13 Flange Types (ASME B16.5)

Quick Reference

Standard ASME B16.5 flanges: Weld Neck (WN), Long Weld Neck (LWN), Slip-On (SO), Socket Weld (SW), Lap Joint (LJ), Threaded, Blind. Special types: Nipoflange, Weldoflange, Elboflange, Latroflange, Swivel, Expander/Reducer. For larger sizes (NPS 26+), see ASME B16.47 Series A-B.

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Need a printable version? Download the ASME B16.5 Flange Dimensions Chart for all pressure classes (150-2500).

Types of Flanges

Standard Types (ASME)

Welding Neck Flange (“WNF”)

The weld neck flange features a tapered hub that provides stress distribution and reinforcement for high-pressure and high/low-temperature applications. The bore matches the pipe ID for unrestricted flow.

Feature	Description
Connection	Single full-penetration V-shaped butt weld
Bore	Machined to match pipe ID (smooth flow, no turbulence)
Standards	ASME B16.5 (≤24”), B16.47 (>24”)
Applications	High P/T, fluctuating conditions, critical services

Advantages: Strong welded joint; tapered hub reduces stress concentration; allows radiographic inspection; no pressure drops at joint.

Weld neck flange dimensions

Long Welding Neck (“LWNF”)

The Long Welding Neck Flange has an extended neck for additional reinforcement in high-stress applications. Used to connect piping to pressure vessels, boilers, and heat exchangers where clearance for insulation is needed.

Feature	Description
Connection	Butt-weld (same as WNF)
Variants	Heavy Barrel (HB), Equal Barrel (E)
Applications	Vessels, columns, barrels; thermal expansion/contraction zones

Advantages: Better stress distribution along extended neck; handles piping misalignment; resists vibration and thermal cycling.

Slip-On Flange

The slip-on flange slides over the pipe and is connected by two fillet welds (inside and outside). Also called “Hubbed Flanges” due to their slim, compact shape. The bore is larger than the pipe OD to allow insertion.

Feature	Description
Connection	Two fillet welds (inside + outside)
Bore	Larger than pipe OD (pipe slides in)
Applications	Lower P/T, non-critical services (water, HVAC)

Advantages: Lower cost; easier alignment than WNF; suitable for tight spaces.

Limitations: Lower strength than WNF; not for high P/T or fatigue conditions.

Slip-on flange dimensions

Weld Neck vs. Slip-On

Aspect	Weld Neck	Slip-On
Strength	Higher (tapered hub)	Lower
Welds	1 butt weld	2 fillet welds
Cost	Higher	Lower
Connection	Pipes + fittings	Pipes only
Application	High P/T, critical	Low P/T, non-critical

Threaded Flange

The pipe screws directly into the flange (NPT threads per ASME B1.20.1) without welding. Small seal welds may be added for extra strength.

Sizes: Up to 4” typically. Applications: Low P/T utility services (water, air); mandatory in explosive areas where welding is prohibited.

Threaded flange dimensions

Socket Weld Flange

The pipe inserts into the socket and is secured by a single fillet weld on the outside. Per ASME B31.1, insert pipe to bottom of socket, then lift 1.6 mm before welding (allows for weld solidification positioning).

Applications: Small-size, high-pressure piping. Not for corrosive fluids-the gap between pipe end and socket shoulder is prone to crevice corrosion.

Strength: Similar static strength to slip-on, but higher fatigue strength (single weld vs. double).

Socket weld flange dimensions

Lap Joint Flange

Lap joint flanges are always used with a stub end. The flange slips over the pipe and seats on the stub end’s flanged portion; bolts hold the assembly together.

Cost-saving design: Use carbon steel lap joint flange with stainless/nickel alloy stub end-only the stub end (in contact with fluid) needs high-grade material. The flange can rotate freely for easy bolt alignment.

Lap joint flange dimensions

Blind Flange

Blind flanges have no center hole-used to seal pipeline ends, valves, or pressure vessels. Must withstand full system pressure plus bolting forces. Easy to unbolt for pipeline access (also used as pressure vessel manholes).

Blind flange dimensions

Special Types (ASME)

Nipoflange

A Nipoflange creates 90° branch connections-a single forged piece combining a weld neck flange and a Nipolet. Weld the Nipolet portion to the run pipe; bolt the flange to the branch pipe. Available in reinforced variants for higher strength.

Materials: A105, A350, A182 (stainless, duplex), nickel alloys.

Weldoflange

A Weldoflange combines a weld neck flange with a branch fitting-weld directly to the run pipe for a reinforced branch connection. Eliminates separate tee + flange combinations; space-saving for congested areas.

Applications: High P/T branch connections in oil & gas, petrochemical, power generation.

Elboflange

An Elboflange integrates an elbow + flange into one piece-changes flow direction while providing a flanged connection. Reduces fittings and welds; ideal for tight spaces.

Applications: Connecting piping to compressors, reactors, tanks, boilers, turbines where direction change + flange connection is needed.

Latroflange

A Latroflange combines a lateral tee + flange-creates angled branch connections (typically 45°) with a flanged outlet. Reduces turbulence vs. 90° branches; easier equipment attachment.

Applications: Process instrumentation connections, bypass lines, flow distribution systems.

Swivel Flange

Swivel flanges rotate freely on the pipe for bolt hole alignment-required for large-diameter pipelines, subsea/offshore installations, and shallow water pipe works.

Availability: All standard flange shapes (WN, SO, LJ, SW); sizes 3/8” to 60”; Classes 150-2500. Materials: A105, A182 F1/F5/F9/F91, A182 F304/F304L/F316/F316L.

Expanding and Reducing Flanges

Expander flanges increase pipe bore; reducer flanges decrease pipe bore. Both limited to 1-2 size changes maximum-for larger changes, use buttweld reducer + standard flange.

Materials: A105, A350, A182. Faces: RF, FF per ASME B16.5.

Related Device

Spectacle blinds are forged products resembling flanges, used for pipeline isolation.

European Types of Flanges (EN/DIN/ISO)

European flanges follow EN 1092-1 (superseding older DIN standards) with pressure ratings in PN (Pressure Nominale, bars) vs. ASME Class system.

Standard	Flange Types
EN 1092-1	Type 01 (plate), Type 02 (loose plate), Type 05 (blind), Type 11 (weld neck), Type 13 (threaded)
DIN	DIN 2501 (bolt/face dimensions), DIN 2631-2638 (weld neck), DIN 2576 (slip-on)
ISO 7005-1	Mirrors EN 1092-1 for global compatibility

Dimensions: DN 10 to DN 4000. Materials: Carbon steel, stainless steel, alloys.

See also:

• EN 1092 Weld Neck Flange Sizes
• EN 1092 Blind Flange Sizes
• EN 1092 Threaded Flange Sizes
• EN 1092 Plate Flange Sizes

Flange Selection Criteria

Factor	Considerations
Pressure/Temperature	WNF for high P/T; SO for moderate conditions
Fluid properties	Corrosive → stainless/alloy; crevice-sensitive → avoid SW
Assembly/Maintenance	LJ for frequent disassembly; threaded for no-weld zones
Space/Weight	Threaded or SW for compact installations
Cost	SO < WNF; LJ + stub end reduces high-grade material use
Safety	WNF for critical services; verify correct P/T rating
Installation	Threaded where welding prohibited; swivel for alignment
Standards	ASME B16.5/B16.47 (US), EN 1092-1 (Europe)