A study on Fatigue Strength for Tank Structures subject to Harmonized CSR Sungdong Shipbuilding & Marine Engineering Hyangduk Seo TSCF 2016 Shipbuilders Meeting

Contents Backgrounds Information of Target Vessel FE Analysis Result Conclusion

Contents Backgrounds Information of Target Vessel FE Analysis Result Conclusion

Class Rules to IMO for GBS verification audit I. Backgrounds IACS Plan Harmonized CSR 1 Jul 2015 Submission of each Class Rules to IMO for GBS verification audit IMO GBS 2011 2012 2013 2014 2015 2016 External review periods Technical Committee review Adoption 1st revision Entry in to force IMO (GBS)

Fatigue Strength Assessment I. Backgrounds Fatigue Strength Assessment Simplified stress analysis Hot spot stress at weld toe of longitudinal stiffener end connection Hot spot stresses are obtained by multiplying nominal stresses by SCF Finite element stress analysis Hot spot stress from very fine mesh model. Hot spot stress is generally highly dependent on the finite element model used for representing the structure. Procedure Screening with fine mesh model Evaluate with very fine mesh model Mandatory area for fatigue strength calculation Omit fatigue evaluation with design standard

Fatigue Strength Assessment I. Backgrounds Fatigue Strength Assessment Structural details toe be assessed by very fine mesh analysis Structural details to be assessed by very fine mesh analysis If not designed in accordance with detail design standard No Critical detail 1 Welded lower hopper knuckle connection (intersection of hopper sloping plate, inner bottom plate, longitudinal girder, floor and transverse web) at the most critical frame location. 2 Radiused lower hopper knuckle connection (intersection of knuckle inner bottom plate, longitudinal girder, floor and transverse web) at the most critical frame location. 3 Welded upper knuckle connection (intersection of hopper slopping plate, inner hull longitudinal bulkhead, transverse web and side stringer) where the angle between hopper plate and inner hull longitudinal bulkhead is less than 130 deg, at the most critical frame location. 4 Connection of transverse bulkhead lower stools to the inner bottom plating in wat of double bottom girders. No Critical detail 1 Radiused upper hopper knuckle connection (intersection of knuckled inner side plate, side girder and transverse web) at the most critical frame location. 2 Corrugations of transverse bulkheads to lower stool or inner bottom plating connection. 3 Cruciform heel connections between side stringers in double side and transverse bulkhead horizontal stringers, for the stringer closest to the mid depth and for the uppermost one. 4 Cut out for longitudinal stiffeners in web frame without web stiffener connection. 5 Scallops in way of block joints on strength deck close to mid hold (and down to 0.1D from deck corner)

Hot spot stress for not Cruciform joints I. Backgrounds Hot spot stress for not Cruciform joints Type “a” and “b” Free surface Cruciform joints in H-CSR : Hopper knuckle connection, transverse bulkhead lower stool to inner bottom connection and horizontal stringer heel Calculation of hot spot stress of Type “a” A Two principal hot spot stress ranges extrapolated from each side of line A-A in between load case ‘i1’ and ‘i2’. The angle between the direction x of the element and the principal direction should be calculated.

Hot spot stress for Cruciform joints I. Backgrounds Hot spot stress for Cruciform joints Cruciform joints in H-CSR : Hopper knuckle connection, transverse bulkhead lower stool to inner bottom connection and horizontal stringer heel Calculation of hot spot stress

I. Backgrounds Details different from web stiffened cruciform joints Fatigue strength assessment method for H-CSR Details different from web stiffened cruciform joints Weld Type Assessment area Element type Element or beam size Welded Type “a” Weld toe on plate surface Shell tnet50 x tnet50 Type “b” Weld toe around the plat edge Dummy beam 10 x 10 Non welded Base material Free surface Details from web stiffened cruciform joints Type Assessment area Shift stress Element type Element size Hot spot stress at flange Flange Applied Shell tnet50 x tnet50 Hot spot stress in the web Web Bent hopper knuckle Bent plate

Contents Backgrounds Information of Target Vessel FE Analysis Result Conclusion

II. Information of Target Vessel 75K Tanker 115K Tanker 158K Tanker Principal Dimension · Length (O.A) : 228.0m · Length (B.P) : 219.0 m · Length (Scant.) : 216.35 m · Breadth (Mld.) : 32.24 m · Depth (Mld.) : 20.9 m · Draught (Scant.) : 14.45 m Principal Dimension · Length (O.A) : 249.9m · Length (B.P) : 239.0 m · Length (Scant.) : 236.13 m · Breadth (Mld.) : 44.0 m · Depth (Mld.) : 21.5 m · Draught (Scant.) : 15.1 m Principal Dimension · Length (O.A) : 277.0m · Length (B.P) : 267.0 m · Length (Scant.) : 263.4 m · Breadth (Mld.) : 48.0 m · Depth (Mld.) : 23.1 m · Draught (Scant.) : 17.15 m

Contents Backgrounds Information of Target Vessel FE Analysis Result Conclusion

Boundary condition & Loading condition III. FE Analysis Boundary condition & Loading condition Boundary Condition Loading Condition

Fatigue Strength Assessment III. FE Analysis Fatigue Strength Assessment Area for Fatigue life evaluation by very fine mesh Fatigue Check Location 1 : Upper Hopper knuckle connection (Bend type) Fatigue Check Location 2 : Lower Hopper knuckle connection (Weld type)

Fatigue Strength Assessment III. FE Analysis Fatigue Strength Assessment Area for Fatigue life evaluation by very fine mesh Fatigue Check Location 3-1 : Back bracket of No.1 horizontal stringer Fatigue Check Location 4-1 : Toe of No.1 horizontal stringer

Fatigue Strength Assessment III. FE Analysis Fatigue Strength Assessment Area for Fatigue life evaluation by very fine mesh Fatigue Check Location 3-2 : Back bracket of No.2 horizontal stringer Fatigue Check Location 4-2 : Toe of No.2 horizontal stringer

Fatigue Strength Assessment III. FE Analysis Fatigue Strength Assessment Area for Fatigue life evaluation by very fine mesh Fatigue Check Location 5-1 : Knuckle connection of Inner Hull to Upper Deck Fatigue Check Location 5-2 : Knuckle connection of Inner Hull to Inner Bottom

Contents Backgrounds Information of Target Vessel FE Analysis Result Conclusion

Position of Fatigue Check Location IV. Result Position of Fatigue Check Location FCL.1 & 2 FCL.3 & 4 FCL.5

IV. Result Fatigue life at FCL.1 ~ 5 Summary of results Location Member Type 75K 115K 158K FCL. 1 Hopper Plate 26 years 17 years 84 years Along the T-Web. Inner Skin 32 years 13 years 39 years Hopper plate 81 years 33 years 35 years Along the No.3 STR Web Section 47 years 23 years 53 years 57 years 123 years No.3 STR. 193 years Over 300 years 232 years 207 years 220 years FCL. 2 Inner Bottom 19 years 28 years 16 years 25 years 44 years 105 years 42 years 18 years 31 years 24 years Side Girder 102 years 172 years 112 years 109 years 180 years 113 years Scarfing Bracket 99 years 74 years 55 years 204 years 259 years 62 years FCL. 3 No.1 STR Bracket Edge 173 years 218 years 88 years Bracket toe 22 years 21 years (Inner Skin) 184 years 241 years 163 years (Transverse BHD.) Stringer Toe 20 years 8 years Stringer Toe edge 48 years STR. Face plate End 15 years Location Member Type 75K　 115K　 158K　 FCL. 4 No.2 STR Bracket Edge 85 years 50 years　 36 years Bracket toe 44 years 38 years 20 years (Inner Skin) 28 years　 50 years 23 years (Transverse BHD.) Stringer Toe 30 years 32 years 24 years Stringer Toe edge 54 years 202 years 60 years STR. Face plate End 20 years　 48 years FCL. 5 Upper Deck Inner Skin 83 years　 37 years 63 years 129 years 83 years 91 years　 92 years　 127 years　 53 years 35 years Over 300 years Inner Bottom 71 years　 141 years　 291 years　 59 years 109 years 61 years 90 years 56 years Bracket

IV. Result Fatigue life at FCL.1 ~ 5 Summary of results

IV. Result Comparison study I Standard design for heel bracket of horizontal stringer Standard size of Bracket VLCC : 800 X 800 X 30, R600 Other Tankers : 800 X 600 X25, R550 Minimum yield stress is not to be less than 315 N/mm2

IV. Result Comparison study I Result Location Ship Size Hot spot 1 (Bkt Edge) (Inner Skin) (Trans. BHD) No.1 STR. 75K 54 years 22 years 45 years 115K 107 years 17 years 151 years 158K 136 years 16 years 58 years No.2 STR. 15 years 25 years 34 years 32 years

IV. Result Comparison study I Time in corrosive environment, TC → Initiation of Fatigue crack in air condition

IV. Result Comparison study II Results of modification for corrosive years Location Member Type 75K 115K 158K FCL. 1 Hopper Plate 26 years 16 years 84 years Along the T-Web. Inner Skin 32 years 13 years 39 years Hopper plate 81 years 30 years 35 years Along the No.3 STR Web Section 47 years 20 years 53 years 57 years 23 years 123 years No.3 STR. 193 years Over 300 years 232 years 207 years 220 years FCL. 2 Inner Bottom 19 years 25 years 29 years 44 years 101 years 42 years 18 years 28 years 24 years Side Girder 102 years 168 years 112 years 109 years 176 years 113 years Scarfing Bracket 99 years 70 years 55 years 204 years 255 years 62 years FCL. 3 No.1 STR Bracket Edge 173 years 215 years 88 years Bracket toe 22 years (Inner Skin) 184 years 237 years 163 years (Transverse BHD.) Stringer Toe 17 years 8 years Stringer Toe edge 45 years STR. Face plate End 15 years Location Member Type 75K 115K 158K FCL. 4 No.2 STR Bracket Edge 85 years 47 years　 36 years Bracket toe 44 years 34 years 20 years (Inner Skin) 28 years　 47 years 23 years (Transverse BHD.) Stringer Toe 30 years 29 years 24 years Stringer Toe edge 54 years 198 years 60 years STR. Face plate End 20 years　 45 years 48 years FCL. 5 Upper Deck Inner Skin 83 years　 63 years 129 years 46 years 83 years Upper Deck 91 years　 88 years　 127 years　 53 years 32 years Over 300 years Inner Bottom 71 years　 137 years　 291 years　 59 years 105 years Inner Bottom 61 years 86 years 56 years Bracket

IV. Result Comparison study II Results of modification for corrosive years Location Member Type 75K 115K 158K FCL. 1 Hopper Plate 26 years 17 years 84 years Along the T-Web. Inner Skin 32 years 13 years 39 years Hopper plate 81 years 33 years 35 years Along the No.3 STR Web Section 47 years 23 years 53 years 57 years 123 years No.3 STR. 193 years Over 300 years 232 years 207 years 220 years FCL. 2 Inner Bottom 19 years 28 years 16 years 25 years 44 years 105 years 42 years 18 years 31 years 24 years Side Girder 102 years 172 years 112 years 109 years 180 years 113 years Scarfing Bracket 99 years 74 years 55 years 204 years 259 years 62 years

Contents Backgrounds Information of Target Vessel FE Analysis Result Conclusion

V. Conclusion Fatigue assessment points are increased than CSR-OT - Standard design suggested to omit the FE analysis. Performed Fatigue assessment for various size of Tankers(Panamax, Aframax, Suezmax) - Hopper connection point is still weak area for fatigue strength from CSR-OT. - Fatigue strength tendency is quite similar but no relation with ship size. - Fatigue strength for knuckle plate(reinforced within 75mm) shows better result than rule guidance(within 50mm). Corrosive year changed from 5 to 10 in urgent rule change 2016. - Generally, fatigue life reduced 0 ~ 20% before. Standard design for bracket of transverse stringer in hold. - Fatigue life is not enough despite standard size applied. - Different tendency by shape(include property) and location of bracket.

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