Aluminum Alloy Sacrificial Anode Alloy Material

1. Sacrificial anode cathodic protection involves connecting a metal with a more negative potential to the protected metal within the same electrolyte, transferring electrons from the anode to the protected metal, thereby maintaining the entire protected metal at a uniformly negative potential. This method is simple, easy to implement, requires no external power source, and rarely causes corrosion interference. It is widely used to protect small metal structures (typically with currents less than 1 ampere) or those in low soil resistivity environments (soil resistivity less than 100 ohm·m), such as urban pipeline networks and small storage tanks. According to domestic reports, there have been many failures in the use of sacrificial anodes, with their service life generally not exceeding 3 years and at most 5 years. The main reason for the failure of sacrificial anode cathodic protection is the formation of a non-conductive hard layer on the anode surface, which limits the current output. The author believes that the primary cause of this issue is the anode composition not meeting specification requirements, followed by the high soil resistivity at the anode's location. Therefore, when designing a sacrificial anode cathodic protection system, in addition to strictly controlling the anode composition, it is essential to select an anode bed location with low soil resistivity.
2. Impressed current cathodic protection uses an external DC power source and auxiliary anodes to force current to flow from the soil to the protected metal, ensuring the protected metal structure's potential is lower than that of the surrounding environment. This method is primarily used to protect large metal structures or those in high soil resistivity soils, such as long-distance buried pipelines and large tank farms.

3. Cathodic protection is divided into sacrificial anode and impressed current methods. Cathodic protection for storage tanks is no exception and can employ either sacrificial anodes or impressed current.
Using sacrificial anodes for tank protection involves the issue of a shorter service life. Once the anodes are consumed, replacement is troublesome, requiring breaking up the hardened ground around the tank to re-bury sacrificial anodes. Therefore, impressed current is generally used for cathodic protection of storage tanks. The anode ground bed materials typically chosen are MMO noble metal ribbon anodes or flexible anodes.

Storage Tank Cathodic Protection Potential

Cathodic protection for storage tanks generally uses impressed current. After construction is completed, the tank's potential can be displayed on the constant potential instrument display cabinet. The principle is the same as for pipelines: one cable is connected to the tank, and another cable is connected to a reference electrode buried around the tank, allowing measurement of the tank's potential.

Potential measurement essentially measures the potential difference between the protected metal and the reference electrode. Since the potential of the reference electrode we use is fixed, any changes in the measured current are considered changes in the structure's potential. However, this is not always the case; the reference electrode's potential might also change. Reference electrodes can be affected by several factors: Temperature effects: Generally, temperature increases can change the solution concentration, causing the reference electrode potential to change. This can also affect the linearity of the reference electrode potential. For common copper/copper sulfate reference electrodes, the temperature effect is approximately 0.9 mV/°C. For conventional pipelines, the measured potential at around 26°C should be -0.85 V, while at about 5°C, the measured potential is approximately -0.825 V. Therefore, when measuring crude oil storage tanks, the effect of crude oil heating should be considered. For portable reference electrodes we use, we must also consider potential changes caused by solar exposure, typically around 10 millivolts. To prevent excessive changes in the reference electrode, it can be wrapped with black tape. Changes in the tank bottom plate can also cause measurement potential variations, such as deformation and bulging due to crude oil heating. When the bottom plate warps, some parts may not contact the tank foundation, receiving insufficient protection current and leading to polarization. To avoid inaccurate data due to this phenomenon, measurements should be taken when the tank liquid level is maintained at about 2/3 for a certain period. Supplied by Jiaozuo Libo Light Alloy Co., Ltd.