Novel stud suitable for medium-pressure steam generator outlet flange ring stud

Abstract

The invention relates to the technical field of fastening connection of high-temperature pressure equipment, in particular to a novel stud suitable for an outlet flange ring stud of a medium-pressure steam generator, which mainly comprises a stud body made of a high-temperature alloy material; the axial center hole penetrates through the stud body; the counter bore type inner polygonal driving part is arranged at one end of the stud body and is used for being matched with a corresponding driving tool; wherein the thread surface of the stud body is coated with a high-temperature anti-seizure lubricant layer. According to the invention, high-temperature alloys such as NiCr20TiAl and the like are adopted, and a specific heat treatment process is combined, so that the stud can still keep high strength, low creep rate and excellent oxidation resistance at 480 DEG C or even higher temperature, and the probability of adhesion is reduced fundamentally; by means of the design of the axial center hole, an induction heating rod or a liquid nitrogen cooling guide pipe is allowed to be involved, initial pre-tightening force is provided or threaded engagement is rapidly relieved according to the principle of thermal expansion and cold contraction, non-destructive disassembly of the stud is achieved, and then the disassembly time of a single stud is greatly shortened.

Description

Technical Field

[0001] This application relates to the field of fastening connection technology for high-temperature and high-pressure equipment, and in particular to a novel stud suitable for threading the outlet flange of a medium-pressure steam generator. Background Technology

[0002] In coal chemical and petrochemical industries, the medium-pressure steam generator, a key piece of equipment in methanol-to-olefins (MTO) plants, often uses threaded double-ended studs for its outlet flange connection. The tube-side medium temperature of this equipment reaches as high as 480℃ and requires long-term continuous operation.

[0003] In existing technologies, this connection typically uses standard solid double-ended studs made of ordinary alloy steel, which often suffers from the following significant drawbacks: Under continuous high temperature and pressure conditions, the stud material is prone to creep, and severe adhesion (commonly known as "seizing") occurs between the threaded pairs due to oxidation, fretting wear, and other reasons. This means that during each planned maintenance, most studs cannot be disassembled using conventional torque tools, such as hydraulic wrenches, and are forced to be removed using destructive methods such as drilling and flame cutting. This process is not only extremely time-consuming but also damages the female threads on the flange body. Although repairs are possible, repeated tapping will lead to failure of the connection pair, seriously threatening the inherent safety and long-term operation of the equipment, and causing huge maintenance costs and production delays. Summary of the Invention

[0004] This application provides a novel stud suitable for threaded bolts on the outlet flange ring of a medium-pressure steam generator, in order to solve the problems in the prior art where traditional flange threaded bolts used at the outlet of steam generators, heat exchangers and other equipment are prone to creep and oxidation, leading to difficult disassembly, high replacement costs, and secondary damage to the equipment body.

[0005] This application provides a novel stud suitable for ring threading on the outlet flange of a medium-pressure steam generator. The stud is a double-ended stud, comprising: The stud body is made of high-temperature alloy material; An axial center hole penetrates the stud body; A countersunk-hole type internal polygonal drive unit is disposed at one end of the stud body and is used to cooperate with the corresponding drive tool; The threaded surface of the stud body is coated with a high-temperature anti-seize lubricant layer.

[0006] Preferably, the high-temperature alloy material is NiCr20TiAl high-temperature alloy bar stock, and its chemical composition by mass percentage includes: Carbon (C): 0.04-0.10%; Chromium (Cr): 18.00-21.00%; Titanium (Ti): 1.80-2.70%; Aluminum (Al): 1.00-1.80%; Silicon (Si) ≤1.00%, Manganese (Mn) ≤1.00%, Phosphorus (P) ≤0.020%, Sulfur (S) ≤0.015%, Nickel (Ni) ≥65.00%, Copper (Cu) ≤2.00%, Cobalt (Co) ≤2.00%, Boron (B) ≤0.006%, with the balance being Iron (Fe) and unavoidable impurities.

[0007] Preferably, the stud body undergoes solution treatment and precipitation hardening heat treatment, wherein: The solution treatment is performed by heating the NiCr20TiAl rod to 1050-1080℃ and then air cooling it. The precipitation hardening treatment is as follows: after the NiCr20TiAl rod is cooled to 840-860℃ in air, it is kept at 840-860℃ for 24 hours and then air-cooled, and then kept at 690-710℃ for 16 hours and then air-cooled.

[0008] Preferably, the countersunk-hole type polygonal driving part is any one of the inner triangular or inner octagonal countersunk holes.

[0009] Preferably, the countersunk-hole polygonal drive part is a countersunk-hole hexagonal structure, the depth of the countersunk-hole hexagonal structure is 35-50% of the length of the stud body, and the depth of the countersunk-hole hexagonal structure is not less than 120mm.

[0010] Preferably, the surface roughness Ra of the hole wall of the axial center hole is ≤3.2μm, and a smooth transition is formed at the intersection of the bottom of the countersunk inner polygonal drive part and the axial center hole.

[0011] Preferably, the axial center hole is a standard through hole, and the diameter of the axial center hole is 15-40% of the nominal diameter of the stud body.

[0012] Preferably, the axial central through hole is a tapered through hole that is larger at the top and smaller at the bottom, with the end furthest from the countersunk inner polygonal drive part being the smaller diameter end; The diameter of the large-diameter end of the axial center through hole is less than or equal to 40% of the nominal diameter of the stud body, and the diameter of the small-diameter end is greater than or equal to 15% of the nominal diameter of the stud body.

[0013] Preferably, when the axial central through hole is a tapered through hole that is larger at the top and smaller at the bottom, a matching filler is inserted into it, and the filler and the axial central through hole are interference fit. The filler is also provided with a hook-shaped / ring-shaped part at one end near the inner polygonal drive part of the countersunk hole, for easy removal later.

[0014] Preferably, the high-temperature anti-seize lubricant is a silver-based anti-seize agent.

[0015] The beneficial effects of this application are as follows: This application presents a novel stud suitable for threaded rings on outlet flanges of medium-pressure steam generators. By employing high-temperature alloys such as NiCr20TiAl and combining them with specific heat treatment processes, the stud maintains high strength, low creep rate, and excellent oxidation resistance even at temperatures of 480℃ or higher, fundamentally reducing the probability of adhesion. Through the axial center hole design, an induction heating rod or liquid nitrogen cooling conduit can be inserted to provide initial preload or quickly release thread engagement using the principle of thermal expansion and contraction, achieving non-destructive disassembly of the stud and significantly improving the disassembly time of a single stud.

[0016] Furthermore, the countersunk-hole polygonal drive unit, with sufficient design depth, allows for efficient and reliable disassembly and assembly operations from the inside out using the appropriate internal angle wrench, even in confined spaces around the equipment flange or when external corrosion makes it difficult to use general clamps for clamping. This greatly improves maintenance efficiency and safety. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 A schematic diagram of the structure of one embodiment of the novel stud provided in this application; Figure 2 for Figure 1 Side view of the new type of stud; Figure 3 A schematic diagram of another embodiment of the novel stud provided in this application.

[0019] Figure label: 1. Stud body; 2. Axial center hole; 3. Countersunk internal polygonal drive part; 4. Filler. Detailed Implementation

[0020] The technical solutions of this application will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0021] The following is combined with Figures 1-3 This application describes a novel stud suitable for threading rings on the outlet flange of a medium-pressure steam generator, as provided in the embodiments of this application.

[0022] Reference Figure 1-3 As shown in the embodiment of this application, a novel stud suitable for threading rings on the outlet flange of a medium-pressure steam generator is provided. It is a double-ended stud, mainly comprising a stud body made of high-temperature alloy material, an axial central hole penetrating the stud body, and a countersunk-type internal polygonal drive part disposed at one end of the stud body for cooperating with a corresponding internal angle drive wrench. The countersunk-type internal polygonal drive part can be any one of internal triangular or internal octagonal countersunk holes, preferably internal hexagonal countersunk holes. The length of the countersunk-type internal polygonal drive part is 35% to 50% of the length of the stud body, and not less than 120 mm, to ensure that the corresponding wrench can be inserted to a certain depth and the torque can be fully applied to the stud body.

[0023] The countersunk-hole internal polygonal drive unit, combined with sufficient design depth, enables efficient and reliable disassembly and assembly operations from the inside out using the appropriate internal angle wrench, even in confined spaces around the equipment flange or when external corrosion makes it difficult to use general clamps for clamping. This greatly improves maintenance efficiency and safety.

[0024] Among them, the end of the stud body away from the countersunk inner polygonal drive part is the pre-screwed end of the equipment. In the specific application process, the thread length of the threaded end needs to be optimized to match the thread hole depth of the equipment flange and disperse the stress at the root of the thread. The threaded surface of the stud body is also coated with a high-temperature anti-seize lubricant layer formed by a silver-based anti-seize agent.

[0025] In some specific embodiments, the high-temperature alloy material is NiCr20TiAl high-temperature alloy bar stock, and the stud body is made of NiCr20TiAl high-temperature alloy bar stock. The chemical composition of this material must be strictly controlled within the range of: C: 0.04-0.10%, Cr: 18.00-21.00%, Ni≥65.00%, Ti: 1.80-2.70%, Al: 1.00-1.80% according to manufacturing standards, to ensure that it has excellent creep resistance, oxidation resistance and good resistance to hydrogen sulfide corrosion below 815℃. Specifically, its chemical composition, by mass percentage, includes: Carbon (C): 0.04-0.10%; Chromium (Cr): 18.00-21.00%; Titanium (Ti): 1.80-2.70%; Aluminum (Al): 1.00-1.80%; Silicon (Si) ≤1.00%, Manganese (Mn) ≤1.00%, Phosphorus (P) ≤0.020%, Sulfur (S) ≤0.015%, Nickel (Ni) ≥65.00%, Copper (Cu) ≤2.00%, Cobalt (Co) ≤2.00%, Boron (B) ≤0.006%, with the balance being Iron (Fe) and unavoidable impurities.

[0026] In addition, in applications with relatively low temperatures or where cost control is more stringent, the material of the stud body 1 can be replaced by materials with relatively low creep resistance, oxidation resistance and hydrogen sulfide corrosion resistance, such as 25CrMoVA.

[0027] In some specific embodiments, the stud body undergoes solution treatment and precipitation hardening heat treatment. The solution treatment involves heating the NiCr20TiAl rod to 1050-1080°C and then air cooling it for 1-2 hours. The precipitation hardening treatment is as follows: after the NiCr20TiAl bar stock is cooled to 840-860℃ in air, it is kept at 840-860℃ for 24 hours and then air-cooled, and then kept at 690-710℃ for 16 hours and then air-cooled to room temperature.

[0028] By using high-temperature alloys such as NiCr20TiAl and combining them with specific heat treatment processes, the studs can maintain high strength, low creep rate and excellent oxidation resistance even at temperatures of 480℃ or higher, thereby reducing the probability of adhesion from the source.

[0029] In some specific embodiments, the surface roughness Ra of the axial center hole wall is ≤3.2μm, and the bottom of the countersunk inner polygonal drive part and the intersection of the axial center hole are smoothly transitioned with rounded corners to reduce stress concentration.

[0030] In some specific embodiments, the axial center hole is a standard through hole or a tapered through hole that is larger at the top and smaller at the bottom, and the diameter of the axial center hole is 15-40% of the nominal diameter of the stud body.

[0031] When the axial center hole is a tapered through hole, the end furthest from the countersunk inner polygonal drive part is the small diameter end, and the diameter of the large diameter end is less than or equal to 40% of the nominal diameter of the stud body, while the diameter of the small diameter end is greater than or equal to 15% of the nominal diameter of the stud body.

[0032] The design of opening an axial center hole 2 provides a channel for subsequent operations. When the studs stick together, a cooling medium such as liquid nitrogen can be injected into the hole, or a heating rod can be inserted. By utilizing the difference in the thermal expansion coefficients of the studs and flange materials, the "thermal expansion and contraction" effect can be achieved, thus easily achieving non-destructive disassembly instead of time-consuming and labor-intensive destructive removal operations.

[0033] Example 1: As Figure 1 and Figure 2 As shown in the embodiment of this application, a novel stud is provided for the outlet flange of the medium-pressure steam generator (E101) in an MTO unit. The stud is a double-ended stud with a total length L of 420 mm and a nominal diameter of M56, i.e., D=56 mm.

[0034] Specifically, the stud body 1 is made of NiCr20TiAl high-temperature alloy bar. First, the bar is heated to 1050-1080℃, held at that temperature for 1.5 hours, and then air-cooled for solution treatment. Then, it is held at 840-860℃ for 24 hours and air-cooled, and then held at 690-710℃ for 16 hours and air-cooled to complete precipitation hardening, so as to obtain the best microstructure and high-temperature performance.

[0035] An axial center hole 2 is machined along the axis of the stud body 1, penetrating the entire body. This axial center hole is a standard through hole with the same diameter as the stud body 1, which is 22mm (approximately 39% of the nominal diameter), i.e., d=22mm. In this embodiment, 22mm is chosen to avoid damaging the load-bearing structure of the stud itself while making it compatible with a common 20mm induction heating rod on the market. The hole wall needs to be finely machined to control the surface roughness Ra below 3.2μm to ensure that the inner wall is smooth.

[0036] In addition, a countersunk hexagonal drive section is machined on the fastening end face of the stud. The countersunk depth is designed to be 192mm, which is about 45.7% of the stud length. This meets the requirement of not less than 120mm and sufficient depth, while also conforming to the GB / T 5356-2021 standard. This allows it to be operated with a standard extended hexagonal wrench without the need to manufacture a corresponding internal wrench. The appropriate depth also ensures that the wrench has sufficient engagement length when subjected to high torque, preventing slippage and tool damage.

[0037] On the other hand, after the thread machining of the stud body 1 is completed, all thread surfaces are cleaned and coated with a layer of silver-based high-temperature anti-seize lubricant to form a high-temperature anti-seize lubricant layer.

[0038] During installation, screw the threaded end into the cleaned flange threaded hole, which has also been coated with anti-seize agent. Tighten to the specified preload using a torque wrench or a countersunk Allen wrench. During disassembly and maintenance, if adhesion occurs, insert a liquid nitrogen delivery pipe into the axial center hole 2 to locally chill the stud body 1 for 3-5 minutes. The cooling effect will create a micro-gap between the stud and the flange threaded hole, allowing it to be easily unscrewed with an Allen wrench. Alternatively, an induction heating rod can be inserted into the axial center hole 2 for rapid heating. The thermal expansion difference between the stud and the flange will break the seizing surface. Cooling with liquid nitrogen or other cooling media will further amplify the cooling effect or directly break the stud body, allowing it to be easily unscrewed with an Allen wrench.

[0039] Example 2: Figure 3 As shown, the difference between this embodiment and Embodiment 1 lies in the structural design of the axial center hole 2.

[0040] In this embodiment, the axial center hole is a tapered through hole with a larger diameter at the top and a smaller diameter at the bottom. Its large diameter end is located on one side of the countersunk inner polygonal drive part, and the diameter of the large diameter end is 22mm, while the diameter of the small diameter end is 15mm. A matching filler 4 is inserted into the tapered through hole. The filler 4 and the tapered through hole are interference fit. In order to facilitate the removal of the filler 4 during subsequent maintenance so that heating or cooling medium can be introduced into the hole, an annular part is provided at one end of the filler 4 near the countersunk hole.

[0041] This design is primarily aimed at applications requiring higher structural rigidity. The presence of filler 4 reinforces the overall load-bearing structure of the stud, reducing potential central deformation during high-temperature and high-pressure applications. During stud installation and service, filler 4 remains within the hole, effectively improving the stress distribution across the stud's cross-section and enhancing its bending stiffness. When cooling and disassembly using the central hole are required, appropriate tools can be used to hook the ring-shaped or hook-shaped component, removing filler 4 from the larger end of the tapered hole. Cooling can then be performed as described in Example 1.

[0042] In particular, the design of the tapered center hole and the removable filler not only optimizes the stress distribution and improves the load-bearing capacity of the stud, but also facilitates the flexible application of the center hole function and further optimizes its structural utilization.

[0043] Furthermore, due to the use of a tapered design that is larger at the top and smaller at the bottom, when subjected to axial compression or thermal stress, the filler 4 will tend to shift upward (towards the larger diameter end). This shifting tendency will push it outward to expose the end face, thereby assisting in the subsequent removal of the ring-shaped part by using a tool, instead of being tightly pressed inside the through hole. This avoids the problem that the filler will be locked inside the hole after long-term pressure, making it inconvenient to fill the corresponding medium into the through hole later.

[0044] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0045] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0046] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between components; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0047] In this application, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0048] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A novel stud suitable for threading the outlet flange ring of a medium-pressure steam generator, wherein the stud is a double-ended stud, characterized in that, include: The stud body is made of high-temperature alloy material; An axial center hole penetrates the stud body; A countersunk-hole type internal polygonal drive unit is disposed at one end of the stud body and is used to cooperate with the corresponding drive tool; The threaded surface of the stud body is coated with a high-temperature anti-seize lubricant layer.

2. The novel stud for threaded rings on the outlet flange of a medium-pressure steam generator according to claim 1, characterized in that, The high-temperature alloy material is a NiCr20TiAl high-temperature alloy bar, and its chemical composition by mass percentage includes: Carbon (C): 0.04-0.10%; Chromium (Cr): 18.00-21.00%; Titanium (Ti): 1.80-2.70%; Aluminum (Al): 1.00-1.80%; Silicon (Si) ≤1.00%, Manganese (Mn) ≤1.00%, Phosphorus (P) ≤0.020%, Sulfur (S) ≤0.015%, Nickel (Ni) ≥65.00%, Copper (Cu) ≤2.00%, Cobalt (Co) ≤2.00%, Boron (B) ≤0.006%, with the balance being Iron (Fe) and unavoidable impurities.

3. The novel stud for threaded rings on the outlet flange of a medium-pressure steam generator according to claim 2, characterized in that, The stud body undergoes solution treatment and precipitation hardening heat treatment, wherein: The solution treatment is performed by heating the NiCr20TiAl rod to 1050-1080℃ and then air cooling it. The precipitation hardening treatment is as follows: after the NiCr20TiAl rod is cooled to 840-860℃ in air, it is kept at 840-860℃ for 24 hours and then air-cooled, and then kept at 690-710℃ for 16 hours and then air-cooled.

4. The novel stud for threaded thread on the outlet flange of a medium-pressure steam generator according to claim 1, characterized in that, The countersunk-type polygonal drive unit can be any one of the following: internal triangular or internal octagonal countersunk holes.

5. The novel stud for threaded rings on the outlet flange of a medium-pressure steam generator according to claim 4, characterized in that, The countersunk-type internal polygonal drive part is a countersunk-hole internal hexagonal structure. The depth of the countersunk-hole internal hexagonal structure is 35-50% of the length of the stud body, and the depth of the countersunk-hole internal hexagonal structure is not less than 120mm.

6. The novel stud for threaded thread on the outlet flange of a medium-pressure steam generator according to claim 1, characterized in that, The surface roughness Ra of the hole wall of the axial center hole is ≤3.2μm, and a smooth transition is formed at the intersection of the bottom of the countersunk inner polygonal drive part and the axial center hole.

7. The novel stud for threaded rings on the outlet flange of a medium-pressure steam generator according to claim 6, characterized in that, The axial center hole is a standard through hole, and the diameter of the axial center hole is 15-40% of the nominal diameter of the stud body.

8. The novel stud for the ring threading of the outlet flange of a medium-pressure steam generator according to claim 6, characterized in that, The axial central through hole is a tapered through hole with a larger upper diameter and a smaller lower diameter, and the end of it that is away from the countersunk inner polygonal drive part is the small diameter end. The diameter of the large-diameter end of the axial center through hole is less than or equal to 40% of the nominal diameter of the stud body, and the diameter of the small-diameter end is greater than or equal to 15% of the nominal diameter of the stud body.

9. The novel stud for the ring threading of the outlet flange of a medium-pressure steam generator according to claim 8, characterized in that, When the axial center through hole is a tapered through hole that is larger at the top and smaller at the bottom, a matching filler is inserted inside it, and the filler and the axial center through hole are interference fit. The filler is also provided with a hook-shaped / ring-shaped part at one end near the inner polygonal drive part of the countersunk hole.

10. The novel stud for threaded thread on the outlet flange of a medium-pressure steam generator according to claim 1, characterized in that, The high-temperature anti-seize lubricant is a silver-based anti-seize agent.

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