51314-4354-Propulsion Shaft Damage Assessment via Multi-modal Embedded Sensors

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Product Number: 51314-4354-SG

ISBN: 4354 2014 CP

Author: Fritz Friedersdorf

Publication Date: 2014

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Maintaining ship propulsion shafting integrity is a critical concern for the US Navy in order to provide full mission capability of fleet assets. Fleet-wide maintenance experience presently dictates drydocking ships at ten year intervals for full shaft removal and inspection to determine whether the glass-reinforced plastic (GRP) covers protecting the shaft-sleeve interface have successfully prevented seawater intrusion and attendant shaft pitting/fatigue damage. This destructive type of inspection can reveal no water ingress or shaft damage meaning that the sleeve was removed before the end of its useful operating life. Conversely inspections have also revealed significant damage evidencing cover failure well before the end of its typical remaining useful life. To meet this critical need Luna Innovations has begun to develop an embedded multi-modal distributed sensing platform to provide an in situ assessment of shaft and barrier coating condition which periodically and non-destructively measures shaft condition at shorter intervals. With this enhanced capability shaft maintenance would be driven by shaft and GRP barrier condition instead of a calendar basis thereby reducing the number of costly drydock cycles over a ship’s lifetime. Frequent monitoring would also reduce the risk of catastrophic shaft failure between inspection cycles were the barrier properties to fail prematurely.The sensing hardware has been designed for a conformal low-profile form factor to permanently reside encased in the fairing compound in the region between the shaft bearing sleeve and GRP cover permanently encased in the fairing compound. A wireless power and signal transfer through the GRP cover to eliminate the need for conductors penetrating the shaft has been designed for the final application. Sensing elements to monitor the coating protection system and localized shaft damage severity have been developed. To detect the degradation of the protection system novel ring shaped sensors have been developed to observe changes in local conductivity and overall barrier using electrochemical impedance spectroscopy (EIS) techniques. To further validate the sea water intrusion measurement circumferential inductive sensors using an eddy-current type inspection measurement have been created for an independent indication of pitting or cracking damage surrounding the shaft. The results and conclusions of Luna’s efforts in the sensor development and embedded electronic design will be presented.