Double Hull Oil Tankers: Guidelines for Surveys, Assessment and Repair of Hull Structures, 3rd Edition

The guidelines focus on the IACS Member Societies' survey procedures but may also be useful in connection with survey/examination schemes of other regulatory bodies, owners and operators.

This manual has been developed using the best information currently available. It is intended only as guidance in support of the sound judgement of Surveyors, and is to be used at the Surveyors' discretion.

This book includes a review of survey preparation guidelines, which cover the safety aspects related to the performance of the survey, the necessary access facilities, and the preparation necessary before the surveys can be carried out.

The survey guidelines encompass the different main structural areas of the hull where damages have been recorded, focusing on the main features of the structural items of each area.

An important feature of the manual is the inclusion of the section which illustrates examples of structural deterioration and damages related to each structural area and gives what to look for, possible cause, and recommended repair methods, when considered appropriate.

The International Association of Classification Societies (IACS) manuals provide guidelines to assist the Surveyors of IACS Member Societies, and other interested parties, involved in the survey, assessment and repair of hull structures for certain ship types.

This manual gives guidelines for a double hull oil tanker which is constructed primarily for the carriage of oil in bulk and has the cargo tanks forming an integral part of the ship?s hull protected by a double hull which extends for the entire length of the cargo area, consisting of double sides and double bottom spaces for the carriage of water ballast or void spaces. Figures 1 & 2 show the general views of typical double hull oil tankers with two longitudinal bulkheads or one centreline longitudinal bulkhead respectively.

The guidelines focus on the IACS Member Societies' survey procedures but may also be useful in connection with survey/examination schemes of other regulatory bodies, owners and operators. The manual includes a review of survey preparation guidelines, which cover the safety aspects related to the performance of the survey, the necessary access facilities, and the preparation necessary before the surveys can be carried out.

The survey guidelines encompass the different main structural areas of the hull where damages have been recorded, focusing on the main features of the structural items of each area. An important feature of the manual is the inclusion of the section, which illustrates examples of structural deterioration and damages related to each structural area and gives what to look for, possible cause, and recommended repair methods, when considered appropriate.

This manual has been developed using the best information currently available. It is intended only as guidance in support of the sound judgment of Surveyors, and is to be used at the Surveyors? discretion. It is recognized that alternative and satisfactory methods are already applied by Surveyors. Should there be any doubt with regard to interpretation or validity in connection with particular applications, clarification should be obtained from the Classification Society concerned. Surveyors dealing with single hull oil tankers should be encouraged to read the ?Guidance Manual for Oil Tankers? by Tanker Structure Co-operative Forum.

IACS Common Structural Rules for Tankers implemented from April 2006 have been developed in response to a consistent and persistent call from industry for an increased standard of structural safety. This has been achieved through enhancing the design basis and applying engineering first principles. The development of the CSR for Tankers included review of existing Rules, new development using a first principle approach, application of the net thickness philosophy, an enhanced design environment and a longer life i.e. 25 years North Atlantic. These Rules are applicable to double hull oil tankers exceeding a length of 150 metres.

Note: Throughout this document reference is made to various IACS Unified Requirements (UR), Procedural Requirements (PR) and Recommendations. All URs and PRs and key recommendations are available from the IACS website (http://www.iacs.org.uk).

CHAPTER 1 Introduction

CHAPTER 2 Classification Survey Requirements

2.1 General

2.2 Annual Surveys

2.3 Intermediate Surveys

2.4 Special Surveys

2.5 Drydocking (Bottom) Surveys

2.6 Damage and Repair Surveys

CHAPTER 3 Technical Background for Surveys

3.1 General

3.2 Definitions

3.3 Structural Load Descriptions

3.4 Structural Defects, Damages and Deterioration

3.4.1 General

3.4.2 Structural Defects

3.4.3 Fatigue

3.4.4 Typical Corrosion Patterns

3.4.5 Factors Influencing Corrosion

3.4.6 Items for Special Attention of the Surveyor

3.4.7 Corrosion Trends in Tank Spaces

3.4.8 In-Service Corrosion Rates

3.4.9 Corrosion Prevention Systems

3.4.10 Fractures

3.4.11 Deformations

3.5 Structural Detail Failures and Repairs

CHAPTER 4 Survey Programme, Preparation and Execution

4.1 General

4.2 Survey Programme

4.3 Survey Planning Meeting

4.4 Conditions for Survey

4.5 Access Arrangements and Safety

4.6 Use of Boats or Rafts

4.7 Personal Equipment

4.8 Thickness Measurement and Fracture Detection

4.9 Survey at Sea or at Anchorage

4.10 Documentation on Board

4.11 Reporting and Evaluation of Survey

CHAPTER 5 Structural Detail Failures and Repairs

5.1 General

5.2 Actions to be Taken by the Classification Society when Fatigue Failures have been Identified

5.3 Catalogue of Structural Detail Failures and Repairs

5.3.1

Group 1 Bilge Hopper

Group 2 Wing Ballast Tank

Group 3 Bottom Ballast Tank

Group 4 Web Frames in Cargo Tanks

Group 5 Transverse Bulkheads in Cargo Tanks

Group 6 Deck Structure

Group 7 Fore and Aft End Regions

Group 8 Machinery and Accommodation Spaces