Spectacle Blind Flange also called as Figure-8 Blind flange. Spectacle Blind Flange is generally a piece of metal that 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 shape is similar to a pair of glasses or “spectacles” – hence the name spectacle blind. 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 systems.
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.
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 bypassed around the blank as this would compromise the safety function of the spectacle blind. The flow has to valved off and pressure relieved prior to loosening flange bolts and swinging the blind.
Spectacle Blinds be applied in systems, which regularly need to be separated from other installations. Normally, a Spectacle Blind is mounted in the “open” position so that flow through the pipe is possible. If the Spectacle Blind in the “close” position is rotated, the pipe is blanked off and no flow is possible.
Maintenance on a pipesystem can be a reason to rotate the spectacle in the “close” position. This run will take place through the hole, that is drilled in the connection piece. By loosening of all bolts, and partial removal of their, the Spectacle Blind can be rotated. After replacing the gaskets (new gaskets are to recommend), the bolts can be re-assembled and tightened.
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#
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
Spades & Ring Spacers
So as for the Spectacle Blind already described, maintenance on a pipesystem can be a reason to temporarily replace a Ring Spacer for a Spade. By loosening of all bolts, and half of the bolts temporarily remove, the Spade or Spacer can be placed. After replacing the gaskets (new gaskets are to recommend), the bolts can be re-assembled and tightened.
A small problem is that we basically can not see, or a Spade or a Spacer mounted between the flanges. Therefore the handles are often specially marked, or both have a different design; a customer often provides its own specification.
What should never lack is, that in the handle, the diameter and the Pressure Class of a Spade or Spacer is engraved; this applies also for the Spectacle Blind.
Surfaces – Dimensions – Material
Spades and Ring Spacers are basically the same as Spectacle Blinds, except that both are not attached to each other.
Spades and Spacers be applied in systems where maintenance is often not necessary, or in applications with large pipe sizes. Depending on the flange size and the Pressure Class, Spades can weigh hundreds of pounds. To prevent unnecessary weight to a flange connections, usually will be chosen not for a Spectacle Blind, but for 2 separate parts.
The sealing surfaces of a Spectacle Blind, Spade or Ring Spacer are usually conducted in accordance with the Face Finish from the flange. The diameter always is slightly larger than the Raised Face of a flange; by a correct assembly, the bolts are just not touched by the Blind or Spacer.
The diameter of them, is depending on the flange size, and the thickness from the Pressure Class of a flange.
Dimensions from Spectacle Blinds, Spades and Ring Spacers, you will find in the main Menu “Flanges”
ASME B16.48 covers pressure-temperature ratings, materials, dimensions, dimensional tolerances, marking, and testing for operating line blanks in sizes NPS 1/2 – NPS 24 for installation between ASME B16.5 flanges in the 150, 300, 600, 900, 1500, and 2500 Pressure Classes.
Spectacle Blinds, Spades and Ring Spacers 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.
If a piece of equipment needs to be inspected or removed from service then the plate covers the ring to form an airtight seal which consequently isolates a section of line or the piece of equipment. It provides a permanent or long term isolation device.
Our spectacle flange are designed to ensure that an item of equipment can be securely blanked off, with no possibility of leakage in the valve.
Because safety is so important to the function, we assure that they are tested rigorously to client’s specifications.
Our spectacle blinds, spades and spacers come in pressure ratings of 150lbs, 300lbs, 600lbs, 900lbs, 1500lbs and 2500lbs
Spectacle blinds, spades and spacers are available dimensionally in accordance with API 590 and ASTM 16.48 or any of our customer requirements.
They can be supplied in any grade such as
- Carbon steel
- Super Duplex
- Nickel Alloy
- Stainless Steel
Dimensions of spectacle blinds according to ASME B16.48
A spectacle flange is a specialty flange made of two metal discs attached in the middle by a small section of steel. Spectable flanges get their name because they look like a pair of reading glasses, or spectacles. Spectacle flanges, also known as spectacle blind flanges, are most commonly used on piping systems that need to be separated regularly or where the flow through the systems is regularly stopped. One end of the spectacle flange is solid, while the other end has a hole in the center. The spectacle flange can be rotated to place either the solid or hollow end within the pipe system, thereby opening or closing the flow.
Advantages of Spectacle Flanges
- Spectacle flanges require no welding for installation
- Spectacle flanges from Sunny Steel Flange have a wide range of pressure tolerances
- Sunny Steel will manufacture spectacle flanges to your specifications