The Important Role of Expansion Joints and Precautions for Installation and Use

Release time:

2021-05-14

Thermal expansion and contraction is a natural phenomenon—whenever the temperature rises, expansion will occur. In equipment that generates heat during operation—for example, the shaft of a large motor heats up and expands during operation—one end must be fixed, while the other must be free; otherwise, the expanding shaft could cause the casing to tip over. This issue also arises in thermal pipelines at cement plants.

The Important Role of Expansion Joints and Precautions for Installation and Use

Since the installation is in a cold state at room temperature, the hot gas generated during the production process will inevitably cause its temperature to rise, leading to thermal expansion and elongation. If expansion joints are not provided to eliminate or absorb this pipe elongation, it will inevitably damage the structure or supports, warranting sufficient attention.

I. Load-bearing of Expansion Joints: 1. As expansion compensation devices for thermal pipelines, these joints can only withstand a certain amount of axial load during operation. Therefore, they should not be installed in locations prone to bending or torsion and must be placed on vertical pipelines. 2. If installed on inclined or horizontal pipelines, sliding guides should be fitted at both ends of the expansion joint. These guides not only support the pipeline but also ensure that the pipeline can slide freely along the supports. 3. During installation, it is crucial to maintain the expansion joint’s natural state and dimensions; otherwise, the joint’s expansion compensation capacity under thermal conditions will be affected. Hence, it is essential to ensure that the expansion joint remains free from external forces when cold. 4. Different specifications and models of expansion joints have varying compensation capacities. Therefore, when designing and selecting an expansion joint, it is necessary to calculate the expected pipeline expansion based on the pipeline length and temperature rise. The selected expansion joint should have sufficient margin to meet the required compensation. 5. After the expansion joint has been installed and thoroughly inspected, remove the bolts originally used to secure the inner and outer casings. Failure to do so will prevent the expansion joint from performing its intended function. 6. The expansion sleeve inside the expansion joint has a gap. After installation, this gap should be filled with materials such as asbestos—materials that do not interfere with the expansion process and also provide thermal insulation.

II. Other Types of Compensation: In the cement industry, compensation primarily refers to thermal pipeline compensation. Although compressed air pipelines may not require compensation due to their small diameter and numerous bends, in practice, the bends and deformations in these pipelines can effectively serve as a form of compensation. Of course, thermal pipelines used for waste-heat power generation must also comply with relevant standards—for instance, U-shaped compensators must be installed at specified intervals. Below are several examples illustrating this point: 1. For example, in cement plants, steel structure bridges connecting different building sections can have one end fixed and the other end free, ensuring flexibility and preventing additional loads from being imposed on the structure. 2. As for platforms mounted on equipment, special consideration must also be given to expansion compensation under specific conditions. Take, for instance, a humidifier tower where atomized water flows along the wall; as the cylinder temperature drops significantly, contraction becomes inevitable. If the platform is rigid, it cannot accommodate such deformation. In severe cases, the platform legs welded onto the cylinder may be pulled apart, causing the platform to tilt or even collapse. 3. Another example is the tertiary air duct connected to the calciner via an expansion joint. Once the compensation is insufficient or fails, the calciner could be directly pushed forward, and the intense bending stress could tear the calciner’s cylindrical shell. 4. Regarding preheaters and inlet ducts, expansion joints should never be directly installed on the preheater itself. This is because expansion joints have poor rigidity on both sides and are prone to twisting and tearing, which can cause serious problems for the entire system. Therefore, regardless of the type of expansion joint used, it must be properly positioned and installed in an appropriate location.

Although expansion joints are static devices and not part of the main equipment, their safety functions should by no means be underestimated. Other types of compensation also play a role; otherwise, structural damage would be unavoidable, and sufficient attention should be paid to them.

Jiangsu Yaxing

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