In our country, when polyethylene pipes were first used as gas pressure pipes, most of them used manual/semi-automatic hot-melt connection. Due to the great influence of human factors, there were many unqualified weld joints. There are similar cases in various gas companies. . Later, electrofusion connections were used in some areas, and the situation was improved. In order to reduce engineering costs, promote the development of the polyethylene pipe business, and be safe and economical, foreign countries have been studying hot-melt connection machines that minimize the influence of human factors. In 1990, they began to use automatic hot-melt butt welding machines. At present, the domestic is also vigorously promoting automatic hot-melt welding machines, such as Beijing, Guangzhou, Shanghai and other regions to phase out manual/semi-automatic hot-melt welding machines and replace them with automatic hot-melt butt welding machines.
In order to better understand the characteristics of manual/semi-automatic hot melt and automatic hot melt butt machine. Here is a comparison of the operating characteristics of manual and fully automatic butt welding machines.
Two, polyethylene pipe welding operation instructions
1 Scope
This work instruction specifies the operating procedures, inspection methods and safety precautions for the welding of polyethylene pipes.
This work instruction is suitable for welding operations of polyethylene pipes.
2 Normative references
The following documents are indispensable for the application of this document. For dated reference documents, only the dated version applies to this document. For undated reference documents, the latest version (including all amendments) is applicable to this document.
CJJ 63-2008 Technical Specification for Polyethylene Gas Pipeline Engineering
3 Terms and definitions
3.1 Connection method of polyethylene pipe
Generally, three methods are used: hot-melt connection, electro-fusion connection, and steel-plastic transition connection.
3.2 hot melt connection
Hot-melt connection is a connection method in which polyethylene pipe joints are heated, melted and pressurized, and then firmly connected together after cooling. According to the connection mode, the hot melt connection can be divided into three forms: butt hot melt connection, socket hot melt connection, and saddle hot melt connection.
3.3 Butt hot melt connection
Butt hot-melt connection is to insert a flat electric heating mold (electric heating plate) between the two pipe interfaces to heat the connecting surface of the pipe. When the connecting surface of the two pipes is heated to a molten state, the electric heating template is drawn out, and the end faces of the two pipes are forced to squeeze. Press together to form a uniform flange, which will be welded firmly after cooling. The method has simple process and convenient operation, and is often used for straight pipe connection of polyethylene pipelines.
3.4 Socket hot melt connection
Socket hot-melt connection is a method of heating and connecting the connecting surface with a socket electric heating mold that matches the pipe (socket) and the pipe (socket). This method has the advantages of high strength, good airtightness, low cost, etc., and is a reliable connection method for small-caliber polyethylene pipes. In order to ensure that the interface can reach the due strength and reliable tightness when the socket is connected, the insertion end should have sufficient depth.
3.5 Saddle hot melt connection
Saddle-shaped hot-melt connection is to fix the saddle-shaped pipe fitting with the branch pipe to the branch pipe that needs to be connected to the main pipe by hot-melting. After the connection, remove the pipe cover on the top of the pipe fitting, and drill through the fixed pipe special drilling tool. Then take out the drilling tool, cover the pipe cover, and connect the branch pipe to the outlet end of the pipe fitting. This method is mainly used for the construction of adding branch pipes to the laid polyethylene main pipe, and the operation is very convenient.
3.6 Electrofusion connection
During the electric fusion connection, the heating of the fusion surface is completed by the electric heating wire buried in the connecting pipe, thereby eliminating the need for the heating process of the electric heating mold in the hot fusion connection, the operation becomes simple, and in poor weather conditions Can also be constructed. Electrofusion connection has the advantages of stable performance, reliable quality, simple operation, etc., but the cost price is higher than that of thermal fusion connection. According to the connection mode, the electrofusion connection can be divided into two modes: electrofusion socket connection and electrofusion saddle connection.
3.7 Electrofusion socket connection
The electric fusion socket connection is to insert the two pipe ports that need to be connected into the socket connector with the electric heating wire, and the electric current is passed through the heating wire to make the connection piece (the socket end) and the pipe (insertion end) The fusion surface is heated to the melting temperature, and after cooling, the connecting piece and the pipe are firmly fused together.
