Joint Tanker Project

1

• Joint Tanker Project
• Development of Common Structural Rules for Oil
  Tankers

2

• Joint Tanker Project
• Overview
• Technical aspects of the JTP Rules
• Relationship with IACS (JBP)
• The Future

3
Aim

• To develop a set of unified Rules and Procedures
  for the determination of the structural
  requirements for oil tankers

4
Objective

• To eliminate competition between class societies
  with regard to structural requirements and
  standards
• To employ the combined experience of all three
  societies to develop a single agreed standard, or
  set of Rules.
• To ensure that a tanker meeting this new standard
  will be recognised by industry as being at least
  as safe and robust as would have been required by
  any of the existing Rules
• To embrace the intentions of the anticipated IMO
  requirements for goal based new construction
  standards.

5
Organisation

• The project is being led by a Steering Group,
  reporting to the CEOs of each society.
• A team drawn from ABS, DNV and LR manages the
  technical work packages, using technical experts
  drawn equally from the three societies.
• An External Review Group of senior, experienced
  technical experts is providing an independent
  industry input throughout the project.
• The Technical Committees of ABS, DNV and LR will
  be given the opportunity to comment on the Rule
  proposals.

6
Deliverables from the project

• A new complete Rule set covering the structural
  requirements for oil tankers for new construction
  and for those ships subsequently in service.
• Supporting guidance to amplify the Rules,
  including the procedures for carrying out direct
  calculations and for fatigue life assessment.
• A background document explaining the implicit
  safety levels, design principles and assumptions
  on which the Rules are based

7
Scope

• The Rules will cover the entire hull structure in
  a consistent and logical manner, including fore
  and aft ends.
• The Rules will be limited to oil tankers, for
  crude and products, of length greater than or
  equal to 150m.
• The Rules will cover the hull envelope,
  transverse and longitudinal bulkheads, main
  supporting members and local structure.
• Simplified approaches for determination of
  fatigue life and sloshing loads will be included.

8
Schedule

• The draft set of Rules will be available for
  comment by the Technical Committees of ABS, DNV
  and LR by end May 2004.
• The draft set of Rules will also be available to
  all IACS members at the same time
• Final Rule version approved by ABS, DNV and LR
  will be published 1 January 2005 and become
  mandatory on 1 July 2005
• Withdrawal of equivalent existing Rules by ABS,
  DNV and LR with effect from 1 July 2005

9
Approach

• The new Rules have been developed under a
  coherent development framework
• The new Rules include some new approaches, where
  there is sufficient confidence and justification
  for their adoption.
• The best and most transparent methods are
  selected for the new Rules.
• The new Rules will be subjected to a major
  programme of testing and calibration to ensure
  that the Rules are internally consistent and
  reflect service experience.

10
Fundamental principles of the Standard

• To ensure that the overall safety of the hull
  structure is equivalent to or better than that
  currently achieved in relation to life,
  environment and property.
• To ensure sufficient durability throughout the
  operational life in terms of corrosion margin and
  fatigue strength.
• To define the minimum state of the structure at
  which steel renewal is required in order to
  continue safe operation.

11
Objective of RulesFramework for the JTP Rule
Development
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Design Basis

• Design Life 25 years
• External Environment
• North Atlantic wave environment
• Air temperature -15 degree C
• Sea temperature 0 degree C
• Internal Environment
• Specific gravity cargo Min 1025 kg/m3 (900 for
  fatigue)
• Specific gravity ballast 1025 kg/m3
• Max cargo temperature 80 degree C
• Min cargo temperature 0 degree C
• Corrosion margins based on 25 years design life

13
Principal new elements

• Net scantling presentation is used throughout the
  rules
• Inclusion of new procedures for the assessment of
  buckling and ultimate limit state of the hull
  girder
• Inclusion of a new method of describing dynamic
  loading
• Development of a Rule format that provides
  transparency and ease of use

14
Principles for Prescriptive Rules

• Similar to existing Rules but based on first
  principles with respect to loads
• Loads based on the North Atlantic sea area with
  10-8 probability level of occurrence
• Presented in a working stress format
• Based on net thickness philosophy

15
Software

• The new set of Rules must be supported by
  software tools.
• At the time of the launch of the common Rules for
  oil tankers suitable rule check software will be
  available to designers.
• ABS, DNV and LR will incorporate the requirements
  of the new Rules into their existing software
  solutions.

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Benefits to industry

• The outcome of this project will be a single,
  clearly recognised standard that has been
  developed, with active input from industry, using
  the combined research and experience of ABS, DNV
  and LR.
• The costs of dealing with a number of similar but
  different Rules sets will be eliminated.
• The efforts of ABS, DNV and LR will be focussed
  on establishing and maintaining a single Rule set.

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Joint Tanker ProjectCommon Scantlings

• Oil tanker structural requirements will not be a
  competitive issue for ABS, DNV and LR

18

• Joint Tanker Project
• Overview
• Technical aspects of the JTP Rules
• Relationship with IACS
• The Future

19

• Joint Tanker Project
• Net thickness approach
• Ultimate Limit State
• Buckling
• Loads
• FEM
• Fatigue
• Prescriptive Rules

20
Net thickness approach and wastage allowance

• The Rules are presented on the basis of
  determination of the net scantlings required for
  adequate strength, with a design corrosion
  margin.
• This approach will result in a unified
  methodology for the determination of renewal
  scantlings, which will provide a more transparent
  estimate of the corrosion margin available before
  renewal.
• To have a direct link between minimum thickness
  accepted during vessel operations and the
  thickness used for strength calculations at
  newbuild.
• Strength calculations during newbuilding are
  based on the net thicknesses of plating and
  structural members.
• Newbuilding gross thickness requirement is
  calculated by the addition of expected wastage
  during the vessel design life to the required net
  thicknesses.

21
Net Thickness
tw
tgross required
tcorr
tcorr 2.5
tSiO renewal
tnet required
Corrosion allowances based on published IACS
data, in mm based on 25 year design life
22
Net Thickness Definitions

• Wastage between inspection, local structure
• The assumed wastage during inspection intervals
  is referred to as t corr_2.5 and links the
  corrosion addition and the allowable wastage
  thus
• t corr t waste t corr_2.5
• The 2.5 suffix indicates inspection periods of
  2.5 years as in existing survey schemes.
• The JTP Rules take t corr_2.5 as 0.5 mm

23
Corrosion Wastage Allowance (mm)
Long.bhd 2.5
Deck trans Web 2.5 Face plate 3.0
Deck 3.5
Internals in upper portion of WBT 3.0
Long stiff. 2.5
Sheerstrake 3.5
To 1.5 m Below Deck
Long bhd stiff 2
Stringer 2.5
Inner skin 2.5
Side shell 2
Face plate cross-tie 3 Web cross-tie 2
Long stiff. 2.5
Web plate 2.5
Long.bhd 2
Face plate 3
Hopper 2.5
Long. Girders 2.5
Long stiff. 2.5
Bottom 3.5
Keel 4.5
inner.bottom 3.5
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Net Thickness Philosophy for Simplified Fatigue
Calculation

• Simplified fatigue assessment
• Local stresses calculated with average
  dimunition of the stiffener web, plate flange,
  and face plate.
• t fatigue t gr offered 0.5 t corr
• t fatigue t net offered 0.5 t corr

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Net Thickness Philosophy for FE Fatigue
Calculation

• Corrosion deduction used for cargo hold FE model
  is based on average corrosion which is less than
  full corrosion designated t corr
• t corr_FE cargo 0.5 t corr
• The cargo hold FE model is therefore built up
  based upon
• t t gr offered 0.5 t corr
• For the modelling of structural elements that act
  as single components (e.g. a cross tie) the full
  deduction t corr is to be used since the large
  area reduction does not apply.
• For local model areas with fine mesh the full
  deduction t corr is to be applied.

26
Net Thickness Philosophy for Buckling Calculation

• The buckling capacity is based upon
• t net offered t gr offered t
  corr
• This ensures consistency with the approach to
  buckling due to pure longitudinal stresses.

27
Hull girder - ultimate limit state

• Prescriptive requirements for single failure of
  local elements based on IACS Unified Requirements
• Introduction of a simplified ULS assessment
  procedure based on method under consideration
  within IACS
• Consideration will be given to a more
  comprehensive approach later

28
Buckling

• New buckling procedure
• Strength assessment of stiffened thin plate
  elements in ship structures

29
Loads

• Clear description of load definition and load
  application
• Load combination factors are used
• Rule design wave loads based on current IACS
  practices
• Load formulations have been validated by direct
  calculations
• Sloshing, slamming and bow impact loads use
  available current methods

30
Head Sea Conditions
31
Bow Quartering Sea
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Beam Sea
33
Basic Concept of JTP load model

• Green sea loads
• Sloshing pressures
• Bottom slamming pressures
• Bow impact pressures

34
Basic concept of JTP dynamic load model
Long-term distribution approach
Rule load at 10-4 Stress combination factors
35
FE Analysis Procedure

• To verify the ship structure meets the required
  standard
• Strength assessment
• Coarse mesh FE cargo tank analysis
• Fine mesh FE local structure analysis
• Fatigue assessment
• Very fine mesh FE fatigue analysis

36
FE Analysis Procedure Strength assessment

• Cargo tank FE model

37
Principles for Fatigue Procedure

• Simplified fatigue procedure for end-connection
  of longitudinals
• Simplified fatigue procedure based on FEM for
  selected critical details e.g. hopper knuckle
• Principles
• Minimum design life 25 years in North Atlantic
• Classic Palmgren-Miner cumulative fatigue
  damage methodology
• Long-term stress distribution

38
Fatigue Assessment Procedure

• Representation of long term distribution of
  stress ranges
• Design S-N curves

39
FE Analysis - Fatigue assessment

• Dynamic fatigue loads
• Tuned on 10-4 probability level, North Atlantic
• Load combination factors - relative phase
  relationship between loads accounted for
• Cargo density, SG gt 0,9
• Fatigue loading conditions
• Full load and ballast used for dynamic loads
• Static loads included for mean stress effect

40
FE Analysis - Fatigue assessment

• Hot spot stress calculated using very fine mesh
  FE analysis (mesh size t x t)
• Model based on average (over life) corroded
  thickness, tgross 0,5 tcorr
• All potential fatigue sites to be investigated

41

Rules Document Overview

• The JTP Rules package

42
The Rules Structure

• Underpinning Principles

• Transparent and modular
• Easy to use and identify requirements
• Logical flow core structure from design
  principles to design verification
• Self-containment where possible
• Inclusion of direct calculation procedures
• Comprehensive Rules but with detailed procedures
  in appendices
• Rules will be supported by a Background Document

43
The Rules Structure

• Rules Background Document
• Contains more information or background
• Explains safety objectives
• Explains design principles
• Rules sub-section by sub-section approach
• Specific version for external use
• Useful for training new users of the Rules

44
The Rules Structure

• Consequence Document
• Incorporates impact on scantling requirements
  applying the JTP Rules to current designs
• Covers all technical aspects but focuses on new
  requirements
• Continuously compiled during development, testing
  and hearing phases
• Available to industry

45

• Joint Tanker Project
• Overview
• Technical aspects of the JTP Rules
• Relationship with IACS
• The Future

46
Relationship with IACS

• The new Rules take cognizance of all relevant
  IACS Unified Requirements
• The new Rules developed by LR, ABS and DNV have
  been offered to IACS and accepted as a pilot
  project with the expectation of adoption within
  IACS Common Structural Rules
• ABS, DNV and LR continue to work with other IACS
  members and to contribute to the development of
  the Joint Bulker Project, Unified Requirements
  and Unified Interpretations through the various
  Working Parties and other groups.

47
Relationship with IACS

• Last week the JTP participants gave a
  presentation on common oil tanker rules to IACS
  in DNV offices in Oslo on Thursday 18th.
• The JBP participants carried out a similar
  exercise on common rules for bulk carriers in
  GLs offices in Hamburg
• The JTP participants are of course LR/DNV ABS
• The JBP participants are the 7 other societies of
  BV/GL/NK/RINA/KR/CCS/RS
• These presentations have highlighted some basic
  fundamental differences in philosophy which IACS
  Council will now seek to resolve and harmonise
  prior to adoption

48

• Joint Tanker Project
• Overview
• Technical aspects of the JTP Rules
• Relationship with IACS
• The Future

49
Rules Document Overview

• Status of Preliminary JTP Rules

Joint Tanker Project Common Structural
Rules For Oil Tankers Preliminary Draft JTP
Preliminary Draft, 05 March 04_V1.0
50
Status of Preliminary Rules

• General

• Currently includes about 75 of the anticipated
  content
• Preliminary Rules are still evolving but moving
  rapidly towards completion
• Calibration and internal testing ongoing

51
Status of Preliminary Rules

• Current Focus

• Development or review of outstanding text and
  formulations
• Further review of all incorporated text and
  formulations
• Ramifications of calibration and internal testing
• Integration of technical aspects
• Consistent style and presentation
• Technical and editorial proof-reading

52
Status of Preliminary Rules

• Summary of Activities Leading to a Complete Rule
  Set by 1st May 2004

• Delivery of outstanding 25 of Rule proposals
• Major editorial and technical review of each
  section Review of text and formulations in the
  light of feed back from calibration and internal
  testing
• Review of the complete Rule set

53
Status of Preliminary Rules

• Future Targets

• Migrate from Preliminary Draft Version to First
  Draft Version by 1st May 2004
• Editorial review and preparation May 2004
• Deliver to the JTP Members Technical Committee
  hearing processes in June 2004
• Incorporation of any amendments following IACS
  Rules harmonization/consistency process after
  June 2004
• Incorporation of any amendments following TC
  hearings

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