Pei Yingying  1862587  9268

The relationship between the reference electrode potential and the protection potential of steel is as follows:

Through extensive experiments, the following conclusions have been drawn: In a cathodic protection system, the protection effect is optimal when the protection potential of steel is set within the following ranges: relative to the silver/silver chloride electrode, the protection range for steel is -0.8 to -1.0V; relative to the copper/saturated copper sulfate electrode, the protection range is -0.85 to -1.05V; relative to the zinc reference electrode, the protection potential for steel is +0.25 to 0V. If the protection potential of steel falls outside these ranges, underprotection or overprotection may occur.

Pipeline Cathodic Protection Technology

1、Cathodic Protection Methods

2、Methods to achieve cathodic protection typically include the sacrificial anode method and the impressed current method. During stray current exclusion, a certain negative potential is retained on the pipeline, providing cathodic protection. Therefore, drainage protection is also a form of cathodic protection under specific conditions. Below, the characteristics of these three methods are compared.

（1）Sacrificial Anode Method: In a corrosion cell, the anode corrodes while the cathode does not. Based on this principle, the method where a sacrificial anode preferentially dissolves, making the metal structure the cathode to achieve protection, is called the sacrificial anode method. For effective protection, the sacrificial anode must have a sufficiently negative potential, not only in the open-circuit state (when the circuit between the sacrificial anode and the protected metal is disconnected) but also in the closed-circuit state (when the circuit is connected), ensuring an adequate closed-circuit potential (or working potential). This guarantees sufficient driving voltage during operation. Driving voltage refers to the difference between the closed-circuit potential of the sacrificial anode and the potential of the metal structure after cathodic polarization, also known as effective voltage.

As a sacrificial anode material, the following conditions should be met:

1、Sufficiently negative potential and high stability

2、Low anode polarization during operation, uniform dissolution, and easy detachment of byproducts

3、High current efficiency, meaning the percentage ratio of actual capacity to theoretical capacity should be large

4、High electrochemical equivalent, i.e., high capacity per unit weight

5、Non-toxic corrosion products that do not pollute the environment

6、Widely available materials, easy to process, and cost-effective

Common anode materials in soil environments include magnesium and magnesium alloys, zinc and zinc alloys; in marine environments, aluminum alloys are also used. These three types of sacrificial anodes are widely applied worldwide.

Pei Yingying    1862587   9268