Abstract

In this work, laboratory test methodologies that employ the combined environmental stressors of time of wetness and salt loading were used to excite corrosion failure modes of coating systems. Real-time measurements via interdigitated electrodes were correlated with reference panel images to monitor the evolution of coating damage. These data can give insights into the coating degradation process and can be used as parameters for developing a predictive coating condition model. A description of the sensors, electrochemical measurements, and methods for coating testing are reported along with the results of atmospheric tests using a range of conditions to produce coating degradation.

Introduction

The corrosion of aircraft costs the U.S. Department of Defense billions of dollars annually and accounts for a significant portion of maintenance time and costs.1 Coatings are the most effective way to protect aircraft, but they have a finite lifetime and must be maintained or replaced before the underlying substrate is damaged by corrosion. Current aircraft maintenance practices call for coating inspections and maintenance based on elapsed time and not on measurements of coating health. Coating lifetime varies depending on the environmental stressors experienced in service, including temperature, humidity, and salt loading.

To enable more effective condition-based maintenance of coated assets, there is a recognized need for predictive coating condition models (PCCMs) to characterize the coating degradation process and make service life predictions in environments of varying severity. A PCCM can be used to manage corrosion protection systems, optimize the timing of maintenance activities to minimize hazardous waste, reduce costs, and increase asset availability. However, model development and validation may be limited by the ability to produce service-relevant failures in well-controlled laboratory tests. Current corrosion test practices rely heavily on operator visual or optical inspections and rating criteria that are applied at the conclusion of an accelerated test or outdoor exposure (ASTM D1654(1), ISO 4628(2)).2,3

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