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 on 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. the stress intensities due to pressure are severely underestimated. Instead of eventually getting full elastic load cycles due to the phenomenon of elastic shake down, one may end up with plastic deformation during each and every single pressure cycle of the vessel. Depending upon the frequency and amplitude of the pressure cycles and of course additional external loads on the nozzle, the vessel might crack up prematurely due to low cycle fatigue. (C) 1998 Elsevier Science Limited. All rights reserved.