We explain weld neck, slip-on, blind, socket weld, threaded, lap joint and orifice flanges — their construction, facing types (RF/FF/RTJ), pressure classes and selection criteria.

📦 Our Flange Products → — weld neck, slip-on, blind and more to ASME B16.5 / B16.47 and EN 1092-1, in pressure classes 150#–2500#.

What Is a Flange?

A flange is a disc-shaped fitting that connects pipes, valves, pumps and equipment in a bolted, demountable way. Two flanges are tightened together with bolts and a gasket in between. Choosing the right flange type is critical for pressure, temperature, dismantling frequency and cost.

The 7 Main Flange Types (ASME B16.5)

1. Weld Neck (WN)

Its tapered hub is butt-welded to the pipe. Because it transfers stress gradually into the pipe, it is the most reliable type under high pressure, high temperature and cyclic loading. The standard for critical process lines.

2. Slip-On (SO)

Slides over the pipe and is fixed with an inside and outside fillet weld. Cheaper than weld neck and easy to fit; common on low-to-medium pressure lines.

3. Blind

A solid disc with no bore; it closes off the end of a line or vessel. Used at closure points that can be opened for maintenance.

4. Socket Weld (SW)

The pipe is inserted into the flange socket and fillet welded. Preferred on small-bore (usually ≤2"), high-pressure lines.

5. Threaded (Screwed)

Has a threaded bore; requires no welding. Used where welding is risky (flammable environments) or on small-bore, low-pressure lines.

6. Lap Joint (LJ)

Used together with a stub end; the flange rotates freely. It eases bolt-hole alignment on frequently dismantled lines and lets the flange be a cheaper material than the (expensive alloy) pipe.

7. Orifice

A special flange pair that carries an orifice plate for flow measurement; includes pressure tappings.

Facing Types

Face	Description	Use
RF (Raised Face)	Raised gasket surface	Most common; general process
FF (Flat Face)	Flat surface	Cast-body equipment, low pressure
RTJ (Ring Type Joint)	Metallic ring groove	High pressure/temperature (oil & gas)

RTJ faces use a metallic ring gasket. For standard and dimension detail, see our ASME B16.5 standard guide.

Pressure Classes and Standards

ASME B16.5 defines flanges in pressure classes 150#, 300#, 600#, 900#, 1500#, 2500# (½"–24"). Sizes above 24" use ASME B16.47; the European side uses EN 1092-1. For the pressure-temperature relationship use our Pressure Class tool, for dimensions our Flange Dimensions table, and for DN↔NPS conversion the DN-NPS Conversion tool.

Material Selection

A105 — forged carbon steel (general purpose)
A182 F304/F316 — stainless/alloy (corrosive service)
A350 LF2 — low-temperature service

How to Choose the Right Flange

Pressure/temperature → class (150#–2500#) and type (weld neck + RTJ if high)
Dismantling frequency → lap joint or blind if frequent
Diameter → small bore + high pressure: socket weld / threaded
Material → carbon / stainless / low-temperature per service

Flange Supply from Aktif Çelik

At Aktif Çelik we supply our flange products to ASME B16.5/B16.47 and EN 1092-1, in all types and pressure classes 150#–2500#, with 3.1 certification — including special designs such as the anchor flange. Our technical team helps you select the right type and material for your project.

Flange Types Guide: The 7 Main Flange Types and How to Choose