The Numerical Investigation On The Mechanical Behavior Of The Connection Process For The Heat Exchanger Tube-to-tubesheet Joint

The shell and tube heat exchanger was used widely on petrochemicals,energy and other industry. And the joint which was used to connect the tube andthe tubesheet in shell&tube heat exchange is the most important part in process.And it’s also the most prone to failure. Therefore, the study on the mechanicalbehavior of connection between the tube and the tubesheet has a large value andspace for research. And it also has a application value in actual industry.In this paper, the finite element analysis was used to simulate and evaluatethe connection process method of mechanical expansion, hydraulic expansionand welding prior to expansion between304L tube and Q235-B tubesheet. Andthe analysis was used to study the mechanical behavior of the structure of tube-to-tubesheet. The result is that:In the process of mechanical expanding, both equivalent stress and contactstress are sharp rise and fall once it experiences roller compaction after tube totubesheet contacts, the stress of tubesheet actually increases under such changesover and over again. And the differences between the rise of equivalent stress andthe fall of equivalent stress decrease gradually. But the differences between therise of the contact stress and the fall of the contact stress increase gradually. Atlast, the residual contact stress was distributed homogeneously in the expandingarea. With the tube plate modulus of190GPa~220GPa, residual contact stressincreases with the increase of elastic modulus. Within the bulging amount of0.13125mm~0.140625mm, the residual contact stress decreases with the decreaseof the bulging amount. And the pulled off strength of joint is about20MPa.In the loading stage of hydraulic expansion, equivalent stress increaseslinearly with the load increasing, and then stays the same. After that, theequivalent stress increases again. But the contact stress presents an approximate linear increase. In the unloading stage, equivalent stress has a linear decrease,and then presents a quadratic curve which rises first and fall later. And contactstress decreases approximately linearly.The maximum equivalent stress of tube-to-tubesheet locates in higher yieldstrength of the welding path and the vicinity of tubesheet after welding. Themaximum radial stress which locates in the tubesheet is tensile stress. Thecircumferential stress of tubesheet is tensile stress. Within the scope of the study,the tubesheet trends to yield. Compared to the hydraulic expanded joint,welding prior to expansion is likely to obtain the maximum residual contactstress under a lower expanding pressure. Besides, the largest average residualcontact stress of welding prior to expansion than hydraulic expansion is bigger.For welding prior to expansion, the work-hardening capacity of tubesheet issmaller and the springback of tubesheet is better under the same expandingpressure.