When to use a spectacle blind flange?
Spectacle blind flanges – also known as figure-8 blind flanges – are generally pieces of metal. Spectacle blind flange 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.
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.
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.
The material of spectacle blind flanges:
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 of spectacle blind flange
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
Types of spectacle blind flanges
A spectacle blind flange is generally a piece of metal that is cut to fit between two pipe flanges and usually sandwiched between two gaskets.There are three types of spectacle flange: spacer fange, spade fange (paddle flange), spectacle blind flange. A spectacle blind flange is a combination of a spade fange and a spacer fange.
Spectacle blind flange (also called figure 8 flange), it’s the most regular spectacle flange.The shape of spectacle flange is like glasses. One part is a blind plate, the other part is a ring which has a same outer diameter with the first part. The two parts are connected with a handle plate. The spectacle blind flange could be produced from one plate,or joint together by welding from three parts: blind plate,ring and handle plate.
Spacer flange, it looks like a steel ring with a handle plate.The spacer has a same usage with the ring part of a spectacle flange.The spacer has a same outer diameter with the paddle flange.
Spectacle blind flange be applied in systems, which regularly need to be separated from other installations. Normally, a Spectacle blind flange 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 pipe system can be a reason to temporarily replace a Ring Spacer flange for a Spade flange. By loosening of all bolts, and half of the bolts temporarily remove, the Spade or Spacer can be placed. After replacing the gaskets,the bolts can be re-assembled and tightened. It is necessary that the pipeline should be valved off and pressure relieved before loosening the flange bolts.
To prevent unnecessary weight to a flange connections,designer usually will choose the seperated two parts (spacer flange and spade flange) instead of the spectacle blind flange.
Source: Network Arrangement – China Spectacle Blind Flange Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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Please notice that you might be interested in the other technical articles we’ve published:
What is difference between spectacle blind and spacer?
Jointly they perform the same function as a Spectacle Blind as essentially a simplistic valve. The Spade or Spacer is fitted in the line between two flanges and is bolted in place. The Spacer is used when the line is required open and the Paddle Blind or Spade is installed when the line is required blocked or closed.
What is the purpose of spectacle blind?
A spectacle blind is a safety device used to isolate a section of line or piece of equipment when the line or equipment needs to be inspected or removed from service. It is different than a valve in that the blind is a permanent or long term isolation device.
How to calculation spectacle blind flange thickness?
Up to 24″, see ASME B16.48.
For 26″ & above, use ASME B31.3 formula.