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Structural features and installation considerations of snap-ring type enamel pipe fittings: Since welding cannot be used to connect steel-plastic composite pipes, connectors become a key issue in promoting the use of such pipes. Currently, the steel-plastic composite pipe fittings available on the market mainly come in two types: the traditional threaded connection method and the quick-installation type. The silk-like connection method retains the advantages of traditional galvanized steel pipes, such as high strength and reliable sealing, but it still has drawbacks including water quality contamination at the connection points, significant loss in flow diameter which prevents accurate control of liquid flow, and higher installation costs. The clamping-type enamel fittings for internal reinforcement embedded plastic-coated steel pipes are of a quick-installation design. This fitting is manufactured using an enamel coating on the inner wall and a painted finish on the outer surface. Practical use has shown that this design offers advantages such as reliable connection, easy and fast installation, attractive appearance, as well as being hygienic and environmentally friendly, making it highly suitable for widespread adoption. I. Structural Features 1. Reliable connection and high pressure resistance: When installing snap-ring type enamel pipe fittings, a groove is first created in the pipe at an appropriate position away from the end face using a special rolling machine designed for plastic-lined steel pipes with internal ribs; then the snap ring is placed in this groove, and after attaching nuts, washers, and sealing rings, it is connected to the pipe fitting. Since the collar is placed in the groove of the pipe and the slope between it and the nut is less than 22.5ºC, it possesses good self-locking properties; as a result, once the nut is tightened, the pipe and the fittings are firmly connected into one unit, granting high pressure resistance – the system can operate at a pressure of up to 2 MPa. 2. Dual-sealing to prevent leakage: When connecting ring-type fittings to pipes, a dual-sealing approach is used, with radial sealing as the primary method and end-face (axial) sealing as a supplementary method. The sealing ring tubing is made of sanitary, non-toxic sealing rubber with strong pressure resistance and corrosion resistance. The principle of radial sealing relies on the nut driving the collar and the pipe to move axially, thereby compressing and deforming the sealing ring between the pipe end face and the pipe itself, achieving sealing as a result ； The end-sealing ring is placed at the end face of the pipe and at the bottom of the socket in the fitting; the nut drives the pipe to move axially, thereby compressing the sealing ring to provide a seal, while also preventing water from coming into contact with the outer metal pipe. 3. The inner wall of the fitting is entirely lined with enamel. The key difference between enamel-clad, corrosion-resistant, snap-fit fittings and other steel-plastic fittings is that the linear expansion coefficient of the enamel layer is similar to that of the fitting itself; as a result, after high-temperature sintering, a strong bond is formed, and the fitting does not deform, delaminate, or peel off at high temperatures. After being connected to the pipe, water is completely separated from the metal layer and can only flow within the enamel layer, ensuring water purity and preventing contamination; at the same time, this enhances the corrosion resistance of the pipes and fittings. 4. No pressure drop, ensures consistent liquid flow. Plastic-lined steel pipe fittings are made by lining ordinary pipes with plastic directly, which results in a reduced diameter and thus affects the liquid flow rate ； The design of the snap-ring type enamel pipe fittings takes into account the system’s diameter, which is essentially consistent with the standard diameter, thereby ensuring proper fluid flow. 5. Quick installation and easy maintenance: All connection accessories for the snap-ring type enamel pipe fittings are supplied in a complete set. During on-site installation, it is sufficient to create a groove in the pipe using a special rolling machine designed for plastic-lined steel pipes with internal ribs, thereby enabling connection without the need for threading or welding. This approach ensures fast installation, high efficiency, low installation costs, and reduces project duration. Since this snap-fit connection method is a quick-install structure, it is easy to disassemble and convenient for maintenance. II. Key installation points: The snap-ring type enamel pipe fittings are installed and used in projects in accordance with the requirements of the \"Technical Specifications for Plastic-lined Steel Pipes for Water Supply (with embedded reinforcement)\“. Its installation is simple; construction workers only need to master the following key installation points to carry out the installation of this pipeline properly. 1. Cutting and grooving: (1) When cutting the pipe, determine the desired length based on on-site measurements, then use a plastic-lined steel pipe grooving machine with internal ribs to cut the pipe, ensuring that the cut surface is perpendicular to the pipe’s axis; at the same time, remove any burrs or excess material. (2) When grooving, corresponding rollers should be selected based on the different specifications of the pipes, and grooves should be formed by pressing according to the groove dimensions. 2. Tube installation (1) Before installing the tube, remove the laminated layer from the connection area of the tube ； (2) Check whether all accessories for the pipe connection are present ； (3) Follow the sequence shown in the diagrams in the fitting assembly instructions to sequentially install the nut, clip, washer, and seal ring on the pipe, then insert the pipe into the fitting’s socket, and finally tighten the nut using a wrench. 3. Install pipe clamps at the stress points of each fitting as required for fixation. It is advisable to use special clamps designed for use with plastic-lined steel pipes equipped with internal rebar for fixation; the clamps should make tight contact with the surface of the pipe, without damaging it.