Acronyms, Notations, and Symbols
Bolted Flange Joints - Features and Components

Bolted flange assemblies are widely used in many demanding industrial sectors, including nuclear facilities, petrochemicals, offshore drilling, and the shipbuilding industry. They are frequently integrated into systems that handle pressurized, high-temperature, cryogenic, or potentially hazardous fluids.

In these environments, a loss of seal integrity in a joint can have significant consequences. Failures can manifest in various forms, ranging from a simple leak to more severe phenomena, such as gasket extrusion, bolt ejection, or flange rupture. Mastering these assemblies is therefore a major industrial challenge, both to ensure the safety of people and the protection of the environment and property, and to guarantee the availability and performance of the facilities.

The operation of a bolted flange joint relies on applying the proper tightening torque to the bolts, which generates sufficient contact pressure on the gasket to ensure the joint is leak-tight. However, such a joint cannot be considered a simple juxtaposition of independent components. The flanges, gasket, and bolts constitute a mechanical system in which the components interact closely. The overall performance of the joint therefore depends on their combined behavior.

With this in mind, this article presents the main components of a bolted flange assembly and describes their essential characteristics. The objective is to provide designers with the necessary information to guide the selection of flanges, gaskets, and fasteners based on operating conditions and the characteristics of the fluid to be contained.

This overview serves as a first step toward understanding the fundamental principles of bolted flange assemblies. Subsequent articles in this series will address the mechanical modeling of these assemblies as well as methods for determining clamping force, particularly using the TBSS (Tight Between Seal and Strength) method.