The European Pressure Vessel Standard EN 13445 provides in its part 3 (Design) a simplified method for fatigue assessment (Clause 17) and a detailed method of fatigue assessment (Clause 18). Clause 18 “Detailed Assessment of Fatigue Life” is under revision within the framework of the European working group CEN/TC 54/WG 53 - Design methods. The latest amendments of Clause 18 are to be presented. All these amendments aim at a significant increase in user friendliness and clear guidelines for application. The following items are to be mentioned in particular in that context:
• Fatigue assessment of welded components based on structural stress and structural hot-spot stress approaches
• Detailed guidelines for determining relevant stresses and stress ranges
• Cycle counting proposals.
The fatigue assessment of welded components is part of paragraphs 18.6 “Stresses for fatigue assessment of welded components and regions” (determination of relevant stress ranges) and 18.10 “Fatigue strength of welded components” (relevant weld details and revised fatigue curves). The basic rules for unwelded components essentially remain unchanged. Stress analyses for clause 18 are usually based on detailed finite element analyses (FEA). As an essential amendment for the practical user the determination of structural stress ranges for the fatigue assessment of welds is further detailed in the new informative annex NA “Instructions for structural stress oriented finite elements analyses using brick and shell elements”. Here, different applicable methods for the determination of structural stresses are explained in connection with the requirements of the finite element models and analyses.
The cycle counting issue is comprehensively treated in the new informative annexes NB “Cycle Counting for a given Load History” and NC “Cycle Counting for Design Data Evaluation” including detailed proposals for implementation in an algorithmic programming framework.