Why does steel corrode, particularly at water parks? An Entech Innovative Engineering senior engineer reviews why steel corrodes and the scientific principle behind Active Cathodic Protection. Active Cathodic Protection is a method of protecting a structural or otherwise valuable piece of base metal, usually iron/steel, from corrosion using an impressed current. While effective, the method does have limitations. Therefore, guidelines are outlined for the effective installation of an Active Cathodic system in water parks.