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Spectacle Blind, Flange Spade, Ring Spacer (ASME B16.48)

Spectacle blind, flange spade, and ring spacer are forged products used to blind pipelines (temporarily or permanently). These devices are cost-effective alternatives to isolation valves. A spectacle blind combines, in one single product, a flange spade and a ring spacer. Flange spades and ring spacers, as separate products, are used when the rotation of a spectacle blind would be difficult due to space constraints. ASME B16.48 covers the dimensions and specifications of these isolation devices.

SPECTACLE BLIND OPERATION

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

Spectacle blinds are available in standard sizes up to 24 inches and in forged material grades like ASTM A105 (high-temperature carbon), A350 low-temperature carbon), and various ASTM A182 grades (alloy, stainless steel, duplex). Click on the link to learn about the chemical and mechanical properties, and the selection criteria, of these common spectacle blind grades (which are the same as flanges).

Where to buy spectacle blinds? Generally, flange factories are also spectacle blind manufacturers.

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

spectable blind

Spectacle blinds (also defined “spectacle 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, spectacle 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 spectacle blind to its closed position.

It is easy to understand if a spectacle 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
Spectacle 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 spectacle 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).

SPECTACLE BLIND TYPES

There are three types of spectacle blinds:

  • Flat face spectacle blind (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 spectacle blind (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.
  • Ring joint face spectacle blind (RTJ): a groove is inscribed on the surface of the disc. This type is used in conjunction with ring joint gaskets.

types of spectable blinds

SPECTACLE BLIND DIMENSIONS in MM ASME B16.48

Spectable blind sizes

CLASS 150

Class 150 Spectacle blind dimensions in mm

Spectacle Blind NPS Dimensions Class 150ABCtW
 1/2451660338
 3/4542170338
1642780338
7342906.438
83481006.438
2102611206.451
107731406.451
3133891506.464
1591021759.764
41721141909.764
51941412159.776
621916824012.776
827621930012.776
1033727336015.7102
1240632443019.1102
1444835647519.1108
1651140646022.4108
1854645758025.4114
2060350863528.4121
2471461075031.8140

CLASS 300

Class 300 Spectacle blind dimensions in mm

Spectable blind sizes

Spectacle Blind NPS Dimensions Class 300ABCtW
 1/25116656.438
 3/46421806.438
17027906.438
79421006.438
92481156.438
2108611259.751
127731509.751
3146891709.764
16210218512.764
417811420012.764
521314123515.776
624816827015.776
830521933022.476
1035927338525.4102
1241932445028.4102
1448335651531.8108
1653640657038.1108
1859445763041.1114
2065150868544.5121
2477261081050.8140

CLASS 600

Class 300 Spectacle blind dimensions in mm

Spectable blind sizes

Spectacle Blind NPS Dimensions Class 600ABCtW
 1/25116656.438
 3/46421806.438
17027906.457
79371009.757
92431159.767
2108551259.757
1276715012.767
31468317012.767
1599618515.776
419110821515.776
523813526519.186
626416229022.486
831821235028.495
1039726543035.1105
1245431549041.1105
1448934652544.5114
1656239760550.8124
1861044865553.8133
2067949772563.5133
2478759784073.2152

CLASS 900

Class 900 Spectacle blind dimensions in mm

Spectable blind sizes

Spectacle Blind NPS Dimensions Class 900ABCtW
 1/26016806.438
 3/46721906.441
176271006.457
86371109.757
95431259.767
21405516512.757
1626719012.767
31658319015.767
420310823519.176
524413528022.486
628616232025.486
835621239535.195
1043226547041.1105
1249531553547.8105
1451834656053.8114
1657239761560.5124
1863544868566.5133
2069649775073.2133
2483559790088.9152

CLASS 1500

Class 1500 Spectacle blind dimensions in mm

Spectable blind sizes

Spectacle Blind NPS Dimensions Class 1500ABCtW
 1/26116806.438
 3/46721909.741
176271009.764
86351109.764
954112512.770
21405316512.770
1626319015.776
31727820519.176
420610224022.489
525112829028.489
627915432035.189
834920339541.1102
1043225548050.8114
1251830357060.5114
1457533363566.5127
1663838170576.2133
1870242977585.9146
2075247883095.3152
24899575990111.3178

CLASS 2500

Class 2500 Spectacle blind dimensions in mm

Spectable blind sizes

Spectacle Blind NPS Dimensions Class 2500ABCtW
 1/26716909.738
 3/47321959.741
183271109.764
1023513012.764
1144114515.770
21435317015.770
1656319519.176
31947823022.476
423210227528.489
527612832535.189
631415437041.189
838419844053.8102
1047324854066.5114
1254628962079.2114

Spectable blind dimensions and weights ASME B16.48
ASME B 16.48 spectacle 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.

FLANGE SPADE AND RING SPACER

A flange spade, otherwise called steel “blanking spade”, or “single-blind”, “blank” or “paddle blind”, is a metallic ring used to isolate a pipe (it has the same scope as a spectacle blind). To close the pipe, the blanking spade is inserted between the flanges; to open the pipe, the spade is removed, and the ring spacer takes its place.

Field staff understands if a pipe is open or closed, as blanking spades have one single signaling hole on the device holder, and ring spacers have instead two holes (look at the image).

Flange spades and ring spacers are manufactured according to the ASME B16.48 specification and belong to the family of pipeline isolation devices.

Flange spade and ring spacer
Ring spacer (left) and blanking spade (right)

 

FLANGE SPADE VS SPECTABLE BLINDS

A spectacle blind combines a flange spade and a ring spacer in a single device (this is the reason why flange spades are called “single-blinds” or “blanks”). The difference is that spectacle blinds may need some space to be rotated, and this space is not always available due to the routing of the piping system. This is when two separate devices are used, as they do not require rotation to be installed.

Spades, ring spacers, and spectacle blinds are available in multiple sizes (from 1/2 inch to 24 inches, and pressure rating from 150 to 2500#) and material grades (the same available for standard flanges) depending on the fluid conveyed by the pipeline.

The difference between spades/ring spacers and spectacle blinds is shown in the image:

difference spade and spectable blind

 

FLANGE SPADE AND RING SPACER DIMENSIONS ASME B16.48

CLASS 150

(Dimensions in mm)

Flange spade and ring spacer
Flange spade and ring spacer

 

NPSABCtW
 1/24516126332
 3/45421131332
16427136332
73421456.432
83481456.432
2102611556.432
107731706.432
3133891706.432
1591022029.738
41721142029.738
51941412259.738
621916822512.738
827621926712.738
1033727332215.744
1240632435719.144
1444835637819.144
1651140641022.444
1854645742725.451
2060350845528.451
2471461051231.851

 

CLASS 300

Flange spade and ring spacer

NPSABCtW
 1/251161296.432
 3/464211366.432
170271396.432
79421506.432
92481506.432
2108611589.732
127731779.732
3146891779.732
16210220512.738
417811420512.738
521314124015.738
624816824015.738
830521928122.438
1035927333325.444
1241932436328.444
1448335639531.844
1653640642238.144
1859445745041.151
2065150848044.551
2477261054050.851

 

CLASS 600

Flange spade and ring spacer

NPSABCtW
 1/251161296.432
 3/464211366.432
170271396.432
79371509.732
92431509.732
2108551589.732
1276717712.732
31468317712.732
1599621115.738
419110821115.738
523813524819.138
626416224822.438
831821228828.438
1039726535235.144
1245431538141.144
1448934639844.544
1656239743550.844
1861044845953.851
2067949749363.551
2478759754773.251

 

CLASS 900

Flange spade and ring spacer

NPSABCtW
 1/260161346.432
 3/467211376.432
176271426.432
86371519.732
95431519.732
21405517412.732
1626718612.732
31658318615.732
420310821719.138
524413525922.438
628616225925.438
835621230735.138
1043226537041.144
1249531540147.844
1451834641253.844
1657239744060.544
1863544847166.551
2069649750173.251
2483559757188.951

 

CLASS 1500

Flange spade and ring spacer

NPSABCtW
 1/261161356.432
 3/467211379.732
176271429.732
86351519.732
954115112.732
21405317412.732
1626319015.732
31727819019.132
420610221922.438
525112825628.438
627915425635.138
834920330341.138
1043225537050.844
1251830341260.544
1457533344266.544
1663838147276.244
1870242950485.951
2075247853095.351
24899575603111.351

 

CLASS 2500

Flange spade and ring spacer

NPSABCtW
 1/267161379.732
 3/473211409.732
183271459.732
1023516112.732
1144116115.732
21435317515.732
1656320119.132
31947820122.432
423210223228.438
527612827335.138
631415427341.138
838419832153.838
1047324839066.544
1254628942779.244

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