[en] Flow Accelerated Corrosion (FAC) requires considerable attention in plant piping management, for its potential of catastrophic pipe rupture of main piping systems. For plant integrity and safety, pipe wall inspection must be conducted with proper prediction of FAC susceptible area and thinning rate. In view of fluid dynamics, the most essential factor to be considered is mass transfer at the inner surface of the pipe. Mass transfer coefficients are determined by fluid properties and piping geometry, however, no universal correlation exists, which is adaptable to various types of piping elements. It would be very useful if the coefficients can be obtained by a common method with inputs of general hydraulic properties. In this study, FAC experiments were conducted with a contracted rectangular duct under PWR condensate water condition. Also, numerical calculations were done to obtain hydraulic features in the duct of the experiment. The modeling of mass transfer coefficient was progressed, in parallel, based on Chilton-Colburn analogy and utilizing 'Effective Friction velocity' and 'Effective Reynolds number' from the hydraulics in the viscous layer along the wall. By considering the turbulent velocity of the viscous layer into the mass transfer coefficient, the correlation with the FAC thinning rate improved, effectively. Future works will be to quantify the turbulence effect and the surface roughness effect to the thinning rate. (author)