Design by Analysis: Direct Route for Cases With Pressure and Thermal Action

This paper focuses on the usage of direct route for design by analysis, which is included in the new European standard for unfired pressure vessels (CEN, 2002, “Unfired Pressure Vessels-Part 3: Design,” European Committee for Standardization No. EN 13445-3, Current Issue 14-2005). The direct route addresses failure modes directly, having, therefore, advantages in comparison to the traditional method, which is stress categorization. Special attention is given to the progressive plastic deformation design check (PD-DC) with space and time-dependent temperature distribution and the fatigue design check (F-DC) with stress components, which do not vary simultaneously. As a simple demonstration example, a nozzle with cold media injection is used to show how the direct route can be applied in such cases. This example is analyzed with abruptly changing injection temperature, which makes a transient thermal analysis necessary. In the case of the PD-DC, Melan’s shakedown theorem and cycling of a finite element model with a linear-elastic ideal-plastic material model are used. In the case of the F-DC, some problems are discussed: One of them is cycle counting in the case of nonproportional loading, and the other one is the use of structural stresses and stress concentration factors.