Valves are usually connected to pipelines in various ways such as threads, flanges, welding, clamps, and sleeve clamps. So, how should we choose in the selection process?     

What are the connection methods between valves and pipelines?    

1. Threaded connection

Threaded connection refers to the form of connecting the interface of the valve with internal or external threads at both ends and the pipeline. Usually, ball valves under 4 inches and globe valves, gate valves, and check valves under 2 inches are often connected with threads. The threaded connection structure is relatively simple, lightweight, and easy to install, disassemble, maintain, and replace. Due to the influence of environmental temperature and medium temperature on the expansion of valves during use, the expansion coefficients of the two materials at the connection end should be fully considered to ensure good sealing. Threaded connections may have large leakage channels, so sealants, sealing tapes, or fillers can be used to block these channels to increase sealing performance. If the process and valve body materials can be welded, the threaded connection can also be sealed, and the sealing performance will be better.    

2. Flange connection

Flange connection is the most common connection method in valves. Installation and disassembly are both very convenient, and the flange connection seal is reliable. It is more common in high-pressure and large-diameter valves. However, the flange end is heavy and the cost is relatively high. Moreover, when the temperature exceeds 350 ℃, the creep relaxation of bolts, gaskets, and flanges will significantly reduce the load on the bolts, which may cause leakage in flange connections under high stress and is not suitable for use.    

3. Welding connection

Welding connections usually have two structural forms: socket welding and butt welding. Generally speaking, socket welding is used for low-pressure valves. The welding structure of socket welding valves is simple to process and the welding installation is also relatively convenient; Butt welding connections are used for high-pressure valves, which have a high cost. Welding requires beveling according to pipeline standards, which is difficult to process and the welding installation process is also complex. In some processes, radiographic non-destructive testing is also required for the connection welding. When the temperature exceeds 350 ℃, the creep relaxation of bolts, gaskets, and flanges will significantly reduce the load on the bolts, which may cause leakage in flange connections under high stress.    

4. Clamp connection

The clamp connection structure is similar to a flange, but it is lightweight and cost-effective, commonly used in sanitary pipelines and devices. Sanitary grade pipelines need to be cleaned, and it is strictly prohibited for residue to produce bacteria. Therefore, flange connections and threaded connections are not suitable, and welding connections are difficult to install and disassemble. Therefore, clamp connections are a common connection method in sanitary grade pipelines.