Study of Multiple Holes Influence on Theoretical Stress Concentration Coefficient in Case of Cylindrical Vessels

In the construction of pressure vessels, especially for steam boilers used in power plants, cylindrical vessels are commonly used. For this important class of mechanical structures, through holes also frequently cause stress concentration which must be taken into account in the design and estimation of their lifetime. In the scientific literature which addresses stress concentration effects for such structures are studied in cases of which the presence of through holes is singular. This paper studies the effect of stress concentration in case of two or more holes placed at a small distance between them, according to construction requirements. In these cases the simplifying assumption of Saint Venant according to which at sufficient distance from the analyzed area the state of stress is not influenced by how the load is applied cannot be accepted. In this paper we study the stress concentration coefficient with numerical methods using the finite element method and more precisely, ABAQUS software package, version 6.9. Different constructive cases of multiple holes are studied: two and three successive holes with the same diameter and different diameters placed on the generating line with variable distance, for which the ratio between the diameter and the distance between the holes varies. Numerical model validation was done by comparing the results obtained for specific computational models in case of which results are known and presented in the literature [1,2]. Based on the results, variation curves of the theoretical stress concentration coefficient were drawn for all cases listed above.