Threaded Flanges

NPT-Threaded Connection for Non-Welded Piping Assemblies

What Is a Threaded Flange?

A threaded flange, also called a companion flange or screwed flange, contains a female NPT (National Pipe Thread) tapered thread in the bore. The pipe is threaded directly into the flange without welding, making it ideal for applications where welding is impractical or not permitted.

Threaded flanges are designed per ASME B16.5 and are available with or without a hub. They provide a simple, cost-effective connection method for small-bore, low-pressure piping systems.

Key Design Features

  • Female NPT taper thread in bore (per ASME B1.20.1)
  • No welding required for assembly
  • Available with or without a small hub
  • Typically available in raised face (RF) and flat face (FF) facings
  • Can be seal-welded for added leak protection

Common Applications

  • Low-pressure utility services (air, water)
  • Galvanized piping systems (where welding would damage the coating)
  • Installations where welding is not permitted (explosive environments)
  • Temporary or frequently modified piping
  • Reducing connections (threaded reducing flanges)

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Available Sizes and Pressure Classes

Per ASME B16.5, threaded flanges are available in NPS 1/2 through 24, in pressure classes 150 through 2500. They are most commonly used in NPS 1/2 through 4. Larger sizes are less common because threading large-bore pipe is impractical and the joint integrity decreases with size.

Common Materials

  • Carbon Steel (A105) — the most widely used material for general service
  • Stainless Steel (A182 F304/F316) — for corrosion-resistant applications
  • Galvanized Carbon Steel — for water and utility piping where corrosion protection is needed

Threaded vs Socket Weld Flanges

Both threaded and socket weld flanges are designed for small-bore piping, but they differ in key ways. Threaded flanges require no welding, which is an advantage in fire-risk areas and explosive environments. Socket weld flanges provide stronger joints with better fatigue resistance and are preferred for higher-pressure services.

Threaded flanges are more prone to leakage under vibration or thermal cycling because the threaded connection can loosen over time. For critical or high-cycle applications, socket weld flanges are generally the better choice.

Related References