Abstract
The creepage of corrosion underneath a coatings film applied to a steel test panel is often used as a performance test for the anti-corrosion properties of a coating system. Creepage is defined as the degree of corrosion (usually measured in mm) emanating away from a scribe line underneath a coating film applied to a steel substrate. There are several factors which may affect the degree of corrosion creep, one of which is the type and width of scribe cut into the coatings film to the steel substrate. There is a variety of scribing methods used in various test methods and specifications; however it is unclear if there is actually a performance difference observed in corrosion creep when using different scribe types.
A study was undertaken to compare the effect on corrosion creep using 6 different scribe types and thicknesses. The study was conducted using a two pack epoxy primer applied over blasted hot rolled steel and smooth cold rolled steel. The scribed coatings were subjected to both continuous neutral salt spray (ASTM B117) and cyclic ammonium sulfate/sodium chloride spray (ASTM G85 Annex A5) for 2000 hours. The test panels were evaluated and analyzed for the effect of scribe width, effect of lateral force on the coating during the scribing process, the effect of coating material left in the valleys of the blast profile, and the effect of profile of the steel substrate on corrosion creep emanating from the scribe.
This study shows for the epoxy primer tested, there is virtually lttle or no statistical difference in the degree of corrosion creep from any of the 6 scribe types employed.
