Valve End Connection Types: Flanged, Threaded, and Welded Joints

Choosing the right end connection for a valve affects installation cost, leak integrity, and maintenance access. Flanged, threaded, and welded connections each suit specific pressure classes and service conditions.

Flanged Connections

Raised face (RF), flat face (FF), and ring-type joint (RTJ) flanges conform to ASME B16.5 or B16.47. RTJ flanges provide metal-to-metal sealing for high-pressure, high-temperature applications such as wellhead equipment.

RF flanges: general process service up to Class 2500FF flanges: brittle flange materials like cast ironRTJ flanges: HP/HT and sour gas service

Threaded (Screwed) Connections

NPT (tapered pipe thread) per ASME B1.20.1 is common in small-bore, low-pressure utility lines. BSPT and BSPP are prevalent outside North America. Thread sealant or PTFE tape prevents leakage at assembly.

Socket Weld and Butt Weld

Socket weld fittings are used for pipe 2 inch NPS and smaller in high-pressure service. Butt-weld ends require full penetration welds and radiographic examination, making them the preferred choice for hazardous or high-cycle service.

Compression and Proprietary Connections

Compression fittings (Swagelok, Parker CPI) and face seal fittings (Swagelok VCR) serve instrument and analytical lines where frequent disassembly is required. They provide reliable zero-leak performance with proper installation.

Selection Guidance

Match flange rating to pipe class scheduleAvoid threaded connections above Class 600 or in cyclic serviceVerify material compatibility at weld jointsSpecify post-weld heat treatment where required by code