Abstract
Recently, cathodic protection is applied to steel in fresh water. This paper discusses the condition which satisfies cathodic protection in practical use.
A sacrificial anode is zinc. Steel being in contacted with zinc is dipped in Tsukuba-city tap water at 25°C for 780h. Weight loss, potential and cathodic current between zinc and steel are measured.
Steel does not corrode when the ratio of area [γ=area of steel/(area of steel+area of zinc)] is lower than 0.75. In this case, the cathodic current density to steel is more than 0.12A/m2 and the potential continues to rise. When steel corrodes, the potential attains the steady value of about -400mV (SHE). We propose the protection criterion considering both the potential and the direction of change of potential.
