A study on the influence of ageing of coatings on their mechanical properties and fracture in ballast tanks

摘要

Inspections have shown that coatings used in water ballast tanks (WBTs) can fracture prior to their target design life. This has led to local corrosion of the substrate and unwanted maintenance which is time-consuming and costly for the shipowner. The objective of the current study is to show that ageing of marine coatings used in WBTs can reduce the coatings' fracture strain to a level lower than the strain of the substrate. Laboratory tests were conducted to subject three commercial WBT coatings to different types of ageing. Changes in their mechanical properties were confirmed. Finite element analyses of a 4400 twenty-foot equivalent unit container vessel were carried out for a number of sea state conditions. The strains of the hull structure (i.e. the substrate) were calculated and compared with the fracture strains of the aged coatings. It was shown that, in many locations, the strain of the substrate can exceed the fracture strain of aged coatings. Finally, systematic study with proactive coating condition performance monitoring is discussed.