Pipe flange standards exist to ensure safety, reliability, and compatibility in industrial piping systems. They define the size, pressure rating, dimensions, and materials for flanges.
When components from different manufacturers meet the same standard, they are designed to fit together and work safely under defined conditions. Understanding these standards is essential for selecting the correct flange and preventing leaks or system failure.
This guide covers the main standard systems used worldwide and how to apply them.
Major Global Flange Standard Systems
There are three primary families of flange standards, based on regional practices. Most other national standards are adaptations of these core systems .
| Standard System | Region of Origin | Key Standards | Pressure Rating System | Key Features |
| ASME/ANSI (American) | North America, Global Oil & Gas | ASME B16.5, ASME B16.47, API standards | Class (e.g., 150, 300, 600). Number indicates pressure-temperature capacity . | Imperial measurements (inches). Most common for high-pressure and critical service worldwide. |
| DIN/EN (European) | Europe, many international projects | EN 1092-1, DIN standards, ISO 7005 | PN (Pressure Nominal) (e.g., PN6, PN10, PN16). Number refers to pressure in bars . | Metric measurements (mm). Common in water treatment, chemical plants, and equipment built to European specs. |
| JIS (Japanese) | Japan, parts of Asia | JIS B2220 | K (e.g., 5K, 10K, 20K) | Metric measurements. Often found on equipment and machinery exported from Japan. |
Key American (ASME/ANSI) Standards Explained
The ASME/ANSI system is the most common in many industries. Here are its core standards:
- ASME B16.5: This is the most important standard for pipe flanges. It covers flanges for pipes from NPS 1/2″ to 24″ in pressure classes from 150 to 2500. It includes dimensions for weld neck, slip-on, blind, socket weld, threaded, and lap joint flanges .
- ASME B16.47: This standard covers large-diameter steel flanges from NPS 26″ to 60″. It is published in two series: Series A (MSS SP-44) and Series B (API 605), which have different dimensions and are not interchangeable .
- API Standards: The American Petroleum Institute publishes standards for specific, demanding applications. API 6A covers wellhead and Christmas tree flanges for ultra-high-pressure oil and gas services .
- AWWA Standards: The American Water Works Association standards, like AWWA C207, are for waterworks systems. They define steel plate flanges (Classes B, D, E, F) used in large-diameter water and wastewater pipelines .
Key European and International Standards
- EN 1092-1: This is the current harmonized European standard, replacing older national standards like DIN 2501. It specifies flanges with PN ratings .
- ISO 7005: This is an international standard that consolidates dimensions from ASME and DIN standards into one document. A flange marked ISO 7005 PN16 will have the same dimensions as an EN 1092-1 PN16 flange .
Critical Differences: Why Standards Are Not Interchangeable
A common and costly mistake is assuming flanges from different systems are compatible. For example, an ASME B16.5 Class 150 flange and an EN 1092-1 PN16 flange are designed for similar pressures but have completely different dimensions.
| Comparison Point | ASME B16.5 Class 150 (NPS 4″) | EN 1092-1 PN16 (DN 100) | Result |
| Outside Diameter | 9 inches (228.6 mm) | 220 mm | Different sizes, will not align. |
| Bolt Circle Diameter | 7.5 inches (190.5 mm) | 180 mm | Bolt holes will not match up. |
| Number of Bolts | 8 | 8 | Same count, but on different circles. |
| Bolt Size | 5/8 inch | M16 | Different thread and size. |
You cannot directly bolt together flanges from different standard systems. Trying to do so will result in misaligned bolt holes, an improper seal, and a dangerous leak path. Connecting different systems requires a specially designed adapter spool.
Frequently Asked Questions
Q: What does “Class 150” or “PN16” actually mean?
A: These are pressure class ratings, not direct pressure values. A Class 150 flange can handle more than 150 PSI at room temperature. The rating is a designation that corresponds to a specific pressure-temperature curve based on the flange material. You must consult reference tables to find the maximum allowable working pressure for your specific material and temperature .
Q: How do I choose the right standard for my project?
A: The choice is usually dictated by the existing equipment, project location, or client specifications.
- Check the mating equipment or existing piping.
- Follow the engineering drawings or contract documents.
- In North America or global oil/gas, ASME is typical. In Europe, DIN/EN is common.
Q: Are “ANSI” and “ASME” flanges the same thing?
A: For modern flanges, they refer to the same physical parts. Historically, ANSI approved the standards. Today, ASME (American Society of Mechanical Engineers) maintains and publishes the standards, like ASME B16.5. When people say “ANSI flange,” they almost always mean a flange made to the current ASME standard .
Q: What information do I need to specify a flange?
A: You must provide these key details:
- Nominal Pipe Size (NPS or DN)
- Pressure Class (e.g., 300) or PN Rating (e.g., PN16)
- Flange Type (e.g., Weld Neck, Blind)
- Facing Type (e.g., Raised Face, Ring-Type Joint)
- Material Specification (e.g., ASTM A105)
- Governing Standard (e.g., ASME B16.5)
Conclusion
Using the correct pipe flange standard is non-negotiable for system safety and integrity. The choice between ASME, DIN, or other systems is fundamental and affects every other specification. Always verify the required standard from your project specifications or existing equipment before ordering any flange.
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