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.

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.

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.

Class 150 Weld Neck Flange Dimensions

Size in Inch	Size in mm	Outer Diameter	Flange Thickness	Hub OD	Weld Neck OD	Welding Neck Length	Bore	RF Diameter	RF Height	PCD	Weld Face
		A	B	C	D	E	F	G	H	I	J
1/2	15	90	9.6	30	21.3	46		34.9	2	60.3	1.6
3/4	20	100	11.2	38	26.7	51		42.9	2	69.9	1.6
1	25	110	12.7	49	33.4	54		50.8	2	79.4	1.6
1 1/4	32	115	14.3	59	42.2	56		63.5	2	88.9	1.6
1 1/2	40	125	15.9	65	48.3	60		73	2	98.4	1.6
2	50	150	17.5	78	60.3	62		92.1	2	120.7	1.6
2 1/2	65	180	20.7	90	73	68		104.8	2	139.7	1.6
3	80	190	22.3	108	88.9	68		127	2	152.4	1.6
3 1/2	90	215	22.3	122	101.6	70	Welding Neck bore is derived from the pipe schedule	139.7	2	177.8	1.6
4	100	230	22.3	135	114.3	75		157.2	2	190.5	1.6
5	125	255	22.3	164	141.3	87		185.7	2	215.9	1.6
6	150	280	23.9	192	168.3	87		215.9	2	241.3	1.6
8	200	345	27	246	219.1	100		269.9	2	298.5	1.6
10	250	405	28.6	305	273	100		323.8	2	362	1.6
12	300	485	30.2	365	323.8	113		381	2	431.8	1.6
14	350	535	33.4	400	355.6	125		412.8	2	476.3	1.6
16	400	595	35	457	406.4	125		469.9	2	539.8	1.6
18	450	635	38.1	505	457.2	138		533.4	2	577.9	1.6
20	500	700	41.3	559	508	143		584.2	2	635	1.6
24	600	815	46.1	663	610	151		692.2	2	749.3	1.6

Class 150 Weld Neck Flange Stud & Bolt Dimensions

Size in Inch	Size in mm	No of Bolts	Bolt Size UNC	Machine Bolt Length	RF Stud Length	Hole Size	ISO Stud Size	Weight in kg
1/2	15	4	1/2	50	55	5/8	M14	0.6
3/4	20	4	1/2	50	65	5/8	M14	0.9
1	25	4	1/2	55	65	5/8	M14	1.4
1 1/4	32	4	1/2	55	70	5/8	M14	1.4
1 1/2	40	4	1/2	65	70	5/8	M14	1.8
2	50	4	5/8	70	85	3/4	M16	2.7
2 1/2	65	4	5/8	75	90	3/4	M16	3.7
3	80	4	5/8	75	90	3/4	M16	4.6
3 1/2	90	8	5/8	75	90	3/4	M16	5.5
4	100	8	5/8	75	90	3/4	M16	6.8
5	125	8	3/4	85	95	7/8	M20	8.7
6	150	8	3/4	85	100	7/8	M20	10.9
8	200	8	3/4	90	110	7/8	M20	17.7
10	250	12	7/8	100	115	1	M24	24
12	300	12	7/8	100	120	1	M24	37
14	350	12	1	115	135	1 1/8	M27	50
16	400	16	1	115	135	1 1/8	M27	64
18	450	16	1 1/8	125	145	1 1/4	M30	68
20	500	20	1 1/8	140	160	1 1/4	M30	82
24	600	20	1 1/4	150	170	1 3/8	M33	118

Class 300 Weld Neck Flange Dimensions

Size in Inch	Size in mm	Outer Diameter	Flange Thickness	Hub OD	Weld Neck OD	Welding Neck Length	Bore	RF Diameter	RF Height	PCD	Weld Face
		A	B	C	D	E	F	G	H	I	J
1/2	15	95	12.7	38	21.3	51		34.9	2	66.7	1.6
3/4	20	115	14.3	48	26.7	56		42.9	2	82.6	1.6
1	25	125	15.9	54	33.4	60		50.8	2	88.9	1.6
1 1/4	32	135	17.5	64	42.2	64		63.5	2	98.4	1.6
1 1/2	40	155	19.1	70	48.3	67		73	2	114.3	1.6
2	50	165	20.7	84	60.3	68		92.1	2	127	1.6
2 1/2	65	190	23.9	100	73	75		104.8	2	149.2	1.6
3	80	210	27	117	88.9	78		127	2	168.3	1.6
3 1/2	90	230	28.6	133	101.6	79	Welding Neck bore is derived from the pipe schedule	139.7	2	184.2	1.6
4	100	255	30.2	146	114.3	84		157.2	2	200	1.6
5	125	280	33.4	178	141.3	97		185.7	2	235	1.6
6	150	320	35	206	168.3	97		215.9	2	269.9	1.6
8	200	380	39.7	260	219.1	110		269.9	2	330.2	1.6
10	250	445	46.1	321	273	116		323.8	2	387.4	1.6
12	300	520	49.3	375	323.8	129		381	2	450.8	1.6
14	350	585	52.4	425	355.6	141		412.8	2	514.4	1.6
16	400	650	55.6	483	406.4	144		469.9	2	571.5	1.6
18	450	710	58.8	533	457	157		533.4	2	628.6	1.6
20	500	775	62	587	508	160		584.2	2	685.8	1.6
24	600	915	68.3	702	610	167		692.2	2	812.8	1.6

Class 300 Weld Neck Flange Stud & Bolt Dimensions

Size in Inch	Size in mm	No of Bolts	Bolt Size UNC	Machine Bolt Length	RF Stud Length	Hole Size	ISO Stud Size	Weight in kg
1/2	15	4	1/2	55	65	5/8	M14	1.4
3/4	20	4	5/8	65	75	3/4	M16	1.4
1	25	4	5/8	65	75	3/4	M16	1.8
1 1/4	32	4	5/8	70	85	3/4	M16	2.3
1 1/2	40	4	3/4	75	90	7/8	M20	3.2
2	50	8	5/8	75	90	3/4	M16	4.1
2 1/2	65	8	3/4	85	100	7/8	M20	5.5
3	80	8	3/4	90	110	7/8	M20	6.8
3 1/2	90	8	3/4	95	110	7/8	M20	8.2
4	100	8	3/4	95	115	7/8	M20	11.4
5	125	8	3/4	110	120	7/8	M20	14.6
6	150	12	3/4	110	120	7/8	M20	19.1
8	200	12	7/8	120	140	1	M24	31
10	250	16	1	140	160	1 1/8	M27	42
12	300	16	1 1/8	145	170	1 1/4	M30	64
14	350	20	1 1/8	160	180	1 1/4	M30	82
16	400	20	1 1/4	165	190	1 3/8	M33	113
18	450	24	1 1/4	170	195	1 3/8	M33	145
20	500	24	1 1/4	185	205	1 3/8	M33	182
24	600	24	1 1/2	205	230	1 5/8	M39	264

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)
½	2	2	3	3	7	7	8
¾	2	3	3.5	4	7	7	9
1	3	4	4	4	8.5	8.5	13
1¼	3	5	4.5	6	10	10	20
1½	4	7	8	8	14	14	28
2	6	9	10	12	24	24	42
2½	10	12	14	18	31	31	52
3	11.5	18	18	23	36	36	94
3½	12	20	26	26	53	53	146
4	16.5	26.5	35	42	86	86	244
5	21	36	43	68	110	110	378
6	26	45	57	81	187	187	576
8	42	69	89	120	268	268	1068
10	54	100	125	190	372	372	1608
12	88	142	175	226	562	562	–
14	114	206	233	347	685	685	–
16	140	250	295	481	924	924	–
18	165	320	360	555	1164	1164	–
20	197	400	445	690	2107	2107	–
22	225	465	505	720	–	–	–
24	268	580	640	977	–	–	–

Weld Neck Flange Tolerance

Dimension	Tolerance
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 Face	1/16 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 Facing	1/32 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

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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Weld Neck Flange

Weld Neck Flange

Long Weld Neck Flange (LWN Flange)

Types of Long Weld Neck Flanges:

Benefits:

Material

Weld Neck Flange Dimension

Class 150 Weld Neck Flange Dimensions

Class 150 Weld Neck Flange Stud & Bolt Dimensions

Class 300 Weld Neck Flange Dimensions

Class 300 Weld Neck Flange Stud & Bolt Dimensions

Weld Neck Flange Weight Chart

Weld Neck Flange Tolerance

Common Outer Diameters

Pressure Class Range

Flange Face Types

Standards

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