Flange Types

Complete Guide to Pipe Flange Styles per ASME B16.5

Pipe flanges come in several standard types, each designed for specific connection methods, pressure ranges, and applications. The flange type determines how it connects to the pipe (welded, threaded, or bolted over a stub end) and influences the strength, cost, and ease of installation of the joint.

All standard flange types below are manufactured per ASME B16.5 (NPS 1/2 through 24) and ASME B16.47 (NPS 26 through 60), unless otherwise noted.

Weld Neck Flanges

Long tapered hub with butt-weld connection. The strongest and most common flange type, ideal for high-pressure and high-temperature service.

Slip-On Flanges

Pipe slides through the bore and is fillet welded on both sides. Cost-effective option for low to moderate pressure systems.

Blind Flanges

Solid disc with no bore, used to blank off pipe ends, nozzles, or valves. Handles the highest mechanical stress of any flange type.

Socket Weld Flanges

Counterbored socket receives the pipe end with a single fillet weld. Primarily used for small-bore, high-pressure piping.

Threaded Flanges

Female NPT thread in the bore — no welding required. Used for low-pressure utility services and where welding is not permitted.

Lap Joint Flanges

Free-rotating flange ring used with a stub end fitting. Allows easy bolt hole alignment and cost savings on exotic materials.

Orifice Flanges

Specialized flanges with pressure tap holes for mounting orifice plates in flow measurement applications. Per ASME B16.36.

Ring Joint Flanges

RTJ facing with precision-machined groove for metallic ring gaskets. Metal-to-metal seal for high-pressure and critical service.

How to Choose the Right Flange Type

The correct flange type depends on several factors: system pressure and temperature, pipe size, whether welding is available on-site, how often the joint needs to be disassembled, and the process fluid. In general:

  • Weld neck is the default choice for critical, high-pressure, or high-temperature service.
  • Slip-on is preferred when cost matters and pressures are moderate.
  • Blind is used wherever a line needs to be sealed off.
  • Socket weld and threaded are for small-bore connections, with socket weld preferred where vibration is present.
  • Lap joint saves cost on exotic materials and simplifies alignment.
  • Orifice is purpose-built for flow measurement.
  • RTJ facing is specified for zero-leakage requirements in high-pressure systems.

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