Integrity Assessment of the Welded Nozzle-Header Joint of the Steam Superheater

Manufacturing flaw in pressure vessels and pipelines, especially in welded joints, poses a major challenge to structural integrity and operational safety.This paper examines the effects of such flaws, focussing on a specific case study of inclusions observed at the root of welded head-nozzle joints in a steam superheater.Finite Element Analysis (FEA) is used to investigate how these flaws affect the load capacity of the pressure vessel.To simulate the behaviour of the welds under operating conditions, two scenarios are considered: one with a sharp elliptical crack between two welded nozzles and another with a full torus-shaped flaw along the entire circumference of the weld root.During the analysis, stress distributions, plastic limit loads, stress intensity factors, fracture toughness and structural integrity are assessed using the Failure Assessment Diagram (FAD) and the SINTAP method.The results show that although the presence of a sharp elliptical crack with the considered dimensions between the nozzles does not significantly affect the static strength of the structure, plastic collapse must be considered as a potential failure mechanism, especially for highly plastic materials.The FAD analysis shows that the structure can withstand the operating pressure without failing, but failure due to plastic collapse can occur at higher pressures.The study emphasises the importance of considering both fracture mechanics and the plastic failure criterion when assessing the integrity of welded components in pressure vessels.