A flange is a mechanical component used to connect pipes, valves, pumps, and other equipment in a piping system. It provides an easy means of assembly and disassembly for maintenance, inspection, or modification. A flanged connection typically consists of two mating flanges, a gasket placed between them to ensure a leak-proof seal, and a set of bolts and nuts to clamp the flanges together. Flanges come in various types depending on the application, including weld neck, slip-on, socket weld, threaded, lap joint, blind, and orifice flanges. Each type has specific advantages; for example, weld neck flanges offer high strength and are suitable for high-pressure systems, while slip-on flanges are easier to install but less robust. Flanges are manufactured in accordance with different standards such as ASME/ANSI (like ASME B16.5), DIN, EN, BS, JIS, and GOST, which ensure compatibility and performance across systems. They are available in various materials including carbon steel, stainless steel, alloy steel, and sometimes non-metallic materials like plastic, depending on the fluid type, pressure, and temperature requirements. Pressure ratings (such as 150, 300, 600 class in ANSI standards) help determine the flange’s suitability for different operating conditions. Overall, flanges are critical in industries such as oil and gas, water treatment, chemical processing, and power generation.
A Weld Neck Flange (WN) is a type of flange designed to be welded to a pipe. It is easily recognizable by its long tapered hub that gradually transitions into the thickness of the pipe, providing reinforcement and reducing stress concentration at the base of the flange. This design makes it ideal for high-pressure, high-temperature, and critical service applications, such as in oil & gas, petrochemical, and power plant piping systems. The tapered hub also aids in distributing mechanical stress evenly between the pipe and the flange, improving strength and durability.
| Specification | Details |
|---|---|
| Standard | ASME B16.5 (up to 24")ASME B16.47 (for larger sizes) |
| Nominal Pipe Size (NPS) | 1/2" to 24" for ASME B16.5Larger sizes for ASME B16.47 |
| Outer Diameter (OD) | Varies with size and pressure class, typically larger than other flange types |
| Face Type | Flat Face (FF), Raised Face (RF), Tongue & Groove (T&G) depending on application |
| Bolt Circle Diameter (BCD) | Varies with NPS and pressure class, ensuring compatibility with bolt pattern |
| Number of Bolt Holes | Typically 4 to 12, depending on flange size and bolt circle diameter |
| Pressure Classes | Class 150, Class 300, Class 600, Class 900, Class 1500, Class 2500 |
| Material Types | Carbon Steel: ASTM A105Stainless Steel: ASTM A182 F304, F316Alloy Steel: ASTM A335 P5, P9Special Alloys: Hastelloy, Inconel, etc. |
| Thickness | Varies with size and pressure class, typically thicker for higher classes and larger sizes |
| Welding and Installation | Tapered hub design for full penetration butt weld, welded to pipe (bevel on flange matches pipe bevel) |
| Flange Facing | Flat face (FF), Raised face (RF), or Tongue & Groove (T&G) depending on system requirements |
A Slip-On Flange (SO) is a type of flange that is slipped over the end of a pipe and then welded both inside and outside to provide strength and prevent leakage. Unlike the weld neck flange, it does not have a long hub; instead, it has a low-profile design, which makes it easier to align and install. Slip-on flanges are typically used in low-pressure and low-temperature systems where welding and alignment are simpler and faster, such as in water lines, HVAC systems, and other general industrial applications.
| Specification | Details |
|---|---|
| Standard | ASME B16.5 (for sizes up to 24")ASME B16.47 (for larger sizes) |
| Nominal Pipe Size (NPS) | 1/2" to 24" for ASME B16.5Larger sizes for ASME B16.47 |
| Outer Diameter (OD) | Varies based on NPS and pressure class, typically smaller than Weld Neck flanges |
| Face Type | Flat Face (FF), Raised Face (RF), Tongue & Groove (T&G) depending on application |
| Bolt Circle Diameter (BCD) | Varies with NPS, matching the flange and pipe size |
| Number of Bolt Holes | Typically 4 to 12, depending on the flange size and bolt circle diameter |
| Pressure Classes | Class 150, Class 300, Class 600, Class 900 |
| Material Types | Carbon Steel: ASTM A105Stainless Steel: ASTM A182 F304, F316Alloy Steel: ASTM A335 P5, P9Special Alloys: Hastelloy, Inconel |
| Thickness | Varies with size and pressure class; thinner than Weld Neck flanges |
| Welding | The flange is slipped over the pipe and then welded on the inside and outside to secure the connection |
| Flange Facing | Flat Face (FF), Raised Face (RF), or Tongue & Groove (T&G) depending on the system requirements |
| Installation | Easier to install compared to Weld Neck flanges; requires less precise alignment |
A Socket Weld Flange (SW) is a type of flange used primarily for small-diameter, high-pressure piping systems. It features a recessed socket into which the pipe is inserted. The pipe is then fillet welded around the outer edge of the flange. This design creates a smooth bore and good flow characteristics, making it suitable for applications where internal weld protrusions must be avoided, such as in chemical processing, hydraulic systems, and high-pressure steam lines. Socket weld flanges are easier to install than butt-weld flanges because they do not require a full-penetration weld, but they are still strong and reliable. However, they are generally limited to pipe sizes 2 inches and below due to the practical limitations of the socket weld design. The flange must be properly gapped before welding (typically around 1/16 inch) to allow for thermal expansion and reduce stress on the weld.
| Specification | Details |
|---|---|
| Standard | ASME B16.5 (for sizes up to 24")ASME B16.47 (for larger sizes) |
| Nominal Pipe Size (NPS) | Typically used for small-diameter pipes (1/2" to 2" nominal pipe size) |
| Outer Diameter (OD) | Varies with NPS and pressure class, but typically smaller than other flanges (Slip-On, Weld Neck) |
| Face Type | Flat Face (FF), Raised Face (RF), Tongue & Groove (T&G), depending on application |
| Bolt Circle Diameter (BCD) | Matches the flange size and pressure class |
| Number of Bolt Holes | Typically 4 to 12, depending on flange size and bolt circle diameter |
| Pressure Classes | Class 150, Class 300, Class 600, Class 900 |
| Material Types | Carbon Steel: ASTM A105Stainless Steel: ASTM A182 F304, F316Alloy Steel: ASTM A335 P5, P9Special Alloys: Hastelloy, Inconel |
| Thickness | Varies by NPS and pressure class; typically thicker than Slip-On Flanges |
| Welding | The pipe is inserted into the socket of the flange, then a fillet weld is applied around the edge |
| Flange Facing | Flat Face (FF), Raised Face (RF), Tongue & Groove (T&G) depending on system requirements |
| Installation | Easier to install than butt-welded flanges; requires less pipe preparation since the pipe is simply inserted into the socket before welding |
A Threaded Flange—also known as a Screwed Flange (TH or SCRD)—is a type of flange that has internal threads machined into the bore, allowing it to be screwed onto a pipe without welding. This makes it especially useful in applications where welding is not feasible, such as in systems carrying flammable gases or liquids, where welding could pose a hazard, or in temporary installations that may need to be disassembled easily. Threaded flanges are commonly used in low-pressure, low-temperature systems, and are typically limited to pipe sizes of 4 inches or smaller. While they are easy to install and remove, they are not suitable for applications involving high stress, vibration, or temperature fluctuations, as the threaded connection can loosen over time.
| Specification | Details |
|---|---|
| Standard | ASME B16.5 (for sizes up to 24")ASME B16.47 (for larger sizes) |
| Nominal Pipe Size (NPS) | Typically used for small-diameter pipes (1/2" to 4" nominal pipe size) |
| Outer Diameter (OD) | Varies depending on the NPS and pressure class |
| Face Type | Flat Face (FF), Raised Face (RF), Tongue & Groove (T&G) depending on application |
| Bolt Circle Diameter (BCD) | Matches the flange size and pressure class |
| Number of Bolt Holes | Typically 4 to 12, depending on flange size and bolt circle diameter |
| Pressure Classes | Class 150, Class 300, Class 600 |
| Material Types | Carbon Steel: ASTM A105Stainless Steel: ASTM A182 F304, F316Alloy Steel: ASTM A335 P5, P9Special Alloys: Hastelloy, Inconel |
| Thickness | Varies by NPS and pressure class, generally thinner than Weld Neck or Socket Weld Flanges |
| Welding | No welding required; flange is screwed onto the pipe with internal threads |
| Flange Facing | Flat Face (FF), Raised Face (RF), Tongue & Groove (T&G) depending on the system requirements |
| Installation | Easy to install since it is screwed onto the pipe without the need for welding, ideal for temporary or non-weldable systems |
| Ideal Use | Suitable for low-pressure systems or environments where welding is impractical (e.g., hazardous or flammable gases) |
A Lap Joint Flange (LJ) is a two-piece flange assembly used in conjunction with a stub end (or lap joint stub end) that is butt-welded to the pipe. The flange itself is not welded or fixed to the pipe but instead slides over the stub end, allowing it to rotate freely. This feature makes it much easier to align bolt holes during installation, especially in large or difficult-to-reach piping systems. Lap joint flanges are particularly useful in systems where frequent disassembly or alignment adjustments are needed, such as in food processing, chemical plants, and systems with corrosive or high-purity fluids. Since the flange does not come into contact with the fluid (only the stub end does), it can be made from less expensive materials, while the stub end is made from a corrosion-resistant alloy suited to the process media.
| Specification | Details |
|---|---|
| Standard | ASME B16.5 (for sizes up to 24")ASME B16.47 (for larger sizes) |
| Nominal Pipe Size (NPS) | Typically used for pipe sizes from 1/2" to 24" (or larger in special applications) |
| Outer Diameter (OD) | Varies with NPS and pressure class, similar to other flanges |
| Face Type | Flat Face (FF), Raised Face (RF), or Tongue & Groove (T&G) depending on the application |
| Number of Bolt Holes | Typically 4 to 12, depending on the flange size and bolt circle diameter |
| Pressure Classes | Class 150, Class 300, Class 600, Class 900 |
| Material Types | Carbon Steel: ASTM A105Stainless Steel: ASTM A182 F304, F316Alloy Steel: ASTM A335 P5, P9Special Alloys: Hastelloy, Inconel |
| Thickness | Varies by NPS and pressure class; typically thinner than Weld Neck flanges |
| Installation | Slip over the stub end, which is welded to the pipe. The flange does not directly weld to the pipe |
| Flange Facing | Flat Face (FF), Raised Face (RF), Tongue & Groove (T&G) depending on system requirements |
| Welding | The lap joint flange is not welded directly to the pipe. It is welded to a stub end, which is then bolted to the flange. |
| Ideal Use | Ideal for systems requiring frequent disassembly or rotating flanges for proper alignment (e.g., corrosive fluids, high-purity applications) |
A Blind Flange (BL) is a solid, disk-shaped flange used to seal the end of a pipe, valve, or pressure vessel opening. Unlike other flanges, it has no bore (center hole) and is designed to block off flow completely. Blind flanges are essential in systems that may require future expansion, inspection access, or pressure testing without dismantling the entire setup. They are bolted in place like other flanges and often include a gasket to ensure a leak-proof seal. Blind flanges are capable of withstanding high pressure and stress, especially at the center, and are frequently used in industries such as oil & gas, chemical processing, water treatment, and power generation.
| Specification | Details |
|---|---|
| Standard | ASME B16.5 (for sizes up to 24")ASME B16.47 (for larger sizes) |
| Nominal Pipe Size (NPS) | Typically used for sizes from 1/2" to 24", but can be made for larger sizes depending on the system |
| Outer Diameter (OD) | Varies based on NPS and pressure class, generally larger than other flanges due to the solid disc shape |
| Face Type | Flat Face (FF), Raised Face (RF), or Tongue & Groove (T&G) depending on system requirements |
| Number of Bolt Holes | Typically 4 to 12, depending on flange size and bolt circle diameter |
| Pressure Classes | Class 150, Class 300, Class 600, Class 900, Class 1500, Class 2500 |
| Material Types | Carbon Steel: ASTM A105Stainless Steel: ASTM A182 F304, F316Alloy Steel: ASTM A335 P5, P9Special Alloys: Hastelloy, Inconel |
| Thickness | Varies by NPS and pressure class; thicker for higher pressure ratings and larger sizes |
| Installation | Blind flanges are bolted onto the pipe or vessel to close off the system, preventing fluid flow |
| Welding | No welding required for installation. The blind flange is typically bolted to the system with a gasket for sealing |
| Ideal Use | Commonly used for pipe system isolation, pressure testing, or future expansion where flow is temporarily blocked |