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Design Design DevelopmenDevelopment t ofofCorrugated BulkheadsCorrugated Bulkheads
Nippon Kaiji Kyokai
TSCF 2010 Shipbuilders Meeting27 October 2010
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Purpose of corrugated bulkheads
Structural types of corrugated bulkheads
Types of damages
Design development
Latest rule requirements
Conclusion
Topics
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DWT100,000 t 50,000 t 30,000 t 10,000 t
Large Small
Typical Hull Structure of Tankers
20,000 t 3
Purpose of corrugated bulkheads
Plane surface as cargo tank boundary
- Complete cargo tank washing - Minimize the cargo residue - Maximum cargo tank capacity
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Purpose of corrugated bulkheads
Structural types of corrugated bulkheads
Types of damages
Design development
Latest rule requirements
Conclusion
Next Topic
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Structural types of corrugated bulkheads
LargeSmallLargeSmall
◎
◎
Horizontally Corrugated BHD
◎
◎
Vertically Corrugated BHD
◎
○
Horizontally Corrugated BHD
○Tank capacity◎Tank cleaning
Vertically Corrugated BHD
Types of cargo tank bulkhead
◎: Very good ○: Good7
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Structural types of corrugated bulkheads
Types of Transverse Corrugated Bulkheads
0
10
20
30
40
50
60
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
ships
Horizontal
Vert ical
Types of Longitudinal Corrugated Bulkheads
0
10
20
30
40
50
60
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
ships
Horizontal
Vert ical
Vertically Corr.
Horizontally Corr. Horizontally Corr.
Vertically Corr.
Longitudinal BHD Transverse BHD
Number of ships (ClassNK)
delivered in 1990-2008
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Purpose of corrugated bulkheads
Structural types of corrugated bulkheads
Types of damages
Design development
Latest rule requirements
Conclusion
Next Topic
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Stress concentration at toes of fillet welding
Typical damages of corrugated bulkheads
Inner Bottom
Corru. BHD
Corru. BHD
Inner Bottom
Cargo TankCargo Tank
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Typical damages of corrugated bulkheads
Defects of welding (Overlapping, Undercutting)
Lack of supporting structures
Lack of continuity (misalignment)
Cause of damages
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Purpose of corrugated bulkheads
Structural types of corrugated bulkheads
Types of damages
Design development
Latest rule requirements
Conclusion
Next Topic
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Design development
1. Design of supporting structures
Stiffeners under corrugation flange
Floors and girders under corrugation flange13
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Design of supporting structures
Effectiveness of supporting structure
2.060.920.620.460.31Depth of stiffener / d0
54321Case
d
d0
Floor
Stiffenerd
d0
Floor
Stiffener
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
0.0 0.5 1.0 1.5 2.0 2.5
Stiffener depth/d0
Str
ess
(m
ises)
Floor
d0=d(double
btm depth)
Relative stress at the corner of corrugation14
Outcome;
Stress of end connection decreases by deeper supporting structure
Half of corrugation depth is considered as effective support depth
Floors/girders are suitable as supporting structure
Design of supporting structures
Suitable supporting structure under flange plate of corrugated bulkhead gives higher reliability
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Design development
2. Application of full penetration welding
Detail stress distribution of corrugation corner
Full penetration welding has been recently applied at the corner of corrugation of lower end connection with weld toe grinder
Fillet welding Full penetration welding
Corrugated BHD
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Design development
Effectiveness of full penetration welding
xx
zz
Fixed
Fixed
Tensile load
Fixed
Gap
Comparative stress evaluation- by bending load and tensile load
- with various gaps17
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Von-Mises stress caused by bending / tensile load
Full penetration Gap 2mmGap 0mm (Fillet)
Tensile load
Bending load
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Von-Mises stress by tensile load
Relative stress at Position A (Stress of Full Penetration = 1.0)
Gap
A
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
Full Pene. Gap_0mm Gap_2mm Gap_4mm Gap_6mm Gap_8mm
Tensile load
Bending load
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10
Experimental test of stainless steel (SUS316L)
Tensile test (as weld)
Tensile test (Grinder) Tensile test (Grinder) Higher tensile load
bending test (as weld)
Tensile test (as weld) Higher tensile load
Weld toe grinding
(ClassNK Research Institute) 20
Application of full penetration welding
Outcome;Cracks by bending load initiate from weld toe regardless of root gap
Cracks by tensile load initiate from weld toe or root
Root gaps lead to higher stress at weld toe and root by tensile load
Gap control and satisfactory throat thickness are important
Full penetration welding contributes ;
- to mitigate the risk of gap control
- to give satisfactory throat thickness
Grinder or TIG welding which gives more smooth surface further contributes to lower the stress concentration at weld toe
Full penetration welding and smoothed weld toe at corrugation corner gives higher reliability
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3. Verification of designs with gussets and shedder plates
Design development
Lower stoolLower stool
300 mm
1500 mm
Shedder plate
Gusset plate
Lower stool
300 mm
1500 mm
300 mm
1500 mm
Shedder plate
Gusset plate
Lower stool300 mm
1500 mm
1200 mm
Shedder plate
Gusset plate
Lower stool
300 mm
1500 mm
1200 mm
300 mm
1500 mm
1200 mm
Shedder plate
Gusset plate
Lower stool
Impact by gusset and shedder plates were investigated22
Impact to the design by gusset and shedder plates
Bracketed stiffener
1. Reduced stress at critical point
2. Stress concentration at the crossing of shedder plates
Lower stoolLower stool
Lower stoolLower stool
3. Extended enclosed space leads to a loss of cargo capacity
Lower stoolLower stool
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Reinforcement by gusset and shedder plate
Outcome;Gusset and shedder plates are often used in the design of corrugated
bulkheads in bulk carriers and recommended in CSR for tankers.
Gusset and shedder plates definitely contribute to lower the stress
However, following deep considerations are necessary ;
- Manholes and air holes to avoid formation of any gas pocket
- Bracketed Stiffener where adjacent shedder plate cross
- Careful workmanship of welding in narrow space
Extended gusset plate leads to some loss of cargo capacity
Better to keep just as recommendation instead of mandatory requirement in tanker designs
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Purpose of corrugated bulkheads
Structural types of corrugated bulkheads
Type of damages
Design development
Latest rule requirements
Conclusion
Next Topic
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CSR Requirements
Prescriptive requirements :
• Local strength (Plate thickness, Section Modulus)
• Arrangement of supporting structures
• Full penetration welding to lower end of vertical corrugated bulkhead connections
Full penetration welding +
Grinder
Corner Part
Recent practice
Full penetration weldingAll Part
CSR 26
Requirements of Finite Element Analysis (FEA):
Overall stress and buckling analysis by Coarse Mesh
Detail stress analysis of lower end connection of vertically corrugated bulkhead by Fine Mesh
CSR Requirements
Target Tank
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Sensitivity of mesh size at corrugation corner
Parametric analysis to know the sensitivity of mesh size
Coarse mesh
Fine meshVery fine mesh
50mm
FlangeWeb
X mm
Coarse Mesh Fine Mesh (50mmx50mm)
Very Fine Mesh (17mm x 17mm)
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Sensitivity of mesh size at corrugation corner
Von-Mises stress depending on mesh size
0
100
200
300
400
500
600
700
800
900
050100150200250300350Distance from corrugation corner (mm)
N/mm2
γ=1.85
γ=1.50
γ=1.30
γ=1.025
γ=0.80
P
S
P
S
Element stress strongly depends on the mesh size near the corner
Definition of mesh size is important when detail analysis is required
MR Tanker
Load Case : B4-1 (Zig-Zag)
Thickness : 22mm(net)
S.G.(t/m3)=0.8, 1.025, 1.3, 1.5, 1.85
Very Fine Mesh
Fine Mesh
Coarse Mesh
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Impact on scantlings by CSR Fine Mesh
Case studies to investigate the impact of CSR criteria- MR Tanker
- Transverse Corrugate Bulkhead (Vertical)
- Critical Load Case : B4-5a (Zig-Zag)
- S.G. = 1.025
Ship A : New design vessel which fully complies with CSR
Ship B : Non-CSR ship with successful service experiences without any damage records
Ship C : Non-CSR ships with damage records
Ship C_with bracket : After reinforcement of ShipC without any further damage records
Ships for study
P
S
P
S
30
0
100
200
300
400
500
600
700
800
-600 -400 -200 0 200 400 600
N/mm2
ship A (fine)
ship B (fine)
ship C (fine)
ship C_withbracket
ship A (coarse)
ship B (coarse)
ship C (coarse)
CSR-T requirement (Fine mesh, HT32)
CSR-T requirement (Coarse mesh, HT32)
Impact on scantlings by CSR Fine Mesh
(mm) from the corner31
Ship C Ship C_with bracket
Ship BShip A
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CSR contribute to more robust corrugated bulkhead designs
Impact on scantlings by CSR Fine Mesh
Further rule development considering such as edge treatment and anti-fatigue steel is anticipated
Considerable scantling increase even from designs having demonstrated history of successful service experiences
Required thickness tends to reach to the maximum allowable thickness for the fabrication of cold-bending
Modification of corrugation span by fitting upper/lower stools or reduction of design cargo density has been required, which inevitably leads to a loss of cargo capacity and deadweight
Feedback from Japanese shipyards
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Conclusion
Corrugated bulkheads are essential structure for product / chemical tankers
Sufficient service records have proved the advantage
Rules and designs have been improved to cover complexities of fabrications and operations
However it has been also reported that designers need to modify the initial design to save unacceptable scantling increase due to latest CSR requirements
Continuous update of rules allowing establishment of new technologies should also be performed, while watching valuable service experiences of existing designs
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Thank you for your Attention
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