Class 300 and Class 600 flanges are pressure-level classifications based on the ASME (American Society of Mechanical Engineers) standard. Flanges are components that connect pipes, valves, pumps, and other equipment, providing a sealed connection between piping systems. The main difference between Class 300 and Class 600 flanges relates to the pressure and temperature ranges they can withstand.
If we want to know the difference between Class 300 and Class 600 flanges, we must first understand the pressure ratings.
Flange Pressure Rating
The flange pressure rating, also known as Pressure Class or Pressure Rating, indicates the maximum working pressure that a flange can handle. These ratings are determined by organizations like ASME (American Society of Mechanical Engineers) and are based on factors such as size, material, design, and operating temperature.
In the ASME B16.5 standard, common flange pressure ratings include:
Class 150 Class 300 Class 400 Class 600 Class 900 Class 1500 Class 2500
Pressure ratings can be indicated in various ways, such as 300 Lb, 300 Lbs, 300#, or Class 300, and they all mean the same thing. However, according to ASME B16.5, the correct indication is the pressure rating, which is a dimensionless number.
Pressure Rating Example
Flanges can withstand different pressures at different temperatures. As the temperature increases, the flange’s pressure rating decreases. For example, a Class 300 carbon steel flange, as shown in the image to the right, is rated for approximately 740 psig at ambient conditions, 635 psig at approximately 400°F, 570 psig at approximately 600°F, and 410 psig at approximately 800°F.
In other words, when pressure drops, temperature rises and vice versa. Other factors include flanges being made of different materials, such as stainless steel, cast and ductile iron, carbon steel, alumina ceramic, etc. Each material has a different pressure rating.
Below is an example of an NPS 12 flange with multiple pressure ratings. As you can see, the inside diameter and raised face diameter are the same; however, the outside diameter, bolt circle, and bolt hole diameter get more extensive in each higher pressure rating.
| Pressure Rating | Number of Bolt Holes | Bolt Hole Diameter (mm) |
| Class 150 | 12 | 25.4 |
| Class 300 | 16 | 28.6 |
| Class 400 | 16 | 34.9 |
| Class 600 | 20 | 34.9 |
| Class 900 | 20 | 38.1 |
| Class 1500 | 16 | 54 |
| Class 2500 | 12 | 73 |
The Difference Between Class 300 and 600 Flange
Now let’s analyze Class 300 and Class 600 flanges.
The difference between Class 300 and Class 600 flanges lies primarily in their pressure ratings and design features, such as size and material strength. Here’s a detailed comparison:
Pressure rating:
– Class 300 flanges are designed for lower-pressure applications and can withstand pressures of about 570 psi at ambient temperature.
– Class 600 flanges are designed for higher-pressure applications and can withstand pressures up to about 1,150 psi at ambient temperature. This class is used when a more robust connection is needed to withstand higher stresses.
Design and size:
– Class 600 flanges are typically thicker than Class 300 flanges and may have a slightly larger outer diameter to accommodate the higher pressure rating, providing greater strength.
– The diameter of the bolt hole circle and the number of bolts may vary between Class 300 and Class 600 flanges. Higher pressure ratings typically require more bolts or a different arrangement to ensure a secure connection.
Applications:
– Class 300 flanges are used in applications with moderate pressure and temperature requirements, such as water distribution systems, low-pressure steam piping, and specific chemical processing environments.
– Class 600 flanges are used in high-pressure systems, such as oil and gas production, high-pressure steam systems, and other industrial applications that require higher-pressure seals.
Material considerations:
The material of a flange affects its pressure rating capabilities. For example, a Class 300 flange made of 304 stainless steel may have different pressure and temperature limits than one made of carbon steel. Similarly, other materials for Class 600 flanges can support different maximum pressures.
Weight and cost:
– Class 600 flanges are typically heavier and more expensive due to the additional materials and more robust design required to handle higher pressures.
– Class 300 flanges are lighter, typically less expensive, and suitable for systems with lower pressure requirements.
ASME B16.5 Flange Dimensions in Inches & mm
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