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Update on the IACS Common Structural Rules for Tankers & Bulk Carriers

Update on the IACS Common Structural Rules for Tankers & Bulk Carriers. Rune Torhaug (DNV) Dr. Chon (KR), Åge Bøe (DNV). Beijing, October 31st. 2005. Preview. IACS CSR Schedule and Scope. Harmonization Progress. Rule Update on JTP. Rule Update on JBP. Discussion.

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Update on the IACS Common Structural Rules for Tankers & Bulk Carriers

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  1. Update on the IACS Common Structural Rulesfor Tankers & Bulk Carriers Rune Torhaug (DNV) Dr. Chon (KR), Åge Bøe (DNV) Beijing, October 31st. 2005

  2. Preview IACS CSR Schedule and Scope Harmonization Progress Rule Update on JTP Rule Update on JBP Discussion

  3. IACS CSR Schedule and Scope Harmonization Progress Rule Update on JTP Rule Update on JBP Discussion

  4. Scope of Rule Developments • JTP : Joint Tanker Project • LRS, ABS & DNV • Complete Set of Structural Rules for Double Hull Oil Tankers • Length greater than or equal to 150m • JBP : Joint Bulker Project • BV, CCS, GL, KR, NK, RINA & RS • Complete set of Structural Rules for SSS and DSS Bulk Carriers • Length greater than or equal to 90m

  5. CSR Development Schedule Final Rules to IACS council Dec 1st Publish 15 Jan 2006 1 Jan 2006 30 Sep 2005 Jun 2004 1 Jan 2005 15 Apr 2005 1 Apr 2006 Short-term Harmonisation 1st Draft available to Public End date for comments on 1st Draft 2nd Draft JTP available to Public End date for comments on 2nd Draft CSR Adopted CSR Effective

  6. IACS CSR Schedule and Scope Harmonization Progress Rule Update on JTP Rule Update on JBP Discussion

  7. CSR Harmonization Roadmap • Short-term Harmonization • Elimination of blocking factors to allow adoption by all 10 societies of both Tanker and Bulk Carrier rules on 1 January 2006 • Long-term Harmonization • Further harmonization will take place afterward in an agreed time frame to be advised to industry. Time plan to be delivered Council November 30th 2005.

  8. CSR Harmonization Roadmap • Short-term • Hull Girder Wave Shear • Hull Girder Ultimate Strength • Prescriptive Buckling • Finite element analysis procedures • Coating and Corrosion additions • Long-term • Wave loads • Fatigue • Finite element analysis • Buckling

  9. Short-term Harmonization • Hull girder wave shear • Hull girder shear force is consistent between Tankers and Bulk Carriers • Hull girder ultimate strength • Capacity will use either Tanker or Bulk Carrier method since they are basically identical • Loads will use two checks, one driven by SWBM and the other one driven by the wave moment

  10. Short-term Harmonization • Buckling • Prescriptive buckling to use closed-form methods • Tanker “advanced buckling” method only to be used in tanker FEM evaluation • Finite element analysis • Tanker procedure (direct only) used in the Tanker Rules • Bulk Carrier procedures (direct and superposition) used in the Bulk Carrier Rules, provided the two methods result in common requirements

  11. Short-term Harmonization • Coating and Corrosion additions • Consistent definition and values for similar areas and environments will be used • Consistent definition of rounding will be used • Based on Recent feedback from Ship Owners’ groups, increases are decided • Requirements to coatings of internal spaces in ballast tanks will be included in the rules (in line with IACS Industry proposal DE48/12)

  12. Harmonised principles • Use JBP two surface approach for determination of wastage allowance and consequently corrosion addition. • Use JTP method for rounding

  13. Common corrosion additions Deck, external surface Internals in Deck and Sheerstrake in WBT upper portion of WBT Stringer in WBT Sideshell in WBT Stiffeners Long.b in WBT Webplate in WBT h 2 d Faceplate in WBT Long girders in WBT Stiffeners Bottom and bilge in WBT

  14. IACS CSR Schedule and Scope Harmonization Progress Rule Update on JTP Rule Update on JBP Discussion

  15. Item 1.2Common Structural Rules for Oil TankersJoint Tanker Project (JTP) Tripartite MeetingBeijing, 31 October 2005

  16. Content • JTP Status • Feedback from industry through recent meeting and 2nd draft rule hearing • Main rule updates from 2nd draft of March 2005

  17. JTP Rule deliveries 1.0 2.0 3.0 3.1 3.2 • 1st draft • Sent for hearing June 2004 • 2nd draft • Sent for hearing April 2005 • Updates based on hearing comments and further Rule development • 3rd draft • Posted on www.jtprules.com October 2005 • Intermediate delivery for Technical Committee meetings • Changes made per 1 September 05 included • Change document package 1 • Expected posted on www.jtprules.com 1 November 05 • Includes updates from 2nd hearing, harmonisation and minor issues from recent industry meetings. • Change document package 2 • Expected posted on www.jtprules.com 9 November 05 • Includes latest hearing comments, final harmonisation issues and updates from 2nd hearing, final harmonisation conclusions and major issues from recent industry meetings.

  18. JTP Rule deliveries • Rule version for council adoption • Available 1 December 2005 • Compilation of 3rd draft, change document 1 & 2 and updates from TC meetings. • Published Rules • Available 15 January 2006

  19. Summary of JTP Feedback • 1st hearing • 2834 comments received during hearing period • 988 (35%) of which resulted in either editorial or rule change • 197 of which are noted for future development • 2nd hearing • 228 comments received during hearing period • 76 (33%) of which will result in either editorial or rule change • 12 of which are noted for future development

  20. JTP Issues from recent industry meetings • Meetings with Korean and Japanese industry (KSA and SAJ/JSA) September 2005 • a) General scantling increase • Issue: Feedback received that the general scantling increase needs justification and not supported by damage records • Rule change: Criteria reviewed and some of the allowable stresses for plate and stiffener requirements have been increased by 5-7%. • b) Localised large increases due from FE buckling assessment • Issue: 2nd draft JTP Rules require in some areas net scantling that are significantly above the as-built scantlings of present fleet. Typically buckling assessment for FE is the cause for the increase. • Rule change: FE procedure has been further reviewed taking into account combined probability of cargo density, loading pattern and dynamic load level. Following this a correction factor will be applied on the cargo pressure for the extreme dynamic load combination. Consequently the related increases on the inner bulkheads and stringers will be reduced.

  21. JTP Issues from recent industry meetings • c)Fatigue • Issue: A fatigue design standard of 25 years operation in North Atlantic wave environment is too severe taking into account the typical operation of the majority of tankers. The criteria in principle disallows designs with material of HT36 in deck. • Rule change: As the 25 NA design standard is given in the draft IMO Goal Based Standard the project has decided not to make any amendments to the fatigue target. • d) Hull girder ultimate strength • Issue: The hull girder ULS requirement as given in second draft is too severe and some existing vessels will not pass the criteria even in the as-built scantlings. Use of material of HT36 is needed for compliance but contradicts the fatigue criteria. • Rule change: Studies performed during the Rule development do not show the same “problem”. Further investigations are being done on the hull girder ULS criteria to see if further adjustment of the load combination factors are needed. • e) IACS recommendation 47 Shipbuilding and Repair Quality Standard • Issue: IACS recommendation is not up to date and may cause conflicts with commonly used national standards. • Rule change: The comment has been forwarded to IACS Survey Panel. The Rules have been updated to make it clear that acceptable national standards are allowed. Rec. 47 is used as common reference document for strength assessment (imperfections)

  22. JTP Issues from recent industry meetings Hull Scantlings Design Service Corrosion Corrosion Margin Corrosion Addition Predicted corrosion in 2.5 years (0.5 mm) Required Renewal Thickness Required Net Thickness • Meetings with Union of Greek Shipowners, October 2005 • a) Corrosion margins • Issue: The corrosion margins are too small for a design life of 25 years and will lead to a significant amount of steel replacement. • Rule change: Opinions and proposals were presented during the meeting and the IACS members agreed to review closely whether it is a need and possibility to update the margins taking into account all industry feedback and service records. • b) Coating performance standard • Issue: The UGS informed that the lack of a minimum performance standard for coating leads to large variation in the standard and actual life of coatings. For some ships the coating is so poor that compete renewal by sandblasting and re-coating is needed after few years in operation. • Rule change: IACS agreed to include a requirement for a minimum performance standard in the common structural Rules. Further discussion will be made within IACS on this but the referenced standard is expected to be based on IACS submission to DE 48.

  23. Main rule updates from 2nd draft 0.55 0.80 • Corrosion addition • Two surface approach for corrosion addition (JBP method) with common values except for C/hold • Minimum coating performance standard based on IACS submission to IMO’ DE 48 added • Longitudinal strength • Buckling capacity method from JBP replaces advanced buckling method in hull girder buckling assessment • Initial hull girder buckling assessment (IACS UR S11) is removed • Hull girder wave shear force reduced to IACS S11 (same as JBP) • Hull girder shear strength, allowable stress for harbour condition increased and rule minimum SWSF introduced, consistent with corresponding FE loading pattern (full/empty across) • Hull girder ultimate strength • Partial safety factors and ultimate moment capacity from JBP added • Bending and shear strength: plates, stiffeners and primary support members • Generally allowable stresses for static/frequent loads increased by 6-7 % • Plates and primary support members, max.allowable stress for extreme load increased by 6-7 % • Cargo hold FE analysis • number of load combinations reduced by ca. 40% • target H.G. shear force only applicable • for full/empty across loading pattern • VLCC, draught changes for loading pattern empty across • (Sea: 0.6=>0.55T Harb.: 0.8=>0.65T) / • full across (Sea: 0.6=>0.8T Harb.: 0.33=>0.7T), • and empty centre tank (Sea: T=> 0.9T ) • Probability factor on cargo liquid pressure taking • into account the extreme load combination of cargo • density, loading pattern & extreme accelerations

  24. IACS CSR Schedule and Scope Harmonization Progress Rule Update on JTP Rule Update on JBP Discussion

  25. Tripartite meetingBeijing, October 31, 2005 Common Structural Rules for Bulk Carriers Joint Bulker Project (JBP)

  26. MAIN PRINCIPLES • SAFETY • Draft Bulk Carriers Rules provide minimum net scantlings • Ship condition is safe as far as scantlings of the ship in service are larger than net required values • Periodic close-up surveys and thickness measurements and 0.5 mm margin between surveys provide adequate guarantee of safety • MAINTAINABILITY • Control local corrosion in holds through periodic inspection and mandatory coating requirements • Allow 25 years of service without extensive steel replacement on a well maintained ship

  27. Subject Ships used in the ramification study acc. 2nd draft # size S-25 D1 cape compliant D2 handymax - D3 handymax - DSS D4 cape compliant D5 cape compliant S1 cape - S2 panamax - Ramification study acc. 2nd draft S3 handymax - S4 cape - S5 panamax - SSS S6 panamax compliant SS1 mini-handy <150m SS2 mini-handy <150m SS3 mini-handy <150m

  28. Weight Increment by 2nd draft • In the ramification study according to 2nd draft, • - Strength against slamming • - Buckling strength of hull-girder • Fatigue strength assessment • On-going changes • have been further considered in addition to: • - Local scantling calculations • - Ultimate strength check • - Yielding check of Hull-girder • - Direct strength analysis Following requirements are newly introduced in the 2nd draft and considered in the study. - Corrosion addition (Wastage allowance) is increased by 0.5mm. - Flooded condition is applied to DSS BC according to the SOLAS regulation CH. XII

  29. Summary of Weight Increment by 2nd draft (1) 2.7 (3.4) 3.1 (3.9) 3.7 (4.6) 3.4 (4.3) 3.6 (4.5) 2.7 (3.4) 3.0 (3.7) • Ratio of steel increment to light weight(steel weight)

  30. CORROSION • Main concern • Local corrosion (grooving, necking effect) and general corrosion of frames of side shell structure is difficult to detect and is behind the majority of hull damages suffered in the past Frequency of incidents per BC Classes

  31. Uniform Corrosion Allowances • Known only in a statistical way • Some vessels have practically no corrosion, others are heavily corroded • Dependant on factors such as cargo carried, environment, quality of coating, etc. • Dependant on maintenance policy • All of these factors are included in the statistical results • Available statistics • NK/IACS statistics are more general and accurate than other existing ones and results correlate well with other CS experience • Wastage allowance corresponding to upper 10% of measurements provide generally adequate margins

  32. MODIFICATIONS OF JBP RULESAFTER THE SECOND DRAFT • MAJOR CHANGES • Larger uniform corrosion wastage allowances for transverse bulkheads in line with 90% probability of non-exceedance • Thickness rounding procedure is modified, due to harmonisation between JTP and JBP • Finite element models are now only three holds models, with modified boundary conditions to provide same results between directand superposition methods

  33. Chapter 1 General Principles MODIFICATIONS OF JBP RULES (1 &3) • 1. Grab notation for Handysize vessels under development • 20 tons grab discharge is mandatory for BC-A and BC-B, but lead to unreasonable reinforcements for Handy’s Chapter 3Structural Design Principles • 2. Modification of thickness rounding procedure and corrosion additions • Harmonization with JTP (see new proposal) • Increase of wastage allowances for transverse bulkheads • 3. Modifications of structural arrangement principles (sec 6) further to Industry comments (UGS)

  34. Chapter 4 Design Loads MODIFICATIONS OF JBP RULES (4 &5) • 4. Detailed mass curves procedure is included (App 1) • 5. Still-water shear force in flooded condition is now defined and definitions of loads clarified (Sec 3) Ch. 5 Hull girder strength • 6. Modification of the requirements for the ultimate strength of the hull girder (Sec 2) • Harmonization with JTP for wave bending moment safety factor • Deletion of nonlinear FEM method, which is still under investigation at ISSC

  35. MODIFICATIONS OF JBP RULES (6) • 7. Redundancy requirements according to the new IMO interpretation of SOLAS XII/6.5.3(Sec 2) under development Ch. 6 Hull scantlings 8. Prescriptive requirements for transverse bulkheads in way of ballast holds of ships of less than 150 m in length (Sec 1 & 2) 9. Modifications of minimum thicknesses for inner side of DSS BC’s and hopper plating (Sec 1) 10. Modification of scantlings for steel coils loading (Sec 1 & 2) 11. Modification of scantlings of ordinary stiffeners in flooding condition (Sec 2)

  36. MODIFICATIONS OF JBP RULES (7) • 12. Unification of FEM models & boundary conditions (Sec 1) • Direct and superposition methods both use a three holds model and common boundary conditions in order to obtain same scantlings • Self-weight of structure is clearly introduced Ch.7 Direct strength assessment 13. Buckling requirements for DSA have been modified in Ch 6 Sec 3 and an how-to procedure introduced in Sec 1

  37. Ch. 8 Fatigue check of structural details MODIFICATIONS OF JBP RULES (8 &9) • 14. Table 1 Sec 4 of stress concentration factors of typical structural details have been completed and amended • 15. Computation of fatigue stress range in hatch corners have been completely revised (Sec 5) Ch. 9 Other structures 16. Impact pressure on flat bottom forward have been modified and transfered in Ch 4 Sec 5

  38. IACS CSR Schedule and Scope Harmonization Progress Rule Update on JTP Rule Update on JBP Discussion

  39. Review IACS CSR Schedule and Scope Harmonization Progress Rule Update on JTP Rule Update on JBP Discussion

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