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This post was last edited by “Hasty Passerby” on October 23, 2018, at 09:06. Selection, advantages, and disadvantages of thermal compensators for heating pipelines: The installation of pipelines is extremely important in every modern building; therefore, ensuring their safety requires great attention from workers. Consequently, it is necessary to have a good understanding of the relevant knowledge regarding pipeline compensators. This article introduces the origin and function of compensators, and focuses on analyzing the advantages, disadvantages, and application conditions of several commonly used compensators. I. The origin of compensators. The basic meaning of compensation is to remedy deficiencies and offset losses. There are also technical solutions for compensation. When there are temperature changes in the medium flowing through the pipeline or in the environment surrounding it, thermal expansion and contraction of the pipeline due to temperature are inevitable. If no measures are taken to compensate for these size changes, high stresses will be generated within the pipe walls, which are then transmitted to the fixed supports or equipment. When the temperature difference exceeds a certain threshold, the resulting stress becomes greater than what the pipe can withstand; in such cases, it is necessary to consider compensation measures. II. The function of compensators In the design of pipeline compensation, the most cost-effective method is natural compensation. Natural compensation utilizes the flexibility inherent in the natural bends of pipes to compensate for thermal displacements. Clearly, the capacity of natural compensation is limited; when it fails to meet the requirements, it is generally necessary to install compensating devices such as metal bellows expansion joints. The loads acting on piping systems are mainly external forces (the weight of the pipes and the flowing medium, internal pressure, wind loads, seismic loads, etc.) and displacement loads. The purpose of installing pipe expansion joints is to eliminate the forces exerted by these external loads on the equipment or pipes, and to divide complex piping systems into sections with simpler shapes that can expand independently, thereby ensuring optimal performance of the expansion joints. Pipe compensators can compensate for and absorb axial, lateral, and angular thermal deformation of pipes, absorb vibrations from equipment, reduce the impact of such vibrations on the pipes, and offset the deformation caused by earthquakes and ground subsidence. Compensators are used at the inlets and outlets of cold and hot piping systems in large venues, as well as in equipment such as flue gas desulfurization and dust removal devices, air heating systems, and flow-assisting blowers in steel plants and thermal power plants; therefore, various types of compensators are widely adopted and promoted. III. Analysis of Several Common Compensators Analysis of Common Compensators (1) Bellows Compensator 1. Meaning of the bellows compensator: A bellows compensator is a compensation device that makes use of the elastic deformation of the bellows elements to absorb the dimensional changes in pipelines, conduits, or containers caused by factors such as thermal expansion and contraction; it constitutes a type of compensation element. 2. Classification of bellows compensators: Bellows compensators (bellows) can be classified according to the type of displacement, and are generally divided into axial, lateral, angular, and pressure-balanced types of bellows expansion joints (bellows). Classified by their ability to absorb the pressure thrust generated by the pressure of the medium inside the pipeline (the blind plate force), they can be divided into unrestrained bellows expansion joints and restrained bellows expansion joints. Classified by the waveform structure parameters of the wave compensator, they can be divided into U-shaped, Ω-shaped, S-shaped, and V-shaped bellows. Currently, most bellows products used domestically and internationally adopt a U-shaped waveform structure. 3. Advantages of wave compensators: Compact structure, occupies less space, can be buried directly ； The disadvantages are that it is difficult to manufacture, has a low voltage tolerance, and limited compensation capability. Its compensating capacity is related to the external dimensions, wall thickness, and diameter of the wave tube: the higher the pressure, the thicker the wave wall, and the smaller the diameter, the greater its rigidity, and the lower its compensating capacity. Waveform compensators are generally used in applications with a nominal pressure of ≤1.0 MPa and a nominal diameter of ≥150 mm; they can also be used in large-diameter pipes under normal and low pressures. Those used in boiler smoke and air ducts can reach DN4000 mm. 4. Disadvantages of bellows compensators: The wall thickness of bellows compensators is relatively thin, making them unable to withstand torque and vibration, resulting in poor safety ； High equipment investment, strict design requirements, high precision in construction and installation; often fails to achieve the expected lifespan ； Axial bellows compensators exert a compressive force on the fixed supports, resulting in high thrust on these supports and consequently higher costs. 5. Application conditions for bellows expansion joints: Bellows expansion joints cannot bear loads and must be lifted separately. Unless reinforcement measures are taken for the bellows expansion joints, it is not permitted to lift them together with the pipes after welding. During installation, the degree of expansion of the bellows compensator should be designed in accordance with the data recommended by the manufacturer. Under no circumstances should the bellows be stretched, compressed, or twisted to compensate for installation errors, as this may affect the proper functioning of the bellows compensator, reduce its service life, and increase the load on the piping system, equipment connections, and supporting components. Sufficient space should be left around the expansion joint to ensure that it can move freely within its designed range. (II) Rotating compensator 1. Advantages of the rotating compensator: (1) High safety performance of the product: The product has a rational structure, and the rotating compensator features a dual-sealing design, with one end seal and one ring seal ； (2) Easy to design: When designing heat networks, the compensation requirements for bellows compensators are quite stringent; the five golden rules must be followed. For sleeve compensators, the principle of \"precise centering\" is essential, and factors such as the stress on bellows and sleeve compensators, as well as the force exerted by blind flanges, must also be taken into account. There are various types of rotary compensators, and by selecting the appropriate type based on the direction in which the pipeline runs, the compensation issues associated with the pipeline can be resolved ； (3) Long product lifespan: The lifespan of the product can exceed 20 years ； (4) Large compensation capacity: The compensation amount can reach 1800 mm (for other compensators, such as bellows compensators, the maximum compensation amount is between 300 and 400 mm). For pipelines with a diameter of DN 200 or larger, the one-sided compensation amount can be 130 to 200 mm; for pipelines with a diameter of ≤DN 200, it can be 100 to 130 mm. It can be used for compensating long-distance steam pipelines ； (5) High economic efficiency in pipeline operation: By using rotary compensators for compensation, the compensation distance increases, which results in fewer elbows compared to natural compensation and sleeve compensation; this reduces pressure drops and thus lowers pipe losses in heat distribution networks. It is one of the main compensation methods for long-distance heat transmission networks ； (6) Diverse installation methods and types: Depending on the layout of the pipelines and the terrain at the site, the appropriate type of rotary compensator can be selected to address the compensation issues associated with steam pipelines. The installation is straightforward; no processes such as cold drawing or pre-tensioning are required, and welding is sufficient ； (7) Lower investment costs: Due to the long compensation distance provided by the rotary compensator, a smaller number of such compensators are required. Additionally, the thrust exerted on the fixed piers is low, resulting in a reduced number of fixed piers as well as smaller-sized piers. **This leads to savings in civil engineering costs; compared to other types of compensators, the total project cost can be reduced by 20%–40%, offering significant economic benefits. 2. Application conditions of rotary compensators: Rotary compensators are generally installed in groups of 200–500 meters along the pipeline (the spacing can be determined based on the natural terrain). There are over 10 different installation methods, and the arrangement can be chosen according to the direction in which the pipeline runs. After installing this type of compensator, the spacing between the fixed supports increases; to prevent bending of the pipe section, it is necessary to increase the number of guide supports appropriately ； To reduce the frictional resistance during the operation of the pipe section, rolling supports should be installed on the sliding brackets. (III) Square compensator 1. Meaning of square compensator: A square compensator, also known as a square expansion element or expansion bend, utilizes the elastic deformation resulting from bending of the pipe to absorb the thermal expansion of the pipeline. To manufacture a square compensator, high-quality seamless steel pipes must be used; it is preferable to form the entire compensator from a single pipe. 2. Advantages of square compensators: (1) They are easy to manufacture and install; compared with sleeve compensators and bellows compensators, they exert less axial thrust on the fixed supports and provide greater thermal compensation, making them suitable for various pressure and temperature conditions ； (2) It has high safety; no maintenance is required during normal operation, and inspection wells are not needed. 3. Application conditions for square compensators: When installing a square compensator, in order to reduce its deformation elastic force and enhance its compensation capacity, its outer arms must be stretched to a certain length in advance before it is installed on the pipeline. IV. Requirements for the installation and use of compensators 1. Before installing a compensator, its model, specifications, and piping configuration should be checked to ensure that they meet the design requirements ； 2. For compensators with an inner sleeve, care should be taken to ensure that the direction of the inner sleeve is consistent with the flow direction of the medium; for hinge-type compensators, the plane of rotation of the hinge should be aligned with the plane of displacement rotation ； 3. For compensators that require \"cold tightening,\" the auxiliary components used for pre-deformation should be removed only after the piping installation is completed ； 4. It is strictly prohibited to use the deformation of metal bellows compensators to adjust installation tolerances of pipelines, as this may affect the normal functioning of the compensators, reduce their service life, and increase the load on the piping system, equipment, and supporting components ； 5. During installation, slag must not splash onto the surface of the wave shell, and the wave shell must not suffer any other mechanical damage ； 6. After the piping system is installed, the yellow auxiliary positioning elements and fasteners used for installation and transportation on the metal bellows compensators should be removed as soon as possible. The limiting devices must then be adjusted to the specified positions in accordance with the design requirements, so that the piping system has sufficient compensation capacity under various environmental conditions ； 7. All movable components of the compensator must not be trapped by external elements or have their range of movement restricted; normal operation of all moving parts must be ensured ； 8. During the hydrostatic test, the secondary support frames at the ends of the pipelines equipped with compensators should be reinforced to prevent the pipelines from moving or rotating. For compensators used with gaseous media and their connected pipelines, attention should be paid to whether temporary supports are needed when filling them with water ； 9. After the hydrostatic test is completed, the water accumulated in the wave tank should be drained as soon as possible, and the inner surface of the wave tank should be dried promptly ； 10. The insulation material in contact with the compensator bellows should be free of chlorine