Papers by Keyword: Filiform Corrosion

Abstract: The surface line type defects on the can twist-off lids from lacquered tinplate material have been analyzed. The analyzed defects manifested themselves like the lines bulged above the surrounding surface. They were aligned roughly perpendicular to the lid circumference; they were mostly arranged on the lower part of lid circumference edge. The defects surface was fully covered by lacquer layer. After lacquer layer removal it was visible in the defective area that tin layer was damaged on some defect areas. The defect presented itself like filiform corrosion which occurred in conditions slightly above room temperature and high humidity under the originally continuous covering layer. According to the findings, corrosion occurred on the hidden sheet cut edges and then propagated first perpendicular to the circumference into the sheet. Then sometimes its direction changed into the sheet rolling direction along the lines with less but still suitable tin layer thickness. This defect can be controlled by special protecting of lid cut edge against corrosion or decreasing of the temperature and the humidity conditions in the stores.

Abstract: The supporting structure of conveyor in a coal power generation plant located in marine environment, was experiencing severe filiform corrosion. The structure has been used since 2009. This supporting structure holds the conveyor for coal transportation from the ship to the turbine. From visual inspection, it was clearly seen that around 80 % of total area of the structure has been corroded, which influenced the strength of the structure. Hence damage evaluation of supporting structure was important to be carried out to determine the level of damage and to give the recommendation for repairment strategies. The damage evaluation method consisted of thickness measuring, chemical composition test, hardness test, microstructure analysis using replica technique and deposit analysis using SEM-EDS. The result showed that the type of material structure was AISI 1020. The highest reduction in measured thickness was 44 %, which occurred dominantly on bottom and top flange of the structure. It was also found that in some joint areas, the material was perforated. The deposit analysis using SEM EDS found that the type of coating used on steel structure was not suitable for the marine environment.

Abstract: The presence of a heavily deformed and corrosion susceptible surface/near-surface region on rolled aluminium alloy has been amongst the most important problems which the aluminium manufacturers are dealing with. While primarily the composition of the alloying elements and the thermo-mechanical treatment play an important role in determining surface activation, the importance of several other secondary parameters cannot be ignored. This paper tries to identify the impact of several factors, associated with sheet metal production, on the corrosion behaviour e.g. (a) type of the cast bar fed into the hot rolling mill, whether scalped or not scalped, (b) importance of homogenisation and in-line heat treatment, in relation to pre-existing understanding of surface activation on AA3005, (c) effect of hot and cold rolling (d) effect of surface finish, etc. The alloy under investigation was recycled AA5050, containing high Fe and Si as impurities, and used commercially for architectural purpose, eg. window facades.

Abstract: Over the past ten years a detailed understanding of the dominant factors controlling the corrosion susceptibility of painted aluminium alloy sheet used for architectural and automotive applications has been developed. Work carried out in this field will be reviewed and the different modes of cosmetic corrosion that can occur-, the mechanisms of surface activation, and the role of different thermo-mechanical processing steps on controlling corrosion susceptibility for different alloy systems, including Al-Mn, Al-Mg and Al-Mg- Si-(Cu) will be discussed. The critical role of chemical or electro-chemical cleaning prior to pre-treatment and coating will be highlighted and prospects for meaningful accelerated testing will be discussed.