Experiments to simulate the corrosion of a mild steel (designated A3) in the open sea have been conducted to explain observed differences between the behaviour of suspended specimens that were electrically connected together on the one hand and unconnected on the other. Reasons for differences between the corrosion behaviour of individually suspended specimens in the laboratory and that of steel in a marine service environment have also been investigated. The following conclusions were made: (1) Laboratory scale experiments indicate that factors influencing the corrosion behaviour of electrically connected and individual specimens during exposure to simulated sea water are different. In the case of electrically connected specimens, corrosion in the simulated tidal zone is generally light whereas corrosion in the simulated immersion zone tends to the heavier. For specimens which are not connected, the situation is reversed, with more severe attack in the tidal zone than in the immersion zone. This is because the electrically connected specimens constitute a macroscopic corrosion cell whereas the unconnected specimens do not. (2) Under laboratory conditions simulating corrosion on shallow seas, corrosion of electrically connected specimens in the immersion zone occurs more rapidly than under simulated deep sea conditions due to the reduced anode are in the macroscopic cell. This is a phenomenon of which marine engineers should be aware. (3) Although electrically connected specimens of steel receive some degree of protection in the tidal zone, corrosion still takes place there, especially in the upper reaches where the immersion time is short, limiting protection and allowing severe corrosion. Moreover, since there is no obvious boundary between the splash zone and the tidal zone, anticorrosion measures taken in the splash zone where corrosion is most severe should also be applied in the tidal zone. (4) The formation of the macroscopic cell between the tidal zone and immersion zone is attributed to differences in the concentration of oxygen.
Corrosion of C-Mn steel in simulated tidal and immersion zones
Korrosion von manganhaltigem C-Stahl in simulierten Gezeiten- und Tauchzonen
British Corrosion Journal ; 36 , 4 ; 310-312
2001
3 Seiten, 5 Bilder, 7 Quellen
Article (Journal)
English
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