Effect of RH Cycling Parameters on Scribe Creep of Coated Steel Panels During Accelerated Corrosion Testing

Abstract As coating systems with reduced environmental impact become available, accelerated corrosion testing capable of reproducing realistic damage is needed. Cyclic TOW during accelerated corrosion tests is known to enhance scribe creep and to produce failures that are similar to those observed in the field. In this work, cyclic exposures consisting of salt fog steps and various relative humidity (RH) cycles were used. Scribe creep was measured for two different coating systems after 28 and 56 days in each environment. The relationship between scribe creep and TOW are explored. The data reveals that regardless of the applied RH cycle, a linear relationship exists between TOW during RH cycling and scribe creep. However, the total observed scribe creep cannot be accounted for using creep values from the combined cyclic RH portion and salt fog portion of the exposure. Additionally, significant differences in relative coating performance are observed after 28 and 56 days of exposure. These differences are likely the result of a multistep scribe creep process. Electrochemical Impedance data collected under immersion conditions are used to support a hypothesized scribe creep mechanism that may serve to refine accelerated corrosion testing methods and produce a method capable of reflecting long-term coating performance.