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spectacle blind

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

Reading Time: 9 minutes

Spectacle blinds, flange spades, and ring spacers 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

WHAT IS A SPECTACLE BLIND

A spectacle blind, also known as a figure-8 blind, is a safety device used in piping systems to isolate a section of the pipe for maintenance, inspection, or shutdown. It consists of two metal discs connected by a small section in the middle, resembling a pair of spectacles or the figure-8, hence its name. One disc is a solid plate (blind), and the other is a ring (spacer). The spectacle blind is inserted between two flange joints to either block the flow completely (using the blind side) or allow it to pass through (using the spacer side).

spectable blind

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

Functionality and Use:

  • Isolation: When the solid plate (blind) side faces the pipeline, it acts as a barrier, preventing flow and ensuring that the section is completely isolated. This is crucial for maintenance work or in emergency shutdown situations where it’s necessary to ensure no fluid passes through a segment of the piping system.
  • Operational Flow: When the system is in normal operation, the ring (spacer) side is positioned to align with the pipe, allowing unrestricted flow. The spacer essentially acts as part of the pipeline during normal operations.
  • Quick Changeover: The design of the spectacle blind enables quick and easy changeover between the open (spacer) and closed (blind) positions by simply rotating the spectacle blind without removing it from the flange. This convenience makes it highly efficient for systems that require frequent switching between operation and maintenance modes.

Advantages:

  • Versatility: Spectacle blinds are suitable for various industrial applications, including oil and gas, chemical processing, and power generation, where pipeline isolation is frequently necessary.
  • Safety: By providing a physical barrier in the pipeline, spectacle blinds significantly enhance safety during maintenance or in case of system failure.
  • Cost-Effectiveness: Since they can be easily rotated without being fully removed from the pipeline, spectacle blinds reduce downtime and labor costs associated with system isolation.

Considerations:

  • Material Compatibility: Spectacle blinds are available in various materials to match the pipeline and flange materials, ensuring chemical compatibility and pressure integrity.
  • Size and Pressure Rating: They must be sized correctly for the pipeline and rated for the operating pressure and temperature conditions of the system.
  • Installation: Proper alignment and installation are crucial to ensure the effectiveness of the seal when the blind side is in use.

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 (carbon steel for high-temperature service), A350 (carbon steel for low-temperature service), and various ASTM A182 grades (alloy, stainless steel, duplex / super duplex). All these materials for forged pipeline products (chemical composition, and mechanical properties) are thoroughly reviewed in this article.

SPECTACLE BLIND MANUFACTURING & USE

Spectacle blinds are generally purchased from manufacturers of flanges but can be produced by steelworking centers as well.

Spectacle blinds (also defined as “spectacle flanges”) are produced starting from steel plates and are basically made of two interconnected discs: one is actually a ring (i.e. a disc with a hole of the same bore size as the pipeline), and the other is a solid disc. Carbon steel spectacle blinds are manufactured out of a single piece of steel, whereas alloy / stainless steel blinds are generally manufactured by welding more than 1 piece together (commonly 2, but up to three).

Usage:
In normal conditions, spectacle blinds are installed in the open position and do not interrupt the flow of the fluid conveyed by the pipeline. The conveyed fluid flows through the pipeline when the spectacle blind is in the open position.
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. As the disc is rotated, the flow is interrupted.

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 about the position.

Spectable blinds for pipelines opening and closing
Spectacle blinds are available in most diameters, from 1/2 to 36 inches generally, and in pressure classes from 150 to 600 pounds (for RTJ flanges, the common pressure ranges are between 300 and 2500 pounds).

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

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

WHAT IS A FLANGE SPADE

A flange spade, also known as a paddle blank, is a piping component used to isolate a section of a pipeline temporarily. It is a flat, round piece of metal with a handle that fits between two flanges, effectively blocking the flow of fluids through the pipeline. The spade is inserted into the piping system when isolation is required for maintenance, inspection, or any other operation where stopping fluid flow is necessary.

flange spade
flange spade

A flange spade, otherwise called steel “blanking spade”, “single-blind”, “blank” or “paddle blind”, has therefore 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).

Key Features and Use:

  • Design: A flange spade is essentially a solid disk without any openings, except for the handle or tab that facilitates easy installation and removal. The diameter of the spade matches the inner diameter of the flanges it is designed to fit between, ensuring a tight seal and effective isolation.

  • Material: Like flanges and other piping components, spades are made from materials compatible with the pipeline and the fluid it carries. This could include carbon steel, stainless steel, alloy steel, and others, chosen based on the specific requirements of pressure, temperature, and corrosion resistance.

  • Pairing with Flange Rings: Flange spades are often used in conjunction with spacer rings (paddle spacers) that maintain the flange separation and gasket compression when the spade is removed, allowing fluid flow. Together, the spade and spacer ring can be considered a spectacle blind when used interchangeably but are separate components.

Applications:

  • Safety and Maintenance: Flange spades provide a safe method for isolating pipeline sections during repairs, modifications, or when a pipeline section must be depressurized and drained.
  • Operational Flexibility: They allow for quick adaptation of the pipeline to changing operational needs, such as diverting flow, shutting down sections for inspection, or integrating new components.

Advantages:

  • Effective Isolation: Provides a secure and reliable means to stop fluid flow, ensuring worker safety and protecting equipment during maintenance or inspection.
  • Cost-Efficiency: Spades are a straightforward and cost-effective solution for pipeline isolation, requiring no special tools for installation or removal.
  • Versatility: Suitable for a wide range of industrial applications, including oil and gas, chemical processing, and power generation, where temporary pipeline isolation is required.

Considerations:

  • Correct Sizing and Rating: The spade must be correctly sized for the flanges and rated for the operating conditions of the pipeline to ensure a proper seal and safe operation.
  • Installation: Care must be taken during installation to ensure the spade is securely placed and the flange bolts are adequately tightened to prevent leaks.
  • Storage and Handling: When not in use, spades should be stored properly to prevent damage and ensure they are readily available for future use.

WHAT IS A RING SPACER

A ring spacer, often used in conjunction with a flange spade, is a piping component designed to maintain flow within a pipeline while ensuring that the space between flanges is appropriately managed. It is essentially a ring-shaped piece of metal that matches the inner diameter of the flanges it is designed to fit between. When placed between two flanges, a ring spacer fills the gap left by the removal of a spade (paddle blank), allowing the fluid to flow through the pipeline uninterrupted.

Key Features and Use:

  • Design: The ring spacer has a simple design, typically a flat, circular piece of metal with a hole in the center corresponding to the pipe’s bore. It may have a handle or tab, similar to a spade, for easier handling and installation.
  • Material: Like other pipeline components, ring spacers are made from materials that match or are compatible with the pipeline system and the fluid it carries. This includes a range of metals such as carbon steel, stainless steel, and alloy materials, chosen based on pressure, temperature, and corrosion resistance requirements.
  • Application with Spades: Ring spacers are often used in a system that alternates between a spade for isolation and a spacer for normal operation. This setup provides operational flexibility, allowing for easy transition between blocking and allowing flow as maintenance or system checks require.

Applications:

  • Operational Flexibility: Ring spacers facilitate routine maintenance, inspections, and system modifications by allowing for easy isolation and restoration of fluid flow in the pipeline.
  • Safety: When used in tandem with a spade, the ring spacer ensures that the pipeline can be safely isolated for work to be performed and then quickly returned to operation, maintaining system integrity and safety.

Advantages:

  • Continuity of Operation: Enables the continued operation of a pipeline system by replacing a spade when it is not necessary to block the flow, thereby minimizing downtime.
  • Cost-Efficiency: Provides an economical solution for managing flow in pipelines, requiring no special tools for installation or removal.
  • Versatility: Suitable for various industrial settings where pipeline fluid flow needs to be managed effectively, including the oil and gas, chemical processing, and power generation sectors.

Considerations:

  • Proper Sizing and Rating: Ensuring the ring spacer is correctly sized for the pipeline and rated for its operating conditions is crucial for maintaining an effective seal and safe operation.
  • Installation Care: Proper installation is essential to ensure the spacer is securely in place, with flange bolts adequately tightened to maintain the integrity of the flange connection.
  • Handling and Storage: Proper handling and storage practices are necessary to maintain the condition of the ring spacer when not in use, ensuring it is ready for future applications.

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 SPECTACLE 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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About the Author

Projectmaterials Team

Projectmaterials Team

Blog.projectmaterials.com is an online resource dedicated to providing in-depth information, analysis, and educational content related to the fields of project materials management, engineering, and procurement, particularly within the oil & gas, construction, shipbuilding, energy, and renewable energy sectors. It aims to serve professionals and enthusiasts in these industries by offering valuable insights into materials, equipment, and techniques used in various projects, focusing on the selection, application, and maintenance of these resources.Key features of the blog include:* Educational Articles: Comprehensive posts that cover topics ranging from the technical aspects of piping products (pipes, valves, fittings, flanges, gaskets, bolts, instrumentation) to structural steel and process equipment (including oil extraction systems, drilling rigs, wellheads, pumps, compressors, and separation systems). * Industry Insights: Updates on the latest trends, technologies, and regulatory changes affecting the industries covered. * Guides and How-Tos: Practical advice on selecting the right materials and equipment for specific applications, as well as tips on installation, maintenance, and troubleshooting. * Safety and Standards: Information on safety equipment for production sites, risk mitigation procedures, and an overview of relevant industry standards and regulatory frameworks.The website is designed to support the professional development of engineers, procurement specialists, project managers, and other stakeholders involved in project plant businesses, by disseminating critical know-how and best practices. Whether readers are new to the field or seasoned professionals, blog.projectmaterials.com offers resources to enhance their understanding and performance in managing project materials effectively.

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6 Responses

  1. Hi, The content is very useful.
    May I know for the spectacle blind more than 24″ what standard normally you referring to?

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