IFMASS10

174

Figure 11: View of deformed nozzle region

Structural stability is assured, since stress and strain values are in allowable limits.

This calculation is an example of general approach in new regulations to technical

harmonization of pressure equipment (PED 97/23/EC), which are related to structural

integrity, i.e. to basic strength safety, calculation and design conditions.

4.2. Analysis of axial crack in welded thin cylindrical shells by REI model

Elastic-plastic analysis of thin cylindrical shells with an axial crack can be analysed by

REI model, with basic assumptions helped to formulate and solve equations:

–

crack shape is rectangular (crack depth is constant) (Fig. 12. a);

–

there is no transversal shear (Kirchhoff’s assumptions for thin shells hold good);

–

material is ideally plastic (there is no strain hardening).

Figure 12: Internal crack in shell with fully plastic ligament

In addition, it is adopted that net cross section, for –

, is fully plastic and it

transmits only membrane stresses close to yield stress value (Fig. 12. c). It is also adopted