Laboratory investigations into the edge corrosion protection capacity of organic coatings

Abstract

The morphology and geometry of free edges on steel structures have a notable influence on the corrosion protection performance of coating systems. A badly prepared edge, whether thermally or mechanically generated, will be a starting point for coating deterioration and subsequent steel corrosion. A research program on how edge geometry and coating type affect the corrosion protection performance of organic coatings on edges involved the use of different edge preparation tools and of different coating systems. The investigations included the use of thermal cutting tools, because these are an integral part of construction lines in modern shipbuilding yards as well as mechanical (milling, grinding) and thermal methods (laser, plasma). Testing methods included the long-term testing of samples in a specially designed ballast tank coating test chamber, condensation chamber tests, electric impedance spectroscopy (EIS), and dry film thickness (DFT) measurements on polished cross sections of coated edges. It was found that the edge geometry parameter does not help to control the corrosion protection performance of organic coatings under simulated water ballast tank conditions. Other effects like edge treatment method/tool and coating application are more important. It seems that DFT, or barrier resistance, is not a suitable parameter to control the deterioration of the coating systems, nor does it control their corrosion protection capability. More complex processes, such as combined mechanical, physical, and thermal loads, are responsible for the corrosion protection action of the systems