Introduction to Expansion Joints for Heat Exchangers
Release time:
2021-04-26
In fixed-tube-sheet heat exchangers, a certain temperature difference exists between the tube bundle and the shell during the heat transfer process. However, the tube sheet, tube bundle, and shell are rigidly connected to each other. When the temperature difference reaches a certain level, excessive thermal stress can often lead to damage to the shell or bending of the tube bundle. Therefore, when the thermal stress is significant, it is advisable to opt for floating-head, U-tube, or bellows-type heat exchangers. Nevertheless, these types of heat exchangers are relatively expensive. If the tubes do not require cleaning, a fixed-tube-sheet heat exchanger can still be used; however, it will be necessary to install a thermal expansion compensation device, such as an expansion joint.
An expansion joint is a flexible component installed on the shell of a fixed-tube-sheet heat exchanger. Due to its large axial deflection, even a small axial force can induce significant deformation. The difference in deformation between the tube bundle and the shell is compensated for by this flexible element, thereby reducing thermal stresses caused by temperature differences between the tube bundle and the shell. At the same time, this helps prevent the joints between the tube bundle and the tube sheet from being pulled apart. Expansion joints can also be used as components for compensating displacement and absorbing vibrations in various industrial equipment, machinery, and piping systems.
The crucial component of an expansion joint is the bellows (also known as a corrugated pipe). The cross-sectional shapes of bellows can vary widely, including flat expansion joints, omega-shaped expansion joints, and corrugated expansion joints, among others.
The thinner the wall of an expansion joint, the better its elasticity and the stronger its compensation capability; however, the lower its pressure-bearing capacity. Bellows expansion joints typically come in two types: single-layer and multi-layer. If the wall is multi-layered, the pressure-bearing capacity can be increased while still maintaining excellent compensation performance. Compared to single-layer expansion joints, multi-layer bellows expansion joints offer numerous advantages. Due to their thin walls and multi-layer structure, these joints exhibit high elasticity, high sensitivity, strong compensation capability, high pressure-bearing capacity, high fatigue strength, long service life, and a compact structure. If greater compensation is required, multi-wave expansion joints can be used.
The compensating capacity of a bellows expansion joint is determined by its shape, dimensions, and material. For example, the lower the wave height, the better the pressure resistance but the poorer the compensating ability; the higher the wave height and the greater the wave spacing, the larger the compensation amount, but the worse the pressure resistance performance.
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