Coating Systems with Long Lifetime - Paint on Thermally Sprayed Zinc

摘要

Thermally sprayed zinc (TSZ) with an organic coating system on top has mainly given very long lasting corrosion protection on Norwegian road bridges. Even in coastal areas up to 40 years lifetime has been achieved. However, there are also examples of bridges where the coatings have failed after about 20 years. Seven bridges in various environments, 12-23 years old, were inspected in this study. Two types of coating failure was found: (1) corrosion of the TSZ in an area where the thickness of the organic coating was too thin, and (2) single spots where the TSZ corroded, probably caused by pinholes in the organic coating. Pinholes are easily formed when organic coatings are applied on TSZ. By diluting the sealer coat to about 30% solids and applying less than 25 urn dry film thickness, the formation of pinholes was avoided.