Selection of sacrificial anode material embedded in heavy oil transmission pipeline

With the increase of temperature, the corrosion rate of aluminum and zinc anode materials increases, the actual capacitance and current efficiency decrease, the consumption rate increases, and the service life decreases. Under the condition of 80 ℃, the corrosion rate and consumption rate of aluminum anode are lower than that of zinc anode, and the coupling current is larger, and the cathodic protection effect is more significant. However, the working potential of zinc anode at 80 ℃ is higher than the minimum protection potential, which does not meet the requirements of the standard. Aluminum alloy is more suitable than zinc alloy as sacrificial anode material for high temperature heavy oil transmission pipeline.

The sacrificial anode is directly installed in the insulation layer. This method can provide cathodic protection for the insulation pipeline after water inflow. The sacrificial anode suitable for installation in the insulation layer includes ribbon anode and sheet anode. At present, the commonly used sacrificial anode materials include aluminum alloy, zinc alloy and magnesium alloy. Magnesium anode is not suitable for long-life sacrificial anode under the insulation layer of high-temperature heavy oil transmission pipeline because of its low current efficiency, fast consumption, and easy hydrogen evolution and spark induction.

With the increase of temperature, the corrosion rate of both aluminum anode and zinc anode increases. At lower temperature (20 ℃ and 50 ℃), the uniform corrosion rate of the two anodes is not much different, but when the temperature reaches 80 ℃, the uniform corrosion rate of zinc anode is significantly higher than that of aluminum anode, and intergranular corrosion occurs. Considering the self corrosion performance, electrochemical performance and coupling performance of the two anode materials, aluminum alloy is more suitable as sacrificial anode material for high temperature heavy oil transmission pipeline.