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Predicting the Impact of Metallic Coating and Paint Degradation on the Corrosion of F-18 Airframes

Picture for Predicting the Impact of Metallic Coating and Paint Degradation on the Corrosion of F-18 Airframes
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Product Number: 51315-5956-SG
ISBN: 5956 2015 CP
Author: Alan Rose
Publication Date: 2015
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Corrosion impacts the safety function and readiness of military assets costing the Department of Defense $22.5 billion each year according to the DoD Corrosion Policy and Oversight Office. Specifically for Navy and Marine Corps aviation this totals $2.6 billion and results in an average of 25 days of corrosion-related non-availability per year for each aircraft on active status.The present approach for considering galvanic incompatibilities is simplistic and static. It issimplistic in that the only thing it takes into account is the galvanic potential difference between two adjacent materials. An estimate of the galvanic corrosion severity is usually based on some form of galvanic potential table as in MIL-STD-889. However in mixed material assemblies it is the galvanic current that determines the severity of corrosion not the galvanicpotential and the two are not directly related. The design engineer needs a way to estimate the true corrosion risk based on both the explicit geometry and all the materials in an assembly.The present approach is static in that it assumes that the condition of an assembly remains constant. However as soon as weapons systems are deployed corrosion protection schemes become compromised over time due to physical and environmental damage. Sacrificial coatings and passivates become depleted while paint systems become damaged and deteriorate. It is essential therefore that the design engineer considers upfront not only how the factory-fresh finish system will perform but the very real impact of environmental degradation and protective finish damage on the integrity of the weapon system over its lifetime.An SBIR project funded by the Office of Naval Research (ONR) has already demonstrated how a new computational modeling approach can identify and quantify the severity of several corrosion issues observed in a fielded F-18 aircraft structure. This paper introduces a more recent development where deterioration is simulated over time accounting for degrading paint layers and the consumption of sacrificial metallic coatings. The insight provided by this approach is invaluable for the first time giving the designer the tools to incorporate protection schemes that are more damage-tolerant and appropriate for the intended operational environment of the weapons system.
Corrosion impacts the safety function and readiness of military assets costing the Department of Defense $22.5 billion each year according to the DoD Corrosion Policy and Oversight Office. Specifically for Navy and Marine Corps aviation this totals $2.6 billion and results in an average of 25 days of corrosion-related non-availability per year for each aircraft on active status.The present approach for considering galvanic incompatibilities is simplistic and static. It issimplistic in that the only thing it takes into account is the galvanic potential difference between two adjacent materials. An estimate of the galvanic corrosion severity is usually based on some form of galvanic potential table as in MIL-STD-889. However in mixed material assemblies it is the galvanic current that determines the severity of corrosion not the galvanicpotential and the two are not directly related. The design engineer needs a way to estimate the true corrosion risk based on both the explicit geometry and all the materials in an assembly.The present approach is static in that it assumes that the condition of an assembly remains constant. However as soon as weapons systems are deployed corrosion protection schemes become compromised over time due to physical and environmental damage. Sacrificial coatings and passivates become depleted while paint systems become damaged and deteriorate. It is essential therefore that the design engineer considers upfront not only how the factory-fresh finish system will perform but the very real impact of environmental degradation and protective finish damage on the integrity of the weapon system over its lifetime.An SBIR project funded by the Office of Naval Research (ONR) has already demonstrated how a new computational modeling approach can identify and quantify the severity of several corrosion issues observed in a fielded F-18 aircraft structure. This paper introduces a more recent development where deterioration is simulated over time accounting for degrading paint layers and the consumption of sacrificial metallic coatings. The insight provided by this approach is invaluable for the first time giving the designer the tools to incorporate protection schemes that are more damage-tolerant and appropriate for the intended operational environment of the weapons system.
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