PRESSURE STRESS INTENSITY AT NOZZLES ON CYLINDRICAL VESSELS - A COMPARISON OF CALCULATION METHODS

Calculation methods for stress intensities at nozzle-vessel junctions due to internal pressure are compared with each other and with results obtained from finite element analyses. For relatively large nozzles o n thin-walled cylindrical vessels the methods from the British BS 5500 , the German AD-Merkblatter, the Dutch Rules for Pressure Vessels and the draft version of the forthcoming Unfired Pressure Vessel Standard of the European Union respectively, become totally unreliable, i.e. th e stress intensities due to pressure are severely underestimated. Inst ead of eventually getting full elastic load cycles due to the phenomen on of elastic shake down, one may end up with plastic deformation duri ng each and every single pressure cycle of the vessel. Depending upon the frequency and amplitude of the pressure cycles and of course addit ional external loads on the nozzle, the vessel might crack up prematur ely due to low cycle fatigue. (C) 1998 Elsevier Science Limited. All r ights reserved.