Why are expansion joints installed in heat exchangers?

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Reason for selection: During the heat exchange process in fixed-tube-sheet heat exchangers, there is a certain temperature difference between the tube bundle and the shell. Since the tube sheet, tube bundle, and shell are rigidly connected to each other, when this temperature difference reaches a certain level, the excessive temperature differential stress can cause damage to the shell or bending of the tube bundle. Therefore, when such high temperature differential stresses occur, floating-head, U-type, or stuffing-box heat exchangers can be used. However, the cost of the aforementioned heat exchangers is relatively high. If cleaning between the tubes is not necessary, a fixed-tube-plate heat exchanger can also be used, but a temperature difference compensation device such as an expansion joint is required. Function: The expansion joint is a flexible component installed on the shell of a fixed-tube-sheet heat exchanger; due to its large axial deflection, it can undergo significant deformation even under modest axial forces. By relying on these deformable flexible components, the difference in deformation between the tube bundle and the shell is compensated, thereby reducing the thermal stress between them caused by temperature differences. This also helps to prevent the connection between the tube bundle and the tube sheet from being pulled apart. Expansion joints can also be used in various industrial equipment, machinery, and pipelines as components to compensate for displacement and absorb vibrations. Structural form: The main component of an expansion joint is the bellows (also known as the wave shell). The cross-sectional shapes of bellows come in various forms, including flat plate expansion joints, Ω-shaped expansion joints, and wave-shaped expansion joints, as shown in the figure below. Images In production practice, wave-shaped expansion joints are the most commonly used, followed by Ω-shaped expansion joints. The former is generally used in situations where a large amount of compensation is required, while the latter is often used in applications with high pressure. The thinner the wall of the expansion joint, the greater its flexibility and compensation capacity, but the lower the pressure it can withstand. Wave-shaped expansion joints generally come in single-layer and multi-layer forms. If the vessel wall is multi-layered, the pressure it can withstand increases, while still maintaining a high compensatory capacity. The structure of multi-layer wave expansion joints offers many advantages over single-layer expansion joints. Due to their thin walls and multiple layers, they possess high elasticity, high sensitivity, strong compensation capacity, high load-bearing capacity and fatigue strength, a long service life, as well as a compact design. When a larger amount of compensation is required, multi-wave expansion joints can be used. The compensation capacity of one wave in an expansion joint is determined by its shape, size, material, etc. For example, the lower the wave height, the better the pressure resistance, but the poorer the compensation capacity ； The higher the wave height and the greater the wave spacing, the larger the compensation amount, but the lower the voltage resistance.