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

The construction of cement mortar fabric should usually be carried out after the spiral pipe has been laid, the pressure test has passed, and the covering soil has been compacted according to the planning requirements. Due to the small stiffness and thin wall of the steel pipe, the pipe must be in a stable state during the fabric construction process. If The fabric anti-corrosion layer is made first and then the pipe is lowered. During construction, large deformation occurs during lifting, transportation, and soil return, which damages the anti-corrosion layer.

Before fabric construction, the inner wall of the pipe must be cleaned to remove loose floating 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 directional deformation shall not be greater than the planning regulations and shall not be greater than 2% of the inner diameter of the pipe.

The anti-corrosion layer within the cement mortar can be constructed by mechanical spraying, manual troweling, dragging, or centrifugal prefabrication. If it is necessary to use the precast method to make the internal anti-corrosion layer, protective measures should be taken for the anti-corrosion layer during transportation, installation, and backfilling.

During construction, cement mortar is first mixed. The mass ratio of cement and sand is 1: (1-2). The slump of cement mortar is 60-80 mm. The compressive strength of cement mortar should not be less than 30 MPa.

The anti-corrosion layer inside the cement mortar constructed by the mechanical spraying method has a smooth, dense surface, uniform thickness, and good effect. Mechanical spraying construction began to be used abroad in the 1930s, and in China, it has been used in Shanghai, Qingdao, Dalian, and other cities since the 1960s. When the mechanical spraying method is used for construction, the elbows, tees, special pipe fittings, and pipe sections adjacent to the gate valve can be modified manually, and a smooth mutation section is connected to the mechanical spraying fabric.

In addition, the drag tube or centrifugal prefabrication method is also widely used and will not be described in detail here. No matter what method of construction is adopted, the maintenance process is a key link to ensure that the anti-corrosion layer in the cement mortar does not crack or hollow. Therefore, after the anti-corrosion layer in the cement mortar is formed, the pipeline must be sealed immediately to prevent air convection; moist maintenance must be carried out after the final setting. Generally, the maintenance time of Portland cement should not be less than 7 days, and slag Portland cement should not be Less than 14 days; it should be continuously sealed and kept moist before flowing water.