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Corrosion in ballast tanks
2002 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

This work, performed at the Swedish Corrosion Institute, was part of a project called AIS (Active Industrial Co-operation) – 43 Surface Protection of Ships. AIS 43 are a co-operating project between partners for improving coating systems for ships which will last for two years. The aim with this project was to look at corrosion in ballast tanks and from that develop a corrosion map, which is a documentation of where the corrosion is localised and which type of corrosion it is. Ballast tanks give ship stability and can be filled with either water or, for example, oil. All tanks involved in this study have been filled with sea water. They also contain the same type of coating, a tar-epoxy. Materials used in ballast tanks are low-alloy steels, which are protected with a coating. There are many different types of coatings. Tar-epoxy coatings were once commonly used but now a pure epoxy or a modified epoxy is more common. Nowadays tar is not used in the coatings because of two reasons: environmental aspects and the fact that it gets very dark in the tanks, which makes it hard to inspect the tanks for corrosion attacks. There are many different types of coating failures, some more common than others. In the ballast tanks inspected the most common type of corrosion failures was blister, which is caused by impurities on the metal surface when the coating is applied. One of the most important steps in the coating process is cleaning. If cleaning of the steel is not performed in a proper way the coating cannot protect the steel. The anodes placed in the ballast tanks will then protect the steel as much as possible. The environment in the ballast tanks is humid and dirty. The dirt, containing different types of micro-organisms, for example bacteria and algae’s, is found at the bottom of the tank where water almost always remains. These micro-organisms are one of the main reasons why the ballast tanks corrode. When micro-organisms, come into the ballast tanks with the water it can continue to live in a biofilm, a thin layer of dirt I the bottom of the ballast tanks. The corrosion in the ballast tanks inspected is microbial influenced corrosion, MIC, probably in combination with ordinary corrosion. The corrosion can be decreased if the quantity of micro-organisms is removed. This can be done by using a water purifier.

Place, publisher, year, edition, pages
2002.
Keyword [en]
Technology, corrosion, ballast tanks, MIC, materialteknik
Keyword [sv]
Teknik
Identifiers
URN: urn:nbn:se:ltu:diva-55475ISRN: LTU-EX--02/350--SELocal ID: c5478173-8645-4254-892b-ffc850f5e3a9OAI: oai:DiVA.org:ltu-55475DiVA: diva2:1028858
Subject / course
Student thesis, at least 30 credits
Educational program
Materials Engineering, master's level
Examiners
Note
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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