25.08.2026
In industrial piping design, how a valve connects to the line is just as critical an engineering decision as the valve body itself. Choosing the wrong connection type can lead to installation difficulties, vibration-related leaks, and lost time during maintenance. The two most common mechanical connection methods in industry are flanged and threaded (screwed) connections.
Features and Advantages of Threaded Valve Connections
Threaded valves are installed by screwing directly onto the pipe using internal or external threads (to NPT or BSP standards):
- Practical for Small Diameters: Offers an economical, fast installation solution on small-diameter lines, generally 2 inches (DN50) and below.
- Low Cost: Since no extra flanges, bolts, or nuts are required, initial investment and installation labor costs are low.
- Compact Design: Fits easily into tight mechanical spaces where there is no room for flange projections.
- Limitations: At larger diameters, thread-cutting becomes difficult, torque transfer weakens, and in lines with vibration the sealing compound/PTFE tape can wear, creating a leak risk.
Features and Advantages of Flanged Valve Connections
A flanged connection secures the valve body's integrated flanges to mating flanges welded onto the pipe end, using a gasket and a bolt-and-nut set:
- High Pressure and Temperature Resistance: Flanges manufactured to DIN and ANSI standards provide excellent sealing and strength on high-pressure lines.
- Suitable for Large Pipe Diameters: The standard, reliable mechanical solution for all large lines DN50 and above.
- Easy Maintenance and Removal: Once flange bolts are removed, the valve can be taken out of the line axially without cutting or rotating the pipe, speeding up periodic valve repair and overhaul.
- Mechanical Stability: Far more resistant to pipe flexing, vibration, and thermal expansion than threaded connections.
Selection Criteria: Which Connection for Which Situation?
The following general engineering guidelines apply when choosing a connection type:
- Below DN50 and Low Pressure: Threaded connections are sufficient and economical for auxiliary lines, air lines, or low-pressure water systems.
- Above DN50 or Hazardous Fluids: In oil refineries, power plants, chemical, and LPG facilities, flanged valves should be used without exception for safety and serviceability.
- Points Requiring Frequent Maintenance: Equipment such as strainers and ball valves that need regular cleaning and disc inspection benefit greatly from the operational ease of a flanged connection.
Frequently Asked Questions
Why aren't threaded valves used on large-diameter industrial pipelines?
As pipe diameter increases, thread strength decreases, the tightening torque required during installation rises sharply, and guaranteeing sealing becomes practically impossible.
What is the biggest maintenance advantage of flanged valves?
Flanged valves can be removed from the line simply by loosening the bolts, without cutting the pipe or rotating adjacent piping, making it easy to send them for workshop overhaul.