Tube-tube sheet joint low-stress welding method

Abstract

The present invention relates to the technical field of petrochemical apparatus manufacturing, and specifically relates to a tube-tube sheet joint low-stress welding method, comprising a pre-positioning step, a partitioning step, a heating step, a stress measurement and control step, a welding step and a heat removal step. By dividing a joint area to be welded into a plurality of welding areas, a plurality of heat exchange tubes of each welding area are simultaneously subjected to temperature control, such that the number of lines is small, thus reducing the likelihood of confusion and facilitating operation; a laser flatness measurement instrument provided beside a second tube sheet is used to measure the flatness of the outer side surface of the second tube sheet, so as to indirectly feed back the amounts of thermal elongation of the heat exchange tubes of each welding area, and there is no need to install linear displacement sensors on the side walls of the heat exchange tubes as in the prior art, thereby avoiding the problem of high installation difficulty of elongation measurement devices, and achieving relatively simple disassembly and assembly; electronic components such as the laser flatness measurement instrument are separated from the heat exchange tubes, such that the impact of the high temperature of the heat exchange tubes on the measurement precision of the electronic components is avoided, thus prolonging the service life thereof, and saving costs.

Description

Low stress welding method for tube-to-tube sheet joints TECHNICAL FIELD

[0001] The present application relates to the technical field of petrochemical equipment manufacturing, in particular to a low stress welding method for tube-to-tube sheet joints. BACKGROUND

[0002] In chemical equipment, the tube heat exchanger is an important device, and the welding joint of the tube sheet and the heat exchange tube is the most important and most likely to fail welding joint in the device, and its quality directly affects the service life of the device and the stability of the device, so the welding between the heat exchange tube and the tube sheet is particularly important.

[0003] The Chinese patent document with publication number CN102151958A discloses a welding method for the welding joint of a heat exchanger tube sheet and a heat exchange tube. In the assembly of the heat exchange tube and the tube sheet, a structure with a recess of 0.5-1mm on the surface of the tube sheet is adopted, and in the welding, a welding sequence from bottom to top is adopted, and a "3" or "S" shaped welding operation route is adopted. During welding, each heat exchange tube is welded for half a circle, and after welding 8-10 heat exchange tubes at a time without arc extinguishing, the arc is extinguished on the tube sheet. Then, according to the same method, the other half circle is welded from bottom to top. In this way, the number of arc striking and extinguishing can be reduced, the welding efficiency can be improved, the number of arc striking and extinguishing points can be reduced, and the probability of producing welding defects can be reduced. In this way, the tungsten electrode can easily penetrate into the root of the included angle between the heat exchange tube and the tube sheet during welding, and during self-fusion welding, the arc can reach the sharp corner position, the root can be completely penetrated, and no cavity is left, which prevents the storage of shell side corrosion medium, avoids gap corrosion, and improves the service life of the weld.

[0004] The quench heat exchanger can quickly cool the pyrolysis raw material after high-temperature cracking, thereby preventing the occurrence of secondary reaction. The quench heat exchanger is one of the key equipment of the cracking furnace. On the cracking furnace, the quench heat exchanger is usually arranged in a single-stage quench heat exchanger or a multi-stage quench heat exchanger. The single-stage quench heat exchanger has the characteristics of low pressure drop and simple arrangement. The multi-stage quench heat exchanger has the characteristics of high ethylene yield, fast termination of secondary reaction and more super-high pressure steam recovery. The two-stage quench heat exchanger is generally a plate-type quench heat exchanger, which mainly comprises a pyrolysis gas inlet header, a quench heat exchanger shell, a pyrolysis gas outlet header, heat exchange tubes, a front tube plate, a rear tube plate, baffle plates, an upcomer joint and a downcomer joint. The quench heat exchanger shell has a plurality of heat exchange tubes. The quench heat exchanger shell and the heat exchange tubes are connected through the front tube plate and the rear tube plate. High-temperature pyrolysis gas is introduced into the heat exchange tubes, and a cooling medium is introduced between the heat exchange tubes and the quench heat exchanger shell during work, so that the high-temperature pyrolysis gas is quickly cooled under the action of the cooling medium. At high temperature, the heat exchange tubes and the quench heat exchanger shell will expand and elongate. However, due to the large temperature difference between the heat exchange tubes and the quench heat exchanger shell, the elongation of the heat exchange tubes will be greater than that of the quench heat exchanger shell. On the other hand, there is also a temperature difference between the plurality of heat exchange tubes. Thus, a large temperature stress is easily formed at the connection position between the heat exchange tubes and the front and rear tube plates, thereby causing cracks in the heat exchange tubes, and even causing the heat exchange tubes to break.

[0005] In order to avoid cracks or breakage of the heat exchange tubes, the heat exchange tubes need to be pre-stressed and elongated to reduce the difference in elongation between the heat exchange tubes and the quench heat exchanger shell. The main method for pre-stressing and elongating the heat exchange tubes at present is to blow hot air into all the heat exchange tubes, heat all the heat exchange tubes at the same time to realize pre-stretching of the heat exchange tubes, and then weld the heat exchange tubes. This method is simple to implement, but the temperature control precision is not high, and the temperature of each heat exchange tube is not uniform. Another method is to insert a heating tool into the hole of each heat exchange tube. However, this method is only used when the number of heat exchange tubes is small. For example, the patent number CN102489908A discloses a quench heat exchanger pre-stress elongation heating device, which is applied to the pre-stress elongation heating device of a single heat exchange tube. If the number of heat exchange tubes required to be heated and elongated at the same time reaches a certain number, such as 60, the temperature of the heat exchange tubes will interfere with each other, especially the heat of the heat exchange tubes located below will be transmitted upward, affecting the temperature of the heat exchange tubes above. Therefore, if the above quench heat exchanger pre-stress elongation heating device is used to pre-stress and elongate multiple heat exchange tubes at the same time, the pre-stress elongation amount will deviate.

[0006] Then the applicant developed a kind of cluster type prestressed elongation heating system for quenching heat exchanger as disclosed in the Chinese patent document with publication number CN109338077A, which comprises an intelligent control module, multiple control modules, multiple heating tools and multiple elongation measuring devices, the intelligent control module is connected with each control module respectively, each control module is connected with one heating tool and one elongation measuring device respectively, the intelligent control module controls the heating tools connected with each control module to heat, so that each heat exchange tube with the heating tool inserted is heated and elongated, and each control module controls the heating amount of each heating tool according to the elongation data fed back by the elongation measuring device, so as to accurately control the elongation of each heat exchange tube with the heating tool inserted. Technical problem

[0007] It is further found in application that the prior art controls the heating amount of the heating tool by measuring the elongation of each heated heat exchange tube, and each heating tool is inserted into the interior of each heat exchange tube, that is, each heat exchange tube is inserted with a heating tool, so that there is room for improvement in that:

[0008] I. When the number of heat exchange tubes corresponding to the same tube plate exceeds sixty or even hundreds, each heat exchange tube is connected with a control module, a heating tool and an elongation measuring device, the number of lines is relatively large, and the operation is easy to confuse;

[0009] II. The heat exchange tubes are densely distributed in clusters, and it is difficult to measure the thermal elongation of the heat exchange tubes located in the middle;

[0010] III. The temperature of the heated and elongated heat exchange tube is relatively high, especially the temperature in the middle is more concentrated, which greatly affects the measurement accuracy of the electronic measuring element, and the high temperature also affects the service life of the measuring element. Solution

[0011] In view of all or part of the above technical problems existing in the prior art, the present application provides a pipe-tube plate joint low stress welding method.

[0012] To achieve the above purpose, the present application provides the following technical solutions:

[0013] A pipe-tube plate joint low stress welding method is provided, comprising the following steps:

[0014] A pre-positioning step, according to the length of the heat exchange tube, the first tube plate and the second tube plate are fixed side by side on the tool, one end of the plurality of heat exchange tubes is correspondingly inserted into the plurality of tube holes of the first tube plate, and the other end of the plurality of heat exchange tubes is correspondingly movably inserted into the plurality of tube holes of the second tube plate;

[0015] Partitioning step: an identification is provided on the outer side of the second tube plate, and a plurality of to-be-welded joint areas formed by the plurality of heat exchange tube ends and the plurality of tube holes are divided into a plurality of welding areas according to a preset number;

[0016] Heating step: in groups, the plurality of heat exchange tubes in the plurality of welding areas are heated respectively by the plurality of heating devices, so that the plurality of heat exchange tubes are heat elongated in a direction away from the first tube plate;

[0017] Stress measurement and control step: the heating devices are electrically connected with a control module and a laser flatness measuring instrument, the laser flatness measuring instrument is located on the outer side of the second tube plate, and is used to measure the flatness of the outer side of the second tube plate in real time; the control module controls the heat generation of each heating device according to the measured flatness change signal, so that the flatness of the outer side of the second tube plate is stabilized at 0.01-0.8 mm;

[0018] Welding step: after the flatness of the outer side of the second tube plate is stabilized, the to-be-welded joint areas in each group of welding areas are welded and fixed in turn, and before welding of the next group of welding areas, the stress measurement and control step is re-implemented;

[0019] Heat removal step: after all the welding areas are completely welded, the plurality of heating devices stop heating the heat exchange tubes.

[0020] As a further optional scheme, in the stress measurement and control step, the flatness of the outer side of the second tube plate is controlled to be ≤0.5 mm.

[0021] As a further optional scheme, the heating device is an electric heating rod inserted into the plurality of heat exchange tubes from the outer side of the first tube plate, and the plurality of electric heating rods in the same welding area are electrically connected with the same control module to control synchronous temperature rise and fall.

[0022] As a further optional scheme, the heating device further comprises a support plate, and the plurality of electric heating rods corresponding to the same welding area are fixed side by side on the support plate, so that the plurality of electric heating rods in the same welding area can be inserted into the corresponding heat exchange tubes synchronously, and the support plate is positioned in close contact with the outer side of the first tube plate.

[0023] Specifically, the outer side of the electric heating rod is provided with a guide support protrusion matched with the inner wall of the heat exchange tube.

[0024] Specifically, the arrangement mode of the plurality of electric heating rods on the support plate is adjustable, which is achieved in that: the support plate is provided with a plurality of positioning holes, the number of the positioning holes is greater than the number of the electric heating rods, and the electric heating rods are selectively and detachably connected with different positioning holes; or the support plate is provided with a plurality of long strip holes, and the ends of the plurality of electric heating rods are loosely installed in different long strip holes.

[0025] As a further optional scheme, in the partitioning step, the identification is a pattern, shape or number provided on the outer side of the second tube plate.

[0026] As a further optional solution, the heating device is a flexible electric heating blanket wrapped around the plurality of heat exchange pipes corresponding to each group of welding zones.

[0027] Specifically, the electric heating blanket includes a heating core in the inner layer and a heat insulation layer in the outer layer, and the heat insulation layer is used to block the heat transfer of the electric heating blanket corresponding to different welding zones.

[0028] Specifically, the electric heating blanket includes a blanket body for wrapping the plurality of heat exchange pipes and a pulling part extending out of all the heat exchange pipes, and an external force pulling the pulling part can pull the electric heating blanket away from the heat exchange pipes. Advantages

[0029] Compared with the prior art, the pipe-to-pipe plate joint low stress welding method has the following advantages:

[0030] I. By dividing the to-be-welded joint area into multiple groups of welding zones, the plurality of heat exchange pipes in each group of welding zones are controlled at the same temperature, the number of lines is small, it is not easy to confuse, and it is convenient to operate;

[0031] II. The planeness of the outer side surface of the second tube plate is measured by the laser planeness measuring instrument arranged on the side of the second tube plate to indirectly feedback the thermal elongation of the heat exchange pipes in each group of welding groups, without installing a linear displacement sensor on the side wall of the heat exchange pipe as in the prior art, thereby avoiding the problem of high difficulty in installing the elongation measuring device, and the disassembly and assembly are relatively simple;

[0032] III. The electronic components such as the laser planeness measuring instrument are separated from the heat exchange pipes, the measurement accuracy of the electronic components is not affected by the high temperature of the heat exchange pipes, the service life of the electronic components is prolonged, and the cost is saved. BRIEF DESCRIPTION OF DRAWINGS

[0033] FIG. 1 is a schematic diagram of the welding method in the embodiment.

[0034] FIG. 2 is a schematic diagram of the partitioning of multiple to-be-welded joints in the embodiment.

[0035] FIG. 3 is a schematic diagram of the heating device in one of the embodiments.

[0036] FIG. 4 is a schematic diagram of the heating device in another embodiment.

[0037] REFERENCE NUMERALS:

[0038] Heat exchange pipe 1, first tube plate 2, second tube plate 3, mark 4;

[0039] Heating device 5;

[0040] Electric heating rod 51, support plate 52, guide support protrusion 53;

[0041] Electric heating blanket 61, heating core 62, heat insulation layer 63, blanket body 64, pulling part 65;

[0042] Laser flatness measuring instrument 7. Best mode of the invention

[0043] The best mode of the invention is entered here. Embodiment of the invention

[0044] The technical solutions in the embodiments of the present application will be clearly and completely described in connection with the drawings in the embodiments of the present application. In the case of no conflict, the following embodiments and features in the embodiments can be combined with each other.

[0045] The low-stress welding method of the present embodiment is used for welding between the tube bundle and the tube plate of the shell-and-tube heat exchanger shown in FIG. 1, the tube bundle comprising a plurality of heat exchange tubes 1 arranged side by side, the two ends of the plurality of heat exchange tubes 1 being respectively provided in a plurality of tube holes of a first tube plate 1 and a second tube plate 2, the right end of the heat exchange tube 1 being welded and fixed with the tube hole of the first tube plate 2 on the right in FIG. 1, and the welding method of the present embodiment being applied to welding between the left end of the heat exchange tube 1 and the tube hole of the second tube plate 3 on the left. In combination with FIGS. 1 to 3, the method specifically comprises the following steps:

[0046] The pre-positioning step is to fix the first tube plate 2 and the second tube plate 3 side by side on a tool according to the length of the heat exchange tube 1, the right end of the plurality of heat exchange tubes 1 being correspondingly provided in and welded to the plurality of tube holes of the first tube plate 2, and the left end of the plurality of heat exchange tubes 1 being correspondingly movably provided in the plurality of tube holes of the second tube plate 3 as joints to be welded. The second tube plate 2 is a flexible tube plate, and the periphery thereof is provided with an arc-shaped flexible portion.

[0047] The partitioning step is to divide a plurality of joints to be welded formed by the end of the plurality of heat exchange tubes 1 and the plurality of tube holes into a plurality of welding zones according to a preset number by setting a mark 4 on the outside of the second tube plate 3. As shown by the dashed line in FIG. 3, nine groups are divided. Of course, other numbers can be divided according to process requirements in practice. The mark 4 is a pattern, shape or number set on the outer surface of the second tube plate 3, for example, each welding zone is circled, different numbers or shapes are marked on each welding zone (for example, all the welding zones are marked with triangles, and all the other welding zones are marked with squares, and so on).

[0048] The heating step is to heat the plurality of heat exchange tubes 1 in each group of welding zones by a plurality of heating devices 5 respectively in a group unit, so that the plurality of heat exchange tubes 1 are heat elongated away from the first tube plate 2. One heating device 5 independently and simultaneously heats the plurality of heat exchange tubes 1 in one welding zone.

[0049] Stress measurement and control step: the heating device 5 is electrically connected with a control module and a laser flatness measuring instrument 7, the laser flatness measuring instrument 7 is located outside the second tube plate 3, and is used for measuring the flatness of the outer side of the second tube plate 3 in real time. After the software engineer programs the control module, the computer function module is constructed to realize: the control module controls the heat output of each heating device 5 according to the measured flatness change signal, so as to control the flatness of the outer side of the second tube plate 3 to be stable at 0.01-0.8 mm. Preferably, the flatness of the outer side of the second tube plate 3 is controlled to be ≤0.5 mm. When the outer side of the second tube plate 3 protrudes outward (the left direction of FIG. 1 is outward), it indicates that the heat elongation of the corresponding heat exchange pipe 1 is too large, and then the heat output of the corresponding heating device is reduced, and vice versa. The heating device 5 controls the heating temperature by controlling the heating power.

[0050] Welding step: after the flatness of the outer side of the second tube plate 3 is stable, the to-be-welded joint area of each group of welding areas is welded in turn, and before welding the next group of welding areas, the above-mentioned stress measurement and control step is re-implemented. In actual operation, the welding can be automatically performed by a robot or manually performed.

[0051] Heat removal step: after all the welding areas are completely welded, the multiple heating devices 5 stop heating the heat exchange pipes 1, and the heating devices 5 are removed.

[0052] It should be noted that the laser flatness measuring instrument 7 is also called a laser leveling instrument, which is an instrument for measuring flatness in the prior art, and will not be described here. However, it is emphasized that the prior art either welds while heating each heat exchange pipe 1 one by one, which cannot achieve the effect of eliminating the influence of thermal stress, or simultaneously and independently heats all the heat exchange pipes 1, which cannot achieve the effects of convenient installation and high detection precision. In the present application, the to-be-welded joint is heated in a partitioned manner, and the flatness of the second tube plate 3 is used to indirectly feedback the heat elongation of the heat exchange pipe 1, which achieves the effects of convenient measurement and high precision, and the two effects are complementary and indispensable. If the heating device 5 is not partitioned, the temperature cannot be controlled according to the flatness, and if the temperature is controlled according to the flatness without partitioning the heating, the equipment is more complex. Therefore, the two are inseparable as a whole, and according to the overall judgment principle of evaluating creativity, in the field of tube-tube plate joint welding technology, the prior art does not simultaneously disclose the partitioned heating of the to-be-welded joint and the indirect feedback of the heat elongation of the heat exchange pipe 1 through the flatness of the second tube plate 3. Therefore, the present application has outstanding substantial features and significant progress.

[0053] In the embodiment, the heating device 5 is an electric heating rod 51 inserted into the plurality of heat exchange pipes 1 from the outer side of the first tube plate 2, that is, from right to left in FIG. 1. The plurality of electric heating rods 51 in the same welding area are electrically connected with the same control module to control the synchronous temperature rise and fall.

[0054] Specifically, the heating device 5 further comprises a support plate 52, and a plurality of electric heating rods 51 corresponding to the same welding area are fixed on the support plate 52 in parallel, so that the plurality of electric heating rods 51 corresponding to the same welding area can be inserted into the corresponding heat exchange pipe 1 synchronously, and the support plate 52 is positioned in close contact with the outer side of the first tube plate 2. Specifically, the outer side of the electric heating rod 51 is provided with a guide support protrusion 53 matched with the inner wall of the heat exchange pipe 1, and the guide support protrusions 53 of adjacent electric heating rods 51 are arranged in a circumferential direction. In practice, the guide support protrusions 53 can be arranged only on part of the electric heating rods 51, or can be arranged on all the electric heating rods 51. Of course, the plurality of electric heating rods 51 of all welding areas can also use one support plate 52 at the same time, which can be inserted at one time, but it is necessary to accurately align the electric heating rods 51 with the ports of the heat exchange pipe 1.

[0055] Actually, the electric heating rod 51 can be designed as an extendable umbrella structure to adapt to heat exchange pipes 1 of different lengths or to change the position of the heat exchange pipe 1.

[0056] Actually, the electric heating rod 51 can be designed as a tubular structure, with a high-temperature-resistant water-cooled jacket on the inner side for circulating refrigerant to quickly adjust the temperature of the electric heating rod 51.

[0057] In practice, a thermal blanket can be provided to wrap the plurality of heat exchange pipes corresponding to each group of welding areas, to avoid temperature influence between heat exchange pipes of different welding areas, and to facilitate temperature control.

[0058] Specifically, the arrangement of the plurality of electric heating rods 51 on the support plate 52 is adjustable, and the installation position of the electric heating rod 51 is adjusted according to different division modes, so that the electric heating rod 51 is suitable for different arrangement modes of the heat exchange pipe 1 of the heat exchanger. This is achieved by that the support plate 52 is provided with a plurality of positioning holes, the number of the positioning holes is greater than the number of the electric heating rods 51, and the electric heating rods 51 are selectively and detachably connected with different positioning holes, such as threaded connection, buckle connection, interference fit, etc. Or the support plate 52 is provided with a plurality of long strip holes, and the ends of the plurality of electric heating rods 51 are loosely installed in different long strip holes, and the electric heating rods 51 are adjusted to the preset position along the length direction of the long strip hole and then fixed.

[0059] Another embodiment of the heating device 5 is shown in FIG. 4, which is a flexible electric heating blanket 61 wrapping the plurality of heat exchange pipes 1 corresponding to each group of welding areas. Before the pre-positioning step, when the plurality of heat exchange pipes 1 are welded and fixed to the first tube plate 2, the heat exchange pipes 1 corresponding to the welding area are welded to the first tube plate 2, and then the electric heating blanket 61 is wrapped outside the plurality of heat exchange pipes 1 corresponding to the welding area.

[0060] Specifically, the electric blanket 61 comprises a heat-generating core 62 in the inner layer and a heat-insulating layer 63 in the outer layer, the heat-insulating layer 63 is used to block the heat transfer of the electric blanket 61 corresponding to different welding zones, reduce the mutual interference of the temperatures of different welding zones, and make the temperature more controllable. The heat-generating core 62 is in contact with each heat exchange pipe 1 corresponding to the welding zone, and the electric heating wire of the heat-generating core 62 is attached to the outer wall of the heat exchange pipe 1 to heat it.

[0061] Specifically, the electric blanket 61 comprises a blanket body 64 for wrapping a plurality of heat exchange pipes 1 and a traction part 65 extending out of all the heat exchange pipes 1, the traction part 65 does not generate heat, and it extends out of the manhole of the shell side shell. After heat removal, the traction part 65 can be pulled out of the heat exchange pipe 1 by external force.

[0062] In the description of the present application, it is obvious that the described embodiments are only part of the embodiments of the present application, not all the embodiments. The components of the embodiments of the present application described and shown in the drawings can be arranged and designed in various different configurations.

[0063] Therefore, the above detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed application, but only represents selected embodiments of the present application. All other embodiments obtained by those skilled in the art based on the embodiments of the present application without creative labor are within the scope of protection of the present application.

[0064] In the description of the present application, it should be noted that the terms "middle", "upper", "lower", "horizontal", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship commonly used when the product is used, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the indicated device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second" and the like are only used for differentiation and cannot be understood as indicating or implying relative importance.

[0065] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "provided", "connected", "connected" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected. It can be mechanically connected or electrically connected. It can be directly connected or indirectly connected through an intermediate medium, and it can be the communication between two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0066]

Claims

1. A low stress welding method for a tube-to-tube sheet joint, characterized by: The method comprises the following steps: A pre-positioning step, according to the length of the heat exchange pipes, the first tube sheet and the second tube sheet are fixed side by side on a tool, one end of the plurality of heat exchange pipes is correspondingly inserted into the plurality of tube holes of the first tube sheet, and the other end of the plurality of heat exchange pipes is correspondingly movably inserted into the plurality of tube holes of the second tube sheet; A partitioning step: a mark is arranged on the outer side of the second tube sheet, and a plurality of to-be-welded joint areas formed by the plurality of heat exchange pipe ends and the plurality of tube holes are divided into a plurality of welding areas according to a preset number; A heating step: in a group unit, the plurality of heat exchange pipes in the plurality of welding areas are heated respectively by a plurality of heating devices, so that the plurality of heat exchange pipes are heat elongated in a direction away from the first tube sheet; A stress measurement and control step: the heating device is electrically connected with a control module and a laser flatness measuring instrument, the laser flatness measuring instrument is located on the outer side of the second tube sheet, and is used for measuring the flatness of the outer side of the second tube sheet in real time; the control module controls the heat generation of each heating device according to the measured flatness change signal, so that the flatness of the outer side of the second tube sheet is stably controlled within 0.01-0.8 mm; A welding step: after the flatness of the outer side of the second tube sheet is stabilized, the to-be-welded joint areas in each group of welding areas are welded and fixed in sequence, and before welding of the next group of welding areas, the stress measurement and control step is re-implemented; A heat removal step: after all the welding areas are completely welded, the plurality of heating devices stop heating the heat exchange pipes.

2. A low stress welding method for tube-to-tube sheet joints as claimed in claim 1, wherein: In the stress measurement and control step, the flatness of the outer side of the second tube sheet is controlled to be less than or equal to 0.5 mm.

3. A low stress welding method for tube-to-tube sheet joints as defined in claim 1, characterized by: The heating device is an electric heating rod inserted into the plurality of heat exchange pipes from the outer side of the first tube sheet, and the plurality of electric heating rods in the same welding area are electrically connected with the same control module to control the synchronous temperature rise and fall.

4. A low stress welding method for tube-to-tube sheet joints according to claim 3, characterized in that: The heating device further comprises a support plate, and the plurality of electric heating rods corresponding to the same welding area are fixed side by side on the support plate, so that the plurality of electric heating rods in the same welding area can be synchronously inserted into the corresponding heat exchange pipes, and the support plate is positioned in close contact with the outer side of the first tube sheet.

5. A low stress welding method for tube-to-tube sheet joints according to claim 4, characterized in that: The outer side of the electric heating rod is provided with a guide support protrusion matched with the inner wall of the heat exchange pipe.

6. A low stress welding method for tube-to-tube sheet joints as defined in claim 4, characterized by: The arrangement mode of the plurality of electric heating rods on the support plate is adjustable, which is achieved in the following way: the support plate is provided with a plurality of positioning holes, the number of the positioning holes is greater than the number of the electric heating rods, and the electric heating rods are selectively and detachably connected with different positioning holes; or the support plate is provided with a plurality of long strip holes, and the ends of the plurality of electric heating rods are loosely installed in different long strip holes.

7. A low stress welding method for tube-to-tube sheet joints as defined in claim 1, characterized by: In the partitioning step, the mark is a pattern, shape or number arranged on the outer side of the second tube sheet.

8. A low stress welding method for tube-to-tube sheet joints as defined in claim 1, characterized by: The heating device is a flexible electric heating blanket wrapped around the plurality of heat exchange pipes corresponding to each group of welding areas.

9. A low stress welding method for tube-to-tube sheet joints as defined in claim 7, characterized by: The electric heating blanket comprises a heating core in an inner layer and a heat insulation layer in an outer layer, and the heat insulation layer is used for blocking heat transfer of the electric heating blankets corresponding to different welding areas.

10. A low stress welding method for tube-to-tube sheet joints as defined in claim 7, characterized by: The electric heating blanket comprises a blanket body for wrapping the plurality of heat exchange pipes and a traction part extending out of all the heat exchange pipes, and an external force pulling the traction part can separate the electric heating blanket from the heat exchange pipes.

Images