Which statement about Class 300 flanges is true compared to Class 150?

Which statement about Class 300 flanges is true compared to Class 150?

• A. They have a thinner hub and lower pressure rating
• B. They have the same hub design and identical pressure rating
• C. They have a thicker hub and higher pressure rating
• D. They require more bolts but lower strength materials

Answer: (C)

In ASME flange practice, the class rating indicates how much internal pressure a flange is designed to withstand. To achieve a higher rating from Class 150 to Class 300, the flange must be made stronger, which is typically accomplished by increasing the hub and overall flange thickness. That thicker hub helps resist the higher stresses at elevated pressure, giving Class 300 flanges the greater pressure capability. The bolt circle and the number of bolts for a given nominal size and face type are usually the same, so you don’t inherently require more bolts, and the material strength isn’t dictated to be lower—in fact, the design aims for adequate strength to handle the higher pressure. Therefore, the statement that best fits the comparison is that Class 300 flanges have a thicker hub and a higher pressure rating.

In ASME flange practice, the class rating indicates how much internal pressure a flange is designed to withstand. To achieve a higher rating from Class 150 to Class 300, the flange must be made stronger, which is typically accomplished by increasing the hub and overall flange thickness. That thicker hub helps resist the higher stresses at elevated pressure, giving Class 300 flanges the greater pressure capability. The bolt circle and the number of bolts for a given nominal size and face type are usually the same, so you don’t inherently require more bolts, and the material strength isn’t dictated to be lower—in fact, the design aims for adequate strength to handle the higher pressure. Therefore, the statement that best fits the comparison is that Class 300 flanges have a thicker hub and a higher pressure rating.