Task Group 1: Fatigue

‘Technical Task Group’

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The ongoing work on the revision of the clauses in EN 13445-3 dedicated to fatigue (principally clauses 17 and 18) within CEN/TC 54/WG 53/DESIGN CRITERIA revealed open items in the fatigue assessment procedure of unwelded and welded parts that cannot be resolved up to now by the existing working group. These open items are addressed in the Technical Note CEN/TC 54/WG 53 N 829. Some of these open items had already been identified during the first revision of the fatigue clauses in the 1990s and have been addressed in the background document “EN 13445 ‘Unfired pressure vessels’. Background to the rules in Part 3 Design”. These open items are in particular

• Mean data fatigue curves for unwelded parts (origin of data, possibly unsafe, strong dependence on ultimate tensile strength).
• Design fatigue curves for unwelded parts (safety/margin factors, correction factors, related probabilities of survival).
• Extrapolation of the component design fatigue curves for welded parts taken from EC3/IIW recommendations into the low cycle fatigue (LCF) range where the available data base is still very scarce. Furthermore, the question of load-controlled or strain controlled testing in this context needs to be resolved.
• Influence of environment on fatigue behavior is mentioned but there is no quantification of this effect on crack initiation or crack propagation.