“Cyclic Corrosion Testing and Failure Mechanisms” by Mr. James Dante
Perhaps the most widely recognized accelerated corrosion test is the ASTM B117 salt fog test. However, numerous studies have demonstrated that this test method has poor correlation to outdoor exposures, particularly for non-chromate primers. As a result, more realistic cyclic environmental exposures have been developed to more closely resemble actual atmospheric corrosion damage. Several existing tests correlate well with the outdoor performance of some materials and assemblies of interest, but not all. As a result, it is possible that promising new environmentally friendly technologies may be incorrectly rejected based on flawed laboratory tests. Further, there is no ability to assess the risk associated with corrosion failures in operational environments.
The development of accurate laboratory corrosion tests requires a basic understanding of the relationship between specific environmental variables and specific modes of corrosion failure. The single most relevant factor in governing atmospheric corrosion is the relative humidity. Significant effort has been expended throughout the course of our work to define how specific values of relative humidity and cyclic variations in relative humidity affect corrosion rates and corrosion modes. The overall goal of this presentation was to demonstrate the role of RH on corrosion, galvanic interactions, coating delamination, and cracking within the context of developing an improved accelerated laboratory corrosion test.
“Development and Validation of a Cyclic Humidity Corrosion test” by Dr. Victor Rodriguez-Santiago
Current accelerated corrosion tests fail to replicate damage observed in field environments. Recent studies indicated that controlling relative humidity is crucial to replicating damage, which is not accurately specified in the current accelerated corrosion tests. The benefit of creating a more representative accelerated corrosion test standard is two-fold: (i) it facilitates ease of implementation of corrosion prevention technologies and (ii) it generates a better understanding of risk. Being able to develop, test, and qualify new corrosion prevention schemes in a timely manner has the potential to reduce testing costs and provide the ability to introduce better technologies as they are developed. Currently, prospective technologies are developed much faster than they can be tested and qualified. For example, a single ASTM B117 test, the most utilized standard in the Department of Defense (DoD) for corrosion assessment, takes 83 days to complete. However, this test replicates neither damage seen in outdoor exposure tests nor damage observed during aircraft maintenance, so prospective coatings are not implemented—even on a trial basis—until many years of outdoor exposure data are generated.
This project finalized the development of a tunable test method that enables users to select exposure severity while providing experimental correlation, for both corrosion severity and mode, to observations from outdoor field exposures. The accelerated test will include control of relative humidity and periodic deposition of salt on test surfaces via a fog step in the cycle. Once validated and demonstrated, the test methodology will be written into a national standard for use in testing and qualification by laboratories across the DoD, original equipment manufacturers, DoD contractors, and other testing laboratories.
Mr. James Dante is currently the Manager of the Environmental Performance of Materials Section at the Southwest Research Institute in San Antonio, Texas. He has over 25 years of experience in the field of aerospace corrosion. His work has focused on assessing the performance of materials, coatings, and other corrosion mitigation strategies under atmospheric conditions. He has worked to develop exposure techniques and metrics to accurately mimic field performance and quantify corrosion damage. James has performed fundamental studies using advanced electrochemical techniques to understand corrosion failure mechanisms and material performance in the ambient atmosphere to both improve test methods and develop improved corrosion resistant materials and mitigation strategies. He has been involved in the design and deployment of atmospheric corrosion sensors. His current work involves the development of complex data analysis algorithms to predict corrosion damage based on sensor output. He is also currently working to develop techniques to assess stress corrosion cracking and corrosion fatigue under thin film electrolyte conditions experienced in ambient atmospheres.
Dr. Victor Rodriguez-Santiago is the Head of the Corrosion and Wear Branch of the Materials Engineering Division at the Naval Air Systems Command (NAVAIR) in Patuxent River, MD. His background includes corrosion, electrochemistry, electrokinetics, and non-thermal plasmas. Prior to joining NAVAIR, Victor worked at the Army Research Laboratory working on the corrosion of aluminum and magnesium alloys, and the surface modification of polymers and ceramic materials. His current research includes corrosion characterization of aluminum alloys and stainless steel fastener materials, environmental corrosion monitoring and assessment, and electrochemical assessment of aluminum-rich primers.