20436 Timescale Correlation between Marine Atmospheric Exposure and Accelerated Corrosion Testing

Monday, August 1, 2011: 3:25 PM
Eliza L. Montgomery*1, Luz M. Calle2, Jerome P. Curran3, and Mark R. Kolody3
(1)NASA Postdoctoral Program; (2)NASA; (3)ESC-Team QNA
Selection of corrosion resistant materials for metal-based structures in marine environments has traditionally relied on their evaluation at atmospheric exposure test sites.  This approach is an invaluable method to predict the long term life performance of a metallic material, but its primary disadvantage is the long timescale required for evaluation, often lasting 3 to 5 years.  A faster method that successfully correlates to atmospheric exposure results is needed to expedite material evaluation and selection.  Traditional accelerated corrosion testing relies on mimicking the actual service conditions, often incorporating salt spray and UV exposure, and subjecting the metal to continuous or cyclic conditions of the corrosive environment.  Correlating these accelerated corrosion tests results to atmospheric exposure long-term performance is a known challenge.  Accelerated laboratory testing, which often focuses on the electrochemical reactions that occur during corrosion, has yet to be accepted as a useful tool in predicting the service life of a metal despite its ability to rapidly induce corrosion.  Although visual and mass loss methods of evaluating corrosion are the standard, and their use is imperative, a method that correlates timescales from accelerated corrosion testing to atmospheric exposure testing results, based on the chemical changes that occur during corrosion, would be very valuable.  This work makes use of surface and electrochemical techniques to interpret the chemical changes occurring on steel substrates during atmospheric and accelerated corrosion conditions testing.  The results obtained by analyzing data from four marine-based corrosion conditions : atmospheric exposure and alternating seawater submersion at the Kennedy Space Center Beachside Atmospheric Test Site, salt fog via ASTM B177, and electrochemical laboratory conditions, to find a timescale correlation between the different conditions will be presented in this paper.
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