An Improved Method for Assessing Transient Thermal Stresses at a Pressure Vessel Nozzle

An improved method for assessing the transient thermal stress distribution in a pressure vessel cylindrical nozzle to sphere intersection is presented. The main purpose of the work is to develop a new method that will give a more versatile solution than the existing simplified method used in Annex G of PD5500:2003. In the first instance, Heisler’s simplified approach is improved. Thereafter, three further methods are used for comparison, namely, an improved analytical method, a numerical method and the finite element method. This allows comparison of the three techniques in contrast with the existing classical solution. From this work, new improved charts are presented which extend the range of applicability of the curves in PD5500. The design curves have been verfied and extended to cover a wider range of applicability. In addition, the approach has been improved to included the step-type as opposed to the less severe ramp-type temperature variation in the fluid temperature from inside the shell to a final steady value. Finally, some case studies are presented which show the effects and improvements gained when using the new analysis method.