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

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Update on the IACS Common Structural Rulesfor
Tankers Bulk Carriers

• Rune Torhaug (DNV)
• Dr. Chon (KR), Åge Bøe (DNV)

Beijing, October 31st. 2005
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Preview
IACS CSR Schedule and Scope
Harmonization Progress
Rule Update on JTP
Rule Update on JBP
Discussion
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IACS CSR Schedule and Scope
Harmonization Progress
Rule Update on JTP
Rule Update on JBP
Discussion
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Scope of Rule Developments
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CSR Development Schedule
Publish 15 Jan 2006
Final Rules to IACS council Dec 1st
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 Effective
CSR Adopted
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IACS CSR Schedule and Scope
Harmonization Progress
Rule Update on JTP
Rule Update on JBP
Discussion
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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.

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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

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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

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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

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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)

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Harmonised principles

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

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Common corrosion additions
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IACS CSR Schedule and Scope
Harmonization Progress
Rule Update on JTP
Rule Update on JBP
Discussion
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Item 1.2Common Structural Rules for Oil
TankersJoint Tanker Project (JTP)
Tripartite MeetingBeijing, 31 October 2005
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Content

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

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JTP Rule deliveries

• 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

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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

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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

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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.

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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)
  

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JTP Issues from recent industry meetings

• 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.

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JTP Issues from recent industry meetings

• c) Rolling tolerances
• Issue The under tolerances are eating into the
  wastage allowance and should not be accepted.
  UGS also commented on lack of specified
  procedures/locations for performing thickness
  measurements.
• Rule change Question/issue is being forwarded to
  IACS council for review and action.
• d) Grinding
• Issue UGS questioned the allowance for grinding
  as a measure for increasing the fatigue life.
• Rule change The CSR Rules will be updated to be
  more specific on where credit may be given for
  grinding and details on what is required in terms
  of the actual grinding.
• e) Approval of national fabrication standards
• Issue UGS raised concern about approval of
  national fabrication standards on a class by
  class basis without common procedures for the
  approval of such
• Rule change The IACS members agreed to forward
  the request to IACS GPG for review and action.

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Main rule updates from 2nd draft

• 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

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IACS CSR Schedule and Scope
Harmonization Progress
Rule Update on JTP
Rule Update on JBP
Discussion
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Tripartite meetingBeijing, October 31, 2005
Common Structural Rules for Bulk Carriers Joint
Bulker Project (JBP)
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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

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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 lt150m
SS2 mini-handy lt150m
SS3 mini-handy lt150m
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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
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Summary of Weight Increment by 2nd draft (1)

• Ratio of steel increment to light weight (steel
  weight)

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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
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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

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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 direct and
  superposition methods

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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
  Handys

Chapter 3 Structural 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)

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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

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MODIFICATIONS OF JBP RULES (6)
Ch. 6 Hull scantlings

• 7. Redundancy requirements according to the new
  IMO interpretation of SOLAS XII/6.5.3 (Sec 2)
  under development

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 BCs 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)
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MODIFICATIONS OF JBP RULES (7)
Ch.7 Direct strength assessment

• 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

13. Buckling requirements for DSA have been
modified in Ch 6 Sec 3 and an how-to procedure
introduced in Sec 1
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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
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IACS CSR Schedule and Scope
Harmonization Progress
Rule Update on JTP
Rule Update on JBP
Discussion
41
Review
IACS CSR Schedule and Scope
Harmonization Progress
Rule Update on JTP
Rule Update on JBP
Discussion