Flanges based on the American Class and European PN standards are among the most commonly used in the engineering field. These two flange standard systems differ significantly in pressure ratings, application ranges, and structural designs. Understanding these differences is crucial for engineers and purchasing professionals in making informed decisions regarding equipment selection, installation, and maintenance.
Standard Systems and Applications
The PN series flanges originate from the European standard EN 1092-1, which is also adopted by China under the chemical industry standard HG/T20592. This system is widely used in Europe, Asia, and international projects, especially in industries such as chemicals, oil and gas, and manufacturing. It emphasizes standardization and interchangeability, making it the dominant system in the European market.
In contrast, Class series flanges adhere to the American ASME B16.5 standard, which in China corresponds to HG/T20615. This system is predominantly used in North America, particularly in the oil and gas and aerospace industries. It is known for its reliability under high-temperature and high-pressure conditions, making it suitable for extreme environments.
Pressure Rating Classifications and Corresponding Differences
The PN series uses metric units, and pressure ratings are given in bars, with common ratings ranging from PN6 to PN160. The Class series, on the other hand, uses imperial units with pressure ratings in psi, spanning from Class150 to Class2500. These two standards are not directly interchangeable due to differences in their testing baselines.
The PN series is based on the maximum allowable working pressure at room temperature (20°C), while the Class series considers high-temperature environments (up to 454°C). This distinction leads to considerable performance differences despite similar nominal pressure ratings. For instance, a Class300 flange performs significantly better under high temperatures compared to a PN50 flange rated for room temperature.
Material and Temperature Effects
The actual pressure-bearing capacity of flanges is heavily influenced by the material used and the operating temperature. For example, a PN25 flange made from 304 stainless steel can only withstand a maximum pressure of 23 bar at 20°C, which is slightly below its nominal rating of 25 bar. Similarly, a Class150 flange can handle around 19 bar at 38°C, which deviates from the simple psi-to-bar conversion.
This highlights that flange selection should not solely rely on the nominal pressure rating. It’s essential to consider factors such as material composition, working temperature, and the operating environment. In high-temperature applications, Class series flanges tend to offer better stability, whereas PN series flanges may provide cost advantages for room-temperature applications.
Purchasing and Usage Recommendations
In domestic projects, PN series flanges are generally preferred due to better compatibility, shorter procurement cycles, and easier installation and maintenance. For international projects, the choice of flange standard largely depends on the location: Class series is common in the Americas, while PN series dominates in Europe.
It’s important to note that PN and Class flanges cannot be directly swapped, even if their pressure ratings appear similar. Differences in bolt hole patterns, sealing surface designs, and other small details may lead to installation difficulties or seal failures. If mixing standards is necessary, it is crucial to verify that the dimensions align perfectly, and consulting with a professional engineer is recommended.
Conclusion
Choosing the right flange standard goes beyond a simple selection between PN or Class. Engineers must consider the project requirements, the working environment, and long-term maintenance costs. When in doubt, refer to authoritative standards like HG/T20592 or ASME B16.5, or consult a professional supplier to ensure the best choice.