If industrial piping systems were the vascular network of a human body, flanges would be the crucial junctions connecting these vessels. Selecting the right flange is as critical as choosing the proper vascular stent. Have terms like DN and PN ever left you perplexed? This article will demystify these flange specifications, empowering you to navigate the world of pipe connections with confidence.

Flanges serve as essential connectors for pipes, valves, and other critical components in industrial settings. However, not all flanges are created equal—they come in various shapes and sizes to meet diverse requirements. Classification depends on multiple factors including form, dimensions, pressure ratings, and material composition. Common materials include carbon steel ,stainless steel and alloy steel, widely used in industrial applications.

Flange categorization primarily considers mechanical properties such as corrosion resistance and environmental factors. Major types include slip-on flanges, threaded flanges, socket weld flanges, blind flanges, and flat face (FF) flanges, each serving specific piping needs. A flange connection involves joining components with bolted flanges, while manufacturing methods significantly impact flange quality.

International standards govern flange production worldwide. Key systems include ASME (American), PN/DIN (European), BS10 (British/Australian), and JIS/KS (Japanese/Korean). Notably, in 1996, the American National Standards Institute discontinued publishing B16.5 in the U.S., with ASME B16.5 serving as its equivalent.

DN stands for "Nominal Diameter," a standardized measurement for flange size corresponding to bolt circle diameter. Importantly, DN doesn't represent actual flange dimensions but rather an industry benchmark ensuring manufacturer compatibility. The DN system typically applies to flanges manufactured under BS EN 1092, a European standard specifying requirements for circular steel flanges suitable for both low/high temperatures and pressure applications. When selecting flanges, material composition, pressure requirements, and application specifics must complement DN considerations.

PN signifies "Nominal Pressure," prefixing a flange's pressure rating. For instance, a PN16 flange can operate at up to 16 bar at 20°C. Standard PN ratings include PN6, PN10, PN16, PN25, PN40, PN64, and PN100. International standards like ISO 7005-1 or DIN EN 2501 use the metric system to specify pressure ratings and flange dimensions for these series.

When defining PN flange specifications, providing actual working pressure is advisable. While components might share similar PN ratings (e.g., PN16), their pressure capacities may differ despite compatible drilling patterns.

In flange terminology, "DN" indicates size while "PN" denotes pressure rating. A designation like DN100 PN10 specifies a 100mm nominal diameter with 10 bar pressure capacity. This dual specification ensures proper flange selection for required pipe dimensions and system pressures.

A flange's pressure rating indicates its maximum pressure capacity at specified temperatures—a critical factor in preventing leaks or ruptures. Ratings appear as numbers followed by pressure units (e.g., "150 psi"). Different flange types (like weld neck vs. slip-on) feature varying pressure capacities due to material and structural differences.

PN16 indicates safe operation at ≤16 bar (232 psi) up to 120°C. This rating ensures system integrity against high-pressure fluids/gases, though actual performance depends on materials, construction, and operating conditions.

The "40" in PN40 signifies 40 bar capacity at 20°C, designed for more demanding pressure requirements.

PN100 flanges withstand 100 bar at 20°C, serving the most rigorous pressure conditions. Similarly, PN6, PN10, PN16, and PN25 correspond to 6, 10, 16, and 25 bar ratings respectively at 20°C.

A DN 50 flange features a 50mm nominal diameter—the standard reference for matching pipe systems. Note that actual outer diameters may exceed nominal sizes due to material thickness and raised flange faces.

The American National Standards Institute (ANSI) establishes U.S. specifications for flange dimensions, materials, and pressures. A PN100 flange roughly equates to an ANSI Class 600# rating.

PN 40 pressure ratings convert approximately to:

• 580 psi (pounds per square inch)
• 4 MPa (megapascals)
• 391 kgf/cm² (kilograms-force per square centimeter)

These conversions provide general guidance, though exact values may vary slightly by specific standards.