Mechanics and technical points of flexible expansion process of tube-to-tubesheet joints in shell-and-tube heat exchangers were briefly introduced. A series of experiments were performed on flexibly expanded tube-to-tubesheet joints to verify the pull-out strength. Carbon steel 20 and stainless steel S30408, two kinds of materials frequently used as tube in heat exchanger construction in China, are employed in the experiment. Specially developed rubber expansion equipment was employed to simulate the flexible expansion process in the experiment as well. Grooves with different widths and depths were used to investigate their influence on the pull-out strength. The results show that the pull-out strength of tube-to-joints with no annular ring grooves in tube holes grows with the increase of expanding pressure during the initial stage of expanding process, and the growth approaches naught when the expanding pressure reached a certain value. Compared with the ungrooved tube-to-tubesheet joints, the pull-out strength of the grooved ones is much higher and can well satisfy the requirements specified in China code & standard at the experimental conditions. The width of groove has remarkable effects on the pull-out strength of joint, and an optimum width of groove exists for a given pipe specifications. Especially, the expansion degree recommended in Chinese standard for heat exchanger is not suit for flexibly expanded tube-to-tubesheet joints.

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