Reducing Flanges | ASME B16.5 | Slip-On & Weld Neck

PM Industries manufactures, supplies, and stocks Reducing Flanges in a range of materials, pressure classes, and size combinations. A reducing flange is a single forged component that combines a standard flange face at one end with a reduced bore at the pipe connection end. The face diameter and bolt circle match the larger pipe size so it connects to the mating flange at full size, while the bore and hub are machined to the smaller pipe size where the pipe attaches. The net result is a direct pipe size transition at the flanged joint without a separate concentric reducer fitting between the flange and the pipe.

The comparison to a weld neck flange plus a concentric reducer is the practical reference point. That combination requires two welds, two pieces of material, and additional face-to-face length in the piping layout. A reducing flange handles the same size transition in one piece, one weld, and a shorter overall assembly. In congested piping areas or systems with many size transitions, those reductions matter.

Weld count reduction is relevant in systems where radiographic inspection of welds is required. Each pressure-containing weld in a high-integrity system is an inspection item. Eliminating the reducer removes one circumferential weld from the assembly and the associated inspection cost. In critical piping systems with many size transitions, that reduction accumulates across the system and contributes to lower fabrication and inspection cost.

Space savings are practical in congested equipment rooms, compressor station headers, and offshore platform piping where installed face-to-face length is constrained. Replacing a reducer plus weld neck flange with a single reducing flange shortens the assembly by the reducer length, which on larger pipe sizes can be several hundred millimeters per location.

Pressure and service rating follows the flange's rated pressure class at the larger bore size. The reducing flange carries the full rating of its pressure class without derating for the bore reduction, provided the flange is manufactured to the applicable ASME standard. Engineers should confirm that the smaller bore pipe, fittings, and components downstream of the reducing flange are also rated for the system design conditions.

Industries and typical applications:

• Oil and gas: process piping size transitions, compressor station headers, pump discharge connections, and wellhead piping.
• Chemical processing: heat exchanger connections, reactor inlet and outlet piping, and size transitions in corrosive process lines.
• Power generation: steam system piping, boiler connections, and turbine inlet piping where size transitions occur at flanged joints.
• Water treatment: pump discharge and distribution piping size transitions.
• General industrial: compressed air, process utilities, and plant piping size changes at flanged equipment connections.

Reducing flanges are available with full material certification to ASTM, ASME, and applicable specifications including NACE MR0175 for sour service. Contact PM Industries for size combination, material grade, pressure class, face type, and pricing.

Specification Reducing Flange

Standards	ANSI/ASME B16.5, B16.48, GOST, DIN, EN-1092, B16.47 Series A & B, AWWA, BS Flanges
JIS Standard	5K, 10K, 16K, 20K, 30K, 40K, 63K
DIN Flanges	DIN 2527, 2627, 2631, 2656, 2576, 2673, 2629, 2628, 2566

Flanges are Available in Following Materials

Stainless Steel	SS 201, SS 202, SS 301, SS 304, SS 304L, SS 310, SS 310S, SS 316L, SS 316TI, SS 317, SS 317L, SS 321, SS 347, SS 409, SS 409M, SS 409L, SS 410, SS 410S, SS 420, SS 430, SS 431, SS 441, SS 444, SS 446, SS 17-4PH, SS 904L.
Duplex Steel	UNS S32205, UNS S31803 Flange
Super Duplex Steel	UNS S32750, UNS S32760 Flanges
Carbon Steel	Carbon steel A105 Flanges, A36 Flanges, IS 2062 Flanges, A350 LF2 Flanges, F42 Flanges, F52 Flanges, F56 Flanges, F60 Flanges, F65 Flanges, F70 Flanges, F80 Flanges, IBR flanges, A694 Flanges, SS400, SF440, ST37-2 Flanges, S235JrG2 Flanges, P250GH Flanges, C22.8 Flanges, etc.
Alloys Steel	Alloy 20, F1, F5, F9, F11, F22, F91 Flanges
Copper Alloys	Cu-Ni 70/30, Cu-Ni 90/10, C 24000, C 75700, C 51100, C 22000, C 27200, C 21000, C 26800, C 52100, C 77000, C 52000, C 11000, C 74500, C 23000, C 28000, C 12200, C 76400, C 51900, C 75400, C 26000, C 51000, C 10200, C 27000
Nickel Alloys	Nickel 200, 201
Inconel	Inconel 600, 601, 625, 718, 800, 825, X-750
Monel	Monel 400, k500
Hastelloy	Hastelloy C-22, C-276, C-4, X
Titanium	Grade 1, 4, 5(Ti 6Al-4V), 6(Ti 5Al-2.5Sn), 7, 11, 6Al-2Sn-4Zr-2Mo, Grade 12, 6Al-6V-25n, Grade 23(Ti 6AL-4V ELI), 8Ai-1Mo-1V, Grade 5 ELI, Grade 9(3Al-2.5V), 6Al-7Nb.
Aluminium	6063, 1100, 6082 A96082, 1050, 2017, 2024 A92024, 7050 A97050, 5083 A95083, 2014A A92014, 2011 A92011, 6061 A96061 A86061, 5754, 7085, 2050, 7071 7020, 7178, 5052 A95052, 7150, 7075 A97075 A87075, 7575, 2219, 7175
Pressure Rating	Class 150 LBS, 300 LBS, 600 LBS, 900 LBS, 1500 LBS, 2500 LBS
Types	Threaded, Plate, Screwed, Forged.
Supporting material	Gasket, Ring Joint, Flange Bolts
Size range	1/2" (15 NB) to 48" (1200NB) DN10~DN5000
High Temperature	Above 200°C (400°F) For Class 150 Or Above 400°C (750°F)
Low Temperature	Above -29 Degree C (−20°F)
Production technique	Forged, machined and Heat treated
Custom design	As per your drawing
Origin	Indian / USA / Korean / West Europe / Japan
Pressure Class	PN 6 TO PN 100
Coating/Surface Treatment:	Zinc Plated, Anti-rust Paint, Oil Black Paint, Yellow Transparent, Cold and Hot Dip Galvanized.
European/African/Russian Standard Flanges	Available
Test	Direct-reading Spectrograph, X-ray detector, UItrasonic flaw detector, Magnetic particle detector, Hydrostatic testing machine.
Marking Standard	Name of Manufacturer
	Schedule
	Type of Flange Facing
	Pressure Class
	Nominal Pipe Size, etc
Test Certificates	EN 10204/3.1B, NACE MR0103, NACE MR0175
	Raw Materials Certificate
	100% Radiography Test Report
	Third Party Inspection Report, etc

Reducing Flange Size Chart

Nominal Pipe Size		Type	Ø A	D	Liner Thickness
DN1	DN2
In.	In.		mm	mm	mm
3/4	1/2	1	98.5	30	5.0
1	1/2	1	108	30	5.0
1	3/4	1	108	30	5.0
1.1/2	1/2	1	127	30	5.0
1.1/2	3/4	1	127	30	5.0
1.1/2	1	1	127	30	5.0
2	1/2	3	152	30	5.0
2	3/4	2	152	30	5.0
2	1	2	152	30	5.0
2	1.1/2	1	152	30	5.0
3	3/4	3	190.5	35	5.0
3	1	3	190.5	35	5.0
3	1.1/2	2	190.5	35	5.0
3	2	1	190.5	35	5.0
4	3/4	3	228.6	35	5.0
4	1	3	228.6	35	5.0
4	1.1/2	3	228.6	35	5.0
4	2	3	228.6	35	5.0
4	3	2	228.6	35	5.0
6	3/4	3	280	40	5.0
6	1	3	280	40	5.0
6	1.1/2	3	280	40	5.0
6	2	3	280	40	5.0
6	3	3	280	40	5.0
6	4	2	280	40	5.0
8	1	3	343	35	5.0
8	1.1/2	3	343	35	5.0
8	2	3	343	40	5.0
8	3	3	343	40	5.0
8	4	3	343	40	5.0
8	6	2	343	40	5.0
10	1	3	406	35	2.5
10	1.1/2	3	406	35	2.5
10	2	3	406	35	2.5
10	3	3	406	35	2.5
10	4	3	406	35	2.5
10	6	3	406	35	2.5
10	8	2	406	35	3.5
12	1	3	483	35	3.5
12	1.1/2	3	483	35	3.5
12	2	3	483	35	3.5
12	3	3	483	35	3.5
12	4	3	483	35	3.5
12	6	3	483	35	3.5
12	8	3	483	35	3.5
12	10	2	483	35	3.5
14	12	1	533	40	3.5
16	12	3	597	40	3.5
16	14	2	597	35	3.5

>

Reducing Flange Gasket Size

Nominal Pipe Size	Gasket Inside Diameter - Inner Diameter - (inch)	Gasket Outside Diameter
		Class 150 LBS	Class 300 LBS	Class 400 LBS	Class 600 LBS	Class 900 LBS
1	1.31	2.625	2.875	2.875	2.875	3.125
3/4	1.06	2.25	2.625	2.625	2.625	2.75
1 1/4	1.66	3	3.25	3.25	3.25	3.50
3	3.50	5.375	5.875	5.875	5.875	6.625
1 1/2	1.91	3.375	3.75	3.75	3.75	3.875
1/2	0.84	1.875	2.125	2.125	2.125	2.50
2	2.38	4.125	4.375	4.375	4.375	5.625
2 1/2	2.88	4.875	5.125	5.125	5.125	6.50
4	4.50	6.875	7.125	7.00	7.625	8.125
5	5.56	7.75	8.50	8.375	9.50	9.75
12	12.75	16.125	16.625	16.50	18.00	19.625
6	6.62	8.75	9.875	9.75	10.50	11.375
8	8.62	11	12.125	12.00	12.625	14.125
10	10.75	13.375	14.25	14.125	15.75	17.125

Stainless Steel Reducing Flange Pressure Rating

Temperature (F°)	150 LBS	300 LBS	400 LBS	600 LBS	900 LBS	1500 LBS	2500 LBS
-20 to 100	285	740	985	1480	2220	3705	6170
750	95	505	675	1015	1520	2535	4230
300	230	655	870	1310	1965	3270	5450
400	200	635	845	1265	1900	3170	5280
500	170	605	805	1205	1810	3015	5025
600	140	570	755	1135	1705	2840	4730
650	125	550	730	1100	1650	2745	4575
200	260	680	905	1360	2035	3395	5655
1000	20	85	115	170	255	430	715
700	110	530	710	1060	1590	2655	4425
800	80	410	550	825	1235	2055	3430
850	65	320	425	640	955	1595	2655
900	50	230	305	460	690	1150	1915
950	35	135	185	275	410	685	1145

Reducing Flange Weight Chart

NPS	O D	Schedule 10	Schedule 20	Schedule 30	Schedule. Wall	Schedule 40	Schedule 60	Extra Strong	Schedule 80	Schedule 100	Schedule 120	Schedule 140	Schedule 160	Double Extra Strong
1/2	0.840	0.674			0.622	0.622		0.546	0.546				0.464	0.252
3/4	1.050	0.884			0.824	0.824		0.742	0.742				0.612	0.434
1	1.315	1.097			1.049	1.049		0.957	0.957				0.815	0.599
1.1/4	1.660	1.442			1.380	1.380		1.278	1.278				1.160	0.896
1.1/2	1.900	1.682			1.610	1.610		1.500	1.500				1.338	1.100
2	2.375	2.157			2.067	2.067		1.939	1.939				1.687	1.503
2.1/2	2.875	2.635			2.469	2.469		2.323	2.323				2.125	1.771
3	3.500	3.260			3.068	3.068		2.900	2.900				2.624	2.300
3-1/2	4.000	3.760			3.548	3.548		3.364	3.364					2.728
4	4.500	4.260			4.026	4.026		3.826	3.826		3.624		3.438	3.152
5	5.563	5.295			5.047	5.047		4.813	4.813		4.563		4.313	4.063
6	6.625	6.357			6.065	6.065		5.761	5.761		5.501		5.187	4.897
20	20.000	19.500	19.250	19.000	19.250	18.812	18.376	19.000	17.938	17.438	17.000	16.500	16.062
8	8.625	8.329	8.125	8.071	7.981	7.981	7.813	7.625	7.625	7.437	7.187	7.001	6.813	6.875
12	12.750	12.390	12.250	12.090	12.000	11.938	11.626	11.750	11.374	11.062	10.750	10.500	10.126	10.750
14	14.000	13.500	13.376	13.250	13.250	13.124	12.812	13.000	12.500	12.124	11.814	11.500	11.188
10	10.750	10.420	10.250	10.136	10.020	10.020	9.750	9.750	9.562	9.312	9.062	8.750	8.500	8.750
16	16.000	15.500	15.376	15.250	15.250	15.000	14.688	15.000	14.312	13.938	13.564	13.124	12.812
18	18.000	17.500	17.376	17.124	17.250	16.876	16.500	17.000	16.124	15.688	15.250	14.876	14.438
24	24.000	23.500	23.250	22.876	23.250	22.624	22.062	23.000	21.562	20.938	20.376	19.876	19.312
30	30.000	29.376	29.000	28.750	29.250			29.000
36	36.000	35.376	35.000	34.750	35.250	34.500		35.000
42	42.000				41.250			41.000

150# Reducing Flange Dimensions

Nominal Pipe Size	Diameter	Thickness	Diameter	Welding	Minimum	Minimum	Minimum	Nexk		Welding		Joint
DN	O	T	A	B	C	D	E	F		G		H
15	133	30.5	34.9		22.2	22.9	23.5	73.0		40		40
3/4	5.50	1.25	1.69		1.09	1.11	1.14	3.12		1.69		1.69
20	140	32.0	42.9		27.8	28.2	29.0	79.4		43		43
1	6.25	1.38	2.00		1.36	1.38	1.41	3.50		1.88		1.88
1/2	5.25	1.19	1.38		0.88	.90	0.93	2.88		1.56		1.56
25	159	35.0	50.8		34.5	34.9	36.0	88.9		48		48
32	184	38.5	63.5		43.3	43.7	44.5	95.2		52		52
1 1/2	8.00	1.75	2.88		1.95	1.97	1.99	4.38		2.38		2.38
40	203	44.5	73.0		49.6	50.0	50.5	111.4		60		60
1 1/4	7.25	1.50	2.50		1.70	1.72	1.75	3.75		2.06		2.06
2	9.25	2.00	3.62	To be	2.44	2.46	2.50	5.00		2.75		2.75
50	235	51.0	92.1		61.9	62.5	63.5	127.0		70		70
65	267	57.5	104.8	74.6	75.4	76	142.9		79		79
3	12.00	2.62	5.00	by	3.57	3.60	3.63	6.62		3.62		3.62
2 1/2	10.50	2.25	4.12		specified	2.94	2.97	3.00	5.62		3.12		3.12
80	305	67.0	127.0	90.7		91.4	92	168.2		92		92
100	356	76.5	157.2		116.1	116.8	118	190.5		108		108
5	16.50	3.62	7.31		5.66	5.69	5.69	9.00		5.12		5.12
125	419	92.5	185.7		143.7	144.5	145	228.6		130		130
4	14.00	3.00	6.19	purchaser	4.57	4.60	4.63	7.50		4.25		4.25
6	19.00	4.25	8.50		6.72	6.75	6.75	10.75		6.0		6.0
150	483	108.0	215.9		170.7	171.4	171	273.0		152		152
8	21.75	5.00	10.62		8.72	8.75	8.75	12.50		7.0		7.0
10	26.50	6.50	12.75		10.88	10.92	10.88	16.50		9.0		9.0
250	675	165.5	323.8		276.2	277.4	276	419.4		229		229
12	30.00	7.25	15.00		12.88	12.92	12.94	18.25		10.0		10.0
200	552	127.0	269.9		221.5	222.2	222	317.5		178		178
300	760	184.5	381.0		327.0	328.2	329	463.6		254		254

Reducing Slip On Flange Dimensions

Normal Pipe Size	Diam.	Thick.	DIA.	Welding	Minimum	Minimum	Minimum	Neck		Welding		Joint
DN	O	T	A	B	C	D	E	F		G		H
1/2	5.25	1.19	1.38		0.88	.90	0.93	2.88		1.56		1.56
15	133	30.5	34.9		22.2	22.9	23.5	73.0		40		40
3/4	5.50	1.25	1.69		1.09	1.11	1.14	3.12		1.69		1.69
20	140	32.0	42.9		27.8	28.2	29.0	79.4		43		43
1	6.25	1.38	2.00		1.36	1.38	1.41	3.50		1.88		1.88
25	159	35.0	50.8		34.5	34.9	36.0	88.9		48		48
1 1/4	7.25	1.50	2.50		1.70	1.72	1.75	3.75		2.06		2.06
32	184	38.5	63.5		43.3	43.7	44.5	95.2		52		52
1 1/2	8.00	1.75	2.88		1.95	1.97	1.99	4.38		2.38		2.38
40	203	44.5	73.0		49.6	50.0	50.5	111.4		60		60
2	9.25	2.00	3.62	To be	2.44	2.46	2.50	5.00		2.75		2.75
50	235	51.0	92.1		61.9	62.5	63.5	127.0		70		70
2 1/2	10.50	2.25	4.12	specified	2.94	2.97	3.00	5.62		3.12		3.12
65	267	57.5	104.8		74.6	75.4	76	142.9		79		79
3	12.00	2.62	5.00	by	3.57	3.60	3.63	6.62		3.62		3.62
80	305	67.0	127.0		90.7	91.4	92	168.2		92		92
4	14.00	3.00	6.19	purchaser	4.57	4.60	4.63	7.50		4.25		4.25
100	356	76.5	157.2		116.1	116.8	118	190.5		108		108
5	16.50	3.62	7.31		5.66	5.69	5.69	9.00		5.12		5.12
125	419	92.5	185.7		143.7	144.5	145	228.6		130		130
6	19.00	4.25	8.50		6.72	6.75	6.75	10.75		6.0		6.0
150	483	108.0	215.9		170.7	171.4	171	273.0		152		152
8	21.75	5.00	10.62		8.72	8.75	8.75	12.50		7.0		7.0
200	552	127.0	269.9		221.5	222.2	222	317.5		178		178
10	26.50	6.50	12.75		10.88	10.92	10.88	16.50		9.0		9.0
250	675	165.5	323.8		276.2	277.4	276	419.4		229		229
12	30.00	7.25	15.00		12.88	12.92	12.94	18.25		10.0		10.0
300	760	184.5	381.0		327.0	328.2	329	463.6		254		254