Selecting the correct blind flange is critical for ensuring the structural integrity of a piping system. Whether you are sealing a high-pressure line in a Texas refinery or a water treatment plant in Sydney, understanding the relationship between size, thickness, and pressure rating is essential.
In this guide, we provide a comprehensive breakdown of ASME B16.5 Blind Flange specifications.
H2: Why Blind Flange Thickness Matters Unlike standard flanges, a blind flange must withstand the full force of the internal pressure against its entire center area. This is why the thickness of an ASME B16.5 blind flange is often greater than that of a matching slip-on or weld neck flange. Using an undersized blind flange can lead to deformation or catastrophic failure.
H2: Blind Flange Dimension Chart (Class 150 Example) To help you with your project planning, here are the common dimensions for Class 150 blind flanges:
| Nominal Pipe Size (NPS) | Outside Diameter (O.D) | Thickness (min) | Bolt Circle Diameter |
| 1/2" | 3.50" | 0.44" | 2.38" |
| 1" | 4.25" | 0.56" | 3.12" |
| 2" | 6.00" | 0.75" | 4.75" |
| 2-1/2" | 7.00" | 0.88" | 5.50" |
| 4" | 9.00" | 0.94" | 7.50" |
Pressure Ratings: Understanding the Limits
The pressure-temperature rating of a flange depends on its material and class. For example, a Carbon Steel A105 Blind Flange rated for Class 150 can handle significantly different pressures at 100℉ versus 500℉ .
-
Class 150: Suitable for low-pressure utility lines.
-
Class 300 & 600: Used in high-pressure oil, gas, and steam applications.
-
FF vs RF: Remember that a Blind Flange FF (Flat Face) is typically used for Class 150/300 systems, while Raised Face (RF) is the standard for higher pressure classes to concentrate more pressure on a smaller gasket area.
How to Measure a Blind Flange for Replacement
If you are on-site in Queensland or Florida and need to identify an existing flange, follow these steps:
-
Measure the Outside Diameter (O.D.).
-
Count the Bolt Holes (4, 8, 12, etc.).
-
Measure the Bolt Circle Diameter (BCD).
-
Identify the Face Type (Is it flat or does it have a raised center?).
Quality You Can Trust
At CTFlange, we ensure all our blind flanged fittings meet or exceed ANSI B16.5 standards. Our dual-inventory system in the USA and Australia means you get the parts you need without the 12-week wait.
Call to Action:
Need a quote for Blind Flange FF 2-1/2" #150 A105 SCH40? Or looking for a specific SS flange dimension? Contact our technical team in Houston or Sydney today for immediate assistance.
