PSI - Issue 19

J. Rudolph et al. / Procedia Structural Integrity 19 (2019) 575–584 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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A new Annex NB “Cycle Counting and determination of equivalent stress range” details the cycle counting issue and the determination of the equivalent stress ranges for the fatigue check. As the latest amendment, a critical plane approach has been implemented. A new Annex NC “Stresses in double - sided fillet welds” provides applicable guidelines for the fatigue check of this kind of weldments. A new Annex ND “Table of stress concentration factors K t ” provides applicable stress concentration factors. Clause 18 includes specific definitions of relevant terms of the detailed fatigue check: critical area, cut-off limit, discontinuity, effective notch stress, effective stress concentration factor, elastic follow-up, endurance limit, equivalent stress range (the Tresca criterion and von Mises criterion are permitted), fatigue, fatigue design curves, gross structural discontinuity, hot spot, load cycle, local structural discontinuity, nominal stress, notch, notch stress, seam weld, stress on the weld throat, stress range, structural stress, structural hot spot stress, theoretical elastic stress concentration factor, partial usage factor, cumulative usage factor (cumulative fatigue damage index), weld throat thickness. The process for detailed fatigue assessment is shown in Figure 1. This process (for welded components) is in line with codes and recommendations such as Eurocode 3 [8] and the IIW fatigue design recommendations [1]- [3]. 2. Process for detailed fatigue assessment

Fig. 1. Process for detailed fatigue assessment according to reference [4]

3. Fatigue assessment of welded components

As mentioned before, in EN 13445-3 [4] back in the 1990s it has been opted for the application of a structural stress parameter and thus the methodology of the above mentioned codes respectively recommendations is followed. The kind of underlying fatigue testing of welded components is explained in the background document EN 13445 "Unfired pressure vesse ls" Background to the rules in Part 3 Design” [9].