowances, otherwise the following paragraphs give recommended factors. If the weight is being estimated at the design stage, then the weights of all components of the module should be established by accurate material take-off and separated into two parts:C
Structural steel weight. To allow for mill tolerances, paint, weld, section size substitution and future additions, the estimated weight of structural steel should be increased by 10%.
C
Weight of equipment and ancillaries. To allow for inaccuracies in the estimation of the equipment weights and the unforeseen addition of equipment and associated steelwork, such as equipment foundations and working platforms, the estimated weight of equipment and ancillaries should be increased by 20%.
After completion, the module shall be weighed using an approved weighing method. The as-weighed weight shall be increased by 3% to account for weighing inaccuracies. Documentation should be provided to demonstrate that the equipment and procedures adopted for weighing have the required accuracy. Similarly, if the module is partially complete then the design lift weight may be established by an approved weighing method and allowances for weighing inaccuracies made. The weight of items which are not yet installed should then be established by an updated material take-off and an appropriate allowance made for inaccuracies and possible future additions.
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If the as-built weight plus contingency exceeds the module design weight then calculations shall be submitted to verify the lift design.
3.3
RIGGING WEIGHT A further component, the Rigging Weight (RW), shall be added to the MDW. This allowance represents the weight of rigging and shall include the estimated weight of all shackles, slings, spreaders and rigging platforms. For preliminary design purposes an assumed weight of rigging of 5 percent of a topsides Module weight may be used (7% if spreader bars are used). For jacket structures the weight assumed in the preliminary design shall reflect the proposed rigging arrangement. In the final design phase the actual weight of rigging (including contingencies) shall be used.
3.4
CENTRE OF GRAVITY AND TILT OF MODULE - SINGLE CRANE The plan position of the centre of gravity shall generally be restricted for the following reasons: C C C
To allow for the use of matched pairs of slings To prevent overstress of the crane hook To control the maximum tilt of the object.
The Module COG should be kept within a design envelope. Figure 3.1 shows the allowable zone within which the centre of gravity should be positioned. The value of `e' in Fig. 3.1 shall not exceed e = 0.02 x vertical distance from the crane hook to the Module centre of gravity. Where the vertical distance between the crane hook and Module centre of gravity is not initially known, the value of `e' in Fig. 3.1 shall not exceed 600mm. Where the centre of gravity is found to be outside the cruciform shown in Fig. 3.1, the strength of the crane hook shall be shown to be sufficient for the design load case. The length of the lifting slings/grommets shall be chosen to control the tilt of the Module. For practical purposes the tilt of the Module should not exceed 2E. When the Module has been weighed, the maximum tilt should be calculated using the measured centre of gravity position and the certified lengths of the rigging arrangement. Also, the relative offset between the centre hook position and the Module centre of gravity should be less than 600mm.
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Figure 3.1 Allowable position of Centre of Gravity
3.5
STATIC HOOK LOAD - SINGLE CRANE LIFT The Rigging Weight (RW) shall be added to the Module Design Weight (MDW) to give the Static Hook Load (SHL):C
MDW + RW = SHL
The Static Hook Load shall be checked against the approved crane capacity curve at the maximum planned outreach. Where the lifting situation may give rise to a dynamic increase in the effective load the Dynamic Hook Load (DHL) shall be calculated in accordance with Section 3.7 below.
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3.6
STATIC HOOK LOAD - DUAL CRANE LIFT For dual crane lifts, the SHL for each crane shall be calculated as follows :C
The SHL shall be the MDW shared between cranes in accordance with static equilibrium, plus allowances of:- 5% of calculated hook load for offset of centre of gravity (comparing actual with predicted); this value may be reduced to 3% after weighing. - 3% for longitudinal tilt of the lifted object during the lift. - RW appropriate for the crane.
C
For subsea lifts using two hooks the buoyancy, hydrodynamic loads and wave slam effects may alter the load distribution between the two hooks. These effects should be taken into account when determining the individual hook loads.
The SHL shall be checked against the approved crane capacity curve at the maximum planned outreach for each crane.
3.7
DYNAMIC HOOK LOAD The Dynamic Hook Load (DHL) shall be obtained by multiplying the SHL by a Dynamic Amplification Factor (DAF):C
DHL = SHL x DAF
The DAF allows for the dynamic loads arising from the relative motions of the crane vessel and/or the cargo barge during the lifting operations. The DHL shall be checked against the approved crane capacity curve at the maximum planned outreach. For lifts in air the dynamic load is normally considered to be highest at the instant when the Module is being lifted off its grillage. This load, and hence the appropriate DAF, should be substantiated by means of an analysis which considers the maximum relative motions between the hook and the cargo barge takes account of the elasticity of the crane falls, the slings, the crane booms and the luffing gear. The description of such an analysis must clearly state the assumed limiting wave heights and periods such that, if the calculated value of DAF is critical to the feasibility of the operation, then those conducting the lift will be aware of the limiting sea states. For lifts with the Module submerged, special investigations should be made taking account of hydrostatic and hydrodynamic effects to calculate an appropriate DAF. Further GuidLFT. February 1996
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recommendations are given in section 3.10. In the absence of a dynamic lift response analysis being carried out the values of DAF given in Table 3.1 may be used for lifts in air using the semisubmersible crane vessels. Weight of Module
< 100 Tonne
100 - 1000 Tonne
> 1000 Tonne
Lift Offshore
1.30
1.20
1.10
Lift Inshore
1.15
1.10
1.05
Table 3.1 DAF values for SSCV For offshore lifts from the deck of a semisubmersible crane vessel the DAF appropriate to an inshore lift may be used. For lifts from a quayside a DAF of 1.0 may be used. When using larger mono-hulled crane vessels, the values of DAF given in table 3.2 may be used as a guideline.
Weight of Module
< 100 Tonne
100 - 1000 Tonne
> 1000 Tonne
Lift Offshore
1.50
1.40
1.30
Lift Inshore
1.30
1.20
1.15
Table 3.2 DAF values for large mono-hulled crane vessels
It should be noted that some crane capacity curves already take due account of the DAF and care should be taken to ensure that the DAF is not considered twice in the design calculations.
3.8
DERIVATION OF LIFTING POINT LOADS - SINGLE CRANE LIFTS Lifting points (padeyes or padears) are the structural elements which connect the lift rigging to the structure of the Module. Spreader bars may also be considered to have lifting points where the slings or grommets are attached. After specification of the lifting point locations and lift rigging lengths, the lifting
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point loads shall be derived from the Design Lift Load (DLL) by consideration of the geometry of the lifting arrangement and the position of the Module centre of gravity:C
DLL = MDW x DAF
An analysis shall be made to determine the load distribution between diagonally opposite pairs of lifting points. This should include an assessment of the torsional rigidity of the Module and spring stiffness of the slings. In such an analysis it is recommended that, in the absence of other information, the fabrication errors listed below should be considered to occur in combination:C Lifting Points. Each lifting point is positioned 12mm from its correct position. The combined effect of all lifting points being out of position shall be summed in the least favourable manner. C Shackles. Two shackles which are 6mm shorter than their standard dimensions are attached to diagonally opposite padeyes, whilst 2 shackles which are 6mm longer than standard are attached at the remaining diagonals. C Slings/Grommets. Slings/grommets which are 0.25% under specified nominal length should be considered to be attached to two diagonally opposite lifting points, whilst slings/grommets which are 0.25% over specified nominal length are attached to the two remaining lifting points. If the above analysis is not carried out the DLL carried by a diagonally opposite pair of lifting points shall be increased by a skew load factor of 1.5, ie the load shall be distributed in the ratio 75/25 across opposite pairs of diagonals. Where a loose spreader bar is used the skew load factor may be reduced to 1.2, ie the load shall be distributed in the ratio 60/40 across opposite pairs of diagonals.
3.9
DERIVATION OF LIFTING POINT LOADS - DUAL CRANE LIFTS
Lifting point loads for dual hook lifts should be derived from the Design Lift Load in accordance with the following principles. The DLL is determined for each crane:C
DLL = DHL - (RW x DAF)
For lift arrangements having four lift points ie two to each crane, the lift point loads are statically determinate, and shall then be derived from the DLL by considering the geometry of the sling arrangement. No skew load factor need be applied. GuidLFT. February 1996
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The lift point load shall be increased by 5% to allow for rotation (yaw) of the lifted object.
3.10
LIFTING THROUGH WATER
This section applies to a Module being lowered through the sea surface to its final position on the seabed. These guidelines are in addition to the foregoing paragraphs. The DAF and modified hook loads applicable when lifting through water shall be determined taking account of the factors given below. The lift design shall be checked accordingly. The buoyancy and centre of buoyancy of the object shall be established on the basis of accurate hydrostatic calculations. For subsea Modules, where wave loading may be significant, environmental loads shall be established for wave conditions consistent with the design and operational criteria. An appropriate range of wave lengths and directions, including swell effects, shall be considered. Wave slam effects in the splash zone shall also be evaluated, as shall the possible uplift of the module and resulting slackening of slings. Hydrostatic loads due to external pressure on the submerged Module shall be considered. The effect of hydrodynamic loads shall be calculated. For objects with complex shapes, a 3D analysis should be carried out to determine the hydrodynamic coefficients. The limiting operational criteria shall be established by considering the predicted motions of the crane vessel for varying seastates and directions. This may be achieved either by model testing or a suitable hydrodynamic analysis. Module impact velocities, in horizontal and vertical directions, due to mating or contacting the seabed, should not be taken as less than 1 m/s. Forces due to current on the object and hoist lines should be evaluated and used to derive off lead (forces away from the crane) and side lead (forces perpendicular to the crane boom axis) loads. At the preliminary design stage a DAF of 1.4 may be assumed for lifts of small structures through water. For jackets a DAF of 1.2 may be assumed.
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4. STRUCTURES 4.1
GENERAL The lifted object shall be designed in accordance with Standards or Codes of Practice given in Section 1.3. Wherever possible, the design should be carried out to the requirements of one code only.
4.2
LRFD AND CONSEQUENCE FACTORS For Load and Resistance Factor Design (LRFD), the combined LRFD and Consequence Factors as given in Table 4.1 below shall be applied to the structural elements in addition to the factors for dynamic effects, weight tolerances, etc. given in Section 3. A material resistance appropriate to the chosen Standard or Code shall be used. For Working Stress Design (WSD), in addition to the factors for dynamic effects, weight tolerances, etc given in Section 3, the consequence factors given in Table 4.1 shall be applied for each element of the structure. Structural Element
Combined LRFD + Consequence Factor
Working Stress Consequence Factor
Lift points, spreader bars, etc.
1.50
1.0
Primary load transferring members
1.50
1.0
Other, secondary, members
1.15
(1)
Table 4.1 Consequence Factors In Table 4.1, a member is considered as being primary if structural collapse could result from failure of that member alone. Generally, primary members will be those members framing directly into the lifting points. Other members are defined as being secondary.
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4.3
METHOD OF ANALYSIS OF MODULE
The Module shall be analysed as a three dimensional elastic space frame, including the slings and appropriate restraints to prevent rigid body rotations. The structural model shall include all primary and secondary members and may take account of the bracing of floor plating, if appropriate. The loads input into the model shall represent structural and non-structural dead load, equipment and finishes. The total input loads shall equal the Module design weight, including overweight contingencies, multiplied by the appropriate DAF. For single hook lifts two load combinations shall be considered, representing the load being distributed unevenly to each diagonally opposite pair of padeyes, as per Section 3.8 above. For dual hook lifts the design load shall be the lifting point loads as determined in Section 3.9.
4.4
STRENGTH OF MODULE The stresses in the member resulting from the lift analyses shall be evaluated and compared with the design resistance or allowable stress of the member computed in accordance with the appropriate design code.
4.5
PADEYE DESIGN Padeyes shall be designed for the following loads:C Lifting point loads calculated in accordance with section 3.8 and 3.9 above. C An additional lateral load equal to 5% of the lifting point load. This shall be assumed to act horizontally at the level of the padeye pinhole. C Where a loose spreader bar is used in the rigging arrangement the additional lateral load above shall be increased to 8%. Padeyes shall be aligned to the theoretical true vertical sling angle but shall be dimensioned for a sling angle tolerance of " 5E. Wherever possible padeyes shall be designed with the main welds in shear rather than tension. Where plates/sections are subjected to tensile loads applied perpendicular to the rolling direction they shall have guaranteed through thickness properties. Wherever possible the padeye main plate shall be continuous into the primary structure.
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Padeyes should not have more than one load-bearing cheek plate on each side of the main plate. The cheek plate thickness should be no greater than the main plate thickness. Pin holes should be machined, and be line bored after the welding of the cheek plates to the main plate All sharp edges likely to damage the sling during handling and transportation shall be radiused.
4.6
PADEARS AND TRUNNIONS Padears and trunnions shall be designed for the following loads:C
C
C
Loads calculated in accordance with Section 3.8 and 3.9 above. Additionally, where doubled slings or grommets are used, a load split in the ratio 55%/45% between sling legs shall be considered; An additional lateral load equal to 5% of the lifting point load. The line of action of this force shall be taken at centre of the trunnion, in the longitudinal and transverse directions; Where a loose spreader bar is used the additional lateral load above shall be increased to 8%.
The central stiffener plate (shear plate) of the trunnion should be slotted through the main plate and should be designed to transfer the total sling load into the main plate, without taking the strength of the trunnion bearing plate into account. The diameter of the trunnion shall be a minimum of 4 times the sling/grommet diameter except where the reduction in strength due to bending losses has been considered. Unless the lift point is profiled the sling will flatten out at the contact area during lifting. Therefore the width of a fabricated trunnion should be a minimum of 1.25 times the overall sling diameter plus 25mm. The trunnion shall be fitted with a sling retaining arrangement. Padears shall be aligned to the theoretical true sling angle but shall be dimensioned for a sling angle tolerance of " 5E, vertically and horizontally. All sharp edges likely to damage the sling during handling and transportation shall be radiused. GuidLFT. February 1996
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4.7
CAST LIFTING POINTS The strength of cast lifting points shall be verified by finite element analyses. The finished castings shall be subject to stringent quality control including dimensional conformity, material properties and NDT.
4.8
FABRICATION AND INSTALLATION OF LIFTING POINTS Fabrication and inspection of lifting points shall be in accordance with Company structural steel fabrication and casting specifications.
4.9
SEAFASTENING Lift rigging, spreaderbars and other temporary lifting equipment shall be seafastened for transportation.
4.10
BUMPERS AND GUIDES For offshore lifts consideration shall be given to the provision of bumpers and guides on the Modules. The bumpers and guides shall:C C
Enable the object to be positioned after the lift within the required tolerances. Protect the lifted object, the adjacent surroundings and equipment from damage during lift.
Particular requirements for bumpers and guides should be determined at the planning stage taking account of lifting procedures and the assessed risk of damage. Fabrication tolerances of guides shall be closely controlled. Prior to lifting an asbuilt dimensional survey of the guide systems shall be carried out to confirm that operational tolerances have been maintained. The design forces on bumpers and guides shall not be less than those given in Table 4.2. The bumpers and guides should be designed for any possible combination of forces, except that the total force perpendicular to the face of the bumper need not exceed 1.1 x MDW.
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The requirements for design impact forces for stab-in guides (eg deck to jacket legs) are given in Table 4.3. The point of the Stab-in guide shall be designed to fail before damage can occur to the receiving guide. Force
Bumpers
Guides
Pin/ Bucket
Vertical forces due to friction
1% MDW
1% MDW
1% MDW
Vertical forces due to direct impact (Fv) (vertical post type)
10% MDW
10% MDW
10% MDW
Horizontal forces due to friction
1% MDW
1% MDW
1% MDW
Horizontal forces due to impact acting normal to face (Fh)
10% MDW
5% MDW
5% MDW
Horizontal forces due to impact acting parallel to the face (Fl)
5% MDW
5% MDW
5% MDW
Table 4.2 Bumper and guide impact force factors
Force
Primary
Secondary
Vertical forces due to direct impact
10% SHL
5% SHL
Horizontal forces due to direct impact in longitudinal direction of deck
10% SHL
5% SHL
Horizontal forces due to direct impact in transverse direction of deck
10% SHL
5% SHL
Table 4.3 Design forces for stab-in guides
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5.
REQUIREMENTS FOR LIFTING EQUIPMENT
5.1
GENERAL Cable laid rope for heavy offshore lifting shall be constructed and used in accordance with the requirements of Guidance Note PM20, issued by the Health and Safety Executive, entitled Cable Laid Slings and Grommets, or an equivalent standard. The Safe Working Load of slings/grommets shall be calculated in accordance with PM20 taking due account of splicing efficiency and strength losses due to any bending of the wire rope.
5.2
SLING FORCE DISTRIBUTION
5.2.1
Doubled Slings To take account of the friction losses where slings have been doubled around the lifting or crane hook the total sling force shall be divided between the two legs of the slings in the ratio 45%/55%.
5.2.2
Grommets When single grommets are used over a padear or trunnion, the total sling load shall be divided between the two legs of the grommet in the ratio 45%/55%. This ratio may be 50%/50% where sheaves are used in the system. In cases where grommets are doubled between the hook and lifting point a distribution of 45%/55% shall be used between each leg and in addition a distribution of 45%/55% between each pair, ie a design factor of 1.21 shall be used on the heaviest loaded grommet leg.
5.2.3
Manufacturing and Tolerances The wire rope construction shall be well suited for the intended use and comply with recognised codes and standards. The length of slings or grommets should normally be within tolerances of plus or minus 0.25 per cent of their nominal length. During measuring, the slings or grommets should be fully supported and adequately tensioned. The tension load should be in range of 2.5% to 5.0% of the MBL. Matched slings should be
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5.2.4
measured with the same tension load and under similar conditions. Construction and Certification Valid certificates for each sling and grommet to be used shall be supplied by the sling Manufacturer and should be available for inspection prior to installation of the slings or grommets on the lifted object. For cable laid slings and grommets the certificates required in accordance with PM20 are as follows:C
C C C
5.2.5
Consolidation Test Certificate which shall contain; Identification details Calculated and actual breaking load for outer and core ropes Summation of breaking loads Calculated sling or grommet breaking load Calculation of Working Load Limit Certificates of Dimensional Conformity Certificates of Examination (The Certificate of Examination is valid for a period of 6 months.)
Inspection and Re-Use of Slings/Grommets Slings/grommets shall be examined by a competent person prior to each use. Where the sling or grommet is not part of the vessel's approved rigging gear, covered by an annual inspection by its Classification Society, then the details of the history of the sling/grommet and a record of lifts for which the slings/grommets have been previously used should be available. The MWS acceptance is subject to a visual inspection of each sling/grommet prior to and after rigging and tie-down is complete. If a sling/grommet is found to have any defects such that the certified Minimum Breaking Load cannot be guaranteed, it shall not be used for lifting purposes.
5.3
SHACKLES Each shackle shall be marked with its Safe Working Load (SWL) as recommended by the manufacturer, who shall be a recognised shackle fabricator. A certificate verifying the proof loading and the SWL of each shackle shall be provided for inspection by the MWS. These certificates shall be issued by a recognised Certifying Authority or testing house. Each shackle shall be clearly
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stamped with an identifying mark with reference to the corresponding certificate. Shackles and their certification will be subject to an inspection by the attending MWS surveyor prior to lift. The SWL of shackles which are attached to lifting padeyes shall not be less than the lifting point load divided by the DAF. Shackles shall be loaded along their centreline, in accordance with the design and load rating principles to which the shackles were fabricated. When selecting shackles for a particular application the proposed sling or grommet diameter shall be taken into account.
5.4
SPREADER BEAMS The requirements of Section 4 shall also apply to the design and fabrication of spreader beams where applicable.
5.5
HYDRAULIC LIFTING DEVICES Hydraulic Lifting Devices (HLD), such as pile lifting clamps, may also be used. The points below should be taken into consideration when designing for such lifts. The HLD should be rated by the manufacturer. The SWL should be documented, preferably by means of test results, in accordance with recognised standards. It shall be used in accordance with the manufacturer's instructions and approved procedures. The SWL of the HLD shall be greater than the Design Lift Load (See Chapter 3) The HLD shall be designed to fail safe. Thus failure of the hydraulic system during lift (e.g. rupture of the control umbilical) shall not lead to the load being dropped. The lifting manual shall document modes of failure and their effects and the appropriate contingency measures. The lifting forces from the HLD to the lifting points should be transmitted in accordance with these guidelines and the code of practice being used in the design of the structural steelwork.
GuidLFT. February 1996
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6.
CRANE AND CRANE VESSELS
6.1
GENERAL The crane, crane vessel and associated equipment shall be fit to perform the planned lift operations in a safe manner. The crane should be equipped with an accurate load monitoring device, sufficient to measure cyclic dynamic loads.
6.2
ALLOWABLE LOAD Prior to lift, the correct value of the Module Design Weight shall be confirmed using the as-weighed Module weight or updated estimates of weight. The Dynamic Hook Load, which includes the DAF, shall be compared to the crane radius curve, adopting the maximum radius to be used for the lift. It shall be demonstrated, by reference to the crane certification, or by calculation of allowable stress levels and safety factors within the components of the crane and its foundations, that the crane has adequate capacity to carry out the lift.
6.3
CRANE RADIUS CURVE A part of the submission made to the MWS for approval purposes shall be a crane radius curve showing the allowable lift capacity of the crane at different lift radii. The crane capacity shall be as specified by the manufacturer of the crane and shall have been validated by a proof load test wherein the crane is loaded to 10% in excess of the crane radius curve. A statement that the crane is in class with a Certification Authority is sufficient confirmation that such a test was carried out.
6.4
MINIMUM CLEARANCES During all phases of a lift the following minimum clearances should be maintained:-
GuidLFT. February 1996
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C C C
Below Module: Between Module and crane boom: Between spreader bar and crane boom :
3m 3m 3m
For offshore lifts: C 6.5
From crane vessel to platform :
3m
CRANE VESSEL STABILITY If the design hook load is less than 80% of the capacity of the cranes and the crane vessel will perform the lift at its normal working draft then no special submission is required by the MWS with regard to stability. However, if the load is near the maximum allowable for the vessel or the vessel will be at a draft outside its normal operational range a stability statement shall be submitted for review. When carrying out tandem lifts, documentation shall be submitted to demonstrate that the crane vessel can safely sustain the changes in hook load which arise from the tilt and yaw factors combined with environmental effects in the lifting calculations, specifically considering allowable cross lead angles for the crane booms.
GuidLFT. February 1996
London Offshore Consultants Appendices GUIDELINES FOR MARINE OPERATIONS LIFTING
APPENDIX 1 LIFTING DESIGN FLOW CHARTS
GuidLFT. February 1996
London Offshore Consultants Appendices GUIDELINES FOR MARINE OPERATIONS LIFTING
(3.2) Module Design Weight (MDW)
(3.3) Rigging Weight (RW)
(3.4) Check COG Position & Tilt
(3.5) MDW + RW = Static Hook Load (SHL)
Check Crane Capacity
(3.7) SHL x DAF = Dynamic Hook Load (DHL)
(3.8) MDW x DAF = Design Lift Load (DLL)
(5.) Rigging Design
(3.8) Lifting Point Forces
(4.2) Consequence Factors for:-
Combined LRFD + Consequence Factor
(a) Lifting points, spreader bars (b) Primary Members (c) Secondary Members
1.50
(4.) Module Structural GuidLFT. February 1996
Working Stress Consequence Factor
1.50
1.0 1.0 1.0 (a increase allowed)
1.15
(4.5 - 4.8) Lifting Point Design
London Offshore Consultants Appendices GUIDELINES FOR MARINE OPERATIONS LIFTING
Strength Figure A1 SUMMARY OF STAGES IN DESIGN/ANALYSIS OF SINGLE CRANE LIFT
GuidLFT. February 1996
London Offshore Consultants Appendices GUIDELINES FOR MARINE OPERATIONS LIFTING
(3.2) Module Design Weight (MDW)
(3.6) (1) (2) (3) Static Hook Load (SHL) = (MDW x a x 1.05 x 1.03 ) + Rigging Weight where:
(1) is the ratio of the CoG position to the length between lift points (2) is the factor to allow for CoG shift (3) is the factor to allow for longitudinal tilt
(3.7) Dynamic Hook Load (DHL) = SHL x DAF
(3.9) DLL = [DHL -(RW x DAF)]
Check Crane Capacity
(5.) Rigging Design
(3.9) (1) Lift Point Load = DLL x 1.05 where: (1) is the factor to allow for yaw
(3.9) Lifting Point Forces
(4.2) Consequence Factors for:-
Combined LRFD + Consequence Factor
(a) Lifting points, spreader bars (b) Primary Members (c) Secondary Members
1.50
GuidLFT. February 1996
1.50
Working Stress Consequence Factor 1.0 1.0
1.15
1.0 (a increase allowed)
London Offshore Consultants Appendices GUIDELINES FOR MARINE OPERATIONS LIFTING
(4.3 -4.4) Module Structural Strength
(4.5 - 4.8) Lifting Point Design
Figure A2 SUMMARY OF STAGES IN DESIGN/ANALYSIS OF DUAL CRANE LIFT
GuidLFT. February 1996