PPT 3.2 Design Development of Corrugated Bulkheads(0)

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Design Development of Corrugated BulkheadsTSCF 2010 Shipbuilders Meeting 27 October 2010

Nippon Kaiji Kyokai1

Topics

Purpose of corrugated bulkheads Structural types of corrugated bulkheads Types of damages Design development Latest rule requirements Conclusion2

1

Typical Hull Structure of Tankers

Small 10,000 t 20,000 t 30,000 t 50,000 t 100,000 t

Large DWT3

Purpose of corrugated bulkheads

Plane surface as cargo tank boundary - Complete cargo tank washing - Minimize the cargo residue - Maximum cargo tank capacity4

2

Next Topic

Purpose of corrugated bulkheads Structural types of corrugated bulkheads Types of damages Design development Latest rule requirements Conclusion6

Structural types of corrugated bulkheads

Types of cargo tank bulkhead

Vertically Corrugated BHD Small Tank cleaning Tank capacity

Vertically Corrugated BHD Large

Horizontally Horizontally Corrugated Corrugated BHD BHD Small Large

: Very good

: Good

7

3

Structural types of corrugated bulkheadsships

Types of Longitudinal Corrugated Bulkheads

ships 60

Types of Transverse Corrugated Bulkheads

60 50 40 30 20 10 019 90 19 92 19 96 19 98 20 00 20 02 20 06 20 08 19 94 20 04

Horizontal Vertical

50 40 30 20 10 019 90

Horizontal Vertical

19 98

19 94

19 96

20 06

20 00

20 02

20 04

19 92

Longitudinal BHD Horizontally Corr.

Transverse BHD Horizontally Corr.

Number of ships (ClassNK)Vertically Corr.

delivered in 1990-2008

Vertically Corr. 8

Next Topic

Purpose of corrugated bulkheads Structural types of corrugated bulkheads Types of damages Design development Latest rule requirements Conclusion9

20 08

4

Typical damages of corrugated bulkheads

Corru. BHD

Cargo Tank

Inner Bottom

Stress concentration at toes of fillet welding

Corru. BHD

Inner Bottom10

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

11

5

Next Topic

Purpose of corrugated bulkheads Structural types of corrugated bulkheads Types of damages Design development Latest rule requirements Conclusion12

Design development1. Design of supporting structures Stiffeners under corrugation flange

Floors and girders under corrugation flange13

6

Design of supporting structuresEffectiveness of supporting structured0

Case Depth of stiffener / d01.4 1.2 Stress (mises) 1.0 0.8 0.6 0.4 0.2 0.0 0.0 0.5

1 0.31

2 0.46

3 0.62

4 0.92

5 2.06Stiffener Floor d

Floor d0=d(double btm depth)

1.0

1.5

2.0

2.5

Relative stress at the corner of corrugation

Stiffener depth/d0

14

Design of supporting structuresOutcome;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

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

15

7

Design development2. Application of full penetration weldingCorrugated 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 grinder16

Design developmentEffectiveness of full penetration weldingFixed Tensile load

Gap

Fixed

Fixed

Comparative stress evaluation- by bending load and tensile load - with various gaps x17

z

8

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

Full penetration

Gap 0mm (Fillet)

Gap 2mm

Tensile load

18

Von-Mises stress by tensile load

3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0Full Pene. Gap_0mm Gap_2mm Gap_4mm Gap_6mm Gap_8mm

ATensile load Bending load

Gap

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

9

Experimental test of stainless steel (SUS316L)

Tensile test (as weld) bending test (as weld)

Tensile test (as weld) Higher tensile load

Weld toe grinding

Tensile test (Grinder)

(ClassNK Research Institute)

Tensile test (Grinder) Higher tensile load 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

21

10

Design development3. Verification of designs with gussets and shedder plates

Shedder plate1200 m m

Shedder plate

1500 mm

Gusset plateG usset plate

300 mmLower stool

1500 m m 300 m m Lower stool

Lower stool

Impact by gusset and shedder plates were investigated

22

Impact to the design by gusset and shedder plates

1. Reduced stress at critical pointLower stool

2. Stress concentration at the crossing of shedder plates

Lower stool

Low stool er

Bracketed stiffener

3. Extended enclosed space leads to a loss of cargo capacity23

11

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

24

Next Topic

Purpose of corrugated bulkheads Structural types of corrugated bulkheads Type of damages Design development Latest rule requirements Conclusion25

12

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 Recent practice

All Part Full penetration welding CSR

26

CSR Requirements

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 MeshTar get Tan k

27

13

Sensitivity of mesh size at corrugation corner

Parametric analysis to know the sensitivity of mesh size

Coarse Mesh

Fine Mesh (50mmx50mm)

Very Fine Mesh (17mm x 17mm)

WebCoarse mesh Fine mesh X mm 50mm

Flange

Very fine mesh 28

Sensitivity of mesh size at corrugation cornerVon-Mises stress depending on mesh size N/mm2P=1.85 =1.50 =1.30

Very Fine Mesh Fine Mesh Coarse Mesh

900 800 700 600 500

S

=1.025 =0.80

400 300 200

MR Tanker Load Case : B4-1 (Zig-Zag) Thickness : 22mm(net) S.G.(t/m3)=0.8, 1.025, 1.3, 1.5, 1.85350 300 250 200 150 100 50 0

100 0

Distance from corrugation corner (mm)

Element stress strongly depends on the mesh size near the corner Definition of mesh size is important when detail analysis is required29

14

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. = 1.025S P

Ships for studyShip 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 CN /mm2

Ship C_with bracket Ship Bship A (fine )

Ship A

800 700 600 500 400 300 200 100 0 -600 -400 -200 0 200 400CSR-T re quire me nt (Coarse me sh, HT 32) CSR-T re quire me nt (Fine me sh, HT 32) ship B (fine ) ship C (fine ) ship C_withbracke t ship A (coarse ) ship B (coarse ) ship C (coarse )

(mm) from the corner 600 31

15

Impact on scantlings by CSR Fine Mesh

CSR contribute to more robust corrugated bulkhead designs Feedback from Japanese shipyards 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

Further rule development cons