WELD NECK FLANGE

A welding neck flange (“WN”)features a long tapered hub that can be welded with a pipe.

This flange type is used, normally, in high-pressure and high/low temperatures applications that require an unrestricted flow of the fluid conveyed by the piping system (the bore of the flange matches with the bore of the pipe).

The absence of pressure drops prevents negative effects as turbulence and erosion/corrosion of the metals in the proximity of the flanged joints.

The tapered hub allows a smooth distribution of the mechanical stress between the pipe and the weld neck flange and facilitates the execution of radiographic inspections to detect possible leakages and welding defects.

The dimension of the flange (NPS and the pipe schedule) shall match the dimension of the connecting pipe.

A welding neck flange is connected to a pipe by a single full penetration V-shaped butt weld

Weld neck flange is the most widely used type in process piping. It gives the highest level of joint integrity due to Butt-welded with a pipe. These types of flanges are used in high pressure and temperature application. Weld neck flanges are Bulky & costly with respect to other types of the flange.

High skill is required for fabrication and also required more space to accommodate in the piping system due to the long hub.
Weld Neck Flange is available in all sizes & it can be FF, RF or RTJ type
You can see the Weld Neck flange welded with pipe

cross section of weldneck flange with weld detail

Weld neck flange dimensions are covered in ASME B16.5 – which covers Pipe Flanges and Flanged Fittings for size NPS ½” to 24” for above NPS 26” to 60” it should be as per ASME B16.47.

During a dimensional inspection of weld neck flange, you should check for

Outer & Inner Diameter of body
Bolt Circle & Bolt hole Diameter
the thickness of weld end
Length of the Hub and
Straightness and alignment of the bolt hole

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	Welding Neck bore is derived from the pipe schedule	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		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	Welding Neck bore is derived from the pipe schedule	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		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

Class 400 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	14.3	38	21.3	52	Welding Neck bore is derived from the pipe schedule	34.9	7	66.7	1.6
3/4	20	115	15.9	48	26.7	57		42.9	7	82.6	1.6
1	25	125	17.5	54	33.4	62		50.8	7	88.9	1.6
1 1/4	32	135	20.7	64	42.2	67		63.5	7	98.4	1.6
1 1/2	40	155	22.3	70	48.3	70		73	7	114.3	1.6
2	50	165	25.4	84	60.3	73		92.1	7	127	1.6
2 1/2	65	190	28.6	100	73	79		104.8	7	149.2	1.6
3	80	210	31.8	117	88.9	83		127	7	168.3	1.6
3 1/2	90	230	35	133	101.6	86		139.7	7	184.2	1.6
4	100	255	35	146	114.3	89		157.2	7	200	1.6
5	125	280	38.1	178	141.3	102		185.7	7	235	1.6
6	150	320	41.3	206	168.3	103		215.9	7	269.9	1.6
8	200	380	47.7	260	219.1	117		269.9	7	330	1.6
10	250	445	54	321	273	124		323.8	7	387.4	1.6
12	300	520	57.2	375	323.8	137		381	7	450.8	1.6
14	350	585	60.4	425	355.6	149		412.8	7	514.4	1.6
16	400	650	63.5	483	406.4	152		469.9	7	571.5	1.6
18	450	710	66.7	533	457	165		533.4	7	628.6	1.6
20	500	775	69.9	587	508	168		584.2	7	685.8	1.6
24	600	915	76.2	702	610	175		692.2	7	812.8	1.6

Class 400 Weld Neck Flange Stud & Bolt Dimensions

Size in Inch	Size in mm	No of Bolts	Bolt Size UNC	RF Stud Length	Hole Size	ISO Stud Size
1/2	15	4	1/2	75	5/8	M14
3/4	20	4	5/8	90	3/4	M16
1	25	4	5/8	90	3/4	M16
1 1/4	32	4	5/8	95	3/4	M16
1 1/2	40	4	3/4	110	7/8	M20
2	50	8	5/8	110	3/4	M16
2 1/2	65	8	3/4	120	7/8	M20
3	80	8	3/4	125	7/8	M20
3 1/2	90	8	7/8	140	1	M24
4	100	8	7/8	140	1	M24
5	125	8	7/8	145	1	M24
6	150	12	7/8	150	1	M24
8	200	12	1	170	1 1/8	M27
10	250	16	1 1/8	190	1 1/4	M30
12	300	16	1 1/4	205	1 3/8	M33
14	350	20	1 1/4	210	1 3/8	M33
16	400	20	1 3/8	220	1 1/2	M36
18	450	24	1 3/8	230	1 1/2	M36
20	500	24	1 1/2	240	1 3/4	M39
24	600	24	1 3/4	265	1 7/8	M45

Class 600 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	14.3	38	21.3	52	Welding Neck bore is derived from the pipe schedule	34.9	7	66.7	1.6
3/4	20	115	15.9	48	26.7	57		42.9	7	82.6	1.6
1	25	125	17.5	54	33.4	62		50.8	7	88.9	1.6
1 1/4	32	135	20.7	64	42.2	67		63.5	7	98.4	1.6
1 1/2	40	155	22.3	70	48.3	70		73	7	114.3	1.6
2	50	165	25.4	84	60.3	73		92.1	7	127	1.6
2 1/2	65	190	28.6	100	73	79		104.8	7	149.2	1.6
3	80	210	31.8	117	88.9	83		127	7	168.3	1.6
3 1/2	90	230	35	133	101.6	86		139.7	7	184.2	1.6
4	100	275	38.1	152	114.3	102		157.2	7	215.9	1.6
5	125	330	44.5	189	141.3	114		185.7	7	266.7	1.6
6	150	355	47.7	222	168.3	117		215.9	7	292.1	1.6
8	200	420	55.6	273	219.1	133		269.9	7	349.2	1.6
10	250	510	63.5	343	273	152		323.8	7	431.8	1.6
12	300	560	66.7	400	323.8	156		381	7	489	1.6
14	350	605	69.9	432	355.6	165		412.8	7	527	1.6
16	400	685	76.2	495	406.4	178		469.9	7	603.2	1.6
18	450	745	82.6	546	457	184		533.4	7	654	1.6
20	500	815	88.9	610	508	190		584.2	7	723.9	1.6
24	600	940	101.6	718	610	203		692.2	7	838.2	1.6

Class 600 Weld Neck Flange Stud & Bolt Dimensions

Size in Inch	Size in mm	No of Bolts	Bolt Size UNC	RF Stud Length	Hole Size	ISO Stud Size	Weight in kg
1/2	15	4	1/2	75	5/8	M14	1.5
3/4	20	4	5/8	90	3/4	M16	1.8
1	25	4	5/8	90	3/4	M16	1.8
1 1/4	32	4	5/8	95	3/4	M16	2.7
1 1/2	40	4	3/4	110	7/8	M20	3.7
2	50	8	5/8	110	3/4	M16	5.5
2 1/2	65	8	3/4	120	7/8	M20	8.2
3	80	8	3/4	125	7/8	M20	10.5
3 1/2	90	8	7/8	140	1	M24	11.8
4	100	8	7/8	145	1	M24	19.1
5	125	8	1	165	1 1/8	M27	31
6	150	12	1	170	1 1/8	M27	36
8	200	12	1 1/8	190	1 1/4	M30	55
10	250	16	1 1/4	215	1 3/8	M33	86
12	300	20	1 1/4	220	1 3/8	M33	102
14	350	20	1 3/8	235	1 1/2	M36	127
16	400	20	1 1/2	255	1 5/8	M39	177
18	450	20	1 5/8	275	1 3/4	M42	216
20	500	24	1 5/8	285	1 3/4	M42	268
24	600	24	1 7/8	330	2	M48	377

Class 900 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	120	22.3	38	21.3	60	Welding Neck bore is derived from the pipe schedule	34.9	7	82.6	1.6
3/4	20	130	25.4	44	26.7	70		42.9	7	88.9	1.6
1	25	150	28.6	52	33.4	73		50.8	7	101.6	1.6
1 1/4	32	160	28.6	64	42.2	73		63.5	7	111.1	1.6
1 1/2	40	180	31.8	70	48.3	83		73	7	123.8	1.6
2	50	215	38.1	105	60.3	102		92.1	7	165.1	1.6
2 1/2	65	245	41.3	124	73	105		104.8	7	190.5	1.6
3	80	240	38.1	127	88.9	102		127	7	190.5	1.6
4	100	290	44.5	159	114.3	114		157.2	7	235	1.6
5	125	350	50.8	190	141.3	127		185.7	7	279.4	1.6
6	150	380	55.6	235	168.3	140		215.9	7	317.5	1.6
8	200	470	63.5	298	219.1	162		269.9	7	393.7	1.6
10	250	545	69.9	368	273	184		323.8	7	469.9	1.6
12	300	610	79.4	419	323.8	200		381	7	533.4	1.6
14	350	640	85.8	451	355.6	213		412.8	7	558.8	1.6
16	400	705	88.9	508	406.4	216		469.9	7	616	1.6
18	450	785	101.6	565	457	229		533.4	7	685.8	1.6
20	500	855	108	622	508	248		584.2	7	749.3	1.6
24	600	1040	139.7	749	610	292		692.2	7	901.7	1.6

Class 900 Weld Neck Flange Stud & Bolt Dimensions

Size in Inch	Size in mm	No of Bolts	Bolt Size UNC	RF Stud Length	Hole Size	ISO Stud Size	Weight in kg
1/2	15	4	3/4	110	7/8	M20	2.3
3/4	20	4	3/4	115	7/8	M20	2.7
1	25	4	7/8	125	1	M24	4.1
1 1/4	32	4	7/8	125	1	M24	4.6
1 1/2	40	4	1	140	1 1/8	M27	5.9
2	50	8	7/8	145	1	M24	11.5
2 1/2	65	8	1	160	1 1/8	M27	16.5
3	80	8	7/8	145	1	M24	14
4	100	8	1 1/8	170	1 1/4	M30	23
5	125	8	1 1/4	190	1 3/8	M33	39.5
6	150	12	1 1/8	190	1 1/4	M30	50
8	200	12	1 3/8	220	1 1/2	M36	80
10	250	16	1 3/8	235	1 1/2	M36	118
12	300	20	1 3/8	255	1 1/2	M36	148
14	350	20	1 1/2	275	1 5/8	M39	182
16	400	20	1 5/8	285	1 3/4	M42	225
18	450	20	1 7/8	325	2	M48	300
20	500	20	2	350	2 1/8	M52	373
24	600	20	2 1/2	440	2 5/8	M64	680

Class 1500 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	120	22.3	38	21.3	60	Welding Neck bore is derived from the pipe schedule	34.9	7	82.6	1.6
3/4	20	130	25.4	44	26.7	70		42.9	7	88.9	1.6
1	25	150	28.6	52	33.4	73		50.8	7	101.6	1.6
1 1/4	32	160	28.6	64	42.2	73		63.5	7	111.1	1.6
1 1/2	40	180	31.8	70	48.3	83		73	7	123.8	1.6
2	50	215	38.1	105	60.3	102		92.1	7	165.1	1.6
2 1/2	65	245	41.3	124	73	105		104.8	7	190.5	1.6
3	80	265	47.7	133	88.9	117		127	7	203.2	1.6
4	100	310	54	162	114.3	124		157.2	7	241.3	1.6
5	125	375	73.1	197	141.3	156		185.7	7	292.1	1.6
6	150	395	82.6	229	168.3	171		215.9	7	317.5	1.6
8	200	485	92.1	292	219.1	213		269.9	7	393.7	1.6
10	250	585	108	368	273	254		323.8	7	482.6	1.6
12	300	675	123.9	451	323.8	283		381	7	571.5	1.6
14	350	750	133.4	495	355.6	298		412.8	7	635	1.6
16	400	825	146.1	552	406.4	311		469.9	7	704.8	1.6
18	450	915	162	597	457	327		533.4	7	774.7	1.6
20	500	985	177.8	641	508	356		584.2	7	831.8	1.6
24	600	1170	203.2	762	610	406		692.2	7	990.6	1.6

Class 1500 Weld Neck Flange Stud & Bolt Dimensions

Size in Inch	Size in mm	No of Bolts	Bolt Size UNC	RF Stud Length	Hole Size	ISO Stud Size	Weight in kg
1/2	15	4	3/4	110	7/8	M20	2.3
3/4	20	4	3/4	115	7/8	M20	2.7
1	25	4	7/8	125	1	M24	4.1
1 1/4	32	4	7/8	125	1	M24	4.6
1 1/2	40	4	1	140	1 1/8	M27	5.9
2	50	8	7/8	145	1	M24	11.4
2 1/2	65	8	1	160	1 1/8	M27	16.4
3	80	8	1 1/8	180	1 1/4	M30	21.8
4	100	8	1 1/4	195	1 3/8	M33	33
5	125	8	1 1/2	250	1 5/8	M39	59
6	150	12	1 3/8	260	1 1/2	M36	75
8	200	12	1 5/8	290	1 3/4	M42	125
10	250	12	1 7/8	335	2	M48	207
12	300	16	2	375	2 1/8	M52	314
14	350	16	2 1/4	405	2 3/8	M56	427
16	400	16	2 1/2	445	2 5/8	M64	568
18	450	16	2 3/4	495	2 7/8	M72	738
20	500	16	3	540	3 1/8	M76	932
24	600	16	3 1/2	615	3 5/8	M90	1511

Class 2500 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	135	30.2	43	21.3	73	Welding Neck bore is derived from the pipe schedule	34.9	7	88.9	1.6
3/4	20	140	31.8	51	26.7	79		42.9	7	95.2	1.6
1	25	160	35	57	33.4	89		50.8	7	108	1.6
1 1/4	32	185	38.1	73	42.2	95		63.5	7	130.2	1.6
1 1/2	40	205	44.5	79	48.3	111		73	7	146	1.6
2	50	235	50.9	95	60.3	127		92.1	7	171.4	1.6
2 1/2	65	265	57.2	114	73	143		104.8	7	196.8	1.6
3	80	305	66.7	133	88.9	168		127	7	228.6	1.6
4	100	355	76.2	165	114.3	190		157.2	7	273	1.6
5	125	420	92.1	203	141.3	229		185.7	7	323.8	1.6
6	150	485	108	235	168.3	273		215.9	7	368.3	1.6
8	200	550	127	305	219.1	318		269.9	7	438.2	1.6
10	250	675	165.1	375	273	419		323.8	7	539.8	1.6
12	300	760	184.2	441	323.8	464		381	7	619.1	1.6

Class 2500 Weld Neck Flange Stud & Bolt Dimensions

Size in Inch	Size in mm	No of Bolts	Bolt Size UNC	RF Stud Length	Hole Size	ISO Stud Size	Weight in kg
1/2	15	4	3/4	120	7/8	M20	3.3
3/4	20	4	3/4	125	7/8	M20	3.7
1	25	4	7/8	140	1	M24	5.5
1 1/4	32	4	1	150	1 1/8	M27	7.8
1 1/2	40	4	1 1/8	170	1 1/4	M30	11.5
2	50	8	1	180	1 1/8	M27	19
2 1/2	65	8	1 1/8	195	1 1/4	M30	24
3	80	8	1 1/4	220	1 3/8	M33	42.8
4	100	8	1 1/2	255	1 5/8	M39	66
5	125	8	1 3/4	300	1 7/8	M45	111
6	150	8	2	345	2 1/8	M52	173
8	200	12	2	380	2 1/8	M52	264
10	250	12	2 1/2	490	2 5/8	M64	490
12	300	12	2 3/4	540	2 7/8	M72	695