Double-seal external pressure corrugated vapor expander and method of installation

Abstract

The application discloses a double-sealing outer pressure corrugated compensator for steam and a mounting method, and belongs to the technical field of corrugated pipe compensators. The compensator adopts an outer pressure structure, a corrugated pipe is connected with a blanking plate and a second end ring through a connecting pipe, the compensator is provided with a double-sealing structure, the corrugated pipe forms a first layer of sealing, sealing filler, packing, a sealing ring and a guide belt form a second layer of sealing, when the corrugated pipe fails, the second layer of sealing can still effectively block steam leakage, and the sealing filler can be supplemented on line under the condition of no stop of conveying to realize pressure leakage blocking. The application also provides a calculation method of a factory pre-compression amount based on an outer pressure correction coefficient, a product is in a pre-compression state when leaving the factory, and a temporary pull rod is not needed during installation; two-stage whole-process quantitative installation verification of adaptive verification before installation and determination of thermal compensation effect after commissioning is established, and long-term safe operation of a steam pipeline is realized.

Description

Technical Field

[0001] This invention belongs to the technical field of bellows compensators, specifically relating to a double-sealed external pressure bellows compensator for steam and its installation method. Background Technology

[0002] In steam pipelines, industrial heating networks, and power system heating pipelines, the axial displacement caused by thermal expansion and contraction during operation is significant due to the high temperature and pressure of the steam medium. Specialized compensation devices must be used to absorb this displacement to prevent damage to pipelines and equipment caused by excessive thermal stress. Currently, steam pipeline thermal compensation devices mainly include two categories: sleeve compensators and bellows compensators. Both types of compensators have certain technical limitations and cannot simultaneously meet the comprehensive requirements of high-pressure steam pipelines for sealing reliability, resistance to instability, and ease of long-term operation and maintenance.

[0003] Sleeve compensators are simple in structure and have a large compensation capacity, but they rely solely on a single packing seal. Under the high temperature, high pressure, and frequent expansion and contraction impact of the steam medium, the sealing packing is prone to wear and failure, leading to steam leakage, high maintenance costs, and the potential for scalding accidents caused by leaked steam, posing significant safety hazards. Traditional internal pressure bellows compensators have good sealing performance, but under the pressure of the internal medium, the bellows crests bear the radial force of outward expansion, making them prone to buckling instability and limiting their service life under high-pressure steam conditions. Furthermore, traditional internal pressure bellows are usually directly welded to the movable pipe, resulting in significant local stress concentration at the weld joint. Under frequent thermal expansion and contraction cyclic loads, this can easily lead to early fatigue cracking. Once the bellows fails, a large amount of medium will leak directly into the external environment, posing a significant safety risk. In addition, existing bellows compensators generally use a single sealing structure, lacking redundant protection measures when the sole sealing element fails, making it impossible to perform online leak sealing without interrupting power supply. In terms of installation technology, existing steam pipeline bellows compensators typically use temporary tie rods to apply pre-compression on-site. This method suffers from problems such as cumbersome operation, difficulty in ensuring adjustment accuracy, and on-site safety risks. Existing pre-compression calculation methods are mainly based on internal pressure bellows, failing to consider the difference in equivalent axial stiffness between external and internal pressure bellows. Directly applying these methods to external pressure compensators will lead to calculation errors, resulting in higher stress levels within the compensator's operating temperature range and shortened fatigue life. Furthermore, existing installation methods lack systematic, end-to-end verification methods, making it impossible to quantitatively check the compensator's pre-compression compatibility and actual thermal compensation effect at each stage of receipt, installation, and commissioning, hindering the timely detection of installation deviations and system anomalies.

[0004] Therefore, developing a steam bellows compensator with strong anti-instability capability under high-pressure steam conditions, dual-seal redundant protection, support for online sealing packing replenishment, and equipped with a scientific external pressure pre-compression calculation method and a full-process installation verification system is of great engineering significance. Summary of the Invention

[0005] To address the problems existing in the background art, the present invention provides a double-sealed external pressure bellows compensator for steam, comprising:

[0006] The movable connector has a chrome-plated outer surface.

[0007] A fixed connector is arranged coaxially opposite to the movable connector.

[0008] A flow guide tube is installed in the internal channel between the movable connector and the fixed connector;

[0009] The first sleeve is fitted onto the outside of the movable connector and the fixed connector; the first end ring is fixedly connected between the fixed connector and the first sleeve.

[0010] The blocking plate is a ring structure, which is sleeved on the outside of the movable connecting pipe and fixedly connected thereto. Its outer edge forms an axially sliding sealing fit with the inner wall of the first sleeve.

[0011] The bellows is located inside the first sleeve and is not directly connected to the movable connecting pipe, and it bears the pressure of the external medium; the connecting pipe connects the plug plate and the bellows.

[0012] The second end ring is fixedly connected to the inner wall of the first sleeve and is not connected to the movable connecting pipe; the second connecting pipe connects the corrugated pipe and the second end ring.

[0013] The second sleeve is fitted onto the outside of the movable connector, with one end fixedly connected to the second end ring; the sealing packing and packing are disposed in the sealing cavity between the second sleeve and the movable connector; the sealing ring is fixedly connected to the end of the second sleeve, and has a groove on its inner wall; the guide band is embedded in the groove of the sealing ring.

[0014] The bellows forms the first sealing structure, and the sealing packing, packing, sealing ring and guide strip form the second sealing structure; the bellows is in a pre-compressed state when the compensator leaves the factory.

[0015] Furthermore, the working medium inside the first sleeve simultaneously fills the space between the first sleeve and the bellows, as well as the space between the first sleeve and the guide tube, ensuring that the bellows is subjected to uniform external pressure; the axial distance between the plug plate and the first end ring is the factory-defined distance. Factory pre-compression and All are provided with the product's manufacturing documentation; during pipeline operation, the movable connector moves towards the fixed connector, the plug plate moves accordingly, and through the connecting pipe, the bellows gradually recovers from its pre-compressed state. The distance between the plug plate and the first end ring is... Reduce to , Less than .

[0016] Furthermore, both the first connecting pipe and the second connecting pipe are cylindrical transition structures; one end of the first connecting pipe is welded to the end face of the plug plate facing the corrugated pipe, and the other end is welded to the corresponding end of the corrugated pipe; one end of the second connecting pipe is welded to the other end of the corrugated pipe, and the other end is welded to the end face of the second end ring facing the corrugated pipe; thus, the corrugated pipe does not bear direct welding stress with the movable connecting pipe.

[0017] Furthermore, the end of the guide tube fixed to the inner wall of the fixed pipe is the fixed end, and the end extending to the inner side of the movable pipe is the free end. The free end is not connected to the movable pipe, forming a cantilever structure with one end fixed and one end free.

[0018] Furthermore, the axial arrangement order of the sealing packing and the packing in the sealing cavity is as follows: from the side near the second end ring to the side near the sealing ring, the order is packing, sealing packing, and packing; the second sleeve wall is provided with injection holes at the axial positions corresponding to the sealing packing, the injection holes are evenly distributed along the circumference, and a check valve is installed at each injection hole; the guide band is evenly distributed along the circumference in the groove of the sealing ring.

[0019] This invention also provides a method for installing a double-seal external pressure bellows compensator for steam, comprising the following steps:

[0020] S1: Verify the factory characteristic distance recorded in the factory documentation. Compared with factory pre-compression And measure the actual distance between the physical block plate and the first end ring;

[0021] S2: Precompression adaptation verification; calculate the required precompression amount on site based on the on-site pipeline parameters. The factory pre-compression amount as stated in the factory documentation. Compare and determine the installation and treatment plan based on the magnitude of the deviation;

[0022] S3: Conduct an acceptance inspection of the chrome plating layer on the surface of the movable pipe to confirm that it meets the installation requirements;

[0023] S4: Weld the two ends of the compensator to the pipeline, and measure the distance between the plug plate and the first end ring after welding. Verify that the axial deviation introduced by welding is within the allowable range;

[0024] S5: Fill the sealing cavity between the second sleeve and the movable pipe with sealing packing and compact it, and install a check valve at the injection hole.

[0025] S6: Insert the guide strip into the groove of the sealing ring, press the sealing ring with the guide strip into the end of the sealing cavity and weld it to the second sleeve for fixation;

[0026] S7: After the pipeline is put into operation, the characteristic distance of the working state is obtained by measuring the distance between the plug plate and the first end ring under stable working conditions. Calculate the actual compensation amount and the theoretical compensation amount to determine the working status of the compensator; when the steam leakage exceeds the allowable value, inject sealing packing into the sealing cavity online through the injection hole.

[0027] Further, step S2 includes the following sub-steps:

[0028] S21: Read the factory pre-compression amount from the factory documentation. Calculate the required precompression amount on site using the following formula. :

[0029] ;

[0030] in, The amount of pre-compression required on site; The coefficient of linear expansion of the pipeline; This refers to the actual length of the compensation pipe section; Design operating temperature for the pipeline; The actual ambient temperature at the time of installation; This is the external pressure correction factor, when the design pressure... hour ,when hour ,when hour ; Generate the required pre-compression amount on site ;

[0031] S22: Calculate the pre-compression adaptation deviation using the following formula. :

[0032] ;

[0033] in, For pre-compression adaptation deviation; This is the factory pre-compression amount; The required precompression amount for the field, calculated using S21; generates the precompression adaptation deviation. ;

[0034] S23: Based on the maximum compensation amount of the bellows To determine the appropriate treatment plan, the following rules shall be followed: When If the match is deemed good, proceed with installation; if... hour, The value is not zero; a thickness of [value missing] is added at the pipe connection flange. Adjusting shims, when When the gasket is installed at the fixed end flange, When the gasket is installed at the movable end flange, the fixed end flange is the pipe connection flange located on the fixed pipe side of the compensator, and the movable end flange is the pipe connection flange located on the movable pipe side of the compensator; when If the factory pre-compression amount is determined to be incompatible with the site conditions, installation will be refused and a new order will be placed according to the site parameters.

[0035] Further, step S5 includes the following sub-steps:

[0036] S51: In the sealing cavity between the second sleeve and the movable connecting pipe, packing, sealing filler and packing are sequentially inserted along the axial direction from the side closest to the second end ring to ensure that the sealing material is evenly distributed in the circumferential direction of the sealing cavity; forming a sealing material combination to be compacted.

[0037] S52: Measure and record the total height of the sealing material after S51 is completed, to obtain the total height of the sealing material before compaction. A hydraulic press was used to axially compact the sealing material, and the total height of the compacted sealing material was measured in real time. Calculate the compression ratio of the sealing material using the following formula. :

[0038] ;

[0039] in, The compression ratio of the sealing material; This refers to the total height of the sealing material before compaction; The total height of the compacted sealing material; the compression ratio of the sealing material. The content is controlled within the range of 20% to 30%; a sealing filler layer with pre-tight sealing force is formed.

[0040] S53: At the axial position of the sealing packing corresponding to the second casing wall, injection holes are drilled evenly along the circumference, and check valves are installed at each injection hole. The opening pressure of the check valves is higher than the working pressure of the pipeline; thus forming an injection channel for online replenishment of sealing packing.

[0041] Further, step S7 includes the following sub-steps:

[0042] S71: After the pipeline reaches a stable operating state, the characteristic distance of the operating state is obtained by measuring the distance between the plug plate and the first end ring. Simultaneously record the measured operating temperature ; Generate working state feature distance and measured operating temperature ;

[0043] S72: Calculate the actual compensation amount using the following two formulas respectively. and theoretical compensation amount :

[0044] ;

[0045] in, This is the actual compensation amount; The distance of the factory-specific features recorded in the factory documentation; The working state characteristic distance measured by S71;

[0046] ;

[0047] in, This is the theoretical compensation amount; The coefficient of linear expansion of the pipeline; This refers to the actual length of the compensation pipe section; This refers to the actual measured operating temperature. The actual ambient temperature at the time of installation; generating the actual compensation amount. With theoretical compensation ;

[0048] S73: Calculate the thermal compensation deviation rate using the following formula. :

[0049] ;

[0050] in, For thermal compensation deviation rate; when When the compensator is deemed to be in normal working condition, it is recorded. Filing; when During the next planned shutdown, check the condition of the fixed supports and guide supports, and re-verify them. ;when If any abnormality is found, immediately investigate at least one of the following: failure of the fixed support, release of pipeline constraints, or interference between the guide tube and the movable connector, and take appropriate measures.

[0051] Furthermore, when steam leakage is detected... Exceeding the limit At this time, follow these steps to replenish the online sealing packing through the injection hole:

[0052] Step 1: Measure the medium pressure at the injection port. Determine the injection pressure using the following formula. :

[0053] ;

[0054] in, To replenish pressure; The pressure of the medium at the injection hole; This is the overpressure coefficient; To overcome the additional pressure difference required for friction; to generate the injection pressure. ;

[0055] Step 2: Calculate the required replenishment volume using the following formula. :

[0056] ;

[0057] in, This is the amount to be replenished; This refers to the inner diameter of the second sleeve. For the outer diameter of the activity takeover; The height of the seal packing that needs to be replenished; based on the injection pressure. A volume of [volume] is injected into the sealed cavity through the check valve. The sealing material; online replenishment of the sealing filler;

[0058] Step 3: After the injection is completed, continue to monitor. If the leakage stops, the injection is considered successful. If the leakage does not stop, repeat steps 1 and 2 once. If the leakage is still not eliminated after repeated injection, schedule a work stoppage for maintenance.

[0059] The beneficial effects achieved by this invention are as follows:

[0060] The external pressure bellows structure designed in this invention places the bellows inside a first sleeve filled with the working medium, where the bellows bears uniform pressure from the external medium. Under external pressure, the bellows crests are constrained inward by the uniform external pressure, and each part is in a state of mutual support. This is fundamentally different from the stress state of the internal pressure bellows, where the bellows crests expand outward under internal pressure. This results in the critical buckling pressure of the external pressure bellows being much higher than that of the internal pressure bellows of the same specifications, giving it stronger resistance to buckling under high-temperature and high-pressure steam conditions and stable operation at higher working pressures without buckling instability. Simultaneously, the uniform load distribution of the external pressure results in a lower stress cycle amplitude and less local stress concentration in the bellows material, thus significantly extending the fatigue life of the bellows, reducing equipment maintenance frequency, and lowering operation and maintenance costs. It is particularly suitable for the long-term reliable operation requirements of high-temperature and high-pressure steam pipelines. Furthermore, the present invention employs a structural design that decouples the corrugated pipe from the movable pipe through connecting pipe one and connecting pipe two via a blocking plate. This design prevents the corrugated pipe from bearing direct welding stress with the movable pipe, eliminating the local stress concentration at the weld joint caused by direct welding of the corrugated pipe and the movable pipe in the traditional structure. This further improves the fatigue performance of the corrugated pipe under long-term reciprocating deformation conditions.

[0061] This invention employs a dual-sealing structure system combining bellows and packing seals. Under normal operating conditions, the bellows forms the first layer of seal, while the packing, packing ring, sealing ring, and guide band form the second layer. The two seals are independent yet connected in series for protection. When the bellows fails due to long-term fatigue or corrosion, the second packing seal can still effectively intercept steam leakage, controlling the leakage within a safe range and buying time for system intervention. This fundamentally eliminates the safety hazard of large-scale steam leakage in a single-layer sealing structure after the main seal fails. The present invention further includes a pre-set injection hole and a check valve at the axial position of the sealing packing corresponding to the second sleeve, forming an online sealing packing replenishment channel. When the second layer of seal leaks, flexible graphite sealing grease can be injected into the sealing cavity through the injection hole without interrupting pipeline operation, achieving online leak sealing under pressure without shutdown for disassembly and maintenance. Compared with the traditional shutdown maintenance method, this significantly shortens the leak handling time, greatly reduces the impact of maintenance operations on the continuous production system, and avoids the additional stress impact on the bellows and various sealing structures caused by drastic temperature changes in the pipeline system during shutdown, thereby improving the safety and economy of the steam pipeline system.

[0062] This invention involves machining and hard chrome plating the outer surface of the movable connector, giving it a contact surface with high hardness and low surface roughness. The high-hardness chrome plating effectively resists the abrasion of the connector surface by the sealing packing during axial reciprocating motion, while the low surface roughness ensures a tighter and more uniform contact between the sealing packing and the movable connector, reducing the probability of interface leakage channels. This significantly improves the initial sealing performance and long-term sealing reliability of the second layer seal, extending the replacement cycle of the packing seal. Furthermore, this invention also includes a guide strip evenly distributed around the circumference within the sealing ring groove. This guide strip provides stable radial support and guidance during the axial reciprocating motion of the movable connector, preventing radial displacement of the second sleeve and ensuring uniform circumferential stress on all sealing materials within the sealing cavity. This avoids excessive localized wear and further extends the service life of the second layer sealing structure. Furthermore, the present invention provides a guide tube in the internal channel of the movable and fixed pipes to guide the steam to flow smoothly along the axial direction, effectively reducing the local flow resistance coefficient of the medium passing through the compensator, and preventing high-speed steam from directly scouring the outer surface of the bellows and the inner wall of the sleeve, thus protecting the bellows from fluid erosion, thereby reducing system energy consumption and extending the overall service life of the compensator.

[0063] This invention proposes a dedicated pre-compression calculation method for external pressure steam compensators. An external pressure correction coefficient is introduced into the calculation formula for the required pre-compression on-site. Different correction values ​​are applied based on different design pressure ranges, scientifically reflecting the difference in stiffness characteristics between the equivalent axial stiffness of the external pressure bellows and that of the internal pressure bellows of the same specification. This ensures that the calculated pre-compression result matches the actual mechanical behavior of the external pressure bellows, controlling the stress level of the compensator within a reasonable range throughout the entire operating temperature range. The bellows are pre-compressed at the factory, eliminating the need for temporary tie rods to apply pre-compression during on-site installation. This avoids the operational risks associated with the installation and removal of temporary tie rods and simplifies the construction process. This invention also establishes a two-stage installation verification system based on the factory characteristic distance. Before installation, the pre-compression adaptation deviation is calculated to confirm the degree of matching between the factory pre-compression amount and the on-site installation conditions, and corresponding measures are taken according to the deviation level. After commissioning, the thermal compensation deviation rate is calculated by measuring the working state characteristic distance and the working state of the compensator is determined according to the classification standard. This constructs a quantitative tracking and verification system for the entire process from factory to installation to operation, which can promptly detect pipeline constraint anomalies and compensation failures, providing a reliable guarantee for the safe and long-term operation of the steam pipeline system. Attached Figure Description

[0064] Figure 1 This is a structural diagram of the steam double-sealed external pressure bellows compensator of the present invention.

[0065] Figure 2 yes Figure 1 Enlarged view of the structure at point A.

[0066] Figure 3 This is a schematic diagram of the pre-compression state of the bellows in the steam double-sealed external pressure bellows compensator of the present invention.

[0067] Figure 4 This is a schematic diagram of the working state of the steam double-sealed external pressure bellows compensator of the present invention.

[0068] Figure 5 This is a diagram showing the flow direction and distribution of the medium in the double-sealed external pressure bellows compensator for steam according to the present invention.

[0069] Numbering on the map:

[0070] 1. Movable connector; 2. Corrugated pipe; 3. Fixed connector; 4. First sleeve; 5. Second sleeve; 6. Sealing ring; 7. Guide strip; 8. Sealing packing; 9. Packing; 10. Plug; 11. First end ring; 12. Second end ring; 13. Flow guide tube; 14. Connecting pipe one; 15. Connecting pipe two. Detailed Implementation

[0071] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. In addition, the forms of the various structures described in the following embodiments are merely illustrative. The present invention is not limited to the structures described in the following embodiments. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0072] Reference Figures 1-5 The steam double-sealed external pressure corrugated compensator of the present invention is provided with a movable pipe 1, a fixed pipe 3, a guide tube 13, a first sleeve 4, a first end ring 11, a plug plate 10, a corrugated pipe 2, a connecting pipe one 14, a second end ring 12, a connecting pipe two 15, a second sleeve 5, a sealing packing 8, a packing 9, a sealing ring 6, and a guide belt 7.

[0073] The movable connector 1 and the fixed connector 3 are arranged coaxially opposite each other and are used to connect to the movable end and fixed end of the steam pipe, respectively. The outer surface of the movable connector 1 is provided with a chrome-plated layer. The chrome plating gives the movable connector 1 a surface with high hardness and low coefficient of friction, which can effectively reduce friction and wear between it and the sealing packing 8 and extend the service life of the second sealing structure.

[0074] The first sleeve 4 is fitted onto the outside of the movable connector 1 and the fixed connector 3, forming the external pressure boundary of the compensator and enclosing the working medium within its internal space. The first end ring 11 is fixedly connected between the fixed connector 3 and the first sleeve 4. Its inner side is welded to the outer wall of the fixed connector 3, and its outer side is welded to the inner wall of the first sleeve 4, so that the first sleeve 4 and the fixed connector 3 form an integral unit and remain relatively fixed during the operation of the compensator.

[0075] The plug plate 10 has a ring structure, is sleeved on the outside of the movable connector 1 and fixedly connected to the movable connector 1, and can move axially together with the movable connector 1. The outer edge of the plug plate 10 forms an axially sliding sealing fit with the inner wall of the first sleeve 4, so that the plug plate 10 can slide freely axially in the first sleeve 4, while preventing the medium in the first sleeve 4 from leaking out in large quantities through this gap.

[0076] The bellows 2 is located inside the first sleeve 4, fitted around the outside of the movable connector 1 and the fixed connector 3. The bellows 2 is not directly connected to the movable connector 1. The bellows 2 is connected to the end plate 10 via connecting pipe one 14 and to the second end ring 12 via connecting pipe two 15. Both connecting pipe one 14 and connecting pipe two 15 are cylindrical transition structures. One end of connecting pipe one 14 is welded to the end face of the end plate 10 facing the bellows 2, and the other end is welded to the end of the bellows 2 near the end plate 10. One end of connecting pipe two 15 is welded to the other end of the bellows 2, and the other end is welded to the end face of the second end ring 12 facing the bellows 2. This decoupling design prevents the bellows 2 from bearing direct welding stress from the movable connector 1, eliminating the localized stress concentration caused by direct welding between the bellows and the movable connector in traditional structures, thereby improving the fatigue life of the bellows 2.

[0077] The second end ring 12 is fixedly connected to the inner wall of the first sleeve 4 and is not connected to the movable connector 1. It remains fixed with the first sleeve 4 when the compensator is working. The second sleeve 5 is sleeved on the outside of the movable connector 1, and one end of it is fixedly connected to the second end ring 12. The inner diameter of the second sleeve 5 is larger than the outer diameter of the movable connector 1, forming a sealing cavity between them to accommodate sealing material.

[0078] When the compensator is working, the working medium fills the entire space inside the first sleeve 4, including the annular space between the first sleeve 4 and the bellows 2, and the space between the first sleeve 4 and the guide tube 13. The bellows 2 therefore bears the pressure of the external medium, forming an external pressure structure. The crests of the external pressure bellows are constrained by uniform external pressure, and its critical instability pressure is much higher than that of an internal pressure bellows of the same specification. This results in a more uniform stress distribution and a longer fatigue life under high-temperature and high-pressure steam conditions.

[0079] The guide tube 13 is installed in the internal channel between the movable connector 1 and the fixed connector 3. One end of the guide tube 13 is fixedly connected to the inner wall of the fixed connector 3, while the other end extends to the inside of the movable connector 1 without being connected to it, forming a cantilever structure with one fixed end and one free end. The free end of the guide tube 13 can freely follow the relative displacement of the movable connector 1 without constraining the compensation function. The guide tube 13 guides the steam to flow smoothly along the axial direction, reducing flow resistance and preventing high-speed steam from directly scouring the inner wall of the first sleeve 4 and the outer surface of the bellows 2, thereby protecting the bellows 2. The length of the guide tube 13... The following relationship must be satisfied: ;

[0080] in Length of the guide tube (mm); The natural length (mm) of bellows 2; The pressure coefficient is the pressure factor when the design pressure is... MPa Take 0.80, when MPa Take 0.70; The pre-compression amount (mm) is the factory pre-compression amount. The physical meaning of the above relationship is that the effective coverage length of the guide tube 13 must still cover the transition channel between the movable pipe 1 and the fixed pipe 3 after the bellows 2 has fully recovered from the pre-compression state, and at the same time, the free end must not interfere with the movable pipe 1 under the maximum compression state; The coefficient decreases as the working pressure increases because the axial stiffness of the bellows 2 increases under high pressure conditions, and the effective compensation stroke decreases accordingly. The design margin of the guide tube 13 needs to be adjusted accordingly.

[0081] The sealing packing 8 and packing 9 are disposed in the sealing cavity between the second sleeve 5 and the movable connector 1, arranged axially from the side near the second end ring 12 to the side near the sealing ring 6, in the order of packing 9, sealing packing 8, and packing 9. The packing 9 at both ends serves as sealing end seals, restricting the sealing packing 8 from being squeezed out to the end of the cavity when axially compressed; the sealing packing 8 in the middle forms the main sealing pressure-bearing zone. The sealing packing 8 and packing 9 are preferably made of flexible graphite material, which has excellent high-temperature resistance, chemical stability, and self-lubricating properties, and can maintain a long-term stable sealing effect under high-temperature steam conditions. After being compacted, the sealing packing 8 and packing 9 maintain a continuous radial pressure on the chrome-plated outer surface of the movable connector 1. When the movable connector 1 slides axially within the second sleeve 5, it forms a dynamic seal, preventing steam from leaking from the gap between the two.

[0082] The second sleeve 5 has injection holes at the axial positions corresponding to the sealing packing 8 on its pipe wall. The injection holes are evenly distributed around the circumference, and each injection hole is equipped with a check valve. Under normal operating conditions, the check valve prevents the medium in the cavity from overflowing in the reverse direction. When online replenishment is required, it allows the injection of external sealing material, thereby achieving online leak sealing without interrupting pipeline operation.

[0083] The sealing ring 6 is fixedly connected to the end of the second sleeve 5, and its inner wall has a groove for accommodating the guide band 7. The guide band 7 is embedded in the groove of the sealing ring 6, located between the sealing ring 6 and the movable connecting pipe 1. It provides radial support and guidance when the movable connecting pipe 1 performs axial reciprocating motion, preventing radial displacement of the second sleeve 5 and ensuring that the sealing materials within the sealing cavity are subjected to uniform force in the circumferential direction, thus avoiding accelerated localized wear. The guide band 7 is evenly distributed circumferentially within the groove, with a nominal diameter of... The compensator uses a three-point evenly distributed design. The compensator is designed with four points evenly distributed to meet the requirements for radial guiding stiffness under different pipe diameters.

[0084] In the above structure, the bellows 2 bears external pressure and forms the first sealing structure, completely sealing the medium inside the first sleeve 4 under normal operating conditions; the sealing packing 8, packing 9, sealing ring 6, and guide band 7 together form the second sealing structure, creating a double sealing system. When the bellows 2 fails due to long-term fatigue or corrosion, the second sealing structure can still effectively prevent steam leakage, and sealing material can be added through the injection hole to maintain pipeline operation.

[0085] When the compensator leaves the factory, the bellows 2 is in a pre-compressed state, and the axial distance between the plug plate 10 and the first end ring 11 is the factory characteristic distance. Factory pre-compression and All documents are provided with the product manufacturer for on-site installation and acceptance. After the steam pipeline is put into operation, the medium fills the internal space of the first sleeve 4, and the bellows 2 bears the external pressure. As the pipeline temperature rises, the pipeline undergoes axial elongation due to thermal expansion. Due to the constraint of the fixed support, this elongation is absorbed by the compensator. At this time, the movable connector 1 moves relative to the fixed connector 3 in its direction, and the plug plate 10 moves synchronously with the movable connector 1. Through the connecting pipe 14, it drives the connecting end of the bellows 2 to move accordingly. The bellows 2 gradually recovers from the pre-compressed state, and its axial elastic deformation absorbs the thermal expansion displacement of the pipeline. During this process, the distance between the plug plate 10 and the first end ring 11 is reduced from... Reduce to , Less than Difference This is the actual amount of thermal expansion compensation absorbed by the compensator. When the pipeline temperature decreases, the pipeline contracts, the movable connector 1 moves in the opposite direction, and the bellows 2 re-enters the compression state. The compensator repeatedly expands and contracts with the temperature cycle, continuously absorbing the thermal expansion and contraction displacement of the pipeline through elastic deformation.

[0086] The following describes in detail each step of the installation method of the present invention.

[0087] S1 first checks the factory feature distance provided with the product's manufacturing documentation. and factory pre-compression Then, use measuring tools to measure the actual distance between the actual blocking plate 10 and the first end ring 11. If the deviation between the measured value and the value recorded in the document exceeds the allowable range, the cause needs to be investigated. For example, external forces during transportation may have changed the pre-compression state. If necessary, the manufacturer should be contacted to reprocess the issue before installation. and It serves as the baseline data for all subsequent installation and verification calculations, and its accuracy directly affects the compensator's adaptation accuracy on site.

[0088] S2 is the pre-compression adaptation verification stage. In steam pipeline engineering, the length of the compensation pipe section, the design operating temperature, and the installation ambient temperature vary at different installation sites, while the pre-compression amount applied when the product leaves the factory... It is predetermined according to the design parameters, so it is necessary to verify the degree of matching between the factory pre-compression amount and the actual installation conditions on site. The S2 stage includes three sub-steps: S21, S22, and S23.

[0089] S21 outlines the steps for calculating the required pre-compression amount on-site. The factory pre-compression amount is read from the factory documentation. Then, based on the actual parameters of the pipeline on site, calculate the required pre-compression amount on site using the following formula. :

[0090] ;

[0091] in The required pre-compression amount (mm) on site; The value is the coefficient of linear expansion of the pipeline (mm / (m·℃)). For carbon steel pipes, a reference value of 0.012 can be taken. The specific value should be selected according to the actual material. The actual length of the compensated pipe section (m) is the length of the pipe between the fixed supports on both sides of the compensator. Design operating temperature (°C) for the pipeline; The actual ambient temperature (°C) at the time of installation; This is the external pressure correction factor, when the design pressure... MPa ,when MPa MPa ,when MPa . The introduction of this factor is a key correction step in the pre-compression calculation of external pressure bellows compensators: the equivalent axial stiffness of external pressure bellows is higher than that of internal pressure bellows of the same specification. Under the same pipeline thermal expansion, the pre-compression required for external pressure compensators should be appropriately smaller than that for internal pressure compensators; and the higher the pressure, the more significant the stiffness gain of external pressure bellows. The value is increased accordingly to reflect the effect of stiffness differences on the precompression amount. Step S21 generates the required precompression amount for the field. .

[0092] S22 outlines the steps for calculating the pre-compression adaptation deviation. The pre-compression adaptation deviation is calculated using the following formula. :

[0093] ;

[0094] in Pre-compression adaptation deviation (mm); The factory pre-compression amount (mm) provided in the factory documentation. The required precompression amount (mm) for the field is calculated based on S21. Step S22 generates the precompression adaptation deviation. This provides input for the discrimination of S23.

[0095] S23 outlines the steps for determining the installation and handling plan. This is based on the maximum compensation amount of bellows 2. To determine the appropriate treatment plan, the following rules shall be followed: When When the factory pre-compression is determined to be a good match with the on-site installation conditions, direct installation is possible without adjustment; when At this time, it is determined that there is a certain deviation but it is still within the adjustable range. If the value is not zero, a thickness of [missing value] should be added at the pipe connection flange. Adjusting shims, when When the factory pre-compression is too large, a gasket is added to the fixed end flange to cause the compensator to shift towards the fixed end. This effectively reduces the actual pre-compression amount when When the factory pre-compression amount is too small, a gasket is added to the movable end flange; the fixed end flange is the pipe connection flange located on the fixed pipe side of the compensator, and the movable end flange is the pipe connection flange located on the movable pipe side of the compensator; when If the deviation exceeds the adjustable range, the product needs to be remanufactured.

[0096] S3 is the acceptance inspection procedure for the chrome plating layer on the surface of the movable connector 1. The surface quality of the chrome plating layer on the movable connector 1 directly affects the dynamic sealing performance and lifespan of the second sealing structure. It needs to be inspected and confirmed before installation. The focus is on checking the uniformity of the chrome plating layer. There should be no defects such as bubbles, cracks, or peeling. Appropriate instruments should be used to test whether the thickness and surface roughness of the chrome plating layer meet the design requirements. Subsequent installation procedures can only be carried out after all inspection items are qualified.

[0097] S4 describes the pipe welding and post-weld verification steps. The two ends of the compensator are connected to the pipes respectively, and welded in place using a welding method compatible with the pipe material. After the weld has cooled to room temperature, the distance between the plug plate 10 and the first end ring 11 is measured using a measuring instrument. Verify whether the axial displacement deviation introduced by the welding operation is within the allowable range. If the deviation exceeds the allowable value, the cause should be identified, including excessive welding shrinkage, uneven pipe end face processing, or misalignment of the pipe axes at both ends, and corresponding corrective measures should be taken.

[0098] S5 is the sealing material filling and compaction step, which includes three sub-steps: S51, S52, and S53.

[0099] S51 is the sealing material placement step. Within the sealing cavity between the second sleeve 5 and the movable connector 1, starting axially from the side closest to the second end ring 12, packing 9, sealing filler 8, and packing 9 are placed sequentially. During placement, it should be ensured that the sealing material is evenly distributed circumferentially within the sealing cavity to avoid localized accumulation. Step S51 forms the sealing material assembly to be compacted.

[0100] S52 is the sealing material compaction step. Measure and record the total height of the sealing material after S51. Then, a hydraulic press is used to axially compact the sealing material, and the total height after compaction is measured in real time. Calculate the compression ratio using the following formula. :

[0101] ;

[0102] in Compression ratio of sealing material (%); The total height of the sealing material before compaction (mm); The total height of the compacted sealing material (mm); The compression ratio should be controlled within the range of 20% to 30%. Within this range, flexible graphite-based sealing materials can generate sufficient radial pre-tightening sealing force. Too low a compression ratio results in insufficient sealing force, while too high a compression ratio leads to a decrease in elastic margin after densification of the sealing material, both of which are detrimental to the long-term stability of the dynamic seal. Step S52 forms a sealing filler layer with pre-tightening sealing force.

[0103] S53 describes the steps for machining the injection holes and installing the check valves. Injection holes are drilled evenly around the circumference at the axial positions corresponding to the sealing packing 8 on the wall of the second sleeve 5. Check valves are installed at each injection hole. The opening pressure of the check valves should be higher than the pipeline's working pressure to ensure that the medium inside the pipe will not overflow back through the injection holes under normal operating conditions. Step S53 forms an injection channel for online replenishment of the sealing packing.

[0104] S6 describes the installation steps for the guide band 7 and the sealing ring 6. The guide band 7 is embedded into the groove of the sealing ring 6, arranged circumferentially according to a specified uniform distribution pattern. The sealing ring 6 with the guide band 7 is then pressed into the end of the sealing cavity, ensuring close contact between the end face of the sealing ring 6 and the surface of the compacted sealing material. The sealing filler 8 and packing 9 are kept in a compacted state. Finally, the sealing ring 6 is welded to the second sleeve 5 for fixation. During welding, the heat input should be controlled to prevent excessive heat transfer to the sealing material, thus avoiding performance degradation due to heat.

[0105] S7 is the step for verifying the thermal compensation effect after the pipeline is put into operation and the online replenishment step, which includes three sub-steps: S71, S72 and S73.

[0106] S71 describes the measurement steps for the characteristic parameters of the operating state. After the pipeline reaches a stable operating state, the distance between the plug plate 10 and the first end ring 11 is measured using a measuring instrument. Simultaneously record the measured operating temperature of the pipeline. Step S71 generates the working state feature distance. and measured operating temperature .

[0107] S72 outlines the steps for calculating the compensation amount. Calculate the actual compensation amount using the following two formulas. and theoretical compensation amount :

[0108] ;

[0109] in Actual compensation amount (mm); The factory feature distance (mm) recorded in the factory documentation; The working state characteristic distance (mm) measured by S71;

[0110] ;

[0111] in Theoretical compensation amount (mm); The linear expansion coefficient of the pipeline is (mm / (m·℃)). The actual length of the compensation pipe section (m); The measured operating temperature (°C) recorded for S71; The actual ambient temperature (°C) at the time of installation. Step S72 generates the actual compensation amount. With theoretical compensation .

[0112] S73 is the step for determining the effectiveness of thermal compensation. The thermal compensation deviation rate is calculated using the following formula. :

[0113] ;

[0114] in Thermal compensation deviation rate (%) The actual compensation amount (mm) calculated for S72; Theoretical compensation amount (mm) calculated for S72; when When the compensator is deemed to be in normal working condition, it is recorded. Filing; when If there is a certain deviation in the assessment, the condition of the fixed support and guide support should be checked and re-verified during the next planned shutdown. ;when When an abnormality in thermal compensation is detected, it is necessary to immediately investigate and address any anomalies such as failure of fixed supports, unexpected release of pipeline constraints, and interference between the guide tube 13 and the movable connector 1, and take appropriate measures. In the above-mentioned grading criteria, a 10% allowable deviation rate covers the normal engineering measurement error range; a deviation between 10% and 25% indicates a potential anomaly in the pipeline system that has not yet affected safe operation; and a deviation exceeding 25% indicates that the compensator may not be functioning properly and immediate intervention is required.

[0115] When steam leakage is detected in S7 Exceeding the limit When this occurs, the online sealing packing replenishment procedure is triggered, and the following steps are executed.

[0116] The first step is to determine the injection pressure by measuring the medium pressure at the injection port. Determine the injection pressure using the following formula. :

[0117] ;

[0118] in The injection pressure is (MPa). The pressure of the medium at the injection hole (MPa); This is the overpressure coefficient, and its value must be chosen to ensure that the injection material can overcome the back pressure of the medium in the sealed cavity and be injected smoothly. It is recommended... Take a value of 1.3 to 1.5; The additional pressure differential (MPa) required to overcome friction depends on factors such as the length of the injection pipeline and the diameter of the injection orifice. This generates the replenishment pressure. .

[0119] The second step is the calculation and injection of the replenishment volume. The required replenishment volume is calculated using the following formula. :

[0120] ;

[0121] in The injection volume is measured in mm³. The inner diameter (mm) of the second sleeve 5; The outer diameter (mm) of the movable connector 1; The height of the sealant packing to be replenished (mm) is the required height. This formula is essentially the product of the cross-sectional area of ​​the sealing cavity and the required replenishment height, representing the volume of sealing material to be added to the sealing cavity. The replenishment pressure is then used. A volume of [volume] is injected into the sealed cavity through the check valve. The sealing material. Online replenishment of the sealing packing is completed.

[0122] The third step is to evaluate the effect of the injection. After the injection is completed, the process is continuously observed. If the leakage stops, the injection is considered successful. If the leakage does not stop, repeat the first and second steps once. If the leakage is still not eliminated after repeated injection, it means that the damage to the sealing cavity exceeds the handling capacity of online injection, and a planned shutdown for maintenance needs to be arranged.

[0123] Example 1: This example applies a double-sealed external pressure bellows compensator for steam to a high-pressure steam transmission pipeline system in a chemical plant. The nominal diameter of the pipeline is DN=150mm, and the design operating temperature is... =350℃, design pressure =1.6MPa, length of compensation pipe section =25m, local historical lowest installation temperature =-10℃, ambient temperature during installation =20℃, pipe material is carbon steel, coefficient of linear expansion =0.012mm / m·℃.

[0124] The compensator's structure consists of the following: A fixed connector connects to the fixed support end of the piping system and remains stationary throughout the compensator's operation. A movable connector is coaxially arranged opposite the fixed connector and connects to the expansion joint of the pipeline. It can move axially relative to the fixed connector to absorb thermal expansion and contraction. The outer surface of the movable connector is machined and hard chrome plated, with a chrome plating thickness of not less than 30μm and a surface roughness of... Not exceeding 1.6μm, hardness A chrome-plated surface with a hardness of no less than 800 and a low coefficient of friction can effectively reduce friction and wear between the chrome plating and the sealing filler, extending the service life of the second layer of seal.

[0125] The first sleeve is fitted onto the outside of the movable and fixed pipes, forming the external pressure boundary of the compensator and enclosing the working medium within the internal space. The first end ring is welded and fixed between the outer wall of the fixed pipe and the inner wall of the left end of the first sleeve, making them a single unit that remains stationary during compensator operation. The plug plate is an annular flange-shaped structure, fitted onto the outside of the movable pipe and welded to it, allowing for axial movement synchronously with the movable pipe; the radial clearance between the outer edge of the plug plate and the inner wall of the first sleeve... =1.5mmDN=150mm belongs to the case of DN≤300. The value ranges from 1.0 mm to 2.0 mm, allowing the plug plate to slide freely axially within the first sleeve and maintain a seal.

[0126] The corrugated pipe adopts a thin-walled, multi-layered, fully enclosed structure made of 316L austenitic stainless steel, with a wall thickness of 0.8mm and a natural length of... =250mm, maximum compensation amount =90mm; The corrugated pipe is located inside the first sleeve, sleeved on the outside of the movable and fixed pipes, and is not directly connected to the movable pipe; The left side of the corrugated pipe is fixedly connected to the end plate through connecting pipe one, and the right side is fixedly connected to the second end ring through connecting pipe two; Connecting pipe one and connecting pipe two are both cylindrical transition structures, made of the same material as the corrugated pipe. Displacement is transmitted through the connecting pipe instead of being directly welded to the movable pipe, eliminating the local stress concentration caused by direct welding of the corrugated pipe and the movable pipe in the traditional structure, thereby extending the fatigue life of the corrugated pipe.

[0127] Because the bellows is placed inside the first sleeve, the annular space between the first sleeve and the bellows, as well as the space between the first sleeve and the guide tube, are filled with the working medium. The bellows bears the pressure of the external medium, forming an external pressure structure. The crest of the external pressure bellows is constrained by uniform external pressure, and its critical instability pressure is much higher than that of the internal pressure bellows of the same specification. It has better fatigue life and instability resistance under high temperature and high pressure steam conditions.

[0128] The second end ring is welded and fixed to the inner wall of the right side of the first sleeve, and is fixedly connected to the outer wall of the second sleeve. It is not connected to the movable connector and remains fixed with the first sleeve during the operation of the compensator. The second sleeve is fitted over the chrome-plated part of the movable connector, and its left end is fixedly connected to the second end ring; the radial gap of the sealing cavity between the second sleeve and the movable connector... =1.5mmDN=150mm≤300mm, The value ranges from 0.5mm to 1.5mm; the movable connector can slide axially within the second sleeve, and the sealing cavity between the two accommodates the second layer of sealing material.

[0129] The guide tube is coaxially installed in the internal channel of the movable and fixed pipes. One end, closer to the fixed pipe, is welded and fixed to the inner wall of the fixed pipe, while the other end extends freely to the inner side of the movable pipe, forming a cantilever structure with one fixed end and one free end. The free end can freely follow the relative displacement of the movable pipe without constraining the compensation function. The guide tube guides the steam to flow smoothly along the axial direction, reducing flow resistance and preventing high-speed steam from directly scouring the inner wall of the first casing and the outer surface of the bellows. The length of the guide tube is calculated using the formula: Pressure... =1.6MPa is greater than 1.0MPa, so the pressure coefficient is taken. =0.70, length of the guide tube mm.

[0130] The second sealing structure consists of sealing packing, packing, a sealing ring, and a guide band. Both the sealing packing and packing are made of flexible graphite material, arranged axially from the side closest to the second end ring to the side closest to the sealing ring, in the order of packing, sealing packing, packing. After being compacted by a hydraulic press, they maintain a continuous radial pressure on the chrome-plated outer surface of the movable connector, forming a dynamic seal. The sealing ring has a groove and is welded to the right end of the second sleeve; the guide band is embedded in the groove of the sealing ring, with a nominal diameter DN=150mm≤200mm. The guide band is evenly distributed at three points at 120° intervals, with the circumferential angle deviation controlled within ±2°; the outer diameter of the movable connector... =159mm, guide belt width The range of mm values ​​is: to The guide belt provides precise radial guidance during the axial reciprocating motion of the movable nozzle, ensuring that the materials in the sealing cavity are subjected to uniform stress.

[0131] The bellows forms the first layer of sealing structure, while the sealing packing, packing, sealing ring, and guide band form the second layer of sealing structure, creating a double sealing system. When the bellows fails due to fatigue or corrosion, the second layer of sealing can still effectively prevent steam leakage. The second sleeve has four injection holes of 8mm in diameter evenly distributed at the axial position of the sealing packing. Each injection hole is equipped with a check valve to support online replenishment of sealing packing without interrupting pipeline operation.

[0132] The factory pre-compression amount is determined by the formula, where =1.6MPa belongs to In this case, the external pressure correction factor =0.50, calculated as follows mm; the bellows is in a pre-compressed state of 54.0 mm at the time of manufacture, and the characteristic distance between the plug plate and the first end ring is... =185mm, and All of these are indicated on the product nameplate and provided with the factory documentation.

[0133] The installation steps are as follows. After receiving the goods in stage S1, use a measuring tool to measure the distance between the actual end plate and the first end ring. The measured value is 185mm, which is consistent with the value marked on the nameplate. =185mm deviation is 0mm, acceptance is qualified; at the same time, the appearance inspection of the chrome plating layer of the movable nozzle is carried out, and the thickness of the chrome plating layer and the surface roughness are tested by coating thickness gauge and roughness gauge respectively. All indicators meet the design requirements, and the acceptance is qualified.

[0134] The required pre-compression amount for the field in stage S2 is calculated using the formula in S21: mm; S22 calculates the pre-compression adaptation deviation: mm; S23 with the maximum compensation amount of the bellows. =90mm is the criterion. mm, absolute value =4.5mm or less =4.5mm, indicating a good match between the factory pre-compression and the on-site installation conditions, allowing for direct installation without adjustment. In stage S3, a comprehensive inspection of the chrome plating thickness, hardness, and roughness of the movable connector was conducted, and all indicators met the requirements. In stage S4, the butt welding of both ends of the compensator to the pipeline was completed, and measurements were taken after cooling to room temperature. =185mm, and The difference is 0mm, which meets the welding tolerance requirements. In stage S5, packing, sealing filler, and packing are sequentially placed inside the sealing cavity. The total height before filling is... =55mm, total height after hydraulic press compaction =41mm, compression ratio To meet a control range of 20% to 30%, four injection holes are drilled evenly and check valves are installed. In stage S6, guide strips distributed at three points are embedded in the sealing ring groove, pressed into the sealing cavity, and then the sealing ring is welded and fixed to the second sleeve. In stage S7, after the pipeline is put into operation and runs stably, the distance between the plug plate and the first end ring is measured. =87mm, synchronously record the measured operating temperature =347℃; Calculate the actual compensation amount mm; Calculate the theoretical compensation amount mm; thermal compensation deviation rate If the percentage does not exceed the 10% threshold, the compensator is functioning normally. Value records are filed.

[0135] Example 2: Application of DN250 medium-pressure steam pipeline compensator; This example is applied to a medium-pressure steam transmission pipeline in a thermal power plant. The pipeline has a nominal diameter of DN=250mm and a design operating temperature of... =280℃, design pressure =1.0MPa, length of compensation pipe section =35m, local historical lowest installation temperature =-5℃, ambient temperature during installation =15℃, pipe material is carbon steel =0.012mm / m·℃. The corrugated pipe is made of 304 stainless steel, with a natural length of... =320mm, maximum compensation amount =120mm; Outer diameter of movable connector =273mm; Radial clearance of the sealing cavity between the second sleeve and the movable connector. =1.2mm, DN=250mm≤300mm, The value ranges from 0.5mm to 1.5mm; the radial gap between the outer edge of the plug plate and the inner wall of the first sleeve. =1.5mm, DN≤300mm, value range 1.0mm to 2.0mm; the guide strip adopts four points evenly distributed at 90°, DN=250mm>200mm, width mm; Total height before sealing material filling =70mm, after compaction =52mm, compression ratio It meets the control range; there are 4 injection holes, each with a diameter of 8mm; and the factory characteristic distance is met. =205mm.

[0136] Factory pre-compression calculation: =1.0MPa belongs to In the case of MPa, =0.45, mm; pressure coefficient =0.80, length of the guide tube mm. S2 phase verification: mm, mm, mm, The absolute value is 3.7mm, which is less than 6.0mm, indicating a good match; direct installation is recommended. (Seal material compression ratio) Qualified. After the pipeline is put into operation and running stably, measurements are taken... =95mm, measured operating temperature =276℃; mm; mm; The device is functioning normally. This embodiment covers... MPa The parameter range is 0.45, and the range of sealing cavity clearance is DN≤300mm.

[0137] Example 3: Application of DN400 High-Temperature and High-Pressure Steam Pipeline Expansion Joint; This example is applied to a high-temperature and high-pressure steam main pipeline in a power plant. The nominal diameter of the pipeline is DN=400mm, and the design operating temperature is... =450℃, design pressure =2.5MPa, length of compensation pipe section =30m, local historical lowest installation temperature =-15℃, ambient temperature during installation =25℃, =0.012mm / m·℃. The corrugated pipe is made of 316L stainless steel, with a natural length of... =380mm, maximum compensation amount =150mm; Outer diameter of movable connector =426mm; radial clearance of sealing cavity =2.0mm, DN=400mm>300mm, value range 1.5mm to 2.5mm; gap at the outer edge of the end plate =2.5mm, DN>300mm, value range 2.0mm to 3.0mm; guide belt evenly distributed at four points at 90°, width mm; =85mm, =63mm, ; 4 injection holes, 10mm in diameter; factory characteristic distance =220mm.

[0138] Factory pre-compression calculation: =2.5MPa belongs to In the case of MPa, =0.50, mm; =0.70, length of the guide tube mm. S2 phase verification: mm, mm, mm, If the absolute value is 7.2mm (less than 7.5mm), the match is considered good, and installation can proceed directly. After the pipeline is put into stable operation, measurements will be taken. =68mm, =446℃; mm; mm; The system is functioning normally. This embodiment covers the sealing cavity gap range with DN>300mm. MPa The parameter range is 0.50, and the typical application scenarios of large-diameter high-temperature and high-pressure steam pipelines.

[0139] Comparative Example 1: A single-layer sealed external pressure compensator without a second sealing layer; the pipeline parameters are exactly the same as in Example 1, and an external pressure bellows structure is used, but the second sealing layer consisting of sealing packing, packing, sealing ring and guide strip is omitted, and no injection hole is provided on the second sleeve, with only the bellows as the sole sealing layer. The remaining structural parameters are exactly the same as in Example 1.

[0140] Comparative Example 2: External pressure double-seal compensator without a guide tube; the pipeline parameters are exactly the same as in Example 1, and an external pressure double-seal structure is adopted, but the guide tube in the internal channel of the movable and fixed pipes is eliminated. High-speed steam flows directly in the inner cavity of the first sleeve, and the airflow directly washes the outer surface of the bellows and the inner wall of the sleeve. The remaining structural parameters are exactly the same as in Example 1.

[0141] Comparative Example 3: External pressure double-seal compensator with unplated movable connector; the piping parameters are exactly the same as in Example 1, and an external pressure double-seal structure is used, but the movable connector surface is only machined and not hard chrome plated, resulting in a surface roughness of... =3.2μm, surface hardness =180. The sealing packing and packing are in direct contact with the rough-surfaced, low-hardness moving part, forming a second seal. All other structural parameters are identical to those in Example 1.

[0142] Comparative Example 4: Traditional internal pressure bellows compensator; the pipeline parameters are exactly the same as in Example 1, but a traditional internal pressure bellows structure is adopted: the two ends of the bellows are directly welded to the movable connector and the fixed connector respectively, the working medium flows inside the bellows, and the bellows bears the internal medium pressure; there are no connecting pipe one, connecting pipe two, plug plate and external pressure characteristic structure; only the bellows itself is used as the sealing layer, and there is no second layer of packing sealing structure.

[0143] Comparative Example 5: Internal pressure compensator installed using temporary tie rod method with pre-compression; the pipeline parameters are the same as in Comparative Example 4, and a traditional internal pressure bellows structure is used. During installation, the pre-compression is applied on-site using the temporary tie rod method, without factory pre-compression and without external pressure correction factor. Correction: The pre-compression amount calculated according to the traditional internal pressure compensator formula is 49.5mm. After applying a pre-compression amount of about 49.5mm on site using temporary tie rods, welding and installation are completed, and then the tie rods are removed. The adjustment of the pre-compression amount relies on on-site visual inspection, lacks a quantitative acceptance system, and there are certain operational risks in the installation and removal of temporary tie rods.

[0144] Comparative Example 6: External pressure double-seal compensator without injection holes; the pipeline parameters are exactly the same as in Example 1, and an external pressure double-seal structure is adopted. The structure of the sealing packing, packing, sealing ring and guide band is exactly the same as in Example 1. However, no injection holes are drilled on the wall of the second casing, and no check valve is installed. When the second seal leaks, the sealing material can only be replaced by planned shutdown for disassembly and maintenance. Online injection of sealing packing is not possible.

[0145] Experiment Example 1: Sealing Performance Comparison Experiment; This experiment uses the compensators of Example 1, Comparative Example 1 and Comparative Example 3 as test objects, and conducts a phased comparative test of sealing performance.

[0146] In the first stage, nitrogen gas was introduced into the three compensators under a design pressure of 1.6 MPa. Leak detection fluid was applied to each pipe joint and sealing area. The initial leakage rate was measured using the flow rate method (mL / min), and a 24-hour pressure holding test was conducted, with pressure drop recorded in MPa. In the second stage, a micro-leakage hole with a diameter of 0.2 mm was artificially created on the bellows to simulate perforation failure of the bellows due to long-term fatigue or corrosion. The overall leakage rate of the three compensators was again measured using the flow rate method (mL / min) to examine the redundant sealing capacity of each structure after the failure of the first layer of sealing bellows. The test results are shown in Table 1.

[0147] Table 1 Sealing performance test results

[0148]

[0149] As shown in Table 1, the initial leakage rate of Example 1 was 0.7 mL / min, far lower than that of Comparative Example 3 (14.8 mL / min). The only structural difference between the two is whether the movable connector is chrome-plated. (Comparative Example 3 movable connector surface roughness...) =3.2μm, hardness =180, while Example 1 after chrome plating μm, This difference indicates that the higher the surface roughness of the movable nozzle, the less tightly the sealing packing adheres to its surface. At the same time, the lower surface hardness leads to increased friction between the sealing packing and the pipe wall, causing the packing to wear out faster during reciprocating motion and significantly reducing the initial sealing effect. This demonstrates the decisive influence of chrome plating parameters on the initial sealing performance of the second layer of packing.

[0150] After the bellows was artificially leaked, the overall leakage rate in Example 1 increased only from 0.7 mL / min to 14.2 mL / min, while in Comparative Example 1, with only a single layer of bellows seal, the overall leakage rate increased directly from 1.1 mL / min to 315.6 mL / min, an increase of approximately 22 times. This significant difference indicates that when the bellows failed, the second-layer sealing structure of Example 1—sealing packing + packing ring + guide strip—effectively intercepted most of the steam leakage, while Comparative Example 1 lacked this second-layer sealing protection, allowing steam to leak directly and in large quantities from the gap between the sleeve and the pipe. The second-layer seal, as redundant protection after the main seal fails, can control the leakage within an acceptable range, buying time for online refilling and preventing safety accidents caused by large-scale steam leakage. The mechanism lies in the fact that the sealing packing and packing maintain a continuous radial pressure on the chrome-plated movable joint under compaction, forming a dynamic sealing cavity. Even if the first-layer bellows seal fails, the second-layer packing seal can still maintain the integrity of the sealing cavity.

[0151] Regarding long-term sealing reliability: the 24-hour pressure drop in Example 1 was only 0.02 MPa, while that in Comparative Example 3 was as high as 0.19 MPa, approximately 9.5 times that of Example 1. Comparative Example 3 already exhibited high initial leakage, and packing wear further intensified during long-term operation, leading to a continuous decline in sealing performance. This conclusion further illustrates that chrome plating plays a crucial role in extending the service life of the second layer of seal and maintaining long-term sealing reliability.

[0152] Experiment Example 2: Comparison Experiment of Compensation Performance and Anti-Instability Capability; This experiment uses the compensators of Example 1, Example 2, Example 3, Comparative Example 2 and Comparative Example 4 as test objects, and conducts axial fatigue test, critical instability pressure test, axial stiffness test and flow resistance coefficient determination respectively.

[0153] Axial fatigue test: Under the design pressure conditions of each compensator, axial reciprocating fatigue tests were conducted with a cyclic amplitude of ±50% of the design compensation and a cyclic frequency of 0.5Hz. The cumulative number of cycles until visible cracks or media leakage appeared in the bellows was recorded as the fatigue life unit: cycles. Critical instability pressure test: The external medium pressure was gradually increased under static conditions, and the critical pressure at which the bellows buckled and became unstable was recorded in MPa. For external pressure structures, since the critical pressure exceeded the upper limit of the testing equipment's range, it was recorded as exceeding 3.5MPa without instability. Axial stiffness: Expressed as the ratio of axial load to corresponding displacement under rated compensation, in N / mm. Flow resistance coefficient: The local flow resistance coefficient of steam passing through the compensator was measured using pipeline hydraulic methods. The test results are shown in Table 2.

[0154] Table 2 Test results of compensation performance and instability resistance

[0155]

[0156] As shown in Table 2, the critical instability pressure of Examples 1 to 3 with external pressure structures all exceeded the upper limit of the testing equipment's range of 3.5 MPa, while that of Comparative Example 4 with internal pressure structures was only 2.1 MPa, indicating a significant difference between the two. Under high-pressure steam conditions, the critical instability pressure of the external pressure bellows is much higher than that of the internal pressure bellows of the same specifications, allowing for stable operation at higher working pressures. The physical mechanism is that the internal pressure bellows, under the action of internal pressure, experiences radial force with outward expansion at the corrugations, making it prone to plastic buckling instability; while the corrugations of the external pressure bellows are constrained inward by uniform external pressure, with the external pressure placing each part of the bellows in a mutually supporting stress state, significantly improving its resistance to instability. Essentially, this is the difference in stress state between uniform external pressure constraint and non-uniform internal pressure expansion.

[0157] Example 1 showed a fatigue life of 21,500 cycles, higher than the 15,800 cycles of Comparative Example 4 with an internal pressure structure, indicating that the external pressure structure can effectively extend the fatigue life of the bellows. The fatigue life decreased slightly with increasing pipe diameter, but the fatigue life of each external pressure structure was significantly better than that of the internal pressure structure, proving that the uniform load distribution of external pressure reduced the stress cycle amplitude of the material and reduced local stress concentration, thereby improving fatigue performance. Comparative Example 2 showed a fatigue life of 21,200 cycles, similar to Example 1, indicating that the guide tube has a relatively small direct impact on fatigue life, but its effect on flow resistance is very significant.

[0158] Regarding the function of the flow guide tube: The flow resistance coefficient of Example 1 is 1.10, while the flow resistance coefficient of Comparative Example 2 is as high as 1.62, which is 47% higher. The increase in flow resistance coefficient means that the steam velocity increases under the same flow conditions. The scouring effect of high-speed steam on the outer surface of the bellows is significantly enhanced. Long-term operation will accelerate the thinning and failure of the bellows wall and increase the system energy consumption.

[0159] Experiment Example 3: Comparative Experiment of Precompression Schemes; This experiment compares three schemes: Example 1, Comparative Example 5, and direct installation without precompression. 50 temperature cycle tests were conducted, ranging from 20℃ to 350℃, to comprehensively examine the stress state of the bellows, the stress on the fixed support, and the fatigue life under each precompression scheme.

[0160] Experimental Methods: Each temperature cycle consisted of three stages: heating, reaching 350℃, holding for 30 min, and natural cooling. The heating rate was approximately 5℃ / min. After every 10 cycles, finite element analysis combined with strain gauge measurements was used to obtain the maximum equivalent stress (MPa) of the bellows; simultaneously, the maximum force (kN) on the fixed support was recorded using sensors. After 50 cycles, the residual deformation (mm) of the bellows was measured, and the fatigue life (cycles) was predicted based on the SN fatigue curve and the measured stress amplitude. The test results are shown in Table 3.

[0161] Table 3 Comparison Test Results of Precompression Schemes

[0162]

[0163] As shown in Table 3, the maximum equivalent stress of the bellows in Example 1 with external pressure pre-compression is 178 MPa, compared to 211 MPa in Comparative Example 5 with internal pressure pre-compression of the temporary tie rod (approximately 18% higher), and 318 MPa without pre-compression (approximately 79% higher). The pre-compression amounts for the three schemes are as follows: =54.0mm (inclusive) Corrected factory external pressure pre-compression, =49.5mm None The modified temporary tie rod internal pressure pre-compression and 0mm no pre-compression. The fundamental reason why the pre-compression amount of Example 1 is better than that of Comparative Example 5 is due to the external pressure correction factor. The introduction of the principle: The equivalent axial stiffness of the external pressure bellows is higher than that of the internal pressure bellows of the same specification. If the pre-compression amount is not corrected by external pressure, the stress level of the compensator will be too high throughout the entire operating temperature range. The physical meaning of the precompression value lies in quantitatively correcting the precompression amount based on the stiffness characteristics of the external pressure bellows, ensuring that the compensator remains at a low stress level throughout the entire temperature range. In Example 1, the maximum force on the support is 8.2 kN, compared to 11.5 kN in Comparative Example 5 (approximately 40% higher), and 16.9 kN in the no-precompression scheme (approximately 106% higher). The support stress is directly related to the bellows stress level. The more reasonable the precompression amount, the smaller the elastic reaction force of the bellows during operation, and the smaller the impact load on the fixed support, which helps extend the service life of the support structure and reduce the maintenance cost of the entire pipeline system.

[0164] Regarding residual deformation and fatigue life: After 50 temperature cycles, the residual deformation in Example 1 was only 1.1 mm, compared to 3.8 mm in Comparative Example 5, and as high as 6.2 mm in the no-pre-compression scheme. The predicted fatigue life of Example 1 was 22,000 cycles, approximately 20% lower than the 17,500 cycles in Comparative Example 5, and approximately 49% lower than the 11,200 cycles in the no-pre-compression scheme. The increased residual deformation indicates that the material underwent significant plastic deformation during the cycles, which will accelerate the accumulation of fatigue damage. A larger stress amplitude directly reduces the fatigue life corresponding to the material on the SN curve. The above data collectively demonstrate that the factory-applied external pressure pre-compression installation method used in Example 1 is superior to the traditional temporary tie rod scheme in reducing stress amplitude, minimizing residual plastic deformation, and improving fatigue life, proving the engineering practical value of the factory-applied pre-compression and its installation verification system of this invention.

[0165] Experiment Example 4: Comparative Experiment on the Effect of Online Sealing Packing Replenishment; This experiment uses the compensators of Example 1 and Comparative Example 6 as comparison objects to verify the effectiveness and economy of the online sealing packing replenishment function in handling steam leaks.

[0166] Experimental method: By simulating the wear and aging of the sealing packing, a high-speed reciprocating friction load of 5000 cycles was applied to the second sealing cavity, causing detectable steam leakage in both compensators. The initial leakage rate was approximately 12 mL / min, exceeding the leakage limit specified in this invention. =0.5mL / min, triggering a replenishment or maintenance procedure. For Example 1, follow the procedures described in S7 and the online replenishment protocol: measure the medium pressure at the injection port. =1.6MPa, according to Overpressure coefficient =1.4, frictional pressure difference =0.10MPa Calculation of injection pressure MPa; according to =162mm, =159mm, additional sealing height required. =8mm Calculation of injection volume mm³, inject flexible graphite sealing grease, and continuously monitor changes in leakage rate. Comparative Example 6, lacking an injection hole, was handled according to standard shutdown and maintenance procedures: after the pipeline cooled, the sealing ring was removed, the old sealing material was taken out, the packing and sealing filler were refilled and compacted, the sealing ring was welded back on, and finally, production was resumed by heating. The comparative results are shown in Table 4.

[0167] Table 4 Comparison of Online Sealing Packing Refill Effects

[0168]

[0169] As shown in Table 4, Example 1 reduced the leakage rate from 12.3 mL / min to 0.8 mL / min through online replenishment, restoring it to the leakage limit. The leakage rate was around 0.5 mL / min, indicating a good sealing repair effect. In Comparative Example 6, the leakage rate decreased to 0.9 mL / min after shutdown and maintenance. Both examples achieved similar sealing effects, demonstrating that online replenishment can achieve the same sealing restoration effect as shutdown and maintenance. Example 1 completed online replenishment without interrupting production, taking approximately 30 minutes. Comparative Example 6 required a shutdown of at least 8 hours, including all procedures such as steam pipeline cooling, disassembly, packing replacement, welding, and reheating to resume production. The shutdown time was approximately 16 times that of Example 1, significantly impacting the production system. For continuous production units such as chemical plants and thermal power plants, unplanned shutdowns of steam pipelines mean production interruptions and capacity losses, with the cost of shutdown far exceeding the direct cost of maintenance itself.

[0170] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for installing a double-sealed external pressure bellows compensator for steam, characterized in that, Steam double-seal external pressure bellows compensators include: The system comprises: a movable connector with a chrome-plated outer surface; a fixed connector arranged coaxially opposite to the movable connector; a guide tube installed in the internal channel of the movable and fixed connectors; a first sleeve fitted over the outside of the movable and fixed connectors; a first end ring fixedly connected between the fixed connector and the first sleeve; a plug plate, an annular structure, fitted over and fixedly connected to the movable connector, with its outer edge forming an axially sliding sealing fit with the inner wall of the first sleeve; a bellows located inside the first sleeve, not directly connected to the movable connector, and bearing external medium pressure; a first connecting pipe connecting the plug plate and the bellows; a second end ring fixedly connected to the inner wall of the first sleeve, not connected to the movable connector; and a second connecting pipe connecting the bellows and the second end ring. A ring; a second sleeve, fitted onto the outside of the movable connector, one end of which is fixedly connected to the second end ring; sealing packing and packing, disposed in the sealing cavity between the second sleeve and the movable connector; a sealing ring, fixedly connected to the end of the second sleeve, with a groove on its inner wall; a guide band, embedded in the groove of the sealing ring; the bellows constitutes the first layer of sealing structure, and the sealing packing, packing, sealing ring, and guide band constitute the second layer of sealing structure; the bellows is in a pre-compressed state when the compensator leaves the factory; the working medium inside the first sleeve simultaneously fills the space between the first sleeve and the bellows and the space between the first sleeve and the guide tube, so that the bellows bears uniform external pressure; the axial distance between the plug plate and the first end ring is the factory characteristic distance. Factory pre-compression and All are provided with the product's manufacturing documentation; during pipeline operation, the movable connector moves towards the fixed connector, the plug plate moves accordingly, and through the connecting pipe, the bellows gradually recovers from its pre-compressed state. The distance between the plug plate and the first end ring is... Reduce to , Less than Both connecting pipe one and connecting pipe two are cylindrical transition structures; one end of connecting pipe one is welded to the end face of the plug plate facing the bellows, and the other end is welded to the corresponding end of the bellows; one end of connecting pipe two is welded to the other end of the bellows, and the other end is welded to the end face of the second end ring facing the bellows; the bellows thus does not bear direct welding stress with the movable connecting pipe; the axial arrangement order of the sealing packing and the packing in the sealing cavity is: from the side near the second end ring to the side near the sealing ring, in sequence, packing, sealing packing, packing; the second sleeve pipe wall is provided with injection holes at the axial position corresponding to the sealing packing, the injection holes are evenly distributed along the circumference, and a check valve is installed at each injection hole; the guide band is evenly distributed along the circumference in the groove of the sealing ring. The installation method includes the following steps: S1: Verify the factory characteristic distance recorded in the factory documentation. Compared with factory pre-compression And measure the actual distance between the physical block plate and the first end ring; S2: Precompression adaptation verification; calculate the required precompression amount on site based on the on-site pipeline parameters. According to the factory documentation Compare and determine the installation and treatment plan according to the magnitude of the deviation; S2 includes the following sub-steps: S21: Read the factory pre-compression amount from the factory documentation. Calculate the required precompression amount on site using the following formula. : ； in, The amount of pre-compression required on site; The coefficient of linear expansion of the pipeline; This refers to the actual length of the compensation pipe section; Design operating temperature for the pipeline; The actual ambient temperature at the time of installation; This is the external pressure correction factor, when the design pressure... hour ,when hour ,when hour ; Generate the required pre-compression amount on site ; S22: Calculate the pre-compression adaptation deviation using the following formula. : ； in, For pre-compression adaptation deviation; The factory pre-compression amount provided in the factory documentation; The required precompression amount for the field, calculated using S21; generates the precompression adaptation deviation. ; S23: Based on the maximum compensation amount of the bellows To determine the appropriate treatment plan, the following rules shall be followed: When If the match is deemed good, proceed with installation; if... At that time, a thickness of [missing information] was added to the pipe flange. Adjusting shims, when When the gasket is installed at the fixed end flange, When the gasket is installed at the moving end flange; If the factory pre-compression amount is determined to be incompatible with the site conditions, installation will be refused and a new order will be placed according to the site parameters. S3: Conduct an acceptance inspection of the chrome plating layer on the surface of the movable pipe to confirm that it meets the installation requirements; S4: Weld the two ends of the compensator to the pipeline, and measure the distance between the plug plate and the first end ring after welding. Verify that the axial deviation introduced by welding is within the allowable range; S5: Fill the sealing cavity between the second sleeve and the movable pipe with sealing packing and compact it, and install a check valve at the injection hole. S6: Insert the guide strip into the groove of the sealing ring, press the sealing ring with the guide strip into the end of the sealing cavity and weld it to the second sleeve for fixation; S7: After the pipeline is put into operation, measure the distance between the plug plate and the first end ring under stable working conditions. Calculate the actual compensation amount and the theoretical compensation amount to determine the working status of the compensator; when the steam leakage exceeds the allowable value, inject sealing packing into the sealing cavity online through the injection hole; S7 includes the following sub-steps: S71: After the pipeline reaches a stable operating state, measure the distance between the plug plate and the first end ring. Simultaneously record the measured operating temperature of the pipeline. ; Generate working state feature distance and measured operating temperature ; S72: Calculate the actual compensation amount using the following two formulas respectively. and theoretical compensation amount : ； in, This is the actual compensation amount; The distance of the factory-specific features recorded in the factory documentation; The working state characteristic distance measured by S71; ； in, This is the theoretical compensation amount; The coefficient of linear expansion of the pipeline; This refers to the actual length of the compensation pipe section; The measured operating temperature recorded for the S71; The actual ambient temperature at the time of installation; generating the actual compensation amount. With theoretical compensation ; S73: Calculate the thermal compensation deviation rate using the following formula. : ； in, For thermal compensation deviation rate; The actual compensation amount calculated for S72; The theoretical compensation amount calculated for S72; when When the compensator is deemed to be in normal working condition, it is recorded. Filing; when During the next planned shutdown, check the condition of the fixed supports and guide supports, and re-verify them. ;when Immediately investigate any abnormalities such as failure of fixed supports, release of pipe constraints, and interference between the guide tube and movable connector, and take appropriate measures; when steam leakage is detected... Exceeding the limit At this time, follow these steps to replenish the online sealing packing through the injection hole: Step 1: Measure the medium pressure at the injection port. Determine the injection pressure using the following formula. : ； in, To replenish pressure; The pressure of the medium at the injection hole; This is the overpressure coefficient; To overcome the additional pressure difference required for friction; to generate the injection pressure. ; Step 2: Calculate the required replenishment amount using the following formula. : ； in, This is the amount to be replenished; This refers to the inner diameter of the second sleeve. For the outer diameter of the activity takeover; The height of the seal packing that needs to be replenished; based on the injection pressure. A volume of [volume] is injected into the sealed cavity through the check valve. The sealing material; online replenishment of the sealing filler; Step 3: After the injection is completed, continue to monitor. If the leakage stops, the injection is considered successful. If the leakage does not stop, repeat steps 1 and 2 once. If the leakage is still not eliminated after repeated injection, schedule a work stoppage for maintenance.

2. The installation method according to claim 1, characterized in that, S5 includes the following sub-steps: S51: In the sealing cavity between the second sleeve and the movable connecting pipe, starting from the side closest to the second end ring along the axial direction, packing, sealing filler, and packing are sequentially inserted to ensure that the sealing material is evenly distributed in the circumferential direction of the sealing cavity; forming a sealing material combination to be compacted. S52: Measure and record the total height of the sealing material after S51 is completed. A hydraulic press was used to axially compact the sealing material, and the total height after compaction was measured in real time. Calculate the compression ratio using the following formula. : ； in, For the compression ratio of the sealing material; This refers to the total height of the sealing material before compaction; This is the total height of the sealant after compaction; The content is controlled within the range of 20% to 30%; a sealing filler layer with pre-tight sealing force is formed. S53: At the axial position of the sealing packing corresponding to the second casing wall, injection holes are drilled evenly along the circumference, and check valves are installed at each injection hole. The opening pressure of the check valves is higher than the working pressure of the pipeline; thus forming an injection channel for online replenishment of sealing packing.

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