Three ports were drilled at an interval of 1 cm from the holiday with an interval of 15 cm along the Lucite block to position the microelectrodes for measurements of local potential, current, solution pH and oxygen concentration, respectively. During the test the polarizationpotentials of steel at individual portswere measured by microelectrodes when various CP potentials (775 mV, 925mV and 1075 mV) were applied