Manufacturing method of spiral finned tube pressure-bearing module for waste heat boiler of floating generator set

Abstract

This invention discloses a manufacturing method for a pressure-bearing module of a floating generator waste heat boiler, comprising: using an infrared positioning instrument for high-precision positioning of the tube sheet; pre-installing positioning sleeves on the spiral finned tubes; using a bottom-up transverse tube-threading sequence, with the aid of guiding fixtures and tube-feeding tools; using a pyramid-shaped sequence from bottom to top and from the middle to both sides for connecting tube welding; performing local heat treatment after welding by laying heating plates flat and filling the gaps with insulation material to form a box-type furnace unit; dividing the module into multiple independent passages for hydrostatic testing before assembling the header, and then purging and drying with compressed air after the test. This invention solves the problems of easy damage to ultra-long spiral finned tubes when threaded between dense tube sheets, low efficiency of local heat treatment of numerous T91 / T22 weld joints, and corrosion caused by incomplete drainage after hydrostatic testing. The weld joint qualification rate reaches 98%, and the heat treatment efficiency is improved by 8 times.

Description

Technical Field

[0001] This invention relates to the field of marine engineering equipment and waste heat boiler manufacturing technology, and more specifically, to a method for manufacturing a spiral finned tube pressure-bearing module for a combined cycle unit waste heat boiler used in an offshore floating power generation platform. Background Technology

[0002] As a core component of gas-fired combined cycle power plants, the modular manufacturing technology of waste heat boilers directly impacts the power generation efficiency and construction period of the combined cycle unit. Spiral finned tubes, due to their ability to significantly expand the heat exchange area, are widely used in the heat transfer surface modules of waste heat boilers. With the development of offshore oil and gas resources extending to deeper waters, floating power generation units place higher demands on the manufacturing of waste heat boiler modules: they must not only meet the strength requirements of land-based equipment but also adapt to the swaying conditions of offshore platforms, salt spray corrosion environments, and limited installation space.

[0003] In the prior art, the patented technologies related to this application mainly include the following aspects.

[0004] Regarding tube-passing guidance technology, patent CN201310220328.X discloses a tube-passing guidance device for finned tubes in a waste heat boiler module. This device includes a guide body with a guide hole at its tail end and a guide head connected to its front end for aligning with the tube holes in the tube sheet to achieve tube passage. This technology solves the basic problem of guide alignment, but only provides an end-guide tooling and does not address systemic process issues such as tube passage sequence optimization, tube collision prevention measures, and concentricity control of multiple tube sheets.

[0005] Regarding welding technology, patent CN201110047863.0 discloses a welding method for assembling an HRSG waste heat furnace. This method employs an assembly sequence from the center outwards, using argon arc welding for the base and manual electric welding for the top to complete the fillet weld between the header and the spiral finned tube. This technology primarily addresses fillet welds; however, it does not provide technical solutions for optimizing the welding sequence of the numerous butt welds on the connecting pipes at both ends of the module, or for addressing the impact of this sequence on the space available for flaw detection and repair.

[0006] Regarding hydrostatic testing technology, patent CN201020166456.2 discloses a hydrostatic testing device for a waste heat boiler module, which achieves hydrostatic testing through a sealed connection between the flange end cap and the pipe joint; patent CN201320577271.4 discloses a hydrostatic testing device for a waste heat boiler evaporator, which achieves sealing by fixing a steel ring to the outer wall of the header body in conjunction with a sealing sleeve. These technologies all focus on the structural design of the sealing device for hydrostatic testing, but do not provide solutions to the problems of water accumulation at low points after overall module hydrostatic testing, or water accumulation during marine transportation and storage leading to pipe wall corrosion.

[0007] Regarding the application of spiral finned tubes, patent CN200710020672.9 discloses a low-temperature waste gas waste heat boiler for sintering coolers and its power generation system, which adopts a vertical layout and tube box structure, with spiral finned tubes on the heating surface. However, this technology mainly involves boiler structural design and does not describe the module manufacturing process.

[0008] In summary, existing technologies have gaps in areas such as pipe threading processes, optimized welding sequences, batch heat treatment of dense weld joints, and post-hydraulic pressure drainage and rust prevention. Particularly in the manufacturing scenario of ultra-long spiral finned tubes (over 15 meters in length), ultra-dense tube arrays (26mm transverse gap, 16mm longitudinal gap), high-grade materials (T91 / T22), and a large number of weld joints (1680) for offshore floating generator sets, existing technologies fail to provide a systematic solution. Therefore, developing a manufacturing method for the pressure-bearing module of spiral finned tubes in the waste heat boiler of floating generator sets that can systematically solve the above-mentioned technical problems is of great significance for promoting the development of marine engineering equipment manufacturing technology. Summary of the Invention

[0009] Purpose of the invention: This invention provides a method for manufacturing a spiral finned tube pressure-bearing module for a floating generator set waste heat boiler, aiming to solve the technical problems in the prior art, such as the easy damage of ultra-long spiral finned tubes when passing through dense tube sheets, the conflict between welding and flaw detection space for connecting pipes, the low efficiency of local heat treatment of weld joints of a large number of T91 / T22 materials, and the corrosion caused by incomplete drainage after water pressure of the module.

[0010] Technical Solution: To achieve the above objectives, the present invention provides the following technical solution: A method for manufacturing a pressure-bearing module of a floating generator set waste heat boiler spiral finned tube, the pressure-bearing module comprising several tube sheets, multi-layer spiral finned tubes passing through the tube holes of the tube sheets, and connecting pipes connecting the two ends of the spiral finned tubes, comprising the following steps: Step (1) High-precision positioning of tube sheets: Use an infrared positioning instrument to calibrate the center line of the tube holes of each tube sheet, so that the tube holes of several tube sheets are concentric. Then fix the tube sheets on the assembly frame by positioning plates and diagonal braces. Step (2), Pre-installation of positioning sleeves for spiral fin tubes: First, weld the first positioning sleeve onto each spiral fin tube. After the tube is inserted into place, the first positioning sleeve fits into the end tube sheet. Then, weld the second positioning sleeve. The spiral fin tube is axially fixed onto the module through the two positioning sleeves. Step (3) Horizontal pipe threading from bottom to top: Pipes are threaded horizontally from bottom to top. Before threading the pipe, the guide tool is inserted into the inner diameter of the front end of the spiral fin tube and temporarily spot-welded to guide it through the pipe hole. Pipe feeding tools are used between adjacent tube sheets to support the tube body and prevent adjacent spiral fin tubes from colliding with each other. Step (4), Pyramid-shaped connecting pipe assembly and welding: The connecting pipes at both ends of the module are assembled and welded in a pyramid-shaped sequence from bottom to top and from the middle to both sides. Flexible neck welding guns are used, and the welding is performed in sections, mirror welding and internal filler wire method. Step (5), Unitized local heat treatment of box-type furnace: The heating plate is laid flat on the upper and lower surfaces of the multi-layer weld joint, and the gaps between the pipes are filled with heat insulation material to form a closed heating unit. At least three thermocouples are arranged in each heating unit for post-weld local heat treatment. Step (6), water pressure test of each channel: Before assembling the intermediate header and the outlet header, the module is divided into multiple independent channels and water pressure tests are carried out separately. After the test, compressed air is used to blow dry.

[0011] In some specific implementations: In step (1), a precision level is used to adjust the adjusting bolts around the assembly frame so that the elevation of each tube sheet mounting base is consistent and the levelness is controlled within ±0.5mm / m; the longitudinal center line and transverse center line of the tube sheet are marked on the base, and the error is controlled within ±0.3mm; after the infrared positioning instrument is calibrated, the concentricity deviation of the tube sheet is controlled within ±0.5mm.

[0012] In some specific embodiments: In step (3), the guide tool is a round head structure with a tapered handle. The tapered handle is inserted into the inner diameter of the spiral fin tube and temporarily spot-welded to fix it. The outer diameter of the round head is smaller than the inner diameter of the tube hole and larger than the outer diameter of the spiral fin tube base tube. The front end of the round head is processed into an arc transition surface. The tube feeding tool consists of a handle, a connecting rod and a bracket. The bracket has a U-shaped opening structure and the inner wall of the bracket is pasted with flexible buffer material.

[0013] In some specific embodiments: the guide tool has a cone shank length of 50mm, an outer diameter of the cone shank that is 0.2-0.5mm smaller than the inner diameter of the spiral finned tube, an outer diameter of the round head that is 0.3-0.8mm smaller than the inner diameter of the tube hole, and a radius of 5mm for the arc transition surface at the front end of the round head; the support opening width of the tube feeding tool is 45mm.

[0014] In some specific implementations: the flexible cushioning material pasted on the inner wall of the tube delivery tool is a rubber pad with a thickness of 5mm.

[0015] In some specific implementations: In step (4), T91 material is preheated to 200℃-250℃ before welding, T22 material is preheated to 150℃-200℃ before welding, and the interpass temperature is controlled below 250℃; the welding current for the lower half of the pipe opening is 70A-100A, the welding current for the upper half of the pipe opening is 90A-120A, the welding voltage is 10V-14V, and the welding speed is 30-50mm / min.

[0016] In some specific implementations: In step (5), each heating unit covers 70-80 weld joints, the heating plate is a track-type ceramic electric heating plate, the insulation material is high-alumina fiber cotton, and the exposed surface of the heating unit is covered with asbestos cloth; the at least three thermocouples are respectively arranged on the upper left side of the first tube on the left side of the heating unit, the lower right side of the last tube on the right side, and the middle part of the tube in the middle area.

[0017] In some specific implementations: In step (5), the post-weld local heat treatment process parameters are: heating rate not greater than 150℃ / h, holding temperature of 745℃±15℃, holding time not less than 1h, cooling rate not greater than 275℃ / h, and furnace exit temperature not greater than 315℃.

[0018] In some specific implementations: In step (6), the module is divided into three independent channels for water pressure testing. The test pressure is 1.64 times the working pressure, the pressure increase rate is 0.05-0.1 MPa / min, the pressure holding time is 20-30 min, and the pressure decrease rate is no more than 0.3 MPa / min.

[0019] In some specific implementations: in step (6), the compressed air pressure for purging is 0.6 MPa, the compressed air dew point is not higher than -40°C, and the purging time is not less than 30 min.

[0020] Beneficial effects: Compared with the prior art, the present invention has the following beneficial effects: First, addressing the technical problem of easy damage to ultra-long spiral finned tubes when threading them between dense tube sheets, this invention uses an infrared positioning device to ensure the concentricity of the tube holes on multiple tube sheets. Combined with a guiding fixture to guide the front end, a tube feeding tool to support the tube body, and a bottom-up transverse threading sequence, a complete threading process system is formed. This solution effectively avoids fin damage when threading ultra-long spiral finned tubes in dense tube row gaps (26mm transverse gap, 16mm longitudinal gap), achieving zero fin damage during threading, while reducing labor intensity and improving threading efficiency.

[0021] Secondly, addressing the technical problem of insufficient space for flaw detection and repair after welding of numerous densely connected pipes at both ends of the module, this invention adopts a pyramid-shaped pipe assembly and welding sequence from bottom to top and from the middle to both sides, creating favorable operating space and shooting angles for welding, flaw detection, and repair. Combined with optimized welding processes using T91 / T22 high-grade materials (T91 material preheated to 200℃-250℃, with the lower half of the pipe end welded using a low current of 70A-100A), the first-pass yield of the weld reaches 98%, superior to the 96.2% of conventional thermal power projects and 95.8% of chemical waste heat projects in existing technologies.

[0022] Third, addressing the technical problem that heating plates cannot be individually wrapped around dense weld joints (52mm horizontal gap, 42mm vertical gap) and the low efficiency of traditional heat treatment methods, this invention innovatively adopts a localized heat treatment method that uses flat heating plates and fills the gaps with insulation material to form a box-like furnace unit. This solution allows each temperature control cabinet to process 72 weld joints at a time, an 8-fold increase compared to the existing technology where each cabinet processes only 9 weld joints. The total heat treatment cycle is shortened from approximately 33 working days to 4.5 working days, a reduction of 84%, while maintaining a temperature control accuracy of ±10℃ and meeting the technical requirements for heat treatment quality.

[0023] Fourth, in response to the technical problems of water accumulation at low points after overall module water pressure and pipe wall corrosion during marine transportation and storage, this invention conducts the water pressure test before the container is assembled, divides the module into multiple independent channels for pressure testing, and uses compressed air to blow and dry after the test, which completely solves the problem of water accumulation at low points after overall water pressure and eliminates the risk of corrosion of the module during marine transportation and storage. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the manufacturing process of the spiral finned tube pressure-bearing component module of the waste heat boiler of the floating generator set according to the present invention. Figure 2 This is a schematic diagram of the overall structure of the pressure-bearing module in Embodiment 1 of the present invention; Figure 3 for Figure 2 Schematic diagram of the left end plate arrangement structure in the middle AA section; Figure 4 for Figure 2 Schematic diagram of the right end plate arrangement structure in the middle BB section; Figure 5 This is a schematic diagram of the spiral finned tube and the positioning sleeve arranged on it in Embodiment 1 of the present invention; Figure 6 This is a schematic diagram of the guide tooling in Embodiment 1 of the present invention; Figure 7 This is a schematic diagram comparing the first-pass yield of welds in Embodiment 1 of the present invention with that of conventional thermal power projects and chemical waste heat projects; Figure 8 This is a schematic diagram of the water pressure test in the branch passage in Embodiment 1 of the present invention; Wherein: 1-connecting pipe; 2-spiral finned tube; 3-tube sheet; 4-outlet header; 5-intermediate header; 6-first positioning sleeve; 7-second positioning sleeve; 8-guide tooling; 81-cone shank; 82-round head. Detailed Implementation

[0025] In this invention, unless otherwise stated, the following terms should be understood to have the following meanings: "Helical finned tube" refers to a heat exchange tube in which spiral fins are continuously welded along the axial direction on the outer surface of the base tube. The height, thickness and pitch of the fins are determined according to the heat exchange requirements.

[0026] "Horizontal pipe laying from bottom to top" refers to the pipe laying sequence that starts with the bottommost pipe row of the module, and then lays pipes one by one in the horizontal direction within the same layer, completing one layer before laying pipes into the adjacent layer above.

[0027] The “pyramid-shaped welding sequence” refers to a welding sequence that starts from the midpoint of the module’s length, first welding the connecting pipe in the middle of the bottom layer, and then expanding upwards layer by layer while simultaneously extending symmetrically to the left and right sides, forming a pyramid shape.

[0028] "Box-type furnace unit" refers to a closed heating space formed by laying heating plates flat on the upper and lower surfaces of multiple weld joints and filling the gaps between the tubes with insulation material. This space plays a role in equalizing the temperature of a box furnace during the heat treatment process.

[0029] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0030] Example 1 This embodiment uses the manufacturing of a single pressure-bearing module in the Wison floating generator project as an example to describe the invention in detail. This module is a component of a 240MW "two-to-one" combined cycle generator unit and is installed on an offshore floating platform.

[0031] like Figure 1 As shown, the manufacturing method of the present invention is executed in the following sequence: First, step (1) high-precision positioning of the tube sheet is performed, followed by step (2) pre-installation of the positioning sleeve for the spiral finned tube; then step (3) horizontal tube insertion from bottom to top is performed; subsequently, step (4) pyramid-shaped connecting tube welding is performed; after welding, step (5) unitized local heat treatment of the box-type furnace is performed; finally, step (6) water pressure test of the separate passage is performed. Necessary inspection points are set between each step to ensure that the quality of the previous step is qualified before proceeding to the next step.

[0032] The specific steps are as follows: Step (1), High-precision positioning of tube sheets: An infrared positioning instrument is used to calibrate the center line of the tube holes on each tube sheet, ensuring that the tube holes of several tube sheets are concentric. Then, the tube sheets are fixed to the assembly frame using positioning plates and diagonal braces. Specifically: The pressure-bearing module manufactured in this embodiment is as follows: Figure 2-4As shown, its structure is as follows: Each module contains 768 spiral finned tubes 2, arranged in 16 layers, with 48 tubes in each layer. The length of a single spiral finned tube 2 is 15565mm. The pressure-bearing module consists of 624 connecting pipes 1 at both ends, and the intermediate header 5 and outlet header 4 of the high-pressure superheater, forming a total of 1680 weld joints.

[0033] The assembly frame and packaging / transport frame of the pressure-bearing module are combined. Each frame has 6 intermediate tube sheets and 1 end tube sheet. Each tube sheet 3 has 16 layers of tube holes, with 48 holes per layer. The bottom 8 layers of tube holes are used to install T91 material spiral finned tubes 2 with a specification of Φ38×3.5mm; the middle 2 layers are used to install T91 material spiral finned tubes 2 with a specification of Φ38×2.5mm; and the top 6 layers are used to install T22 material spiral finned tubes 2 with a specification of Φ38×2.7mm. The spacing between adjacent tube sheets 3 is 2460mm. After the tubes are installed, the lateral clearance of the tube rows is 26mm and the longitudinal clearance is 16mm.

[0034] The high-precision tube sheet positioning in this embodiment involves the following specific steps: a. Assemble the assembly frame and packaging / transportation frame into one unit and place it on a level platform. Use a precision level to adjust the adjusting bolts around the assembly frame to ensure that the elevation of each tube sheet mounting base is consistent, and the levelness is controlled within ±0.5mm / m.

[0035] b. On each tube sheet mounting base, use a scribing tool to draw the longitudinal center line and the transverse center line of tube sheet 3. The scribing error of the center line should be controlled within ±0.3mm.

[0036] c. Use a workshop overhead crane to hoist the tube sheets 3 one by one onto the corresponding bases. Keep the tube sheets 3 vertical during hoisting and lower them into place slowly.

[0037] d. Install infrared positioning devices at both ends of the pressure-bearing module. Adjust the infrared emission direction so that the infrared beam passes through the corresponding holes on the end tube sheet and the intermediate tube sheet simultaneously. Observe the projection position of the beam on each tube sheet 3, and fine-tune the position of the tube sheet 3 until the center of the beam completely coincides with the center line of the tube sheet. Repeat this process to ensure that the centers of the holes of all tube sheets 3 are on the same axis, and the concentricity deviation is controlled within ±0.5mm.

[0038] e. After position calibration, first use positioning plates to spot weld the bottom of tube sheet 3 to the base. At least 4 positioning plates are welded to each tube sheet 3, located in the front, back, left, and right directions of the tube sheet 3. Then, weld channel steel diagonal braces to the upper two sides of the tube sheet 3. The lower end of the channel steel diagonal brace is connected to the assembly frame, and the upper end is welded to the side of the tube sheet to prevent the tube sheet 3 from tilting or shifting during the subsequent tube insertion process.

[0039] Step (2), Pre-installation of positioning sleeves on spiral finned tubes: First, weld the first positioning sleeve onto each spiral finned tube. After the tube is inserted into place, the first positioning sleeve fits against the end tube sheet. Then, weld the second positioning sleeve. The spiral finned tube is axially fixed to the module through the two positioning sleeves. Specifically: like Figure 5 As shown, each spiral fin tube 2 is provided with two positioning sleeves, namely the first positioning sleeve 6 and the second positioning sleeve 7, wherein the first positioning sleeve 6 is a short sleeve and the second positioning sleeve 7 is a long sleeve.

[0040] Before inserting the tube, the first positioning sleeve 6 is spot-welded and fixed to the spiral finned tube 2 according to the design position. The first positioning sleeve 6 is located close to one end of the spiral finned tube 2, and its function is to fit against the end tube sheet after the tube is inserted to achieve axial positioning. After the spiral finned tube 2 is inserted and the first positioning sleeve 6 is fitted against the end tube sheet, the second positioning sleeve 7 is then welded on. The spiral finned tube is axially fixed to the module through the two positioning sleeves.

[0041] Step (3), Horizontal pipe threading from bottom to top: Pipes are threaded horizontally from bottom to top. Before threading, a guide fixture is inserted into the inner diameter of the front end of the spiral finned tube and temporarily spot-welded to guide it through the tube hole. A pipe feeding tool is used between adjacent tube sheets to support the tube body and prevent adjacent spiral finned tubes from colliding with each other. Specifically: In this embodiment, 768 spiral finned tubes 2 need to pass through 7 tube sheets 3. If a vertical method is used for tube threading, the 16 layers of spiral finned tubes 2 have 3 different materials and specifications, which would require frequent changes in the type of spiral finned tube 2 during the threading process, causing trouble and potentially leading to incorrect tube threading. If a horizontal method is used to thread the tubes from top to bottom, the workers between the tube sheets 3 would have to support the spiral finned tubes 2, which would be tiring and there would be no place for them to stand. Considering all factors, a horizontal method from bottom to top is ultimately adopted, which avoids the above-mentioned problems. That is, the bottom layer of 48 spiral finned tubes 2 are threaded first, from left to right, then the second layer is threaded, and so on upwards until the 16th layer.

[0042] The pipe-threading operation was carried out using a crane lifting method. Two 5-ton cranes worked together, with the crane hooks using nylon slings to horizontally lift the spiral finned tube 2, keeping the tube level.

[0043] To ensure the smooth passage of the spiral finned tube 2 through the intermediate tube sheet hole without damage, this embodiment employs a guide fixture. The guide fixture controls the gap between the spiral finned tube 2 and the hole, guiding the tube 2 through the tube sheet hole. The guide fixture is installed at the front end of the spiral finned tube 2, such as... Figure 6As shown, the guide fixture 8 is a round head with a tapered shank, made of 45# steel. The tapered shank 81 is 50mm long and has an outer diameter of 36.8mm, smaller than the inner diameter of the spiral finned tube 2, with a gap of 0.2-0.5mm between them. After the tapered shank 81 is inserted into the inner diameter of the spiral finned tube 2, it is temporarily fixed by two circumferential spot welds. These temporary spot welds can be easily removed after the tube is inserted and do not constitute a permanent connection to the spiral finned tube 2. The round head 82 has an outer diameter of 37.5mm, smaller than the inner diameter of the tube hole, with a gap of 0.3-0.8mm between them, and the outer diameter of the round head 82 is larger than the outer diameter of the spiral finned tube 2. The front end of the round head 82 is machined into a circular arc transition surface with a radius of 5mm.

[0044] During the tube insertion process, one worker operates a crane at one end of the module to control the forward speed of the spiral finned tube 2. Two other workers are positioned between the first and second tube sheets 3, and between the second and third tube sheets 3, respectively, each holding a tube insertion tool to support the middle of the spiral finned tube 2. The insertion tool consists of a handle, a connecting rod, and a bracket. The bracket has a U-shaped opening with a width of 45mm to accommodate the spiral finned tube 2. A 5mm thick rubber pad is attached to the inner wall of the bracket for cushioning and anti-slip purposes. The worker holds the handle and lifts the spiral finned tube 2 from below, keeping it horizontal and preventing collisions with adjacent inserted spiral finned tubes 2.

[0045] During the tube insertion process, the round head 82 of the guide fixture 8 first enters the tube hole of the first tube sheet 3, guiding the spiral fin tube 2 to pass smoothly. Since the outer diameter of the round head 82 is smaller than the inner diameter of the tube hole and larger than the outer diameter of the spiral fin tube 2, the spiral fin tube 2 will not directly hit the edge of the tube hole during the insertion process.

[0046] Complete the installation of the 48 tubes in the first layer one by one using the above method, and then proceed with the installation of the tubes in the second to the sixteenth layers until all 768 spiral finned tubes are installed.

[0047] In this embodiment, the tube-threading operation of 768 spiral finned tubes 2 took 72 man-hours, with no damage to the fins and a 100% success rate in tube-threading on the first attempt.

[0048] Step (4), Pyramid-shaped connecting pipe assembly and welding: The connecting pipes at both ends of the module are assembled and welded in a pyramid-shaped sequence from bottom to top and from the middle to both sides, using a flexible neck welding gun, and employing zone welding, mirror welding, and internal filler wire method. Specifically: In this embodiment, each module has 624 connecting pipes 1 that need to be welded at both ends. The connecting pipes 1 are densely packed, and the welding space is limited. If the conventional method is used for longitudinal or transverse assembly, the welded connecting pipes 1 would obstruct each other, making flaw detection and rework difficult. Considering factors such as welding posture, flaw detection, and rework, this invention adopts a pyramid-shaped welding method from bottom to top and from the middle to both sides. This assembly method provides better position and space for welding and rework, creates a better shooting angle for flaw detection, and allows each process to be carried out intermittently without interfering with each other. Furthermore, welding experience with high-grade materials such as T91 and T22 waste heat boilers is applied to this invention, and the process parameters and operating specifications are strictly followed. The specific steps are as follows: First, weld the connecting pipe 1 in the middle of the bottom layer, i.e., the first layer. Starting from the midpoint of the module length, weld symmetrically to the left and right sides. When welding the bottom layer, the worker should stand on the ground or a lower platform.

[0049] After completing the welding of all connecting pipes at the bottom layer, the process moves to the second layer, where welding proceeds symmetrically from the center outwards. As the number of layers increases, workers utilize ladders or scaffolding for operation. The upper connecting pipes are supported by the already welded lower connecting pipes, improving stability during the welding process.

[0050] The welding method in this embodiment uses tungsten inert gas (TIG) welding. ER90S-B9 welding wire is used for T91 material, and ER80S-B2 welding wire is used for T22 material. Preheating is performed: T91 material is preheated to 200℃-250℃, and T22 material is preheated to 150℃-200℃. The interpass temperature is controlled below 250℃. Welding current is controlled in segments: 90A-120A for the upper half of the pipe opening (flat and vertical welding positions), and 70A-100A for the lower half (overhead welding position). The welding voltage is 10V-14V, and the welding speed is 30-50mm / min.

[0051] For obstructed areas where the operating space is limited and the welding torch cannot reach directly, a flexible neck welding torch is used for welding. The bent part of the flexible neck welding torch can be bent within the range of 15°-45°.

[0052] For weld joints that are not visible from the back, a mirror welding technique is used: a stainless steel reflector with a magnetic base is placed behind the weld joint, with a mirror size of 20mm × 30mm. Workers perform welding operations by observing the image reflected by the mirror. For weld joints with extremely small gaps that cannot be filled with welding wire, an internal filling method is used: the welding wire is pre-inserted from inside the pipe opening to the position to be welded, and the welding is achieved by melting the welding wire from the outside.

[0053] After each pyramid unit is welded, the weld joint is immediately subjected to 100% radiographic testing. Since connecting pipes are not yet installed in adjacent unwelded areas, the exposure direction of the testing equipment is unobstructed. If defects are found, there is sufficient space to use an angle grinder to remove them and re-weld them during rework.

[0054] This embodiment overcomes numerous problems such as high material grade, dense weld joints, and limited welding space, ultimately achieving a high weld joint qualification rate. Figure 7 As shown, the first-pass yield rate of the 1680 weld joints in this embodiment is 98%, meaning that 1646 weld joints are qualified and 34 weld joints require repair. This yield rate is superior to the 96.2% of conventional thermal power projects and the 95.8% of chemical waste heat projects in the prior art.

[0055] Step (5), Unitized Local Heat Treatment in a Box-Type Furnace: A heating plate is laid flat on the upper and lower surfaces of the multi-layer weld joint. Insulation material is used to fill the gaps between the pipes to form a closed heating unit. At least three thermocouples are arranged in each heating unit for post-weld local heat treatment. Specifically: In this embodiment, there are approximately 1200 weld joints involving T91 material, all of which require post-weld local heat treatment. In previous waste heat boiler projects, electric heating plates could be used to cover the weld joints, with each temperature control cabinet handling up to 9 weld joints at a time. The module of this invention has a large number of weld joints with small gaps between them (52 ​​mm laterally and 42 mm longitudinally), and the end connecting pipes are arranged in a crisscross pattern, making it difficult for the heating plate to pass through the gaps and cover the weld joints. The difficulty in covering the weld joints and the large number of weld joints mean that using the previous method would be extremely labor-intensive and significantly impact the project timeline. Considering the above factors and the analysis of the product structure, this invention improves the method of local heat treatment.

[0056] First, the area of ​​the module end connecting pipe 1 is divided into several heating units, each unit covering 70 to 80 weld joints. In this embodiment, it is divided into 17 heating units.

[0057] A tracked ceramic electric heating plate is laid flat on the upper and lower surfaces of each heating unit. The heating plate measures 600mm × 300mm and has a power of 10kW. The heating plate directly covers the weld joint and the surrounding pipes.

[0058] The gaps between the tubes are filled with high-alumina fiber cotton, which is compacted during filling to ensure there are no voids, thus forming a closed, box-like furnace structure for the entire heating unit. The exposed surface of the heating unit is covered with two layers of asbestos cloth, with a total thickness of 10mm.

[0059] Each heating unit is equipped with at least three thermocouples, with an accuracy of ±0.75%. The first thermocouple is located on the upper left side of the first tube on the left side of the heating unit, the second thermocouple is located on the lower right side of the last tube on the right side of the heating unit, and the third thermocouple is located in the middle of a tube in the middle area of ​​the heating unit. The thermocouples are fixed to the tube wall surface by spot welding or magnetic attraction.

[0060] The heat treatment process parameters are as follows: heating rate not greater than 150℃ / h, actually controlled at 120℃ / h; holding temperature 745℃±15℃, actual temperature control accuracy reaching ±10℃; holding time not less than 1h, actually holding for 1h; cooling rate not greater than 275℃ / h, using furnace cooling, actual cooling rate 200-250℃ / h; furnace exit temperature not greater than 315℃, actually stopping heating and removing the heating unit after dropping below 300℃.

[0061] The 17 heating units were divided into 6 batches for heat treatment (approximately 200 weld joints per batch, operated simultaneously by 3 temperature control cabinets). Each temperature control cabinet controlled one heating unit, with a total of 3 cabinets operating simultaneously. The total time for a single heat treatment (including heating, holding, and cooling) was approximately 9 hours. The temperature change curve of each thermocouple was recorded during the heat treatment process. In this embodiment, the maximum temperature difference between the three thermocouples within the same heating unit was 8°C.

[0062] Using the method of this invention, each temperature control cabinet can process 72 weld joints at a time, and when 3 temperature control cabinets are operating simultaneously, each batch can process 216 weld joints. It takes about 6 batches to complete all approximately 1200 weld joints, and the total heat treatment calendar time is 54 hours (approximately 6.8 working days).

[0063] In contrast, if the existing technology is adopted, where each temperature control cabinet can only process 9 weld joints at a time, under the same condition of using 3 temperature control cabinets to operate simultaneously, only 27 weld joints can be processed per batch. It would take about 45 batches to complete all approximately 1200 weld joints, and the total heat treatment calendar time would be 405 hours (approximately 50.6 working days).

[0064] Compared with the prior art, this invention reduces the total heat treatment calendar time from approximately 50.6 working days to approximately 6.8 working days under the same equipment resources, a reduction of 86.6%. At the same time, the single processing capacity of each temperature control cabinet is increased from 9 weld joints to 72 weld joints, an increase of 8 times, and the temperature control accuracy reaches ±10℃, while the heat treatment quality meets the technical requirements.

[0065] Step (6), Separate Channel Hydraulic Pressure Test: Before assembling the intermediate and outlet headers, the module is divided into multiple independent channels for separate hydraulic pressure tests. After the tests, compressed air is used for purging and drying. Specifically: According to the characteristics of the modular circuit of the present invention, if an overall hydrostatic test is used, the problem of incomplete drainage will inevitably occur. Therefore, the present invention conducts a hydrostatic test before assembling the intermediate header 5 and the outlet header 4, and tests the module separately in three independent channels. Figure 8 As shown.

[0066] Before pressure testing, remove the intermediate header 5 and outlet header 4 of the module to make the three circuits of the main module—high-pressure circuit, medium-pressure circuit, and low-pressure circuit—independent. Clean the inside of each circuit's piping with a ball (85% of the pipe's inner diameter) to ensure the piping is free of debris and unobstructed. Clean the external welds, flanges, and accessory surfaces of the pipe assembly. Prepare clean fresh water as the test medium, with a chloride ion content not exceeding 0.2 mg / L, and a water temperature controlled between 20℃ and 70℃ (25℃ in this embodiment). Control the ambient temperature to be no lower than 5℃ (18℃ in this embodiment). Ensure the pipe assembly wall temperature is no lower than 21℃, achieved through hot water circulation preheating. Prepare two pressure gauges with an accuracy of 1.6 grade and a range of 0-25 MPa, which have been calibrated.

[0067] An internal expansion sealing fixture is installed at the inlet and outlet of each loop. The internal expansion sealing fixture consists of an expansion plug, a rubber sealing ring, and a locking nut. After being inserted into the pipe opening, the nut is tightened, and the sealing ring expands radially to fit tightly against the inner wall of the pipe to achieve a seal.

[0068] Open all air vents, positioned at the highest point of each loop. Slowly inject test water from the bottom of the pipe assembly (the bottom inlet of the module) at a rate of 50L per minute. Continue injecting water until water flows continuously from the top inlet without any air bubbles, indicating that the air has been expelled. Then close the air vents.

[0069] Start the pressure testing pump, controlling the pressurization rate at 0.05-0.1 MPa / min. In this embodiment, the actual pressurization rate is 0.08 MPa / min. Pause pressurization when the pressure reaches the working pressure of 8.22 MPa. Conduct a comprehensive inspection of the pipe assembly, including welds, flanges, pipe materials, and sealing fixtures. Spray suspected areas with a leak detection agent (soapy water) and observe for any bubbles. Continue pressurizing after confirming there are no leaks.

[0070] Continue increasing the pressure to the test pressure of 13.5 MPa, which is 1.64 times the working pressure of 8.22 MPa. Hold the pressure for 20-30 minutes; in this example, the actual holding time was 25 minutes. During the pressure holding period, observe the pressure gauge for any pressure drop; a pressure drop of no more than 0.1 MPa is considered acceptable. Simultaneously, check the pipe assembly for any visible deformation. During the pressure holding period, it is strictly forbidden to strike the test assembly or loosen the fastening nuts.

[0071] After the pressure holding time is completed, slowly open the pressure relief valve to release pressure, controlling the pressure reduction rate to be no more than 0.3 MPa / min. In this embodiment, the actual pressure reduction rate is 0.2 MPa / min. When the pressure drops to the working pressure of 8.22 MPa again, perform a second comprehensive inspection of the pipe assembly to confirm that there are no leaks. Record the inspection results and continue to reduce the pressure to atmospheric pressure.

[0072] Open all low-point drain valves and high-point vent valves to drain any accumulated water. Dry the module by purging with compressed air: Introduce 0.6 MPa of dry compressed air (dew point not exceeding -40°C) through the top inlet of the module and expel it through the bottom inlet, continuing purging for 30 minutes. After purging, wipe the inner wall of the pipe with a white cloth to confirm there is no residual moisture.

[0073] Following the steps described above, hydrostatic tests were performed on the three independent circuits sequentially. In this embodiment, all three circuits passed the test on the first attempt, with no leakage, no pressure drop, and no deformation. Although the improved hydrostatic testing scheme increased the number of tests, the process was more clearly inspected, the operation was safer, and the removal of accumulated water was more thorough, solving the problem of internal wall corrosion caused by incomplete drainage after the hydrostatic test.

[0074] The selection of key process parameters in this embodiment is based on the following considerations: (1) Regarding the post-weld heat treatment holding temperature of 745℃±15℃: The post-weld heat treatment specification for T91 material requires a holding temperature between 740℃ and 760℃. Below 730℃, the martensitic transformation is incomplete, and the residual stress is not sufficiently eliminated; above 770℃, the grains coarsen, and the material toughness decreases. This application selects 745℃±15℃, which not only meets the specification requirements but also adapts to the temperature difference control capability of the box-type furnace unit (the actual temperature control accuracy reaches ±10℃).

[0075] (2) Regarding the pressure increase rate of the water pressure test: 0.05-0.1MPa / min: when it is below 0.05MPa / min, the test efficiency is too low and the production cycle is affected; when it is above 0.1MPa / min, the pressure impact may cause the sealing fixture to fail or the pipe assembly to generate additional stress, which poses a safety hazard.

[0076] (3) Regarding the compressed air purging pressure of 0.6MPa: when the airflow velocity is below 0.4MPa, it is insufficient to effectively blow away the water accumulation at the low point; when it is above 0.8MPa, it may cause impact damage to the pipe wall, especially for thin-walled pipes (wall thickness 2.5mm-3.5mm) which are at risk of deformation.

[0077] To verify the technical effect of the present invention, the applicant compared the manufacturing process of the present invention (this embodiment) and the prior art method on waste heat boiler modules of the same specifications (768 spiral finned tubes, 1680 welds, material T91 / T22).

[0078] (1) In the pipe threading process, the fin damage rate of the existing technical method (using manual hole alignment, pipe threading from top to bottom, without guide tooling and pipe feeding tool) is 5.2%, and the total pipe threading time is 120 man-hours; the fin damage rate of the method of the present invention is 0%, and the total pipe threading time is 72 man-hours.

[0079] (2) In the welding process, the first-time flaw detection pass rate of the existing technical method (using the conventional welding sequence, not the pyramid sequence) is 91.5%, and the average time for rework is 45 minutes per location; the first-time flaw detection pass rate of the method of the present invention is 98%, and the average time for rework is 20 minutes per location.

[0080] (3) In the heat treatment process, the heat treatment cycle of the existing technology (using a heating plate wrapped in a single opening) is 33 working days; the heat treatment cycle of the method of the present invention is 4.5 working days.

[0081] (4) In the water pressure process, the existing technical method (overall water pressure) was inspected after 30 days of sea transport, and obvious pitted corrosion appeared on the inner wall of the pipe; the method of the present invention (separate channel water pressure + compressed air purging) under the same conditions, the inner wall of the pipe was smooth and free of corrosion.

[0082] Comparative experimental results show that the method of the present invention is significantly superior to the prior art in terms of pipe threading efficiency, welding quality, heat treatment cycle and rust prevention capability.

[0083] The module of this invention arrived at the installation site after being transported by sea for 30 days. Upon opening the cover for inspection, it was found that the inner surface of the pipe wall was smooth and free of rust.

[0084] This embodiment completes the manufacturing of the spiral finned tube pressure-bearing component module of the waste heat boiler of the floating generator set according to the above method. The technical effects are summarized as follows: the damage rate of the tube fins is zero; the first-pass yield rate of the weld is 98%; the heat treatment efficiency is 72 welds per temperature control cabinet at a time, and the heat treatment cycle is 4.5 working days; there is no residual moisture on the inner wall of the tube after the water pressure test, and there is no rust after sea transport.

[0085] Comparative Example 1 (Adjustment of Guide Fixture Dimensions) The difference between this comparative example and Example 1 lies in the specific dimensions of the guide fixture. For a Φ51×3.5mm spiral finned tube (inner diameter 44mm, base tube outer diameter 51mm), the outer diameter of the tapered shank of the guide fixture is adjusted to 43mm (0.5~1.0mm gap between the tapered shank and the inner diameter of the tube), the outer diameter of the round head is adjusted to 50.5mm (0.5mm gap between the round head and the tube hole), and the radius of the arc transition surface at the front end of the round head is adjusted to 6mm. The remaining steps are the same as in Example 1. The tube-threading effect of this comparative example is comparable to that of Example 1, with a fin damage rate of 0% and a total tube-threading time of 78 man-hours, verifying the scalability of the guide fixture of the present invention and its applicability to spiral finned tubes of different specifications.

[0086] Example 2 This embodiment uses a waste heat boiler module of another specification as an example to illustrate the versatility of the present invention. The module parameters of this embodiment are as follows: the number of spiral finned tubes is 512, arranged in 12 layers; the length of the spiral finned tubes is 12000mm; the number of tube sheets is 5; the material is mainly T22, with T91 used in some areas; the number of connecting pipes is 400.

[0087] This embodiment is implemented using the same method as Embodiment 1, specifically including: using an infrared positioning instrument for high-precision positioning of the tube sheet; pre-installing the first positioning sleeve; using a bottom-up transverse tube insertion sequence, with the aid of guide fixtures and tube delivery tools; using a pyramid-shaped sequence from bottom to top and from the middle to both sides for connecting tube welding; using a method of laying out heating plates and filling the gaps with insulation material to form a box-type furnace unit for post-weld local heat treatment, with the number of heating units adjusted to 12; and dividing the module into two independent passages for hydrostatic testing before assembling the header.

[0088] The manufacturing results of this embodiment show that: the damage rate of the tube fins is 0.5%; the first-pass yield rate of the weld is 97.5%; the heat treatment cycle is shortened by 75% compared with the traditional method; and there is no water residue after the hydrostatic test.

[0089] This embodiment verifies the applicability of the manufacturing method of the present invention to waste heat boiler modules of different specifications.

[0090] The manufacturing method for the spiral finned tube pressure-bearing component module of the waste heat boiler in a floating generator set, provided by this invention, has been successfully applied in the manufacturing of waste heat boiler modules for a 240MW "two-to-one" combined cycle unit. This method is applicable to the manufacturing of various large heat exchanger modules, and is particularly suitable for floating power generation equipment in marine engineering equipment requiring high reliability and corrosion resistance. The method of this invention features stable processes and strong repeatability. The required equipment and tooling, such as infrared positioning instruments, guiding fixtures, pipe delivery tools, and tracked heating plates, are all commonly used industrial equipment and are easy to promote and implement. Therefore, this invention has good industrial applicability.

[0091] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for manufacturing a pressure part module of a spiral finned tube of a floating generator unit waste heat boiler, said pressure part module comprising a number of tube sheets, a plurality of layers of spiral finned tubes passing through tube holes of the tube sheets, and connecting tubes connected to both ends of the spiral finned tubes, characterized in that: Includes the following steps: Step (1) High-precision positioning of tube sheets: Use an infrared positioning instrument to calibrate the center line of the tube holes of each tube sheet, so that the tube holes of several tube sheets are concentric. Then fix the tube sheets on the assembly frame by positioning plates and diagonal braces. Step (2), Pre-installation of positioning sleeves for spiral fin tubes: First, weld the first positioning sleeve onto each spiral fin tube. After the tube is inserted into place, the first positioning sleeve fits into the end tube sheet. Then, weld the second positioning sleeve. The spiral fin tube is axially fixed onto the module through the two positioning sleeves. Step (3) Horizontal pipe threading from bottom to top: Pipes are threaded horizontally from bottom to top. Before threading the pipe, the guide tool is inserted into the inner diameter of the front end of the spiral fin tube and temporarily spot-welded to guide it through the pipe hole. Pipe feeding tools are used between adjacent tube sheets to support the tube body and prevent adjacent spiral fin tubes from colliding with each other. Step (4), Pyramid-shaped connecting pipe assembly and welding: The connecting pipes at both ends of the module are assembled and welded in a pyramid-shaped sequence from bottom to top and from the middle to both sides. Flexible neck welding guns are used, and the welding is performed in sections, mirror welding and internal filler wire method. Step (5), Unitized local heat treatment of box-type furnace: The heating plate is laid flat on the upper and lower surfaces of the multi-layer weld joint, and the gaps between the pipes are filled with heat insulation material to form a closed heating unit. At least three thermocouples are arranged in each heating unit for post-weld local heat treatment. Step (6), water pressure test of each channel: Before assembling the intermediate header and the outlet header, the module is divided into multiple independent channels and water pressure tests are carried out separately. After the test, compressed air is used to blow dry.

2. The method of manufacturing a floating generator set waste heat boiler helical finned tube pressure part module according to claim 1, characterized in that: In step (1), a precision level is used to adjust the adjusting bolts around the assembly frame so that the elevation of each tube sheet mounting base is consistent and the levelness is controlled within ±0.5mm / m; the longitudinal center line and transverse center line of the tube sheet are marked on the base, and the error is controlled within ±0.3mm; after the infrared positioning instrument is calibrated, the concentricity deviation of the tube sheet is controlled within ±0.5mm.

3. The manufacturing method of the spiral finned tube pressure-bearing component module of the waste heat boiler of the floating generator set according to claim 1, characterized in that: In step (3), the guide fixture is a round head structure with a tapered handle. The tapered handle is inserted into the inner diameter of the spiral fin tube and temporarily spot-welded to fix it. The outer diameter of the round head is smaller than the inner diameter of the tube hole and larger than the outer diameter of the spiral fin tube base tube. The front end of the round head is machined into an arc transition surface. The tube feeding tool consists of a handle, a connecting rod and a bracket. The bracket has a U-shaped opening structure and flexible cushioning material is pasted on the inner wall of the bracket.

4. The manufacturing method of the spiral finned tube pressure-bearing component module of the waste heat boiler of the floating generator set according to claim 3, characterized in that: The guide tool has a cone shank length of 50mm, an outer diameter of shank that is 0.2-0.5mm smaller than the inner diameter of the spiral finned tube, an outer diameter of round head that is 0.3-0.8mm smaller than the inner diameter of the tube hole, and a radius of 5mm for the arc transition surface at the front end of the round head; the tube feeding tool has a bracket opening width of 45mm.

5. The manufacturing method of the spiral finned tube pressure-bearing component module of the waste heat boiler of the floating generator set according to claim 3, characterized in that: The flexible cushioning material attached to the inner wall of the tube delivery tool is a 5mm thick rubber pad.

6. The manufacturing method of the spiral finned tube pressure-bearing component module of the waste heat boiler of the floating generator set according to claim 1, characterized in that: In step (4), T91 material is preheated to 200℃-250℃ before welding, T22 material is preheated to 150℃-200℃ before welding, and the interpass temperature is controlled below 250℃; the welding current for the lower half of the pipe opening is 70A-100A, the welding current for the upper half of the pipe opening is 90A-120A, the welding voltage is 10V-14V, and the welding speed is 30-50mm / min.

7. The manufacturing method of the spiral finned tube pressure-bearing component module of the waste heat boiler of the floating generator set according to claim 1, characterized in that: In step (5), each heating unit covers 70-80 weld joints, the heating plate is a track-type ceramic electric heating plate, the insulation material is high-alumina fiber cotton, and the exposed surface of the heating unit is covered with asbestos cloth; the at least three thermocouples are respectively arranged on the upper left side of the first tube on the left side of the heating unit, the lower right side of the last tube on the right side, and the middle part of the tube in the middle area.

8. The manufacturing method of the spiral finned tube pressure-bearing component module of the waste heat boiler of the floating generator set according to claim 7, characterized in that: In step (5), the post-weld local heat treatment process parameters are: heating rate not greater than 150℃ / h, holding temperature of 745℃±15℃, holding time not less than 1h, cooling rate not greater than 275℃ / h, and furnace exit temperature not greater than 315℃.

9. The manufacturing method of the spiral finned tube pressure-bearing component module of the waste heat boiler of the floating generator set according to claim 1, characterized in that: In step (6), the module is divided into three independent channels for water pressure testing. The test pressure is 1.64 times the working pressure, the pressure increase rate is 0.05-0.1 MPa / min, the pressure holding time is 20-30 min, and the pressure decrease rate is no more than 0.3 MPa / min.

10. The manufacturing method of the spiral finned tube pressure-bearing component module of the waste heat boiler of the floating generator set according to claim 9, characterized in that: In step (6), the compressed air pressure for purging is 0.6 MPa, the compressed air dew point is not higher than -40℃, and the purging time is not less than 30 min.

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