Sacrificial Anode Cathodic Protection of Steel in Tap Water

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.