Weld Neck Flanges

INTRO

We Manufacture Stainless Steel Weld Neck Flange from Size 1/2 to 24 NPS, pressure classes from 150 to 2500. Low MoQ, Direct to Factory Price and available for custom bolt hole, size options. For more details, please refer to Table of Dimensions below, or ASK OUR ENGINEER for more assistance.

Standard：
GB/T9119-2010 HG/T20592-2009 HG/T20615-2009 DIN ASME BS JIS

Material：
304：F304 S30408 S30408II S30408III S30400
304L：S30403 S30403II 30403 30403II
316L：31603 31603II 31603III
2507（F53） 2205（F51） TP310S（06Cr5Ni20） TP321（06Cr18Ni11） S22053III=2205III T321-32168=321

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DESCRIPTION DOWNLOAD

Our Weld Neck Flanges are designed for high-pressure and high-temperature applications. Manufactured with precise tolerances and in compliance with ANSI, ASTM, DIN and JIS standards.

Manufacturer Intro

Longan Flange is a dedicated stainless steel weld neck flange manufacturer based in Wenzhou, China. We produce weld neck flanges from DN15 to DN600, covering Class 150 through Class 2500 per ASME B16.5, as well as DIN and GOST standards. Materials include SS304, 304L, 316L, duplex 2205 (F51), and super duplex 2507 (F53). Every flange is forged, machined, and inspected in-house with full material traceability. Weld neck flange dimensions and weight data for each pressure class are listed in the specification tables below. ISO 9001 & PED certified. Get a quote within 24 hours.

Tapered Hub Design: Why Weld Neck Flanges Handle High Pressure

Unlike slip-on or lap joint flanges, a weld neck flange is butt-welded directly to the pipe, with a tapered hub that gradually transitions the flange’s thickness into the pipe wall. Complete weld neck flange dimensions for Class 150 through Class 2500 are listed in the tables above.

Bevel-Welded Joint

The flange is butt-welded to the pipe with a full-penetration weld, providing a joint strength comparable to the pipe itself — the reason weld neck flanges are the standard choice for high-pressure and high-temperature piping.

Tapered Hub

The gradual taper from the flange body to the pipe wall reduces stress concentration at the weld, improving fatigue resistance under cyclic pressure and temperature loads compared to a fillet-welded connection.

Weld Neck vs. Slip-On Flange: Which One Do You Need?

A weld neck flange is butt-welded to the pipe for maximum joint strength, making it the preferred choice for high-pressure, high-temperature, and critical piping systems. A slip-on flange slides over the pipe and is fillet-welded on both sides — easier and more affordable to install, but with lower joint strength, so it’s typically limited to Class 150–300 services. See our Slip-On Flanges page for full details if your application falls in that range.

Quality Control for High-Pressure Weld Integrity

Material Testing

Spectral detection for composition

Forging

Solid forged, no cast components

CNC Machining

Hub taper & bevel precision

Final Inspection

Dimensional check & material traceability

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MOQ from 1 Piece

Standard sizes and classes available from a single piece.

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Quote Within 24 Hours

Factory-direct technical quotations delivered within 24 hours of your inquiry.

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ISO 9001 / ISO 14001 / ISO 45001 / CE / PED

Manufactured in a certified facility, compliant with ASME B16.5, DIN, and GOST standards. MTC per EN 10204 3.1 supplied with every order.

Also Available: Long Weld Neck Flanges

In addition to standard weld neck flanges, Longan Flange also manufactures long weld neck flanges (extended hub length) for applications such as vessel and tank nozzle connections. Please contact us with your required class and dimensions for a technical quotation.

FAQ

What sizes of stainless steel weld neck flanges do you manufacture?

We manufacture stainless steel weld neck flanges from DN15 (NPS ½”) to DN600 (NPS 24″) as standard. For larger sizes up to DN4000, please contact us for custom manufacturing options.

What pressure classes are available for your weld neck flanges?

Our weld neck flanges are available in Class 150, 300, 600, 900, 1500, and 2500 per ASME B16.5. DIN PN ratings and GOST standards are also available. See the dimension tables above for detailed specifications by class.

Can you supply weld neck flanges in duplex stainless steel?

Yes. We manufacture weld neck flanges in duplex 2205 (F51) and super duplex 2507 (F53) in addition to standard grades SS304, 304L, and 316L. All materials come with full mill test certificates.

What is the lead time for weld neck flanges?

Lead time depends on size, quantity, and material — larger diameters and duplex alloys generally require more production time than standard sizes in stock alloys. We confirm the exact delivery schedule in your quotation. Quotes are provided within 24 hours of receiving your inquiry.”

Do you provide material test certificates with your flanges?

Yes. Every flange ships with a material test report. Our quality process includes NDT, hardness testing, and full material traceability from raw billet to finished product.

###Class 150###

Nominal size		Steel Pipe outer diameter	Connection size					flange thickness	flange inner diameter	flange neck big end	flange height
DN	NPS	A	Flange outer diameter D	Central circle diameter K	Bolt hole diameter L	Number of bolt holes n	Bolt Th	C	B	N	H
15	1/2	21.3	90	60.3	16	4	M14	9.6	15.5	30	46
20	3/4	26.9	100	69.9	16	4	M14	11.2	21	38	51
25	1	33.7	110	79.4	16	4	M14	12.7	27	49	54
32	1 1/4	42.4	115	88.9	16	4	M14	14.3	35	59	56
40	1 1/2	48.3	125	98.4	16	4	M14	15.9	41	65	60
50	2	60.3	150	120.7	18	4	M16	17.5	52	78	62
65	2 1/2	76.1	180	139.7	18	4	M16	20.7	66	90	68
80	3	88.9	190	152.4	18	4	M16	22.3	77.5	108	68
100	4	114.3	230	190.5	18	8	M16	22.3	101.5	135	75
125	5	139.7	255	215.9	22	8	M20	22.3	127	164	87
150	6	168.3	280	241.3	22	8	M20	23.9	154	192	87
200	8	219.1	345	298.5	22	8	M20	27	203	246	100
250	10	273	405	362	26	12	M24	28.6	255	305	100
300	12	323.9	485	431.8	26	12	M24	30.2	303.5	365	113
350	14	355.6	535	476.3	30	12	M27	33.4	–	400	125
400	16	406.4	595	539.8	30	16	M27	35	–	457	125
450	18	457	635	577.9	33	16	M30	38.1	–	505	138
500	20	508	700	635	33	20	M30	41.3	–	559	143
600	24	610	815	749.3	36	20	M33	46.1	–	663	151

###Class 300###

Nominal size		Steel Pipe outer diameter	Connection size					flange thickness	flange inner diameter	flange neck big end	flange height
DN	NPS	A	Flange outer diameter D	Central circle diameter K	Bolt hole diameter L	Number of bolt holes n	Bolt Th	C	B	N	H
15	1/2	21.3	95	66.7	16	4	M14	12.7	15.5	38	51
20	3/4	26.9	115	82.6	18	4	M16	14.3	21	48	56
25	1	33.7	125	88.9	18	4	M16	15.9	27	54	60
32	1 1/4	42.4	135	98.4	18	4	M16	17.5	35	64	64
40	1 1/2	48.3	155	114.3	22	4	M20	19.1	41	70	67
50	2	60.3	165	127	18	8	M16	20.7	52	84	68
65	2 1/2	76.1	190	149.2	22	8	M20	23.9	66	100	75
80	3	88.9	210	168.3	22	8	M20	27	77.5	117	78
100	4	114.3	255	200	22	8	M20	30.2	101.5	146	84
125	5	139.7	280	235	22	8	M20	33.4	127	178	97
150	6	168.3	320	269.9	22	12	M20	35	154	206	97
200	8	219.1	380	330.2	26	12	M24	39.7	203	260	110
250	10	273	445	387.4	30	16	M27	46.1	255	321	116
300	12	323.9	520	450.8	33	16	M30	49.3	303.5	375	129
350	14	355.6	585	514.4	33	20	M30	52.4	–	425	141
400	16	406.4	650	571.5	36	20	M33	55.6	–	483	144
450	18	457	710	628.6	36	24	M33	58.8	–	533	157
500	20	508	775	685.8	36	24	M33	62	–	587	160
600	24	610	915	812.8	42	24	M39X3	68.3	–	702	167

###Class 600###

Nominal size		Steel Pipe outer diameter	Connection size					flange thickness	flange inner diameter	flange neck big end	flange height
DN	NPS	A	Flange outer diameter D	Central circle diameter K	Bolt hole diameter L	Number of bolt holes n	Bolt Th	C	B	N	H
15	1/2	21.3	95	66.7	16	4	M14	14.3	–	38	52
20	3/4	26.9	115	82.6	18	4	M16	15.9	–	48	57
25	1	33.7	125	88.9	18	4	M16	17.5	–	54	62
32	1 1/4	42.4	135	98.4	18	4	M16	20.7	–	64	67
40	1 1/2	48.3	155	114.3	22	4	M20	22.3	–	70	70
50	2	60.3	165	127	18	8	M16	25.4	–	84	73
65	2 1/2	76.1	190	149.2	22	8	M20	28.6	–	100	79
80	3	88.9	210	168.3	22	8	M20	31.8	–	117	83
100	4	114.3	275	215.9	26	8	M24	38.1	–	152	102
125	5	139.7	330	266.7	30	8	M27	44.5	–	189	114
150	6	168.3	355	292.1	30	12	M27	47.7	–	222	117
200	8	219.1	420	349.2	33	12	M30	55.6	–	273	133
250	10	273	510	431.8	36	16	M33	63.5	–	343	152
300	12	323.9	560	489	36	20	M33	66.7	–	400	156
350	14	355.6	605	527	39	20	M36X3	69.9	–	432	165
400	16	406.4	685	603.2	42	20	M39X3	76.2	–	495	178
450	18	457	745	654	45	20	M42X3	82.6	–	546	184
500	20	508	815	723.9	45	24	M42X3	88.9	–	610	190
600	24	610	940	838.2	51	24	M48X3	101.6	–	718	203

###Class 900###

Nominal size		Steel Pipe outer diameter	Connection size					flange thickness	flange inner diameter	flange neck big end	flange height
DN	NPS	A	Flange outer diameter D	Central circle diameter K	Bolt hole diameter L	Number of bolt holes n	Bolt Th	C	B	N	H
15	1/2	21.3	120	82.6	22	4	M20	22.3	–	38	60
20	3/4	26.9	130	88.9	22	4	M20	25.4	–	44	70
25	1	33.7	150	101.6	26	4	M24	28.6	–	52	73
32	1 1/4	42.4	160	111.1	26	4	M24	28.6	–	64	73
40	1 1/2	48.3	180	123.8	30	4	M27	31.8	–	70	83
50	2	60.3	215	165.1	26	8	M24	38.1	–	105	102
65	2 1/2	76.1	245	190.5	30	8	M27	41.3	–	124	105
80	3	88.9	240	190.5	26	8	M24	38.1	–	127	102
100	4	114.3	290	235	33	8	M30	44.5	–	159	114
125	5	139.7	350	279.4	36	8	M33	50.8	–	190	127
150	6	168.3	380	317.5	33	12	M30	55.6	–	235	140
200	8	219.1	470	393.7	39	12	M36X3	63.5	–	298	162
250	10	273	545	469.9	39	16	M36X3	69.9	–	368	184
300	12	323.9	610	533.4	39	20	M36X3	79.4	–	419	200
350	14	355.6	640	558.8	42	20	M39X3	85.8	–	451	213
400	16	406.4	705	616	45	20	M42X3	88.9	–	508	216
450	18	457	785	685.8	51	20	M48X3	101.6	–	565	229
500	20	508	855	749.3	55	20	M52X3	108	–	622	248
600	24	610	1040	901.7	68	20	M64X3	139.7	–	749	292

###Class 1500###

Nominal size		Steel Pipe outer diameter	Connection size					flange thickness	flange inner diameter	flange neck big end	flange height
DN	NPS	A	Flange outer diameter D	Central circle diameter K	Bolt hole diameter L	Number of bolt holes n	Bolt Th	C	B	N	H
15	1/2	21.3	120	82.6	22	4	M20	22.3	–	38	60
20	3/4	26.9	130	88.9	22	4	M20	25.4	–	44	70
25	1	33.7	150	101.6	26	4	M24	28.6	–	52	73
32	1 1/4	42.4	160	111.1	26	4	M24	28.6	–	64	73
40	1 1/2	48.3	180	123.8	30	4	M27	31.8	–	70	83
50	2	60.3	215	165.1	26	8	M24	38.1	–	105	102
65	2 1/2	76.1	245	190.5	30	8	M27	41.3	–	124	105
80	3	88.9	265	203.2	33	8	M30	47.7	–	133	117
100	4	114.3	310	241.3	36	8	M33	54	–	162	124
125	5	139.7	375	292.1	42	8	M39X3	73.1	–	197	156
150	6	168.3	395	317.5	39	12	M36X3	82.6	–	229	171
200	8	219.1	485	393.7	45	12	M42X3	92.1	–	292	213
250	10	273	585	482.6	51	12	M48X3	108	–	368	254
300	12	323.9	675	571.5	55	16	M52X3	123.9	–	451	283
350	14	355.6	750	635	60	16	M56X3	133.4	–	495	298
400	16	406.4	825	704.8	68	16	M64X3	146.1	–	552	311
450	18	457	915	774.7	74	16	M70X3	162	–	597	327
500	20	508	985	831.8	80	16	M76X3	177.8	–	641	356
600	24	610	1170	990.6	94	16	M90X3	203.2	–	762	406

###Class 2500###

Nominal size		Steel Pipe outer diameter	Connection size					flange thickness	flange inner diameter	flange neck big end	flange height
DN	NPS	A	Flange outer diameter D	Central circle diameter K	Bolt hole diameter L	Number of bolt holes n	Bolt Th	C	B	N	H
15	1/2	21.3	135	88.9	22	4	M20	30.2	–	43	73
20	3/4	26.9	140	95.2	22	4	M20	31.8	–	51	79
25	1	33.7	160	108	26	4	M24	35	–	57	89
32	1 1/4	42.4	185	130.2	30	4	M27	38.1	–	73	95
40	1 1/2	48.3	205	146	33	4	M30	44.5	–	79	111
50	2	60.3	235	171.4	30	8	M27	50.9	–	95	127
65	21/2	76.1	265	196.8	33	8	M30	57.2	–	114	143
80	3	88.9	305	228.6	36	8	M33	66.7	–	133	168
100	4	114.3	355	273	42	8	M39X3	76.2	–	165	190
125	5	139.7	420	323.8	48	8	M45X3	92.1	–	203	229
150	6	168.3	485	368.3	55	8	M52X3	108	–	235	273
200	8	219.1	550	438.2	55	12	M52X3	127	–	305	318
250	10	273	675	539.8	68	12	M64X3	165.1	–	375	419
300	12	323.9	760	619.1	74	12	M70X3	184.2	–	441	464