In the installation of metal pipelines, the commonly used connection methods mainly include the following:

1、 Welding

arc welding

Principle: Electric arc welding uses the high temperature generated by the arc to melt the connection between the welding rod and the workpiece, causing them to fuse together to form a weld seam. During the welding process, the welding rod serves as a filler metal, and under the action of the arc, the melted metal fills the gap between the workpieces, forming a strong connection after cooling.

Scope of application: Widely used for pipeline connections of various carbon steel, alloy steel and other materials. For example, carbon steel pipelines used to transport high-pressure steam in industrial plants are often connected using arc welding, which can withstand high pressure and temperature.

Features: High welding strength, able to provide good sealing, suitable for pipeline systems that can withstand high pressure and load. But the technical requirements for welding workers are high, and the welding quality is greatly affected by welding process parameters (such as current, voltage, welding speed, etc.) and environmental factors. The welded pipeline may undergo deformation and requires appropriate correction treatment.

Argon arc welding

Principle: Argon arc welding is a welding method that uses argon gas as a shielding gas. During welding, argon gas forms a stable airflow around the arc, isolating the air from the welding area and preventing harmful effects of oxygen, nitrogen, and other gases in the air on the weld metal, thereby ensuring the quality of the weld.

Scope of application: Commonly used for connecting non-ferrous metal pipelines such as stainless steel, aluminum, copper, etc. For example, in the stainless steel pipeline system of the food processing industry, argon arc welding is an ideal connection method due to the high requirements for cleanliness and corrosion resistance inside the pipeline.

Features: High welding quality, beautiful and smooth welds, no slag, can effectively ensure the corrosion resistance of pipelines. However, argon arc welding equipment is relatively complex, expensive, and has a slow welding speed.

Gas welding

Principle: Gas welding is the use of a flame generated by the combustion of combustible gases (such as acetylene) and oxygen to melt metal for welding. During the welding process, different types of flames can be obtained by adjusting the ratio of oxygen and combustible gases, such as neutral flame, oxidizing flame, and carbonization flame, to meet the welding requirements of different metal materials.

Scope of application: Suitable for the connection of some thin-walled metal pipes and small-diameter pipes, as well as occasions where welding quality requirements are not particularly high. For example, in some small indoor plumbing installations, if the pipe diameter is small and the pressure is low, gas welding can be used as a connection method.

Features: The device is simple, easy to operate, and does not require a power source. But the welding speed is slow, the welding quality is relatively low, the flame temperature is difficult to control accurately, the heat affected zone is large, and it is easy to cause deformation of the pipeline.

2、 Flange connection

Flat welding flange connection

Principle: Flat welding flange is to connect the flange and the pipeline through welding, then place gaskets between the flanges, and use bolts to fasten the two flanges together, so as to connect the pipeline. The gasket plays a sealing role to prevent medium leakage.

Scope of application: Widely used in pipeline systems of various pressure levels, especially in large-diameter pipelines and pipeline connections that require frequent disassembly and maintenance. For example, in large-scale pipeline transportation systems in chemical production, when equipment inside the pipeline needs to be inspected, flat welding flange connections are convenient for disassembly and reinstallation.

Features: High connection strength, able to withstand certain pressure and axial force. Installation and disassembly are relatively convenient, making it easy to maintain and repair pipelines. But flange connections require a certain amount of space, and the sealing performance is greatly affected by the gasket material and installation quality.

Welding flange connection

Principle: The butt welding flange is connected to the pipeline by butt welding, and then the two butt welding flanges are connected together by bolts and gaskets. This connection method makes the connection between the flange and the pipeline more secure, and the weld strength is higher.

Scope of application: Mainly used for high temperature, high pressure, large-diameter pipeline systems, as well as occasions with extremely high requirements for pipeline connection strength and sealing. Such as high-pressure steam pipelines and large crude oil pipelines in the petrochemical industry.

Features: Strong connection, good sealing performance, able to adapt to harsh working environments. But strict requirements are placed on welding quality, and the coaxiality and perpendicularity of the flange need to be ensured during installation, otherwise it will affect the sealing effect.

3、 Threaded connection

Cylindrical pipe threaded connection

Principle: Cylindrical pipe thread is a type of thread with a certain taper. When connecting, threaded fittings (such as pipe joints, valves, etc.) are screwed onto the threaded part of the pipeline, and the connection and sealing are achieved through a tight fit between the threads. Generally, it is necessary to wrap sealing materials (such as polytetrafluoroethylene tape) around the threads to enhance the sealing effect.

Scope of application: Commonly used in low-pressure, small-diameter (generally less than DN100) pipeline systems, such as household water supply and drainage pipelines and some instrument pipelines.

Features: Simple and convenient connection, no need for special tools, easy to install and disassemble. However, the sealing performance is relatively poor and can only be used for low-pressure pipeline systems, and threaded connections may become loose and leak in environments with frequent vibrations.

Conical pipe threaded connection

Principle: The thread of a conical tube has its own sealing properties, and the taper of its thread can tightly fit between the threads during the tightening process, thereby achieving sealing. When connecting, the fittings with conical pipe threads are also screwed onto the threaded part of the pipeline.

Scope of application: Suitable for low-pressure pipeline systems that transport media such as water and gas, especially in situations where slightly higher sealing requirements are needed, such as partial connections of indoor gas pipelines.

Characteristics: Compared to cylindrical pipe threaded connections, conical pipe threaded connections have better sealing performance. However, high precision is required for the machining of threads, and it is necessary to control the appropriate force when tightening, otherwise it may damage the threads or cause poor sealing.

4、 Socket connection

Rigid socket connection

Principle: Rigid socket connection is to insert one end of a pipeline into the socket of another pipeline, and then fill the sealing material (such as cement, asbestos cement, etc.) between the socket and the plug to achieve connection and sealing. The filled sealing material can withstand a certain pressure after curing to prevent medium leakage.

Scope of application: Commonly used for connecting brittle materials such as cast iron pipes and ceramic pipes, and has applications in water supply and drainage systems and some chemical corrosion-resistant pipeline systems. For example, in the installation of cast iron pipes for urban water supply and drainage, rigid socket connections are a common method.

Features: Simple connection method and low cost. But this connection method belongs to rigid connection and cannot withstand large axial displacement and deformation. Once the pipeline foundation settles or the pipeline is impacted by external forces, it is easy to cause damage to the connection.

Flexible socket connection

Principle: Flexible socket connection is similar to rigid socket connection, which involves inserting one end of a pipeline into the socket of another pipeline, but with differences in the selection of sealing materials and connection structure. Flexible socket connections use elastic sealing materials such as rubber sealing rings, which can adapt to the axial displacement and deformation of pipelines to a certain extent, and play a good sealing role.

Scope of application: Suitable for connecting pipes of various materials, especially in situations where the expansion and seismic resistance of pipes need to be considered. For example, in the indoor drainage pipeline system of buildings, flexible socket connections are often used to adapt to the settlement of buildings and the thermal expansion and contraction of pipelines.

Characteristics: It has good seismic resistance and scalability, which can effectively prevent leakage caused by pipeline deformation. But the quality and installation requirements for sealing materials are high, and the service life of sealing materials may affect the long-term stability of pipeline connections.