Abstract
A method utilizing divided steel plates was used to investigate the corrosion of coated steel plates with impact defect while continuously submerged in 3% NaCl solution. The polarization behavior of circular divided steel plates was first compared to that of undivided ones. Half-cell potential and polarization resistance results show similar trend in divided and undivided form especially at the later stages of exposure. The method of using circular divided steel plates was then used to monitor the macrocell as well as microcell corrosion in coated steel plates induced with defect. The test results show that the defect causes macrocell corrosion to occur between the defect and sound portions. The impact defect also caused the reduction in the polarization resistance and consequently higher microcell corrosion at the neighbouring sound coated portions.
Highlights
Under ideal conditions paint coating protects the steel by preventing the access of aggressive elements
A coated steel structure exposed directly to the harsh water of the sea can be hit or bombarded by floating objects that leaves impact defects on the coating surface. It is on these impact defects where the steel substrate becomes directly exposed to the aggressive elements of the marine water allowing the process of corrosion to instigate
The conclusions derived from the results of the laboratory investigation are summarized as follows: (1) The circular divided steel plate has the capacity to act as an undivided steel plate by showing similar trends in halfcell potential and polarization resistance behavior its use as a method to investigate the macrocell corrosion and microcell corrosion in steel plates is valid; (2) The use divided steel plates allowed for the measurement of corrosion at the defect and sound portions of the coated steel plates under continuous submersion to 3% NaCl solution
Summary
Under ideal conditions paint coating protects the steel by preventing the access of aggressive elements. It is one of the practical materials used to protect metals against corrosion [1, 2]. A coated steel structure exposed directly to the harsh water of the sea can be hit or bombarded by floating objects that leaves impact defects on the coating surface. It is on these impact defects where the steel substrate becomes directly exposed to the aggressive elements of the marine water allowing the process of corrosion to instigate. It is reported that once the corrosion is instigated on steel panel protected by an organic paint system, growing blisters appear on the intact portions followed by rapid deterioration [3, 4]
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