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For the cathodic protection system, it is very important to evaluate the effectiveness through on-site measurements. Relevant technical personnel should master the correct testing steps, understand the functions and usage of field equipment and instruments, be familiar with the theoretical basis of the tests, and know how to identify and solve problems reflected in the test results.
To determine the effectiveness of cathodic protection against corrosion, the following parameters should be evaluated:
Structure-to-reference potential
Specimen potential
Surface potential
Soil resistivity
Stray current
Structure-to-electrolyte potential (including pipeline-to-ground potential, storage tank-to-ground potential, and pipeline-to-electrolyte potential) refers to the potential difference between the metal surface of the structure and the electrolyte, measured using a reference electrode in contact with the electrolyte.
The electrolyte potential of the structure is measured using a voltmeter connected in parallel within the circuit. Since the external circuit resistance is high, a high-input impedance voltmeter must be used to prevent deviations caused by voltage shunting effects in the structure.
Potentiometric measurement is a common method used to determine whether sufficient cathodic protection is achieved. As the current in the environment acts on the protected structure, its potential will shift relative to the environment. This potential change represents polarization. By measuring it, one can determine whether the system meets relevant cathodic protection standards.
It is also essential to account for and exclude the voltage drop that occurs across the structure–electrolyte interface to accurately evaluate the effectiveness of the cathodic protection system through fixed potential measurements.
