Update on the IACS Common Update on the IACS Common

Structural RulesStructural Rules

for Tankers & Bulk Carriersfor Tankers & Bulk Carriers

Beijing, October 31st. 2005Beijing, October 31st. 2005

Rune Torhaug (DNV)

Dr. Chon (KR), Åge Bøe (DNV)

PreviewPreview

Rule Update on JTP

Rule Update on JBP

Discussion

IACS CSR Schedule and Scope

Harmonization Progress

Rule Update on JTP

Rule Update on JBP

Discussion

IACS CSR Schedule and Scope

Harmonization Progress

Scope of Rule DevelopmentsScope of Rule Developments

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

JTP : Joint Tanker Project– LRS, ABS & DNV– Complete Set of Structural Rules for

Double Hull Oil Tankers– Length greater than or equal to 150m

CSR Development ScheduleCSR Development Schedule

Jun 2004 1 Jan 2005

1st Draft available to Public End date for

comments on 1st Draft

2nd Draft JTP available to Public

30 Sep 200515 Apr 2005

Publish15 Jan 2006

CSR Effective

Short-termHarmonisation

1 Apr 2006

CSR Adopted

End date for comments on 2nd Draft

1 Jan 2006

Final Rules to IACS councilDec 1st

Rule Update on JTP

Rule Update on JBP

Discussion

IACS CSR Schedule and Scope

Harmonization Progress

CSR Harmonization RoadmapCSR 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.

CSR Harmonization RoadmapCSR 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

Short-term HarmonizationShort-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

Short-term HarmonizationShort-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

Short-term HarmonizationShort-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)

Harmonised principles Harmonised principles

–Use JBP two surface approach for determination of wastage allowance and consequently corrosion addition.

–Use JTP method for rounding

25.0)( roundcorrreqnetreqgrs ttt

Common corrosion additionsCommon corrosion additions

Long.bhd

2

Deck, external surface

Internals inupper portion

of WBT

Stringer in WBT

Stiffeners

in WBT

Deck and Sheerstrake in WBT

Sideshell in WBT

Webplate in WBT

Long girders in WBT Bottom and bilge

Faceplate in WBT

Stiffenersin WBT

Rule Update on JTP

Rule Update on JBP

Discussion

IACS CSR Schedule and Scope

Harmonization Progress

Item 1.2Item 1.2Common Structural Rules for Oil Common Structural Rules for Oil

TankersTankersJoint Tanker Project (JTP)Joint Tanker Project (JTP)

Tripartite MeetingTripartite MeetingBeijing, 31 October 2005Beijing, 31 October 2005

• JTP Status

• Feedback from industry through recent meeting and 2nd draft rule hearing

• Main rule updates from 2nd draft of March 2005

ContentContent

JTP Rule deliveriesJTP 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– 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.

1.0

2.0

3.0 3.1 3.2

JTP Rule deliveriesJTP 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

Summary of JTP FeedbackSummary 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

JTP Issues from recent industry JTP Issues from recent industry meetingsmeetings

Meetings with Korean and Japanese industry (KSA and SAJ/JSA) September 2005

a) General scantling increaseIssue: 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 assessmentIssue: 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.

JTP Issues from recent industry JTP Issues from recent industry meetingsmeetingsc) FatigueIssue: 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 strengthIssue: 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)

JTP Issues from recent industry JTP Issues from recent industry meetingsmeetingsMeetings with Union of Greek Shipowners, October 2005

a) Corrosion marginsIssue: 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 standardIssue: 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.

Predicted corrosion

in 2.5 years (0.5

mm)

Hull Scantlings

RequiredNet

Thickness

CorrosionAddition

Design

RequiredRenewalThickness

CorrosionCorrosionMargin

Service

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

Main rule updates from 2nd draftMain rule updates from 2nd draft

0.55

0.80

Rule Update on JTP

Rule Update on JBP

Discussion

IACS CSR Schedule and Scope

Harmonization Progress

Tripartite meetingTripartite meetingBeijing, October 31, 2005Beijing, October 31, 2005

Common Structural Rules for Common Structural Rules for Bulk CarriersBulk Carriers

Joint Bulker Project (JBP)Joint Bulker Project (JBP)

MAIN PRINCIPLESMAIN 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

Subject Ships used in theSubject Ships used in the ramification study acc. ramification study acc. 2nd 2nd

draftdraft

D1 cape compliantD2 handymax -

S1 cape -S2 panamax -

DS

SSS

S

# size S-25

D3 handymax -D4 cape compliantD5 cape compliant

S3 handymax -S4 cape -S5 panamax -S6 panamax compliantSS1 mini-handy <150m

SS3 mini-handy <150mSS2 mini-handy <150m

Ram

ifica

tion

stu

dy

acc

. 2

nd d

raft

In the ramification study according to 2In the ramification study according to 2ndnd draft, draft, - Strength against slamming- Strength against slamming- Buckling strength of hull-girder- Buckling strength of hull-girder- Fatigue strength assessmentFatigue strength assessment- On-going changes On-going changes have been further considered in addition to: 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 Following requirements are newly introduced in the 2in the 2ndnd draft and considered in the study draft and considered in the study. - Corrosion addition (Wastage allowance) is - Corrosion addition (Wastage allowance) is increased by 0.5mm.increased by 0.5mm.- Flooded condition is applied to DSS BC - Flooded condition is applied to DSS BC according to the SOLAS regulation CH. XIIaccording to the SOLAS regulation CH. XII

Weight Increment by 2nd draftWeight Increment by 2nd draft

Summary of Weight Summary of Weight Increment by Increment by 22ndnd draft draft (1) (1)

0 1 2 3 4 5

SS3

SS2

SS1

S6

D5

D4

D1

outer Inner Girder Trans T.Bhd

%

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)

CORROSIONCORROSION

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

0.00E+00

5.00E-04

1.00E-03

1.50E-03

2.00E-03

2.50E-03

3.00E-03

Hatchcover Pipes&valves

Side Shell Side Shell(Collision)

Bottom Shell Deck Side ShellPenetration

categories of incidents

freq

uenc

y of

inci

dent

s pe

r shi

p ye

ar

Mini

Handysize

Handymax

Panamax

Cape size

Frequency of incidents per BC Classes

Uniform Uniform Corrosion AllowanceCorrosion Allowancess

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

MODIFICATIONS OF JBP RULESMODIFICATIONS OF JBP RULESAFTER THE SECOND DRAFTAFTER 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

Chapter 1 General PrinciplesChapter 1 General Principles

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 3Chapter 3 Structural Design PrinciplesStructural Design Principles2. 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)

MODIFICATIONS OF JBP RULES (1 &3)MODIFICATIONS OF JBP RULES (1 &3)

Chapter 4 Design LoadsChapter 4 Design Loads

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)

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

MODIFICATIONS OF JBP RULES (4 &5)MODIFICATIONS OF JBP RULES (4 &5)

Ch. 5 Hull girder strength

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 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)

MODIFICATIONS OF JBP RULES (6)MODIFICATIONS OF JBP RULES (6)

Ch. 6 Hull scantlings

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

MODIFICATIONS OF JBP RULES (7)MODIFICATIONS OF JBP RULES (7)

Ch.7 Direct strength assessment

Ch. 8 Fatigue check of structural details

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)

MODIFICATIONS OF JBP RULES (8 &9)MODIFICATIONS OF JBP RULES (8 &9)

Ch. 9 Other structures

16. Impact pressure on flat bottom forward have been modified and transfered in Ch 4 Sec 5

Rule Update on JTP

Rule Update on JBP

Discussion

IACS CSR Schedule and Scope

Harmonization Progress

ReviewReview

Rule Update on JTP

Rule Update on JBP

Discussion

IACS CSR Schedule and Scope

Harmonization Progress