The ASME B16.5 blind flange specification provides the definitive set of guidelines for the manufacturing, dimensions, and pressure ratings of this essential piping component. Understanding this standard is critical for engineers, designers, and procurement specialists to ensure system safety, integrity, and compatibility. This guide offers a detailed overview of the key aspects of the ASME B16.5 blind flange specification.
ASME B16.5 Standard
The ASME B16.5 standard, titled “Pipe Flanges and Flanged Fittings,” covers pressure-temperature ratings, dimensions, tolerances, marking, and materials for pipe flanges. This widely adopted standard applies to flanges in sizes from NPS 1/2″ to NPS 24″ and for pressure classes ranging from 150 to 2500. The ASME B16.5 blind flange specification is a crucial part of this broader standard, defining the requirements for blank flanges used across various industries.
The Role of Blind Flanges
A blind flange is a solid disk used to blank off the end of a pipe, valve, or vessel nozzle. Its primary function is to provide positive isolation for maintenance, safety, or future expansion of a piping system. The robustness dictated by the ASME B16.5 blind flange specification ensures they can withstand full system pressure, making them the preferred choice for pressure testing applications.
Key Dimensions and Tolerances for B16.5 Blind Flanges
Outside Diameter (OD) and Thickness
The outside diameter (OD) and thickness of blind flanges vary with nominal pipe size (NPS) and pressure class. For example, a Class 150 blind flange for NPS 6 has different thickness and OD compared to Class 600.
Bolt Circle and Bolt Hole Specifications
Bolt circle diameter (BCD), number of bolt holes, and bolt hole size are standardized across flange types. This ensures that weld neck, slip-on, and blind flanges within the same pressure class share identical bolt patterns for interchangeability.
Dimensional Tolerances: What’s Allowed?
The ASME B16.5 blind flange specification defines allowable tolerances for outside diameter, thickness, and bolt-hole placement.
Class 150 Blind Flange Dimension
| Norminal Pipe Size | Outside Diameter | Overall Diameter | Flange Thickness min | Face Diameter | Numberof Holes | Bolt Hole Diameter | Diameter of Circle of Holes |
| inch | mm | mm | mm | mm | mm | mm | |
| 1/2 | 21.3 | 88.9 | 11.2 | 35. 10 | 4 | 15.7 | 60.45 |
| 3/4 | 26.7 | 98.6 | 12.7 | 42.9 | 4 | 15.7 | 69.85 |
| 1 | 33.4 | 108 | 14.2 | 50.8 | 4 | 15.7 | 79.25 |
| 11/4 | 42.2 | 117.3 | 15.7 | 63.5 | 4 | 15.7 | 88.9 |
| 11/2 | 48.3 | 127 | 17.5 | 73. 15 | 4 | 15.7 | 98.6 |
| 2 | 60.3 | 152.4 | 19. 10 | 91.9 | 4 | 19.1 | 120.7 |
| 21/2 | 73.0 | 177.8 | 22.4 | 104.6 | 4 | 19.1 | 139.7 |
| 3 | 88.9 | 190.5 | 23.9 | 127 | 4 | 19.1 | 152.4 |
| 31/2 | 101.6 | 215.9 | 23.9 | 139.7 | 8 | 19.1 | 177.8 |
| 4 | 114.3 | 228.6 | 23.9 | 157.2 | 8 | 19.1 | 190.5 |
| 5 | 141.3 | 254 | 23.9 | 185.7 | 8 | 22.4 | 215.9 |
| 6 | 168.3 | 279.4 | 25.4 | 215.9 | 8 | 22.4 | 241.3 |
| 8 | 219.1 | 342.9 | 28.4 | 269.7 | 8 | 22.4 | 298.5 |
| 10 | 273.0 | 406.4 | 30.2 | 323.9 | 12 | 25.4 | 362 |
| 12 | 323.8 | 482.6 | 31.75 | 381 | 12 | 25.4 | 431.8 |
| 14 | 355.6 | 533.4 | 35. 10 | 412.8 | 12 | 28.4 | 476.3 |
| 16 | 406.4 | 596.9 | 36.6 | 469.9 | 16 | 28.4 | 539.8 |
| 18 | 457.2 | 635 | 39.6 | 533.4 | 16 | 31.75 | 577.9 |
| 20 | 508.0 | 698.5 | 42.9 | 584.2 | 20 | 31.75 | 635 |
| 24 | 609.6 | 812.8 | 47.8 | 692.2 | 20 | 35.1 | 749.3 |
ASTM Standards
Alloy Steel Flange Fittings
ASTM A182 F1, F5, F9, F11, F12, F22, F91
Carbon Steel Flange Fittings
ASTM A105, A350 LF2,LF3. A694 F52, F60, F65, F70
Stainless Steel Flange Fittings
ASTM A182 F304, F316, F317, F321, F310
Duplex Stainless Steel Flange Fittings
ASTM A182 F51, F53, F55
Manufacturing, and Marking Requirements
Manufacturing Processes: Forging and Machining
Blind flanges are typically produced by forging and subsequent machining. This process provides the required mechanical strength and ensures compliance with dimensional tolerances defined in the ASME B16.5 blind flange specification.
Mandatory Marking for Traceability
Each flange must be marked with the manufacturer’s trademark, material designation, pressure class, nominal size, and standard reference. These markings ensure full traceability throughout the supply chain.
How to Select the Right B16.5 Blind Flange
Step-by-Step Selection Guide
•Step 1: Identify system design pressure and operating temperature.
•Step 2: Use pressure-temperature rating tables to determine the required pressure class.
•Step 3: Choose a flange material based on piping material and corrosion environment.
•Step 4: Select flange size based on NPS and bolt pattern requirements.
Important Considerations for Installation
Use proper grade and number of bolts according to the standard. Ensure correct gasket type and tightening sequence to achieve optimal sealing performance.
Conclusion
The ASME B16.5 blind flange specification is more than just a dimensional standard; it is a comprehensive framework that ensures safety, reliability, and global interchangeability. A thorough understanding of its requirements for dimensions, pressure-temperature ratings, materials, and marking is fundamental for anyone involved in the design, procurement, or maintenance of pressurized piping systems.
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