The pitting corrosion of copper tubes in tap water has been investigated by electrochemical measurements. The measurements of corrosion potentials, potentiodynamic polarization tests and potentiostatic corrosion tests were carried out in two types of tap water: one type of water was taken in the area where the moundless pitting has occurred (called as "pitting area's water") and another type was taken in the area where the pitting has not occurred (called as "pitting-free area's water"). The corrosion potential in the pitting area's water was higher than that in the pitting-free area's water and shifted to a nobler value gradually. Current densities of the pitting area's water also indicated higher values than those of the pitting-free area's water in both polarization tests and corrosion potentiostatic tests. Many visible pits existed on the surface of the specimen after the potentiostatic tests at 200 mV (Ag/AgCl) in the pitting area's water.
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