A Spectable Blind is a mechanical device used to blind pipelines temporarily or permanently and facilitate the execution of maintenance works. Spectable blinds are a cost-effective option to isolation valves, which would be way more expensive to install. Spectable blinds, ring spacers, and line blanks are available in multiple forged material grades, from carbon steel ASTM A105 to alloy and stainless steel ASTM A182 (in bare steel or coated).

 

Spectacle blinds, spades, and ring spacers are installed between flanges to sections of a pipeline permanently or temporarily as shown in the video:

The reference specification for pipeline isolation devices (including spectable blind, ring spacers, and line blanks) is ASME B16.48.

spectable blind

Spectable blinds (also defined “spectable flanges”) are manufactured from steel plates and are basically two interconnected discs: one is actually a ring (i.e. a disc with a hole of the same bore size of the pipeline), the other is a solid disc.

In normal conditions, spectable blinds are installed in the open position and do not interrupt the flow of the fluid conveyed by the pipeline. To blind the pipeline, and interrupt the flow, the site staff has simply to unscrew the flange bolts and rotate the spectable blind to its closed position. It is easy to understand if a spectable blind is in an open or closed position, as one of the two discs is always outside the pipe (so when the ring is visible, the pipeline is closed; when the solid disc is visible outside, the pipeline is open). For spades and ring spacers, holes on the hangers inform the staff.

 

Spectable blinds for pipelines opening and closing

Spectable blind in an open position: the conveyed fluid can flow through the pipeline. As the disc is rotated, the flow is interrupted.

These products are available in most diameters, from 1/2 to 36 inch generally, and in pressure classes from 150 to 600 pounds (for RTJ flanges, the common pressure ranges are between 300 and 2500 pounds). Carbon steel spectable blinds are manufactured out of a single piece of steel, whereas alloy / stainless steel blinds can be manufactured by welding more pieces together (generally up to three).

 

SPECTABLE BLIND TYPES

There are three types of blinds:

  • Flat (FF): similar to a flat face flange, the surface of the disc is flat (suited for flat face gaskets, for low-pressure applications).
  • raised face (RF): likewise raised face flanges, there is an additional thickness on the surface of the disc. This type fits semi-metallic gaskets, as the spiral wound type.
  • RTJ (ring joint): a groove is inscribed on the surface of the disc. This type is used in conjunction with ring joint gaskets.

types of spectable blinds

 

SPECTABLE BLIND DIMENSIONS ASME B16.48

 

Spectable blind sizes

 

CLASS 150 SPECTABLE BLIND DIMENSIONS, ASME B16.48

CLASS 150
SPECTABLE BLIND ASME B16.48

NPS A B C t W
 1/2 45 16 60 3 38
 3/4 54 21 70 3 38
1 64 27 80 3 38
73 42 90 6.4 38
83 48 100 6.4 38
2 102 61 120 6.4 51
107 73 140 6.4 51
3 133 89 150 6.4 64
159 102 175 9.7 64
4 172 114 190 9.7 64
5 194 141 215 9.7 76
6 219 168 240 12.7 76
8 276 219 300 12.7 76
10 337 273 360 15.7 102
12 406 324 430 19.1 102
14 448 356 475 19.1 108
16 511 406 460 22.4 108
18 546 457 580 25.4 114
20 603 508 635 28.4 121
24 714 610 750 31.8 140

CLASS 300
SPECTABLE
BLIND ASME B16.48

NPS A B C t W
 1/2 51 16 65 6.4 38
 3/4 64 21 80 6.4 38
1 70 27 90 6.4 38
79 42 100 6.4 38
92 48 115 6.4 38
2 108 61 125 9.7 51
127 73 150 9.7 51
3 146 89 170 9.7 64
162 102 185 12.7 64
4 178 114 200 12.7 64
5 213 141 235 15.7 76
6 248 168 270 15.7 76
8 305 219 330 22.4 76
10 359 273 385 25.4 102
12 419 324 450 28.4 102
14 483 356 515 31.8 108
16 536 406 570 38.1 108
18 594 457 630 41.1 114
20 651 508 685 44.5 121
24 772 610 810 50.8 140

CLASS 600
SPECTABLE
BLIND ASME B16.48

NPS A B C t W
 1/2 51 16 65 6.4 38
 3/4 64 21 80 6.4 38
1 70 27 90 6.4 57
79 37 100 9.7 57
92 43 115 9.7 67
2 108 55 125 9.7 57
127 67 150 12.7 67
3 146 83 170 12.7 67
159 96 185 15.7 76
4 191 108 215 15.7 76
5 238 135 265 19.1 86
6 264 162 290 22.4 86
8 318 212 350 28.4 95
10 397 265 430 35.1 105
12 454 315 490 41.1 105
14 489 346 525 44.5 114
16 562 397 605 50.8 124
18 610 448 655 53.8 133
20 679 497 725 63.5 133
24 787 597 840 73.2 152

CLASS 900
SPECTABLE
BLIND ASME B16.48

NPS A B C t W
 1/2 60 16 80 6.4 38
 3/4 67 21 90 6.4 41
1 76 27 100 6.4 57
86 37 110 9.7 57
95 43 125 9.7 67
2 140 55 165 12.7 57
162 67 190 12.7 67
3 165 83 190 15.7 67
4 203 108 235 19.1 76
5 244 135 280 22.4 86
6 286 162 320 25.4 86
8 356 212 395 35.1 95
10 432 265 470 41.1 105
12 495 315 535 47.8 105
14 518 346 560 53.8 114
16 572 397 615 60.5 124
18 635 448 685 66.5 133
20 696 497 750 73.2 133
24 835 597 900 88.9 152

CLASS 1500
SPECTABLE
BLIND ASME B16.48

NPS A B C t W
 1/2 61 16 80 6.4 38
 3/4 67 21 90 9.7 41
1 76 27 100 9.7 64
86 35 110 9.7 64
95 41 125 12.7 70
2 140 53 165 12.7 70
162 63 190 15.7 76
3 172 78 205 19.1 76
4 206 102 240 22.4 89
5 251 128 290 28.4 89
6 279 154 320 35.1 89
8 349 203 395 41.1 102
10 432 255 480 50.8 114
12 518 303 570 60.5 114
14 575 333 635 66.5 127
16 638 381 705 76.2 133
18 702 429 775 85.9 146
20 752 478 830 95.3 152
24 899 575 990 111.3 178

CLASS 2500
SPECTABLE
BLIND ASME B16.48

NPS A B C t W
 1/2 67 16 90 9.7 38
 3/4 73 21 95 9.7 41
1 83 27 110 9.7 64
102 35 130 12.7 64
114 41 145 15.7 70
2 143 53 170 15.7 70
165 63 195 19.1 76
3 194 78 230 22.4 76
4 232 102 275 28.4 89
5 276 128 325 35.1 89
6 314 154 370 41.1 89
8 384 198 440 53.8 102
10 473 248 540 66.5 114
12 546 289 620 79.2 114

 

ASME B16.48 SPECTABLE BLIND DIMENSIONS

Spectable blind dimensions and weights ASME B16.48
ASME B 16.48 spectable blinds dimension and weight.pdf

This norm covers the dimensions, marking, pressure-temperature ratings, materials, dimensional tolerances and testing for line blanks in sizes between NPS 1/2 and NPS 24 for installation between ASME B16.5 flanges in the classes from 150 to 2500.