Gaskets are relatively simple pieces of equipment in principle, yet are entirely critical in many types of chemical process industries (CPI) applications, including pipes and vessels. An understanding of gasket function, and of the forces and stresses acting on gaskets provides a basis for decisions on gasket types and materials.
Functions and types
Acting as a retaining seal between two rigid stationary surfaces, the gasket material is normally softer than the parts it is sealing, so to some extent, it flows into the irregularities in the joint faces. The gasket will stay seated when the friction between the gasket and the sealing surface is large enough to overcome the pressure exerted on it from the process fluid inside the vessel or pipe.
Gaskets generally fall into two categories: those used in full-faced joints, and those wholly situated within the bolt circle (the circle defined by connecting the centers of the bolts. Since full-faced gaskets have greater surface area, a greater compressive load is required for sealing compared to that used by those within the bolt circle.
Full-faced gaskets are typically used in piping systems with operating pressures up to about 300 psi, while gaskets situated within the bolt circle can…