A Complete Guide to Steel Flanges

Discover our comprehensive guide on steel flanges, designed to provide you with a deep understanding of what steel flanges are and how they can be selected based on your specific application needs.

Steel flanges are typically connected to other pipe fittings using welding attachments and sealed together using bolts and gaskets. These essential components are widely used in industrial processes, such as in water pipelines, oil filtration machinery, food processing equipment, and pressure vessels, among others.

Over the years, various specifications have been developed for these industrial elements, each playing a crucial role across different sectors.

Ensuring that pipes remain securely connected is vital to prevent leaks in the piping system. Flanges help maintain accurate connections and ensure safe operation over an extended period.

Table of contents

  • Steel Flanges Specification
  • 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 Pipe Flange Torque Chart
  • Weld Neck Pipe Flange Bolt Chart

Steel Flanges Specification

Steel Flanges Size
  • 1/2" to 24"
Flange Face Types
  • Flat
  • Raised
  • RTJ
WNRF Flange Standards
  • ASME B16.5
Steel Pipe Flange Pressure class
  • 150 to 2500
Steel Flanges Types
  • Blind
  • Weld neck
  • Socket weld
  • Lap joint
  • Galvanized pipe flange
  • Threaded
  • Reducing weld neck flange
  • Slip on flanges
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Steel Flanges Specification

Manufacturing standard of pipe flanges is ASME B16.5

This standard includes NPS ½ to NPS 24 metric inches, covering pressure-temperature ratings, dimensions, tolerances, materials, sizes, tolerances, marking, testing, and opening methods of flanges.

The flange class rating includes 150, 300, 400, 600, 900, and 1500, available in sizes from NPS ½ to NPS 24 metric inches. Class 2500 is available up to NPS 12, with bolt diameters and flange bolt holes specified in inch units.

ASME B16.5 flanges are made from forged or cast materials. Blind flanges and certain reducing flanges are fabricated from forged, cast, or plate materials. This standard also includes requirements and recommendations regarding flange bolting, gaskets, and joints.

Different Types of Flanges

Weld Neck Flanges Weld Neck Flanges
  • This type of flange is welded to the pipe ends at the neck
  • Typically butt welded to a pipe
  • Used in high-pressure situations
  • Longer lifespan than slip-on flanges under stress
Slip On Flanges Slip On Flanges
  • This pipe flange slips over the pipe
  • More cost-effective than weld neck flanges
  • Manufactured with an ID slightly larger than the pipe’s OD
Socket Weld Flanges Socket Weld Flanges
  • It has a female socket where the pipe is fitted
  • Fillet welding is done from the OD on the pipe
  • Similar to slip-on flanges, but with a bore and counter-bore dimension
  • Counter-bore is larger than the O.D. of the matching pipe
  • Suitable for pipes with a nominal diameter of 150 or less
Lap Joint Flanges Lap Joint Flanges
  • Used on piping with lapped pipe (lap joint stub ends)
  • Composed of two parts: stub end and a loose backing flange
  • Similar to a slip-on flange, but with a radius at the flange face and bore
Threaded Flange Threaded Flange
  • Also known as screwed flange
  • Has threads within the flange bore that align with the pipe's male thread
  • Used in utility services like air and water
  • Like the Slip-On flange, but with a threaded bore
Blind Flange Blind Flange
  • A blind flange is a round plate with no center hole and all necessary bolt holes
  • Used to close off the ends of a piping system
Orifice Flange Orifice Flange
  • Used with orifice meters
  • Measures the flow rate of liquid or gas in the pipeline
Long Welding Neck Flange Long Welding Neck Flange
  • Features a very long neck
  • Has a tapered neck and a bevel end
  • Includes a straight short pipe as the neck of a long weld neck flange
Weldoflange and Nipoflange Weldoflange and Nipoflange
  • A Welding Neck flange combined with a Weldolet or Nipolet
Expander and Reducing Flange Expander and Reducing Flange
  • Used to increase or decrease the bore size of a pipeline
  • A 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 corrosion resistance
  • 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 flange have pressure rating of class 150 to class 2500

ASME creates the flange class, taking into account there are several pressure and temperature ratings. There are seven classes i.e. 150, 300, 400, 600, 900, 1500 and 2500. And the reducing weld neck flange can be worked at this pressure rating of class. The pressure rating specifies the highest tolerable pressure at a stated temperature. For instance, a class 2500 flange can resist more pressure and it is heavier compared to 1500 flange. Here, the class 2500 flange signifies that the flange is workable at this rated temperature without getting crack or damaged.

Galvanized Pipe Flange Working Pressure

Reducing weld neck flange
Working Pressure Bar [psi]
Temp (°C) (°F) 29 – 38 (-20.2 – 100) 50 -122 100 -212 150 -302 200 -392 250
Class 150 19.6 -284 19.2 -278 17.7 -257 15.8 -229 13.8 -200 12.1
300 51.1 -741 50.1 -723 46.6 -675 45.1 -654 43.8 -635 41.9
400 68.1 -987 66.8 -968 62.1 -900 60.1 -871 58.4 -846 55.9
600 102.1 -1480 100.2 -1452 93.2 -1351 90.2 -1307 87.6 -1270 83.9
900 153.2 -2220 150.4 -2180 139.8 -2026 135.2 -1959 131.4 -1904 125.8
1500 255.3 -3700 250.6 -3632 233 -3377 225.4 -3267 219 -3174 209.7
2500 425.5 -6167 417.7 -6054 388.3 -5628 375.6 -5443 365 -5290 349.5
Temp (°C) (°F) -482 300 -572 325 -617 350 -662 375 -707 400 -752
Class 150 -175 10.2 -148 9.3 -135 8.4 -122 7.4 -107 6.5 -94.2
300 -607 39.8 -577 38.7 -561 37.6 -545 36.4 -528 34.7 -503
400 -810 53.1 -770 51.6 -748 50.1 -726 48.5 -703 46.3 -671
600 -1216 79.6 -1154 77.4 -1122 75.1 -1088 72.7 -1054 69.4 -1006
900 -1823 119.5 -1732 116.1 -1683 112.7 -1633 109.1 -1581 104.2 -1510
1500 -3039 199.1 -2886 193.6 -2806 187.8 -2722 181.8 -2635 173.6 -2516
2500 -5065 331.8 -4809 322.6 -4675 313 -4536 303.1 -4393 289.3 -4193

Standard size range of socket weld and slip on flanges is 1/2″ to 24″

The standard size range for socket weld and slip on flanges is important for various industries as it provides fastening for the piping system. Socket weld and slip on flanges are typically manufactured in the standard size range from ½” to 24”.

Understanding the categorization and differences between flanges across countries is essential for seamless integration and consistency in global projects.

Flange standardization ensures safety and uniformity across a broad range of global industries. It facilitates international trade by providing a common base for fabricators, suppliers, and consumers.

Steel Flange Dimension Chart

Steel Flange
NPS 01/2 03/4 1 1 1/ 2 2 3 4 5 6
O.D.(Inch) 3.5 3.88 4.25 5 6 7.5 9 10 11
SORF Bore Inner Dia (MM) 9.65 11.17 34.54 49.53 61.97 90.67 116.07 143.7 170.68
Bolt Holes No 4 4 4 4 4 4 8 8 8
Holes Dia (MM) 15.74 15.74 15.74 15.74 19.05 19.05 19.05 22.35 22.35
Bolt Circle (Inch) 2.38 2.75 3.12 3.88 4.75 6 7.5 8.5 9.5
WNRF Bore Inner Dia (MM) 22.35 27.68 26.67 40.89 52.57 77.97 102.36 128.2 154.17
Dia Hub Base (Inch) 15.74 20.82 1.94 2.56 3.06 4.25 5.31 6.44 7.56
Min WT (MM) 1.19 1.5 12.7 15.74 17.52 22.35 22.35 22.35 23.87
RF Dia(Inch) 1.38 1.69 2 2.88 3.62 5 6.19 7.31 8.5
NPS 8 10 12 16 18 20 22 24
O.D.(Inch) 13.5 16 19 23.5 25 27.5 29.5 32
SORF Bore Inner Dia (MM) 221.48 276.35 327.15 410.46 461.77 513.08 564.38 615.95
Bolt Holes No 8 12 12 16 16 20 20 20
Holes Dia (MM) 22.35 25.4 25.4 28.44 31.75 31.75 35.05 35.05
Bolt Circle (Inch) 11.75 14.25 17 21.25 22.75 25 27.25 29.5
WNRF Bore Inner Dia (MM) 202.69 254.5 304.8 387.35 438.15 488.95 539.75 590.55
Dia Hub Base (Inch) 9.69 12 14.38 18 19.88 22 24.25 26.12
Min WT (MM) 26.92 28.44 30.22 35.05 38.1 41.14 44.45 45.97
RF Dia(Inch) 10.62 12.75 15 18.5 21 23 25.25 27.25

WNRF Flange Weight Chart

NPS 1/2 3/4 1 1¼ 1½ 2 3 4 5
WNRF (KG) 0.9 0.9 1.4 1.4 1.8 2.7 5.2 7.4 9.5
SORF (LBS) 1.1 1.98 1.98 3.08 3.08 5.07 9.03 13 14.99
BRF (LBS) 1.98 1.98 1.98 3.08 3.96 5.07 9.03 16.97 19.84
NPT (KG) 0.5 0.9 0.9 1.4 1.4 2.3 4.1 5.9 6.8
LJRF (KG) 0.5 0.9 0.9 1.4 1.4 2.3 4.1 5.9 6.8
SWRF (LBS) 1.98 1.98 1.98 3.08 3.08 5.07 9.03 13 14.99
NPS 6 8 12 14 16 18 20 22 24
WNRF (KG) 11.7 18.9 39.6 51.3 63 74.3 88.7 101.3 120.6
SORF (LBS) 18.95 29.76 63.49 89.28 105.16 128.97 163.8 183.64 218.25
BRF (LBS) 26.89 46.73 122.13 138.8 178.57 218.25 282

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