what is a spectacle blind flange

A spectacle blind flange (also known as a figure-8 blind flage) is generally a piece of metal that is cut to fit between two pipe flanges and usually sandwiched between two gaskets. A spectacle blind flange is often made from two metal discs that are attached to each other by a small section of steel.

Spectacle Blinds are generally applied to permanently separating pipesystems, or just to connect with each other. A Spectacle Blind is a steel plate cut into two discs of a certain thickness.

The two discs are attached to each other by section of steel similar to the nose piece of a pair of glasses. One of the discs is a solid plate, and the other is a ring, whose inside diameter is equal to that of a flange.

This kind of flange is generally a piece of metal than is cut to fit between two pipe flanges and usually sandwiched between two gaskets a spectacle blind is often made from two metal discs that are attached to each other by a small section of steel. The Sharp is similar to a pair of glasses or spectacles – hence the name spectacle blind flange. One end of the blind will have an opening to allow flow through the pipe during operation and the other end is solid to block flow during maintenance. They are generally installed as a permanent device to separate process piping system.

The whole idea of a spectacle blind is so that one can be absolutely sure that an item of equipment is properly and securely blanked off with no possibility of any flow or leakage through a valve during maintenance. The flow can be perted to other items of equipment but not just by passed around the blank as this would compromise the safety function of the spectacle blind. The flow has to valve off and pressure relieved prior to loosening flange bolts and swinging the blind.

These Flanges are available in the following range.

Stainless Steel: ASTM a182 F304, F304L, F304H, F316, F316L, F316Ti, F310, F310S, F321, F321H, F317, F347, F347H, F904L. 

Duplex Stainless Steel: UNS S31803, UNS S32750 

Carbon Steel: ASTM a105, 

Alloy Steel: ASTM a182 F1, F11, F22, F5, F9, F91 

Nickel Alloys: Monel 400 & 500, Inconel 600 & 625, Incoloy 800, 825, Hastelloy C22, C276 

Copper Alloys: Copper, Brass & Gunmetal 

Size: 1/8″ NB TO 48″NB. 

Class: 150#, 300#, 400#, 600#, 900#, 1500#, 2500# 

Dimensional Standard

ANSI: ANSI B16.5, ANSI B16.47, MSS SP44, ANSI B16.36, ANSI B16.48 

DIN: DIN 2527, DIN 2566, DIN 2573, DIN 2576, DIN 2641, DIN 2642, DIN 2655, DIN 2656, DIN 2627, DIN 2628, DIN 2629, DIN 2631, DIN 2632, DIN 2633, DIN 2634, DIN 2635, DIN 2636, DIN 2637, DIN 2638, DIN 2673 

B.S: BS 4504, BS4504, BS1560, BS10

DIMENSIONS OF CLASS 150 SPECTACLE BLIND FLANGES AS PER ANSI B 16.48
NB		a	B	C	D	E	T1	T2
½”	15	48	14	60		26	5	4
¾”	20	57	21	70		32	5	4
1”	25	67	27	79		38	5	4
1 ½”	40	86	41	98		52	5	4
2”	50	105	52	120	20	64	6	4
3”	80	137	78	152	20	86	8	6
4”	100	175	103	190	20	114	9	7
6”	150	222	154	241	22	148	12	10
8”	200	279	203	298	22	188	15	12
10”	250	340	254	362	26	154	18	15
12”	300	410	303	432	26	190	21	18
14”	350	451	343	476	30	208	23	20
16”	400	515	394	540	30	176	25	23
18”	450	550	445	578	33	188	28	26
20”	500	605	495	635	33	162	31	29
24”	600	720	597	749	36	194	37	34

DIMENSIONS OF CLASS 300 SPECTACLE BLIND FLANGES AS PER ANSI B 16.48
NB		a	B	C	D	E	T1	T2
½”	15	54	14	66		30	5	4
¾”	20	67	21	83		36	5	4
1”	25	73	27	89		42	5	4
1 ½”	40	95	41	114		58	7	5
2”	50	111	52	127	20	68	8	6
3”	80	149	78	168	22	96	11	8
4”	100	181	103	200	22	118	13	10
6”	150	251	154	270	22	112	18	15
8”	200	308	203	330	26	138	23	19
10”	250	362	254	387	30	118	27	24
12”	300	422	303	451	33	138	32	28
14”	350	486	343	514	33	124	35	33
16”	400	540	394	571	36	140	39	37
18”	450	595	445	628	36	126	44	42
20”	500	655	495	686	36	140	49	47
24”	600	775	597	813	42	168	58	56

DIMENSIONS OF CLASS 600 SPECTACLE BLIND FLANGES AS PER ANSI B 16.48
NB		a	B	C	D	E	T1	T2
½”	15	54	14	66		30	5	4
¾”	20	67	21	82		36	6	4
1”	25	73	27	89		42	7	4
1 ½”	40	95	41	114		58	9	6
2”	50	111	52	127	20	68	11	8
3”	80	149	78	168	22	96	15	12
4”	100	194	103	216	26	126	18	15
6”	150	267	154	292	30	116	24	21
8”	200	321	203	349	33	140	31	27
10”	250	400	254	432	36	128	38	33
12”	300	457	303	489	36	114	44	39
14”	350	492	343	527	39	122	48	44
16”	400	565	394	603	42	144	55	53
18”	450	613	445	654	45	155	62	60
20”	500	682	495	724	45	140	68	67
24”	600	790	597	838	52	164	81	80

All dimensions are in millimeters unless otherwise indicated. 



General notes: 

• D = Hole size (where required) should be the same as the flange bolt hole. In practice, these dimensions have been rounded round off upwards.

• T1 = Thickness Carbon Steel.

• T2 = Thickness Stainless Steel.

• W = Thickness of the web (or tie bar) should be 0.25 inch (6 mm) minimum, or equal to T1 and T2 if less than 0.25 inch (6 mm).

• Spectacle Blinds should be made from a plate or forging specification, approved for use by ASME B31.3, of essentially the same chemical composition as the mating flanges

   and piping involved.

• Depending on a customer specification, the dimensions can be different from what on this page is defined.

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