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Title of the paper on internal anti-corrosion treatment using cement mortar in steel pipes: Internal Anti-Corrosion Treatment Using Cement Mortar in Steel Pipes. Authors: Ding Yuqin, Li Xiaoyan. Abstract: Most of the pipes inside and outside the Jiangxinzhou Wastewater Treatment Plant in Nanjing are made of steel pipes, with diameters ranging from 500 to 2200 mm. Internal anti-corrosion involves using insulating materials to separate the steel pipe from corrosive substances inside it, thereby preventing the formation of a corrosion cell between them. For the internal anti-corrosion treatment of steel pipes in this factory, polyvinyl acetate cement mortar is used. It offers advantages such as good anti-corrosion performance, low cost, non-toxicity, and ease of application. The application methods include mechanical spraying and manual troweling. Keywords: corrosion prevention; steel pipe cement mortar. Most of the pipes inside and leading out of the Jiangxinzhou Wastewater Treatment Plant in Nanjing are made of steel pipes, with diameters ranging from 500 to 2200 mm. Internal anti-corrosion involves using insulating materials to separate the steel pipe from corrosive substances inside it, thereby preventing the formation of a corrosion cell between them. For the internal anti-corrosion treatment of steel pipes in this factory, polyvinyl acetate cement mortar is used. It offers advantages such as good anti-corrosion performance, low cost, non-toxicity, and ease of application. The application methods include mechanical spraying and manual troweling. 1 Mechanical spraying (1) Construction preparation: Manholes should be installed every 200–400 meters along the pipeline, with no bends in the sections between them, to facilitate the entry and exit of machinery as well as the transportation of materials. It is also required that the inner wall of the pipe be free of rust and dirt, with no water accumulation inside. Before spraying, soil should be placed over the top of the pipe to maintain a constant and stable temperature inside it. (2) Raw materials and mix ratio: The cement used is 525 grade ordinary Portland cement. The sand is sieved to be medium-grained, with coarse sand and impurities removed, along with 50% polyvinyl acetate emulsion. The mixing ratio is: cement:sand:polyvinyl acetate emulsion:water = 1:1.5:0.15:0.43. A distance of 150 m is appropriate for spreading the ash, which should be applied from below the manhole. (3) Operation of the sprayer The sprayer consists of four mechanical units: a crane, a slurry delivery system, nozzles, and a finishing mechanism. The operation method involves placing high-consistency mortar into a bucket; it is then pushed to the nozzle by a mortar feed screw. The nozzle rotates at high speed due to centrifugal force, causing the cement mortar to form fine particles that accumulate on the wall of the tube. At this point, a rotating smoothing tool is used to apply pressure in a circular motion along the tube wall, while the machine moves backward slowly, thereby creating a good inner wall coating. The coating thickness is generally between 5 and 14 mm, varying with the driving speed – it is thinner when driving fast and thicker otherwise. After spraying, cure for 36–48 hours. The lining for the corner elbow is prefabricated on the ground. 2 Manual troweling (1) Construction preparation: It is similar to mechanical spraying, but the spacing between manholes must be ≤100m and their diameter must be ≥80cm; power ventilation facilities should be installed if necessary. (2) Construction of the manual troweled lining layer: The following 3-layer method is employed. To prevent residual rust and dust on the pipe wall from remaining, the pipe wall is first wiped with polyvinyl acetate emulsion once before applying the plastering material, to make it moist (without any water droplets remaining). The transition layer is 4 mm thick and is applied using polyvinyl acetate cement mortar. During application, start from the midpoint on the inner side of the pipe and apply the material upward, working first on the upper half before moving on to the lower half. After each section is applied, use a small broom to brush out any excess bristles on the surface. Waterproof insulation layer: Once the transition layer has hardened and no voids or delamination are detected upon inspection, apply plain mortar in 2 coats, with a thickness of 1.5 mm per coat. The water barrier layer is 5 mm thick cement mortar, which is applied gently while the insulation layer is still in the setting stage, ensuring that the sand particles in the mortar do not penetrate the insulation layer. (3) Maintenance: Seal the manhole immediately after lining it to prevent air from circulating. After 10 hours, mist the surface with water for curing to keep it consistently moist.