Compensator Special Topic

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1. Function and working principle of the compensator A bellows compensator* is also commonly referred to as an expansion joint or telescopic joint. It consists of a bellows, which is the main component that enables its operation and functions as an elastic element, along with additional parts such as end tubes, supports, flanges, and ducts. It is a compensation device used to utilize the effective stretching and contracting deformation of the elastic element in the bellows compensator in order to absorb the dimensional changes in pipelines, conduits, or containers caused by factors such as thermal expansion and contraction; it belongs to a type of compensation element. It can absorb axial, lateral, and angular displacements, and is used to address thermal and mechanical displacements in pipes, equipment, and systems, to absorb vibrations, and to reduce noise. It has a wide range of applications in modern industry. 　　 2. Standards for compensator manufacture: Metal bellows shall comply with GB/T12777-2008, and the design is optimized with reference to the American “EJMA” standards. It features a rational structure, stable performance, high strength, good elasticity, and high fatigue resistance. The material used is 1Cr18Ni9Ti and OCr19Ni9 austenitic stainless steel, while the connecting pipes or flanges at both ends are made of low-carbon steel or low-alloy steel. 　　　Metal bellows – For use as compensators, U-shaped waves are employed; they can be made in single or multiple layers. They offer a large degree of compensation capability, with a pressure resistance of up to 4 Mpa. The operating temperature range is from -196°C to 450°C. These bellows feature a compact structure, low installation costs, corrosion resistance, good elasticity, and a low stiffness value. They can withstand 1000 cycles of fatigue. They address the issues related to thermal expansion and contraction of pipes, as well as providing a flexible connection between pipes and mechanical vibrations. They are widely used in pipelines in industries such as petroleum, heating, power generation, gas, and chemicals. 　　 3. Compensation device connection method: The connection methods for compensation devices include flange connection and welding. Direct-buried pipeline compensators are generally welded (except for those installed in trenches). 4. Types of compensators: Compensators are divided into three main types – axial, lateral, and angular – with over twenty different varieties available. 　　Axial compensators mainly include: internal pressure type, external pressure type, combined type, balanced type, directly-buried compensators, etc. 　　Transverse compensators include: large tie rod transverse compensators, universal joint transverse compensators, etc. 　　Angular compensators include: hinge compensators, universal hinge compensators, etc. 　　 II. Function of the compensator: The compensator is also known as a expansion joint, bellows compensator, or wave compensator. Compensators are divided into several types, including bellows compensators, sleeve compensators, rotary compensators, and square natural compensators. Among them, bellows compensators are the most commonly used; they serve to ensure the safe operation of pipelines and have the following functions: 1. Compensating for axial, lateral, and angular thermal deformations of pipelines. 　　2. The expansion amount of the corrugated compensator facilitates the installation and removal of valves and pipelines. 　　3. Absorb equipment vibrations and reduce the impact of such vibrations on the pipelines. 　　4. Absorb the deformation of pipelines caused by ** and land subsidence. 　　The square natural compensator serves two purposes: 1. When pipes pass through foundation beams or basement walls, a square compensator is needed to prevent the pressure exerted on the pipes due to foundation settlement. 　　2. When thermal pipelines are too long, square compensators need to be installed to reduce the stretching of the pipes caused by thermal expansion and contraction. 　　III. Calculation of thermal deformation of pipes:
Formula: X = a * L * △T
Where X is the amount of expansion of the pipe; a is the coefficient of linear expansion, taken as 0.0133 mm/m; L is the length of the compensation pipe (the distance between the fixed supports required for compensation); △T is the temperature difference (temperature of the medium – ambient temperature at the time of installation).

III. Requirements for pipe system and pipe rack design regarding axial, lateral, and angular compensators
(A) Axial compensators
1. At the pipe sections where axial compensators are installed, main fixed pipe racks must be provided at the blind ends of the pipes, at bends, at locations with varying pipe diameters, at areas where stop valves or pressure reducing valves are installed, and at the entrances where side pipes connect to the main pipe line. The main fixed pipe rack must take into account the static pressure thrust of the bellows as well as the elastic force resulting from deformation. The thrust calculation formula is as follows: Fp=100*P*A Where Fp represents the axial pressure exerted by the compensator (N), A is the effective area corresponding to the average diameter of the corrugations (cm2), and P is the maximum pressure in that pipe section (MPa). 　　The formula for calculating the axial elastic force is as follows: Fx = f * Kx * X. FX represents the axial elastic force of the compensator (in N), while KX represents the axial stiffness of the compensator (in N/mm) ； 　　The f-factor: when there is \"pre-deformation\" (including the case where the pre-deformation amount △X=0), f=1/2; otherwise, f=1. 　　In addition to the aforementioned areas, intermediate fixing pipe racks can be installed on the pipeline. The intermediate fixed pipe rack does not need to take into account the effect of pressure thrust. 　　2. Only one axial type compensator may be installed between the two fixed pipe supports of a pipe segment. 　　3. The layout of the fixed pipe racks and guide pipe racks is recommended to be configured as shown in the figure below. 　　One end of the compensator should be close to the fixed pipe rack; if it is too long, guide racks must be installed in accordance with the requirements for the first guide rack. The maximum spacing between other guide racks can be calculated as follows: LGmax – maximum guide spacing (m) ； 　　E-pipe material elastic modulus (N/cm2) ； 　　i-tp pipe cross-sectional moment of inertia (cm4) ； 　　KX – Axial stiffness of the compensator (N/mm), X0 – Displacement amount for compensating adjustment (mm). 　　When the compensator is compressed, the symbol is “+”; when it is stretched, the symbol is “-”. When the pipe wall thickness is designed according to the standard thickness, LGmax can be selected in accordance with relevant standards. 　　(II) Transverse and angular compensators 1. Transverse compensators installed near pipe elbows have one guide support at each end; one of these should be a flat guide sleeve. The upper and lower clearance gaps are calculated using the following formula: ε – Clearance gap (mm) ； 　　L-Compensator effective length (mm) ； 　　△Thermal expansion of Y-pipe section (mm) ； 　　△X – Thermal expansion of the vertical pipe section, excluding the L length (mm) ； 　　2. Angular compensators should be used in groups of two or three to absorb the lateral displacement of the pipeline; between two fixed pipe supports for Z-shaped and L-shaped pipe sections, only one lateral compensator or one group of angular compensators may be installed. At this point, the axis of the planar hinge pin must be perpendicular to the plane formed by the bent pipe segment (universal hinge compensators are not subject to this restriction). 　　For a pipe segment equipped with a set of hinge compensators, the clearance ε of its planar guide frame can also be calculated using the above formula. However, the L length should be the distance between the hinge axes of the two compensators, and △X is the thermal expansion amount of the entire vertical pipe section. 　　3. The guide supports on both sides of the compensator should be close to it, and the type of these supports should enable the compensator to move in a directed manner. 　　 III. Installation requirements for directly-buried compensators in heating pipelines （1）Purpose: Directly-buried corrugated compensators are primarily used for axial compensation of directly-buried pipelines. They possess bending resistance, so the effect of pipeline settlement need not be considered. These products feature a large compensation capacity and a long service life. 　　 (II) Instructions for use: The directly buried corrugated compensator is mainly suitable for axial compensation; it also possesses excellent bending resistance, so the effect of pipe settlement is not a concern. It achieves free expansion and contraction compensation under the protection of a directly buried corrugated compensation housing and guide sleeve; its other properties are the same as those of ordinary corrugated compensators. 　　 (III) Selection and Installation: 3.1 Calculation of the maximum installation length of pipes Pipes buried directly with compensation mechanisms should be fixed at two high points: one at the end of the straight pipe section, and the other at the branch point of the pipe. In a long, unbranched straight pipeline, fixed points may not be necessary between the two compensators; the natural \"stagnation points\" formed within the pipeline can serve as fixed points. The stagnation point is the fixed point in the pipeline between the two compensators; when the pipe diameters are the same and the burial depths are identical, the distance from the stagnation point to each of the two compensators is equal. The distance from the expansion joint (including the natural expansion joint at corners) to the fixed point shall not exceed the maximum installation length Lmax of the pipeline. The maximum installation length of the pipeline is defined as the distance from the fixed point to the free end (expansion joint), and the friction force generated at this length shall not exceed the elastic force corresponding to the allowable stress of the pipeline. 　　Lmax is calculated using the following formula: the maximum installation length Lmax for commonly used pipes. The combined effect of the circumferential stress generated by pressures up to 16 kgf/cm2 should be considered. 　　 3.2 Design calculations for fixed supports 　　　For pipelines with 2 branches and a curved section on the main pipeline, the placement of compensators should satisfy the condition that Ln＜Lmax. The thrust at the fixed points G1 and G2 is zero; therefore, there is no need to install fixed supports at these locations. However, to prevent drift of these fixed points due to uneven backfilling, inconsistencies in burial depth, or irregularities in the surface texture of the prefabricated insulation pipes, it is necessary to install supports at the pipe branches located at these fixed points, G1 and G2. Taking G1 as an example, its axial thrust can be calculated using the following formula: F1 = Pb2 + L2f – 0.8(Pb3 + L2f). Here, F1 represents the horizontal thrust on the fixed support G1, in kgf ； f – Friction force per unit length of the pipe, Kgf/m; Pb2-B2 – Elastic force of the expansion joint, Kg ； Elastic force of Pb3-B3 expansion joint, Kgf  Stiffness of k2-B2 expansion joint, Kgf/mm ； 　　△Compensation amount of L2-B2 expansion joint, mm ； 　　Distance from L2-expansion joint to G1, m ； 　　Suppose a branch, such as the one branching off from G2, is equipped with a compensator B. Thus, G2 is also subjected to a lateral thrust, represented by F2(y) in the figure. When L5 is short (and it should indeed be short in actual installations), the magnitude of the lateral force F2(y) is given by:
F2(y) = Pn * A5 + Pb5
Where Pn is the operating pressure of the pipeline, in Kgf/cm2, and A5 is the effective area of the B5 expansion joint, in cm2 ； 　　Elastic force of Pb5-B5 expansion joint in kgf. 　　The fixed support G3 is also at a stationary point; due to the friction between the pipeline and the soil, this point is subjected to two forces of equal magnitude but opposite directions. It should be noted, however, that this point is also affected by the force exerted by the blind plate at the corner. Taking into account the effect of stationary point drift, the thrust on the fixed support G3 is given by F3 = 1.2Pn*A4, where F3 represents the horizontal thrust acting on the fixed support G3, in Kgf ； 　　Pn – Working pressure of the pipeline, Kgf/cm2 ； 　　Effective area of A4-B4 expansion joint, cm2. 　　 3.3 Calculation for the selection of compensators Due to the effect of soil friction, the actual thermal expansion of pipes buried directly in the ground is less than that of pipes installed overhead or in trenches. 　　Extension during overhead and trench installation: α·△t·L. The reduction in thermal expansion due to soil friction forces when the pipe is installed directly in the ground: The actual thermal expansion amount is: Where E is the elastic modulus of the steel pipe, in kgf/cm2 ； 　　The linear expansion coefficient of α-stainless steel is taken as 0.0133 mm/m℃ ； 　　△t-pipe temperature difference ； 　　A, f-same formula① ； 　　Distance between the two fixing points of L (maximum installation length) in meters. 　　In practical applications, the thermal expansion of directly buried pipes is calculated using a simplified algorithm from the Danish company Møller. 　　The symbols in the formula are the same as those in the previous formulas. 　　After calculating the actual thermal elongation using formula ② or ③, select the appropriate compensator from the list. 　　 3.4 Installation When installing directly-buried expansion joints (excluding those that are designed for one-time use), two protective rings should be used (as shown in the figure below), and the wall thickness of these rings should not be less than that of the pipeline. The purpose of using these protective rings is to prevent soil, sand, and other materials from entering within dimension A when the pipeline expands due to heat. The dimensions shown in the figure are as follows: When directly-buried corrugated expansion joints leave the factory, all exposed surfaces have been coated with rust-proof paint twice. Other requirements regarding these expansion joints and the pipelines they are installed in include: (1) When the insulation-covered pipeline is buried underground, it should be filled with sand with a particle size of less than 20 millimeters around it, after which the original soil should be placed on top. The thickness of the sand fill should be no less than 200 millimeters. 　　(2) The burial depth of the top of the insulation pipe generally should not exceed 1.2 meters, but it should also not be less than 0.7 meters; the insulation pipe can be buried directly beneath various pipes. 　　(3) As shown in the figure, insulation is provided in all areas except at A; since no insulation is needed at A when the pipeline expands, it does not result in significant heat loss. Also thanks to the function of the protective ring, the directly-buried compensator can be buried directly beneath the road surface. 　　(4) For the installation of directly-buried compensators, there is no need for cold tightening, nor is it necessary to connect all the steel pipes along the line first, cut off sections of pipe equal in length to those of the expansion joints, and then weld them together. By using directly-buried expansion joints, guide supports are not required. 　　(5) During installation, care must be taken to ensure that the direction of the guide sleeve matches the flow direction. 　　(6) The medium inside the compensator should be treated to remove free oxygen and chloride ions, with the chloride ion content not exceeding 25 PPm. 　　(7) The compensator allows a system hydrostatic test at a pressure not exceeding 1.5 times the nominal pressure. 　　(8) Before conducting the system hydrostatic test after the compensator has been installed, both ends of the pipeline must be secured to prevent the internal pressure from stretching the compensator. 　　 IV. Requirements for the installation and use of compensators 1. Before installation, the model, specifications, and piping configuration of the compensator 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 complete. 　　 4. It is strictly prohibited to use the deformation of wave compensators to adjust the 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 wave compensators should be removed as soon as possible. The limiting devices should 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 blocked by external elements or have their range of motion restricted; normal operation of all moving parts must be ensured. 　　 8. During the hydrostatic test, the secondary support brackets at the ends of the pipelines equipped with compensators should be reinforced to prevent the pipelines from moving or rotating. For compensators used in gas media and their connecting pipelines, attention should be paid to whether temporary supports are needed when filling them with water. The chloride ion content in the cleaning solution used for hydrostatic testing shall not exceed 25PPM. 　　 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 shall be free of chloride ions. 　　 Compensator product categories: QB type ball compensators, DSB-I and II types, one-way self-guiding expansion compensators, JTW type universal hoses, stainless steel shock-absorbing corrugated compensators, directly-buried corrugated compensators, FUB duct compensators, axial external-pressure corrugated compensators of the JZW type, hinge-type transverse compensators of the JJH type, universal hinge compensators of the JWJ type, axial internal-pressure corrugated compensators of the JDZ type, and three-dimensional compensators. 　　An analysis of the causes of failure in bellows compensators. The reason why bellows compensators are widely used in many industries is, apart from their excellent compensation capabilities, their high reliability. Its reliability is ensured through various stages such as design, manufacturing, installation, and operational management; any malfunction in one of these stages can lead to a reduced lifespan of the compensator or even its failure. Through years of statistical analysis, the author found that the reasons for the failure of bellows compensators are as follows: design accounts for 10%, shoddy work by manufacturers accounts for 50%, improper installation not in accordance with the equipment instructions accounts for 20%, and the remainder is caused by poor operation and maintenance. 　　 2. Failure types and cause analysis of bellows compensators　　　 2.1 Failure types　　Failures of bellows occur during pipeline pressure testing as well as during operation. There are mainly three types of problems that occur during pipeline pressure testing: improper temporary support for the pipeline system, or unreasonable installation of fixed supports, which leads to the failure of those supports and excessive deformation of the bellows, resulting in their failure ； Due to insufficient safety margins for pressure or displacement considered in the bellows design, the bellows undergoes unstable deformation and failure during pipeline pressure testing ； Quality issues in the manufacture of the compensators: the manufacturer cuts corners by using only 3 layers or fewer of stainless steel instead of the required 5 layers. 　　The failures of bellows during operation mainly manifest in two forms: corrosion-induced leakage and unstable deformation, with corrosion failure being the more common one. An anatomical analysis of corroded and failed bellows reveals that corrosion failure typically occurs in the forms of pitting corrosion and stress corrosion cracking, with chloride-induced stress corrosion cracking accounting for approximately 95% of all cases of corrosion failure. Bellow instability comes in two types: strength instability and structural instability. Strength instability includes planar instability of internally and externally pressurized bellows as well as circumferential instability of externally pressurized bellows ； Structural instability is the column instability of internal pressure bellows compensators. 　　 2.2 Relationship between design fatigue life, stability, and stress corrosion The design of bellows takes into account three main factors: pressure resistance, stability, and fatigue performance. Although **both the standards and the American EJMA standards provide clear regulations for the calculation and evaluation of these aspects, years of practical application and analysis of bellows failures have shown that the methods provided in the standards for calculating and evaluating stability are not comprehensive enough; moreover, only rough range limits are given for fatigue life (with an average fatigue life ranging from 103 to 105). Sometimes, a product that fully meets the standard requirements can still encounter some problems in actual use. In the pre-deformation state of internal-pressure axial compensators, the bellows are prone to planar instability during pressure tests; in the full-displacement operation state of large-diameter external-pressure axial compensators, the bellows are prone to circumferential instability; whereas in the full-displacement operation state of small-diameter composite tie-rod compensators and hinge-type compensators, column instability is likely to occur. Excessive deformation of the bellows not only affects its stability but also creates favorable conditions for stress corrosion. 　　 2.2.1 Fatigue life of bellows and its combined stress: The compensation amount of a bellows depends on its fatigue life; the higher the fatigue life, the smaller the single-wave compensation amount of the bellows. To reduce costs and increase the single-wave compensation amount, some manufacturers set the allowable fatigue life of the bellows very low; this results in high meridional bending stresses in the bellows due to displacement, as well as high overall stresses, **which reduces the stability of the bellows. Table 1 shows the relationship between the allowable fatigue life of unreinforced U-shaped bellows and the meridional composite stress as well as the single-wave compensation amount. 　　 2.2.2 Comprehensive stress of bellows and its pressure resistance strength: It can be seen from the calculation methods and evaluation criteria for planar stability and circumferential stability of bellows given in the standards that both relate to strength issues. When the allowable service life of the bellows design is low, not only is the meridional composite stress high, but the circumferential stress is also high, causing the bellows to enter plastic deformation rapidly in certain areas and leading to its instability. 　　In the case of internal-pressure bellows, the displacement stress creates plastic hinges at the peaks and troughs of the bellows; combined with the pressure stress, this leads to rapid planar instability of the bellows. This is the fundamental reason why the plane instability pressure of bellows with low fatigue life under displacement conditions is much lower than that of bellows with high fatigue life. For example, in the pre-deformation state, that is, when the displacement of the bellows is 1/2 of the allowable value, a bellows with an allowable fatigue life of 200 cycles will experience planar instability even before reaching its permitted design pressure ； For a bellows with an allowable fatigue life of 1000 cycles, it is in a planar stable state at the design pressure, and it reaches a critical instability state at 1.5 times the design pressure ； When the bellows, with an allowable fatigue life of 2000 cycles, reaches 1.5 times the design pressure, it remains in a planar stable state. 　　From a longitudinal cross-section of the externally pressurized bellows, it appears as a beam under compression; during operation, the bellows is in a tensile state, which is equivalent to the arch height of the beam decreasing, thereby reducing its ability to resist instability. When the single-wave displacement of the bellows is too large, the straight sections of the corrugations tilt, causing the diameter of the wave peaks to tend to decrease. However, the diameter of the circular rings at the wave peaks remains constant; in order to accommodate this deformation, the wave peaks collapse, leading to circumferential instability of the bellows. In the relevant domestic and international standards, the effect of displacement on the circumferential stability of bellows under external pressure is not addressed, and further investigation is needed. 　　In summary, although no fatigue-induced failures have been observed to date in the application of thermal piping systems, an excessively low design fatigue life for bellows could lead to catastrophic consequences. 　　 2.2.3 Compensator displacement and its column stability: For the double tie-type and hinge-type compensators, lateral displacement is achieved through the tilting of the intermediate tube section caused by the angular deformation of the bellows. When the bellows undergoes angular displacement, the pressure-bearing area on the protruding side of the bellows is greater than that on the recessed side, resulting in an additional lateral force on the compensator; this makes column instability more likely to occur compared to axial-type compensators. Obviously, the greater the single-wave displacement of the bellows, the greater the lateral displacement of the compensator, and the more likely column instability will occur. 　　　 3. Reliability of bellows compensators The reliability of bellows compensators depends on various factors such as design, manufacturing, installation, and operational management. Reliability should also be considered from these aspects. 　　 3.1 Reliability Design　　 3.1.1 Material Selection When selecting materials for bellows used in heating pipelines, in addition to considering the working medium, operating temperature, and external environment, factors such as the possibility of stress corrosion, as well as the impact of water treatment agents and pipeline cleaning agents on the material, must also be taken into account. On this basis, taking into account the weldability and formability of the bellow material as well as its cost-performance ratio, an economical and practical material for manufacturing bellows should be chosen. 　　Under normal circumstances, the material chosen for bellows should meet the following requirements: (1) Good plasticity, to facilitate the processing and shaping of the bellows, and the ability to achieve sufficient hardness and strength through subsequent treatment processes (such as cold working and heat treatment). (2) High elastic limit, tensile strength, and fatigue strength to ensure the proper operation of the bellows. (3) Good weldability, meeting the welding requirements during the manufacturing process of bellows. (4) Good corrosion resistance, meeting the operational requirements of bellows in various environments. Most manufacturers use austenitic stainless steels, such as grades 0Cr18Ni9 (equivalent to 304), 00Cr19Ni10 (equivalent to 304L), 0Cr17NiMo2 (equivalent to 316), and 00Cr17Ni4Mo2 (equivalent to 316L). To improve the corrosion resistance of bellows, materials such as 316 or 316L are now commonly used for bellows in heating pipelines; these two materials offer an excellent performance-to-cost ratio for use in thermal piping systems. 　　For thermal piping systems laid in trenches, when the pipeline where the compensator is located is at a lower elevation, rainwater or accidental sewage can soak the bellows; in such cases, materials with greater corrosion resistance, such as iron-nickel alloys or high-nickel alloys, should be considered. Due to the high cost of such materials, when manufacturing bellows, it is possible to consider adding a layer of corrosion-resistant alloy only on the surfaces that come into contact with corrosive media. 　　 3.1.2 Fatigue life design: As can be seen from the analysis of the failure types and causes of bellows compensators, the planar stability, circumferential stability, and corrosion resistance of the bellows are all related to its displacement amount, that is, its fatigue life. An excessively low fatigue life will lead to a decrease in the stability and corrosion resistance of the bellows. Based on testing and practical experience, the fatigue life of bellows used in heating systems should be no less than 1,000 cycles. 　　Most failures of bellows are caused by corrosion from the external environment; therefore, when designing the structure of compensators, it is possible to consider preventing contact between external corrosive agents and the bellows. For external-pressure axial compensators, a packing seal can be added between the outlet end ring and the outlet pipe; its function is similar to that of a sleeve compensator. It not only prevents the intrusion of external corrosive substances but also provides an additional safety barrier for the bellows compensator. Even if the bellows are damaged, the compensator can still carry out its compensatory function and prevent failure of the bellows. 　　 3.2 Ensure installation quality The bellows cannot bear weight and should be lifted separately ； Apart from the pre-deformation amount required by design for pre-stretching or cold tightening, it is strictly prohibited to use methods that deform the bellows in order to adjust the installation deviation of the pipeline ； During installation, slag splashing onto the surface of the bellows and other forms of mechanical damage must be avoided ； All moving components of the bellows must not be blocked by external elements or have their movement restricted, preventing them from functioning properly ； The water used for pressure testing must be clean and non-corrosive; for austenitic stainless steel, the chloride ion content in the water should be strictly controlled to not exceed 25×10-6, and any water accumulated in the corrugations must be drained promptly. 　　 4. Conclusion      The main problems with compensators are the stability of the bellows and corrosion. The stability issues of bellows can be resolved through measures such as properly designing the bellows waveform parameters and fatigue life, ensuring correct installation, and conducting thorough stress analysis of the piping system. Regarding corrosion issues, they can be resolved in two ways: (1) by selecting appropriate bellows materials and designing the compensator structure to prevent corrosion sources. 　　(2) Strengthen the management of water accumulation in small chambers to fundamentally resolve corrosion issues.