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Sequential Combining of Ultraviolet Light and Salt Spray Stresses: Toward the Next Generation of Test Methods

Sequential Combining of Ultraviolet Light and Salt Spray Stresses: Toward the Next Generation of Test Methods
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Protective coatings exposed to sunlight must withstand multiple environmental stresses: ultraviolet light, moisture, heat, corrosive chlorides and other salts, and atmospheric pollutants. Two decades after the publication of a sequential UV and cyclic salt spray test method in ASTM D5894, some efforts to create better and more predictive test methods have focused on delivering both UV and salt spray in a single chamber and adding additional stresses such as ozone exposure, air pressure fluctuations, atmospheric pollutants such as sulfur dioxide, and other environmental factors. 

Product Number: 51218-111-SG
Author: Sean Fowler, Andy Francis, Bill Tobin, David Duecker
Publication Date: 2018
Industries: Corrosion Monitoring and Control , Coatings
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$20.00
$20.00

Protective coatings exposed to sunlight must withstand multiple environmental stresses: ultraviolet light, moisture, heat, corrosive chlorides and other salts, and atmospheric pollutants. Two decades after the publication of a sequential UV and cyclic salt spray test method in ASTM D5894, some efforts to create better and more predictive test methods have focused on delivering both UV and salt spray in a single chamber and adding additional stresses such as ozone exposure, air pressure fluctuations, atmospheric pollutants such as sulfur dioxide, and other environmental factors. A goal of such programs is an all-in-one test that combines most known stresses in order to accurately correlate real-world performance to the laboratory. There is sound logic in this approach because combining stresses reduces the risk of missing synergistic degradation pathways. However, these ambitious projects have yet to result in widely-adopted practices or new technology. It may be the case that such an approach will not be practical in the near future. At the same time, little work has been done to incrementally improve on the original, sequential method, despite a greatly increased chance of success. ISO 20340 standardized a similar sequential test cycle, but it has been criticized for its poor reproducibility. This paper will focus on the corrosion portion of these cycles because the weathering test has already been updated to provide better reproducibility. Although there are opportunities to create better weathering cycles, the critical factors in weathering have been controlled to a greater extent than corrosion tests for about 20 years. The paper will discuss flaws in common accelerated corrosion wet/dry cyclic tests, which are rooted in the technology available when they were developed. This critique will first be done from a simple theoretical framework supported by recent research. Experimental data using electrochemical corrosion measurement panels will be presented to supplement this framework and explore the potential to use this technology to accelerate the development of laboratory test methods.

Protective coatings exposed to sunlight must withstand multiple environmental stresses: ultraviolet light, moisture, heat, corrosive chlorides and other salts, and atmospheric pollutants. Two decades after the publication of a sequential UV and cyclic salt spray test method in ASTM D5894, some efforts to create better and more predictive test methods have focused on delivering both UV and salt spray in a single chamber and adding additional stresses such as ozone exposure, air pressure fluctuations, atmospheric pollutants such as sulfur dioxide, and other environmental factors. A goal of such programs is an all-in-one test that combines most known stresses in order to accurately correlate real-world performance to the laboratory. There is sound logic in this approach because combining stresses reduces the risk of missing synergistic degradation pathways. However, these ambitious projects have yet to result in widely-adopted practices or new technology. It may be the case that such an approach will not be practical in the near future. At the same time, little work has been done to incrementally improve on the original, sequential method, despite a greatly increased chance of success. ISO 20340 standardized a similar sequential test cycle, but it has been criticized for its poor reproducibility. This paper will focus on the corrosion portion of these cycles because the weathering test has already been updated to provide better reproducibility. Although there are opportunities to create better weathering cycles, the critical factors in weathering have been controlled to a greater extent than corrosion tests for about 20 years. The paper will discuss flaws in common accelerated corrosion wet/dry cyclic tests, which are rooted in the technology available when they were developed. This critique will first be done from a simple theoretical framework supported by recent research. Experimental data using electrochemical corrosion measurement panels will be presented to supplement this framework and explore the potential to use this technology to accelerate the development of laboratory test methods.

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