Lined plastic composite pipes are steel-plastic composite pipes that use hot-dip galvanized steel pipes as the base pipe and are lined with thin-walled plastic pipes on the inner wall of the steel pipe. The base pipe, if it is a straight-seam welded steel pipe, should comply with the provisions of GB/T3091-2015; if the external anti-corrosion of the base pipe is galvanized, its galvanized layer is divided into 300g and 500g of zinc coating. If the base pipe is a seamless steel pipe, it should comply with the provisions of GB/T8163. Therefore, the implementation standards for lined plastic composite pipes include GB/T3091-2015 "Welded Steel Pipes for Low Pressure Liquid Delivery" and GB/T28897-2012 "Steel-Plastic Composite Pipes". It combines the mechanical properties of steel pipes with the corrosion resistance of plastic pipes, and its service life is three times that of ordinary galvanized pipes. At the same time, it has a smooth inner wall, low fluid resistance inside the pipe, no scaling, no microbial growth, and no secondary pollution of the fluid. It is an ideal pipeline for conveying direct drinking water, acids, alkalis, salts, corrosive gases, and other media. The diameter of lined plastic composite pipes ranges from DN15 to DN300 based on the standard nominal diameter of the base pipe, and can even be made larger. The cut-to-length length is the same as above, with a tolerance of +2mm. According to the conveying medium, it can be divided into lined plastic pipes for cold water and lined plastic pipes for hot water. The inner plastic layer of lined plastic pipes for cold water is polyethylene (PE), and the bonding strength between the base pipe and the inner plastic lining is not less than 1.0 MPa. The inner plastic layer of lined plastic pipes for hot water is heat-resistant polyethylene (PE-RT), and the bonding strength between the base pipe and the inner plastic lining is not less than 1.5 MPa. As pressure water supply pipes, their compressive strength reaches 1.6 MPa and 2.5 MPa depending on the wall thickness of the base pipe.