Abstract
Corrosion prevention compounds (CPC) are relatively inexpensive, temporary corrosion control products commonly used on commercial and military aircraft. The effectiveness of CPC in suppressing attack of occluded regions within typical aircraft structures such as lap joints is uncertain, in part because their ability to wick into and displace water from occluded sites has not been quantified. This work demonstrates experimental methods that enable quantification of the wicking and water displacement capability of CPC in occluded regions, using simulated aircraft lap joints instrumented with small profile fiber optic sensors. The sensors are able to differentiate between air, water, and CPC as the surrounding media. The sensors were used to monitor the local environment in situ in real time such that the penetration kinetics and water-displacing ability of four commercial CPC were measured. Both water and CPC rapidly wick into dry occluded regions, but egress at ambient conditions is much slower. The CPC displacement of water from pristine joints is also more than an order of magnitude slower than CPC wicking into dry joints. Large relative standard deviations (RSD) in the wicking rate (40% to 90%) are indicative of the high variability in wicking kinetics and water displacement processes; the large variability in ingress kinetics is supported by visual observations. Areas of the faying surface in some cases remain nonwetted and unprotected by the CPC. In addition, these compounds may actually trap water within the joint. The slow and incomplete coverage of CPC within the simulated lap joints raises concern regarding the corrosion protection provided by CPC, particularly when applied to wet structures. Wicking experiments on corroded joints corroborate predictions based on the surface property measurements that some CPC are not effective at penetrating and displacing water from a corroded aluminum alloy (AA)2024 (UNS A92024) surface.
