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Weld Neck Flange

Weld Neck Flange

A Weld neck flange is a type of flange designed to be welded onto the end of a pipe. It’s distinguished by its long neck, which is beveled to match the bevel on the pipe. The purpose of the neck is to transfer stress from the flange to the pipe, reducing the concentration of stress at the base of the flange. This design helps to prevent cracking and leaking, making weld neck flanges particularly suitable for high-pressure and high-temperature applications.

Weld neck flanges typically have a raised face, which provides a sealing surface when bolted to a mating flange or fitting. They are commonly used in industries such as oil and gas, petrochemical, power generation, and process piping systems where reliable sealing under extreme conditions is essential.

stainless-steel-weld-neck-flange
Stainless Steel Weld Neck Flange
carbon-steel-weld-neck-flange
Carbon Steel Weld Neck Flange

Long Weld Neck Flange (LWN Flange)

A Long Weld Neck Flange (LWN Flange) is a specialized type of flange commonly used in high-pressure and high-temperature piping systems. It is characterized by its long, tapered neck that seamlessly connects to a pipe, providing enhanced structural integrity and reducing stress concentrations in critical applications.

long-weld-neck-flange
Long Weld Neck Flange

Types of Long Weld Neck Flanges:

  • Standard Long Weld Neck: Regular design for general-purpose use.
  • Heavy Wall Long Weld Neck: Extra thickness for added strength in heavy-duty applications.
  • Custom Designs: Tailored to meet specific project requirements.

Benefits:

  • Reduces the risk of leakage due to its strong weld connection.
  • Minimizes stress at the junction of the flange and pipe.
  • Provides a seamless connection for critical applications.

Material

  • Carbon Steel 
    1. ASTM A105, ASTM A350 LF2, ASTM A694
    2. Cost-effective and widely used for general-purpose applications.
  • Stainless Steel
    1. Grades: 304/304L, 316/316L, 904L, Duplex (2205), Super Duplex (2507)
    2. Offers excellent corrosion resistance and durability.
  • Alloy Steel
    1. Grades: ASTM A182 F5, F9, F11, F22, F91
    2. Designed for high-temperature and high-pressure environments.

Weld Neck Flange Dimension

weld-neck-flange-dimension

Class 150 Weld Neck Flange Dimensions

Size in InchSize in mmOuter DiameterFlange ThicknessHub ODWeld Neck ODWelding Neck LengthBoreRF DiameterRF HeightPCDWeld Face
ABCDEFGHIJ
1/215909.63021.34634.9260.31.6
3/42010011.23826.75142.9269.91.6
12511012.74933.45450.8279.41.6
1 1/43211514.35942.25663.5288.91.6
1 1/24012515.96548.36073298.41.6
25015017.57860.36292.12120.71.6
2 1/26518020.7907368104.82139.71.6
38019022.310888.9681272152.41.6
3 1/29021522.3122101.670Welding Neck bore is derived from the pipe schedule139.72177.81.6
410023022.3135114.375157.22190.51.6
512525522.3164141.387185.72215.91.6
615028023.9192168.387215.92241.31.6
820034527246219.1100269.92298.51.6
1025040528.6305273100323.823621.6
1230048530.2365323.81133812431.81.6
1435053533.4400355.6125412.82476.31.6
1640059535457406.4125469.92539.81.6
1845063538.1505457.2138533.42577.91.6
2050070041.3559508143584.226351.6
2460081546.1663610151692.22749.31.6

Class 150 Weld Neck Flange Stud & Bolt Dimensions

Size in InchSize in mmNo of BoltsBolt Size UNCMachine Bolt LengthRF Stud LengthHole SizeISO Stud SizeWeight in kg
1/21541/250555/8M140.6
3/42041/250655/8M140.9
12541/255655/8M141.4
1 1/43241/255705/8M141.4
1 1/24041/265705/8M141.8
25045/870853/4M162.7
2 1/26545/875903/4M163.7
38045/875903/4M164.6
3 1/29085/875903/4M165.5
410085/875903/4M166.8
512583/485957/8M208.7
615083/4851007/8M2010.9
820083/4901107/8M2017.7
10250127/81001151M2424
12300127/81001201M2437
143501211151351 1/8M2750
164001611151351 1/8M2764
18450161 1/81251451 1/4M3068
20500201 1/81401601 1/4M3082
24600201 1/41501701 3/8M33118

Class 300 Weld Neck Flange Dimensions

Size in InchSize in mmOuter DiameterFlange ThicknessHub ODWeld Neck ODWelding Neck LengthBoreRF DiameterRF HeightPCDWeld Face
ABCDEFGHIJ
1/2159512.73821.35134.9266.71.6
3/42011514.34826.75642.9282.61.6
12512515.95433.46050.8288.91.6
1 1/43213517.56442.26463.5298.41.6
1 1/24015519.17048.367732114.31.6
25016520.78460.36892.121271.6
2 1/26519023.91007375104.82149.21.6
3802102711788.9781272168.31.6
3 1/29023028.6133101.679Welding Neck bore is derived from the pipe schedule139.72184.21.6
410025530.2146114.384157.222001.6
512528033.4178141.397185.722351.6
615032035206168.397215.92269.91.6
820038039.7260219.1110269.92330.21.6
1025044546.1321273116323.82387.41.6
1230052049.3375323.81293812450.81.6
1435058552.4425355.6141412.82514.41.6
1640065055.6483406.4144469.92571.51.6
1845071058.8533457157533.42628.61.6
2050077562587508160584.22685.81.6
2460091568.3702610167692.22812.81.6

Class 300 Weld Neck Flange Stud & Bolt Dimensions

Size in InchSize in mmNo of BoltsBolt Size UNCMachine Bolt LengthRF Stud LengthHole SizeISO Stud SizeWeight in kg
1/21541/255655/8M141.4
3/42045/865753/4M161.4
12545/865753/4M161.8
1 1/43245/870853/4M162.3
1 1/24043/475907/8M203.2
25085/875903/4M164.1
2 1/26583/4851007/8M205.5
38083/4901107/8M206.8
3 1/29083/4951107/8M208.2
410083/4951157/8M2011.4
512583/41101207/8M2014.6
6150123/41101207/8M2019.1
8200127/81201401M2431
102501611401601 1/8M2742
12300161 1/81451701 1/4M3064
14350201 1/81601801 1/4M3082
16400201 1/41651901 3/8M33113
18450241 1/41701951 3/8M33145
20500241 1/41852051 3/8M33182
24600241 1/22052301 5/8M39264

 

Class 400 Weld Neck Flange Dimensions as per ASME B16.5

Size in InchSize in mmOuter DiameterFlange ThicknessHub ODWeld Neck ODWelding Neck LengthBoreRF DiameterRF HeightPCDWeld Face
ABCDEFGHIJ
1/2159514.33821.35234.9766.71.6
3/42011515.94826.75742.9782.61.6
12512517.55433.46250.8788.91.6
1 1/43213520.76442.26763.5798.41.6
1 1/24015522.37048.370737114.31.6
25016525.48460.37392.171271.6
2 1/26519028.61007379104.87149.21.6
38021031.811788.9831277168.31.6
3 1/29023035133101.686According to Schedule139.77184.21.6
410025535146114.389157.272001.6
512528038.1178141.3102185.772351.6
615032041.3206168.3103215.97269.91.6
820038047.7260219.1117269.973301.6
1025044554321273124323.87387.41.6
1230052057.2375323.81373817450.81.6
1435058560.4425355.6149412.87514.41.6
1640065063.5483406.4152469.97571.51.6
1845071066.7533457165533.47628.61.6
2050077569.9587508168584.27685.81.6
2460091576.2702610175692.27812.81.6

Class 400 Weld Neck Flange Stud & Bolt Dimesions

Size in InchSize in mmNo of BoltsBolt Size UNCRF Stud LengthHole SizeISO Stud Size
1/21541/2755/8M14
3/42045/8903/4M16
12545/8903/4M16
1 1/43245/8953/4M16
1 1/24043/41107/8M20
25085/81103/4M16
2 1/26583/41207/8M20
38083/41257/8M20
3 1/29087/81401M24
410087/81401M24
512587/81451M24
6150127/81501M24
82001211701 1/8M27
10250161 1/81901 1/4M30
12300161 1/42051 3/8M33
14350201 1/42101 3/8M33
16400201 3/82201 1/2M36
18450241 3/82301 1/2M36
20500241 1/22401 3/4M39
24600241 3/42651 7/8M45

Class 600 Weld Neck Flange Dimensions as per ASME B16.5

Size in InchSize in mmOuter DiameterFlange ThicknessHub ODWeld Neck ODWelding Neck LengthBoreRF DiameterRF HeightPCDWeld Face
ABCDEFGHIJ
1/2159514.33821.352According to Schedule34.9766.71.6
3/42011515.94826.75742.9782.61.6
12512517.55433.46250.8788.91.6
1 1/43213520.76442.26763.5798.41.6
1 1/24015522.37048.370737114.31.6
25016525.48460.37392.171271.6
2 1/26519028.61007379104.87149.21.6
38021031.811788.9831277168.31.6
3 1/29023035133101.686139.77184.21.6
410027538.1152114.3102157.27215.91.6
512533044.5189141.3114185.77266.71.6
615035547.7222168.3117215.97292.11.6
820042055.6273219.1133269.97349.21.6
1025051063.5343273152323.87431.81.6
1230056066.7400323.815638174891.6
1435060569.9432355.6165412.875271.6
1640068576.2495406.4178469.97603.21.6
1845074582.6546457184533.476541.6
2050081588.9610508190584.27723.91.6
24600940101.6718610203692.27838.21.6

Class 600 Weld Neck Flange Stud & Bolt Dimesions

Size in InchSize in mmNo of BoltsBolt Size UNCRF Stud LengthHole SizeISO Stud SizeWeight in kg
1/21541/2755/8M141.5
3/42045/8903/4M161.8
12545/8903/4M161.8
1 1/43245/8953/4M162.7
1 1/24043/41107/8M203.7
25085/81103/4M165.5
2 1/26583/41207/8M208.2
38083/41257/8M2010.5
3 1/29087/81401M2411.8
410087/81451M2419.1
5125811651 1/8M2731
61501211701 1/8M2736
8200121 1/81901 1/4M3055
10250161 1/42151 3/8M3386
12300201 1/42201 3/8M33102
14350201 3/82351 1/2M36127
16400201 1/22551 5/8M39177
18450201 5/82751 3/4M42216
20500241 5/82851 3/4M42268
24600241 7/83302M48377

Class 900 Weld Neck Flange Dimensions as per ASME B16.5

Size in InchSize in mmOuter DiameterFlange ThicknessHub ODWeld Neck ODWelding Neck LengthBoreRF DiameterRF HeightPCDWeld Face
ABCDEFGHIJ
1/21512022.33821.36034.9782.61.6
3/42013025.44426.77042.9788.91.6
12515028.65233.47350.87101.61.6
1 1/43216028.66442.27363.57111.11.6
1 1/24018031.87048.383737123.81.6
25021538.110560.310292.17165.11.6
2 1/26524541.312473105104.87190.51.6
38024038.112788.91021277190.51.6
410029044.5159114.3114157.272351.6
512535050.8190141.3127According to Schedule185.77279.41.6
615038055.6235168.3140215.97317.51.6
820047063.5298219.1162269.97393.71.6
1025054569.9368273184323.87469.91.6
1230061079.4419323.82003817533.41.6
1435064085.8451355.6213412.87558.81.6
1640070588.9508406.4216469.976161.6
18450785101.6565457229533.47685.81.6
20500855108622508248584.27749.31.6
246001040139.7749610292692.27901.71.6

Class 900 Weld Neck Flange Stud & Bolt Dimesions

Size in InchSize in mmNo of BoltsBolt Size UNCRF Stud LengthHole SizeISO Stud SizeWeight in kg
1/21543/41107/8M202.3
3/42043/41157/8M202.7
12547/81251M244.1
1 1/43247/81251M244.6
1 1/240411401 1/8M275.9
25087/81451M2411.5
2 1/265811601 1/8M2716.5
38087/81451M2414
410081 1/81701 1/4M3023
512581 1/41901 3/8M3339.5
6150121 1/81901 1/4M3050
8200121 3/82201 1/2M3680
10250161 3/82351 1/2M36118
12300201 3/82551 1/2M36148
14350201 1/22751 5/8M39182
16400201 5/82851 3/4M42225
18450201 7/83252M48300
205002023502 1/8M52373
24600202 1/24402 5/8M64680

Class 1500 Weld Neck Flange Dimensions as per ASME B16.5

Size in InchSize in mmOuter DiameterFlange ThicknessHub ODWeld Neck ODWelding Neck LengthBoreRF DiameterRF HeightPCDWeld Face
ABCDEFGHIJ
1/21512022.33821.36034.9782.61.6
3/42013025.44426.77042.9788.91.6
12515028.65233.47350.87101.61.6
1 1/43216028.66442.27363.57111.11.6
1 1/24018031.87048.383737123.81.6
25021538.110560.310292.17165.11.6
2 1/26524541.312473105104.87190.51.6
38026547.713388.91171277203.21.6
410031054162114.3124According to Schedule157.27241.31.6
512537573.1197141.3156185.77292.11.6
615039582.6229168.3171215.97317.51.6
820048592.1292219.1213269.97393.71.6
10250585108368273254323.87482.61.6
12300675123.9451323.82833817571.51.6
14350750133.4495355.6298412.876351.6
16400825146.1552406.4311469.97704.81.6
18450915162597457327533.47774.71.6
20500985177.8641508356584.27831.81.6
246001170203.2762610406692.27990.61.6

Class 1500 Weld Neck Flange Stud & Bolt Dimesions

Size in InchSize in mmNo of BoltsBolt Size UNCRF Stud LengthHole SizeISO Stud SizeWeight in kg
1/21543/41107/8M202.3
3/42043/41157/8M202.7
12547/81251M244.1
1 1/43247/81251M244.6
1 1/240411401 1/8M275.9
25087/81451M2411.4
2 1/265811601 1/8M2716.4
38081 1/81801 1/4M3021.8
410081 1/41951 3/8M3333
512581 1/22501 5/8M3959
6150121 3/82601 1/2M3675
8200121 5/82901 3/4M42125
10250121 7/83352M48207
123001623752 1/8M52314
14350162 1/44052 3/8M56427
16400162 1/24452 5/8M64568
18450162 3/44952 7/8M72738
205001635403 1/8M76932
24600163 1/26153 5/8M901511

Class 2500 Weld Neck Flange Dimensions as per ASME B16.5

Size in InchSize in mmOuter DiameterFlange ThicknessHub ODWeld Neck ODWelding Neck LengthBoreRF DiameterRF HeightPCDWeld Face
ABCDEFGHIJ
1/21513530.24321.37334.9788.91.6
3/42014031.85126.77942.9795.21.6
125160355733.48950.871081.6
1 1/43218538.17342.29563.57130.21.6
1 1/24020544.57948.31117371461.6
25023550.99560.3127According to Schedule92.17171.41.6
2 1/26526557.211473143104.87196.81.6
38030566.713388.91681277228.61.6
410035576.2165114.3190157.272731.6
512542092.1203141.3229185.77323.81.6
6150485108235168.3273215.97368.31.6
8200550127305219.1318269.97438.21.6
10250675165.1375273419323.87539.81.6
12300760184.2441323.84643817619.11.6

Class 2500 Weld Neck Flange Stud & Bolt Dimesions

Size in InchSize in mmNo of BoltsBolt Size UNCRF Stud LengthHole SizeISO Stud SizeWeight in kg
1/21543/41207/8M203.3
3/42043/41257/8M203.7
12547/81401M245.5
1 1/432411501 1/8M277.8
1 1/24041 1/81701 1/4M3011.5
250811801 1/8M2719
2 1/26581 1/81951 1/4M3024
38081 1/42201 3/8M3342.8
410081 1/22551 5/8M3966
512581 3/43001 7/8M45111
6150823452 1/8M52173
82001223802 1/8M52264
10250122 1/24902 5/8M64490
12300122 3/45402 7/8M72695

Weld Neck Flange Weight Chart

Flange Size (inches)Class 150 (lbs)Class 300 (lbs)Class 400 (lbs)Class 600 (lbs)Class 900 (lbs)Class 1500 (lbs)Class 2500 (lbs)
½2233778
¾233.54779
134448.58.513
354.56101020
4788141428
2691012242442
10121418313152
311.5181823363694
122026265353146
416.526.535428686244
521364368110110378
626455781187187576
84269891202682681068
10541001251903723721608
1288142175226562562
14114206233347685685
16140250295481924924
1816532036055511641164
2019740044569021072107
22225465505720
24268580640977

Weld Neck Flange Tolerance

DimensionTolerance
Outside Diameter (OD)±1/16 in for ODs up to 24 in
±1/8 in for ODs over 24 in
Inside Diameter (ID)±1/32 in for diameters up to 10 in
+1/16 in for diameters 12-18 in
+1/8 in, -1/16 in for diameters over 20 in
Diameter of Contact Face1/16 in
Raised Face±1/32 in
Tongue and Groove or Male and Female±1/64 in
Diameter of Hub at Point of Welding+3/32 in, -1/32 in for hubs up to 5 in
+5/32 in, -1/32 in for hubs over 6 in
Diameter of Hub at Base±1/16 in for hub bases up to 24 in
±1/8 in for hub bases over 24 in
Bolt Circle±1/16 in
Bolt Hole Spacing+1/32 in
Eccentricity of Bolt Circle and Facing1/32 in max
Length Thru Hub±1/16 in for lengths up to 10 in
±1/8 in for lengths over 12 in
Thickness+1/8 in, -0 in for thicknesses up to 18 in
+3/16 in, -0 in for thicknesses over 20 in

Common Outer Diameters

  • 2 inches (50.8 mm)
  • 4 inches (101.6 mm)
  • 6 inches (152.4 mm)
  • 8 inches (203.2 mm)
  • 12 inches (304.8 mm)
  • 16 inches (406.4 mm)
  • 24 inches (609.6 mm)

Pressure Class Range

  • Class 150
  • Class 300
  • Class 600
  • Class 900
  • Class 1500

Flange Face Types

  • Raised Face (RF): Provides a better seal and is most common for process applications.
  • Flat Face (FF): Used for low-pressure and non-critical applications.
  • Ring Type Joint (RTJ): Designed for high-pressure and high-temperature applications.
  • Male and Female (M&F): Used in specialized applications requiring alignment.
  • Tongue and Groove (T&G): Ensures precise mating for critical joints.

Standards

  • ASME B16.5: For pipe flanges and flanged fittings (sizes up to 24″).
  • ASME B16.47: For large-diameter flanges (sizes above 24″).
  • API 605: Applicable for large-diameter steel flanges.
  • MSS SP-44: For pipeline flanges.
  • DIN EN 1092-1: European standard for steel flanges.
  • ISO 7005-1: International standard for metallic flanges.

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