Threaded Flange

A threaded flange, also known as a screwed flange, is a type of pipe flange that connects to a pipe by screwing onto its externally threaded end. Unlike weld neck or slip-on flanges, no welding is required during installation, making it ideal for environments where welding is impractical or prohibited.

How It Works

The threaded flange features an internal thread that matches the external thread on the pipe end. The flange is simply screwed onto the pipe until a secure, pressure-tight connection is achieved. A sealant or thread tape (PTFE) is typically applied to the threads to ensure a leak-free joint. The flange face is then bolted to a mating flange or valve in the conventional manner.

Typical Applications

Threaded flanges are widely used across industries where welding is not feasible or safe:

• Low-pressure piping systems (water, air, gas)
• Hazardous and flammable environments where open-flame welding is prohibited
• Refineries, chemical plants, and petrochemical facilities
• Instrumentation and small-bore piping connections
• Temporary or maintenance piping where quick assembly and disassembly is required

Materials

Threaded flanges are available in the following materials to suit a range of service conditions:

• Carbon Steel — Cost-effective and suitable for general-purpose applications including water, oil, and gas services.
• Stainless Steel 316 — Excellent corrosion resistance, ideal for chemical, marine, and food-grade applications.

Thread Standards

Two internationally recognised thread standards are available:

• NPT (National Pipe Taper) — American standard, tapered thread for a pressure-tight seal.
• BSP (British Standard Pipe) — Widely used in Europe, the Middle East, and Asia-Pacific regions.

Sizes and Pressure Classes

Threaded flanges are available in a size range of 1/2" to 4" nominal pipe size, and in pressure classes from Class 150 to Class 600 in accordance with ASME B16.5. Higher pressure classes provide greater wall thickness and bolt-circle dimensions to withstand elevated operating pressures.

Face Types

Two standard face types are offered to match the mating flange or equipment:

• Raised Face (RF) — The most common face type; concentrates bolt load on a smaller gasket area for improved sealing.
• Flat Face (FF) — Used when connecting to cast iron or non-metallic equipment to prevent flange distortion.

Installation Advantages

The threaded flange offers several practical advantages over welded alternatives:

• No welding equipment or certified welders required on-site
• Faster installation and reduced labour costs
• Safe for use in explosive or flammable atmospheres
• Easily removable for maintenance, inspection, or system modifications
• Compliant with ASME B16.5 dimensional and pressure-temperature rating standards