by George Rallis
Diploma Thesis, July 2006
The present work investigates the local stresses and deformations that develop in the vicinity of nozzles and other welded details in industrial vessels. These local stresses under repeated loading can cause fatigue of the weld, resulting in a loss of the structural integrity of the vessel and - most likely - loss of containment. Furthermore, the nozzle may be subjected to an extreme loading condition (axial load or bending moment), due to an earthquake or an explosion. Under this extreme loading condition, the nozzle may be severely deformed and the corresponding stresses may cause collapse of the vessel.
Characteristic details from typical pressure vessels are modelled with finite elements, using program ABAQUS. Using linear elastic analysis, the local stress distribution at the vicinity of the weld is determine and its fatigue capacity is assessed. Furthermore, using large-strain elastic-plastic finite elements, the ultimate capacity of welded nozzles under axial loads and bending moments (in the presence of internal pressure) is examined.