The pressure of epoxy resin coated composite steel pipes used for water supply is generally divided into five levels: 0.6Mpa, 1.0Mpa, 1.6Mpa, 2.5Mpa, and 5.0Mpa. The connection methods are divided into double flange sealing connection and groove (clamp) connection. When the pressure of the coated composite steel pipe is 4Mpa, the base pipe material should be seamless steel pipe, and the connection method can be fixed flange connection at both ends; The flange material is Q235B or 20 # steel forged flange.