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
IACS CSR Schedule and Scope
Harmonization Progress
Rule Update on JTP
Rule Update on JBP
Discussion
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
CSR Development Schedule
Final Rules to
IACS council
Dec 1st
Jun 2004
1st Draft
available to
Public
1 Jan 2005
30 Sep 2005
15 Apr 2005
1 Jan
2006
Publish
15 Jan
2006
1 Apr 2006
Short-term
Harmonisation
End date for
comments
on 1st Draft
2nd Draft JTP
available to
Public
End date for
comments
on 2nd Draft
CSR
Adopted
CSR
Effective
IACS CSR Schedule and Scope
Harmonization Progress
Rule Update on JTP
Rule Update on JBP
Discussion
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.
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
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
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
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)
Harmonised principles
– Use JBP two surface approach
for determination of wastage
allowance and consequently
corrosion addition.
– Use JTP method for rounding
t grsreq  (tnet req  tcorr )round0.25
Common corrosion additions
Deck, external surface
Internals in
upper portion
of WBT
Deck and Sheerstrake in WBT
Stringer in WBT
Stiffeners
in WBT
Sideshell in WBT
Long.b
h
2
d
Webplate in WBT
Faceplate in WBT
Stiffeners
in WBT
Long girders in WBT
Bottom and bilge
IACS CSR Schedule and Scope
Harmonization Progress
Rule Update on JTP
Rule Update on JBP
Discussion
Tripartite Meeting
Beijing, 31 October 2005
Item 1.2
Common Structural Rules for Oil
Tankers
Joint Tanker Project (JTP)
Content
•
JTP Status
•
Feedback from industry through recent
meeting and 2nd draft rule hearing
•
Main rule updates from 2nd draft of March
2005
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
•
1.0
2.0
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.
3.0
3.1 3.2
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
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
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.
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)
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.
Hull Scantlings
Design
Service
Corrosion
Addition
Required
Net
Thickness
Predicted
corrosion
in 2.5 years
(0.5 mm)
Corrosion
Corrosion
Margin
Required
Renewal
Thicknes
s
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%
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
0.55
0.80
IACS CSR Schedule and Scope
Harmonization Progress
Rule Update on JTP
Rule Update on JBP
Discussion
Tripartite meeting
Beijing, October 31, 2005
Common Structural Rules for
Bulk Carriers
Joint Bulker Project (JBP)
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
#
D1
D2
D3
D4
D5
size
cape
handymax
handymax
cape
cape
S-25
compliant
compliant
compliant
S1
S2
S3
S4
S5
S6
SS1
SS2
SS3
cape
panamax
handymax
cape
panamax
panamax
mini-handy
mini-handy
mini-handy
compliant
<150m
<150m
<150m
Ramification study
acc. 2nd draft
SSS
DSS
Subject Ships used in the
ramification study acc. 2nd draft
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
Summary of Weight
Increment by 2nd draft (1)
Ratio of steel increment to light weight (steel weight)
2.7 (3.4)
D1
3.1 (3.9)
D4
3.7 (4.6)
D5
3.4 (4.3)
S6
3.6 (4.5)
SS1
2.7 (3.4)
SS2
3.0 (3.7)
SS3
%
0
1
outer
2
Inner
3
Girder
4
Trans
5
T.Bhd
CORROSION
Main concern
fre que ncy of incide nts pe r ship ye ar
–
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
Mini
3.00E-03
Handysize
Handymax
2.50E-03
Panamax
2.00E-03
Cape size
1.50E-03
1.00E-03
5.00E-04
0.00E+00
Hatchcover
Pipes&
valves
Side Shell
Side Shell Bottom Shell
(Collision)
categories of incidents
Frequency of incidents per BC Classes
Deck
Side Shell
Penetration
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
MODIFICATIONS OF JBP RULES
AFTER 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
MODIFICATIONS OF JBP RULES (1 &3)
Chapter 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 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)
MODIFICATIONS OF JBP RULES (4 &5)
Chapter 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)
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
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 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 (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
MODIFICATIONS OF JBP RULES (8 &9)
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)
Ch. 9 Other structures
16. Impact pressure on flat bottom forward have been
modified and transfered in Ch 4 Sec 5
IACS CSR Schedule and Scope
Harmonization Progress
Rule Update on JTP
Rule Update on JBP
Discussion
Review
IACS CSR Schedule and Scope
Harmonization Progress
Rule Update on JTP
Rule Update on JBP
Discussion