What is the primary purpose of a gasket in a flange joint?

• A. To provide a seal against leakage under operating pressure
• B. To absorb thermal expansion
• C. To reinforce bolt tension
• D. To prevent corrosion at the flange

Answer: (A)

The gasket’s main job in a flange joint is to form a leak-tight seal between the mating flange faces under operating pressure. When the bolts are tightened, the gasket is compressed to fill microscopic gaps and surface irregularities, creating a barrier that keeps the fluid from escaping as pressure pushes outward. The gasket material must be compatible with the fluid, temperature, and pressure to maintain that seal over the life of the joint. While a gasket can accommodate some thermal movement and surface imperfections, its primary function remains sealing. Other roles like maintaining bolt preload or preventing corrosion are handled by bolt tension design and material choices, not by the gasket itself.