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what is a spectacle blind flange

DataTime:[2016-6-16]
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 diverted 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.

spectacle blind flange

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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