Method for controlling the surface quality of heat exchange tubes during hydraulic expansion of tube sheets in nuclear power heat exchangers

Abstract

The present invention discloses a method for controlling the surface quality of heat exchange tubes during hydraulic expansion of tube sheets of nuclear power heat exchangers. In this method, the straightness of the expansion core shaft is finely controlled to ensure the accuracy of the expansion reference, and the dimensions of the expansion stop ring at each position are further finely controlled to ensure that the gap between the expansion stop ring and other positions is reasonable. At the same time, the surface quality of the expansion components is strictly controlled. After the wearing parts of the expansion core shaft and the expansion stop ring are replaced, the test piece is put into the expansion work of the heat exchange tube product after passing the expansion test. By comprehensively controlling the safety characteristics of each part and link, high-quality expanded heat exchange tubes without scratches or indentations are finally obtained.

Description

Technical Field

[0001] The present invention relates to a general technology for controlling the surface quality of heat exchange tubes during the full-depth hydraulic expansion process of tube sheets of nuclear power heat exchangers, and in particular to a technology for controlling the surface quality of heat exchange tubes during the full-depth hydraulic expansion process of tube sheets of nuclear power pressure steam generators. Background Art

[0002] Expansion is an important way to connect tubes and tube sheets in heat exchanger products. In nuclear island heat exchange equipment, the heat exchange tubes are the first barrier to isolate radioactive substances. Tube and tube sheet expansion technology is a key technology in the manufacturing of heat exchanger products. Operating experience of nuclear island heat exchanger equipment shows that the tube and tube sheet expansion area is prone to accumulation of impurities, deterioration of heat transfer and stress corrosion, making the quality of tube and tube sheet expansion related to the safe operation of nuclear power plants.

[0003] At present, hydraulic expansion of tubes and tube sheets has gradually become a relatively mature and widely used technology. However, current research on expansion quality mainly focuses on the firmness of the expansion and the dimensional accuracy of the expanded parts. For example, the hydraulic expansion equipment involved in Chinese patent 2015104432475 can meet the quality requirements for expansion of heat exchange tubes and tube sheets at home and abroad at that time. However, in fact, after expansion using this expansion equipment, indentations or scratches on the inner wall of the heat exchange tube are quite common. According to testing, a few scratches and indentations do not have a significant impact on the strength of the heat exchange tube. No one has studied the indentations and scratches on the heat exchange tube caused by the expansion process. Until now, there is no suitable means to remove scratches or indentations on the inner wall of the heat exchange tube. With the continuous increase in the capacity of nuclear power units and the gradual improvement of safety performance requirements, it is known through practical experience and theoretical inference that the service life of heat exchange tubes with indentations or scratches is shorter than that of heat exchange tubes without indentations or scratches. Based on this, the tube-to-tube sheet expansion technology is studied, and the surface quality of the heat exchange tubes after the expansion of the tubes and tube sheets of nuclear island equipment is systematically studied. The control method that can improve the surface quality of the heat exchange tubes after expansion is designed. It can also provide strong technical support for further improving the manufacturing quality of nuclear power products and thus improving the safety of nuclear power plant operation. It is also a necessary way to meet the higher quality requirements of nuclear power products in the new era and is of great significance to the further development of nuclear power technology. Summary of the Invention

[0004] In response to the above problems, the inventors conducted intensive research and designed a method for controlling the surface quality of heat exchange tubes during hydraulic expansion of tube sheets of nuclear power heat exchangers. In this method, the straightness of the expansion core shaft is finely controlled to ensure the accuracy of the expansion reference, and the dimensions of each position of the expansion stop ring are finely controlled to ensure that the gap between the expansion stop ring and other positions is reasonable. At the same time, the surface quality of the expansion components is strictly controlled. After replacing the consumable parts of the expansion core shaft and the expansion stop ring, the test piece is put into the expansion work of the heat exchange tube product after passing the test expansion. By comprehensively controlling the safety characteristics of each part and link, high-quality expanded heat exchange tubes without scratches and indentations are finally obtained, thus completing the present invention.

[0005] Specifically, the present invention aims to provide a method for controlling the surface quality of heat exchange tubes during hydraulic expansion of tube sheets in nuclear power heat exchangers, the method comprising:

[0006] S1, before expansion, measure the straightness of the expansion mandrel 1 and control the straightness of the expansion mandrel to be below 0.05mm;

[0007] S2, before expansion, measure and control the size of the expansion stop ring 2;

[0008] S3, before expansion, check the surface quality of the expansion mandrel, expansion stop ring, back nut, and front nut to ensure there are no burrs or scars;

[0009] S4. After expansion, perform a visual inspection on the inner wall of the heat exchange tube. The inspection range includes the expansion area and the area at a certain depth below the expansion area.

[0010] Wherein, in S2, the size of the control expansion joint stop ring 2 includes:

[0011] Measure and control the radial gap size between the expansion mandrel 1 and the expansion stop ring 2.

[0012] Preferably, the gap size is controlled to be below 0.05 mm; more preferably 0.03-0.05 mm.

[0013] Wherein, in S2, the size of the control expansion joint stop ring 2 further includes:

[0014] Measure and control the gap size between the expansion joint stop ring 2 and the front support ring 3 and the backing nut 4 in the axial direction;

[0015] Preferably, at the beginning of expansion, the distance between the expansion stop ring 2 and the backing nut 4 is within 3 mm, that is, during the expansion process, the expansion stop ring 2 moves within 3 mm under the push of the front support ring 3;

[0016] Further preferably, the distance between the expansion stop ring 2 and the backing nut 4 is 2-3 mm.

[0017] Wherein, in S2, the size of the control expansion joint stop ring 2 further includes:

[0018] Measure and control the radial gap size between the expansion joint stop ring 2 and the inner wall of the heat exchange tube 5,

[0019] Preferably, the gap size is controlled to be 0.05 mm-0.08 mm; more preferably 0.06-0.07 mm.

[0020] Wherein, in S2, the size of the control expansion joint stop ring 2 further includes:

[0021] Measure and control the chamfer angle on the expansion stop ring 2 to be 9.5°-11°; the axial length of the chamfer area is 2-3mm;

[0022] Preferably, the chamfer angle is 10°; and the axial length of the chamfered area is 2.5 mm.

[0023] In S4, the detection range includes the expansion zone and the area within a depth of 70 mm below the expansion zone.

[0024] The method further includes:

[0025] S5. After replacing the expansion core shaft 1 and the expansion stop ring 2, first conduct a test expansion on the test piece. After passing the visual inspection, proceed with product expansion.

[0026] The beneficial effects of the present invention include:

[0027] (1) In the method for controlling the surface quality of heat exchange tubes during hydraulic expansion of tube sheets of nuclear power heat exchangers provided by the present invention, the straightness of the expansion mandrel itself is controlled to be below 0.05 mm, thereby preventing the expansion mandrel from contacting the inner wall of the heat exchange tube during the insertion and removal of the expansion mandrel from the heat exchange tube and the expansion process of the expansion mandrel in the heat exchange tube, thereby ensuring that the expansion mandrel does not cause indentations or scratches on the inner wall of the heat exchange tube;

[0028] (2) In the method for controlling the surface quality of heat exchange tubes during hydraulic expansion of tube sheets of nuclear power heat exchangers provided by the present invention, the radial clearance between the expansion core shaft and the expansion stop ring is controlled to be less than 0.05 mm, which can ensure that during the expansion process, the expansion stop ring will not contact the inner wall of the heat exchange tube due to objective conditions such as uneven circumferential force on the expansion stop ring, and misalignment between the expansion core shaft and the expansion stop ring, thereby causing indentations or scratches on the inner wall of the heat exchange tube;

[0029] (3) In the method for controlling the surface quality of heat exchange tubes during hydraulic expansion of tube sheets of nuclear power heat exchangers provided by the present invention, a chamfer is provided at the front end of the expansion stop ring, and the chamfer angle is controlled to 10°, which can greatly reduce the circumferential indentation generated after expansion; by avoiding hard contact between the front end of the expansion stop ring and the inner wall of the heat exchange tube, damage to the inner wall of the heat exchange tube is prevented;

[0030] (4) In the method for controlling the surface quality of heat exchange tubes during hydraulic expansion of tube sheets of nuclear power heat exchangers provided by the present invention, during the expansion process, the front end O-ring is separated from the groove on the expansion core shaft by the action of high-pressure water, and the front end support ring and the expansion stop ring are pushed forward to a distance of less than 3 mm, so as to prevent the expansion stop ring from scratching the inner wall of the heat exchange tube during movement;

[0031] (5) In the method for controlling the surface quality of heat exchange tubes during hydraulic expansion of tube sheets of nuclear power heat exchangers provided by the present invention, the gap between the expansion stop ring and the inner wall of the heat exchange tube is controlled to avoid the front support ring from being squeezed into the gap between the expansion stop ring and the heat exchange tube due to the gap being too large, thereby affecting the expansion length and over-expansion; at the same time, the gap is prevented from being too small, thereby avoiding scratches and indentations caused by the expansion stop ring contacting the inner wall of the heat exchange tube;

[0032] (6) In the method for controlling the surface quality of heat exchange tubes during hydraulic expansion of tube sheets in nuclear power heat exchangers provided by the present invention, the visual inspection range of the heat exchange tubes is expanded to 70 mm outside the expansion zone; thus, accidental damage can be discovered and handled promptly;

[0033] (7) In the method for controlling the surface quality of heat exchange tubes during hydraulic expansion of tube sheets of nuclear power heat exchangers provided by the present invention, when replacing the expansion core shaft and the expansion stop ring, before expansion on the product, a trial expansion is carried out on the pre-shift test piece, and the product expansion is started only after passing the visual inspection, thereby avoiding accidental damage and improving the expansion success rate and the surface quality of the heat exchange tubes. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A schematic structural diagram of an expansion device used in a method for controlling the surface quality of heat exchange tubes during hydraulic expansion of tube sheets of a nuclear power heat exchanger provided by the present invention is shown;

[0035] Figure 2 A schematic structural diagram of the expansion joint in the method for controlling the surface quality of heat exchange tubes during hydraulic expansion joint of tube sheets of nuclear power heat exchangers provided by the present invention is shown;

[0036] Figure 3 A schematic structural diagram of an expansion stop ring in a method for controlling the surface quality of heat exchange tubes during hydraulic expansion of tube sheets of a nuclear power heat exchanger provided by the present invention is shown.

[0037] Reference numerals

[0038] 1-Expansion mandrel

[0039] 2-Expansion stop ring

[0040] 3-Front end support ring

[0041] 4-Tightening nut

[0042] 5-Heat exchange tube

[0043] 6-Front end O-ring

[0044] 7-Rear end O-ring

[0045] 8-Rear end support ring

[0046] 9-Metal split ring with convex shaft

[0047] 10-Regulator

[0048] 11-Tube sheet DETAILED DESCRIPTION

[0049] The present invention will be described in further detail below with reference to the accompanying drawings and examples, through which the features and advantages of the present invention will become more clearly understood.

[0050] The word "exemplary" is used exclusively herein to mean "serving as an example, example, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments. Although various aspects of the embodiments are shown in the drawings, the drawings are not necessarily drawn to scale unless otherwise indicated.

[0051] According to the present invention, a method for controlling the surface quality of heat exchange tubes during hydraulic expansion of tube sheets of nuclear power heat exchangers is provided. In this method, the heat exchange tubes are expanded by an expansion device, and the expansion device is as follows: Figure 1 and Figure 2 As shown in FIG, the expansion core shaft 1 includes an expansion core shaft 1 having an infusion hole disposed along its axis. High-pressure liquid enters the heat exchange tube through this infusion hole. One end of the infusion hole is connected to the high-pressure liquid inlet. At the other end of the infusion hole, a radial hole is provided that penetrates the expansion core shaft 1. The radial hole is perpendicular to and connected to the infusion hole. High-pressure liquid enters along the infusion hole and is ejected through the radial hole, thereby hydraulically expanding the tube to be expanded, which is sleeved on the expansion core shaft 1.

[0052] Two grooves are formed on the outer surface of the expansion mandrel 1. When the expansion equipment is in expansion operation, both grooves are located inside the tube sheet 11 and are close to both ends of the tube sheet. A backing nut 4, an expansion stop ring 2, a front support ring 3, a front O-ring 6, a rear O-ring 7, a rear support ring 8, a metal split ring with a protruding shaft 9, and an adjuster 10 are sequentially sleeved on the outside of the expansion mandrel 1.

[0053] The front O-ring 6 and the rear O-ring 7 are each located in a groove. The expansion ring 2 is inserted into the heat exchange tube below the tube sheet. Figure 2 As shown in .

[0054] The metal split ring 9 with the convex shaft is compressed and deformed, and is tightly attached to the edge of the regulator 10. The front end O-ring 6 and the rear end O-ring 7 are compressed and deformed, and their outer diameters increase, and they are tightly sealed with the outer wall of the expansion core shaft 1 and the inner wall of the heat exchange tube 5 to be expanded. The space between the front end O-ring 6 and the rear end O-ring 7 constitutes an expansion cavity, thereby realizing the expansion of the heat exchange tube 5.

[0055] Furthermore, the method includes: S1, before expansion, measuring the straightness of the expansion core shaft 1, and controlling the straightness of the expansion core shaft to be below 0.05mm; in the present application, the straightness of the expansion core shaft itself is controlled to be below 0.05mm to avoid the expansion core shaft from contacting the inner wall of the heat exchange tube during the insertion and removal of the expansion core shaft from the heat exchange tube and the expansion process of the expansion core shaft in the heat exchange tube, thereby ensuring that the expansion core shaft will not cause indentations or scratches on the inner wall of the heat exchange tube. The smaller the straightness, the better. Due to the limitations of processing accuracy and the actual needs of mass production as a consumable part, the critical value of the straightness is set to 0.05mm, which just meets the use requirements of no indentations or scratches.

[0056] S2, before expansion, measure and control the size of the expansion stop ring 2;

[0057] S3. Before expansion, check the surface quality of the expansion core shaft, expansion stop ring, backing nut and front end nut to ensure that there are no burrs or scars, that is, ensure that the surface of each component of the expansion equipment is smooth to avoid affecting the expansion quality due to the processing quality of the expansion equipment; preferably, before expansion, check the surface condition of the front end support ring 3 and the expansion stop ring 2, and trim and chamfer the front end, and ensure that the circumferential chamfer is as uniform as possible; because during the expansion process, the front end support ring is forced to squeeze the expansion stop ring, and the outer diameter expands and squeezes into the gap between the expansion stop ring and the heat exchange tube. If the chamfer of the front end of the support ring is uneven, it will cause the stop ring to deflect and cause indentations.

[0058] S4. After expansion, perform a visual inspection on the inner wall of the heat exchange tube. The inspection range includes the expansion area and the area at a certain depth below the expansion area.

[0059] In a preferred embodiment, in S2, the control of the size of the expansion stop ring 2 includes: measuring and controlling the gap size in the radial direction between the expansion core shaft 1 and the expansion stop ring 2, preferably, controlling the gap size to be below 0.05mm; more preferably, 0.03-0.05mm; the expansion stop ring in this application is a wearing part and has certain life requirements. During the entire expansion operation, the expansion stop ring needs to be replaced many times. If the gap is too small, it is not conducive to disassembly and replacement, and it is easy to cause scratches during the disassembly and replacement process. The gap size in the radial direction between the expansion core shaft 1 and the expansion stop ring 2 in this application refers to the size of one side, that is, the expansion core shaft 1 is placed in the middle position, and on any cross section, there is a gap size between its two sides and the inner wall of the expansion stop ring 2.

[0060] In the present application, the function of the expansion stop ring is mainly to control the expansion length and prevent the front support ring from expanding beyond the secondary side surface of the tube sheet during the expansion process, thereby causing over-expansion.

[0061] In this application, the radial gap between the expansion mandrel 1 and the expansion stop ring 2 is controlled to be less than 0.05mm. This ensures that during the expansion process, the expansion stop ring will not contact the inner wall of the heat exchange tube, causing indentations or scratches on the inner wall of the heat exchange tube due to objective conditions such as uneven circumferential force on the expansion stop ring or misalignment between the expansion mandrel and the expansion stop ring. At the same time, in order to ensure that the expansion mandrel 1 can slide smoothly on the expansion mandrel 1, the gap size is limited to not less than 0, and is preferably greater than 0.03mm.

[0062] In a preferred embodiment, in S2, controlling the size of the expansion stop ring 2 further comprises: measuring and controlling the gap size between the expansion stop ring 2 and the front end support ring 3 and the backing nut 4 in the axial direction;

[0063] When the expansion joint device is inserted into the heat exchange tube, the expansion joint stop ring 2 is affected by friction and moves away from the backing nut 4 and abuts against the front support ring 3;

[0064] Preferably, at the beginning of expansion, the front O-ring is disengaged from the groove on the core shaft, pushing the front support ring and the expansion stop ring forward; by setting the distance between the expansion stop ring 2 and the backing nut 4 to be within 3 mm, that is, during the expansion process, the expansion stop ring is pushed by the front support ring 3 and moves within 3 mm, so as to prevent the expansion stop ring from scratching the inner wall of the heat exchange tube during movement;

[0065] Further preferably, the distance between the expansion stop ring 2 and the backing nut 4 is 2-3 mm. In this application, this distance should be neither too large nor too small. Before expansion, the front O-ring 6 is stuck in the groove of the core shaft (a groove is provided on the core shaft at the position of the front O-ring 6). During the expansion process, the front O-ring 6 jumps out of the groove and squeezes onto the front support ring 3 due to the action of high-pressure water. At the same time, the front O-ring 6 itself is squeezed. Therefore, a gap is required for the front O-ring 6 to jump out of the groove. Generally, this distance is preferably 3 mm.

[0066] In a preferred embodiment, in S2, controlling the size of the expansion stop ring 2 further includes measuring and controlling the radial gap between the expansion stop ring 2 and the inner wall of the heat exchange tube 5. Preferably, the gap is controlled to be between 0.05 mm and 0.08 mm, and more preferably between 0.06 mm and 0.07 mm. The radial gap between the expansion stop ring 2 and the inner wall of the heat exchange tube 5 in this application refers to a single-sided gap. That is, when the expansion stop ring 2 is placed in the middle, a gap of one dimension exists between each side of the expansion stop ring and the inner wall of the heat exchange tube 5 on any cross-section.

[0067] In the present application, the function of the expansion stop ring is to block the forward movement distance of the front support ring, control the expansion position, and avoid over-expansion. The relative position of the expansion stop ring on the core shaft remains unchanged. When the expansion equipment is assembled, the position of the regulator is adjusted according to the predetermined unexpanded length of the secondary side to control the unexpanded length of the secondary side. When the gap between the expansion stop ring and the heat exchange tube is too large, the front support ring is squeezed by the high-pressure water during expansion and squeezed into the gap between the expansion stop ring and the heat exchange tube, causing damage to the front support ring, affecting the expansion length, and even causing over-expansion in severe cases; when the gap between the expansion stop ring and the heat exchange tube is too small, during the expansion process, the expansion stop ring contacts the inner wall of the heat exchange tube and there is a great risk of scratches and indentations. In the present application, the gap between the expansion stop ring and the inner wall of the heat exchange tube is controlled to be 0.05mm-0.08mm, which can ensure that over-expansion does not occur during the expansion process, and at the same time, the expansion stop ring is controlled not to scratch the inner wall of the heat exchange tube, ensuring that no damage is caused to the inner wall of the heat exchange tube.

[0068] In a preferred embodiment, in S2, the control of the size of the expansion stop ring 2 also includes: measuring and controlling the chamfer angle on the expansion stop ring 2 to be 9.5°-11°; the axial length of the chamfer area is 2-3mm; preferably, the chamfer angle is 10°; the axial length of the chamfer area is 2.5mm.

[0069] The inventors of this application found that when the front end structure of the expansion stop ring is set to a non-chamfered state or a chamfered state, indentations always appear on the heat exchange tube obtained after expansion, and adjusting the size parameters of the chamfer cannot eliminate the indentations. When the front end structure of the expansion stop ring is set to a chamfered state, the indentations still exist in most cases. Only when the chamfer meets a specific size, the frequency of indentations is greatly reduced, and the requirements for surface quality control of the heat exchange tube can be met, that is, when the angle of the chamfer is 10° and the axial length of the chamfered area is 2.5 mm, the surface quality of the heat exchange tube after expansion is good and there are no indentations.

[0070] In a preferred embodiment, in S4, the inspection range includes the expansion zone and the area within 70 mm below the expansion zone. The inventors of this application have discovered that after expansion of heat exchange tubes, indentations or scratches may appear not only on the tubesheet, but also in the area within 70 mm below the tubesheet. Therefore, to ensure the quality of the inner surface of the heat exchange tubes, it is necessary to expand the inspection range to include all areas that may have indentations and scratches.

[0071] In a preferred embodiment, the method further includes: S5, after replacing the expansion mandrel 1 and the expansion stop ring 2, first conducting a test expansion on a test piece, and only proceeding with the product expansion after passing a visual inspection. Because the expansion mandrel 1 and the expansion stop ring 2 are both consumable parts, they need to be replaced multiple times during the expansion of thousands or even tens of thousands of heat exchange tubes. Each replacement introduces new safety risks, and the likelihood of scratches or indentations appearing on the first expansion after replacement is relatively high. Therefore, using test pieces to verify the reliability of the expansion equipment reduces the risk of damaging the surface quality of the heat exchange tubes.

[0072] Example

[0073] use Figure 1 and Figure 2 The expansion equipment shown is used to expand the heat exchange tubes. During the expansion process, the surface quality of the heat exchange tubes is controlled by the following methods:

[0074] S1, before expansion, measure the straightness of the expansion mandrel 1 and control the straightness of the expansion mandrel to be below 0.05mm. The maximum measured straightness is 0.041mm.

[0075] S2, before expansion, measure and control the size of the expansion stop ring 2;

[0076] The radial gap between the expansion core shaft 1 and the expansion stop ring 2 is measured and controlled to be less than 0.05 mm. The actual measured gap size is 0.031 mm.

[0077] Measure and control the axial clearance between the expansion stop ring 2, the front support ring 3, and the backing nut 4. Ensure that during the expansion process, the expansion stop ring, pushed by the front support ring 3, moves within 3 mm. The measured movement distance is 2.25 mm.

[0078] Measure and control the radial gap between the expansion stop ring 2 and the inner wall of the heat exchange tube 5 to be between 0.05mm and 0.08mm. For the 10 heat exchange tubes to be expanded, the measured gap size is concentrated between 0.06mm and 0.068mm.

[0079] Measure and control the chamfer angle on the expansion stop ring 2 to be 10°; the axial length of the chamfer area is 2.5mm;

[0080] S3, before expansion, check the surface quality of the expansion mandrel, expansion stop ring, back nut, and front nut to ensure there are no burrs or scars;

[0081] S4, after replacing the expansion core shaft 1 and the expansion stop ring 2, first conduct a test expansion on the test piece. After the visual inspection is qualified, the product expansion can be carried out;

[0082] After expansion, the inner wall of the heat exchange tube is visually inspected. The inspection range includes the expansion area and the area within 70mm below the expansion area.

[0083] Ten heat exchange tubes were continuously expanded using the above equipment and method, and no scratches or indentations were found.

[0084] Comparative Example 1

[0085] The same heat exchange tubes were expanded using an expansion device and method that were basically the same as those in the embodiment. The only difference was that the straightness of the expansion core shaft in the expansion device was controlled below 0.07 mm. In actual measurements, there was an area on the expansion core shaft with a straightness of 0.065 mm.

[0086] Ten heat exchange tubes were continuously expanded using the above-mentioned equipment and method, and scratches or indentations were found on the inner walls of seven of the heat exchange tubes.

[0087] Comparative Example 2

[0088] The same heat exchange tubes were expanded using an expansion device and method that were basically the same as those in the embodiment. The only difference was that the radial gap size between the expansion core shaft 1 and the expansion stop ring 2 in the expansion device was controlled to be below 0.07 mm. The actual measured radial gap size between the expansion core shaft 1 and the expansion stop ring 2 in the expansion device was 0.065 mm.

[0089] Ten heat exchange tubes were continuously expanded using the above-mentioned equipment and method, and scratches or indentations were found on the inner walls of six of the heat exchange tubes.

[0090] Comparative Example 3

[0091] The same heat exchange tubes are expanded using expansion equipment and methods that are basically the same as those in the embodiment. The only difference is that the expansion equipment controls the gap size between the expansion stop ring 2 and the front support ring 3 and the backing nut 4 in the axial direction; so that during the expansion process, the expansion stop ring is pushed by the front support ring 3 and moves within 7 mm.

[0092] Ten heat exchange tubes were continuously expanded using the above-mentioned equipment and method, and scratches or indentations were found on the inner walls of three of the heat exchange tubes.

[0093] Comparative Example 4

[0094] The same heat exchange tubes were expanded using an expansion device and method that were basically the same as those in the embodiment. The only difference was that the radial gap size between the expansion stop ring 2 and the inner wall of the heat exchange tube 5 was controlled to be less than 0.05 in the expansion device. For the 10 heat exchange tubes to be expanded, the radial gap sizes between the expansion stop ring 2 and the inner wall of the heat exchange tube 5 were measured to be concentrated between 0.03 mm and 0.042 mm.

[0095] Ten heat exchange tubes were continuously expanded using the above-mentioned equipment and method, and scratches or indentations were found on the inner walls of seven of the heat exchange tubes.

[0096] Comparative Example 5

[0097] The same heat exchange tubes were expanded using an expansion device and method that were basically the same as those in the embodiment. The only difference was that the radial gap size between the expansion stop ring 2 and the inner wall of the heat exchange tube 5 was controlled to be less than 0.1 in the expansion device. For the 10 heat exchange tubes to be expanded, the radial gap size between the expansion stop ring 2 and the inner wall of the heat exchange tube 5 was measured to be concentrated between 0.09 mm and 0.095 mm.

[0098] Ten heat exchange tubes were continuously expanded using the above-mentioned equipment and method, and scratches or indentations were found on the inner walls of three of the heat exchange tubes.

[0099] Comparative Example 6

[0100] The same heat exchange tubes were expanded using an expansion device and method that were basically the same as those in the embodiment. The only difference was that the front end of the expansion stop ring 2 in the expansion device was rounded, and the rounding radius was 1 mm.

[0101] Ten heat exchange tubes were continuously expanded using the above-mentioned equipment and method, and scratches or indentations were found on the inner walls of seven of the heat exchange tubes.

[0102] Comparative Example 7

[0103] The same heat exchange tubes were expanded using an expansion device and method that were basically the same as those in the embodiment. The only difference was that the front end of the expansion stop ring 2 in the expansion device was rounded, and the rounding radius was 0.5 mm.

[0104] Ten heat exchange tubes were continuously expanded using the above-mentioned equipment and method, and scratches or indentations were found on the inner walls of eight of the heat exchange tubes.

[0105] Comparative Example 8

[0106] The same heat exchange tubes were expanded using an expansion device and method that were basically the same as those in the embodiment. The only difference was that a chamfer was provided at the front end of the expansion stop ring 2 in the expansion device. The axial length of the chamfered area was measured to be 2.5 mm, and the chamfer angle was 7°.

[0107] Ten heat exchange tubes were continuously expanded using the above-mentioned equipment and method, and scratches or indentations were found on the inner walls of eight of the heat exchange tubes.

[0108] Comparative Example 9

[0109] The same heat exchange tubes were expanded using an expansion device and method that were basically the same as those in the embodiment. The only difference was that a chamfer was provided at the front end of the expansion stop ring 2 in the expansion device. The axial length of the chamfered area was measured to be 2.5 mm, and the chamfer angle was 12°.

[0110] Ten heat exchange tubes were continuously expanded using the above-mentioned equipment and method, and scratches or indentations were found on the inner walls of five of the heat exchange tubes.

[0111] It can be seen from the results of the above embodiments and comparative examples that the specific dimensional requirements specified by the control method in this application are just enough to obtain heat exchange tubes with good surface quality and avoid scratches and indentations on the heat exchange tubes. However, changing the specific dimensional requirements in the above method will cause damage to the heat exchange tubes, scratches or indentations, which may affect the service life of nuclear power equipment.

[0112] The present invention has been described above with reference to preferred embodiments, but these embodiments are merely exemplary and serve only as illustrations. On this basis, various replacements and improvements can be made to the present invention, all of which fall within the scope of protection of the present invention.

Claims

1. A method for controlling the surface quality of heat exchange tubes during hydraulic expansion of tube sheets in nuclear power heat exchangers, characterized in that: The method includes: S1, before expansion, measure the straightness of the expansion mandrel (1), and control the straightness of the expansion mandrel to be below 0.05 mm; S2, before expansion, measure and control the size of the expansion stop ring (2); S3, before expansion, check the surface quality of the expansion mandrel, expansion stop ring, and back-up nut to ensure there are no burrs or scars; Two grooves are provided on the outer surface of the expansion core shaft (1). When the expansion equipment is in expansion operation, the two grooves are located inside the tube sheet (11) and are close to both ends of the tube sheet. A back-tightening nut (4), an expansion stop ring (2), a front support ring (3), a front O-ring (6), a rear O-ring (7), a rear support ring (8), a metal split ring with a protruding shaft (9), and an adjuster (10) are sequentially sleeved on the outside of the expansion core shaft (1). The front O-ring (6) and the rear O-ring (7) are each located in a groove; the expansion joint stop ring (2) is inserted into the heat exchange tube below the tube sheet; The metal split ring (9) with the convex shaft is deformed under pressure and closely adheres to the edge of the regulator (10). The front O-ring (6) and the rear O-ring (7) are deformed under pressure, and their outer diameters increase. They are closely adhered and sealed to the outer wall of the expansion core shaft (1) and the inner wall of the heat exchange tube (5) to be expanded. The space between the front O-ring (6) and the rear O-ring (7) forms an expansion cavity, thereby achieving expansion of the heat exchange tube (5). S4, after expansion, conduct a visual inspection of the inner wall of the heat exchange tube. The inspection range includes the expansion area and the area at a certain depth below the expansion area. In S2, the size of the control expansion stop ring (2) includes: Measure and control the radial gap size between the expansion core shaft (1) and the expansion stop ring (2). The gap size in the radial direction is controlled to be less than 0.05 mm; In S2, the size of the control expansion joint stop ring (2) further includes: Measuring and controlling the gap size between the expansion joint stop ring (2) and the front end support ring (3) and the backing nut (4) in the axial direction; At the beginning of expansion, the distance between the expansion stop ring (2) and the backing nut (4) is within 3 mm, that is, during the expansion process, the expansion stop ring (2) moves within 3 mm under the push of the front support ring (3); In S2, the size of the control expansion joint stop ring (2) further includes: Measure and control the radial gap size between the expansion joint stop ring (2) and the inner wall of the heat exchange tube (5), The gap size is controlled at 0.05mm-0.08mm; In S2, the size of the control expansion joint stop ring (2) further includes: The chamfer angle on the expansion stop ring (2) is measured and controlled to be 9.5°-11°; and the axial length of the chamfer area is 2-3 mm.

2. The method for controlling the surface quality of heat exchange tubes during hydraulic expansion of tube sheets of nuclear power heat exchangers according to claim 1, characterized in that: The chamfer angle is 10°; the axial length of the chamfer area is 2.5 mm.

3. The method for controlling the surface quality of heat exchange tubes during hydraulic expansion of tube sheets of nuclear power heat exchangers according to claim 1, characterized in that: In S4, the detection range includes the expansion zone and the area within a depth of 70 mm below the expansion zone.

4. The method for controlling the surface quality of heat exchange tubes during hydraulic expansion of tube sheets of nuclear power heat exchangers according to claim 1, characterized in that: The method further includes: S5, after replacing the expansion core shaft (1) and the expansion stop ring (2), first conduct expansion test on the test piece, and then expand the product after passing the visual inspection.

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