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Installation Engineering of Topside Modules on Ship Shaped Offshore Floating
Structures
Conference Paper · December 2010
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Proceedings of 4th PAAMES and AMEC2010
Dec. 6-8, 2010, Singapore
Installation Engineering of Topside Modules on Ship
Shaped Offshore Floating Structures
Kumar D Roy 1, Arun Kr Dev 2, Seref Aksu 2
1
MPhil Student, Newcastle University Marine International Singapore
2
Newcastle University Marine International Singapore
Abstract
In this review paper, the study begins with investigation of governing technical parameters for heavy lifting.
This is then followed by installation phase and hull integration covering necessary structural modifications on
deck of ship shaped offshore floating structures for the stated purpose. The interrelationships amongst a number
of key parameters/aspects of installation process of a topside module such as weight control, heavy lifting and
rigging consideration, local FEM analysis of lifting points and members, installation tolerance and design of
fine guides are studied. Findings of the study include their contributions to the topside module installation
process.
Keywords: Topside Module, Module Support, Weight Control, Heavy Lifting, Rigging Analysis, Pad Eye,
Trunion, CoG Envelope, Hull Integration, Hull Deflection, Local FEM Analysis, Fine Guiding, Decision
Support Diagram
Abbreviation: PAU-Preassembled Unit, DAF-Dynamic Amplification Factor, SKF-Skew Load Factor
FEA Finite Element Analysis, COG-Centre of Gravity
1 Introduction
Several technical considerations and proper
interfacing among the parties involved within a
time constraint are decisively important for topside
module installation engineering on a ship shaped
floating structure, like a FPSO/FSO. The aim of this
paper is to study the main technical parameters
limited to installation and hull integration of topside
modules only. The study is carried out on available
industry guidelines, technical notes as well as actual
projects for identification of technical nature and
importance of the keyword parameters.
Figure 1 shows a heavy lifting crane carrying a
topside module for installation on a floating FPSO
hull with a typical 4 point rigging arrangement.
2 Literature review
Basic topside layout design considerations like
process flow, storage, load effects, etc. and their
impact on initial layout are discussed by Chakrabarti
et al (2005). Consideration among operational
requirements from topside modules with priorities
and statutory recommendations are also briefly cited
with two practical design layout discussions by the
same author.
Marshall and Smith (2002) presented a detailed
account of FPSO design issues. Issues such as hull
deformation of pre-assembled units (PAUs),
utilization of deck space, structural production
facilities, interface supports arrangement, effects of
contractual arrangement for topside fabrication, cross
linking of PAUs and other factors are also outlined in
Marshall and Smith (2002).
Fig.1 Heavy Lift crane with Topside Module
The primary functions of the foundation structures
(module support structures) and the spaces adjoining
them are as follows as mentioned by Paik and
1
Thayamaballi, (2007) originated from a paper by
Krekel and Kaminski (2002):
Table 1 Dominant Loads and components
a. Provide support to the topsides modules on
the hull upper deck,
b. Provide space for deck piping and hull
equipment,
c. Provide space for safeguard and utility
systems on the hull upper deck,
d. Allow for sufficient natural ventilation on
the hull upper deck; for example, so as to
prevent explosive gaseous mixtures,
e. Help in creation of a fire barrier between the
topsides and the hull upper deck,
f. Help in the creation of a hazardous-area
subdivision for equipment (e.g., electrical).
For any engineering analysis, it is essential that
loads acting on the structure are clearly defined
and determined. The main dominant basic loads
acting on the main FPSO hull are described in
Henriksen et al (2008) and given in Table 1. The
foundation effect on topside modules from hull
girder deflection is also described in Henriksen et
al (2008) and given in Table 2.
Dominant Hull Girder Loads
Load
Components
Hull Girder Bending
Still Water and Wave
Induced
Hull Girder Shear
Still Water and Wave
Induced
Differential Pressure on
Static and Inertia
Transverse Bulkheads
Pressure
Differential Pressure on Static and Inertia
Longitudinal Bulkheads
Pressure
Dominant Topside Loads
Loads
Components
Module Reaction Loads Static and Dynamic
from Hull Deflection and Loads
Tank Loads
Loads due to FPSO Static and Dynamic
Inclination
Accelerations
Module
Mass
Distribution and Centre
of Gravity
Module Location on
FPSO, i.e. each module
gets unique combination
of 6 degree of freedom
accelerations and hull
girder loads
Static and Dynamic
Accelerations
Static and Dynamic
Accelerations
Table 2 Foundation and Topside Effect
Foundation Effect on Topside Modules from Hull Girder Deflection
Relative Deflection Mode
Load
Origin
Longitudinal
Still Water and Wave Hull Girder
Vertical and Horizontal Bending
Vertical
Hull Vertical Bending
Transverse
Transverse Bending
Primary Factors
Hull Length, Hull Breadth, Block
Coefficient, Longitudinal Strength,
Topside Installation Height
Hull Length, Hull Breadth, Block
Coefficient, Longitudinal Strength
Transverse Strength, Topside Installation
Height, Topside Module Width
Topside Module Effect on Hull
Relative Deflection Mode
Longitudinal
Vertical
Transverse
Load Origin
Primary Factors
Surge, Pitch, Yaw Inclination
Topside Module Mass, Topside Module
and Acceleration
Centre of Gravity
Heave, Pitch, Roll Inclination and Topside Module Mass, Topside Module
Acceleration
Centre of Gravity, Topside Module Width,
Topside Module Length
Sway, Roll, Yaw Inclination
Topside Module Mass, Topside Module
and Acceleration
Centre of Gravity
2
Topside weights are generally known when the
project enters into the structural design phase. Their
distribution on the topside structure is known only
after a first design analysis. Moreover, the load
distribution among different supports between the
hull and the topside also depends on the design
engineering of the topside structure.
Gourdet (2008) described the important
parameters of hull-topside structural assessment as
•
•
•
•
•
•
•
•
3 Weight Control
Weight control procedure is mainly maintained by
two basic ways: first by the basic module designer’s
weight control guided by basic design parameters
and second by the module designer followed by
actual fabrication feed back. Module designer’s
weight control plan has to cover load cases such as
load out, transport, lift, dry installation, normal
operating conditions and maximum future operating
condition.
Topside loads,
Hull motions and accelerations from
hydrodynamic analysis,
Hull girder deformations (Horizontal and
Vertical bending moment, torsion),
Effects leading to deck stresses concentration,
Effects of alternate filling,
Poisson effect,
Steel dilatation,
Effect of attached structures.
Further, Gourdet (2008) suggested possible analysis
solutions for the structural assessment of the
interface structure. These include
a. Hull partial models and topside loads (3 hold
hull topside force assumed).
b. Hull partial models and main structure of
topsides (3 hold hull and first main topside
structure).
c. Complete hull model and main structure of
topsides (Full hull and primary topside structure).
d. Integrated model (Full hull and topside coupled
model).
An example to an integrated study discussed by
Gourdet (2008) can be given as one that is carried
out by Henriksen et al (2008). The authors carried
out and presented FE analysis findings based on
horizontal and vertical deflections using iterative
analysis.
Detailed analysis leading to site specific design
and on deck installation is not the finishing line for
the topsides. Apart from conventional maintenance
items like painting deterioration, subsequent
corrosion, ageing of material potential water ingress,
consideration to be given on fatigue induced
responses not only by the sea state during normal
operations but also from towing to construction yard.
A risk based inspection procedure considering
probabilities of evaluation, risk acceptance criteria
showing level of probability, consequence and risk
can be adopted (Trouchton et al, 2007).
Fig. 2 A snapshot of chronographic weight and
centre of gravity (CoG) tracking.
The module fabricator maintains a weight budget
and weight need not to exceed budget. The module
fabricator’s weight is based on the contract weight,
material take off (MTO) from PDMS (Plant Design
Management System) manual, MTO from various
disciplines and master equipment list.
A standard procedure is to be prepared for weight
and centre of gravity tracking information in every
phase from design, fabrication to installation on
board (see Figure 2). As blocks are fabricated in
various locations and in differing capacities, weight
tracking then becomes more crucial.
4 Transportation
Upon completion of the fabrication of a module, it
is transported to the installation yard. From the
fabrication ground it is lifted or skidded onto a
transportation barge. Skidding is commonly done for
load out on a transportation barge. Ground
transportation is mostly carried out by trailer type
transport systems.
3
A methodical discussion on module transportation
and load out is given in guideline documents by
Noble Denton (2005). Proper sea fastening, structural
load effects due to a particular sea route are key
technical considerations for the transportation. Often,
specialist contractors are engaged for the task. An
operational risk analysis procedure can play an
important role in reducing the risk associated with
the transportation of the module assemblies.
Practical cases of load out and transportation with
numerous illustrative examples in different
geographic locations and operating environments are
discussed by Gerwick (1999).
5 Engineering on Deck
Dimensional accuracy in both longitudinal and
transverse directions is very critical for both stool
bottom to main deck and skid top to topside module.
Quite often, the shipyard engages a separate third
party dimension measuring contractor for the
accuracy. Laser, theodolite or string based
dimensional measurement techniques are used to
achieve the required dimensional accuracy with very
small tolerances. It is important to note that once the
topside modules are placed, it is very difficult to
make further modifications.
The piece and weld map drawing (a drawing that
shows all the details of welding throat size for all
critical connections) are to be followed. The main
load bearing connections has to be verified by non
destructive testing (NDT) which is usually carried
out by a third party company. The longitudinal and
transverse distances need to be as accurate to the
design condition as possible (Figure 3). As the
volume of upper deck piping is massive, it is
expected that they are carried out simultaneously
with topside support installation and preferably
before the topside module installation.
For the safe installation of topside modules, the
designer
should
also
consider
Dynamic
Amplification Factor (DAF), Skew Load Factor
(SKF) and sling Minimum Breaking Load (MBL).
These are discussed by Chakrabarti (2001).
The empirical values are derived from theoretical
studies, model tests and actual feedback from
operations. Loads in the lifting points, lifting point
design, standard clearances, rigging factors and loads
due to uncertainty of rigging alignment are also
provided in Noble Denton (2006). The design of
topside module main beams has a vital impact on the
type of lift, specifics of lifting arrangement as well as
sling and shackles.
6 Effect on structure
The effect of resolved load on each lifting point and
its effect on the primary members need to be rechecked for each lifting condition, as the actual
fabrication condition may have weight, dimensional
or other condition which was not studied at the early
design stage. The most vulnerable places are the
newly added lifting pad eye installations. These areas
are to be studied by a suitable finite element analysis
for the adequacy of the structural design. In practice,
the pad eye and trunion are to be examined by NDT.
An example of such FEA study results of topside
module base frame with lifting pad eye for a specific
lift condition is shown in Figure 4. This is a basic
study to predict the yield behaviour of the primary
girders. The equipment loads used for the study are
to be authentic and supported by equipment
manufacturer’s provided information.
The critical areas for verification are
• Connection of lifting eye and topside module,
• Local buckling of plating around lifting pad eye,
• Bending of primary supporting members.
Fig.3 Tubular topside module supports.
4
shown in Figure 6, compiled for inshore and static
condition from guideline documents by Noble
Denton (2006). The flow chart can be used to
determine to acceptability of the lifting arrangement.
Operational considerations as described in Figure 5
are not considered here. Empirical formulas and
numeric values of factors like SKF, DAF and
consequence factor are stated in Noble Denton
(2006). The flow chart can detect the specific area
where it can be recalculated rather than revising the
full set of different calculations.
Fig. 4 Utilising FEA to check the module
Primary structure.
7 Decision support parameters
Parameters like selection of heavy lift crane,
location of installation, calculating lift hook load,
selection of rigging arrangement, selection of shackle
and wire are very much interconnected to each other.
Figure 5 shows the main decision support
parameters for heavy lifting operation. The
parameters are production and planning oriented.
Change in one parameter affects design, technical,
operational and other factors. For example, ‘D’
(distance between lifting points) is the distance on
the module to be lifted and is fixed at the installation
time. ‘D’ contributes to ‘A’ (distance between crane
and vessel), ’G’ (sling angle with pad eye at X
direction), ’J’ (independent and combined SWL of
‘A frame’ and fly jib), ‘M’ (rigging arrangement)
and ‘H’ (Boom/fly jib angle). The horizontal
projected distance between ‘A frame’ and fly jib is to
be same as the distance between lifting points. The
horizontal projected distance is controlled by the
boom angle and vessel to crane distance. In a
particular angle the sling reaction on ‘A frame’ and
fly jib is to be within maximum allowed load curve
provided by the crane operator. Tie down of two
slings at X direction also can keep the distance equal.
Figure 5 can help project manager and lift engineer
to predict the interconnectivity among different
lifting parameters and take lifting decision.
Figure 7 shows a typical rigging arrangement with
all necessary rigging details. For the arrangement
shown in the figure, the weighted or calculated
weight for the module is 958 tonnes. Addition for the
dynamic factor and the weight of rigging wires and
shackles increases the hook load to 1026 tonnes. This
represents an increase of 68 tonnes from the
calculated module weight, approximately 7 % of the
calculated module weight. The maximum expected
load on all four points on ‘A frame’ and fly jib are
also available in Figure 7. The values of T1, T2, T3
and T4 are to be verified against the safe working
load of ‘A frame’ and Fly jib.
The use of special plate shackle for obtaining a
particular pad eye angle is also shown in Figure 7.
This angle guides the pad eye design. Tie down wire
as shown in Figure 7 is controlled by the actual
distance of points on the ‘A frame’ and fly jib of the
lifting crane. Tie down slings are vital for keeping
the module loads perfectly as vertical as possible in
the lifting slings.
8 Effect of Turning
For fast and time efficient fabrication, topside
modules are sometimes fabricated in a different
orientation other than the actual orientation at
installation condition which requires overturning.
Pad eye is not suitable for overturning operation as
the common industry practice on lateral angle of
sling and pad eye is maximum 3 degree. This is
because of huge bending moment experienced at the
pad eye base. A trunion is commonly used for such
overturning operation where lifting sling can rotate
to the desired direction with minor friction without
experiencing bending moment at transverse direction.
An example of FEA study results of topside module
base frame with trunion for a very conservative
overturning moment is shown in Figure 8. It is a
local strength analysis to predict the yielding and
buckling tendency around the trunion.
A standard flowchart for lifting factors and load is
5
Fig.5 Parameters of lifting and their dependence.
6
Fig.6 Flow chart for lifting arrangement.
Fig.7 Rigging arrangement with plate shackle
7
Narrow installation gap and lack of rigging space at
the sides are commonly faced installation problems.
Plate shackle of special type (see Figure 10) is used
to resolve the obstacle.
Fig.8 Trunion for overturning.
A common problem encountered in design for a
pad eye is very large size and high thickness of plates
although high strength steel is often chosen. The
main causes are heavy sling loads, limited number of
pad eye for rigging difficulty and limitation of lateral
angle of sling with pad eye. Appropriate under deck
stiffening immediately below pad eye and horse shoe
plate instead of conventional ring plates can be used
to counter the problem. The special features and
limitation of a pad eye with horse shoe plates (Figure
9) are:
• The increase of thickness from bottom to top
gives a proper flow of stress from top to base
where conventional ring doublers have a sharp
thickness increase.
• The most loaded part on the top is thicker
compared to same thickness for round ring
plates.
• The main limitation is to achieve a similar
sling angle as per the designed pad eye angle.
Fig.10 Plate shackle aligned with pad eye.
9 Fine Guiding
Tolerance of misalignment for topside modules on
module support are very sensitive, misalignment may
lead to a condition where a specific connection is
overloaded and which was not a designed condition.
Most of the lifting operations in shipyards give a
better placing accuracy than in purely offshore
condition where wave and wind forces can be quite
high for static station keeping of the vessel. Factors
such as marine traffic movement nearby, wave and
wind forces on vessel are compensated by the
dynamic positioning system of the crane vessel in
shipyard condition. In practical situation one
particular side of the module comes earlier than the
other side. A structural fine guiding is required to
tackle misalignment. Fine guiding can be done with
wire string or structural guide plate. Figure 11 shows
a U shaped cut plate both in longitudinal and
transverse direction. The module on top can easily sit
on guide plate slot. Structural guiding works even
one particular side or member hits earlier than the
other sides. An earlier marking on the offset between
ships centerline and skid reference line gives more
accurate measurement of very minor misalignment
also. After the operation they are verified for
dimensional tolerance again so that the exact amount
of misalignment is known after the installation is
completed.
Fig.9 Pad eye with horse shoe plate.
8
11 References
Fig.11 Fine guiding with guide plate
10 Conclusions
In this paper, technical considerations for the
installation of topside modules are studied which can
then be further extended to a more detailed and
methodical assessment. The following is the
summary of the main points.
•
Decision support diagrams can thus be used
for technical assessment of the procedure.
•
The findings can be applied to rationalize the
assumptions made much earlier than actual
installation by the hull and module designer
as installation is a vital part for the life cycle
of the module.
•
The integration of topside and main hull in
terms of ship’s life cycle is subject to more
detailed theoretical studies and model testing.
•
As a future work, a parametric study of
lifting arrangement factors can be carried out
testing.
•
New and finer methods of dimensional
control and tolerance can be studied.
Bai, Y. 2003 Marine Structural Design, Structural
Design Principle, Elsevier, pp. 100-102.
Chakrabarti, S. K. 2005 Handbook of Offshore
Engineering, Volume I & II, Elsevier, pp.1101-1109,
1089-1092
Gourdet, G. 2008 Connection hull-topsides: principles,
designs and returns of experience, Bureau Veritas
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Gerwick Jr, B. C. and Morris M.D. 1999 Construction
of Marine and Offshore Structures, CRC Press, Art
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Henriksen, L. O., Williams, B. D., Wang, X. and Liu,
D. 2008 Structural Design and Analysis of FPSO
Topside Module Supports, ABS Technical Paper.
Krekel, M. H. and Kaminski, M. L. 2002 FPSOs:
Design considerations for the structural Interface
hull and topsides. Offshore Technology Conference,
OTC 13996, Houston.
Marshall, R. W. and Smith, S. L. 2002 UKOOA FPSO
Design Guidance Notes For UKCS Service,
UKOOA.
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By Floating Crane Vessels, No 27/NDI, Noble
Denton Technical Policy Board.
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Transportations, No 030/NDI, Noble Denton
Technical Policy Board.
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Based Inspection Approach for Topside Structural
Components, Offshore Technology Conference
9
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