Electrical Current Distribution and Potential Measurement in Ca-thodic Protection

The CP level depends on the density of impressed current on the surface of electrolytic solution contacting with structures. In order to get all over CP protection, the structure should have uniform current density. In fact, however, the current distribution over the structure can not be uniform due to many factors which affect the current distributions, including distance between anode and structure and anodes allocation, the variation of soil resistivity, the position of reference electrodes. By analyzing in detail these factors, it is concluded that (1)anode allocation is vital important in the CP design, and the current distribution can be improved effectively by adopting flexible anodes for the pipeline with aged coating; (2)the key to the measurement of pipe-to-soil potential is to place the reference eletrodes on the holidays, the CIPS and DCVG methods are proved to be reliable in measuring the true protective potential at the holidays, (3)the reference electrodes shall be located near the structures to be measured for the local CP; (4)the minimum protective potential at holidays should be lower than-0. 85.