In this article, we shall explore the different types of flanges. We shall see their schematic diagram and the application they serve. Let’s get going
Pipe fittings come in various types to meet diverse service conditions. Engineers consider factors like corrosion resistance, erosion resistance, pressure temperature rating (Class), required welds for attachment, physical size (taking space constraints into account), and cost when selecting flanges.
What are flanges
Flanges, crucial components widely used in pipe installations and machinery, play a vital role in connecting pipes, valves, pumps, and equipment. They are essential for system safety, with various types produced in different sizes and materials tailored to specific needs. Flanges offer flexibility during the maintenance of pipe systems and are commonly made from materials like brass, copper, or iron.
Flange connections involve joining materials through inner and outer lip parts with decking in between. Tightness is ensured with sealing elements, and alignment during bolt tightening is critical for a secure seal. Flanges, threaded or welded, facilitate easy disassembly and reassembly of pipes or components in a piping system.
Types of Flanges
Common types of flange include Welding Neck Flange, Slip-on Flange, Socket Weld Flange, Lap Joint Flange, Threaded Flange, Blind Flange, as well as other variations like male and female, and tongue and groove. Less common designs involve orifice, expander, reducing, and long welding neck flanges.
To connect with their associated piping, flange ends may be screwed, welded, or lapped with metal-to-metal contact, providing versatility in pipe fitting applications.
Weld Neck Flanges
Weld Neck Flanges feature a distinctive long-tapered hub, providing crucial mechanical strength for applications involving high pressure and extreme temperatures. This design resists ‘dishing’ and ‘bowing’ during repeated bending, offering versatility in various scenarios.
Key Features and Benefits
The gradual transition from flange to pipe or fitting wall thickness ensures optimal performance under variable forces. Precise bore matching eliminates flow restrictions, reducing turbulence and erosion. The flanges facilitate a single full penetration V-weld, ensuring durability in severe conditions, such as high-pressure systems.
Advantages and Considerations
These flanges boast excellent stress distribution, unrestricted flow, high cyclical loading capability, and ample space for non-destructive testing on larger-diameter flanges. However, their higher cost is a factor to consider.
Inspection and Standards
Various non-destructive testing (NDT) methods, including ultrasonic and radiographic techniques, ensure weld integrity. ASME standards (B16.5 and B31.3) guide installation, maintenance, and testing processes.
Slip On Flanges
Key Features and Benefits
Slip On Flanges, or ‘hubbed flanges,’ boast a low-profile hub and connect to pipes via one or two fillet welds. The X measure prevents flange face damage during welding, but a drawback is the sequential welding requirement—pipe first, then fitting. The calculated strength is two-thirds that of Welding Neck flanges, and fatigue life is one-third.
Advantages and Considerations
Despite limitations, slip-on flanges are favored for ASME class ≤ 600 applications, offering cost-effectiveness, simplified welding, and reduced pipe preparation. However, they face challenges with two welds, reduced mechanical strength, unsuitability for cyclic loading, and constraints on non-destructive testing.
Inspection and Standards
ASME B16.5 and ASME B31.3 standards govern slip-on flange installation, maintenance, and testing, ensuring adherence to industry benchmarks. Specific non-destructive testing techniques are not mandated, but visual inspections and dye penetrant tests on fillet welds are common practices.
Socket Weld Flanges
Key Features and Benefits:
Socket Weld Flanges, designed for small high-pressure piping, utilize a single fillet weld on the flange’s exterior. Their static strength matches Slip-On flanges, and a 1⁄16th inch (1.5mm) gap accommodates thermal expansion during welding. Suited for non-critical applications up to 2 inches, their simple design provides ease of use.
Advantages and Considerations:
Socket weld flanges offer simplicity and ease of use for small pipe sizes. However, a critical consideration is the required gap before welding, which may lead to corrosion issues in corrosive environments. Their usage is limited to lower pressure classes (≤ ASME 600) with flat or raised faces.
Inspection and Standards:
Inspection methods for socket weld flanges include radiography (impractical), magnetic particle inspection (MPI), and dye penetrant inspection (DPI). ASME standards, like B31.3, mandate a 1⁄16th inch (1.5mm) gap to address thermal expansion. Notably, socket weld flanges are not specified in ASME class 2500 ratings per ASME B16.5.
Lap Joint Flanges
Key Features and Benefits:
Lap Joint Flanges, paired with Stub Ends, lack a raised face and boast a unique design with a radius for Stub End accommodation. Their versatility allows easy swiveling around the pipe, aiding bolt-hole alignment. Cost-effective and suitable for corrosive environments, they require only a single full penetration butt weld. Salvageable for re-use, these flanges excel in systems prone to erosion or corrosion.
Advantages and Considerations:
Lap Joint Flanges offer cost efficiency, single butt weld requirement, and adaptability for frequent disassembly. Ideal for corrosive applications, their bulkier design limits use in small piping. However, their unique features make them suitable for specific scenarios, compensating for their limitations.
Inspection and Standards:
Non-destructive testing methods (MPI, DPI, RT, UT) validate butt weld integrity in Lap Joint Flanges. ASME B16.9 standards define dimensions for stub ends, distinct from ASME B16.5 due to the stub end’s classification as a pipe fitting.
Threaded Flanges
Key Features and Benefits:
Threaded Flanges, known as ‘screwed flanges,’ facilitate pipe connection via a screw thread. Ideal for smaller pipes (≤ 4 inches) and low-pressure, low-temperature applications, they offer weld-free connections crucial in explosive environments. Quick assembly and disassembly enhance efficiency, but limitations arise in high-temperature scenarios due to potential thread distortion and leakage.
Advantages and Considerations:
Threaded flanges excel in scenarios where welding is impractical or hazardous, especially in smaller sizes (≤ 4 inches). Their weld-free design reduces ignition risks in explosive areas and quick assembly benefits efficiency. However, limitations include incompatibility with high-temperature applications, unsuitability for thin-walled pipes, and a higher risk of leakage.
Inspection and Standards:
Non-destructive testing techniques, including radiography, validate threaded flange integrity. ASME B1.20.1 and ASME B31.3 standards outline requirements for these connections. Thicker wall thickness is recommended for threaded pipes in specific conditions, as per the ASME B31.3 Piping Guide.
Blind Flanges
Key Features and Benefits:
Blind Flanges, or ‘closure plate flanges,’ terminate pipes without a bore, suiting various sizes and classes with flat, raised, or ring-type joint faces. Versatile for higher-pressure applications, they efficiently replace butt weld caps for extensions and inspections, offering slip-on or threaded options.
Advantages and Considerations:
Excel in terminating pipes and isolating valves, Blind Flanges handle high stress in larger sizes with bending near the center. Their versatility extends to rod access in drains, allowing drilling for slip-on or tapping for threaded use. Despite the simplicity, their relative expense and the absence of routine inspection should be considered.
Inspection and Standards:
Blind flanges typically lack routine inspection, occasionally measured for thickness. ASME B16.5 standards dictate dimensions and tolerances, ensuring standardized manufacturing and usage practices.
Types of Flange Summary Table
| Flange Type | NPS (inch) | ASME Class | Faces | Joint Integrity | Weld | ASME Standards |
|---|---|---|---|---|---|---|
| Welding Neck Flange | All | All | All | High | One butt weld. | B16.5, B31.3 |
| Slip-on Flange | Many | Generally, ≤ 600 | FF, RF | Medium | One or two fillet welds. | B16.5, B31.3 |
| Socket Weld Flange | Generally, ≤ ½ to 2. Max ≤ 4″ | ≤ 600 | FF, RF | Medium | One fillet weld. | B16.5, B31.3 |
| Lap Joint Ring Flange | Not used for small sizes. | NA | FF | NA | None | B16.5, B31.3 |
| Stub End of Lap Joint Flange | Not used for small sizes. | 150 to 2500 | FF, RF, RTJ | High | One butt weld. | B16.9, B31.3 |
| Threaded Flange | Generally, ≤ ½ to 2. Max ≤ 4″ | ≤ 300 | FF, RF | Low | None | B1.20.1, B31.3 |
| Blind Flange | All | All | All | NA | None | B16.5, B31.3 |
Conclusion
In conclusion, understanding the various types of flanges is crucial for engineers selecting components for pipe systems. Each type offers unique features and benefits, catering to different applications. Factors such as material, design, and connection method play vital roles in determining the suitability of a flange for specific scenarios.
Adherence to industry standards, such as those outlined by ASME, ensures the integrity and safety of flange installations. The versatility of flanges in facilitating easy assembly, disassembly, and maintenance makes them indispensable components in piping systems, contributing to overall system efficiency and safety.
