Scribe Creep and Underpaint Corrosion on Ultra-High Molecular Weight Epoxy Resin Coated 1018 Steel Part 2: Scribe Creep Model as a Function of Environmental Severity Factors

The scribe creep of ultra-high molecular weight epoxy-resin-coated AISI 1018 steel (UNS G10180) has been found to be a complex function of environmental severity factors (ESFs). In this work, a fractional factorial design of experiments (FFA) was employed to probe the effects of ESFs. The environmental variables explored were temperature, relative humidity (%RH), chloride, ultraviolet light (UV), and wet/dry cycling. The effects of ESFs were examined using controlled laboratory exposures by systematic variation of ESFs at high and low levels across a series of experiments. Corrosion, scribe creep, and coating degradation of epoxy resin coated steel were investigated with high-level surveillance methods capable of interrogating both coating and substrate degradation. Fractional factorial experiments, which included both high temperature and high cycling, could not be modelled accurately. It is possible that there was an interaction between temperature and cycling that is only manifested in scribe creep when both ESFs are at the high levels established in the FFA experimental design. An empirical model for scribe creep of coated steel showed good agreement with experiment, but only for fractional factorial experiments that did not have high levels of both temperature and cycling. For these experiments, cycling was found to have the greatest effect, followed by temperature.