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2) Attachments for Cathodically Protected Pipelines

(1) Test coupons.

The material of the test coupon should be the same as that of the protected pipeline, used for quantitative analysis of the effectiveness of cathodic protection and the corrosiveness of the soil. There are also test coupons used for other purposes, such as representing the pipeline in sacrificial anode protection sections to measure natural potentials.

The recommended dimensions for test coupons are 100mm × 50mm × 5mm, produced by sawing or gas cutting. To avoid altering the metallurgical state of the test coupon, 20–30mm should be removed from the gas-cut edges. Test coupons should have mounting holes and serial numbers, which can be stamped using steel character dies.

Test coupons should generally be buried in representative corrosive areas (environments), such as polluted zones, high saline-alkali regions, areas with severe stray currents, and the ends of the pipeline's cathodic protection range.

(2) Test stations.

To measure the electrical parameters of cathodically protected pipelines, test stations with different functions should be designed along the pipeline. The principles for setting up test stations are as follows:

① Potential test stations: generally installed every kilometer, with the possibility of increasing or decreasing density as needed;

② Current test stations: installed every 5–8km;

③ Casing test stations: installed at one or both ends of casings;

④ Insulating joint test stations: installed at each insulating joint;

⑤ Bonding test stations: installed at intersections with other pipelines, cables, or structures;

⑥ In-station test stations: installed as needed;

⑦ Sacrificial anode test stations: generally installed midway between two groups of anodes.

The test stations set up as above can measure parameters such as the protection potential of the pipeline, the magnitude and direction of the protection current, electrical insulation performance, and interference-related parameters.

The main difference in the functions of test stations lies in the wiring. The simplest is the potential test station, requiring only two leads; measuring pipeline current requires four leads; measuring interference or insulation between two structures requires two leads from each adjacent structure. The functions of test stations can be combined, and sometimes test stations can also be integrated with mileage markers.

II. Cathodic Protection for Pipeline Routes

1. Impressed Current Cathodic Protection

1) Application Principles

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

(2) The design life of the auxiliary anode should match that of the protected pipeline, generally selectable as 20 years.

(3) When external metal structures near the pipeline may be affected by interference, appropriate protective measures should be taken.

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

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