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) Auxiliary Anode

The auxiliary anode used in impressed current cathodic protection is to transmit the impressed current through it to the protected metal pipeline for cathodic polarization. Therefore, it must meet the following requirements: good electrical conductivity, good mechanical strength, easy processing, low cost, and when a large protection current is required, the anode should be made of insoluble materials.

(1) Common anode materials and their properties.

In pipeline impressed current cathodic protection, commonly used anode materials include carbon steel, graphite, and high-silicon cast iron. The properties of anode materials are shown in Table 6-4.Design of auxiliary anodes.

Chapter 12 Cathodic Protection Facilities and Installation Procedures

The equipment, materials, instruments, and meters used in cathodic protection must be strictly installed according to the procedures. During the installation of the constant potential instrument, it is crucial not to reverse the positive and negative power supply terminals, otherwise it will cause serious corrosion consequences. The anode cable must be strictly sealed, as damage to the insulation layer will cause the cable to corrode and break quickly.

12.1 Installation of Block Sacrificial Anode Systems

12.1.1 Sacrificial Anode Installation Location

Compared with impressed current cathodic protection, the installation of sacrificial anodes is relatively simple. When there are several anodes at one location, the anodes should be arranged in a straight line to reduce resistance. The anodes can be perpendicular to the pipeline, as shown in Figure 12-1, or parallel to the pipeline. To reduce the influence of the anode field, when the anodes are parallel to the pipeline, the distance between magnesium anodes and the pipeline should be ≥5m; the distance between zinc anodes and the pipeline should be ≥1.5m (if space permits, the spacing is best at 3m).Figure12-1 Group installation of sacrificial anodes

The maintenance of the sacrificial anode cathodic protection system is very simple. Regularly check the output current of the anode, and replace it in time after the anode is consumed.

12.1.2 Sacrificial Anode Installation Procedure

① First, check whether the goods certificate and packing list are complete.

② Check whether the anode lead wire is intact and undamaged, and check whether the anode is centered in the backfill bag.

③ Excavate the anode pit at the designated location according to the design requirements, and place the anode in the anode pit.

④ Open the pipeline coating, clean, weld the lead wire, and seal; lead the cable to the test station.

⑤ Soak the anode with clean water, and then backfill.

12.2 Ribbon Anode Installation

12.2.1 Zinc Ribbon Anode Installation Location

Zinc ribbon anodes are suitable for cathodic protection of pipelines in areas with low soil resistivity. The zinc ribbon anode can be laid in the same trench as the pipeline, with a distance greater than 300mm from the outer wall of the pipeline, at the bottom of the trench. The iron core of the zinc ribbon is crimped to the cable with a copper tube, and the cable is connected to the pipeline through a connection or directly to the pipeline.

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