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DOCUMENT CONTROL SHEET
GUIDELINES FOR MARINE OPERATIONS
Marine Lifting
0 May 2003 Reformatted version of original document VK DB
Rev. Date Reason For Issue Author Check Client
LOC Doc. Title Marine Lifting
LOC Ref No. LOCH/GUIDELINES/R003
Client Doc Title
Client Ref No.
LOC Field Marine Operations Guidelines
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TABLE OF CONTENTS PAGE
1. INTRODUCTION 1
1.1. Scope of Guidelines 1
1.2. Definitions 2
1.3. Reference Documents 2
1.4. Certificates of Approval 2
2. PLANNING OF MARINE LIFTS 3
2.1. General 3
2.2. Site Survey 3
2.3. Lifting Manual 3
2.4. Documentation 4
2.5. Design Calculations 5
2.6. Operational Aspects 5
3. LOADS AND ANALYSIS 6
3.1. General 6
3.2. Module Design Weight 6
3.3. Rigging Weight 7
3.4. Centre of Gravity and Tilt of Module - Single Crane 7
3.5. Static Hook Load Single Crane Lift 8
3.6. Static Hook Load - Dual Crane Lift 9
3.7. Dynamic Hook Load 9
3.8. Derivation of Lifting Point Loads - Single Crane Lifts
11
3.9. Derivation of Lifting Point Loads - Dual Crane Lifts 12
3.10. Lifting Through Water 12
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4. STRUCTURES 14
4.1. General 14
4.2. LRFD and Consequence Factors 14
4.3. Method of Analysis of Module 14
4.4. Strength of Module 15
4.5. Padeye Design 15
4.6. Padears and Trunnions 16
4.7. Cast Lifting Points 17
4.8. Fabrication and Installation of Lifting Points 17
4.9. Seafastening 17
4.10. Bumpers and Guides 17
5. REQUIREMENTS FOR LIFTING EQUIPMENT 19
5.1. General 19
5.2. Sling Force Distribution 19
5.3. Shackles 20
5.4. Spreader Beams 21
5.5. Hydraulic Lifting Devices 21
6. CRANE AND CRANE VESSELS 22
6.1. General 22
6.2. Allowable Load 22
6.3. Crane Radius Curve 22
6.4. Minimum Clearances 22
6.5. Crane Vessel Stability 23
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1. INTRODUCTION
1.1. Scope of Guidelines
1.1.1 These guidelines are a basis for the planning, design and
operational aspects of marine
lifting.
1.1.2 The purpose of these guidelines 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.
1.1.3 These guidelines are intended to cover any lifting
operation that is subject to approval by
the Marine Warranty Surveyor. For example:
Topsides Module Lifting
Subsea Structure Lifting
Jacket Lifting
1.1.4 Other considerations may apply for other categories of
lift.
1.1.5 These guidelines are based on experience over a large
number of lifting operations.
However, as knowledge advances in specific areas, Marine
Warranty Surveyors should
recognize 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.
1.1.6 The Marine Warranty Surveyor for a project will be
required to review the following for
any lifting operation requiring approval:
Design specifications
Proposed lifting procedure
Rigging design
Crane vessel details
1.1.7 This information should be made available to the Marine
Warranty Surveyor in sufficient
time to enable the completion of these reviews well before the
planned operations.
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1.2. Definitions
1.2.1 Company: Warranted Company or representatives acting on
their behalf.
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 rope spun together and spliced such that there is no end.
Dynamic Amplification Factor (DAF): A factor accounting for the
global dynamic effects that 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
1.3.1 MWS review of technical documents will include checks to
current editions of relevant
codes and standards.
1.4. Certificates of Approval
1.4.1 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.
1.4.2 An 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
2.1.1 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.
2.1.2 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.
2.1.3 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
2.2.1 Drawings shall be prepared to document that the lifting
site is suitable for the planned
lifting operation.
2.2.2 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
2.3.1 A lifting manual shall be prepared and shall include, as a
minimum, details of the
following:
Time schedule
Module dimensions
Module weight and COG information
Module buoyancy and COB information
Organization and communication
Site information
Crane vessel tugs and barges
Clearances module/crane/vessel/barge
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Crane vessel mooring and/or DP arrangement
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
2.4. Documentation
2.4.1 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.
2.4.2 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).
2.4.3 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.
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2.5. Design Calculations
2.5.1 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.
2.5.2 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.
2.6. Operational Aspects
2.6.1 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.
2.6.2 Where the limiting criteria for a lift have been derived
by dynamic analysis resulting in a
limiting criteria based on an allowable significant wave height,
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
3.1.1 This section gives guidelines concerning the derivation of
the loads for which the lifting
equipment, structure and crane vessels should be assessed.
3.1.2 The stages in the design or analysis of a lift are
summarized 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
3.2.1 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.
3.2.2 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:
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%.
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%.
3.2.3 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.
3.2.4 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
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updated material take-off and an appropriate allowance made for
inaccuracies and
possible future additions.
3.2.5 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
3.3.1 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% 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
3.4.1 The plan position of the centre of gravity shall generally
be restricted for the following
reasons:
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.
3.4.2 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.
3.4.3 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.
3.4.4 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
2 degrees.
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3.4.5 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.
Figure 3.1 Allowable position of Centre of Gravity
3.5. Static Hook Load Single Crane Lift
3.5.1 The Rigging Weight (RW) shall be added to the Module
Design Weight (MDW) to give
the Static Hook Load (SHL):
MDW + RW = SHL
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3.5.2 The Static Hook Load shall be checked against the approved
crane capacity curve at the
maximum planned outreach.
3.5.3 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.
3.6. Static Hook Load - Dual Crane Lift
3.6.1 For dual crane lifts, the SHL for each crane shall be
calculated as follows:
The SHL shall be the MDW shared between cranes in accordance
with static
equilibrium, plus allowances of:
a) 5% of calculated hook load for offset of centre of gravity
(comparing
actual with predicted); this value may be reduced to 3% after
weighing.
b) 3% for longitudinal tilt of the lifted object during the
lift
c) RW appropriate for the crane.
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.
3.6.2 The SHL shall be checked against the approved crane
capacity curve at the maximum
planned outreach for each crane.
3.7. Dynamic Hook Load
3.7.1 The Dynamic Hook Load (DHL) shall be obtained by
multiplying the SHL by a Dynamic
Amplification Factor (DAF):
DHL = SHL x DAF
3.7.2 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.
3.7.3 The DHL shall be checked against the approved crane
capacity curve at the maximum
planned outreach.
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3.7.4 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.
3.7.5 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 seastates
3.7.6 For lifts with the module submerged, special
investigations should be made taking
account of hydrostatic and hydrodynamic effects to calculate an
appropriate DAF.
Further recommendations are given in section 3.10.
3.7.7 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
semi-submersible crane vessels
Weight of Module < 100 Tonnes 100 1,000 Tonnes > 1,000
Tonnes
Lift Offshore 1.30 1.20 1.10
Lift Inshore 1.15 1.10 1.05
Table 3.1 DAF values for SSCV
3.7.8 For offshore lifts from the deck of a semi-submersible
crane vessel the DAF appropriate
to an inshore lift may be used.
3.7.9 For lifts from a quayside a DAF of 1.0 may be used.
3.7.10 When using larger mono-hulled crane vessels, the values
of DAF given in table 3.2 may
be used as a guideline.
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Weight of Module < 100 Tonnes 100 1,000 Tonnes > 1,000
Tonnes
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
3.7.11 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
3.8.1 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.
3.8.2 After specification of the lifting point locations and
lift rigging lengths, the lifting 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:
DLL = MDW x DAF
3.8.3 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:
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
favorable manner
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.
Slings/Grommets: Slings/grommets that are 0.25% under specified
nominal length
should be considered to be attached to two diagonally opposite
lifting points, whilst
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slings/grommets that are 0.25% over specified nominal length are
attached to the two
remaining lifting points.
3.8.4 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,
i.e. the load shall be
distributed in the ratio 75/25 across opposite pairs of
diagonals.
3.8.5 Where a loose spreader bar is used the skew load factor
may be reduced to 1.2, i.e. the
load shall be distributed in the ratio 60/40 across opposite
pairs of diagonals.
3.9. Derivation of Lifting Point Loads Using Two Crane
3.9.1 Lifting point loads for two cranes should be derived from
the Design Lift Load in
accordance with the following principles.
3.9.2 The DLL is determined for each crane:
DLL = DHL - (RW x DAF)
3.9.3 For lift arrangements having four lift points i.e. 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.
3.9.4 The lift point load shall be increased by 5% to allow for
rotation (yaw) of the lifted object.
3.10. Lifting Through Water
3.10.1 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.
3.10.2 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.
3.10.3 The buoyancy and centre of buoyancy of the object shall
be established on the basis of
accurate hydrostatic calculations.
3.10.4 For subsea modules, where wave loading may be
significant, environmental loads shall
be established for wave conditions consistent with the design
and operational criteria.
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An appropriate range of wavelengths 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.
3.10.5 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 co-
efficient.
3.10.6 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.
3.10.7 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.
3.10.8 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.
3.10.9 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
4.1.1 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
4.2.1 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.
4.2.2 A material resistance appropriate to the chosen Standard
or Code shall be used.
4.2.3 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 1.0
Table 4.1 Consequence Factors
4.2.4 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.
4.3. Method of Analysis of Module
4.3.1 The module shall be analyzed as a three dimensional
elastic space frame, including the
slings and appropriate restraints to prevent rigid body
rotations. The structural model
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shall include all primary and secondary members and may take
account of the bracing of
floor plating, if appropriate.
4.3.2 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.
4.3.3 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
4.4.1 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
4.5.1 Padeyes shall be designed for the following loads:
Lifting point loads calculated in accordance with Section 3.8
and 3.9.
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.
Where a loose spreader bar is used in the rigging arrangement
the additional lateral load
above shall be increased to 8%.
4.5.2 Padeyes shall be aligned to the theoretical true vertical
sling angle but shall be
dimensioned for a sling angle tolerance of 5.
4.5.3 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.
4.5.4 Wherever possible the padeye main plate shall be
continuous into the primary structure.
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4.5.5 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.
4.5.6 Pin holes should be machined, and be line bored after the
welding of the cheek plates to
the main plate
4.5.7 All sharp edges likely to damage the sling during handling
and transportation shall be
radiused.
4.6. Padears and Trunnions
4.6.1 Padears and trunnions shall be designed for the following
loads:
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%.
4.6.2 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.
4.6.3 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.
4.6.4 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.
4.6.5 The trunnion shall be fitted with a sling retaining
arrangement.
4.6.6 Padears shall be aligned to the theoretical true sling
angle but shall be dimensioned for
a sling angle tolerance of 5, vertically and horizontally.
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4.6.7 All sharp edges likely to damage the sling during handling
and transportation shall be
radiused.
4.7. Cast Lifting Points
4.7.1 The strength of cast lifting points shall be verified by
finite element analyses.
4.7.2 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
4.8.1 Fabrication and inspection of lifting points shall be in
accordance with Company
structural steel fabrication and casting specifications.
4.9. Seafastening
4.9.1 Lift rigging, spreader bars and other temporary lifting
equipment shall be seafastened for
transportation.
4.10. Bumpers and Guides
4.10.1 For offshore lifts consideration shall be given to the
provision of bumpers and guides on
the modules. The bumpers and guides shall
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.
4.10.2 Particular requirements for bumpers and guides should be
determined at the planning
stage taking account of lifting procedures and the assessed risk
of damage.
4.10.3 Fabrication tolerances of guides shall be closely
controlled. Prior to lifting an as-built
dimensional survey of the guide systems shall be carried out to
confirm that operational
tolerances have been maintained.
4.10.4 The design forces on bumpers and guides shall not be less
than those given in Table
4.2.
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4.10.5 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.
4.10.6 The requirements for design impact forces for stab-in
guides (e.g. deck to jacket legs)
are given in Table 4.3.
4.10.7 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
For bumpers and guide designed as secondary systems the forces
Fv, Fh and FI may be taken to be 50 % of those given in
Table.4.2
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
5.1.1 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.
5.1.2 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 50%/55%
between each pair, i.e. 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 recognized codes and standards.
The length of slings or grommets should normally be within
tolerances of plus or minus
0.25% 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 measured with the same
tension load and
under similar conditions.
5.2.4 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.
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For cable laid slings and grommets the certificates required in
accordance with PM20 are as
follows:
Consolidation Test Certificate that 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)
5.2.5 Inspection and re-use of 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.
5.2.6 The MWS acceptance is subject to a visual inspection of
each sling/grommet prior to
and after rigging and tie-down is complete.
5.2.7 During sling lay down, particularly with cable laid
rigging, care must be taken to avoid
any twisting of the slings/grommets. Where possible, a line
should be painted along the
length of the sling/grommet during manufacture, to facilitate
correct lay down of the
rigging.
5.2.8 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
5.3.1 Each shackle shall be marked with its Safe Working Load
(SWL) as recommended by
the manufacturer, who shall be a recognized shackle
fabricator
5.3.2 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 recognized Certifying
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Authority or testing. Each shackle shall be clearly stamped with
an identifying mark with
reference to the corresponding certificate.
5.3.3 Shackles and their certification will be subject to an
inspection by the attending MWS
surveyor prior to lift. T
5.3.4 The SWL of shackles, which are attached to lifting
padeyes, shall not be less than the
lifting point load divided by the DAF.
5.3.5 Shackles shall be loaded along their centreline, in
accordance with the design and load
rating principles to which the shackles were fabricated.
5.3.6 When selecting shackles for a particular application the
proposed sling or grommet
diameter shall be taken into account.
5.4. Spreader Beams
5.4.1 The requirements of Section 4 shall also apply to the
design and fabrication of spreader
beams where applicable.
5.5. Hydraulic Lifting Devices
5.5.1 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.
5.5.2 The HLD should rate by the manufacturer. The SWL should be
documented, preferably
by means of test results, in accordance with recognized
standards. It shall be used in
accordance with the manufacturer's instructions and approved
procedures.
5.5.3 The SWL of the HLD shall be greater than the Design Lift
Load (See Chapter 3)
5.5.4 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.
5.5.5 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.
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6. CRANE AND CRANE VESSELS
6.1. General
6.1.1 The crane, crane vessel and associated equipment shall be
fit to perform the planned lift
operations in a safe manner.
6.1.2 The crane should be equipped with an accurate
load-monitoring device, sufficient to
measure cyclic dynamic loads.
6.2. Allowable Load
6.2.1 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.
6.2.2 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.
6.2.3 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
6.3.1 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.
6.3.2 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
6.4.1 During all phases of a lift the following minimum
clearances should be maintained:
Below module: 3m
Between module and crane boom: 3m
Between spreader bar and crane boom: 3m
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6.4.2 For offshore lifts:
From crane vessel to platform: 3m
From crane vessel to platform: 10 m (Crane vessel on DP)
6.5. Crane Vessel Stability
6.5.1 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.
6.5.2 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.
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Appendix A1 Summary of Stages in Design/Analysis of Lift Using
Single Crane.
3.2.
Module Design Weight (MDW)
3.3. Rigging Weight (RW)
(3.7) SHL x DAF = Dynamic Hook Load (DHL)
(3.5) MDW + RW = Static Hook Load (SHL)
(3.4) Check COG Position & Tilt
(5.) Rigging Design
(3.8) MDW x DAF = Design Lift Load (DLL)
(4.) Module Structural Strength
(4.5 4.8) Lifting Point Design
Check Crane Capacity
4.2 Combined LRFD + Working Stress Consequence Factors for:
Consequence Factor Consequence Factor
(a) Lifting Points, Spreader Bars 1.50 1.0 (b) Primary Members
1.50 1.0 (c) Secondary Members 1.15 1.0 ( increase allowed)
(3.8) Lifting Point Forces
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Appendix A2 Summary of Stages in Design/Analysis of Lift Using
Two Cranes
(3.2) Module Design Weight (MDW)
(3.9) Lifting Point Forces
(3.7) Dynamic Hook Load (DHL) = SHL x DAF
(5.) Rigging Design
3.6 Static Hook Load (SHL) = (MDW x a (1) x 1.05i(2) x 1.03(3) )
+ 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
(3.9) DLL = {DHL (RW x DAF)}
Check Crane Capacity
(4.2) Combined LRFD + Working Stresses Consequence Factors for:
Consequence Factor Consequence Factor (a) Lifting Points, Spreader
Bars 1.50 1.0 (b) Primary Members 1.50 1.0 (c) Secondary Members
1.15 1.0 ( increase allowed)
(4.3 4.4) Module Structural Strength
(4.5 4.8) Lifting Point Design
(3.9) Lift Point Load = DLL x 1.05(1) where: (1) is the factor
to allow for yaw