Orifice Flange Sizes (ASME B16.36)

Quick Reference

Orifice flanges hold an orifice plate between two flanges to measure fluid flow rate via differential pressure. Standard: ASME B16.36. Classes: 300, 400, 600, 900, 1500, 2500. Types: Weld neck (most common), slip-on, threaded.

Orifice Flange

Overview

An orifice flange assembly consists of a pair of flanges, orifice plate, gaskets, and bolts. The orifice plate (thin disc with a precise central hole) creates a pressure drop that correlates to flow rate. Integrated pressure taps measure the differential pressure upstream and downstream of the plate.

Specification	Details
Standard	ASME B16.36
Classes	300, 400, 600, 900, 1500, 2500
Types	Weld neck (most common), slip-on, threaded
Materials	A105, A350, A694, A182 (all forged grades)
Applications	Oil & gas, water treatment, chemical processing

Advantages: High accuracy when properly calibrated; durable for high P/T environments; versatile across fluid types.

Installation Critical

Orifice plate must be centered and properly aligned. Pressure taps must be correctly positioned. Regular calibration maintains measurement accuracy.

Operating Principle

Orifice meters work via differential pressure measurement (Bernoulli Principle):

1. Constriction: Fluid flows through the orifice plate’s smaller opening, accelerating
2. Pressure drop: Velocity increase causes pressure decrease across the plate
3. Measurement: Pressure taps measure differential pressure (ΔP) upstream vs. downstream
4. Calculation: Flow rate calculated from ΔP using Bernoulli/Continuity equations, orifice coefficient, and fluid density

Types of Orifice Flanges

Type	Application	Features
Weld Neck	High P/T, critical services	Tapered neck for stress distribution; bore matches pipe ID
Slip-On	Moderate conditions, cost-sensitive	Simpler design, lighter; lower strength than WN
Socket Weld	Small diameter, high pressure	Smooth bore; good strength
Threaded	No-weld zones, low P/T	Quick install/removal; limited P/T capability
RTJ	High P/T, offshore	Metal ring gasket in grooved face; excellent seal

Corner-Tap Configuration

Corner tap orifice flanges have pressure taps located at the orifice plate edges (where plate meets flange face)-provides immediate ΔP reading.

Best for: Clean liquids/gases in smaller pipes with well-developed flow profiles.

Limitations: Not for slurries or particulate-laden fluids (tap clogging risk); more challenging installation/maintenance than flange taps.

Orifice Flange Dimensions ASME B16.36

Notes for data shown in tables:

• Dimensions are in millimeters (excluding bolts and bolt holes).
• Different NPT sizes than 1/2 are available
• Bolt lengths for RF flanges include an allowance for orifice and gasket thickness of 6 mm (0.25 in.) for NPS 1 to NPS 12. Bolt lengths for ring-type joint flanges include the allowance of 15 mm (0.62 in.) for NPS 1 to NPS 3.
• Bore (B) has to be specified by the buyer
• Stud Bolt lengths excl. the height of the chamfers

Weld Neck RF, Class 300

NPS	A	R	O	T	H	X	Tg
1	33.4	50.8	125	36.6	81	54	6.4
1½	48.3	73	155	36.6	84	70	6.4
2	60.3	92.1	165	36.6	84	84	6.4
2½	73	104.8	190	36.6	87	100	6.4
3	88.9	127	210	36.6	87	117	9.5
4	114.3	157.2	255	36.6	90	146	12.7
6	168.3	215.9	320	36.6	98	206	12.7
8	219.1	269.9	380	39.7	110	260	12.7
10	273	323.8	445	46.1	116	321	12.7
12	323.8	381	520	49.3	129	375	12.7
14	355.6	412.8	585	52.4	141	425	12.7
16	406.4	469.9	650	55.6	144	483	12.7
18	457	533.4	710	58.8	157	533	12.7
20	508	584.2	775	62	160	587	12.7
24	610	692.2	915	68.3	167	702	12.7

NPS	Bolt Diameter	# Bolts	Bolt holes diameter	Bolts Diameter	Bolts length mm.
1	88.9	4	11/16	5/8	125
1½	114.3	4	13/16	3/4	135
2	127	8	11/16	5/8	125
2½	149.2	8	13/16	3/4	135
3	168.3	8	13/16	3/4	135
4	200	8	13/16	3/4	135
6	269.9	12	7/8	3/4	135
8	330.2	12	1	7/8	145
10	387.4	16	1 1/8	1	165
12	450.8	16	1¼	1 1/8	180
14	514.4	20	1¼	1 1/8	185
16	571.5	20	1 3/8	1¼	195
18	628.6	24	1 3/8	1¼	205
20	685.8	24	1 3/8	1¼	215
24	812.8	24	1 3/8	1½	240

COMMENTS: The height of Raised Face (RF) in CLASS 300 is 2 mm

Weld Neck RF, Class 600

NPS	A	R	O	T	H	X	Tg
1	33.5	50.8	125	36.6	81	54	6.4
1½	48.3	73	155	36.6	84	70	6.4
2	60.3	92.1	165	36.6	84	84	6.4
2½	73	104.8	190	36.6	87	100	6.4
3	88.9	127	210	36.6	87	117	9.5
4	114.3	157.2	275	38.1	102	152	12.7
6	168.3	215.9	355	47.7	117	222	12.7
8	219.1	269.9	420	55.6	133	273	12.7
10	273	323.8	510	63.5	152	343	12.7
12	323.8	381	560	66.7	156	400	12.7
14	355.6	412.8	605	69.9	165	432	12.7
16	406.4	469.9	685	76.2	178	495	12.7
18	457.2	533.4	745	82.6	184	546	12.7
20	508	584.2	815	88.9	190	610	12.7
24	609.6	692.2	940	101.6	203	718	12.7

NPS	BOLT CIRCLE DIAM.	BOLTS #	HOLES DIAM.	BOLTS DIAMETER	BOLTS LENGTH
1	88.9	4	11/16	5/8	125
1½	114.3	4	13/16	3/4	135
2	127	8	11/16	5/8	125
2½	149.2	8	13/16	3/4	135
3	168.3	8	13/16	3/4	135
4	215.9	8	1	7/8	150
6	292.1	12	1 1/8	1	180
8	349.2	12	1¼	1 1/8	195
10	431.8	16	1 3/8	1¼	220
12	489	20	1 3/8	1¼	230
14	527	20	1½	1 3/8	240
16	603.2	20	1 5/8	1½	260
18	654	20	1 3/4	1 5/8	280
20	723.9	24	1 3/4	1 5/8	300
24	838.2	24	2	1 5/8	335

COMMENTS: The height of Raised Face (RF) in CLASS 600 is 2 mm at NPS 1 - NPS 3, and 7 mm at NPS 4 - NPS 24.

Weld Neck RF, Class 900

NPS	R	O	T	H	X	A	Tg
1	50.8	125	36.6	81	54	33.5	6.4
1½	73	155	36.6	84	70	48.3	6.4
2	92.1	165	36.6	84	84	60.3	6.4
2½	104.8	190	36.6	87	100	73	6.4
3	127	240	38.1	102	127	88.9	9.5
4	157.2	290	44.5	114	159	114.3	12.7
6	215.9	380	55.6	140	235	168.3	12.7
8	269.9	470	63.5	162	298	219.1	12.7
10	323.8	545	69.9	184	368	273	12.7
12	381	610	79.4	200	419	323.8	12.7
14	412.8	640	85.8	213	451	355.6	12.7
16	469.9	705	88.9	216	508	406.4	12.7
18	533.4	785	101.6	229	565	457.2	12.7
20	584.2	855	108	248	622	508	12.7
24	692.2	1040	139.7	292	749	609.6	12.7

NPS	BOLT CIRCLE DIAM.	BOLTS #	HOLES DIAM.	BOLTS DIAMETER	BOLTS LENGTH
1	88.9	4	11/16	5/8	125
1½	114.3	4	13/16	3/4	135
2	127	8	11/16	5/8	125
2½	149.2	8	13/16	3/4	135
3	190.5	8	1	7/8	150
4	235	8	1¼	1 1/8	180
6	317.5	12	1¼	1 1/8	195
8	393.7	12	1½	1 3/8	230
10	469.9	16	1½	1 3/8	240
12	533.4	20	1½	1 3/8	260
14	558.8	20	1 5/8	1½	280
16	616	20	1 3/4	1 5/8	290
18	685.8	20	2	1 7/8	330
20	749.3	20	2 1/8	2	355
24	901.7	20	2 1/8	2½	445

COMMENTS: The height of Raised Face (RF) in CLASS 900 is 7 mm.

Weld Neck RF, Class 1500

NPS	R	O	T	H	X	A	Tg
1	50.8	150	38.1	83	52	33.5	6.4
1½	73	180	38.1	89	70	48.3	6.4
2	92.1	215	38.1	102	105	60.3	6.4
2½	104.8	245	41.3	105	124	73	6.4
3	127	265	47.7	117	133	88.9	9.5
4	157.2	310	54	124	162	114.3	12.7
6	215.9	395	82.6	171	229	168.3	12.7
8	269.9	485	92.1	213	292	219.1	12.7
10	323.8	585	108	254	368	273	12.7
12	381	675	123.9	283	451	323.8	12.7
14	412.8	750	133.4	298	495	355.6	12.7
16	469.9	825	146.1	311	552	406.4	12.7
18	533.4	915	162	327	597	457.2	12.7
20	584.2	985	177.8	356	641	508	12.7
24	692.2	1170	203.2	406	762	609.6	12.7

NPS	BOLT CIRCLE DIAM.	BOLTS #	HOLES DIAM.	BOLTS DIAMETER	BOLTS LENGTH
1	101.6	4	1	7/8	150
1½	123.8	4	1 1/8	1¼	160
2	165.1	8	1	7/8	150
2½	190.5	8	1 1/8	1	165
3	203.2	8	1¼	1 1/8	185
4	241.3	8	1 3/8	1¼	205
6	317.5	12	1½	1 3/8	265
8	393.7	12	1 3/4	1 5/8	300
10	482.6	12	2	1 7/8	345
12	571.6	16	2 1/8	2	380
14	635	16	2 3/8	2¼	415
16	704.8	16	2 5/8	2½	450
18	774.7	16	2 7/8	2 3/4	500
20	831.8	16	3 1/8	3	545
24	990.6	16	3 5/8	3½	620

COMMENTS: The height of Raised Face (RF) in CLASS 1500 is 7 mm

Weld Neck RF, Class 2500

NPS	R	O	T	H	X	A	Tg
1	50.8	160	38.1	92	57	33.5	6.4
1½	73	205	44.5	111	79	48.3	6.4
2	92.1	235	50.8	127	95	60.3	6.4
2½	104.8	265	57.2	143	114	73	6.4
3	127	305	66.7	168	133	88.9	9.5
4	157.2	355	76.2	190	165	114.3	12.7
6	215.9	485	108	273	235	168.3	12.7
8	269.9	550	127	318	305	219.1	12.7
10	323.8	675	165.1	419	375	273	12.7
12	381	760	184.2	464	441	323.8	12.7

NPS	BOLT CIRCLE DIAM.	BOLTS #	HOLES DIAM.	BOLTS DIAMETER	BOLTS LENGTH
1	108	4	1	7/8	150
1½	146	4	1¼	1 1/8	180
2	171.4	8	1 1/8	1	185
2½	196.8	8	1¼	1 1/8	205
3	228.6	8	1 3/8	1¼	230
4	273	8	1 5/8	1½	260
6	368.3	8	2 1/8	2	350
8	438.2	12	2 1/8	2	385
10	539.8	12	2 5/8	2½	490
12	619.1	12	2 7/8	2 3/4	540

COMMENTS: The height of Raised Face (RF) in CLASS 2500 is 7 mm.

Weld Neck RTJ, Class 600

NPS	O	T	H	GROOVE #	P	E
1	125	36.6	81	R16	50.8	6.35
1½	155	36.6	84	R20	68.27	6.35
2	165	36.6	84	R23	82.55	7.92
2½	190	36.6	87	R26	101.6	7.92
3	210	36.6	87	R31	123.83	7.92
4	275	38.1	102	R37	149.23	7.92
6	355	47.7	117	R45	211.12	7.92
8	420	55.6	133	R49	269.88	7.92
10	510	63.5	152	R53	323.85	7.92
12	560	66.7	156	R57	381	7.92
14	605	69.9	165	R61	419.1	7.92
16	685	76.2	178	R65	469.9	7.92
18	745	82.6	184	R69	533.4	7.92
20	815	88.9	190	R73	584.2	9.53
24	940	101.6	203	R77	692.15	11.13

NPS	F	R	W	X	A	Tg
1	8.74	0.8	25.4	54	33.5	6.4
1½	8.74	0.8	25.4	70	48.3	6.4
2	11.91	0.8	27	84	60.3	6.4
2½	11.91	0.8	27	100	73	6.4
3	11.91	0.8	27	117	88.9	9.5
4	11.91	0.8	27	152	114.3	12.7
6	11.91	0.8	27	222	168.3	12.7
8	11.91	0.8	27	273	219.1	12.7
10	11.91	0.8	27	343	273	12.7
12	11.91	0.8	27	400	323.8	12.7
14	11.91	0.8	27	432	355.6	12.7
16	11.91	0.8	30.2	495	406.4	12.7
18	11.91	0.8	30.2	546	457.2	12.7
20	13.49	1.5	31.8	610	508	12.7
24	16.66	1.5	36.5	718	609.6	12.7

Weld Neck RTJ, Class 900

NPS	O	T	H	GROOVE #	P	E
1	125	36.6	81	R16	50.8	6.35
1½	155	36.6	84	R20	68.27	6.35
2	165	36.6	84	R23	82.55	7.92
2½	190	36.6	87	R26	101.6	7.92
3	240	38.1	102	R31	123.83	7.92
4	290	44.5	114	R37	149.23	7.92
6	380	55.6	140	R45	211.12	7.92
8	470	63.5	162	R49	269.88	7.92
10	545	69.9	184	R53	323.85	7.92
12	610	79.4	200	R57	381	7.92
14	640	85.8	213	R62	419.1	11.13
16	705	88.9	216	R66	469.9	11.13
18	785	101.6	229	R70	533.4	12.7
20	855	108	248	R74	584.2	12.7
24	1040	139.7	292	R78	692.15	15.88

NPS	F	R	W	X	A	Tg
1	8.74	0.8	25.4	54	33.5	6.4
1½	8.74	0.8	25.4	70	48.3	6.4
2	11.91	0.8	27	84	60.3	6.4
2½	11.91	0.8	27	100	73	6.4
3	11.91	0.8	27	127	88.9	9.5
4	11.91	0.8	27	159	114.3	12.7
6	11.91	0.8	27	235	168.3	12.7
8	11.91	0.8	27	298	219.1	12.7
10	11.91	0.8	27	368	273	12.7
12	11.91	0.8	27	419	323.8	12.7
14	16.66	1.5	33.3	451	355.6	12.7
16	16.66	1.5	36.5	508	406.4	12.7
18	19.84	1.5	39.7	565	457.2	12.7
20	19.84	1.5	39.7	622	508	12.7
24	26.97	2.4	47.6	749	609.6	12.7

Weld Neck RTJ, Class 1500

NPS	O	T	H	GROOVE #	P	E
1	150	38.1	83	R16	50.8	6.35
1½	180	38.1	89	R20	68.27	6.35
2	215	38.1	102	R24	95.25	7.92
2½	245	41.3	105	R27	107.95	7.92
3	265	47.7	117	R35	136.53	7.92
4	310	54	124	R39	161.93	7.92
6	395	82.6	171	R46	211.14	9.52
8	485	92.1	213	R50	269.88	11.13
10	585	108	254	R54	323.85	11.13
12	675	123.9	283	R58	381	14.27
14	750	133.4	298	R63	419.1	15.88
16	825	146.1	311	R67	469.9	17.48
18	915	162	327	R71	533.4	17.48
20	985	177.8	356	R75	584.2	17.48
24	1170	203.2	406	R79	692.15	20.62

NPS	F	R	W	X	A	Tg
1	8.74	0.8	25.4	52	33.5	6.4
1½	8.74	0.8	25.4	70	48.3	6.4
2	11.91	0.8	27	105	60.3	6.4
2½	11.91	0.8	27	124	73	6.4
3	11.91	0.8	27	133	88.9	9.5
4	11.91	0.8	27	162	114.3	12.7
6	13.49	1.5	28.6	229	168.3	12.7
8	16.66	1.5	33.3	292	219.1	12.7
10	16.66	1.5	33.3	368	273	12.7
12	23.01	1.5	39.7	451	323.8	12.7
14	26.97	2.4	44.4	495	355.6	12.7
16	30.18	2.4	50.8	552	406.4	12.7
18	30.18	2.4	50.8	597	457.2	12.7
20	33.32	2.4	54	641	508	12.7
24	36.53	2.4	58.7	762	609.6	12.7

Weld Neck RTJ, Class 2500

NPS	O	T	H	GROOVE #	P	E
1	160	38.1	92	R18	60.33	6.35
1½	205	44.5	111	R23	82.55	7.92
2	235	50.8	127	R26	101.6	7.92
2½	265	57.2	143	R28	111.13	9.53
3	305	66.7	168	R32	127	9.53
4	355	76.2	190	R38	157.18	11.13
6	485	108	273	R47	228.6	12.7
8	550	127	318	R51	279.4	14.27
10	675	165.1	419	R55	342.9	17.48
12	760	184.2	464	R60	406.4	17.48

NPS	F	R	W	X	A	Tg
1	8.74	0.8	25.4	57	33.5	6.4
1½	11.91	0.8	27	79	48.3	6.4
2	11.91	0.8	27	95	60.3	6.4
2½	13.49	1.5	30.2	114	73	6.4
3	13.49	1.5	30.2	133	88.9	9.5
4	16.66	1.5	33.3	165	114.3	12.7
6	19.84	1.5	36.5	235	168.3	12.7
8	23.01	1.5	39.7	305	219.1	12.7
10	30.18	2.4	47.6	375	273	12.7
12	33.32	2.4	50.8	441	323.8	12.7