The strip magnesium anode is made of pure magnesium or MG-Mn alloy cold rolled. The open-circuit potential (Cu/CuSO4) is -1.7V, and the mass per unit length is 0.37kg/m. It is suitable for use in the environment with resistivity ≥100Ω·m. The output current of magnesium band is 10mA/m in soil with resistivity of 50Ω·m and 3mA/m in fresh water with resistivity of 150Ω·m. The surface area of the ribbon magnesium anode of the same mass is much larger than that of the ingot magnesium anode. For example, the surface area of the 11kg magnesium ingot is 0.27m2, while the 11kg magnesium ribbon length is 30m, and the surface area of the 1.9m2 is 7 times that of the former. The anode output current is proportional to the surface area and inversely proportional to the resistivity. Anode quality determines anode life. The LOCAL SOIL RESISTIVITY SHOULD BE CONSIDERED IN THE DESIGN, AND THE WINDING of the magnesium tape on the crossing or casing pipe SHOULD be considered to have a service life comparable to the pipe life. If the design life is 20 years and the local soil resistivity is low, it is not advisable to use a magnesium band, but a spindle magnesium anode.
The conventional design of the cross section or casing pipe is usually installed with magnesium tape winding method. The sectional size of the banded magnesium anode used in the Shaoxing natural gas utilization project is (19±0.5)mm×(9.5±0.5)mm. Each steel pipe is wound with two banded magnesium anodes, which are symmetrically distributed on both sides of the pipeline. A binding belt is set every 1-2m, and the material is nylon belt. The cable and magnesium anode are welded by filling tin. The insulation layer adopts composite insulation structure, which is composed of epoxy resin, electrical adhesive tape, plastic adhesive tape, heat shrinkable sleeve and anti-corrosion adhesive tape from inside to outside. Each layer of adhesive tape is overlapped when winding. The cable and the pipe are connected by double-point thermite welding. The cable runs smoothly and has a surplus. The distance between the two solder joints is >10cm, the size of the coating break is 3cm×3cm, and the size of the repair is greater than 5cm×5cm. However, in the actual construction, it is difficult to operate this method of magnesium belt winding installation, especially when the pipeline in the crossing section is dragged back, the wound magnesium belt will increase the drag resistance, and the magnesium belt is easy to fall off and break. Therefore, for the pipeline in the crossing section, it is recommended not to use magnesium belt, but to add ingot magnesium anodes at the outlet and entry points, and set up test piles to regularly detect anode consumption. For pipes in the casing, it is recommended that the magnesium tape should be installed parallel to the pipe without reducing the amount of magnesium tape instead of winding, so as to facilitate the pipe to enter the casing without damaging the magnesium tape.