Simplified fatigue assessment according to EN13445-3 Clause 17

With NextGen it is possible to calculate an item subjected to fatigue "by formulae", for projects according to EN13445. This allows a fatigue calculation in a simpler and faster way than normally needed when a finite analysis is involved.

Fatigue calculation is composed by two main operations:

  • Definition on Item level of fatigue conditions and required number of cycles
  • Definition on Component level of weld details or critical non-welded parts

General definition of fatigue occurs in Item properties (File > Item properties > Fatigue). Fatigue detail fields appear once "Enable simplified fatigue assessment" is enabled:

After this options are defined, enabled components will show a new "Fatigue" tab: welded and unwelded critical areas details are then available under this tab according to what's stated in calculation code. Bear in mind that enabling fatigue assesment alone doesn't mean that a calculation is made: at least one detail in a component must be defined to actually produce an output.

The following screenshot shows definition of details on a cylindrical shell:

In this example both longitudinal and circumferential welds are defined. Longitudinal weld has a general case of combined imperfections, with default automatically calculated values for offset, ovality and peeking. As always, user can manually set values by unlocking the padlock icon. Circumferential weld has an unequal thickness imperfection without offset. For both welds a weld class is defined.

All properties under this section have a contextual help ("?" button) that shows suggestions and tables taken from the calculation code.

Calculation occurs like other pressure parts, in real time once all data are filled in. Detailed calculation is available in calculation report; component report is enriched with a new section:

Complete item report has a summary page stating how much each component detail weights in the total damage index:

Author: Matteo Bagattini
Permalink: KB969721
Published on: 08 Mar 2017