For small-diameter valves below DN40, should welding connection or flange connection be used?
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Everyone is welcome to share their opinions actively; it would be best if those opinions are backed by some evidence.
Check the pressure, medium condition, temperature, and so on
For small-diameter pipes, the connection method is ferrule coupling, and welding is of the plug welding type. Flange connections are used for diameters equal to or greater than DN50; however, this decision also depends on various factors of the project (pressure, temperature, medium, installation conditions, process parameters, etc.)
There are all of them; there is no mandatory requirement to use flanges, threads, or welding.
The valve connection method is not related to the diameter; it generally depends on its application scenario. For example, in the primary loop of nuclear power plants, since the fluid flowing through the pipes is at high temperature and pressure and is radioactive, the connection methods used are all welding ； For normal use, the flange type is generally chosen, as it results in lower installation and operation costs.
For RHF, it depends on the actual usage conditions: medium corrosion, frequent use, and various other factors. However, flange connections are generally preferred as they facilitate maintenance. The product quality cannot be guaranteed now.
All I know is that for toxic and hazardous media, as well as high-temperature media, welding is the best option.
Welding is used for low temperatures, toxic, and harmful environments. The remaining flange connections and screw connections are all acceptable. The fire protection pipes are also connected using clamps
Consider the operating conditions of the valve; whenever replacement is feasible, prefer flange connections