, and the polarization potential range of both are within the linear range (±10mV OCP ).
triangular wave scanning linear polarization is to apply a triangular wave scanning signal based on potential or current control to the system, and its scanning rate is generally 0.5mV/s ~ 5mV/s . the polarization resistance R p is calculated by dividing the polarization potential DE by the slope of the polarization current DI . Then calculate the polarization current density I corr according to Stern equation (2) .
AC impedance is a sine wave signal with a certain frequency amplitude within 10mV applied to the electrode system, and the measured potential signal is divided by the current signal to obtain the complex impedance value. Because the sine wave frequency is single and pure, without complex harmonic components, the signal-to-noise ratio can be improved by correlation integral, so that the impedance test method based on sine wave excitation can be greatly improved compared with the triangular wave scanning method. By measuring the impedance values in the high and low frequency regions, the AC impedance technique can measure the dielectric resistance and charge transfer resistance, which cannot be done by the triangular wave scanning linear polarization technique. It can be said that the AC impedance is further optimized on the basis of the conventional linear polarization principle.
polarization curve can be divided into three regions according to the polarization potential interval: linear polarization region (5 ~ 20mV ), weak polarization region (20 ~ 50mV ), strong polarization region /Tafel region (50 ~ 100mV ). For long-term corrosion monitoring, linear polarization technology is generally used, because too high polarization potential ( weak polarization or strong polarization ) will cause large changes in the state of the electrode surface, and its electrochemical dissolution behavior will cause the metal surface to seriously deviate from the real pipeline corrosion state, making the monitoring data lose long-term comparative significance. Therefore, in the long-term corrosion monitoring process, only the polarization overpotential of 5 ~ 10mV can be applied, so that the surface state of the electrode will not be greatly changed, so that the electrode can quickly restore the natural corrosion state without taking out and re-polishing, and ensure the consistency between the subsequent corrosion monitoring results and the real corrosion state.
Generally, the linear polarization technology of triangular wave scanning adopts the scanning range of -10mV ~ 10mV ( vs OCP ), while the sine wave amplitude of the linear polarization technology of sine wave scanning (AC impedance) is generally set to 5mV, and does not exceed 10mV . The high frequency end is set to 100Hz ~ 1000Hz , and the low frequency end is set to 0.01Hz ~ 0.002Hz .