Bellows compensator Also known as expansion joints or flexible connectors, they consist of a bellows, end pipes, supports, flanges, guides, and other accessories. Their function is attributed to their elastic elements. By leveraging the useful elastic deformation of the bellows—their working element—they can absorb dimensional changes in pipelines, conduits, vessels, and the like caused by thermal expansion and contraction, or compensate for axial, lateral, and angular displacements in pipelines, conduits, vessels, and similar structures. They can also help reduce noise and vibration. These devices are widely used in modern industry.

　　In district heating systems, to prevent thermal expansion or temperature-induced stresses from deforming or damaging the heating pipelines, compensators must be installed along the pipelines to accommodate thermal expansion. This helps reduce stress on the pipe walls and minimizes the forces exerted on valves or support structures. The compensator’s cross-section is rectangular, while its corrugated shape is circular. A single expansion joint in a pipeline can accommodate two-dimensional displacement. A bent pipe composed of two expansion joints can accommodate three-dimensional displacement.

　　Bellows expansion joints have gained widespread popularity due to their numerous advantages and play an important role in piping systems. Metal bellows expansion joints boast comprehensive performance characteristics, including small footprint, resistance to leakage, large compensation capacity, long service life, high safety and reliability, and material savings. Compared with traditional tension-type expansion joints, bellows expansion joints feature a smaller footprint, lower engineering costs, and easier installation and maintenance. When compared with sleeve-type expansion joints, bellows expansion joints offer superior sealing performance and convenient installation and maintenance. They also possess the following features:

　　1. The corrugated compensator adopts a multi-layer (3-12 layers) structure, which enhances its compensation capacity, reduces the amount of materials required for the project, and lowers project costs.

　　2. The product’s structural design is scientifically sound and reasonably optimized, with reliable measures for connection, installation, flow guidance, positioning, and limit-setting. As a result, it is widely used in industries such as petrochemicals, gas supply, power generation, textiles, food processing, shipbuilding, and others. It has become a new component for thermal displacement compensation or seismic isolation in piping systems.

　　What should be noted during the pressure test of a bellows compensator?

　　During the hydrostatic pressure test of pipelines equipped with bellows expansion joints, the nuts at both ends of the expansion joint’s tie rods should be securely tightened, and the expansion joint itself should be held in place by the tension from the tie rods. Although this construction method effectively addresses the issue of expansion joint deformation during pressure testing, according to the product’s usage and installation instructions, after the pipeline pressure test is completed, the transport tie rods should be loosened to allow all moving parts of the expansion joint to operate freely without being obstructed or constrained by external components. In actual operation, however, due to the water pressure within the pipeline, the pipe may expand and shift. As a result, some construction units choose to keep the nuts on the transport tie rods tightly fastened, thereby permanently fixing the expansion joint in place. Consequently, the expansion joint completely loses its intended functionality.

　　Bellows expansion joints have unique advantages in thermal pipelines.

　　Due to their flexibility, bellows compensators can accommodate thermal expansion and other types of deformation between equipment and pipelines, while also preventing vibrations, reducing the thrust exerted by pipelines on equipment, and adapting to uneven settlement of oil tank foundations. Because they are sealed, these compensators find wide application in sectors such as chemical engineering, oil refining, power generation, light industry, atomic energy, metallurgy, machinery, instrumentation, shipbuilding, aerospace, and others. Given the extensive use of power and heating pipelines in both industrial and civil applications, the demand for compensators is extremely high. In recent years, many large and medium-sized cities have been constructing a significant number of residential buildings. During the renovation of existing urban heating systems, one particularly troublesome issue has been the difficulty in routing heating pipelines—especially square compensators, which, due to their large footprint, are challenging to install. At such times, bellows compensators, with their compact structure, can fully leverage their unique advantages. Performance testing of bellows compensators:

　　Stiffness Testing: Proposes measurement methods and boundary condition requirements for axial stiffness, lateral stiffness, and flexural stiffness, and provides guidelines on the number of test repetitions and data processing procedures.

　　Fatigue Testing: Conduct fatigue tests on axial compensators, straight-tube pressure-balancing compensators, hinge compensators, tension compensators, and flexible compensators under simulated actual deformation conditions. Provide the test methods and acceptance criteria.

　　Vibration Testing: Specifies the requirements for vibration modes, frequency ranges, vibration acceleration, and scanning times for each frequency band.

　　Impact Test: Specifies the impact acceleration, pulse duration, number of impacts, and boundary conditions for the impact test.