Elastic and inelastic finite element analyses have been carried out for the shell to tubesheet junction of a C2- Hydrogenation reactor subject to pressure and temperature actions.
Three geometrically different models have been tested to select the most efficient one for applying the analysis. These models are symmetrical and differ from each other by the amount of tube to tubesheet perforations and the type of the supporting tubes. It has been shown that a tubesheet FE model with full perforation supported by combination of the link and three- dimensional elements produces quite reasonable results as compared to other proposed models.
FE elastic analysis was carried out for tubesheet thickness as per datasheet, and also for reduced tubesheet and shell thicknesses. Results indicate that the lower thickness can be employed and additional thickening of the tubesheet and adjacent shells is not required.
Inelastic analyses for the gross plastic deformation and progressive plastic deformation design checks have been carried out for the data sheet original thickness as well as the reduced thicknesses. Results indicate that in either case larger pressure in comparison with data sheet values can be carried safely by tubesheet and adjacent shells.
Moreover, employing Melaln's shakedown theorem, it is shown that the residual stress field created during a loading and unloading cycle will not grow during successive load and unload cycles once the tube sheet is subject to cyclic actions and, hence, the tubesheet shakes down to completely elastic behavior.
Fatigue analysis for both welded and unwelded region of tubesheet and shell junction at the groove location have indicated that the number of life cycles for this reactor is much larger than the number of operating cycles anticipated to occur during the reactor life.
Radii effect analysis was performed in order to study the effect of radii size on the magnitude of the stresses. Results of analysis indicate that small radii result in larger stresses, that increase of this transition radius results in decrease of stresses down to a minimum, and further increase leads to an increase of stresses. The optimum radius size has been reported.
A manual calculation according to ASME Sec. VIII and EN 13445-3 Appendix 13 and Annex J was performed to show the difference in results obtained according to these codes.