Spectacle Blind Flanges | ASME B16.48 | Figure-8 Blanks

PM Industries manufactures, supplies, and stocks Spectacle Blind Flanges in a range of materials, pressure ratings, and pipe sizes. A spectacle blind is a single flat component made from two circular discs connected by a central bar, shaped like a pair of spectacles. One disc is solid, providing complete positive isolation when rotated into the pipeline. The other disc is an open ring with the same outer diameter and bolt pattern, allowing normal flow through the line when rotated into position. Both discs stay connected as one piece throughout service. Switching between isolation and flow involves loosening the flange bolts, rotating the spectacle blind so the required disc is centered between the flanges, and retightening.

That single-piece rotating design distinguishes the spectacle blind from the spade and spacer ring arrangement, which is a two-piece alternative serving the same function. Both approaches achieve positive isolation. The spectacle blind keeps both the isolation disc and the flow ring physically connected and always present at the isolation point, which eliminates the possibility of a component being misplaced or left out of the installation. The spade and spacer ring pair is preferred for larger pipe sizes where the spectacle blind would be too large and heavy to rotate in place, but for smaller to medium bore sizes, the spectacle blind's single-piece configuration is practical and widely used.

Positive isolation for safe work is the engineering justification for spectacle blinds in process plants. A closed valve is not positive isolation. Valves leak through seat wear, packing degradation, and actuator failure. When a permit-to-work requires isolation before breaking a flange, entering a vessel, or working on equipment connected to a live process line, a closed valve alone doesn't satisfy most safety management systems. A solid blind in place between the flanges provides a physical barrier that can be visually confirmed and that cannot leak regardless of valve condition upstream or downstream.

Visual line status confirmation is operationally valuable in dense piping environments. Walking through a process area and reading the position of spectacle blind handles gives an unambiguous status of which lines are isolated and which are in flow service without relying on valve position indicators, DCS readings, or instrument data. In a complex refinery or chemical plant, that visual read-down capability during pre-startup checks and maintenance planning has direct safety value.

Rotating in place is practical for small to medium bore spectacle blinds. Larger sizes become heavy enough that rotation between flanges requires mechanical assistance. The practical size limit for in-place rotation varies by pipe size, pressure class, and the specific installation, but most specifications suggest that pipe sizes above approximately NPS 8 to NPS 12 are better served by spade and spacer ring pairs rather than one-piece spectacle blinds.

Spectacle blind flanges are available with full material certification to applicable ASTM, ASME, and process plant standards including NACE MR0175/ISO 15156 for sour service. Contact PM Industries for pipe size, pressure class, material grade, and pricing.

Specification Spectacle Blind 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

SS Spectacle Blind Flange Pressure ratings

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

Weight Of Spectacle Blind Flanges

Normal Pipe Size		Dimensions		Weight in Kg
NPS (In.)	DN (millimeter)	FLANGES Outer Diameter Millimeter Millimeter	FLANGES Thickness D millimeter	SOW Socket Weld	Weld Neck	Blind
1/2	15	88.9	11.2	0.4	0.5	0.4
2	50	152.4	19.1	2.1	2.6	2.4
1	25	108	14.2	0.8	1	0.9
1 1/4	32	117.3	15.7	1	1.3	1.2
1 1/2	40	127	17.5	1.3	1.7	1.5
3/4	20	98.6	12.7	0.6	0.7	0.6
2 1/2	65	177.8	22.4	3.3	4.1	3.9
3	80	190.5	23.9	3.9	4.9	4.9
3 1/2	90	215.9	23.9	4.8	6.1	6.2
4	100	228.6	23.9	5.3	6.8	7.0
24	600	812.8	47.8	86.9	115	185.0
6	150	279.4	25.4	7.5	10.6	11.3
8	200	342.9	28.4	12.1	17.6	19.6
10	250	406.4	30.2	16.5	24	28.6
12	300	482.6	31.8	26.2	36.5	43.2
14	350	533.4	35.1	34.6	48.4	58.1
5	125	254	23.9	6.1	8.6	8.6
16	400	596.9	36.6	44.8	60.6	76.1
18	450	635	39.6	48.9	68.3	93.7
20	500	698.5	42.9	61.9	84.5	122.0

Asme 16.48 Spectacle Blind Dimensions

Size in In.	Size in Millimeter	Internal Diameter	Outer Diameter	Center to Center	Thickness	Web Width	Web Thickness	Hole Diameter	Spectacle Blind Weight in Kg	Paddle Blank Weight in Kg	Paddle Spacer Blank Weight in Kg
2 1/2	65	73	107	140	6.4	51	4	19.05	0.7	0.46	0.24
3/4	20	21	54	70	3	38	2	15.875	0.1	0.05	0.04
1	25	27	64	80	3	38	2	15.875	0.14	0.07	0.06
1 1/4	32	42	73	90	6.4	38	4	15.875	0.35	0.21	0.14
1 1/2	40	48	83	100	6.4	38	4	15.875	0.46	0.27	0.18
1/2	15	16	45	60	3	38	2	15.875	0.07	0.03	0.03
2	50	61	102	120	6.4	51	4	19.05	0.68	0.41	0.26
3	80	89	133	150	6.4	64	4	19.05	1.1	0.71	0.39
3 1/2	90	102	159	175	9.7	64	5	19.05	2.44	1.54	0.9
4	100	114	172	190	9.7	64	5	19.05	2.81	1.8	1.01
20	500	508	603	635	28.4	121	22	31.75	83.67	64.85	18.82
6	150	168	219	240	12.7	76	7	22.225	5.39	3.82	1.57
8	200	219	276	300	12.7	76	10	22.225	8.32	6.07	2.25
10	250	273	337	360	15.7	102	12	25.4	15.04	11.19	3.84
12	300	324	406	430	19.1	102	15	25.4	26.95	19.77	7.18
5	130	141	194	215	9.7	76	5	22.225	3.37	2.29	1.08
14	350	356	448	475	19.1	108	15	28.575	32.94	24.07	8.87
16	400	406	511	540	22.4	108	17	28.575	50.27	36.73	13.54
18	450	457	546	580	25.4	114	20	31.75	61.79	47.55	14.23
24	600	610	714	750	31.8	140	24	34.925	129.3	101.8	27.49

Spectacle Blind Flange Class 150 Dimension Chart

Size in In.	Size in Millimeter	Internal Diameter	Outer Diameter	Center to Center	Thickness	Web Width	Web Thickness	Hole Diameter	Spectacle Blind Weight in Kg	Paddle Blank Weight in Kg	Paddle Spacer Blank Weight in Kg
1/2	15	16	51	65	6.4	38	4	15.875	0.19	0.1	0.09
1	25	27	70	90	6.4	38	4	19.05	0.36	0.19	0.16
1 1/4	32	42	79	100	6.4	38	4	19.05	0.43	0.25	0.17
1 1/2	40	48	92	115	6.4	38	4	22.225	0.58	0.34	0.24
2	50	61	108	125	9.7	51	5	19.05	1.19	0.71	0.48
2 1/2	65	73	127	150	9.7	51	5	22.225	1.64	0.98	0.65
3/4	20	21	64	80	6.4	38	4	19.05	0.31	0.16	0.14
3	80	89	146	170	9.7	64	5	22.225	2.11	1.29	0.81
3 1/2	90	102	162	185	12.7	64	7	22.225	3.35	2.09	1.26
5	130	141	213	235	15.7	76	8	22.225	6.98	4.47	2.51
6	150	168	248	270	15.7	76	8	22.225	9.34	6.06	3.28
8	200	219	305	330	22.4	76	17	25.4	19.42	13.08	6.33
10	250	273	359	385	25.4	102	20	28.575	29.22	20.55	8.66
4	100	114	178	200	12.7	64	7	22.225	4.01	2.52	1.49
12	300	324	419	450	28.4	102	22	31.75	43.9	31.31	12.58
14	350	356	483	515	31.8	108	24	31.75	67.86	46.58	21.27
16	400	406	536	570	38.1	108	29	34.925	98.04	68.74	29.3
20	500	508	651	685	44.5	121	34	34.925	164.75	118.43	46.31
24	600	610	772	810	50.8	140	39	41.275	261.55	190.13	71.42
18	450	457	594	630	41.1	114	31	34.925	128.23	91.06	37.16

Carbon Steel Spectacle Blank 300 LB Dimension

Size in In.	Size in Millimeter	Internal Diameter	Outer Diameter	Center to Center	Thickness	Web Width	Web Thickness	Hole Diameter	Spectacle Blind Weight in Kg	Paddle Blank Weight in Kg	Paddle Spacer Blank Weight in Kg
1/2	15	16	51	65	6.4	38	4	15.875	0.19	0.1	0.09
1	25	27	70	90	6.4	57	4	19.05	0.36	0.19	0.16
1 1/4	32	37	79	100	9.7	57	5	19.05	0.67	0.38	0.29
1 1/2	40	43	92	115	9.7	67	5	22.225	0.91	0.51	0.4
2	50	55	108	125	9.7	57	5	19.05	1.23	0.71	0.52
4	100	108	191	215	15.7	76	8	25.4	6.04	3.59	2.44
3/4	20	21	64	80	6.4	38	4	19.05	0.31	0.16	0.14
2 1/2	65	67	127	150	12.7	67	7	22.225	2.21	1.28	0.92
3	80	83	146	170	12.7	67	7	22.225	2.85	1.7	1.15
3 1/2	90	96	159	185	15.7	76	8	25.4	4.07	2.49	1.58
5	130	135	238	265	19.1	86	10	28.575	11.4	6.79	4.6
6	150	162	264	290	22.4	86	12	28.575	15.91	9.8	6.11
8	200	212	318	350	28.4	95	22	31.75	28.05	18.03	10.01
18	450	448	610	655	53.8	133	41	44.45	183.62	125.71	57.9
10	250	265	397	430	35.1	105	27	34.925	54	34.74	19.26
12	300	315	454	490	41.1	105	31	34.925	80.78	53.2	27.58
14	350	346	489	525	44.5	114	34	38.1	100.19	66.82	33.36
20	500	497	679	725	63.5	133	48	44.45	269.2	183.85	85.35
24	600	597	787	840	73.2	152	55	50.8	405.6	284.72	120.88
16	400	397	562	605	50.8	124	39	41.275	151.24	100.76	50.48

#600 SS Spectacle Blind Flange Dimension table

Size in In.	Size in MM	Internal Diameter	Outer Diameter	Center to Center	Thickness	Web Width	Web Thick.	Hole Diameter	Spectacle Blind Weight in Kg	Paddle Blank Weight in Kg	Paddle Spacer Blank Weight in Kg
1/2	15	16	60	80	6.4	38	4	22.225	0.27	0.14	0.13
1	25	27	76	100	6.4	57	4	25.4	0.43	0.23	0.2
1 1/4	32	37	86	110	9.7	57	5	25.4	0.81	0.45	0.36
1 1/2	40	43	95	125	9.7	67	5	28.575	0.98	0.54	0.43
2	50	55	140	165	12.7	57	7	25.4	2.88	1.56	1.32
3/4	20	21	67	90	6.4	41	4	22.225	0.34	0.18	0.16
2 1/2	65	67	162	190	12.7	67	7	28.575	3.82	2.09	1.73
3	80	83	165	190	15.7	67	8	25.4	4.68	2.68	2
4	100	108	203	235	19.1	76	10	31.75	8.48	4.94	3.54
6	150	162	286	320	25.4	86	13	31.75	21.9	13.04	8.86
8	200	212	356	395	35.1	95	27	38.1	45.96	27.93	18.02
10	250	265	432	470	41.1	105	31	38.1	78.21	48.16	30.04
5	130	135	244	280	22.4	86	12	34.925	14.18	8.37	5.81
12	300	315	495	535	47.8	105	36	38.1	117.31	73.55	43.76
14	350	346	518	560	53.8	114	41	41.275	140.86	90.65	50.2
18	450	448	635	685	66.5	133	50	50.8	252.97	168.39	84.57
20	500	497	696	750	73.2	133	55	53.975	331.81	222.68	109.13
24	600	597	835	900	88.9	152	67	66.675	579.52	389.25	190.27
16	400	397	572	615	60.5	124	46	44.45	188.73	124.31	64.42

Dimension of Class 900 Asme 16.48 Spectacle Flange

Size in In.	Size in Millimeter	Internal Diameter	Outer Diameter	Center to Center	Thickness	Width	Thickness	Hole Diameter	Spectacle Blind Weight in kg	Paddle Blank Weight in kg	Paddle Spacer Blank Weight in kg
1/2	15	16	61	80	6.4	38	4	22.225	0.28	0.14	0.13
4	100	102	206	240	22.4	89	12	34.925	10.47	5.96	4.5
1	25	27	76	100	9.7	64	5	25.4	0.65	0.35	0.3
1 1/4	32	35	86	110	9.7	64	5	25.4	0.82	0.45	0.37
1 1/2	40	41	95	125	12.7	70	7	28.575	1.3	0.71	0.58
2	50	53	140	165	12.7	70	7	25.4	2.9	1.56	1.33
3/4	20	21	67	90	9.7	41	5	22.225	0.52	0.27	0.24
2 1/2	65	63	162	190	15.7	76	8	28.575	4.78	2.58	2.19
3	80	78	172	205	19.1	76	10	31.75	6.36	3.54	2.81
5	130	128	251	290	28.4	89	15	41.275	19.55	11.23	8.31
6	150	154	279	320	35.1	89	18	38.1	29.08	17.15	11.93
8	200	203	349	395	41.1	102	31	44.45	52.23	31.43	20.8
24	600	575	899	990	111.3	178	84	92.075	898.71	564.9	333.8
12	300	303	518	570	60.5	114	46	53.975	169.01	101.94	67.06
14	350	333	575	635	66.5	127	50	60.325	229.84	138.07	91.76
16	400	381	638	705	76.2	133	58	66.675	320.1	194.78	125.32
18	450	429	702	775	85.9	146	65	73.025	432.4	265.84	166.56
10	250	255	432	480	50.8	114	39	50.8	98.33	59.53	38.79
20	500	478	752	830	95.3	152	72	79.375	540.14	338.44	201.7