Structural design criteria

Code...............................................................................................................30 3.4 Allowable stress limits in the ASME Boiler and Pressure Vessel

Code...............................................................................................................31 3.5 Service limits................................................................................................34 3.6 Design for cyclic loading ...........................................................................36 3.7 Protection against fracture.........................................................................37 References ..............................................................................................................38 Problems.................................................................................................................38

3.1 Modes of failure Two basic modes of failure are assumed for the design of pressure vessels. These are: (a) elastic failure, governed by the theory of elasticity; and (b) plastic failure, governed by the theory of plasticity. Except for thick-walled pressure vessels, elastic failure is assumed. When the material is stretched beyond the elastic limit, excessive plastic deformation or rupture is expected. The relevant material properties are the yield strength and ultimate strength. In real vessels we have a multiaxial stress situation, where the failure is not governed by the individual components of stress but by some combination of all stress components.