Socket Weld Flanges — ASME B16.5

What is a Socket Weld Flange?

A socket weld (SW) flange has a socket machined to receive the pipe end, with a shoulder at the bottom and a smaller bore below it matching the pipe ID. The pipe is inserted, withdrawn about 1.6 mm (1/16″) to leave an expansion gap, and fillet-welded at the hub. The joint is compact and leak-tight without a butt weld, which makes it common on small-bore, high-pressure lines. Because of the crevice between pipe and socket, it is avoided in corrosive or crevice-sensitive services and where full radiography is required.

Key features

• Socket counterbore for the pipe; single external fillet weld
• Bore below the socket matched to pipe schedule
• Raised face standard; RTJ when specified
• Compact and lighter than a weld neck in small sizes
• Pairs with ASME B16.11 socket weld fittings on the same line

Specification

Applications

• Small-bore process and utility lines
• Instrument and sampling connections
• Hydraulic and lube oil systems
• Steam drains and trap stations
• Chemical dosing lines

Socket weld flange vs threaded flange

Both suit small bores. A socket weld flange is welded, so it is leak-tight under vibration and temperature cycles but cannot be dismantled at the pipe joint. A threaded flange needs no welding and is used where hot work is restricted, but threads can leak under cycling and are not recommended for high temperatures. For hydrocarbon and steam lines, socket weld is the more common choice.