Types of Stainless Steel Flanges – Weld Neck, Slip-On, Blind & How to Choose

Types of Stainless Steel Flanges – Weld Neck, Slip-On, Blind & How to Choose

Flanges are among the most critical components in any industrial piping system. They connect pipes to valves, equipment nozzles, and other fittings; allow for system inspection and maintenance access; and must reliably seal against the full operating pressure and temperature of the process. Choosing the wrong flange type can lead to leaks, premature failure, and costly downtime — which is why understanding the differences between flange types is fundamental for any piping engineer or procurement specialist.

Metinox Overseas manufactures and exports stainless steel flanges in all major types, grades, and pressure classes under ASME B16.5, ASME B16.47, and MSS SP-44 standards. Our full flanges catalogue and stainless steel flanges range cover every requirement. We also manufacture duplex and super duplex flanges and nickel alloy flanges.

The Six Most Common Flange Types Under ASME B16.5

1. Weld Neck Flange

The weld neck flange is the most specified type for high-pressure, high-temperature, and critical service. Its long, tapered hub transitions stress evenly from the flange into the pipe wall, reducing the concentration of stress at the flange-to-pipe junction. The pipe is butt-welded to the flange bore, creating a full-penetration weld with excellent fatigue resistance.

2. Slip-On Flange

The slip-on flange slides over the pipe and is secured with both internal and external fillet welds. It is easier to align and install than a weld neck, requires less precise pipe end preparation, and costs less to manufacture. However, its fatigue resistance is approximately one-third of a weld neck, making it unsuitable for severe cyclic service.

3. Blind Flange

A blind flange is a solid disc used to terminate the end of a pipe, vessel nozzle, or valve. It has no bore and is used to isolate sections of a piping system for maintenance, to cap off unused nozzles, or to facilitate hydrostatic pressure testing. Despite carrying no flow, blind flanges experience high bending stress at their centre under system pressure — their thickness must be carefully sized to ASME B16.5 requirements.

4. Socket Weld Flange

Socket weld flanges have a recessed socket into which the pipe is inserted before a fillet weld secures the joint. A small gap (approximately 1.6mm) is left at the base of the socket to allow for thermal expansion of the pipe. Socket weld flanges offer high pressure ratings for small-bore piping and provide a clean internal bore with minimal turbulence.

5. Threaded Flange

Threaded flanges connect to the pipe via internal threads without welding, making them ideal for locations where welding is impractical or hazardous — such as near explosive gases. They are limited to smaller pipe sizes and lower pressure classes and should not be used in cyclic or high-vibration service.

6. Lap Joint Flange

Lap joint flanges are used with stub ends — the pipe stub end is butt-welded to the pipe, and the backing flange slides freely over the pipe. Because the flange does not contact the process fluid, an inexpensive carbon steel backing flange can be used even with stainless or alloy stub ends, reducing material cost. The rotating flange also makes bolt-hole alignment much easier.

Flange Face Types

Beyond the flange type, the face (sealing surface) must also be specified:

• Raised Face (RF): The most common face type. The gasket seats on a raised surface, allowing higher bolt loads to be concentrated on a smaller seating area.
• Flat Face (FF): Used where the mating flange is cast iron or other brittle material. The full face gasket distributes the bolt load more evenly.
• Ring Type Joint (RTJ): A machined groove accepts a metallic ring gasket — the highest-integrity seal, specified for high-pressure, high-temperature, and sour service.

Selecting Flange Material and Grade

Metinox supplies flanges across all major stainless steel, duplex, and nickel alloy grades:

• SS 304 Flanges
• SS 316 Flanges
• SS 321 Flanges
• SS 347 Flanges
• SS 904L Flanges
• Duplex 2205 Flanges
• Inconel 625 Flanges
• Hastelloy C276 Flanges
• Monel 400 Flanges
• Alloy 20 Flanges

Frequently Asked Questions