A Complete Guide to Steel Flanges

Explore our comprehensive guide to steel flanges, which will help you gain a deep understanding of what a steel flange is and how to choose the right one for your application needs.

Steel flanges are typically attached to other pipe fittings using welding attachments and are sealed to other flanges with bolts and gaskets. These components play a crucial role 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 serving an important function across multiple industries.

It's essential to ensure that pipes are connected safely to prevent leaks in the piping system. Flanges maintain accurate connections and help the system operate safely for a longer 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 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 covers NPS ½ to NPS 24 metric inches, including pressure-temperature ratings, dimensions, tolerances, materials, sizes, marking, testing, and flange opening methods.

Flange class ratings include 150, 300, 400, 600, 900, 1500, and 2500, available in sizes from NPS ½ to NPS 24 metric inches. Class 2500 flanges are available up to NPS 12 in both metric and U.S. units, with bolt diameters and hole sizes specified in inches.

ASME B16.5 flanges are made from forged or cast materials. Blind flanges and certain reducing flanges can be fabricated from forged, cast, or plate materials. This standard also includes requirements for bolting, gaskets, and flange 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
  • More durable than slip-on flanges under stress
Slip On Flanges Slip On Flanges
  • This pipe flange slips over the pipe
  • Lower price compared to weld neck flanges
  • Manufactured with an ID slightly larger than the pipe’s OD
Socket Weld Flanges Socket Weld Flanges
  • Features a female socket where the pipe is inserted
  • Fillet welding is done from the outside diameter of the pipe
  • Similar to slip-on flanges but with a bore and counter bore dimension
  • Counter bore is larger than the pipe's outer diameter
  • Suitable for pipes with a nominal diameter of 150 or less
Lap Joint Flanges Lap Joint Flanges
  • Used on piping systems with lapped pipe (lap joint stub ends)
  • Composed of two parts: a stub end and a loose backing flange
  • Similar to a slip-on flange but with a radius where the flange face and bore meet
Threaded Flange Threaded Flange
  • Also known as screwed flange
  • Has threads within the flange bore that match the pipe's male thread
  • Used in utility services like air and water
  • Similar to a 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 liquids or gases in pipelines
Long Welding Neck Flange Long Welding Neck Flange
  • Has a very long neck
  • Features a tapered neck and a bevel end
  • Has 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, considering several pressure and temperature ratings. There are seven classes: 150, 300, 400, 600, 900, 1500, and 2500. Reducing weld neck flanges can operate at these pressure ratings. The pressure rating specifies the maximum allowable pressure at a given temperature. For example, a class 2500 flange can withstand higher pressure and is heavier than a class 1500 flange. A class 2500 flange indicates it is suitable for use at this rated temperature without cracking or damage.

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 crucial for many industries, as it provides fastening for piping systems. These flanges are usually manufactured in standard sizes from ½” to 24”.

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

Flange standardization ensures safety and uniformity across the broad range of global industries, enabling 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 46.73 122.13 138.8 178.57 218.25 282.85 352.29

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