paper3.2 design development of corrugated bulkhead …tscforum.org/tscf/bfiles/2010/ppt 3.2 design...

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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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2

DWT100,000 t 50,000 t 30,000 t 10,000 t

Large Small

Typical Hull Structure of Tankers

20,000 t 3


Plane surface as cargo tank boundary

- Complete cargo tank washing - Minimize the cargo residue - Maximum cargo tank capacity

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3



Types of damages

Design development


Conclusion

Next Topic

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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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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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Types of damages

Design development


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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Types of damages

Design development


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



3. Extended enclosed space leads to a loss of cargo capacity


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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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Type of damages

Design development


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)


(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


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

Nippon Kaiji KyokaiA World Leader in Ship Classification

paper3.2 design development of corrugated bulkhead …tscforum.org/tscf/bfiles/2010/ppt 3.2 design...

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