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December, 2011
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1. Introduction
2. Objectives and Scope of Works
3. Code and Standard
4. Methodology
5. Data
6. Calculation of Static Load
7. Finite Element Model
8. Stress Analysis Result
9. Remaining life
10. Conclusion and Recommendation
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The Pertamina Hulu Energi (PHE) ONWJ production sharing contracts in
the Java Sea cover 8,300 square kilometers, from north of Cirebon in the
east to Pulau Seribu in the west.
PHE ONWJ will assess the structural of Arco Ardjuna Hull based on actual
condition.
The condition influenced by problems of aging hull structural such as
general corrosion and local pitting, thinner material leads to higher stress
and lower buckling capacity and fatigue damage accumulation, cracks
and crack growth.
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Arco Ardjuna Hull structural assessment for evaluation of FSO hull
strength is needs to be done to provide the necessary structural integrity
throughout its service life.
For this purpose, the environmental condition is defined with a specific
combination of wind, waves and current.
This environmental load combined to the operational and deformation
load used as load input to the analysis.
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turalAssessment The objective of this assessment is to obtain safety factor from stress
analysis result and life time for the hull structure based on actual
condition.
Data collection and preliminary study
Site visit
Calculation of environmental, operational and deformation load
Perform stress analysis for hull structural using finite element method with
static, dynamic and impact loading
Strength/structural integrity evaluation
Calculation of hull structural life time with consideration of: Corrosion
Fatigue
Stability due to cargo transfer operation
Stability due to buckling or collapse
Mechanical damage Generate conclusion and recommendation
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Preliminary Study
Site Visit
Data Collection
Stress Analysis
Structural Integrity
Evaluation
Remaining Life
Presentation
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Floating Storage and Offloading Barge (FSO)ARCO Ardjuna
Name ARCO Ardjuna
Description Floating Storage and Offloading Barge (FSO)
Classification society American Bureau of Shipping (ABS)
Class notation A1, Oil Tank Barge, Storage Service
LOA (Length Overall) 142.6 m
LBP (Length Between
Perpendicular)142.6 m
Molded Breadth 48.2 m
Molded Depth 26.5 m
Max. Draft (design) 24.0 m
Min. Draft (Light Load) 6 m
Dead weight 137,673 tonnes
Gross tonnage 54,236 tonnes
Net tonnage 53,653 tonnes
Light ship weight 15,529 tonnes
Light draft 2.52 m
Summer draft 19.68 m
Free board 6.87 m
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1. Static Hull Girder Loadsa. Hull girder still water bending moment
b. Hull girder still water shear force
2. Local Static Loads
a. Static sea pressureb. Static tank pressure
c. Static deck loadSagging
Hogging
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Data Symbol Value UnitWave coefficient Cwv 8.775
Block coefficient Cb 0.6
SAGGINGat amidship Msw -579747.4 kNmat any longitudinal position
Still-water Bending Moment at 0.4L
amidship Msw -579747.4 kNmStill-water Bending Moment at 0.1L from
A.P. or F.P. Msw -86962.1 kNmStill-water Bending Moment at A.P. or F.P. Msw 0.0 kNm
HOGGINGat amidship Msw 931483.5 kNmat any longitudinal position
Still-water Bending Moment at 0.4L
amidship Msw 931483.5 kNmStill-water Bending Moment at 0.1L from
A.P. or F.P. Msw 139722.5 kNmStill-water Bending Moment at A.P. or F.P. Msw 0.0 kNm
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Still-water Shear Force Symbol Value Unit
Considering the Side Shell
Plating
SWSFp (at 0L) #DIV/0!
kN
SWSFp (at 0.2L-0.3L) #DIV/0!SWSFp (at 0.4L-0.6L) #DIV/0!SWSF (at 0.7L-0.85L) #DIV/0!
SWSFp (at L) #DIV/0!SWSFn (at 0L) #DIV/0!
SWSFn (at 0.2L-0.3L)
#DIV/0!
SWSFn (at 0.4L-0.6L) #DIV/0!SWSn (at 0.7L-0.85L) #DIV/0!
SWSFn (at L) #DIV/0!
Considering Various
Longitudinal Bulkhead Plating
SWSFp (at 0L) #DIV/0!
kN
SWSFp (at 0.2L-0.3L) #DIV/0!SWSFp (at 0.4L-0.6L) #DIV/0!SWSF (at 0.7L-0.85L)
#DIV/0!
SWSFp (at L) #DIV/0!SWSFn (at 0L) #DIV/0!
SWSFn (at 0.2L-0.3L) #DIV/0!SWSFn (at 0.4L-0.6L) #DIV/0!SWSn (at 0.7L-0.85L) #DIV/0!
SWSFn (at L) #DIV/0!
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Local Static Loads Symbol Value Unit
Static sea pressure Phys kN/m2
Static tank pressure Pin-tk kN/m2
Static deck Pdeck 16 kN/m2
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Modeling:Geometry, Material, Property
Input Parameter:Constrain and Loads
Finite Element Analysis
Convergent Result
Output:
Stress Contour andDeformation
No
Yes
The FEM software that used forcalculate and analyze the
maximum stress is performed by
MSC Nastran.
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Bottom Stiffener
Bottom Stiffener
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Amidship and Bracket
Amidship Stiffener
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OT Stiffener
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Swash Stiffener
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RemainingLife
Corrosion
Fatigue
Stability dueto cargotransfer
operation Stability due
to bucklingor collapse
Mechanicaldamage
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Remaining Life
ratecorrosion
ttLifemaining actual minRe
Where:
tactual = the thickness, in mm, recorded at the time of inspection for a
given location or componenttmin = minimum allowable thickness, in mm, for a given location or
component
Corrosion Rate
actualprevious
actualprevious
tandtbetweenyears
ttRateCorrosion
Where:
tprevious = the thickness, in inches (millimeters), recorded at the same
location as t actual measured during a previous inspection.
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Main Deck 25 30 17.5 14.7 0.278 -10
Bottom Plating - CT1 21 20 16.8 21.9 0.278 18
Bottom Plating - WT1 21 20 16.8 21.5 0.278 17
Bottom Plating - CT2 21 20 16.8 21.6 0.278 17
Bottom Plating - WT2 21 20 16.8 21.8 0.278 18Bottom Plating - CT3 21 20 16.8 21.7 0.278 18
Bottom Plating - WT3 21 20 16.8 21.5 0.278 17
17 25 12.75 22.4 0.278 35
18 25 13.5 22 0.278 31
Remaining
Life (Years)
Side Shell
Original
Thickness
[mm]
Max. Alwb
Dim
[%]
Min allowable
thickness
(mm)
Min actual
thickness
(mm)
Max corrosion
rate
(mm/year)
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Based on Palmgren-Miner cumulative damagerule. The fatigue capability is not acceptable
if DM > 1
The fatigue assessment is to be applied towelded connections where the steel has a
minimum yield strength of less than
400N/mm2.
=
=
=1
ni: Number of cycles of stress range Si
Ni: Number of cycles to failure at stress range Si
ntot: Total number of stress range blocks
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Materials
Data
Stress Range
Load
Selection ofthe Design S-
N Curve
Calculation ofCummulative
Damage =
2
=1
=
1
+
2
+
3
+
4
/
2
= 2
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Static loadWave induced loads
Impact loads
Cyclic loads
Transient loads
Residual stress
Hull girder loads
Dynamic wave pressuresDynamic tank pressure loads resulting from
ship motion
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fSN 1,06; factor to account for joint in combined
protected & unprotected environment
f1, f2, f3, and f4 stress combination factor
Sv Stress range due to vertical bending moment,N/mm2
Sh Stress range due to horizontal bending moment,
N/mm2
Se Stress range due to external wave or internaltank pressure, N/mm2
Si Stress range due to external wave or internal
tank pressure, N/mm2
=
1
+
2
+
3
+
4
/
2
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S Stress range cumulative
N predicted number of cycles to failure
under stress range
m constant depending on material andweld type, type of loading, geometrical
configuration and environmental conditions
(air or sea water)
K2 constant depending on material and
weld type, type of loading, geometrical
configuration and environmental conditions
(air or sea water)
= 2
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DMi Cumulative fatigue damage ratio for
the applicable loading condition
i = 1 for full load condition
= 2 for normal ballast condition
=2
=1
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