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Long Weld Neck Flange

Long Weld Neck Flange: Specifications | Materials | Types | Dimensions | Weight Chart | Tolerances | FAQ

Reliable ASME B16.5 Long Weld Neck Flanges from a trusted manufacturer and exporter of carbon, stainless, alloy, and nickel alloys. Available in sizes from ½” to 24” and pressure classes from 150 to 2500. Delivered worldwide including Spain, Turkey, South Korea, and Argentina.

ASME B16.5 Long Weld Neck Flange Supplier

Best Export Prices: sales@midlandforgefittings.com

Midland Forge and Fittings Pvt. Ltd, is a globally recognized manufacturer and exporter of high-quality Long Weld Neck Flanges, catering to diverse industries including oil & gas, petrochemical, power, and shipbuilding. Our products are meticulously engineered to meet international standards such as ASME B16.5, ensuring precision, durability, and optimum performance in high-pressure and high-temperature applications.

We specialize in Long Weld Neck Flanges made from a wide range of materials including carbon steel, stainless steel, alloy steel, and high nickel alloys, offering versatility for various chemical, industrial, and mechanical applications. Each flange is crafted to provide a smooth transition between pipe and flange, reducing stress concentrations and enhancing the structural integrity of piping systems.

LWN Flanges are available in sizes ranging from ½” to 24” and pressure classes from 150# to 2500#, accommodating both standard and custom requirements. With strict adherence to quality control protocols, we ensure every flange undergoes dimensional inspection, material testing, and surface finishing to meet client specifications and industry standards.

Our commitment to excellence extends beyond manufacturing. As a reliable global exporter, We delivers Long Weld Neck Flanges worldwide, including regions like USA, Germany, UAE, Singapore, and Australia. Our efficient logistics, competitive pricing, and dedicated customer support make us a preferred choice for international clients seeking high-performance flanges.

Choose Midland Forge and Fittings Pvt. Ltd for long-lasting, precision-engineered Long Weld Neck Flanges that combine superior material strength, reliable performance, and seamless integration into critical piping systems.

ASME B16.5 LWN Flange

Long Weld Neck Pipe Flange Specifications

Size Range

15mm ( 1/2" NPS ) up to 600mm ( 24" NPS ), For 2500# in sizes from NPS 1/2 to NPS 12

Pressure Rating - Class

150 LBS, 300 LBS, 600 LBS, 900 LBS, 1500 LBS, 2500 LBS

Marking

Grade / Material, Size (NPS or DN), Pressure Class (PN), Heat No, Standard, Manufacturer’s Name or Trademark

Face Type / Flange Connection Type

Flat Face (FF), Raise Face (RF), Ring Joint (RJT), Tongue and Groove (T&G), Male and Female (M&F)

Flange Form

LWNF

Manufacturing Standards

ASTM (A105, A182, A350, A694, B564), ASME/ANSI, MSS-SP-44, API 6A.

Materials

Stainless Steel, Carbon Steel, Alloy Steel, Duplex Steel, Super Duplex, Nickel, Inconel, Incoloy, Hastelloy, Monel, Alloy 20, 254 SMO, Copper Nickel, Titanium.

Test Certificates

EN 10204/3.1B, Raw Materials Certificate, 100% Radiography Test Report, Third Party Inspection Report, etc

Dimensional Standards

ANSI B16.5, ANSI B16.47, ANSI B16.36, ANSI B16.48, BS 4504, EN1092, UNI 2277/2278, DIN, JIS, SABS1123, GOST-12820

Testing

Direct-reading Spectrograph, Hydrostatic testing machine, X-ray detector, UI trasonic flaw detector, Magnetic particle detector

Flange Coating/Surface Treatment

Anti-rust Paint, Oil Black Paint, Yellow Transparent, Zinc Plated, Cold and Hot Dip Galvanized

Production technique

Forged, Heat treated and machined
ASME B16.47, MSS SP - 44 LWN Flange

Long Weld Neck Flange – Materials, Grades & Standards

Material Category Standards / Grades (ASTM / ASME) Pressure Class / Size Range Typical Use / Application
Stainless Steel ASTM A182 F304 / F304L / F304H Class 150 – 2500, Size ½”–48” General purpose, corrosion-resistant piping
ASTM A182 F316 / F316L / F316H Class 150 – 2500, Size ½”–48” Chemical, marine, food & pharma industries
ASTM A182 F321 / F321H Class 150 – 1500, Size ½”–24” High temperature, stabilized service
Carbon Steel ASTM A105 (Forged CS) Class 150 – 2500, Size ½”–48” Pressure piping, oil & gas, general industries
ASTM A350 LF2 (Low Temp CS) Class 150 – 1500, Size ½”–24” Cryogenic & low temperature applications
Alloy Steel ASTM A182 F11 / F22 (Cr-Mo) Class 150 – 2500, Size ½”–24” Power plants, refineries, steam pipelines
ASTM A182 F91 Class 150 – 2500, Size ½”–24” High-temperature, power generation
Duplex / Super Duplex ASTM A182 F51 / F53 / F55 / F60 (UNS S31803 / S32205 / S32750 / S32760) Class 150 – 2500, Size ½”–24” Offshore, seawater, high corrosion service
Nickel Alloys ASTM B564 Inconel 600 / 625 / 718 Class 150 – 2500, Size ½”–24” Heat exchangers, chemical, aerospace
ASTM B564 Monel 400 / K500 Class 150 – 2500, Size ½”–24” Marine, seawater handling, pumps
Copper Nickel ASTM B151 / B467 (Cu-Ni 90/10, 70/30) Class 150 – 600, Size ½”–24” Shipbuilding, desalination, seawater systems
Titanium ASTM B381 Gr. 2 / Gr. 5 Class 150 – 600, Size ½”–12” Aerospace, seawater, lightweight piping
Aluminium ASTM B247 6061 / 5083 Class 150 – 300, Size ½”–12” Lightweight, non-corrosive, low-pressure piping
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ANSI/ASME B16.5 Class 150 Long Weld Neck Flange – Dimensions & Sizes in mm

Dimensions of ANSI/ASME B16.5 LWN Flanges
Size Flange Barrel OD Bolting Nut Stud Bolt Weights Length
Nom Bore LWN & E Bore HB OD Thk. RF of OD LWN HB E # of Holes Hole Size Bolt Circle Stop Dia Relief Dia Relief Length Size RF Length RTJ Length LWN HB E Base
B  B O  T R  D D D C NS NR NL Base Per  1″ Base Per 1″ Base Per  1″ L 
 1/2 0.5 0.55 3.5 0.44 1.38 1.25 1.5 3.5 4 0.62 2.38 1.5 1.25 0.75 1/2  2 1/4 2 3/4 3 0.3 5 0.4 21 2.7 9
 3/4 0.75 0.74 3.88 0.5 1.69 1.62 1.88 3.88 4 0.62 2.75 1.88 1.62 0.75 1/2  2 1/2 3 5 0.5 7 0.7 27 3.2 9
1 1 0.96 4.25 0.56 2 2 2.25 4.25 4 0.62 3.12 2.25 2 0.75 1/2  2 1/2 3 7 0.7 10 0.9 30 3.8 9
1 1/4 1.25 1.28 4.62 0.62 2.5 2.38 2.62 4.62 4 0.62 3.5 2.62 2.38 0.75 1/2  2 3/4 3 1/4 10 0.9 12 1.2 36 4.4 9
1 1/2 1.5 1.5 5 0.69 2.88 2.62 3 5 4 0.62 3.88 3 2.62 0.75 1/2  2 3/4 3 1/4 12 1 16 1.5 41 5.1 9
2 2 1.94 6 0.75 3.62 3.06 3.69 6 4 0.75 4.75 3.69 3.06 0.88 5/8  3 1/4 3 3/4 15 1.2 23 2.2 57 7.1 9
2 1/2 2.5 2.32 7 0.88 4.12 3.75 4.44 7 4 0.75 5.5 4.44 3.75 0.88 5/8  3 1/2 4 22 1.7 34 3.2 79 10 9
3 3 2.9 7.5 0.94 5 4.25 4.94 7.5 4 0.75 6 4.94 4.25 0.88 5/8  3 1/2 4 1/4 25 2 38 3.6 86 11 9
3 1/2 3.5 3.36 8.5 0.94 5.5 4.88 5.94 8.5 8 0.75 7 5.94 4.88 0.88 5/8  3 1/2 4 1/4 32 2.6 55 5.3 110 13 9
4 4 3.83 9 0.94 6.19 5.5 6.44 9 8 0.75 7.5 6.44 5.5 0.88 5/8  3 1/2 4 1/4 47 3.2 78 6 164 14 12
5 5 4.81 10 0.94 7.31 6.50 7.25 10 8 0.88 8.5 7.25 6.50 1 3/4  3 3/4 4 1/2 57 3.8 87 6.50 189 17 12
6 6 5.76 11 1 8.5 7.75 8.25 11 8 0.88 9.5 8.25 7.75 1 3/4  4 4 1/2 75 5.4 103 7.8 216 19 12
8 8 7.62 13.5 1.12 10.62 9.75 10.5 13.5 8 0.88 11.75 10.5 9.75 1 3/4  4 1/4 4 3/4 102 6.9 157 11 292 26 12
10 10 9.56 16 1.19 12.75 12 12.81 16 12 1 14.25 12.81 12 1.12 7/8  4 3/4 5 1/4 143 9.8 214 16 382 35 12
12 12 11.38 19 1.25 15 14.38 15.56 19 12 1 17 15.56 14.38 1.12 7/8  4 3/4 5 1/2 205 14 329 25 535 48 12
14 14 14 21 1.38 16.25 16 17.12 21 12 1.12 18.75 17.12 16 1.25 1 5 1/4 6 211 13 296 22 585 55 12
16 16 16 23.5 1.44 18.5 18 19.62 23.5 16 1.12 21.25 19.62 18 1.25 1 5 1/2 6 246 15 388 29 714 66 12
18 18 18 25 1.56 21 20 20.94 25 16 1.25 22.75 20.94 20 1.38 1  1/8 6 6 1/2 270 17 362 25 711 67 12
20 20 20 27.5 1.69 23 22 23.19 27.5 20 1.25 25 23.19 22 1.38 1  1/8 6 1/4 7 311 19 434 31 840 79 12
24 24 24 32 1.88 27.25 26.25 27.5 32 20 1.38 29.5 27.5 26.25 1.5 1  1/4 7 7 3/4 423 25 574 40 1046 100 12

ANSI/ASME B16.5 Class 300 LWN Flange – Dimensions & Sizes in mm

Size     Flange     Barrel OD     Bolting     Nut     Stud Bolt     Weights           Length
Nom Bore LWN & E Bore HB OD Thk RF of OD LWN HB E # ofHoles Hole Size Bolt Circle Stop Dia Relief Dia Relief Length Size RF Length RTJ Length LWN   HB   E   Base
  B  B O  T R  D D D     C NS NR NL       Base Per  1″ Base Per  1″ Base Per  1″ L 
 1/2 0.5 0.55 3.75 0.56 1.38 1.5 1.75 3.75 4 0.62 2.62 1.75 1.5 0.75 1/2  2 1/2 3    5 0.4 7 0.6 24 3.1 9
 3/4 0.75 0.74 4.62 0.62 1.69 1.88 2.19 4.62 4 0.75 3.25 2.19 1.88 0.88 5/8  3    3 1/2 9 0.7 11 0.9 37 4.6 9
1 1 0.96 4.88 0.69 2 2.12 2.44 4.88 4 0.75 3.5 2.44 2.12 0.88 5/8  3 1/4 3 1/2 9 0.8 12 1.1 40 5.1 9
1 1/4 1.25 1.28 5.25 0.75 2.5 2.5 2.81 5.25 4 0.75 3.88 2.81 2.5 0.88 5/8  3 1/4 3 3/4 13 1 15 1.4 45 5.8 9
1 1/2 1.5 1.5 6.12 0.81 2.88 2.75 3.25 6.12 4 0.88 4.5 3.25 2.75 1 3/4  3 1/2 4    15 1.2 21 1.9 61 7.8 9
2 2 1.94 6.5 0.88 3.62 3.31 3.94 6.5 8 0.75 5 3.94 3.31 0.88 5/8  3 1/2 4 1/4 20 1.5 28 2.6 68 8.5 9
2 1/2 2.5 2.32 7.5 1 4.12 3.94 4.62 7.5 8 0.88 5.88 4.62 3.94 1 3/4  4    4 1/2 25 2.1 38 3.6 89 11 9
3 3 2.9 8.25 1.12 5 4.62 5.38 8.25 8 0.88 6.62 5.38 4.62 1 3/4  4 1/4 5    35 2.7 49 4.6 106 13 9
3 1/2 3.5 3.36 9 1.19 5.5 5.25 6 9 8 0.88 7.25 6 5.25 1 3/4  4 1/4 5    42 3.4 59 5.5 122 15 9
4 4 3.83 10 1.25 6.19 5.75 6.62 10 8 0.88 7.88 6.62 5.75 1 3/4  4 1/2 5 1/4 62 3.8 91 6.5 207 19 12
5 5 4.81 11 1.38 7.31 7 8 11 8 0.88 9.25 8 7 1 3/4  4 3/4 5 1/4 84 5.3 124 9.1 241 21 12
6 6 5.76 12.5 1.44 8.5 8.12 9.38 12.5 12 0.88 10.62 9.38 8.12 1 3/4  4 3/4 5 3/4 105 6.7 165 12 303 27 12
8 8 7.62 15 1.62 10.62 10.25 11.56 15 12 1 13 11.56 10.25 1.12 7/8  5 1/2 6 1/4 148 9.1 228 17 405 36 12
10 10 9.56 17.5 1.88 12.75 12.62 13.62 17.5 16 1.12 15.25 13.62 12.62 1.25 1 6 1/4 7 1/4 210 13 291 21 499 46 12
12 12 11.38 20.5 2 15 14.75 15.94  20.5 16 1.25 17.75 15.94 14.75 1.38 1 1/8  6 3/4 7 1/2 275 16 392 28 651 61 12
14 14 14 23 2.12 16.25 16.75 18.44 23 20 1.25 20.25 18.44 16.75 1.38 1 1/8  7    7 3/4 324 19 456 32 785 74 12
16 16 16 25.5 2.25 18.5 19 20.5 25.5 20 1.38 22.5 20.5 19 1.5 1 1/4  7 1/2 8 1/2 404 23 529 37 914 88 12
18 18 18 28 2.38 21 21 22.75 28 24 1.38 24.75 22.75 21 1.5 1 1/4  7 3/4 8 1/4 465 26 630 43 1066 102 12
20 20 20 30.5 2.5 23 23.12 25 30.5 24 1.38 27 25 23.12 1.5 1 1/4  8 1/4 9 1/4 549 30 741 50 1228 118 12
24 24 24 36 2.75 27.25 27.62 29.62 36 24 1.62 32 29.62 27.62 1.75 1 1/2  9 1/4 10 1/4 778 42 1016 67 1627 160 12

ANSI/ASME B16.5 Class 600 Long Weld Neck Flange – Dimensions & Sizes in mm

Size     Flange     Barrel OD     Bolting     Nut     Stud Bolt     Weights           Length
Nom Bore LWN & E Bore HB OD Thk RF of OD LWN HB E # ofHoles Hole Size Bolt Circle Stop Dia Relief Dia Relief Length Size RF Length RTJ Length LWN   HB   E   Base
  B  B O  T R  D D D     C NS NR NL       Base Per  1″ Base Per  1″ Base Per  1″ L 
 1/2 0.5 0.55 3.75 0.56 1.38 1.5 1.75 3.75 4 0.62 2.62 1.75 1.5 0.75 1/2 3    3    5 0.4 7 0.6 24 3.1 9
 3/4 0.75 0.74 4.62 0.62 1.69 1.88 2.19 4.62 4 0.75 3.25 2.19 1.88 0.88 5/8 3 1/2 3 1/2 8 0.7 11 0.9 36 4.6 9
1 1 0.96 4.88 0.69 2 2.12 2.44 4.88 4 0.75 3.5 2.44 2.12 0.88 5/8 3 1/2 3 1/2 9 0.8 12 1.1 39 5.1 9
1 1/4 1.25 1.28 5.25 0.81 2.5 2.5 2.81 5.25 4 0.75 3.88 2.81 2.5 0.88 5/8 3 3/4 3 3/4 13 1 15 1.4 44 5.8 9
1 1/2 1.5 1.5 6.12 0.88 2.88 2.75 3.25 6.12 4 0.88 4.5 3.25 2.75 1 3/4 4 1/4 4 1/4 16 1.2 21 1.9 59 7.8 9
2 2 1.94 6.5 1 3.62 3.31 3.94 6.5 8 0.75 5 3.94 3.31 0.88 5/8 4 1/4 4 1/4 20 1.5 29 2.6 67 8.5 9
2 1/2 2.5 2.32 7.5 1.12 4.12 3.94 4.62 7.5 8 0.88 5.88 4.62 3.94 1 3/4 5 4 3/4 27 2.1 39 3.6 85 11 9
3 3 2.9 8.25 1.25 5 4.62 5.38 8.25 8 0.88 6.62 5.38 4.62 1 3/4 5 5 1/4 36 2.7 50 4.6 104 13 9
3 1/2 3.5 3.36 9 1.38 5.5 5.25 5.81 9 8 1 7.25 5.81 5.25 1.12 7/8 5 1/2 5 1/2 45 3.4 57 5 116 15 9
4 4 3.83 10.75 1.5 6.19 6 7.06 10.75 8 1 8.5 7.06 6 1.12 7/8 5 3/4 6 77 4.5 113 7.8 238 22 12
5 5 4.81 13 1.75 7.31 7.5 8.88 13 8 1.12 10.5 8.88 7.5 1.25 1    6 1/2 6 1/2 123 7 180 12 336 32 12
6 6 5.76 14 1.88 8.5 8.75 9.88 14 12 1.12 11.5 9.88 8.75 1.25 1    6 3/4 7 152 9 207 14 373 36 12
8 8 7.62 16.5 2.19 10.62 10.75 11.94 16.5 12 1.25 13.75 11.94 10.75 1.38 1 1/8 7 3/4 8 207 11 277 19 478 46 12
10 10 9.56 20 2.5 12.75 13.5 15 20 16 1.38 17 15 13.5 1.5 1 1/4 8 1/2 8 3/4 324 18 433 30 683 67 12
12 12 11.38 22 2.62 15 15.75 17.25 22 20 1.38 19.25 17.25 15.75 1.5 1 1/4 8 3/4 9 393 23 533 37 779 76 12
14 14 14 23.75 2.75 16.25 17 18.56 23.75 20 1.5 20.75 18.56 17 1.62 1 3/8 9 1/4 9 1/2 471 21 631 33 1149 82 16
16 16 16 27 3 18.5 19.5 21.38 27 20 1.62 23.75 21.38 19.5 1.75 1 1/2 10    10 1/4 638 28 856 45 1471 105 16
18 18 18 29.25 3.25 21 21.5 23.19 29.25 20 1.75 25.75 23.19 21.5 1.88 1 5/8 10 3/4 11 731 31 941 48 1628 118 16
20 20 20 32 3.5 23 24 25.94 32 24 1.75 28.5 25.94 24 1.88 1 5/8 11 1/2 11 3/4 916 39 1180 61 1920 139 16
24 24 24 37 4 27.25 28.25 30.06 37 24 2 33 30.06 28.25 2.12 1 7/8 13 13 1/2 1210 49 1486 73 2376 176 16

ANSI/ASME B16.5 Class 900 LWN Flange – Dimensions & Sizes in mm

Size     Flange     Barrel OD     Bolting     Nut     Stud Bolt     Weights           Length
Nom Bore LWN & E Bore HB OD Thk RF of OD LWN HB E # ofHoles Hole Size Bolt Circle Stop Dia Relief Dia Relief Length Size RF Length RTJ Length LWN   HB   E   Base
  B  B O  T R  D D D     C NS NR NL       Base Per 1″ Base Per 1″ Base Per 1″ L
 1/2 0.5 0.55 4.75 0.88 1.38 1.56 2 4.75 4 0.88 3.25 2 1.56 1 3/4  4 1/4 4 1/4 8 0.5 10 0.8 37 5 9
 3/4 0.75 0.74 5.12 1 1.69 1.81 2.25 5.12 4 0.88 3.5 2.25 1.81 1 3/4  4 1/2 4 1/2 10 0.6 13 1 42 5.7 9
1 1 0.96 5.88 1.12 2 2.12 2.56 5.88 4 1 4 2.56 2.12 1.12 7/8  5 5 13 0.8 17 1.3 54 7.5 9
1 1/4 1.25 1.28 6.25 1.12 2.5 2.5 2.94 6.25 4 1 4.38 2.94 2.5 1.12 7/8  5 5 17 1 20 1.6 61 8.3 9
1 1/2 1.5 1.5 7 1.25 2.88 2.75 3.25 7 4 1.12 4.88 3.25 2.75 1.25 1 5 1/2 5 1/2 21 1.2 26 1.9 77 10 9
2 2 1.94 8.5 1.5 3.62 4.12 5.06 8.5 8 1 6.5 5.06 4.12 1.12 7/8  5 3/4 5 3/4 42 2.9 56 4.9 115 15 9
2 1/2 2.5 2.32 9.62 1.62 4.12 4.88 5.88 9.62 8 1.12 7.5 5.88 4.88 1.25 1 6 1/4 6 1/4 56 3.9 75 6.5 144 19 9
3 3 2.9 9.5 1.5 5 5 6.06 9.5 8 1 7.5 6.06 5 1.12 7/8  5 3/4 5 3/4 51 3.6 71 6.3 139 18 9
4 4 3.83 11.5 1.75 6.19 6.25 7.44 11.5 8 1.25 9.25 7.44 6.25 1.38 1 1/8  6 3/4 6 3/4 93 5.1 133 9.1 270 26 12
5 5 4.81 13.75 2 7.31 7.5 9 13.75 8 1.38 11 9 7.5 1.5 1 1/4 7 1/2 7 1/2 135 7 194 13 376 37 12
6 6 5.76 15 2.19 8.5 9.25 10.69 15 12 1.25 12.5 10.69 9.25 1.38 1 1/8 7 1/2 7 3/4 191 11 259 18 436 42 12
8 8 7.62 18.5 2.5 10.62 11.75 13.31 18.5 12 1.5 15.5 13.31 11.75 1.62 1 3/8 8 3/4 8 3/4 297 16 389 27 626 62 12
10 10 9.56 21.5 2.75 12.75 14.5 16.31 21.5 16 1.5 18.5 16.31 14.5 1.62 1 3/8 9 1/4 9 1/4 422 25 558 39 824 81 12
12 12 11.38 24 3.12 15 16.5 18.81 24 20 1.5 21 18.81 16.5 1.62 1 3/8 10    10 518 29 715 50 984 96 12
14 14 14 25.25 3.38 16.25 17.75 19.62 25.25 20 1.62 22 19.62 17.75 1.75 1 1/2 10 3/4 11 624 26 817 42 1368 98 16
16 16 16 27.75 3.5 18.5 20 21.69 27.75 20 1.75 24.25 21.69 20 1.88 1 5/8 11 1/4 11 1/2 750 32 942 48 1573 114 16
18 18 18 31 4 21 22.25 24.06 31 20 2 27 24.06 22.25 2.12 1 7/8 12 3/4 13 1/4 950 38 1169 57 1898 142 16
20 20 20 33.75 4.25 23 24.5 26.38 33.75 20 2.12 29.5 26.38 24.5 2.25 2 13 3/4 14 1/4 1121 43 1378 66 2182 164 16
24 24 24 41 5.5 27.25 29.5 31.62 41 20 2.62 35.5 31.62 29.5 2.75 2 1/2 17 1/4 18 1865 65 2160 94 3084 246 16

ANSI/ASME B16.5 Class 1500 Long Weld Neck Flange – Dimensions & Sizes in mm

Size     Flange     Barrel OD     Bolting     Nut     Stud Bolt     Weights           Length
Nom Bore LWN & E Bore HB OD Thk RF of OD LWN HB E # ofHoles Hole Size Bolt Circle Stop Dia Relief Dia Relief Length Size RF Length RTJ Length LWN   HB   E Base
  B  B O  T R  D D D     C NS NR NL       Base Per 1″ Base Per 1″ Base Per 1″ L 
 1/2 0.5 0.55 4.75 0.88 1.38 1.56 2 4.75 4 0.88 3.25 2 1.56 1 3/4  4 1/4 4 1/4 8 0.5 10 0.8 37 5 9
 3/4 0.75 0.74 5.12 1 1.69 1.81 2.25 5.12 4 0.88 3.5 2.25 1.81 1 3/4  4 1/2 4 1/2 10 0.6 13 1 42 5.7 9
1 1 0.96 5.88 1.12 2 2.12 2.56 5.88 4 1 4 2.56 2.12 1.12 7/8  5    5    13 0.8 17 1.3 54 7.5 9
1 1/4 1.25 1.28 6.25 1.12 2.5 2.5 2.94 6.25 4 1 4.38 2.94 2.5 1.12 7/8  5    5    17 1 20 1.6 61 8.3 9
1 1/2 1.5 1.5 7 1.25 2.88 2.75 3.25 7 4 1.12 4.88 3.25 2.75 1.25 1 5 1/2 5 1/2 21 1.2 26 1.9 77 10 9
2 2 1.94 8.5 1.5 3.62 4.12 5.06 8.5 8 1 6.5 5.06 4.12 1.12   7/8  5 3/4 5 3/4 42 2.9 56 4.9 115 15 9
2 1/2 2.5 2.32 9.62 1.62 4.12 4.88 5.88 9.62 8 1.12 7.5 5.88 4.88 1.25 1 6 1/4 6 1/4 56 3.9 75 6.5 144 19 9
3 3 2.9 10.5 1.88 5 5.25 6.19 10.5 8 1.25 8 6.19 5.25 1.38 1 1/8  7    7    67 4.1 84 6.7 161 23 9
4 4 3.83 12.25 2.12 6.19 6.38 7.5 12.25 8 1.38 9.5 7.5 6.38 1.5 1 1/4  7 3/4 7 3/4 110 5.5 147 9.3 302 30 12
5 5 4.81 14.75 2.88 7.31 7.75 9.12 14.75 8 1.62 11.5 9.12 7.75 1.75 1 1/2  9 3/4 9 3/4 181 7.8 233 13 414 43 12
6 6 5.76 15.5 3.25 8.5 9 10.31 15.5 12 1.5 12.5 10.31 9 1.62 1 3/8  10 1/4 10 1/2 215 10 272 16 445 46 12
8 8 7.62 19 3.62 10.62 11.5 12.94 19 12 1.75 15.5 12.94 11.5 1.88 1 5/8  11 1/2 12 3/4 337 15 417 24 629 67 12
10 10 9.56 23 4.25 12.75 14.5 16.06 23 12 2 19 16.06 14.5 2.12 1 7/8  13 1/4 13 1/2 546 25 651 37 888 97 12
12 12 11.38 26.5 4.88 15 17.75 19.38 26.5 16 2.12 22.5 19.38 17.75 2.25 2 14 3/4 15 1/4 946 38 1148 55 1683 127 16
14 14 14 29.5 5.25 16.25 19.5 21.5 29.5 16 2.38 25 21.5 19.5 2.5 2 1/4  16    16 3/4 1116 41 1308 59 1929 150 16
16 16 16 32.5 5.75 18.5 21.75 23.88 32.5 16 2.62 27.75 23.88 21.75 2.75 2 1/2  17 1/2 18 1/2 1371 48 1588 70 2238 178 16
18 18 18 36 6.38 21 23.5 26.25 36 16 2.88 30.5 26.25 23.5 3 2 3/4  19 1/2 20 3/4 1674 51 1959 81 2629 216 16
20 20 20 38.75 7 23 25.25 28.12 38.75 16 3.12 32.75 28.12 25.25 3.25 3 21 1/4 22 1/4 1943 53 2241 87 2868 245 16
24 24 24 46 8 27.25 30 33.62 46 16 3.62 39 33.62 30 3.75 3 1/2  24 1/4 25 1/2 2936 72 3334 123 3819 343 16

ANSI/ASME B16.5 Class 2500 LWN Flange – Dimensions & Sizes in mm

Size Flange Barrel OD Bolting Nut Stud Bolt Weights Length
Nom Bore LWN & E Bore HB OD Thk RF of OD LWN HB E # ofHoles Hole Size Bolt Circle Stop Dia Relief Dia Relief Length Size RF Length RTJ Length LWN HB E Base
B  B O  T R  D D D C NS NR NL Base Per 1″ Base Per 1″ Base Per 1″ L 
 1/2 0.5 0.55 5.25 1.19 1.38 1.81 2.25 5.25 4 0.88 3.5 2.25 1.81 1 3/4  4 3/4 4 3/4 11 0.7 14 1.1 45 6.1 9
 3/4 0.75 0.74 5.5 1.25 1.69 2.06 2.5 5.5 4 0.88 3.75 2.5 2.06 1 3/4  5    5    13 0.8 17 1.3 49 6.6 9
1 1 0.96 6.25 1.38 2 2.25 2.81 6.25 4 1 4.25 2.81 2.25 1.12 7/8  5 1/2 5 1/2 18 0.9 22 1.6 62 8.5 9
1 1/4 1.25 1.28 7.25 1.5 2.5 2.88 3.5 7.25 4 1.12 5.12 3.5 2.88 1.25 1 6    6    27 1.5 32 2.4 84 11 9
1 1/2 1.5 1.5 8 1.75 2.88 3.12 3.94 8 4 1.25 5.75 3.94 3.12 1.38 1 1/8  6 3/4 6 3/4 33 1.7 42 3 94 14 9
2 2 1.94 9.25 2 3.62 3.75 5.12 9.25 8 1.12 6.75 5.12 3.75 1.25 1 7    7    48 2.2 66 5 131 18 9
2 1/2 2.5 2.32 10.5 2.25 4.12 4.5 5.94 10.5 8 1.25 7.75 5.94 4.5 1.38 1 1/8  7 3/4 8    66 3.1 90 6.7 165 23 9
3 3 2.9 12 2.62 5 5.25 7 12 8 1.38 9 7 5.25 1.5 1 1/4  8 3/4 9    97 4.1 127 9 210 30 9
4 4 3.83 14 3 6.19 6.5 8.38 14 8 1.62 10.75 8.38 6.5 1.75 1 1/2  10    10 1/4 159 5.8 218 12 391 40 12
5 5 4.81 16.5 3.62 7.31 8 10 16.5 8 1.88 12.75 10 8 2 1 3/4  11 3/4 12 1/4 248 8.7 319 17 518 55 12
6 6 5.76 19 4.25 8.5 9.25 11.38 19 8 2.12 14.5 11.38 9.25 2.25 2 13 1/2 14    358 11 441 21 641 73 12
8 8 7.62 21.75 5 10.62 12 14.12 21.75 12 2.12 17.25 14.12 12 2.25 2 15    15 1/2 589 18 743 31 1167 92 16
10 10 9.56 26.5 6.5 12.75 14.75 17.38 26.50 12 2.62 21.25 17.38 14.75 2.75 2 1/2  19 1/4 20    997 26 1202 47 1625 134 16
12 12 11.38 30 7.25 15 17.38 20.12 30 12 2.88 24.38 20.12 17.38 3 2 3/4  21 1/4 22    1363 35 1609 61 1995 168 16

LWN Piping Flange Weight Chart (lbs) – Pressure Class 150 to 2500

Nominal Pipe Size Class 150 (lbs) Class 300 (lbs) Class 400 (lbs) Class 600 (lbs) Class 900 (lbs) Class 1500 (lbs) Class 2500 (lbs)
½” 5 6 6 7 8 10 12
¾” 6 7 8 9 10 12 14
1″ 7 9 10 12 13 15 18
1½” 10 13 14 16 18 22 25
2″ 12 16 18 20 22 26 30
3″ 20 26 28 32 35 40 48
4″ 28 36 38 44 48 55 65
6″ 45 58 62 72 78 90 110
8″ 72 92 98 112 120 140 170
10″ 110 140 150 172 185 210 250
12″ 145 185 200 230 250 280 330
14″ 200 250 270 310 335 370 440
16″ 260 320 350 400 430 480 560
18″ 330 400 440 500 540 600 700
20″ 400 500 550 620 670 740 850
24″ 600 750 820 920 1000 1100 1300

Long Weld Neck Flange Tolerances as per ANSI / ASME B16.5, 16.47

Parameter Tolerance (Class 150–600) Tolerance (Class 900–2500) Standard Reference
Outside Diameter (OD)> ±1/8″ (3.2 mm) ±1/8″ to ±1/4″ (3.2–6.4 mm) depending on size ASME B16.5, B16.47
Thickness of Flange (B)> ±1/16″ (1.6 mm) ±1/16″ to ±1/8″ (1.6–3.2 mm) ASME B16.5, B16.47
Bolt Circle Diameter (K)> ±1/32″ (0.8 mm) ±1/16″ (1.6 mm) ASME B16.5, B16.47
Bolt Hole Diameter (L)> +1/64″ / -0 +1/64″ / -0 ASME B16.5, B16.47
Raised Face Diameter (G)> ±1/32″ (0.8 mm) ±1/32″ to ±1/16″ (0.8–1.6 mm) ASME B16.5, B16.47
Hub Diameter at Base (A)> ±1/32″ (0.8 mm) ±1/32″ to ±1/16″ (0.8–1.6 mm) ASME B16.5, B16.47
Hub Length / Neck Length (H)> ±1/16″ (1.6 mm) ±1/16″ to ±1/8″ (1.6–3.2 mm) ASME B16.5, B16.47
Concentricity / Runout> 1/16″ max 1/16″ to 1/8″ max ASME B16.5, B16.47
Face Flatness> 0.005″ per inch of diameter 0.005″ per inch of diameter ASME B16.5, B16.47
What is a Long Weld Neck Flange?

A Long Weld Neck (LWN) Flange is a type of flange designed to be welded to the pipe at its neck, providing a smooth transition from flange thickness to pipe wall thickness. This design helps in reducing stress concentration at the base of the flange, making it suitable for high-pressure, high-temperature, and critical service applications.

Key Features:

  • Extended hub length compared to standard weld neck flanges.
  • Smooth stress distribution along the hub.
  • Compatible with butt-welded piping systems.
  • Available in carbon steel, stainless steel, alloy steel, and nickel alloys.

The manufacturing of LWN Flanges involves several precise processes to ensure performance and compliance with standards:

  • Forging: The flange is forged from a solid piece of metal for superior strength.
  • Machining: Critical dimensions such as flange thickness, OD, hub length, and bolt holes are machined to exact tolerances.
  • Heat Treatment: Improves material strength, toughness, and stress relief.
  • Inspection & Testing: Includes dimensional checks, pressure testing, and sometimes NDT (Non-Destructive Testing) for critical applications.

Proper maintenance ensures long-term reliability:

  • Regular Inspection: Check for signs of corrosion, cracks, or leaks.
  • Torque Checks: Ensure bolts are tightened to recommended specifications.
  • Cleaning: Remove deposits, scale, or rust to prevent corrosion.
  • NDT (Non-Destructive Testing): Ultrasonic or dye-penetrant testing for critical applications.
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