What is an ASME B16.5 Blind Flange?
An ASME B16.5 blind flange is a solid, flat disc used to close the end of a pipe, valve, or pressure vessel. Also known as a blank flange or flange cover, it has no center opening and is designed to block fluid flow, enable pressure testing, or provide a permanent pipe termination.
ASME B16.5 is the most widely used international standard for pipe flanges and flanged fittings in industrial piping systems. It defines dimensions, pressure ratings, materials, tolerances, and testing requirements for flanges used in oil and gas, petrochemical, power plants, and general industrial applications.
A blind flange helps isolate sections of a pipeline, simplify system maintenance, and ensure safe operation under pressure. It is installed using bolts, gaskets, and matching flanges to create a tight, leak-proof seal.
Pressure Classes & Ratings for ASME B16.5 Blind Flange
ASME B16.5 blind flanges are manufactured according to standard pressure classes that indicate their maximum allowable working pressure. The pressure rating depends on material, temperature, and size.
Common pressure classes for ASME B16.5 blind flanges include:
- Class 150: Used for low-pressure applications
- Class 300: Suitable for medium-pressure systems
- Class 600, 900, 1500, 2500: Designed for high-pressure and extreme-service conditions
Each class follows strict dimensional and performance requirements under the ASME B16.5 standard. Selecting the correct pressure class is critical to avoid failure, leakage, or safety risks in piping systems.
Facing Types of ASME B16.5 Blind Flange
The sealing face of a blind flange is one of its most important features, as it directly creates the pressure-tight seal needed for pipe closure and isolation. Under ASME B16.5 standard, blind flanges are produced with three common facing types to fit different working conditions.
- Raised Face (RF)
The raised face is the most popular choice for blind flanges. A small, raised surface helps concentrate compression on the gasket, delivering strong and reliable sealing. This type is widely used for general blind flange applications such as pipeline closing, pressure testing, and routine maintenance.
- Flat Face (FF)
Flat face blind flanges have a full, flat sealing surface across the flange. This design distributes bolt loading evenly, making it ideal when connecting blind flanges to cast iron or brittle flanges. It is commonly used in low-pressure piping systems.
- Ring Type Joint (RTJ)
RTJ blind flanges use a precision-machined groove to hold metal ring gaskets. This structure provides an extremely strong seal under high pressure and high temperature. For this reason, RTJ blind flanges are widely used in oil, gas, petrochemical, and heavy industrial applications.
Matching the facing type with the correct gasket is essential to ensure the blind flange operates safely and without leakage. For more comprehensive learning, please click.
ASME B16.5 Blind Flange Weight Reference (Carbon Steel)
| NPS | 150LB | 300LB | 400LB | 600LB | 900LB | 1500LB | 2500LB |
| 1/2 | 0.91 | 0.91 | 0.91 | 0.91 | 1.82 | 1.82 | 3.18 |
| 3/4 | 0.91 | 1.16 | 1.36 | 1.36 | 2.72 | 2.72 | 4.54 |
| 1 | 0.91 | 1.82 | 1.82 | 1.82 | 4.09 | 4.09 | 5.45 |
| 1 1/4 | 1.36 | 2.72 | 2.72 | 2.72 | 4.54 | 4.54 | 8.17 |
| 1 1/2 | 1.58 | 3.18 | 3.63 | 3.63 | 6.36 | 6.36 | 11.35 |
| 2 | 2.39 | 3.63 | 4.54 | 4.54 | 11.35 | 11.35 | 17.71 |
| 2 1/2 | 4.07 | 5.45 | 6.81 | 6.81 | 15.89 | 15.89 | 25.42 |
| 3 | 4.92 | 7.26 | 9.08 | 9.08 | 19.53 | 21.79 | 39.04 |
| 3 1/2 | 5.9 | 9.53 | 13.17 | 13.17 | / | / | / |
| 4 | 7.72 | 12.71 | 14.98 | 18.61 | 24.52 | 33.14 | 60.38 |
| 5 | 9.08 | 16.8 | 19.98 | 30.87 | 39.5 | 64.47 | 101.24 |
| 6 | 12.26 | 21.79 | 27.69 | 39.04 | 51.3 | 72.19 | 156.63 |
| 8 | 21.34 | 35.87 | 45.4 | 63.11 | 89.44 | 137.11 | 241.98 |
| 10 | 30.42 | 55.39 | 70.37 | 104.87 | 131.66 | 230.18 | 465.35 |
| 12 | 45 | 83.48 | 102.6 | 133.93 | 187.5 | 351.85 | 644.66 |
| 14 | 63.11 | 109.41 | 140.74 | 148.91 | 224.28 | / | / |
| 16 | 84.9 | 143.01 | 180.69 | 239.26 | 281.03 | / | / |
| 18 | 98.52 | 187.96 | 227.91 | 301.91 | 399.52 | / | / |
| 20 | 128.48 | 233.81 | 281.93 | 388.17 | 502.58 | / | / |
| 24 | 188.41 | 363.2 | 424.94 | 533.45 | 952.95 | / | / |
For more specific data or customized flange, please contact our team.
Common Materials for ASME B16.5 Blind Flange
ASME B16.5 blind flanges are available in various forged materials to suit different temperatures, pressures, and corrosive environments.
Carbon Steel
- ASTM A105
- Used for general-purpose, low-to-medium temperature applications
Stainless Steel
- ASTM A182 F304, F316
- Corrosion-resistant, ideal for chemical, food, and marine applications
- A182 F11, F22, F91
- Used in high-temperature and high-pressure service such as power plants
Most blind flanges are forged for better structural integrity, density, and pressure resistance compared to cast products.
Installation & Maintenance
Proper installation and maintenance extend the service life of ASME B16.5 blind flanges and prevent leakage.
Installation Tips
- Clean flange faces and remove dirt or scratches
- Use a compatible gasket matching the facing type
- Tighten bolts evenly in a cross pattern to avoid distortion
- Follow torque specifications based on flange size and class
Maintenance
- Regularly inspect for leaks, corrosion, or deformation
- Replace worn gaskets during system shutdowns
- Check bolt tightness after initial operation and temperature changes
- Protect flange surfaces from mechanical damage and harsh environments
Safe installation and routine maintenance ensure reliable performance in industrial piping systems.