Socket Weld Flanges

Recessed-Bore Connection for Small-Diameter, High-Pressure Piping

What Is a Socket Weld Flange?

A socket weld flange has a recessed (counterbored) area that the pipe inserts into, then a single fillet weld is applied around the outside of the joint. This connection type is primarily used for small-bore piping in sizes NPS 1/2 through 4, though socket weld flanges are available up to NPS 24.

Designed per ASME B16.5, socket weld flanges provide good fatigue resistance for small lines and are a reliable alternative to threaded connections where welding is acceptable.

Key Design Features

  • Counterbored socket receives the pipe end
  • Single fillet weld on the outer edge
  • Pipe must be backed off approximately 1/16" before welding to allow for thermal expansion
  • Bore varies with pipe schedule
  • Available in RF and RTJ facings

Common Applications

  • Small-bore high-pressure piping (instrument lines, sampling systems)
  • Steam lines NPS 2 and smaller
  • Chemical process piping
  • Hydraulic systems
  • Drain and vent connections

Access flange data offline in the field.

Download the Flange Bolt Chart app for instant access to flange dimensions, bolt sizes, and torque values — no internet required.

App Store badge for the Flange Bolt Chart appGet it on Google Play

Available Sizes and Pressure Classes

Under ASME B16.5, socket weld flanges are available in NPS 1/2 through 24 in Classes 150, 300, 600, 900, 1500, and 2500. They are most commonly used in sizes NPS 1/2 through 4.

Socket bore dimensions vary by pipe schedule (Sch 40, 80, 160, etc.), so the correct schedule must be specified when ordering to ensure proper fit with the pipe.

Common Materials

  • Carbon Steel (A105) — the most common material for general-purpose service
  • Stainless Steel (A182 F304/F316) — for corrosion-resistant applications
  • Alloy Steel (A182 F11/F22) — for high-temperature service

Socket Weld vs Threaded Flanges

Both socket weld and threaded flanges are used for small-bore connections, but they differ in joint integrity. Socket weld flanges provide stronger, more leak-resistant joints due to the fillet weld. Threaded flanges allow assembly without welding, which can be advantageous in certain environments.

Socket weld flanges are preferred where vibration or thermal cycling is present, as the welded connection is more resistant to fatigue failure than threads. Threaded flanges are typically chosen for low-pressure utility services or where hot work permits are difficult to obtain.

Related References