What must be replaced when a flanged joint is opened?

When a flanged joint is opened, the gasket must be replaced. The gasket serves as a critical component that seals the joint between the two flanges, preventing leaks of the material being transported, such as propane. Gaskets can be made from various materials and can degrade over time due to factors like pressure, temperature, and exposure to different chemicals.

When you unbolt or open a flanged joint, the integrity of the gasket is compromised, and even if it appears to be in good condition, it may not create an adequate seal upon reassembly. Therefore, replacing the gasket is essential to ensure a proper seal, enhance safety, and maintain system efficiency. Neglecting to replace the gasket could lead to leaks, which are especially dangerous in applications involving flammable materials like propane.

The other options might seem relevant to the joint's integrity, but they do not address the primary sealing function that the gasket performs. For instance, while the pipe and connection might remain intact, and sealant might be used for different types of joints, they do not substitute for the specific sealing purpose of a gasket in flanged joints.