Relationship between natural exposure testing and cyclic corrosion testing ISO 20340 for the assessment of the durability of powder-coated steel

The corrosion propagation rate during natural exposure tests of powder coated steel and the relationship between natural exposure and accelerated cyclic corrosion testing (ISO 20340) results were investigated. Generally, during natural exposure, an initial fast increase in the corrosion area followed by a period where the corroded area grows very slowly are observed. As a consequence, the relative ranking between coating systems varies significantly as a function of test time. Correlation between natural exposure results and cyclic test results was not found; in many cases, a better performance in one test is associated with a worst performance in the other.