Study On The Performance Of Sacrificial Anodes And Interference In The Pulsed Current Cathodic Protection

The pulsed current cathodic protection (PCCP) is a new kind of cathodic protection (CP) technology, which has great potential application value. However, there are only few of application reports about this technique. In this thesis, the influence of the impressed current (square wave pulsed current or DC) on the performance of the sacrificial anode and the interference in PCCP systems were investigated by using a simulated CP system.The impressed current will influence the output current and working potential of the sacrificial anode once the impressed current is applied. And the influence decreases with the increase of the distance between the sacrificial anode and auxiliary anode. The output current of the sacrificial anode decreases with the direct current (I) increasing. But the output current of the sacrificial anode changes from DC to pulsed current with the same frequency of the impressed pulsed current, due to applying impressed pulsed current. The output current decreases in the on-time period with the amplitude of the pulsed current (Im) increasing. However the output current doesn't decrease and even increases in the off-time period with the Im and duty cycle increasing. The output current is independent to the frequency of the impressed pulsed current. The sacrificial anode is polarized by the impressed DC or pulsed current, and the working potential of the sacrificial anode (Es) decreases with the I, Im and duty cycle increasing. But the Es is independent to the frequency. Therefore the output current of the sacrificial anode must be measured to estimate the effect of cathodic protection. The contribution of the sacrificial anode to the cathodic polarization decreases and then disappears with the direct current increasing. However, this contribution does not decrease with the increasing of the Im and duty cycle of the pulsed current. These results verify the advantage of the PCCP.There has interference effect between PCCP and other systems. The polarized potential and its waveform of the interfered cathode or the unprotected system are influenced. The waveform of polarized potential, which is coupling of two separate systems, presents different characteristic in the cathodic area, polarity alternating area and anode area of the interference. The upper potential of the interfered cathode decreases and the nether potential increases with the increasing of current parameters of the interference system, and the interference is intensified. The upper potential of the interfered cathode decreases and the nether potential increases with the decreasing of the distance of the systems or of the assistant anode and the interfered cathode (or the unprotected system), and the interference is intensified. When the burying depth of the assistant anode of the interference system increases, the upper potential of the interfered cathode (or the unprotected system) distributes more uniformly, and the variation of the nether potential is ignored. When there are several PCCP systems in one area, their pulsed current had better have the same frequency and duty cycle, and the design requirement can be obtained by adjusting the amplitude of their pulsed current. The distance of different systems should be as farthermost as they can. The effect of assistant anode station on the interference is hypersensitive, and the assistant anode should be buried as far as it can from the cathode of other systems.