A method for manufacturing a dilution steam superheater
By improving the manufacturing method of the dilution steam superheater, the heat exchange tubes are first installed and tested, and then the shell and tube sheet are assembled. The use of guide head tooling solves the problems of high assembly difficulty and high weld risk in the existing technology, and realizes a more efficient and reliable production process.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- JIANGNAN BOILERS & PRESSURE VESSELS ZHANGJIAGANG
- Filing Date
- 2023-12-25
- Publication Date
- 2026-07-03
Smart Images
Figure CN117680862B_ABST
Abstract
Description
Technical Field
[0001] This application relates to dilution steam superheaters, and more particularly to a method for manufacturing a dilution steam superheater. Background Technology
[0002] The dilution steam superheater is mainly used in the cracking process of ethylene plants. The main process is as follows: dilution steam is injected into the cracking feedstock in one step. The feedstock is preheated in the convection section and then mixed with the superheated dilution steam in the convection section. The cracking feedstock oil after the dilution steam injection is preheated to the cross temperature of the feedstock in the convection section and then sent to the radiant coil. In the radiant section, the material inside the tube heats up rapidly, and the cracking reaction of the feedstock takes place simultaneously, producing cracked gas containing many components such as ethylene, propylene, butadiene, methane, and ethane.
[0003] Currently, the tube sheet and heat exchange tubes at the inlet end of the dilution steam superheater in China are welded together using an internal butt welding method. This structure is mainly used in high-temperature, high-pressure applications with corrosive media. Compared to the traditional external tube head welding method, it has the following advantages:
[0004] 1) Welded joints have relatively high reliability;
[0005] 2) The heat exchange tubes and tube sheet have a fully welded structure, which prevents crevice corrosion and provides good resistance to stress corrosion.
[0006] 3) Welds are easy to inspect using radiographic testing;
[0007] 4) No residual stress is generated during tube expansion;
[0008] 5) There is no stress concentration at the root cut of the weld in the end weld joint, and cracks are not easily generated during operation.
[0009] After the heat exchanger tubes are butt-welded to the inner bore of the tube sheet, 100% radiographic testing (RT) is required. A Level II test is acceptable, and the technical grade is AB. Current radiographic testing methods require: 1) Welding of a row must be completed and all sections must pass radiographic testing before proceeding; any section failing must be repaired. 2) The shell-side section near the inner bore weld must not be obstructed by any other shell section. According to the existing process, the assembly sequence is: scaffolding → insert and fix a portion of the heat exchanger tubes → install the shell section (leaving the section near the inner bore weld uninstalled) → install the other tube sheet → insert the remaining heat exchanger tubes → weld the inner bore butt-welded tube ends first → finally weld the protruding ends of the tube ends. The current process leaves one section of the shell uninstalled, providing space for external gas protection during inner bore welding, RT testing of the inner bore weld, and weld repair.
[0010] The process of leaving one section of the cylinder unassembled involves assembling it after the inner bore welded pipe end has passed flaw detection. This cylinder section is integrally pressed and welded, and the circumferential seams at both ends are machined before being cut in half along the center using the longitudinal seam of the cylinder section. Finally, it is assembled by butt-jointing the two sections together. This process has the following drawbacks:
[0011] 1) After the cylinder is formed, it is cut in half. After cutting, there will be springback, and the ovality of the cylinder section cannot be guaranteed.
[0012] 2) After the two sections were assembled, an additional longitudinal seam was added to the cylinder section, increasing the risk of leakage;
[0013] 3) The assembly is difficult. After the longitudinal seam of the cylinder section is welded, due to the uncontrollable ellipticity, when the two ends are assembled with the tube sheet and another cylinder section respectively, the misalignment of the bevel is not the same all around. The argon arc welding root pass is uncontrollable and is prone to welding defects. Summary of the Invention
[0014] The purpose of this invention is to provide a method for manufacturing a dilution steam superheater, which abandons the previous method of assembling a two-section cylinder together at the end. This reduces assembly steps, assembly difficulty, and the risk of an extra weld. During circumferential seam assembly, the misalignment of the bevel is reduced, ensuring the pass rate of the argon arc welding root pass. In terms of flaw detection, the original process route could not perform 100% RT testing on the longitudinal seam after the two-section cylinder was finally assembled and welded. Only existing methods such as UT / TOFD ultrasonic testing could be used. The new process solution does not have this problem. The cylinder sections can be welded and assembled together for 100% RT testing.
[0015] To achieve the above objectives, the present invention provides the following technical solution.
[0016] This application discloses a method for manufacturing a dilution steam superheater. The dilution steam superheater includes a front tube box, a left tube sheet, a cylinder, a right tube sheet, and a rear tube box connected sequentially from left to right. The cylinder has a cavity inside, and a frame is installed inside the cavity. Multiple heat exchange tubes are mounted on the frame, and the two ends of each heat exchange tube are connected to the left tube sheet and the right tube sheet, respectively. The manufacturing method includes the following steps in sequence:
[0017] S1. Start by assembling the frame using the left tube sheet. After the frame is assembled, fix it with steel to ensure it is level. Begin by vertically threading the heat exchange tubes one row at a time from the center outwards and cleaning the tube holes. First, thread the two central vertical rows of heat exchange tubes. After welding, use a helium leak detection tool to perform a helium leak test. After the self-inspection is qualified, perform a 100% RT test on the butt weld joint of the two rows of heat exchange tubes. After it is qualified, assemble and weld the two vertical rows of heat exchange tubes respectively. Repeat this step until all heat exchange tubes are welded.
[0018] After the welding of the left tube sheet and the heat exchange tube is completed and qualified, the cylinder body is assembled. After assembly, the cylinder body is spot welded to the circumferential seam of the left tube sheet.
[0019] S3 After the right end of all the heat exchange tubes is inserted into the guide head tooling, the right tube sheet is inserted. After completion, the right tube sheet is spot welded to the circumferential seam of the cylinder.
[0020] S4 performs argon arc welding on the circumferential seam that is spot-welded to the cylinder and the left tube sheet / the right tube sheet. After the root weld is completed, the right tube sheet and the heat exchange tube are welded together. After the root weld is completed, the two circumferential seams that were rooted are welded together.
[0021] S5 finally assembles the front-end pipe box and the rear-end pipe box.
[0022] Preferably, in the above-described method for manufacturing a dilution steam superheater, in step S4, the heat exchange tube protrudes from the right tube sheet.
[0023] Preferably, in the above-described method for manufacturing a dilution steam superheater, the guide head fixture includes a first column, a second column, and a frustum connected sequentially from left to right. The first column is inserted into the heat exchange tube, the end face of the second column abuts against the end of the heat exchange tube, the outer diameter of the frustum gradually decreases from left to right, the frustum is inserted into the right tube sheet, and the outer diameter of the second column is less than or equal to the outer diameter of the heat exchange tube.
[0024] Preferably, in the above-described method for manufacturing a dilution steam superheater, the top of the cylinder has two first openings arranged opposite to each other.
[0025] Preferably, in the above-described method for manufacturing a dilution steam superheater, a second port is formed at the bottom center of the cylinder.
[0026] Preferably, in the above-described method for manufacturing a dilution steam superheater, a third port is formed at the center of the top of the cylinder.
[0027] Preferably, in the above-described method for manufacturing a dilution steam superheater, a fourth port is formed on one side of the bottom of the cylinder.
[0028] Preferably, in the above-described method for manufacturing the dilution steam superheater, a fifth port is formed at the top and bottom of the front-end tube box.
[0029] Preferably, in the above-described method for manufacturing the dilution steam superheater, a sixth port is formed at the top of the rear end tube box.
[0030] Compared with the prior art, the advantages of the present invention are as follows:
[0031] 1. Reduced production steps and lower labor costs: The cylinder sections do not need to be cut in half after forming and then assembled at the end;
[0032] 2. Reduced risk factors: Cutting the cylinder section in half and then assembling it creates an extra longitudinal seam, which increases the probability of welding defects. Furthermore, if the ovality cannot be guaranteed, it increases the difficulty of adjusting the bevel misalignment when assembling the circumferential seam, which also increases the probability of welding defects.
[0033] 3. The flaw detection process is simplified. The cylinder section does not need to be reassembled after being split in half. The 100% RT test of the longitudinal and circumferential seams can be completed in one go after the cylinder section is assembled. Moreover, the two-piece section cannot be tested by RT and can only be tested by ultrasonic testing. Attached Figure Description
[0034] To more clearly illustrate the technical solutions in the embodiments of this application 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 some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0035] Figure 1 The diagram shown is a schematic of a dilution steam superheater in a specific embodiment of the present invention;
[0036] Figure 2 The image shown is a front view of the guide head tooling in a specific embodiment of the present invention. Detailed Implementation
[0037] The technical solutions of the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0038] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for 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. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.
[0039] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.
[0040] Combination Figure 1-2 As shown, the manufacturing method of the dilution steam superheater 100 includes a front tube box 101, a left tube sheet 102, a cylinder 103, a right tube sheet 104, and a rear tube box 105 connected sequentially from left to right. A cavity 106 is formed inside the cylinder 103, and a frame 107 is installed inside the cavity 106. Multiple heat exchange tubes 108 are mounted on the frame 107, and both ends of the heat exchange tubes 108 are connected to the left tube sheet 102 and the right tube sheet 104, respectively. The manufacturing method includes the following steps:
[0041] S1 begins by assembling the frame 107 using the left tube sheet 102. After the frame 107 is erected, it is fixed with structural steel to ensure it is level. Starting from the center, heat exchange tubes 108 are vertically threaded row by row from both sides, and the tube holes are cleaned. First, the two central vertical rows of heat exchange tubes 108 are threaded. After welding, a helium leak detection tool is used to perform a helium leak detection. After the self-inspection is qualified, the butt weld joints of the two rows of heat exchange tubes 108 are subjected to 100% RT testing. After passing the test, the two vertical rows of heat exchange tubes 108 are assembled and welded separately. This process is repeated until all heat exchange tubes 108 are welded.
[0042] After the welding of the left tube sheet 102 and the heat exchange tube 108 is completed and qualified, the cylinder 103 is assembled. After assembly, the circumferential seam of the cylinder 103 and the left tube sheet 102 are spot welded.
[0043] After the right end of all heat exchange tubes 108 in S3 is inserted into the guide head fixture 109, it is inserted into the right tube sheet 104. After completion, the right tube sheet 104 and the cylinder 103 are spot welded together. The guide head fixture 109 includes a first column 1091, a second column 1092, and a frustum 1093 connected from left to right. The first column 1091 is inserted into the heat exchange tube 108. The end face of the second column 1092 abuts against the end of the heat exchange tube 108. The outer diameter of the frustum 1093 gradually decreases from left to right. The frustum 1093 is inserted into the right tube sheet 104. The outer diameter of the second column 1092 is less than or equal to the outer diameter of the heat exchange tube 108.
[0044] S4 performs argon arc welding on the circumferential seam that is spot welded between the cylinder 103 and the left tube sheet 102 / right tube sheet 104. After the root pass is completed, the right tube sheet 104 and the heat exchange tube 108 are welded together. After completion, the two circumferential seams of the root pass are welded together. The heat exchange tube 108 protrudes from the right tube sheet 104.
[0045] The S5 is finally assembled with the front end pipe box 101 and the rear end pipe box 105.
[0046] In addition, to achieve general functionality, two first ports 110 are formed opposite to each other on the top of the cylinder 103. A second port 111 is formed in the middle of the bottom of the cylinder 103. A third port 112 is formed in the middle of the top of the cylinder 103. A fourth port 113 is formed on one side of the bottom of the cylinder 103. A fifth port 114 is formed on the top and bottom of the front end pipe box 101. A sixth port 115 is formed on the top of the rear end pipe box 105. These are used for functions such as liquid input or discharge.
[0047] The working principle of the dilution steam superheater in this project is as follows: Dilution steam flows out of the boiler, passes through the front-end tube box, and then through the superheater, which consists of a large number of heat exchange tubes. The dilution steam flows through the heat exchange tubes and exits from the rear-end tube box. Medium-pressure steam enters the superheater shell through the first inlet and flows through the outside of the heat exchange tubes. Due to the high temperature of the dilution steam, the medium-pressure steam is heated to above its saturation temperature, making it supersaturated steam, which increases the steam's temperature and thermal energy, and finally exits from the second inlet.
[0048] The left tube sheet has an inner hole butt joint structure. During the process of dilution steam entering the heat exchange tube from the front tube box, other sulfide impurities will corrode the tube head weld under high temperature conditions. The inner hole butt joint welding method reasonably avoids stress corrosion at this point.
[0049] The dilution steam superheater in this project adopted a new assembly process to achieve the effects described above. The specific new process is described below:
[0050] 1. Start by assembling the frame using the left tube sheet (internal bore butt joint structure). After the frame is erected, fix it with structural steel to ensure it is level. Begin by vertically threading the heat exchange tubes row by row from the center outwards and cleaning the tube holes. First, thread the two central vertical rows of heat exchange tubes. After welding, use a helium leak detection tool to perform a helium leak test. After the self-inspection is qualified, perform a 100% RT test on the butt joint of the two rows of heat exchange tubes. After it is qualified, assemble and weld the two vertical rows of heat exchange tubes respectively. Follow this step until all heat exchange tubes are welded.
[0051] 2. After the welding of the left tube sheet and heat exchange tubes is completed and qualified, the cylinder body is assembled. After assembly, the circumferential seam of the cylinder body to the left tube sheet is spot welded.
[0052] 3. After completing the above steps, the right tube sheet needs to be assembled. Since all heat exchange tubes have been assembled, assembling the right tube sheet is more difficult. A guide head tool is needed to guide it. Each heat exchange tube needs to be equipped with a guide head tool in order to successfully assemble the right tube sheet. After assembly, spot weld it to the circumferential seam of the shell.
[0053] 4. Perform argon arc welding on the circumferential seams that are spot-welded to the cylinder and the left and right tube sheets. After the root pass is completed, weld the heat exchange tube to the right tube sheet (this weld joint is an extension structure of the heat exchange tube, and the extension length of the heat exchange tube is scraped according to the drawing requirements). After the extension structure of the heat exchange tube is welded, complete the welding of the two circumferential seams that were used for the root pass.
[0054] 5. Finally, assemble the front-end and rear-end pipe boxes.
[0055] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.
[0056] The above description is only a specific embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.
Claims
1. A method for manufacturing a dilution steam superheater, characterized in that, The dilution steam superheater includes a front tube box, a left tube sheet, a cylinder, a right tube sheet, and a rear tube box connected sequentially from left to right. The cylinder has an internal cavity, and a frame is installed within the cavity. Multiple heat exchange tubes are mounted on the frame, and both ends of each heat exchange tube are connected to the left tube sheet and the right tube sheet, respectively. The manufacturing method includes the following steps: S1. Start by assembling the frame using the left tube sheet. After the frame is assembled, fix it with steel to ensure it is level. Begin by vertically threading the heat exchange tubes row by row from the center outwards and cleaning the tube holes. First, thread the two central vertical rows of heat exchange tubes. After welding, use a helium leak detection tool to perform a helium leak test. After the self-inspection is qualified, perform a 100% RT test on the butt weld joint of the two rows of heat exchange tubes. After it is qualified, assemble and weld the two vertical rows of heat exchange tubes respectively. Follow this step until all heat exchange tubes are welded. S2 After the welding of the left tube sheet and the heat exchange tube is completed and qualified, the cylinder body is assembled and then spot welded to the circumferential seam of the left tube sheet. S3 After the right end of all the heat exchange tubes is inserted into the guide head tooling, the right tube sheet is inserted. After completion, the right tube sheet is spot welded to the circumferential seam of the cylinder. S4. Perform argon arc welding on the circumferential seam that is spot-welded between the cylinder and the left tube sheet. After the root weld is completed, weld the right tube sheet and the heat exchange tube. Then, perform argon arc welding on the circumferential seam that is spot-welded between the cylinder and the right tube sheet. After the root weld is completed, continue to weld the two circumferential seams. The heat exchange tube protrudes from the right tube sheet. S5 Finally, assemble the front-end pipe box and the rear-end pipe box. The guide head fixture includes a first column, a second column, and a frustum connected sequentially from left to right. The first column is inserted into the heat exchange tube, the end face of the second column abuts against the end of the heat exchange tube, the outer diameter of the frustum gradually decreases from left to right, the frustum is inserted into the right tube sheet, and the outer diameter of the second column is less than or equal to the outer diameter of the heat exchange tube.
2. The method for manufacturing a dilution steam superheater according to claim 1, characterized in that, The top of the cylinder has two first openings arranged opposite to each other.
3. The method for manufacturing a dilution steam superheater according to claim 1, characterized in that, A second opening is formed in the middle of the bottom of the cylinder.
4. The method for manufacturing a dilution steam superheater according to claim 1, characterized in that, A third opening is formed in the middle of the top of the cylinder.
5. The method for manufacturing a dilution steam superheater according to claim 1, characterized in that, A fourth opening is formed on one side of the bottom of the cylinder.
6. The method for manufacturing a dilution steam superheater according to claim 1, characterized in that, The top and bottom of the front-end pipe box are respectively formed with a fifth pipe opening.
7. The method for manufacturing a dilution steam superheater according to claim 1, characterized in that, A sixth port is formed at the top of the rear-end pipe box.