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Common Uses and Features of Blind Pipe Flanges

Blinds are flanges without a center bore (hole or opening) and are available in both Raised Face (RF) and Flat Face (FF) styles. While most flange types create a connection point that allows the flow of liquid, gas, or air, blind flanges are used to seal the end of a piping system and prevent flow. Blind flanges may be used when testing pipe pressure, to create an access point in a piping system, to temporarily seal a piping system while modifying or repairing the line, or to create a long-term seal to terminate a piping system.

A blind flange is bolted, rather than welded in place. This allows easier access as needed for pipe system upkeep, inspection, or to allow for future expansion. Pairing with a gasket creates a tight seal: The gasket fills the space between the flange faces, which prevents liquid or gas leaks.

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How to Choose the Right Blind Flange

Blind pipe flanges may be produced to match bolt hole measurements for slip-on or weld neck flanges, or if needed, can be custom machined to any other specifications. Either way, when purchasing flanges, choose the appropriate flange features, material, dimensions, and class to meet your application needs.

 

Find the Best Blind Flange Material for the Job

When choosing blind flanges, you must consider the best flange material and dimensions in relation to the piping standards and requirements of your intended application. Generally, your flange material should match the connecting pipe material. The most common blind flange materials are steel and stainless steel.

  • Steel is preferred for strength. API International stocks blind flanges in both forged and plate steel.
  • Stainless steel flanges are also available in forged or plate varieties in 304L and 316L. Stainless steel flanges are often preferred for corrosion resistance.

In many cases, import material is acceptable to save on cost – in these cases, the flanges will still meet all the standards for pressure applications. In instances where domestic flanges are specified, API International manufactures flanges meeting “Buy American” or meeting American Iron and Steel Institute (AISI) requirements.

 

blind flange drawing

Choosing Blind Flange Dimensions

Blind flanges are available in the same pressure classes and bolt hole patterns as other flange types, but they tend to be thicker. To determine the appropriate blind flange size, important measurements include the outer diameter (OD), bolt hole circle (BHC), bolt hole diameter, and thickness. While most flanges are round, square blind flanges may be used to close off hydraulic piping systems.

Blind flange dimension requirements and materials specifications are designated under AWWA C207 and C228, and ASME B16.5 and B16.47. The general dimensions by blind flange type are included in the chart below, and you can refer to the tables on individual flange listings to determine more specific measurements—such as thickness—based on diameter and pressure rating.

 

AWWA Blind Flange Dimensions by Type

Blind Flange Style

Available Size Range

B, D, E

4” – 72”

F, SF

4” – 48”

SA

2” – 8”

SB, SD, SE

2” – 72”

Note: AWWA recommends the use of Dish Assemblies for blind flange sizes above 72”. Contact us for additional information.

The larger the blind flange, the more stress the flange must withstand—mainly at the center of the flange—and too much pressure can cause damage. This is why you don't typically see large diameter blind flanges.

 

ANSI Blind Flange Dimensions by Class

Spec

Class

Available Size Range

B16.5

150

0.5” – 24”

B16.5

300

0.5” – 24”

B16.47

150

26” – 60”

B16.47

300

26” – 60”

 

Flange Face and Thickness Requirements

Blind flanges are commonly available in Raised Face (RF) and Flat Face (FF) styles. When choosing blind flange thickness, refer to the standard measurements. The flange selected should be thick enough to withstand the pressure of the system, but not so thick that it is unnecessarily unwieldy—for the appropriate thickness, a common recommendation is to choose the minimum thickness that can handle the max pressure that your system could experience.

 

Consider Class Rating and Flange Standards

To choose the appropriate blind flange, consult the requirements set out by piping standards, including AWWA, ASME/ANSI, and ASTM. For example, ANSI-style blind flanges are available in both class 150 and 300, in dimensions between 2 inches to 72 inches to suit a range of applications.

Class ratings provide details regarding what pressure and temperature conditions a flange will withstand. Generally, a flange with a higher class rating must be used for high-temperature applications since the higher temperature reduces the pressure capacity of the flange. Forged steel blind flanges are rated for use in high-pressure and high-temperature applications because the material is stronger than plate blind flanges, while other materials are rated for lower-pressure, cooler operating piping systems.

If the options you require aren’t available, our Custom Machining Shop can manufacture custom parts as well as modify stock items, so you can get exactly what you need.