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TECHNICAL PAPERS

Assessment of Corrosion Risks to Aging Ships Using an Experience Database

[+] Author and Article Information
Ge Wang

 American Bureau of Shipping, 16855 Northchase Drive, Houston, TX 77060gwang@eagle.org

John Spencer, Haihong Sun

 American Bureau of Shipping, 16855 Northchase Drive, Houston, TX 77060

J. Offshore Mech. Arct. Eng 127(2), 167-174 (Jan 07, 2005) (8 pages) doi:10.1115/1.1894404 History: Received November 02, 2003; Revised January 07, 2005

Damages to ships due to corrosion are very likely, and the likelihood increases with the aging of ships. Risk and reliability approaches are more and more frequently applied in design and maintenance planning. These advanced approaches require reliable data reflecting the structural condition of ships in service. Such data is scarce. This paper presents a database of corrosion wastage. It is based on over 110,000 thickness measurements recently collected from 140 trading tankers. This database is larger than most other corrosion databases in the public domain. Corrosion wastage exhibits a high level of variability. In addition to thickness measurements of individual structural members, this database also has information on hull girder’s geometrical properties and strength of ships in service. Corrosion wastage has an influence on the hull girder strength. Statistical interpretations of the database are used to represent corrosion wastage in oil tankers. The severity of corrosion is ranked by three levels: slight, moderate, and severe levels corresponding respectively to 50%, 75%, and 95% cumulative probability on the database. The risks of corrosion wastage to aging ships’ structural integrity are assessed using the observations of the corrosion wastage database. The investigated risks are loss of local member’s strength, loss of global hull girder strength, and shortened inspection intervals. The experience database can be used in many aspects, such as design requirements for corrosion additions and wastage allowance for plate renewal, establishment of limits to hull girder strength of FPSOs, time variant reliability approach, and risk based inspection schemes.

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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

Heavily corroded under-deck of a 22year old oil tanker (1)

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Figure 2

Profile of ship age at the time of thickness measurement (157 gauging reports, 140 oil tankers)

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Figure 3

Profile of ship length (157 gauging reports, 140 oil tankers)

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Figure 4

Corrosion wastage of deck plate in cargo tanks (4665 thickness readings, 157 gauging reports, 140 oil tankers)

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Figure 5

Loss of hull girder section modulus to deck over time (599 sections)

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Figure 6

Annual reliability index of a stiffened panel at a tanker’s bottom for different corrosion levels

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Figure 7

Annual reliability index of a stiffened panel at a tanker’s deck for different corrosion levels

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Figure 8

Annual reliability index of the hull girder strength of an oil tanker for different corrosion levels.

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