Valve End Connection Types: Flanged, Threaded, Butt Weld, and Socket Weld

Valve end connections determine how the valve integrates into the piping system. Each connection type has specific applications, pressure limitations, and installation requirements.

Flanged End Connections

Flanged valves are the most common end connection type in process plants. Bolted flanges allow valve removal for maintenance without cutting the pipeline.

• Raised face (RF): Standard facing for most services; compatible with spiral wound gaskets

• Ring type joint (RTJ): Metal ring gasket for high pressure and high temperature service

• Flat face (FF): Required when connecting to cast iron flanges to prevent bending

• Pressure classes: ASME Class 150 through Class 2500; PN 6 through PN 400

Butt Weld End Connections

Butt weld ends provide a full-penetration weld joint between valve and pipe. This creates a smooth bore, minimizes turbulence, and is the most leak-free connection type for permanent installations.

• Schedule match: Valve bore schedule must match pipe schedule for proper weld prep

• Bevel dimensions: Per ASME B16.25 for standard bevel preparations

• PWHT: Required on higher alloy materials; affects valve seat and packing

• Access: Valve cannot be removed without cutting welds; consider flange option for maintainability

Socket Weld End Connections

Socket weld valves accept pipe inserted into a socket and fillet welded on the outside. They are limited to smaller sizes (NPS 2 and below) and lower pressure classes.

• Size limit: NPS 2 maximum per most standards; NPS 3 in some specifications

• 1.5 mm gap: Pipe must not bottom out in socket; gap allows for thermal expansion

• Crevice corrosion: Socket interior is a potential crevice; avoid in corrosive or hygienic service

• Radiography: Socket welds cannot be radiographed; rely on visual and MT examination

Threaded End Connections

Threaded valves use NPT (tapered) or BSPT threads for small diameter utility services. They are convenient for installation but susceptible to leakage and stress corrosion cracking in demanding service.

• NPT: American National Pipe Taper; most common in North America

• BSPT: British Standard Pipe Taper; used in European and Asian projects

• Seal tape or compound: PTFE tape or anaerobic sealant required for leakproof assembly

• Limitations: Maximum NPS 2; avoid in vibrating, cyclic, or critical service above Class 600