Application Of Finite Element Method In The Light-Weight Design Of Tubesheet

Heat exchangers are widely used in nearly all industries. As the key component of heat exchanger, tubesheet plays very important role in safety operation, energy saving and cost reduction of the equipment. With the development of national economics and increase of the industry production scale, heat exchangers are geting larger and larger and, as a result, reasonable design of the tubesheet is becoming increasingly important. Owing to more accurate in calculation, finite element method is more and more widely used in the design of engineering structures. Specifically, combined with the standard of design-by-analysis, it provides a feasible approach for the light-weight design of tubesheet by improving the structure or decreasing the thickness. In this thesis, two practical tubesheet structures were analyzed by using finite element method for demonstrating the light-weight design of tubesheet.A finite element model was established to perform stress analysis and strength check on the tubesheet of methanol reactor under three different loading cases, namely hydraulic test loading case, design loading case and operation loading case. Results show that under the hydraulic test loading case, some local strength cannot conform to the requirement of JB 4732-1995 Steel Pressure Vessels -Design By Analysis. Increasing the thickness of the tubesheet can satisfy the strength requirement, but the cost is increased and the stress distribution is not reasonable.Based on the stress distributions, improvement of the tubesheet structure was introduced which included the central structure and the connection of the tubesheet and the cylinders. Again, finite element analysis was performed and the results show all strength requirements for the improved tubesheet structure under the three loading cases are satisfied. Compared with the original one, the thickness of the improved tubesheet is decreased by 40mm, and, as a result, the material for the tubesheet is reduced significantly and the cost of the equipment is lowered remarkably.As for the cracking problem of the circular-oil steam generator, a finite element model for the generator was also established and stress analysis was performed under seven different loading cases, namely tube-side hydraulic test loading, shell-side hydraulic test loading, thermal loading, tube-side working pressure loading, sell-side working pressure loading, tube-side working pressure plus thermal loading and shell-side working pressure plus thermal loading. Results indicate that actual support of the heat exchange tubes on the tubesheet is much stronger than that considered in conventional design code of heat exchangers. Compared with the standard of design-by-rules, using finite element method together with the standard of design-by-analysis can significantly reduce the thickness of the tubesheet. Of course, decreasing of thickness can effectively reduce the thermal stress and, thus, lower the possibility of tubesheet cracking.