A Comprehensive Guide to Steel Flanges
When it comes to industrial piping systems, steel flanges play a pivotal role in ensuring safe and efficient operations. These flanges are typically connected to other fittings through welding and sealed using bolts and gaskets. They are essential in a variety of industries, including water supply lines, oil filtration equipment, food processing plants, and pressure vessels.
Over the years, steel flanges have been manufactured in numerous specifications, each playing a crucial role across multiple sectors. Their primary function is to securely connect pipes, preventing leaks and ensuring the system operates smoothly and safely over time.
Table of Contents:
- Steel Flanges Specifications
- Different Types of Flanges
- Steel Pipe Flange Material Grades
- Galvanized Pipe Flange Working Pressure
- Steel Flange Dimension Chart
- WNRF Flange Weight Chart
- Steel Flange Face Types
- Reducing Weld Neck Flange Thickness Chart
- Steel Pipe Flange Torque Chart
- Weld Neck Pipe Flange Bolt Chart
Steel Flanges Specifications:
- Size: 1/2" to 24"
- Face Types: Flat, Raised, RTJ
- WNRF Flange Standards: ASME B16.5
- Pressure Class: 150 to 2500
- Types: Blind, Weld Neck, Socket Weld, Lap Joint, Galvanized, Threaded, Reducing Weld Neck, Slip On
The manufacturing standard for pipe flanges is ASME B16.5, which covers sizes from NPS ½ to NPS 24 metric inches. It includes specifications for pressure-temperature ratings, dimensions, tolerances, materials, and testing methods.
Different Types of Flanges:
Weld Neck Flanges:
- Welded to the pipe end at the neck
- Used in high-pressure applications
- Longer lifespan compared to slip-on flanges under stress
Slip On Flanges:
- Slipped over the pipe
- Lower cost than weld neck flanges
- Manufactured with an ID slightly larger than the pipe's OD
Socket Weld Flanges:
- Possess a female socket for pipe insertion
- Fillet welding is done from the OD of the pipe
- Similar to slip-on flanges but with a bore and counter bore dimension
Lap Joint Flanges:
- Used with lap joint stub ends
- Two components: stub end and a loose backing flange
- Radius where the flange face and bore meet
Threaded Flanges:
- Also known as screwed flanges
- Threaded within the flange bore aligning with the pipe's male thread
- Suitable for utility services like air and water
Blind Flanges:
- Round plate with no center hole and all necessary bolt holes
- Used to close off the ends of a piping system
Orifice Flanges:
- Used with orifice meters
- Measures liquid or gas flow rate in the appropriate pipeline
Long Weld Neck Flanges:
- Long neck with a tapered section and beveled end
- Straight short pipe as the neck of a long weld neck flange
Weldoflange and Nipoflange:
- Combination of a welding neck flange with a Weldolet or Nipolet
Expander and Reducing Flanges:
- Used to increase or decrease the bore size of a pipeline
- Strong alternative to butt weld reducers
Steel Pipe Flange Material Grades:
| Material | Grades | Features |
|----------|--------|----------|
| Carbon Steel | ASTM A105, A350 LF2 | High tensile strength, good corrosion resistance |
| Stainless Steel | 304, 304L, 316, 316L, 317, 317L | Superior corrosion resistance, excellent at high temperatures |
| Alloy Steel | ASTM A182, F5, F9, F11, F22, F91 | High-pressure, high-temperature |
| Duplex | S31803/2205 | Superior corrosion resistance |
| Super Duplex | S32750/2507 | High strength, excellent corrosion resistance |
| Nickel Alloys Flanges | Monel 400, Inconel 600, Alloy 625 | Excellent mechanical properties |
Reducing weld neck flanges have pressure ratings ranging from class 150 to class 2500. ASME defines these classes based on pressure and temperature ratings. The higher the class, the greater the pressure rating. For example, a class 2500 flange can withstand more pressure than a class 1500 flange and is heavier.
Galvanized Pipe Flange Working Pressure:
| Temperature (°C) | (°F) | Pressure (Bar) [psi] |
|------------------|------|-----------------------|
| -482 | 300 | 425.5 [-6167] |
| -572 | 325 | 417.7 [-6054] |
| -617 | 350 | 388.3 [-5628] |
| ... | ... | ... |
Standard size ranges for socket weld and slip on flanges are 1/2" to 24". These sizes are critical for securing piping systems across various industries. Standardization ensures safety and consistency globally, enabling seamless integration across international projects.
Steel Flange Dimension Chart:
| NPS | O.D. (Inch) | SORF Bore Inner Dia (mm) | Bolt Holes No | Holes Dia (mm) | Bolt Circle (Inch) | WNRF Bore Inner Dia (mm) | Dia Hub Base (Inch) | Min WT (mm) | RF Dia (Inch) |
|-----|-------------|---------------------------|---------------|----------------|--------------------|--------------------------|---------------------|-------------|---------------|
| 1/2 | 3.5 | 9.65 | 4 | 15.74 | 2.38 | 22.35 | 15.74 | 1.19 | 1.38 |
| 3/4 | 3.88 | 11.17 | 4 | 15.74 | 2.75 | 27.68 | 20.82 | 1.5 | 1.69 |
| ... | ... | ... | ... | ... | ... | ... | ... | ... | ... |
WNRF Flange Weight Chart:
| NPS | WNRF (KG) | SORF (LBS) | BRF (LBS) | NPT (KG) | LJRF (KG) | SWRF (LBS) |
|-----|-----------|------------|-----------|----------|-----------|------------|
| 1/2 | 0.9 | 1.1 | 1.98 | 0.5 | 0.5 | 1.98 |
| 3/4 | 0.9 | 1.98 | 1.98 | 0.9 | 0.9 | 1.98 |
| ... | ... | ... | ... | ... | ... | ... |
Steel flanges come in various face types such as RF, FF, and RTJ. RF (Raised Face) flanges have a circular sealing face extending from the flange bolting circle plane. They are suitable for a wide range of temperature and pressure ratings, making them ideal for oil, gas, and chemical industries. FF (Flat Face) flanges lack any raised surfaces and use a "full face" gasket. RTJ (Ring-Type Joint) flanges are used in critical applications requiring leak-proof seals under high pressure or temperature conditions.
Reducing Weld Neck Flange Thickness Chart:
| NPS | SCH 20 | SCH 80 | SCH 120 |
|-----|---------|---------|---------|
| 1/2 | – | – | – |
| 1 | – | – | – |
| 3/4 | – | – | – |
| 1 1/4 | – | – | – |
| ... | ... | ... | ... |
Steel Pipe Flange Torque Chart:
| Size (MM) | Size (Inch) | No of Bolt | Bolt Dia | Thread Type | Bolt Stress (lb/in²) | Torque (lbf.ft.) | Torque (Nm) |
|-----------|-------------|------------|----------|-------------|-----------------------|-------------------|--------------|
| 15 | 1/2 | 4 | 1/2" | UNC | 25,000 | 22 | 30 |
| 20 | 3/4 | 4 | 1/2" | UNC | 30,000 | 26 | 36 |
| ... | ... | ... | ... | ... | ... | ... | ... |
Weld Neck Pipe Flange Bolt Chart:
| NPS | Flange Dia | Bolt Holes Dia (MM) | Bolt Circle | Bolts Number | Bolts Dia (MM) |
|-----|------------|----------------------|-------------|--------------|----------------|
| 1/4 | 15.74 | 2 1/4 | 3 3/8 | 4 | 12.7 |
| 1/2 | 15.74 | 2 5/8 | 3 3/4 | 4 | 12.7 |
| ... | ... | ... | ... | ... | ... |
Understanding the specifications, types, and standards of steel flanges is crucial for selecting the right product for specific applications. Whether you're working with low-pressure water pipelines or high-pressure oil filtration systems, choosing the correct flange ensures optimal performance and longevity of your piping infrastructure.
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