Test posts are installed along the natural gas pipeline. There are three types of test posts: potential test posts, current test posts, and insulation test posts. Insulation test posts are installed at pipeline insulation joints. Test posts can also serve as route mileage markers. Adjustments can be made based on specific field conditions. Additional test posts may be added in cases such as directional drilling. The specific locations and quantities of test posts can be adjusted during construction according to field conditions.
Test posts are generally located along roadsides, field ridges, or ditch edges, close to the pipeline excavation. They should be placed as near as possible to sections where the pipeline crosses rivers, ponds, ditches, or roads.
Test posts should be installed at the following locations:
Where the pipeline crosses or runs parallel to AC/DC electrified railways; at insulation joints;
at grounding system connection points;
at metal casing locations; where connections are made to other pipelines or facilities; at auxiliary test coupon and grounding device connection points;
where the pipeline crosses external pipelines;
where the pipeline crosses major roads or embankments; where it crosses railways or rivers;
where it is adjacent to external metal structures.
Cathodic protection test devices should be installed simultaneously with the cathodic protection system. Test devices should be arranged along the pipeline route, with intervals between adjacent test devices not exceeding 3 km. In urban or industrial areas, the interval should not exceed 1 km; in areas affected by stray current interference, test devices may be appropriately increased. Test devices should be installed above the pipeline and clearly marked. Smart test posts should monitor the following parameters: DC pipe-to-soil potential, test coupon instant-off potential, test coupon current; AC voltage, AC current. The area of the DC potential test coupon should be 6.5–10 cm2, and the area of the AC test coupon should be 1.0 cm2.
For station-area cathodic protection, installing test posts is not recommended. Instead, reference tubes should be buried at locations where pipe-to-soil potential measurements are needed to facilitate the placement of portable reference electrodes. Any above-ground metal can serve as a contact point for the red probe during measurements. Since all pipelines within the station are interconnected and form an equipotential body, connecting at any location to the station structure will not affect potential readings.
(1) Test devices should be installed at the following locations:
① Insulation joints;
② Metal casing locations;
③ Test coupon and drainage grounding device connection points;
④ Auxiliary anode locations, sacrificial anode installation points;
⑤ Pipeline directional drilling crossing points.
(2) Smart test posts should be installed at the following locations:
① Where pipeline characteristics are discontinuous (elbows, phase changes of high-voltage lines, turning points);
② Locations with low soil resistivity;
③ Cathodic protection station drainage points, midpoints of cathodic protection stations;
④ Locations affected by DC interference.
(3) Other considerations:
① Install potential test coupons every 5–10 km along the pipeline;
② When metal casings have high-quality coatings, leave a 2-meter bare section at both ends of the casing;
③ Ensure electrical continuity between valve room instruments and the valve body, with the valve body connected to the grounding grid via lightning arresters or DC decouplers;
④ Install surge protection devices at all insulation isolation points.