Guidance Manual for Maintenance of Tanker Structures

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This publication covers the process of planning, inspecting and repairing the steel structure and any protective coatings or protection systems. Reference is made to the requirements of the ISM Code. The practices and procedures described can be applied to both single- and double-hulled tankers. The recommendations apply to oil tankers of any size and configuration.


Many regulations and publications on the survey and operation of tankers require that the Owner, or his manager, applies "effective maintenance" or "normal Maintenance" to the ship's structure. The documentation required for planning class renewal surveys includes records of Owner's inspections, which are to form part of the survey report file on board. The certificates issued by some classification societies state that the ship is classed "subject to normal maintenance". However, when asking different tanker Owners what they understood by "normal maintenance", all had their own ideas and it was apparent that there is no internationally accepted concept of "normal circumstances", even allowing for the fact that tankers of different ages and designs will require different approaches to maintenance. 

The Tanker Structure Co-operative Forum (TSCF) has published several Manuals on the Maintenance and Repair of Structures, but these have never been assembled in a format that provides an answer to the question "what is meant by effective maintenance?" The purpose of this manual, therefore, is to draw on previously published guidance, combined with the latest experience of the TSCF's and INTERTANKO's membership to produce a book that can be used by any Owner or manager of any tanker afloat as a guide to effective maintenance of the structure. Advice on how inspection and maintenance can be facilitated by improved design is included in Appendix 3. 

Furthermore, the Guide suggests practices for the various elements of maintenance, such as paint condition, steel thickness and handling of fractures. 

If an Owner adopts the practices set down in this manual, he should be confident that he will meet the ISM requirement to establish procedures to ensure that the ship's structure is maintained in conformity with the provisions of relevant rules and regulations. 



2.1 Introduction
2.2 International Maritime Organisation Conventions
2.2.1 Safety Management Systems
2.2.2 Enhanced Surveys Survey Programme Documentation Onboard
2.2.3 Condition Assessment Scheme
2.3 Classification Rules
2.3.1 General
2.3.2 Special survey
2.3.3 Annual Survey
2.3.4 Intermediate Survey
2.3.5 Drydocking (Bottom) Survey
2.3.6 Damage and Repair Surveys
2.3.7 Voyage Repairs and Maintenance

3.1 Corrosion
3.1.1 Uncoated Surfaces
(a) General Corrosion
(b) Pitting Corrosion
(c) Grooving Corrosion
(d) Microbially Influenced Corrosion (MIC)
3.1.2 Coated Surfaces
(a) Localised Corrosion
(b) Pitting Corrosion
(c) Grooving Corrosion
3.2 Structural Elements Important for Global Strength
3.2.1 Bottom Structures
3.2.2 Side Shell, Longitudinal and Transverse Bulkheads
3.2.3 Deck Structures
3.2.4 Vibration Damage
3.3 Local Strength Issues
3.3.1 Buckling
3.3.2 Fatigue Fatigue Analysis Typical Locations for High Sensitivity to Fatigue Failure The Effect of Higher Tensile Steel (HTS)
3.3.3 Brittle Fracture

4.1 Benefits and Challenges
4.2 Vessel Age, Design, Operational Profile and Cargoes – Factors affecting Scope of Inspection
4.2.1 Vessel Age
4.2.2 Design
4.2.3 Operational Profile
4.2.4 Cargoes

5.1 The Inspection and Maintenance Plan ("IMP") 
5.1.1 Structure Included in the Scope of an IMP
5.1.2 Types of Inspection Conducted by Owners General Condition Inspections Detailed Condition Inspections Repair Specification Inspections
5.1.3 Frequency of Inspections
5.2 Development of the Inspection and Maintenance Plan (IMP)
5.3 Inspection Preparation
5.3.1 Identification of Areas for Inspection
5.3.2 Access and Reachability for Inspection Safe Entry Requirements Cleaning Accessibility of the Areas of the Space to be Inspected
1. Temporary Staging
2. Mobile Platforms
3. Rafting
4. Remotely Operated Vehicles (ROVs)
5. Use of Divers
6. In Tank Camera
7. Industrial Rope Access
8. Other Devices Summary
5.4 Inspection Execution
5.4.1 What to look for and where Fore Peak Tanks Aft Peak Tanks Wing Tanks Cargo Tanks Ballast Tanks Centre Cargo Tanks Double Bottom Ballast Tanks Double Side Ballast Tanks Deck Area Structure Shell Plating Bunker and Fresh Water Tanks Other Accessible Spaces Sea Connections and Overboard Discharges Sea Chests Rudders, Rudder Horn, Sternframe
5.5 Inspection reports
5.5.1 Report Content
5.5.2 Report Format
5.6 Inspection Result Analysis
5.6.1 Steel Condition
5.7 Acceptance Criteria
5.7.1 Thickness Measurements General Isolated area Structural Element Zone Pitting Pitting Intensity Acceptable Wastage Repairs
5.7.2 Fractures
5.8 Revision of IMP

6.1 Scope
6.2 General Requirements
6.3 Steel Repair Practice and Quality Standard
6.3.1 Welded Repairs Afloat
6.3.2 Welded Repairs in Drydock
6.3.3 Renewal of Plates
6.3.4 Renewal of Internals
6.3.5 Insert Plates
6.3.6 Large Shell Plate Insert with Stiffeners
6.3.7 Welding of Pits and Grooving
6.3.8 Indents
6.3.9 Fatigue Cracks Stopping and Welding Preventive Measures
6.3.10 Grinding of Shallow Cracks

7.1 The Causes and Types of Corrosion
7.2 Corrosion Control
7.2.1 General
7.2.2 Coatings – Paint Organic Coatings In-organic Paint Coatings
7.2.3 Galvanising/Cladding
7.2.4 Failure of Inorganic Primers, Galvanising, Cladding
7.3 Composite Systems –- Brief Overview
7.3.1 Hull Coating - – Antifouling systems
7.3.2 Topsides
7.4 Specific Shipboard Applications and Conditions
7.4.1 Ballast Tank Coatings
7.4.2 Potable Water Tank Coatings
7.4.3 Other Fresh Water Tank Coatings
7.4.4 Cargo Tank Coatings
7.4.5 Microbially Influenced Corrosion
7.5 Cathodic Protection Systems
7.5.1 General
7.5.2 Anode Design Basis for Ballast Tanks
7.6 IACS Guidelines for In-Service Monitoring Reports
7.7 Repairs in Service –- In Service Maintenance of Coating Systems
7.7.1 General
7.7.2 Repairs in Yard versus Repairs at Sea
7.7.3 Methods of Surface Preparation
7.7.4 The Steps for Tanks Coating Maintenance/Repairs
7.7.5 Major Considerations

Appendix 1
Pitting Intensity Diagrams

Appendix 2
Example of an Inspection and Maintenance Plan, including sample report forms for copying

Appendix 3
Designing for ease of Inspection and Maintenance
1. Use of Higher Tensile Steel
2. Cargo Tank Corrosion Problems
3. Inspection of Cargo Tanks
4. Inspection in Ballast Tanks
Preparation for Coating
Appendix 4
Examples of Permanent Means of Access
Appendix 5
List of Standards in Preparation and Coating
Appendix 6
Definition of "Areas under Consideration"

About the Author

INTERTANKO is the International Association of Independent Tanker Owners. INTERTANKO has been the voice of independent tanker owners since 1970, ensuring that the liquid energy that keeps the world turning is shipped safely, responsibly and competitively.


Title: INTERTANKO Guidance Manual for Maintenance of Tanker Structures
Number of Volumes: 1
Edition: First
Number of Pages: 90
Product Code: WS1023K
Published Date: January 2008
Binding Format: Paperback
Book Height: 300 mm
Book Width: 210 mm
Book Spine: 7 mm
Weight: 0.30 kg
Author: Intertanko

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