9 Bolted-Flange Joints and Connections

Although flanged joints are essential components in nearly all pressurized systems, they are also one of the most complex. Many factors are involved in determining the successful design and operation of a bolted flange joint in service—namely, the interaction between the bolting, flange, and gasket, as well as important nonlinear variables such as friction and gasket properties. Safety considerations are, of course, extremely important; just as the Pressure Vessel and Piping Codes were developed with safety in mind, so, too, were the rules for bolted flange joints. The Code Bolted-Flange Joint Design Rules provide a method for sizing the flange and bolts to be structurally adequate for the specified design conditions; however, the rules do not address assembly and special requirements, nor do they guarantee a leak-tight joint for all transient operating conditions. The latter issue is discussed further in the sections on tightness-based design and flange-joint assembly.