PPT 3.2 Design Development of Corrugated Bulkheads(0)

Design Development of Corrugated Bulkheads TSCF 2010 Shipbuilders Meeting 27 October 2010

Nippon Kaiji Kyokai 1

Topics

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Purpose of corrugated bulkheads

‹

Structural types of corrugated bulkheads

‹

Types of damages

‹

Design development

‹

Latest rule requirements

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Conclusion 2

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Typical Hull Structure of Tankers

Small 10,000 t

Large 20,000 t

30,000 t

50,000 t

100,000 t

DWT 3

Purpose of corrugated bulkheads

Plane surface as cargo tank boundary - Complete cargo tank washing - Minimize the cargo residue - Maximum cargo tank capacity 4

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Next Topic

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Purpose of corrugated bulkheads

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Structural types of corrugated bulkheads

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Types of damages

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Design development

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Latest rule requirements

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Conclusion 6

Structural types of corrugated bulkheads

Types of cargo tank bulkhead

Vertically Corrugated BHD Tank cleaning Tank capacity

Vertically Corrugated BHD

Horizontally Horizontally Corrugated Corrugated BHD BHD

Small

Large

Small

Large

◎ ◎

◎ ○

◎ ◎

○ ◎

◎: Very good

○: Good

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Structural types of corrugated bulkheads ships

ships

Types of Longitudinal Corrugated Bulkheads

50

20 08

20 06

20 04

20 02

20 00

19 98

Horizontal Vertical

19 96

19 90

20 08

20 06

20 02

0 20 04

10

0 20 00

10

19 98

20

19 96

30

20

19 94

30

19 92

40

19 94

Horizontal Vertical

40

19 92

50

19 90

Types of Transverse Corrugated Bulkheads

60

60

Transverse BHD

Longitudinal BHD Horizontally Corr.

Horizontally Corr.

Number of ships (ClassNK) Vertically Corr.

delivered in 1990-2008

Vertically Corr. 8

Next Topic

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Purpose of corrugated bulkheads

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Structural types of corrugated bulkheads

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Types of damages

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Design development

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Latest rule requirements

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Conclusion 9

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Typical damages of corrugated bulkheads

Corru. BHD

Cargo Tank

Inner Bottom

Stress concentration at toes of fillet welding

Corru. BHD

Inner Bottom 10

Typical damages of corrugated bulkheads Cause of damages 9Defects of welding (Overlapping, Undercutting) 9 Lack of supporting structures 9 Lack of continuity (misalignment)

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Next Topic

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Purpose of corrugated bulkheads

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Structural types of corrugated bulkheads

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Types of damages

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Design development

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Latest rule requirements

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Conclusion 12

Design development 1. Design of supporting structures Stiffeners under corrugation flange

Floors and girders under corrugation flange 13

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Design of supporting structures Effectiveness of supporting structure d0

Case

1

2

3

4

5

Depth of stiffener / d0

0.31

0.46

0.62

0.92

2.06 Stiffener

1.4

d Floor

Stress (mises)

1.2 1.0 0.8 0.6

Floor d0=d(double btm depth)

0.4 0.2 0.0 0.0

0.5

1.0

1.5

2.0

2.5

Stiffener depth/d0

Relative stress at the corner of corrugation

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Design of supporting structures Outcome; ¾ Stress of end connection decreases by deeper supporting structure ¾ Half of corrugation depth is considered as effective support depth ¾ Floors/girders are suitable as supporting structure

Suitable supporting structure under flange plate of corrugated bulkhead gives higher reliability

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Design development 2. Application of full penetration welding Corrugated BHD

Fillet welding

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 16

Design development Effectiveness of full penetration welding Fixed

Tensile load

Gap

Fixed

Fixed

Comparative stress evaluation z

- by bending load and tensile load - with various gaps x

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Von-Mises stress caused by bending / tensile load Bending load

Full penetration

Gap 2mm

Gap 0mm (Fillet)

Tensile load

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Von-Mises stress by tensile load

3.5 3.0

A Tensile load Bending load

Gap

2.5 2.0 1.5 1.0 0.5 0.0 Full Pene. Gap_0mm Gap_2mm

Gap_4mm Gap_6mm

Gap_8mm

Relative stress at Position A (Stress of Full Penetration = 1.0) 19

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Experimental test of stainless steel (SUS316L)

Tensile test (as weld)

Tensile test (as weld) Higher tensile load

Weld toe grinding

bending test (as weld)

Tensile test (Grinder)

(ClassNK Research Institute)

Tensile test (Grinder) Higher tensile load 20

Application of full penetration welding Outcome; ¾ Cracks by bending load initiate from weld toe regardless of root gap ¾ Cracks by tensile load initiate from weld toe or root ¾ Root gaps lead to higher stress at weld toe and root by tensile load ¾ Gap control and satisfactory throat thickness are important ¾ Full penetration welding contributes ; - to mitigate the risk of gap control - to give satisfactory throat thickness ¾ 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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Design development 3. Verification of designs with gussets and shedder plates

Shedder plate

Shedder plate 1200 m m

Gusset plate

1500 mm

G usset plate

300 mm Lower stool

1500 m m 300 m m

Lower stool Lower stool

Impact by gusset and shedder plates were investigated

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Impact to the design by gusset and shedder plates

1. Reduced stress at critical point Lower stool

2. Stress concentration at the crossing of shedder plates

Lower stool

Lower stool

Bracketed stiffener

3. Extended enclosed space leads to a loss of cargo capacity 23

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Reinforcement by gusset and shedder plate Outcome; ¾Gusset and shedder plates are often used in the design of corrugated bulkheads in bulk carriers and recommended in CSR for tankers. ¾Gusset and shedder plates definitely contribute to lower the stress ¾ 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 ¾Extended 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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Next Topic

‹

Purpose of corrugated bulkheads

‹

Structural types of corrugated bulkheads

‹

Type of damages

‹

Design development

‹

Latest rule requirements

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Conclusion 25

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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

Corner Part Full penetration welding + Grinder

All Part Full penetration welding CSR

Recent practice

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CSR Requirements

Requirements of Finite Element Analysis (FEA): 9 Overall stress and buckling analysis by Coarse Mesh 9 Detail stress analysis of lower end connection of vertically corrugated bulkhead by Fine Mesh Tar get Tan k

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Sensitivity of mesh size at corrugation corner

Parametric analysis to know the sensitivity of mesh size

Coarse Mesh

Very Fine Mesh (17mm x 17mm)

Fine Mesh (50mmx50mm)

Flange

Web Coarse mesh

50mm

Fine mesh Very fine mesh

X mm

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Sensitivity of mesh size at corrugation corner Von-Mises stress depending on mesh size N/mm2 P

γ=1.50

800 700

Fine Mesh

γ=1.30

S

900

Very Fine Mesh

γ=1.85

600 500

γ=1.025

Coarse Mesh

400 300

γ=0.80

200

9 MR Tanker 9 Load Case : B4-1 (Zig-Zag) 9 Thickness : 22mm(net)

100 0

350

300

250

200

150

100

50

0

Distance from corrugation corner (mm)

9 S.G.(t/m3)=0.8, 1.025, 1.3, 1.5, 1.85

¾ Element stress strongly depends on the mesh size near the corner ¾ Definition of mesh size is important when detail analysis is required 29

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Impact on scantlings by CSR Fine Mesh

Case studies to investigate the impact of CSR criteria - MR Tanker

P

- Transverse Corrugate Bulkhead (Vertical) - Critical Load Case : B4-5a (Zig-Zag) - S.G. = 1.025

S

Ships for study 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 30

Impact on scantlings by CSR Fine Mesh

Ship C N /mm2

Ship A

Ship C_with bracket Ship B

800 700 600

ship A (fine )

CSR-T re quire me nt (Coarse me sh, HT 32)

CSR-T re quire me nt (Fine me sh, HT 32)

500

ship B (fine ) ship C (fine ) ship C_withbracke t

400

ship A (coarse )

300

ship B (coarse ) ship C (coarse )

200 100 0 -600

-400

-200

0

200

400

(mm) from the corner 600 31

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Impact on scantlings by CSR Fine Mesh

¾CSR contribute to more robust corrugated bulkhead designs Feedback from Japanese shipyards ¾Considerable scantling increase even from designs having demonstrated history of successful service experiences ¾Required thickness tends to reach to the maximum allowable thickness for the fabrication of cold-bending ¾ 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

Further rule development considering such as edge treatment and anti-fatigue steel is anticipated 32

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 33

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Thank you for your Attention

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