The distribution of sacrificial anodes on the pipeline should be distributed in a single branch or concentrated group, and the same group of anodes should be used in the same batch number or with similar open-circuit potential, and the burial methods are vertical and horizontal, and the burial position is axial and radial. Under normal circumstances, the anode burial position should be 3 5m away from the pipeline, and the minimum should not be less than 0 3m When buried in a group, the anode spacing should be 2 3m. In some cases, the sacrificial anode should not be too close to the pipe. For example, when sacrificial anodes are used to protect hot oil pipes with zinc anodes, the increase in temperature causes a reversal of the polarity of the anode (zinc becomes the cathode and the pipe becomes the anode). In addition, as with impressed current cathodic protection systems, there should be no metal structure between the anode and the pipe. The burial depth of the sacrificial anode should be not less than 1m from the ground at the top of the anode. In cold regions, the anode must be buried below the freezing line. In dry areas where the groundwater table is less than 3m, the anode should be buried deeply. In rivers, the anode should be buried in a safe part of the riverbed to prevent damage during erosion and dredging.
Construction of sacrificial anode systems.
1) The surface of the anode should be free of oxide scale, no oil stains, no dust, and should be polished with a wire brush or sandpaper before construction, and it is strictly forbidden to take it directly by hand after cleaning.
2) The anode cable and the steel core can be connected by brazing or soldering. After welding, the unstripped cable should be tied with the steel core with nylon rope, and the two sides of the anode welded end and the bottom end should be insulated with epoxy resin to reduce the end effect of the anode.
3) Under normal circumstances, the construction of packing materials can be prepared indoors, and after the quality is allocated, dry and wet can be adjusted according to the dosage. After the wet-conditioned anode is bagged, it should be buried underground on the same day. Regardless of dry or wet conditioning, it is necessary to ensure that the amount of packing material is sufficient and that the backfill is compact.
4) The anode cable can be directly connected with the pipe, and can also be connected through the junction box in the test pile. The cable and the pipe are connected by thermite welding, and the connection should be insulated with materials compatible with the anti-corrosion layer of the pipeline. The cable should have a certain margin to adapt to the sinking of the backfill loose soil.
5) After the anode is in place, first backfill part of the fine soil, then pour a certain amount of water into the anode pit, and then backfill a large amount of soil.