Internal anti-corrosion treatment method of large-diameter spiral steel pipe

the construction of cement mortar fabric should usually be carried out after the spiral steel pipe is laid, the pressure test is qualified, and the soil is compacted according to the planning requirements. due to the small rigidity and thin wall of the steel pipe, the pipeline must be in a stable state during the construction of the fabric. if first makes the fabric an anti-corrosion layer and then lower the pipe. during the construction, the anti-corrosion layer is damaged due to large deformation during lifting, transportation, and soil return.

before fabric construction, the inner wall of the spiral steel pipe must be cleaned to remove loose rust, soil, oxide scale, grease, welding slag, and other attachments; the convexity of the inner wall of the steel pipe shall not be greater than 1/3 of the planned thickness of the anti-corrosion layer; the vertical deformation shall not be greater than the planning rules, and shall not be greater than 2% of the inner diameter of the pipe. the anti-corrosion layer in the cement mortar can be constructed by mechanical spraying, manual plastering, dragging, or centrifugal prefabrication. if it is necessary to use the prefabrication method as the inner anti-corrosion layer, protective measures should be taken for the anti-corrosion layer during transportation, installation, and backfilling. during construction, the first step is to mix cement mortar, the ratio of cement to sand quality is 1: (1-2), the slump of cement mortar is 60-80 mm, and the compressive strength of cement mortar should not be less than 30 mpa. the inner surface of the anti-corrosion layer of the cement mortar constructed by the mechanical spraying method is smooth, fine, and uniform in thickness, and the effect is better. in the 1930s, foreign countries began to use mechanical spraying for construction. since the 1960s, china has successively used them in shanghai, qingdao, dalian, and other cities. when the mechanical spraying method is used for construction, the elbows, tee, special pipe fittings, and the adjacent pipe sections of the gate valve can be modified manually, and the lubricated sudden change section is connected with the mechanical spraying fabric.

other drag tubes or centrifugal prefabrication methods are also widely used, and will not be described in detail here. no matter what method is adopted for construction, the maintenance process is the key link to ensure that the anti-corrosion layer in the cement mortar will not crack and be hollow. therefore, after the anti-corrosion layer in the cement mortar is formed, it is necessary to immediately block the pipeline so as not to form air convection; after the final setting, wet maintenance is carried out. generally, the maintenance time of portland cement should not be less than 7d, and the maintenance time of slag portland cement should not be less than 7 days. less than 14 days; it should be blocked and kept moist before water is passed.