ASME B16.48 Spectacle Blind

ASME B16.48 is a B16 standard for valves, flanges, fittings, and gaskets.The blind works as isolation and cut-off as the head, cap and welding plug. Because of its good sealing performance, it is generally used as a reliable means of isolation for systems requiring complete isolation.

Spectacle Blind is a pipe fitting used to isolate or connect piping systems. The spectacle blind has a structure of half blind plate and half flange. It is often used for pipeline flanges requiring process change to facilitate pipeline maintenance. Usually use the space occupied by one end of flange to keep the pipeline unblocked. If necessary, replace it with blind plate of the same thickness at the other end to cut off the pipeline. Avoid forced expansion of pipeline caused by temporary replacement of other blind plates and affecting the whole system. Commonly used for pipe flanges requiring process change, mainly made of carbon steel, stainless steel, and alloys, which can be selected according to pipe pressure level and pipe media.

Specification of Spectacle Blind 

There are many standards for flanges. American standard, German standard and British Standard all have their own standards. Common flange standards include ASME B16.5, ASME B16.47, and the standard for spectacle blind flange is ASME B16.48.

Structure of ASME B16.48 Spectacle Blind

Spectacle blind is usually isolated from other facilities or installations in piping systems. Typically, the spectacle blind is located in the open position so that the fluid passes through the pipe. When spectacle blind is in the closed position, the pipe is closed and the fluid is blocked.There is a drill hole in the connecting web of spectacle blind. Loosen and disassemble some bolts. The spectacle blind can rotate between the flanges. After replacing gaskets, the bolts can be reassembled and tightened.

• 1-Baffler

• 2-Sealing structure

• 3-Reinforcing structure

• 4-First connection station

• 5-Connection structure

• 6-Second connection station

• 7-Flow plate

  
  

Setting Principles

• If discharge of medium and high pressure equipment and pipelines is connected to open or close discharge and manual discharge is carried out, spectacle blind shall be set behind the shut-off valve.

• The spectacle blind plate shall be set at the shutoff valve at the interface reserved for the later construction equipment or device.

• Factory air, instrument air, nitrogen and supply line to LNG are equipped with valves and spectacle blinds between shutoff valve and our unit.

• When the units are to be repaired, checked or switched over regularly, when the equipment involved needs to be completely isolated, spectacle blinds shall be set at the shut-off valve, such as coalescence filters for feed gas, coalescence filters for purified gas, etc.

  
  

Material & Grades of Spectacle Blind 

Carbon Steel : ASTM A105 / A105N

Carbon steel has low cost and has good strength and toughness. Good processing performance, can be convenient for cutting, welding and other processing operations, suitable for the ordinary medium transmission pipeline is not high for corrosion resistance requirements.

Low Temperature Carbon Steel : ASTM A350, LF2, LF3

Low-temperature steel refers to the steel material that can maintain good mechanical properties in a low-temperature environment. When the ambient temperature is lower than the brittleness transition temperature of steel, the toughness of steel will decline sharply, and brittle fracture is easy to occur. However, the brittleness transition temperature of low temperature steel eight blind plate is low, which can adapt to the low temperature condition.

Pipeline Steel: A694 F42 / 46 / 52 / 56 / 65 / 70

Alloy Steel : ASTM A182 F5 / F9 / F11 / F12 / F22 / F91 / F92

Alloy steel can obtain higher strength, hardness and high temperature resistance by adding various alloy elements, such as chromium, molybdenum and vanadium. The wear resistance of alloy steel is also good, in some pipes containing solid particle medium, can reduce the impact of wear on the eight-character blind plate.

Stainless Steel : ASTM A182, A240 F304/304L/304H - F316/316L - F317 - F310S - F321 - F347 - F904L

Duplex Stainless Steel : ASME A182 F51, F53, F55, F60.

Stainless steel has good corrosion resistance, in the pipe system with weak acid or alkaline medium, stainless steel eight character blind plate can effectively prevent corrosion. The surface finish of stainless steel is relatively high, which is a very important feature for some pipe systems with high cleanliness requirements.

Dimension of ASME B16.48 Flange

The figure-8 blanks under the ASME B16.48 standard ranges from 1 / 2 "to 48" with a pressure range of Class 150,300,600,900,1500,2500 lb

Class 150 Spectacle Blind Flange

Connecting Surface of ASME B16.48 Spectacle Blind

• Raised Face 

• Male Face 

• Female Face 

• Tongue Face

• Groove Face

• Ring Joint Face

• Flat Face

Pressure Rating of ASME B16.48 Spectacle Blind

• Class 150lb

• Class 300lb

• Class 400lb

• Class 600lb

• Class 900lb

• Class 1500lb

• Class 2500lb

Functions and Uses

● Isolation and Conduction

When a certain section of the pipeline system needs to be completely isolated, the spectacle blind flange can be installed as a blind plate to partially block the pipeline. For example, when a certain device in the pipeline is being repaired, the figure-8 blank can be installed as a blind to prevent the medium in other pipelines from flowing into the pipeline section where the device is located, ensuring the safety of the maintenance.

●Pressure Test

After the pipeline system is installed, a pressure test is required. The figure-8 blank can be used to close the end of the pipeline of the test section so that the medium (such as water or air, etc.) can be injected into the test section for pressure testing. By observing the pressure changes, the tightness and strength of the pipeline system can be detected.

●Process Switching

In some complex industrial production processes, there are multiple material flow directions or operation modes. The figure-8 blank can easily realize the switching between different processes. For example, in an oil refinery, the production processes of different oil products may have some shared pipelines. By adjusting figure-8 blank, it is possible to switch between the production of different oil products.