100 mV polarization criterion for cathodic protection

This Code stipulates that when the minimum cathodic polarization value between the surface of the structure and the stable reference electrode reaches 100mV, it can be considered as sufficient protection. The polarization value can be measured by measuring polarization formation or attenuation. Before measurement, it should be confirmed that the cathodic protection is in normal operation and the structure has been fully polarized. During the measurement, the current synchronous interrupter shall be installed in the cathodic protection power supply which has an impact on the measurement interval to synchronously interrupt all cathodic protection currents.

The polarization formation method is to measure the natural corrosion potential of metal structures before applying cathodic protection, and then apply cathodic protection current. After the structure is fully polarized, the power-off potential is measured. Then the off potential and the spontaneous potential are compared. If the potential difference exceeds 100mV, the requirements of this criterion are met.

The polarization attenuation method is to first cut off the protection current, and then continuously measure the depolarization potential of metal structures. The difference between the instantaneous off potential and the depolarization potential is the actual polarization value. As long as the depolarization reaches 100 mV, it can meet the requirements of polarization value criterion. However, the depolarization potential does not necessarily return to the spontaneous potential.

The 100 mV polarization criterion can be used not only for steel and cast iron structures, but also for aluminum and copper structures, as well as steel bars in concrete.

Compared with other methods, the 100 mV polarization criterion has the following advantages:


① It is especially suitable for bare pipe or pipeline with poor coating;

② This method is very effective when the corrosion potential is very low and / or the current required to reach the negative 850mv polarization potential criterion is very high;

③ It can reduce the damage to the coating and avoid hydrogen embrittlement.

The disadvantages of the 100 mV polarization criterion are as follows

① The measurement time is long and the cost is high;

② If there is stray current, or the sacrificial anode is directly connected to the structure, or there is external forced current equipment and can not be interrupted, it is difficult to obtain ideal results, or the measurement results can not be analyzed;

③ It can not be used in high temperature conditions, SRB soil with stray current interference and heterogeneous metal electrical connection structure.

Shandong Linyi Bosi conductive materials Co., Ltd. is a high-tech enterprise specializing in the production of MMO flexible anode, conductive polymer flexible anode and titanium coated anode, mainly providing cathodic protection technology, engineering design, installation and technical services.