Fluoroplastic expansion joint for low-temperature flue and preparation method of fluoroplastic expansion joint

Abstract

The invention belongs to the technical field of flue compensation devices, and discloses a fluoroplastic expansion joint for a low-temperature flue and a preparation method of the fluoroplastic expansion joint. The expansion joint comprises a core compensation unit and an external protection unit. The core compensation unit is fixed between the flues, and the outer protection unit wraps the outer side of the core compensation unit and is fixed to the outer walls of the flues. The expansion joint is excellent in low-temperature performance, high in corrosion resistance, reliable in protection performance, good in sealing performance, simple in structure and convenient to maintain.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flue compensation devices, and particularly relates to a fluoroplastic expansion joint for low-temperature flues and a preparation method thereof. BACKGROUND

[0002] In the industrial production processes of metallurgy, chemical industry, electric power and the like, low-temperature flue systems are widely used for conveying low-temperature flue gas (such as liquefied natural gas combustion tail gas, chemical synthesis low-temperature tail gas and the like). Due to the fact that the low-temperature flue will generate a large temperature change when starting and stopping or when the working condition fluctuates, the flue will expand and contract due to heat, and if this deformation cannot be effectively compensated, a large thermal stress will be generated in the flue, thereby causing potential safety hazards such as flue joint leakage, flue bending deformation and even flue rupture. Therefore, as a key compensation component in the flue system, the performance of the expansion joint directly affects the safe and stable operation of the entire flue system.

[0003] At present, the expansion joints commonly used in the industry are mostly metal bellows expansion joints, which are mainly composed of a metal bellows, flanges and a flow guide cylinder and the like, and the elastic deformation of the metal bellows is used to absorb the thermal expansion and contraction of the flue. However, under the working condition of the low-temperature flue, the metal bellows expansion joint has many technical defects: firstly, the metal material (such as stainless steel, carbon steel) is prone to low-temperature embrittlement in a low-temperature environment (especially below -100 DEG C), which causes the toughness of the bellows to decrease, and cracks are easily generated when the bellows is subjected to external force or thermal stress, thereby seriously affecting the service life; secondly, the flue gas in the low-temperature flue often contains acidic media (such as HCl, SO2 and the like) or corrosive gases, and the metal bellows is prone to corrosion failure, which causes the sealing performance to decrease and flue gas leakage problems to occur; in addition, the structure of the metal bellows expansion joint is complex, the manufacturing process is high in requirement, the cost is high, and the maintenance is difficult, and once the bellows is damaged, the entire bellows needs to be replaced, thereby increasing the operating cost of the enterprise.

[0004] In order to solve the above problems, the industry attempts to use non-metallic materials to replace metal materials to prepare expansion joints. PTFE (polytetrafluoroethylene) and PFA (perfluoroalkoxy resin) are high-performance fluoroplastics, which have excellent low-temperature toughness, corrosion resistance and chemical stability, can still maintain good elasticity and toughness in a low-temperature environment of -200 DEG C, and have strong resistance to various acid-base media and corrosive gases, and are ideal materials for preparing low-temperature flue expansion joints. However, the mechanical strength of PTFE and PFA materials is relatively low, and in the process of operation of the flue system, the materials are prone to damage due to external impact, collision with foreign matters or flue vibration, thereby limiting the application of the materials in the flue expansion joint.

[0005] Therefore, it is of great significance to research a fluoroplastic expansion joint for low-temperature flues and a preparation method thereof, which has a simple structure, reliable performance and long service life. SUMMARY

[0006] The purpose of this invention is to provide a fluoroplastic expansion joint for low-temperature flue gas and its preparation method, thereby solving the problems of traditional metal corrugated expansion joints being prone to low-temperature brittle cracking, corrosion failure, and high maintenance costs under low-temperature flue gas conditions.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a fluoroplastic expansion joint for low-temperature flues, the expansion joint comprising a core compensation unit and an external protection unit; The core compensation unit is fixed between the flues, and the external protection unit covers the outside of the core compensation unit and is fixed to the outer wall of the flue.

[0008] Preferably, the core compensation unit is made of polytetrafluoroethylene or perfluoroalkoxy resin, with a density of 2.1~2.3 g / cm³. 3 ; The external protective unit is made of 2205 duplex stainless steel wire mesh with a wire diameter of 0.3~0.5mm, a mesh size of 8~12 meshes, and a serration width of 15~25mm.

[0009] Preferably, the core compensation unit is fixed by flange connection or welding; The outer protective unit is covered by a locking edge process; The external protective unit is fixed to the outer wall of the flue by a clamping assembly; The clamping assembly includes a pressure plate, bolts, and nuts. The pressure plate is made of 2205 stainless steel or carbon steel and has a thickness of 8-12 mm. An elastic gasket is provided on the inner side of the pressure plate. The elastic gasket is made of fluororubber or soft PTFE and has a thickness of 3-5 mm.

[0010] This invention also provides a method for preparing a fluoroplastic expansion joint for low-temperature flues, the method comprising the following steps: 1) Core compensation unit preparation: Cut the ring plate into the corresponding size according to the diameter of the flue, chamfer the inner and outer edges of the ring plate, and then preheat the ring plate. 2) External protection unit preparation: Cut the wire mesh according to the dimensions of the core compensation unit; 3) Assembly: Connect the preheated core compensation unit to the flue, then cover the outside of the core compensation unit with the outer protective unit and leave a buffer gap. Then install the clamping components at both ends of the outer protective unit and control the pressure of the clamping components. 4) The assembled expansion joints are cured and cooled sequentially to obtain fluoroplastic expansion joints.

[0011] Preferably, in step 1), the cutting process is laser cutting, the precision of laser cutting is -0.2~0.2mm, and the roughness of the cut surface is ≤0.8μm.

[0012] Preferably, in step 1), the chamfering process has an angle of 45° and a radius of 2-3 mm; the preheating process has a temperature of 80-150°C and a time of 2-3 hours.

[0013] Preferably, in step 3), the installation clamping assembly is installed by bolts, and the bolt installation is tightened by a symmetrical step-by-step tightening method, which is completed in 3 times, with each tightening torque being 5~8 N·m, 12~15 N·m and 15~20 N·m respectively.

[0014] Preferably, in step 3), the buffer gap is 3~5mm and the pressure of the clamping component is 15~20 N·m.

[0015] Preferably, in step 4), the curing temperature is 120~150℃, the curing time is 4~6h, and the cooling temperature is 20~30℃.

[0016] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects: (1) Excellent low temperature performance: The core compensation unit uses PTFE (or PFA) sheet material, which can maintain good elasticity and toughness in the range of -200~150℃, completely solving the problem of low temperature brittleness of traditional metal corrugated expansion joints, and is suitable for various low temperature flue working conditions; (2) Strong corrosion resistance: PTFE (or PFA) material has extremely strong resistance to acid and alkali media and corrosive gases. The external protection unit also has excellent corrosion resistance, which can effectively resist the erosion of corrosive media in low temperature flue and extend the service life of expansion joint. (3) Reliable protection performance: The external protection unit covers the outside of the core compensation unit, which can effectively resist the damage to the PTFE (PFA) sheet caused by external impact, foreign object collision and flue vibration. At the same time, the locking edge process ensures the integrity of the wire mesh and avoids wire breakage.

[0017] (4) Simple structure and convenient maintenance: The corrugated (or single or multi-corrugated) structural design simplifies the structure of the expansion joint, reducing manufacturing difficulty and cost; the core compensation unit and the protection unit can be replaced separately, with low maintenance cost and a simple and quick replacement process. The working part is corrosion resistant, and the excellent wear resistance of fluoroplastics can effectively reduce wear. It has high flexibility and plasticity (after heating), and damaged parts can be repaired by welding (or by using Teflon tape) without the need for overall replacement. Fluoroplastic plates are easy to drill holes in, and the dimensions can be adjusted on-site.

[0018] (5) Good sealing performance: Through the cooperation of the sealing groove and PTFE sealing packing, and the setting of elastic gaskets in the compression assembly, the sealing performance of the expansion joint is effectively improved, preventing low-temperature flue gas leakage and ensuring the safe operation of the flue system. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the fluoroplastic expansion joint for low-temperature flue gas ducts of the present invention. Detailed Implementation

[0021] This invention provides a fluoroplastic expansion joint for low-temperature flues, the expansion joint comprising a core compensation unit and an external protection unit; The core compensation unit is fixed between the flues, and the external protection unit covers the outside of the core compensation unit and is fixed to the outer wall of the flue.

[0022] In this invention, the core compensation unit is preferably made of polytetrafluoroethylene or perfluoroalkoxy resin, and the material density is preferably 2.1~2.3 g / cm³. 3 More preferably, it is 2.15~2.25 g / cm³. 3 More preferably 2.2 g / cm³ 3 ; The material of the external protective unit is preferably 2205 duplex stainless steel overlock wire mesh, the wire diameter is preferably 0.3~0.5mm, more preferably 0.35~0.45mm, and even more preferably 0.4mm, the mesh size is preferably 8~12 meshes, more preferably 9~11 meshes, and even more preferably 10 meshes, and the overlock width is preferably 15~25mm, more preferably 18~24mm, and even more preferably 20~22mm.

[0023] In this invention, the connection surface between the core compensation unit and the flue is preferably provided with a sealing groove, the sealing groove is filled with polytetrafluoroethylene sealing filler, the depth of the sealing groove is preferably 3~5mm, more preferably 3.5~4.5mm, more preferably 4mm, and the width of the sealing groove is preferably 3~5mm, more preferably 3.5~4.5mm, more preferably 4mm. The sealing groove is preferably pressed by a mechanical drum press.

[0024] In this invention, the tensile strength of the polytetrafluoroethylene or perfluoroalkoxy resin is preferably ≥20MPa, more preferably ≥22MPa, and even more preferably ≥25MPa; the elongation at break is preferably ≥300%, more preferably ≥320%, and even more preferably ≥350%; it does not exhibit brittleness at a low temperature of -200℃; and its acid and alkali corrosion resistance meets the requirements of GB / T 17632-1998 standard.

[0025] In this invention, the thickness of the core compensation unit is preferably 5mm. The thickness selection can ensure sufficient elastic deformation capacity to absorb the thermal expansion and contraction of the flue, and also provide a certain structural strength to avoid excessive deformation or damage due to excessive thickness.

[0026] In this invention, the tensile strength at the edge of the 2205 duplex stainless steel overlock wire mesh is preferably ≥300MPa, more preferably ≥310MPa, and even more preferably ≥320MPa, and the coverage of the overlock wire mesh is preferably 100%.

[0027] In this invention, the 2205 duplex stainless steel is a high-performance material that combines the advantages of austenitic and ferritic stainless steels. It has high strength, high toughness, excellent corrosion resistance and fatigue resistance, and its tensile strength can reach 480~620MPa. It can still maintain good mechanical properties in low-temperature environments. Using 2205 duplex stainless steel wire mesh as a protective structure to cover the outside of PTFE (PFA) sheet can effectively improve the impact resistance and structural stability of the expansion joint, while not affecting the elastic deformation capability of the core compensation unit.

[0028] In this invention, the edge-locking process can effectively prevent the wire mesh from coming loose at the edges, improving the overall integrity of the protective structure; the reserved buffer gap can ensure that the core compensation unit is not bound by the wire mesh when it undergoes elastic deformation, and at the same time, the gap can play a buffering role when subjected to external impact, protecting the core compensation unit.

[0029] In this invention, the preferred method for fixing the core compensation unit is flange connection or welding; The preferred method for covering the external protective unit is a locking edge process; The external protective unit is preferably fixed to the outer wall of the flue by a clamping assembly; The clamping assembly preferably includes a pressure plate, bolts, and nuts. The pressure plate is preferably made of 2205 stainless steel or carbon steel, and its thickness is preferably 8-12 mm, more preferably 9-11 mm, and even more preferably 10 mm. An elastic gasket is provided on the inner side of the pressure plate. The elastic gasket is preferably made of fluororubber or soft PTFE, and its thickness is preferably 3-5 mm, more preferably 3.5-4.5 mm, and even more preferably 4 mm.

[0030] In this invention, the elastic gasket can effectively alleviate stress concentration when the bolt is tightened, while improving the sealing performance and preventing flue gas from leaking from the gap between the pressure plate and the flue.

[0031] In this invention, the combination of the sealing groove and the PTFE sealing filler can significantly improve the sealing performance of the connection and prevent low-temperature flue gas leakage.

[0032] This invention also provides a method for preparing a fluoroplastic expansion joint for low-temperature flues, the method comprising the following steps: 1) Core compensation unit preparation: Cut the ring plate into the corresponding size according to the diameter of the flue, chamfer the inner and outer edges of the ring plate, and then preheat the ring plate. 2) External protection unit preparation: Cut the wire mesh according to the dimensions of the core compensation unit; 3) Assembly: Connect the preheated core compensation unit to the flue, then cover the outside of the core compensation unit with the outer protective unit and leave a buffer gap. Then install the clamping components at both ends of the outer protective unit and control the pressure of the clamping components. 4) The assembled expansion joints are cured and cooled sequentially to obtain fluoroplastic expansion joints.

[0033] In this invention, in step 1), the cutting process is preferably laser cutting, the laser cutting precision is preferably -0.2~0.2mm, more preferably -0.15~0.15mm, and even more preferably -0.1~0.1mm, and the roughness of the cut surface is preferably ≤0.8μm, more preferably ≤0.7μm, and even more preferably ≤0.6μm.

[0034] In this invention, in step 1), the chamfering process preferably has an angle of 45° and a radius of 2-3 mm, more preferably 2.2-2.8 mm, and even more preferably 2.5-2.6 mm; the preheating process preferably has a temperature of 80-150°C, more preferably 100-140°C, and even more preferably 120-130°C, and a time of 2-3 h, and even more preferably 2.5 h.

[0035] In this invention, in step 1), the laser cutting process can ensure cutting accuracy, the chamfering treatment can avoid stress concentration caused by sharp edges, and the preheating treatment can remove moisture from the board and prevent moisture from freezing under low temperature conditions, thus affecting the sealing performance. The preheating treatment can remove moisture from the inside of the board.

[0036] In this invention, in step 1), for larger expansion joints, if on-site preparation is required, a ruler and a paper cutter can be used for cutting, and the chamfer can be ground to the required angle using a flap wheel; when heat-treated fluoroplastic sheets are used, or when the flue gas pressure is ≤5KPa, the heating and curing process after molding is omitted and natural curing is used instead.

[0037] In this invention, during the preparation of the core compensation unit in step 1), the sheet material can be set with a "V" shaped slope according to the shrinkage amount.

[0038] In this invention, in step 3), the installation and clamping assembly is installed by bolts. The bolts are tightened using a symmetrical step-by-step tightening method, which is completed in three steps. The tightening torque for each step is preferably 5~8 N·m, 12~15 N·m and 15~20 N·m, more preferably 6~7 N·m, 13~14 N·m and 16~19 N·m, and even more preferably 6~7 N·m, 13~14 N·m and 17~18 N·m.

[0039] In this invention, the center-to-center spacing of the bolts used for bolt installation is preferably ≤100mm, more preferably ≤95mm, and even more preferably ≤90mm.

[0040] In this invention, in step 3), the symmetrical step-by-step tightening method can ensure that the flange is subjected to uniform force and avoid deformation of the core compensation unit due to uneven force.

[0041] In this invention, in step 3), the buffer gap is preferably 3~5mm, more preferably 3.5~4.5mm, and even more preferably 4mm, and the pressure of the clamping assembly is preferably 15~20 N·m, more preferably 16~19 N·m, and even more preferably 17~18 N·m.

[0042] In this invention, in step 4), the curing temperature is preferably 120~150℃, more preferably 125~145℃, and even more preferably 130~140℃; the curing time is preferably 4~6h, more preferably 4.5~5.5h, and even more preferably 5h; and the cooling temperature is preferably 20~30℃, more preferably 22~28℃, and even more preferably 24~26℃.

[0043] In this invention, in step 4), the curing process allows the PTFE sealing filler to fully adhere to the connection surface, improving sealing performance and connection strength.

[0044] In this invention, in step 4), after cooling, it is preferable to perform performance testing on the cooled component. If the performance test meets the requirements, it is considered qualified. If the test fails, the defective part is repaired, and the performance test is performed again until it meets the design requirements. The performance detection preferably includes airtightness detection, low-temperature toughness detection, and tensile strength detection; The airtightness detection adopts the air pressure method. There is no leakage after maintaining the pressure for 30 minutes. The test pressure is preferably 0.3~0.5 MPa, more preferably 0.35~0.45 MPa, and even more preferably 0.4 MPa; The low-temperature toughness detection is preferably carried out in an environment of -200 °C, and there are no cracks after repeated stretching and compression for 50 times; The tensile strength detection uses a tensile testing machine. The tested tensile strength ≥ 20 MPa, and it is qualified if it meets the design requirements.

[0045] The technical solutions provided by the present invention will be described in detail below in conjunction with embodiments, but they cannot be understood as limiting the protection scope of the present invention.

[0046] Embodiment 1 In this embodiment, the flue is a large-diameter rectangular low-temperature flue of 3000×5000 mm, which is adapted to the low-temperature acidic flue gas flues in the metallurgy and power industries. The working condition temperature is -15~180 °C, and the medium contains sulfur and nitrate mixed acid gas, solving the problems of low-temperature brittle fracture, corrosion and leakage of traditional metal expansion joints.

[0047] Core parameters of the expansion joint: Core compensation unit: PTFE plate with a thickness of 5 mm, density = 2.25 g / cm 3 , tensile strength 23 MPa, elongation at break 360%, no brittle fracture at -200 °C, acid and alkali resistance meets the requirements of GB / T 17632-1998 standard; External protection unit: 2205 duplex stainless steel lock-edge wire mesh, wire diameter 0.45 mm, mesh size 11 meshes, lock-edge width 2 mm, lock-edge tensile strength 325 MPa, coating coverage rate 100%, with a 4 mm buffer gap reserved between the fluoroplastics board; The pressing component uses a 2205 stainless steel pressing plate (thickness 11 mm) + 4 mm soft PTFE gasket; it is fixed between the flues by flange connection.

[0048] Preparation steps: Preparation of the core compensation unit: The PTFE plate is laser cut into a 3000×5000 mm ring, and chamfering treatment is carried out (45° chamfering at the inner and outer edges, radius 2.8 mm), the laser cutting accuracy is ±0.18 mm, and the roughness Ra = 0.7 μm; then it is heat treated at 130 °C for 2.8 h to remove the internal moisture of the plate; Preparation of the external protection unit: 2205 steel wire is woven into an 11-mesh wire mesh, cut to fit the size, and locked with a lock-edge machine for 25 mm, without wire breakage or skipping; Assembly: After preheating, the PTFE unit is placed between the flue flanges. The flange end face is sealed with sealant to fix the sealing gasket. The bolts are tightened symmetrically in steps (torque 7 N·m, 13 N·m, 19 N·m); wire mesh is wrapped to ensure a 4 mm buffer gap, and pressure plate gaskets are installed at both ends with a tightening torque of 19 N·m. Curing: The sealant cures naturally for 24 hours under flue gas pressure less than 5 kPa and without any other external temperature interference.

[0049] Performance testing: No leakage after holding at 0.45MPa for 30 minutes; no cracks after repeated stretching and compression 50 times at -200℃; no corrosion after acid immersion for 72 hours, thus passing the test.

[0050] Application results: After 10 months of use, the displacement compensation is accurate, with no corrosion, damage, or leakage, and it is suitable for the thermal expansion and contraction requirements of large-diameter rectangular flues.

[0051] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A fluoroplastic expansion joint for low temperature flues, characterized in that, The expansion joint comprises a core compensation unit and an external protection unit. The core compensation unit is fixed between flues, and the external protection unit is wrapped outside the core compensation unit and fixed with the outer wall of the flue.

2. A cryogenic flue fluoroplastic expansion joint as claimed in claim 1, wherein The material of the core compensation unit is polytetrafluoroethylene or perfluoroalkoxy resin, and the density of the material is 2.1-2.3 g / cm 3 ; The material of the external protection unit is 2205 double-phase stainless steel lock edge wire mesh, the wire diameter is 0.3-0.5 mm, the mesh size is 8-12 meshes, and the lock edge width is 15-25 mm.

3. A cryogenic flue fluoroplastic expansion joint according to claim 2, wherein The fixing method of the core compensation unit is flange connection or welding. The wrapping method of the external protection unit is a lock edge process. The external protection unit is fixed with the outer wall of the flue by a pressing assembly. The pressing assembly comprises a pressing plate, a bolt and a nut, the material of the pressing plate is 2205 stainless steel or carbon steel, the thickness of the pressing plate is 8-12 mm, an elastic gasket is arranged on the inner side of the pressing plate, the material of the elastic gasket is fluorine rubber or soft fluorine, and the thickness of the elastic gasket is 3-5 mm.

4. A process for the production of a fluoroplastic expansion joint for low-temperature flues according to any one of claims 1 to 3, characterized in that, The preparation method comprises the following steps: 1) core compensation unit preparation: cutting a ring-shaped plate according to the caliber of the flue, chamfering the inner and outer edges of the ring-shaped plate, and then preheating the ring-shaped plate; 2) external protection unit preparation: cutting a wire mesh according to the size of the core compensation unit; 3) assembly: connecting the preheated core compensation unit to the flue, wrapping the external protection unit outside the core compensation unit, reserving a buffer gap, and installing a pressing assembly at both ends of the external protection unit and controlling the pressure of the pressing assembly; 4) sequentially solidifying and cooling the assembled expansion joint to obtain a fluoroplastic expansion joint.

5. The process for the production of fluoroplastic expansion joint for low temperature flue gas duct as claimed in claim 4 wherein, In step 1), the cutting process is laser cutting, the precision of laser cutting is-0.2-0.2 mm, and the roughness of the cutting surface is ≤0.8 μm.

6. The process for the production of fluoroplastic expansion joint for cryogenic flue duct according to claim 5, characterized in that, In step 1), in the chamfering process, the angle is 45° and the radius is 2-3 mm; in the preheating process, the temperature is 80-150℃ and the time is 2-3 h.

7. The process for the production of fluoroplastic expansion joint for low temperature flue gas duct as claimed in claim 4 wherein, In step 3), the pressing assembly is installed by bolt installation, the tightening of the bolt installation adopts a symmetric step-by-step tightening method, and the tightening torque is completed in 3 times, and the tightening torque is 5-8 N·m, 12-15 N·m and 15-20 N·m in turn.

8. The process for the production of a cryogenic flue fluoroplastic expansion joint according to claim 7, characterized in that, In step 3), the buffer gap is 3-5 mm, and the pressure of the pressing assembly is 15-20 N·m.

9. The process for the production of fluoro-plastic expansion joint for low temperature flue gas duct as claimed in claim 4 wherein, In step 4), the solidification temperature is 120-150℃, the solidification time is 4-6 h, and the cooling temperature is 20-30℃.

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