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Cathodic Protection of Pipeline Systems

1. Impressed Current Cathodic Protection

1) Application Principles

(1) The protection length shall include a 10% margin based on process calculations.

(2) The design life of auxiliary anodes should match that of the protected pipeline, typically 20 years.

(3) When external metal structures near the pipeline may be subject to interference, appropriate protective measures shall be adopted.

(4) The rated power of the DC power supply design shall include a 50% margin, and its output impedance shall match the loop resistance.

2) Application Conditions

(1) The protected pipeline should have good longitudinal electrical continuity; for non-welded pipeline joints, jumper cables should be added.

(2) To reduce current loss and ensure protection effectiveness, insulating flanges or buried insulating joints shall be installed at the following locations of the pipeline:

① Connection points between trunk pipelines and plants, stations, storage facilities, or wells;

② Connection points between trunk pipelines and branch pipelines;

③ Both ends of large crossings or spans;

④ Areas with strong stray current interference;

⑤ Junctions of different metals;

⑥ Transition areas between coated and bare pipelines.

(3) The pipeline should be electrically insulated from supporting piers, columns, pipe bridges, fixed piers, pipe clamps, or reinforcing steel in concrete.

(4) When the protected pipeline crosses other pipelines, cables, or metal structures, the insulation level should be enhanced within 5–20 m of the crossing point, and the minimum spacing should be no less than 30 cm.

(5) The distance between the pipeline and the base of transmission line towers, substations, or power plant grounding grids should not be less than 3 m.

3) Process Calculation

There are two main methods for process calculation of impressed current cathodic protection: one uses surface resistivity as the primary parameter, and the other uses current density as the primary parameter. The former is mainly introduced here; the latter can be performed according to GB/T 21448-2008 "Technical Standard for Cathodic Protection of Buried Steel Pipelines" and will not be repeated here.

4) Power Equipment

(1) Requirements for AC power supply: capable of long-term uninterrupted power supply, with priority given to municipal electricity or stable and reliable AC power sources from various stations. When agricultural electricity is used, backup power or specialized uninterrupted power supply equipment should be installed.

(2) Alternative power sources for impressed current cathodic protection in areas without municipal electricity:

① Solar cells;

② Unmanned enclosed cycle generator sets;

③ High-capacity batteries;

④ Thermoelectric generators;

⑤ Wind turbines.

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