ASTM permeability cup method and capacitance technique were used to study water (vapor) transport processes in inhibitor-free, and praseodymium (Pr)-containing aerospace primer films. The water transport rate from the cup method was found much higher in inhibitor-free epoxy film than Pr-containing aerospace primer films when fully cured. The change in film capacitance, determined by electrochemical impedance spectroscopy (EIS), was quantitatively correlated with the total amount of in-plane water transported in primer films. The water diffusion coefficients derived from the permeability cup and capacitance data were in an order of magnitude of 10~(-8) ～ 10~(-7) -cm~2/s, while the diffusion coefficient of inhibitor ion (Pr~(+3)), calculated from the side-by-side diffusion cell measurements, was in an order of magnitude of 10~(10) cm~2/s, significantly lower than water transport within primer films. The effects of inhibitor ion (Pr~(+3)) concentration, solution pH on inhibitor transport process were also studied. It was found that both Pr and Ca-containing pigments were dissolved (leached) more significantly in strong acidic (pH ～2) than in weak acidic (pH ～ 5.5) environments.
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