Corrosion of Hawk Lead-in-Fighter Hydraulic Pipe Work
DEFENCE SCIENCE AND TECHNOLOGY ORGANISATION EDINBURGH (AUSTRALIA) MARITIME OPERATIONS DIV
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In 2003, corrosion damage to hydraulic and nitrogen pipe work resulted in thirteen RAAF Hawk aircraft being declared unserviceable. The reason for the corrosion was not readily apparent and DSTO was approached to identify the cause and recommend suitable prevention measures. Initial appearances indicated that the corrosion was most likely due to either incorrect use of corrosion protective coatings or their application andor galvanic corrosion due to exposure in a marine environment. Upon receipt of this task a test programme that involved electrochemical potentiodynamic and galvanic studies, exposure trials of a model of the pipe work and quality control studies of the protective coatings used was initiated to identify the cause of the corrosion. It was concluded from this testing that the premature failure of the Hawk hydraulic fittings was due to galvanic interactions between the cadmium, mild steel and unprotected stainless steel component parts , combined with the use of the aircraft in a coastal location and the cadmium coating thicknesses being below the specified levels. To minimize the risk of further corrosion a suitable coating should be applied to the pipe work adjacent to and over the fitting, the pipe work should be passivated and the specified cadmium coating thickness applied to the fittings.
- Metallurgy and Metallography