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To Cycle or Not to Cycle: That is the Question

To Cycle or Not to Cycle: That is the Question
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Previous papers by two of the authors have examined 1) the futility of attempting to correlate accelerated corrosion testing results to real world corrosion observations, and 2) how corrosion testing is useful as an indicator of performance without the need for real world correlation and what may be expected in a corrosive environment and how these results can be usefully applied in the real world. This third paper in the trilogy, examines a specific attribute of accelerated corrosion testing, that being the utility of wet/dry cycling testing versus continuous fog methods. 

Product Number: 51217-037-SG
Author: Carl Reed, Travis Boerma, Kat Coronado, Steve Vento
Publication Date: 2017
Industries: Cathodic Protection , Corrosion Monitoring and Control
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$20.00
$20.00

Previous papers by two of the authors have examined 1) the futility of attempting to correlate accelerated corrosion testing results to real world corrosion observations, and 2) how corrosion testing is useful as an indicator of performance without the need for real world correlation and what may be expected in a corrosive environment and how these results can be usefully applied in the real world. This third paper in the trilogy, examines a specific attribute of accelerated corrosion testing, that being the utility of wet/dry cycling testing versus continuous fog methods. For 30+ years, wet/dry cyclic accelerated corrosion testing has been lauded as a much improved method of accelerated corrosion testing versus continuous electrolyte fog methodology. Yet, there has been little objective evidence to support this contention, one way or the other. Evidence has generally been observational and anecdotal without using the scientific method for evaluation to determine if the methodology is in fact improved. In this study, panels with applied scribes are subjected to wet/dry cycling (1-hour wet and 1-hour dry) and to continuous electrolyte fog. The exposure times for the wet/dry cycle is 1500 hours while the exposure time for the continuous exposure is 1000 hours. The electrolytes used are 5% NaCl aqueous solution (as used in ASTM B117) and Timmons solution, an aqueous solution of 0.35% NaSO4 + 0.05% NaCl (as used in ASTM G85 Annex A5). The panels are coated with two different epoxy coatings, the composition between the two being the same except one contains aluminum pigment and the other does not. The panels are evaluated for corrosion at the scribe and scribe creep and cathodic delamination. Expectation from this study is to be able to determine if there is a mechanistic difference in using wet/dry cycling over continuous exposure for corrosion evaluation. This will then allow the user to choose an accelerated corrosion method that better suits the environment and timing for coatings evaluation.

Previous papers by two of the authors have examined 1) the futility of attempting to correlate accelerated corrosion testing results to real world corrosion observations, and 2) how corrosion testing is useful as an indicator of performance without the need for real world correlation and what may be expected in a corrosive environment and how these results can be usefully applied in the real world. This third paper in the trilogy, examines a specific attribute of accelerated corrosion testing, that being the utility of wet/dry cycling testing versus continuous fog methods. For 30+ years, wet/dry cyclic accelerated corrosion testing has been lauded as a much improved method of accelerated corrosion testing versus continuous electrolyte fog methodology. Yet, there has been little objective evidence to support this contention, one way or the other. Evidence has generally been observational and anecdotal without using the scientific method for evaluation to determine if the methodology is in fact improved. In this study, panels with applied scribes are subjected to wet/dry cycling (1-hour wet and 1-hour dry) and to continuous electrolyte fog. The exposure times for the wet/dry cycle is 1500 hours while the exposure time for the continuous exposure is 1000 hours. The electrolytes used are 5% NaCl aqueous solution (as used in ASTM B117) and Timmons solution, an aqueous solution of 0.35% NaSO4 + 0.05% NaCl (as used in ASTM G85 Annex A5). The panels are coated with two different epoxy coatings, the composition between the two being the same except one contains aluminum pigment and the other does not. The panels are evaluated for corrosion at the scribe and scribe creep and cathodic delamination. Expectation from this study is to be able to determine if there is a mechanistic difference in using wet/dry cycling over continuous exposure for corrosion evaluation. This will then allow the user to choose an accelerated corrosion method that better suits the environment and timing for coatings evaluation.

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