Flanges are essential components in piping systems, connecting pipes, valves, pumps, and other equipment. However, not all flanges are created equal. One of the most important factors to consider when selecting a flange is its pressure rating. This rating determines the maximum pressure the flange can handle under specific temperature conditions. In this article, we will explain what flange pressure ratings are, how they work, and why they matter in industrial applications.

As a professional flange supplier, sasaflange offers a wide range of pressure-rated flanges to meet the demands of different industries and applications. Understanding these ratings can help you select the right flange for your project and ensure safety, durability, and compliance.

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What Are Flange Pressure Ratings?

Flange pressure ratings, also known as pressure classes, indicate the amount of internal pressure a flange can safely withstand at a given temperature. These ratings are defined by international standards such as:

• ASME B16.5 (used in the US and internationally)

• EN 1092-1 (European standard)

• DIN (German standards)

Common pressure ratings in ASME B16.5 include:

• Class 150

• Class 300

• Class 600

• Class 900

• Class 1500

• Class 2500

Each class refers to a range of pressure capacities, not a fixed number of pounds per square inch (psi).

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Pressure Rating vs Actual Pressure

It is important to note that a Class 150 flange does not mean it can handle exactly 150 psi. The pressure capacity varies depending on:

• Flange material

• Operating temperature

• Corrosion allowance

• Pipe schedule

For example, a Class 150 stainless steel flange may handle 285 psi at 100°F, but its capacity decreases as the temperature increases.

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Temperature Effects on Pressure Ratings

Flange pressure ratings are temperature-dependent. The higher the temperature, the lower the pressure rating. This is due to the weakening of the flange material at elevated temperatures.

For example:

• Class 300 flange in carbon steel may handle:

  • 570 psi at 100°F

  • 260 psi at 600°F

Different materials (like stainless steel or alloy steel) will have different reductions in capacity.

sasaflange provides material-specific pressure rating tables to help customers select the right flange under their expected temperature range.

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Flange Rating Conversion: ASME vs EN

If you work with global suppliers, you may encounter different rating systems: