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Abstract Corrosion preventative compounds (CPCs) are used to slow corrosion of United States Marine Corps (USMC) assets. CPC coatings are temporary, and reapplication intervals are necessary to maintain the corrosion reducing ability of these compounds. Methods to perform condition based maintenance, including reapplication of CPCs as needed, are being sought in an effort to reduce the costs of USMC asset maintenance. To aid in this effort, coating degradation sensors integrated with a mote-based wireless network were deployed on actual USMC ground vehicles under a variety of storage options at Camp Lejeune, NC and Kaneohe Bay, HI. Results from each site were contrasted as a function of exposure conditions.
Introduction United States Marine Corps ground vehicles are subjected to corrosive environments as a consequence of mission operations. To delay vehicle corrosion, temporary coatings of corrosion preventative compounds (CPCs) are utilized for exposed metal surfaces. However, no current method is available to assess the integrity of the applied coating, and therefore, determine when coating reapplication or corrosion maintenance needs to be performed. Therefore, maintenance is performed at predetermined intervals which can result in extra costs for conservative maintenance intervals, or conversely, can result in inadequate maintenance resulting in diminished asset readiness and performance lifetime. Given the volume, size and dispersion of these vehicles, a wireless sensor network to monitor the condition of CPCs on applied vehicles is desired. Through this, condition based maintenance (CBM) may be possible if the sensors can alert maintenance personnel in real time if the coating at a specific location on an individual vehicle falls below a predetermined threshold, triggering a maintenance action for that vehicle.
Background Coating Degradation Sensors (CDS) have been developed as a method to monitor the condition of a coating on a metal (US Patent 6,911,828). CDS constitute a two-pin impedance sensor on a witness coupon. A schematic diagram and actual image of a CDS are shown in Figure 1. The specific details of the sensor functionality have been detailed previously, and are not mentioned here. The sensors are able to determine, through impedance measurements at a single frequency, the time at when a protective coating degrades to a point where it no longer protects against corrosion. Coating failure is noted by a significant drop in the overall sensor impedance , as well as a drop in the impedance phase angle. By integrating this sensor with a mote communication platform, a wireless CDS network is obtained. The mote is able to interrogate the sensor, record the sensor reading, and communicate this wirelessly through an ad-hoc multi-hop network to a base station which uploads the data to a web portal. In the instance a direct line to the base station is not imminently available, the motes and readers are programmed to "store and forward" the data for transmission when a line becomes available. This way, no lapse in monitoring history develops as vehicles are transported in and out of range of the network. In addition, the network communication works both ways, and individual motes may be addressed and reprogrammed "over the air" in the instance a monitoring frequency or change in the sensor interrogation is desired.
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