Valve End Connection Types: Flanged, BW, SW, Threaded & Wafer

A valve with incompatible end connections cannot be installed — and discovering this after procurement causes costly delays. End connection selection is determined by pressure class, pipe bore, process fluid, installation requirements (removability vs permanent), and applicable piping standard. This guide covers every common valve end connection type in industrial piping systems.

Raised Face (RF) Flanged End

The raised face (RF) is the most common flange facing in industrial piping. The gasket bearing surface is raised above the bolt circle face — typically 1.6 mm (1/16") for Class 150 and Class 300, and 6.4 mm (1/4") for Class 400 and above. The raised face concentrates the bolt load on the gasket, improving sealing efficiency. RF flanges are used with full-face or spiral-wound (SW) or ring-joint gaskets. For Class 150 and 300, SW gaskets with inner and outer rings are standard. RF flanged valves are specified per ASME B16.5 (NPS ½ to NPS 24) or ASME B16.47 (NPS 26 to NPS 60, Series A and B).

Ring-Type Joint (RTJ) Flanged End

Ring-Type Joint (RTJ) flanges have a machined groove in the face that accepts a solid metallic ring gasket (oval or octagonal cross-section). The ring gasket (API R, RX, or BX type) is plastically deformed by the bolt load into the groove, creating a metal-to-metal seal. RTJ is required for Class 600 and above in hydrocarbon and high-temperature service, and mandatory for Class 900 and above per ASME B31.3 and most refinery piping specifications. The hard-faced flange groove prevents repeated re-use without refacing — RTJ flanges must be inspected for groove damage before reassembly. Ring gasket material: soft iron (Class 150–600), low-carbon steel (Class 600–1500), or SS 316 (Class 600–2500 corrosive service).

ASME B16.5 vs ASME B16.47 — Flange Standard Selection

ASME B16.5 covers pipe flanges and flanged fittings from NPS ½ through NPS 24, pressure Classes 150 through 2500. It specifies bore dimensions, pressure-temperature ratings, bolt circle dimensions, and facing requirements. ASME B16.47 covers large-diameter flanges from NPS 26 through NPS 60 in two series: Series A (formerly API 605, typically used in refinery and process piping) and Series B (formerly MSS SP-44, typically used in pipeline applications). The two series have different bolt circle and bolt hole dimensions — a Series A flange is not interchangeable with a Series B flange at the same NPS. Always specify the series when ordering large-bore flanged valves.

Butt Weld (BW) End Connection

Butt weld (BW) end valves have bevelled ends that are welded directly to the pipe. The weld eliminates the flange joint — the single greatest source of external leakage in piping systems. BW end valves are specified when: zero external leakage is required (toxic or expensive fluids), high-pressure/temperature makes flange joints impractical, pigging operations require smooth bore, or underground installation prevents maintenance access to flanged joints. BW end valve bores must match the pipe bore — Schedule designation (Sch 40, Sch 80, Sch 160, etc.) must be specified when ordering. Per ASME B16.25, the bevel angle is 37.5° for wall thickness up to 22 mm, and compound bevel for thicker walls. BW valve inspection per API 6D requires radiographic (RT) or UT examination of welds.

Socket Weld (SW) End Connection

Socket weld (SW) ends are used for small-bore piping (NPS ½ through NPS 2, occasionally to NPS 4). The pipe is inserted into a socket in the valve body and a fillet weld is applied around the outside. SW joints provide better alignment than threaded joints and are less susceptible to vibration loosening. However, the crevice between the pipe end and socket is a corrosion trap — SW is not recommended for severely corrosive or high-purity service where crevice corrosion or product contamination is a concern. Socket weld fittings and valve ends are specified per ASME B16.11 (forged fittings, socket weld and threaded).

Threaded (NPT and BSP) End Connections

Threaded end valves are used for small-bore, low-pressure utility applications (NPS ½ to NPS 2). NPT (National Pipe Taper, ASME B1.20.1) is the North American standard: the taper (1:16 or 3/4" per foot) creates a mechanical seal when the male and female threads are engaged with thread sealant (PTFE tape or pipe dope). BSP (British Standard Pipe, ISO 7-1) is used in Europe, the Middle East, and Asia — BSP Parallel (BSPP/G thread) requires a face seal with gasket; BSP Taper (BSPT/R thread) is self-sealing like NPT. Specify the thread standard explicitly — NPT and BSPT have the same taper but different thread forms and are not interchangeable. Threaded joints should not be used above Class 2000 or in vibration-intensive service without locking compound.

Wafer, Lug, and Double-Flanged Butterfly Valves

Butterfly valve body styles determine installation flexibility. Wafer (centerline) style: the valve body fits between two flanges in the pipeline, clamped by through-bolts or stud bolts. Lightest and cheapest — but cannot be used as an end-of-line valve without a blind flange; pipeline must be fully supported when the valve is removed. Lug style (single-flanged): has threaded bolt holes on both sides — can be used as an end-of-line valve; one side of piping can be removed while the valve remains bolted to the other side. Double-flanged (wafer-flanged): has integral flanges on both sides — heaviest and most expensive, but fully self-supporting and suitable for Class 600 and above; required for large-bore (> DN 600) and high-pressure service.

End Connection Selection Summary