Local heat treatment method for heat exchanger with unequal-thickness structure

Abstract

The invention discloses a local heat treatment method for a heat exchanger with an unequal-thickness structure, the heat exchanger with the unequal-thickness structure comprises a thick-wall cylinder, a thin-wall cylinder and a circumferential weld which are connected with one another, and the method comprises the following steps: respectively heating the heat exchanger with the unequal-thickness structure for the first time by utilizing a first heating element and a second heating element; when the temperature of the heat exchanger with the unequal-thickness structure rises to a first set temperature, heating is stopped; removing the first heating element and the second heating element after the temperature of the heat exchanger with the unequal-thickness structure is reduced to a second set temperature; and the third heating element and the fourth heating element are used for heating the unequal-thickness structure heat exchanger for the second time, and heating is stopped when the temperature of the unequal-thickness structure heat exchanger rises to a third set temperature. According to the method, the structure and the mechanical property of the circumferential weld on the inner wall of the heat exchanger with the unequal-thickness structure and the stress distribution of the inner wall of the pipeline are improved by heating the heat exchanger with the unequal-thickness structure for the first time and the second time, so that the stress near the circumferential weld on the inner wall is reduced into pressure stress, and stress concentration is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of local heat treatment and temperature uniformity control, and in particular to a local heat treatment method for a heat exchanger with unequal thickness structure. Background Art

[0002] In the manufacturing process of high-pressure heat exchangers, unequal thickness butt joint is a common problem in the manufacturing process, especially the butt joint of the cylinder and the head often uses unequal thickness butt joint, thus forming a structural discontinuity zone in the pressure vessel manufacturing. The device has been in service for a long time in a high temperature (operating temperature 360-440℃) and high pressure environment, and is also in harsh operating conditions with corrosive media such as hydrogen and hydrogen sulfide. Under the synergistic effect of the corrosive medium and the high stress state of the reactor, it has a significant tendency to stress corrosion, which is easy to cause stress corrosion cracking failure, causing huge economic losses and safety hazards. Among them, the high welding residual stress at the unequal thickness connection of the reactor is the key factor in the generation of stress corrosion. Heat treatment is often used in engineering to eliminate stress. However, for unequal thickness structures, local heat treatment has a poor effect on the stress elimination of the inner surface. At the same time, due to inconsistent wall thickness, it is easy to cause unreasonable distribution of heat treatment temperature, which will have an adverse effect on the performance and life of the welded joint.

[0003] Based on this technical background, the present invention proposes a local heat treatment method for a heat exchanger with unequal thickness structure. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention proposes a local heat treatment method for a heat exchanger with unequal thickness structure. The method improves the microstructure and mechanical properties of the inner wall girth weld of the heat exchanger with unequal thickness structure by heating the heat exchanger with unequal thickness structure for the first time, and improves the stress distribution of the inner wall of the pipeline of the heat exchanger with unequal thickness structure by heating it for the second time, so that the stress near the inner wall girth weld is reduced to compressive stress, which is of great significance to the safe service of the high-pressure heat exchanger with unequal thickness structure.

[0005] In order to achieve the above object, the present invention provides a method for local heat treatment of a heat exchanger with unequal thickness structure, wherein the heat exchanger with unequal thickness structure comprises a thick-walled cylinder and a thin-walled cylinder connected to each other, a circumferential weld is provided at the connection between the thick-walled cylinder and the thin-walled cylinder, and the inner diameters of the thick-walled cylinder and the thin-walled cylinder are the same, and the method comprises the following steps:

[0006] Taking the center of the annular weld as a starting point, a first heating element is arranged on the outer wall of the thick-walled cylinder, and a second heating element is arranged on the outer wall of the thin-walled cylinder;

[0007] Connecting the first power supply to the first heating element and the second power supply to the second heating element respectively, heating the heat exchanger with unequal thickness structure for the first time, and stopping heating when the temperature of the heat exchanger with unequal thickness structure rises to a first set temperature;

[0008] After the temperature of the heat exchanger with unequal thickness structure drops to a second set temperature, the first heating element and the second heating element are removed;

[0009] The third heating element is arranged on the outer wall of the thick-walled cylinder with the first auxiliary positioning loop on the thick-walled cylinder as the center line; the fourth heating element is arranged on the outer wall of the thin-walled cylinder with the second auxiliary positioning loop on the thin-walled cylinder as the center line;

[0010] The third power supply is connected to the third heating element, and the fourth power supply is connected to the fourth heating element, respectively, to heat the unequal thickness structure heat exchanger for the second time, and the heating is stopped when the temperature of the unequal thickness structure heat exchanger rises to the third set temperature.

[0011] The effects of the present invention are:

[0012] (1) The present invention proposes a local heat treatment method for a heat exchanger with unequal thickness structure. The method improves the microstructure and mechanical properties of the inner wall circumferential weld of the heat exchanger with unequal thickness structure by heating the heat exchanger with unequal thickness structure for the first time, and improves the stress distribution of the inner wall of the heat exchanger with unequal thickness structure pipe by heating it for the second time, so that the stress near the inner wall circumferential weld is reduced to compressive stress, which is of great significance to the safe service of the high-pressure heat exchanger with unequal thickness structure.

[0013] (2) The local heat treatment method for unequal thickness structure heat exchangers proposed in the present invention can significantly reduce the axial stress and circumferential stress of the circumferential weld of the inner wall of the unequal thickness structure heat exchanger, and even present a compressive stress state, thereby solving the problem of excessive tensile stress after heat treatment of the inner wall of the unequal thickness structure heat exchanger after welding, avoiding stress concentration, and fundamentally reducing the probability of stress corrosion cracking during service.

[0014] (3) The local heat treatment method for the heat exchanger with unequal thickness structure proposed in the present invention improves the microstructure and mechanical properties of the ring weld of the heat exchanger with unequal thickness structure by accurately setting the setting width of the first heating element and the second heating element, the heat provided by the first power supply and the second power supply, and the first set temperature, and makes the microstructure of the ring weld of the heat exchanger with unequal thickness structure precisely controllable.

[0015] (4) The local heat treatment method for a heat exchanger with an unequal thickness structure proposed in the present invention makes the stress distribution on the inner wall of the heat exchanger with an unequal thickness structure precisely controllable by precisely setting the setting width of the third heating element and the fourth heating element, the first auxiliary distance and the second auxiliary distance, the heat provided by the third power supply and the fourth power supply, and the third set temperature.

[0016] (5) The local heat treatment method for the unequal thickness structure heat exchanger proposed in the present invention evenly distributes multiple inner wall thermocouples and multiple outer wall thermocouples in the radial direction of the inner wall and outer wall of the thick-walled cylinder, thereby realizing real-time monitoring of the temperature of the unequal thickness structure heat exchanger.

[0017] (6) The method for local heat treatment of a heat exchanger with unequal thickness structure proposed in the present invention comprises laying the corresponding first outer insulation cotton, second outer insulation cotton, third outer insulation cotton, fourth outer insulation cotton, first inner insulation cotton, second inner insulation cotton, and third inner insulation cotton before performing the first heating and the second heating on the heat exchanger with unequal thickness structure, thereby ensuring the local heat treatment and temperature uniformity control effect of the heat exchanger with unequal thickness structure.

[0018] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The above and other objects, features and advantages of the present invention will become more apparent through a more detailed description of exemplary embodiments of the present invention in conjunction with the accompanying drawings, wherein like reference numerals generally represent like components throughout the exemplary embodiments of the present invention.

[0020] Figure 1 The figure is a schematic flow chart of the local heat treatment method for a heat exchanger with unequal thickness structure proposed by the present invention.

[0021] Figure 2 This is a schematic diagram of the structure of the heat exchanger with unequal thickness structure proposed by the present invention;

[0022] Figure 3 A schematic diagram of an axial stress curve of an inner wall circumferential weld of a heat exchanger with unequal thickness structure in a specific implementation of the local heat treatment method of a heat exchanger with unequal thickness structure proposed by the present invention;

[0023] Figure 4 A schematic diagram of a radial stress curve of an inner wall circumferential weld of a heat exchanger with unequal thickness structure in a specific implementation of the local heat treatment method for a heat exchanger with unequal thickness structure proposed by the present invention.

[0024] Description of reference numerals:

[0025] 1-Heat exchanger with unequal thickness structure;

[0026] 101 - thick-walled cylinder, 102 - thin-walled cylinder, 103 - annular weld, 104 - a first heating element or a third heating element, 105 - a second heating element or a fourth heating element. DETAILED DESCRIPTION

[0027] The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein.

[0028] In the present invention, unless otherwise specified, directional words such as "upper" and "lower" generally refer to the upper and lower parts of a device in normal use. Figure 1 In the drawing direction, "inside" and "outside" refer to the outline of the device. In addition, the terms "first, second, third" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first, second, third" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0029] The present invention provides a method for local heat treatment of a heat exchanger with unequal thickness structure, such as Figure 1 , Figure 2 As shown, the unequal thickness structure heat exchanger 1 comprises a thick-walled cylinder 101 and a thin-walled cylinder 102 connected to each other, a ring weld 103 is provided at the connection between the thick-walled cylinder 101 and the thin-walled cylinder 102, and the inner diameters of the thick-walled cylinder 101 and the thin-walled cylinder 102 are the same. The method comprises the following steps:

[0030] Taking the center of the annular weld 103 as the starting point, the first heating element is disposed on the outer wall of the thick-walled cylinder 101, and the second heating element is disposed on the outer wall of the thin-walled cylinder 102;

[0031] The first power source (not shown) is connected to the first heating element, and the second power source (not shown) is connected to the second heating element, respectively, to heat the unequal thickness structure heat exchanger 1 for the first time, and the heating is stopped when the temperature of the unequal thickness structure heat exchanger 1 rises to the first set temperature;

[0032] After the temperature of the unequal thickness structure heat exchanger 1 drops to the second set temperature, the first heating element and the second heating element are removed;

[0033] The third heating element is arranged on the outer wall of the thick-walled cylinder 101 with the first auxiliary positioning loop line on the thick-walled cylinder 101 as the center line; the fourth heating element is arranged on the outer wall of the thin-walled cylinder 102 with the second auxiliary positioning loop line on the thin-walled cylinder 102 as the center line;

[0034] The third power supply (not shown) is connected to the third heating element, and the fourth power supply (not shown) is connected to the fourth heating element, respectively, to heat the unequal thickness structure heat exchanger 1 for the second time. When the temperature of the unequal thickness structure heat exchanger 1 rises to the third set temperature, the heating is stopped.

[0035] In the present invention, the microstructure and mechanical properties of the inner wall circumferential weld 103 of the unequal thickness structure heat exchanger 1 are improved by heating the unequal thickness structure heat exchanger 1 for the first time, and the stress distribution on the inner wall of the pipe of the unequal thickness structure heat exchanger 1 is improved by heating the unequal thickness structure heat exchanger 1 for the second time, so that the stress near the inner wall circumferential weld 103 is reduced to compressive stress, which is of great significance to the safe service of the high-pressure unequal thickness structure heat exchanger 1.

[0036] In the present invention, the axial stress and the hoop stress of the inner wall ring weld 103 of the unequal thickness structure heat exchanger 1 are greatly reduced, and even in a compressive stress state, so as to solve the problem of excessive tensile stress after heat treatment of the inner wall of the unequal thickness structure heat exchanger 1 after welding, avoid stress concentration, and fundamentally reduce the probability of stress corrosion cracking during service.

[0037] According to the present invention, the setting width of the first heating element is calculated according to the following formula:

[0038] L1=(3-4)·δ1;

[0039] The setting width of the second heating element is calculated according to the following formula:

[0040] L2=(3-4)·δ2;

[0041] Wherein, L1 is the setting width of the first heating element, L2 is the setting width of the second heating element, δ1 is the wall thickness of the thick-walled cylinder, and δ2 is the wall thickness of the thin-walled cylinder.

[0042] According to the present invention, the distance between the first auxiliary positioning loop line and the plane where the ring weld 103 is located is used as the first auxiliary distance, and the first auxiliary distance is calculated according to the following formula:

[0043]

[0044] The distance between the second auxiliary positioning ring line and the plane where the ring weld 103 is located is used as the second auxiliary distance, and the second auxiliary distance is calculated according to the following formula:

[0045]

[0046] The setting width of the third heating element is calculated according to the following formula:

[0047] L3 = (1.5-2)·δ1;

[0048] The setting width of the fourth heating element is calculated according to the following formula:

[0049] L4 = (1.5-2)·δ2;

[0050] Wherein, L3 is the setting width of the third heating element, L4 is the setting width of the fourth heating element, H1 is the first auxiliary distance, H2 is the second auxiliary distance, and r is the inner diameter of the heat exchanger with unequal thickness structure.

[0051] According to the present invention, the required heat of the first power supply is calculated according to the following formula:

[0052] Q1=cπ(2r+δ1)δ1L1ρ(T1-T0);

[0053] The rated power of the second power supply is calculated according to the following formula:

[0054] Q2=cπ(2r+δ2)δ2L2ρ(T1-T0);

[0055] The rated power of the third power supply is calculated according to the following formula:

[0056] Q3=cπ(2r+δ1)δ1L3ρ(T3-T0);

[0057] The rated power of the fourth power supply is calculated according to the following formula:

[0058] Q4=cπ(2r+δ2)δ2L4ρ(T3-T0);

[0059] Among them, c is the specific heat capacity of the material of the unequal thickness structure heat exchanger, ρ is the density of the material of the unequal thickness structure heat exchanger, T0 is the initial temperature of the unequal thickness structure heat exchanger, T1 is the first set temperature, T3 is the third set temperature, Q1 is the heat provided by the first power supply, Q2 is the heat provided by the second power supply, Q3 is the heat provided by the third power supply, and Q4 is the heat provided by the fourth power supply.

[0060] Preferably, when the first heating element and the second heating element are connected in series, the heat provided by the second power source (not shown) is calculated according to the following formula:

[0061] Q2 = Q1 (1 + 15%);

[0062] When the third heating element and the fourth heating element are connected in series, the heat provided by the fourth power source (not shown) is calculated according to the following formula:

[0063] Q4 = Q3 (1 + 15%);

[0064] The first heating element, the second heating element, the third heating element and the fourth heating element are each independently selected from any one of a ceramic sheet, an induction cable and a heating rope.

[0065] In the present invention, by accurately setting the setting widths of the first heating element and the second heating element, the rated powers of the first power supply (not shown) and the second power supply (not shown), and the first set temperature, the organization and mechanical properties of the circumferential weld 103 of the heat exchanger 1 with unequal thickness structure are improved, and the microstructure of the circumferential weld 103 of the heat exchanger 1 with unequal thickness structure is made precisely controllable.

[0066] In the present invention, by accurately setting the setting widths of the third heating element and the fourth heating element, the first auxiliary distance, the second auxiliary distance, the rated powers of the third power supply (not shown) and the fourth power supply (not shown), and the third set temperature, the stress distribution on the inner wall of the unequal thickness structure heat exchanger 1 can be accurately controlled.

[0067] Preferably, the method further comprises the following steps:

[0068] Before heating the unequal thickness structure heat exchanger 1 for the first time, multiple inner wall thermocouples (not shown) are evenly distributed in the radial direction of the inner wall of the thick-walled cylinder 101, and multiple outer wall thermocouples (not shown) are evenly distributed in the radial direction of the outer wall of the thick-walled cylinder 101. The average value of the temperatures measured by the multiple inner wall thermocouples (not shown) and the multiple outer wall thermocouples (not shown) is used to monitor the real-time temperature of the unequal thickness structure heat exchanger 1;

[0069] Before heating the heat exchanger 1 with unequal thickness structure for the first time, a first outer thermal insulation cotton (not shown) is laid on the outer surface of the first heating element, or a first outer thermal insulation cotton (not shown) is laid between the first heating element and the thick-walled cylinder 101; a second outer thermal insulation cotton (not shown) is laid on the outer surface of the second heating element, or a second outer thermal insulation cotton (not shown) is laid between the second heating element and the thin-walled cylinder 102;

[0070] Before the second heating of the unequal thickness structure heat exchanger 1, a third outer thermal insulation cotton (not shown) is laid on the outer surface of the third heating element, or a third outer thermal insulation cotton (not shown) is laid between the third heating element and the thick-walled cylinder 101; a fourth outer thermal insulation cotton (not shown) is laid on the outer surface of the fourth heating element, or a fourth outer thermal insulation cotton (not shown) is laid between the fourth heating element and the thin-walled cylinder 102;

[0071] Before heating the unequal thickness structure heat exchanger 1 for the first time, an optional first inner thermal insulation cotton (not shown) is arranged on the inner wall of the unequal thickness structure heat exchanger 1, and the first inner thermal insulation cotton (not shown) is arranged opposite to the first outer thermal insulation cotton (not shown) and the second outer thermal insulation cotton (not shown);

[0072] Before heating the unequal thickness structure heat exchanger 1 for the second time, an optional second inner thermal insulation cotton (not shown) and an optional third inner thermal insulation cotton (not shown) are arranged on the inner wall of the unequal thickness structure heat exchanger 1, the second inner thermal insulation cotton (not shown) is arranged opposite to the third outer thermal insulation cotton (not shown), and the third inner thermal insulation cotton (not shown) is arranged opposite to the fourth outer thermal insulation cotton (not shown);

[0073] After the temperature of the unequal thickness structure heat exchanger 1 drops to the second set temperature, the first outer thermal insulation cotton (not shown), the second outer thermal insulation cotton (not shown) and the first inner thermal insulation cotton (not shown) are removed.

[0074] In the present invention, multiple inner wall thermocouples (not shown) and multiple outer wall thermocouples (not shown) are evenly distributed radially on the inner wall and outer wall of the thick-walled cylinder 101, thereby achieving real-time monitoring of the temperature of the heat exchanger 1 with unequal thickness structure.

[0075] According to the present invention, the arrangement width of the first outer thermal insulation cotton (not shown) is calculated according to the following formula:

[0076] L5 = L1 + (400-600) mm;

[0077] The layout width of the second outer thermal insulation cotton (not shown) is calculated according to the following formula:

[0078] L6 = L2 + (300-500) mm;

[0079] The layout width of the first inner thermal insulation cotton (not shown) is calculated according to the following formula:

[0080] L7=L5+L6;

[0081] Among them, L5 is the layout width of the first outer thermal insulation cotton, L6 is the layout width of the second outer thermal insulation cotton, and L7 is the layout width of the first inner thermal insulation cotton.

[0082] Preferably, the arrangement width of the third outer thermal insulation cotton (not shown) is calculated according to the following formula:

[0083] L8 = L3 + (400-600) mm;

[0084] The layout width of the fourth outer thermal insulation cotton (not shown) is calculated according to the following formula:

[0085] L9 = L4 + (300-500) mm;

[0086] The layout width of the second inner thermal insulation cotton (not shown) is calculated according to the following formula:

[0087] L 10 =L8;

[0088] The layout width of the third inner thermal insulation cotton (not shown) is calculated according to the following formula:

[0089] L 11 =L9;

[0090] Among them, L8 is the layout width of the third outer insulation cotton, L9 is the layout width of the fourth outer insulation cotton, L 10 L is the layout width of the second inner insulation cotton. 11 It is the layout width of the third inner insulation cotton.

[0091] According to the present invention, the plane where the annular weld 103 is located is perpendicular to the axis of the unequal thickness structure heat exchanger 1;

[0092] The planes where the first auxiliary positioning loop line and the second auxiliary positioning loop line are located are both perpendicular to the axis of the unequal thickness structure heat exchanger 1;

[0093] The first set temperature is 600-705°C, the second set temperature is not greater than 50°C, and the third set temperature is 250-450°C.

[0094] Preferably, when the first heating element, the second heating element, the third heating element and the fourth heating element are all induction cables, the first external thermal insulation cotton (not shown) is arranged between the first heating element and the thick-walled cylinder 101, the second external thermal insulation cotton (not shown) is arranged between the second heating element and the thin-walled cylinder 102, the third external thermal insulation cotton (not shown) is arranged between the third heating element and the thick-walled cylinder 101, and the fourth external thermal insulation cotton (not shown) is arranged between the fourth heating element and the thin-walled cylinder 102;

[0095] When the first heating element, the second heating element, the third heating element and the fourth heating element are not induction cables, the first outer thermal insulation cotton (not shown) is arranged on the outer surface of the first heating element, the second outer thermal insulation cotton (not shown) is arranged on the outer surface of the second heating element, the third outer thermal insulation cotton (not shown) is arranged on the outer surface of the third heating element, and the fourth outer thermal insulation cotton (not shown) is arranged on the outer surface of the fourth heating element.

[0096] In the present invention, before the first and second heating of the unequal thickness structure heat exchanger 1, the corresponding first outer insulation cotton (not shown), second outer insulation cotton (not shown), third outer insulation cotton (not shown), fourth outer insulation cotton (not shown), first inner insulation cotton (not shown), second inner insulation cotton (not shown), and third inner insulation cotton (not shown) are laid to ensure the local heat treatment and temperature uniformity control effect of the unequal thickness structure heat exchanger 1.

[0097] The present invention is described in more detail below through a specific embodiment.

[0098] Example 1

[0099] This embodiment provides a method for local heat treatment of a heat exchanger with unequal thickness structure, such as Figure 1 , Figure 2 As shown, in this embodiment, the unequal thickness structure heat exchanger 1 includes a thick-walled cylinder 101 and a thin-walled cylinder 102 connected to each other, the wall thickness δ1 of the thick-walled cylinder is 200 mm, the wall thickness δ2 of the thin-walled cylinder is 88 mm, and a girth weld 103 is provided at the connection between the thick-walled cylinder 101 and the thin-walled cylinder 102. The thickness of the girth weld 103 is 6.5 mm, the material is E309L+E316L stainless steel, the base material is SR626, the material specific heat capacity c of the unequal thickness structure heat exchanger 1 is 0.51 kJ / (m3·℃), the density ρ is 7850 kg / m3, the initial temperature T0 is 25℃, the first set temperature T1 is 620℃, the second set temperature T2 is 40℃, and the third set temperature T3 is 300℃. The inner diameter r of the thick-walled cylinder 101 and the thin-walled cylinder 102 is the same and is 1422 mm. The method comprises the following steps:

[0100] Taking the center of the annular weld 103 as the starting point, the first heating element is disposed on the outer wall of the thick-walled cylinder 101, and the second heating element is disposed on the outer wall of the thin-walled cylinder 102;

[0101] The first power source (not shown) is connected to the first heating element, and the second power source (not shown) is connected to the second heating element, respectively, to heat the unequal thickness structure heat exchanger 1 for the first time, and the heating is stopped when the temperature of the unequal thickness structure heat exchanger 1 rises to the first set temperature;

[0102] After the temperature of the unequal thickness structure heat exchanger 1 drops to the second set temperature, the first heating element and the second heating element are removed;

[0103] The third heating element is arranged on the outer wall of the thick-walled cylinder 101 with the first auxiliary positioning loop line on the thick-walled cylinder 101 as the center line; the fourth heating element is arranged on the outer wall of the thin-walled cylinder 102 with the second auxiliary positioning loop line on the thin-walled cylinder 102 as the center line;

[0104] The third power source (not shown) is connected to the third heating element, and the fourth power source (not shown) is connected to the fourth heating element, respectively, to heat the unequal thickness structure heat exchanger 1 for the second time, and the heating is stopped when the temperature of the unequal thickness structure heat exchanger 1 rises to the third set temperature;

[0105] The plane where the annular weld 103 is located is perpendicular to the axis of the heat exchanger 1 with unequal thickness structure;

[0106] The planes where the first auxiliary positioning loop line and the second auxiliary positioning loop line are located are both perpendicular to the axis of the unequal thickness structure heat exchanger 1;

[0107] The first heating element, the second heating element, the third heating element and the fourth heating element are all induction cables;

[0108] The setting width L1 of the first heating element is calculated according to the following formula:

[0109] L1=(3-4)·δ1=600-800mm, the value is 800mm;

[0110] The setting width L2 of the second heating element is calculated according to the following formula:

[0111] L2 = (3-4)·δ2 = 264-352 mm, the value is 352 mm;

[0112] The distance between the first auxiliary positioning ring line and the plane where the ring weld 103 is located is taken as the first auxiliary distance. The first auxiliary distance H1 is calculated according to the following formula:

[0113]

[0114] The distance between the second auxiliary positioning ring line and the plane where the ring weld 103 is located is used as the second auxiliary distance. The second auxiliary distance H2 is calculated according to the following formula:

[0115]

[0116] The setting width L3 of the third heating element is calculated according to the following formula:

[0117] L3 = (1.5-2)·δ1 = 300-400mm, the value is 400mm;

[0118] The setting width L4 of the fourth heating element is calculated according to the following formula:

[0119] L4 = (1.5-2)·δ2 = 132-176 mm, the value is 176 mm;

[0120] The heat Q1 provided by the first power supply is calculated according to the following formula:

[0121] Q1=cπ(2r+δ1)δ1L1ρ(T1-T0)=1011.9KWH,;

[0122] The heat Q2 provided by the second power supply is calculated according to the following formula:

[0123] Q2=cπ(2r+δ2)δ2L2ρ(T1-T0)=171.1KWH;

[0124] The heat provided by the third power supply Q3 is calculated according to the following formula:

[0125] Q3=cπ(2r+δ1)δ1L3ρ(T3-T0)=233.8KWH;

[0126] The heat provided by the fourth power supply Q4 is calculated according to the following formula:

[0127] Q4=cπ(2r+δ2)δ2L4ρ(T3-T0)=43.6KWH;

[0128] The method further comprises the following steps:

[0129] Before heating the unequal thickness structure heat exchanger 1 for the first time, four inner wall thermocouples (not shown) are evenly distributed in the radial direction of the inner wall of the thick-walled cylinder 101, wherein two of the four inner wall thermocouples (not shown) are located at the highest point and the lowest point of the inner wall of the thick-walled cylinder 101, and four outer wall thermocouples (not shown) are evenly distributed in the radial direction of the outer wall of the thick-walled cylinder 101, wherein two of the four outer wall thermocouples (not shown) are located at the highest point and the lowest point of the outer wall of the thick-walled cylinder 101. The average value of the temperatures measured by the four inner wall thermocouples (not shown) and the four outer wall thermocouples (not shown) is used to monitor the real-time temperature of the unequal thickness structure heat exchanger 1;

[0130] Before heating the unequal thickness structure heat exchanger 1 for the first time, a first outer thermal insulation cotton (not shown) is laid between the first heating element and the thick-walled cylinder 101; a second outer thermal insulation cotton (not shown) is laid between the second heating element and the thin-walled cylinder 102;

[0131] Before heating the unequal thickness structure heat exchanger 1 for the second time, a third outer thermal insulation cotton (not shown) is laid between the third heating element and the thick-walled cylinder 101; a fourth outer thermal insulation cotton (not shown) is laid between the fourth heating element and the thin-walled cylinder 102;

[0132] Before heating the unequal thickness structure heat exchanger 1 for the first time, a first inner thermal insulation cotton (not shown) is arranged on the inner wall of the unequal thickness structure heat exchanger 1, and the first inner thermal insulation cotton (not shown) is arranged opposite to the first outer thermal insulation cotton (not shown) and the second outer thermal insulation cotton (not shown);

[0133] Before heating the unequal thickness structure heat exchanger 1 for the second time, a second inner thermal insulation cotton (not shown) and a third inner thermal insulation cotton (not shown) are arranged on the inner wall of the unequal thickness structure heat exchanger 1, the second inner thermal insulation cotton (not shown) is arranged opposite to the third outer thermal insulation cotton (not shown), and the third inner thermal insulation cotton (not shown) is arranged opposite to the fourth outer thermal insulation cotton (not shown);

[0134] Before the first and second heating of the unequal thickness structure heat exchanger 1, the openings of the unequal thickness structure heat exchanger 1 are blocked with thermal insulation cotton (not shown) to eliminate or reduce the air flow in the pipeline;

[0135] After the temperature of the unequal thickness structure heat exchanger 1 drops to the second set temperature, the first outer thermal insulation cotton (not shown), the second outer thermal insulation cotton (not shown) and the first inner thermal insulation cotton (not shown) are removed;

[0136] The arrangement width L5 of the first outer thermal insulation cotton (not shown) is calculated according to the following formula:

[0137] L5 = L1 + (400 ~ 600) mm, the value is 1400 mm;

[0138] The arrangement width L6 of the second outer thermal insulation cotton (not shown) is calculated according to the following formula:

[0139] L6=L2+(300~500)mm takes the value of 750mm;

[0140] The arrangement width L7 of the first inner thermal insulation cotton (not shown) is calculated according to the following formula:

[0141] L7=L5+L6 takes the value of 2150mm;

[0142] The layout width of the third outer thermal insulation cotton (not shown) is calculated according to the following formula:

[0143] L8=L3+(400~600)mm takes the value of 900mm;

[0144] The arrangement width L8 of the fourth outer thermal insulation cotton (not shown) is calculated according to the following formula:

[0145] L9=L4+(300~500)mm takes the value of 600mm;

[0146] The layout width L of the second inner thermal insulation cotton (not shown) 10 Calculated according to the following formula:

[0147] L 10 =L8 value is 900mm;

[0148] The layout width L of the third inner thermal insulation cotton (not shown) 11 Calculated according to the following formula:

[0149] L 11 =L9 value is 600mm.

[0150] Depend on Figure 3 and Figure 4 It can be seen that the local heat treatment method of the unequal thickness structure heat exchanger 1 in this embodiment can effectively reduce the axial stress and hoop stress of the inner wall ring weld 103 of the unequal thickness structure heat exchanger 1, and even put it into a compressive stress state, compared with the traditional heat treatment method, solve the problem of excessive tensile stress after heat treatment of the inner wall of the unequal thickness structure heat exchanger 1 after welding, avoid stress concentration, and fundamentally reduce the probability of stress corrosion cracking during service.

[0151] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for local heat treatment of a heat exchanger with unequal thickness structure, wherein the heat exchanger with unequal thickness structure comprises a thick-walled cylinder and a thin-walled cylinder connected to each other, a circumferential weld is provided at the connection between the thick-walled cylinder and the thin-walled cylinder, and the inner diameters of the thick-walled cylinder and the thin-walled cylinder are the same, characterized in that: The method comprises the following steps: Taking the center of the annular weld as a starting point, a first heating element is arranged on the outer wall of the thick-walled cylinder, and a second heating element is arranged on the outer wall of the thin-walled cylinder; Connecting the first power supply to the first heating element and the second power supply to the second heating element respectively, heating the heat exchanger with unequal thickness structure for the first time, and stopping heating when the temperature of the heat exchanger with unequal thickness structure rises to a first set temperature; After the temperature of the heat exchanger with unequal thickness structure drops to a second set temperature, the first heating element and the second heating element are removed; The third heating element is arranged on the outer wall of the thick-walled cylinder with the first auxiliary positioning loop on the thick-walled cylinder as the center line; the fourth heating element is arranged on the outer wall of the thin-walled cylinder with the second auxiliary positioning loop on the thin-walled cylinder as the center line; The third power supply is connected to the third heating element, and the fourth power supply is connected to the fourth heating element, respectively, to heat the unequal thickness structure heat exchanger for the second time, and the heating is stopped when the temperature of the unequal thickness structure heat exchanger rises to the third set temperature.

2. The method according to claim 1, characterized in that The setting width of the first heating element is calculated according to the following formula: L1=(3-4)·δ1; The setting width of the second heating element is calculated according to the following formula: L2=(3-4)·δ2; Wherein, L1 is the setting width of the first heating element, L2 is the setting width of the second heating element, δ1 is the wall thickness of the thick-walled cylinder, and δ2 is the wall thickness of the thin-walled cylinder.

3. The method according to claim 2, characterized in that The distance between the first auxiliary positioning loop and the plane where the ring weld is located is used as the first auxiliary distance, and the first auxiliary distance is calculated according to the following formula: The distance between the second auxiliary positioning ring line and the plane where the ring weld is located is used as the second auxiliary distance, and the second auxiliary distance is calculated according to the following formula: The setting width of the third heating element is calculated according to the following formula: L3 = (1.5-2)·δ1; The setting width of the fourth heating element is calculated according to the following formula: L4 = (1.5-2)·δ2; Wherein, L3 is the setting width of the third heating element, L4 is the setting width of the fourth heating element, H1 is the first auxiliary distance, H2 is the second auxiliary distance, and r is the inner diameter of the heat exchanger with unequal thickness structure.

4. The method according to claim 3, characterized in that The heat provided by the first power supply is calculated according to the following formula: Q1=cπ(2r+δ1)δ1L1ρ(T1-T0); The heat provided by the second power supply is calculated according to the following formula: Q2=cπ(2r+δ2)δ2L2ρ(T1-T0); The heat provided by the third power supply is calculated according to the following formula: Q3=cπ(2r+δ1)δ1L3ρ(T3-T0); The heat provided by the fourth power supply is calculated according to the following formula: Q4=cπ(2r+δ2)δ2L4ρ(T3-T0); Among them, c is the specific heat capacity of the material of the unequal thickness structure heat exchanger, ρ is the density of the material of the unequal thickness structure heat exchanger, T0 is the initial temperature of the unequal thickness structure heat exchanger, T1 is the first set temperature, T3 is the third set temperature, Q1 is the heat provided by the first power supply, Q2 is the heat provided by the second power supply, Q3 is the heat provided by the third power supply, and Q4 is the heat provided by the fourth power supply.

5. The method according to claim 4, characterized in that When the first heating element and the second heating element are connected in series, the heat provided by the second power supply is calculated according to the following formula: Q2 = Q1 (1 + 15%); When the third heating element and the fourth heating element are connected in series, the heat provided by the fourth power supply is calculated according to the following formula: Q4 = Q3 (1 + 15%); The first heating element, the second heating element, the third heating element and the fourth heating element are each independently selected from any one of a ceramic sheet, an induction cable and a heating rope.

6. The method according to claim 5, characterized in that The method further comprises the following steps: Before heating the unequal thickness structure heat exchanger for the first time, a plurality of inner wall thermocouples are evenly distributed radially on the inner wall of the thick-walled cylinder, and a plurality of outer wall thermocouples are evenly distributed radially on the outer wall of the thick-walled cylinder. The average value of the temperatures measured by the plurality of inner wall thermocouples and the plurality of outer wall thermocouples is used to monitor the real-time temperature of the unequal thickness structure heat exchanger. Before heating the unequal thickness structure heat exchanger for the first time, a first outer thermal insulation cotton is laid on the outer surface of the first heating element, or a first outer thermal insulation cotton is laid between the first heating element and the thick-walled cylinder; a second outer thermal insulation cotton is laid on the outer surface of the second heating element, or a second outer thermal insulation cotton is laid between the second heating element and the thin-walled cylinder; Before heating the unequal thickness structure heat exchanger for the second time, a third outer thermal insulation cotton is laid on the outer surface of the third heating element, or a third outer thermal insulation cotton is laid between the third heating element and the thick-walled cylinder; a fourth outer thermal insulation cotton is laid on the outer surface of the fourth heating element, or a fourth outer thermal insulation cotton is laid between the fourth heating element and the thin-walled cylinder; Before heating the unequal thickness structure heat exchanger for the first time, an optional first inner thermal insulation cotton is arranged on the inner wall of the unequal thickness structure heat exchanger, wherein the first inner thermal insulation cotton is arranged opposite to the first outer thermal insulation cotton and the second outer thermal insulation cotton; Before heating the unequal thickness structure heat exchanger for the second time, an optional second inner thermal insulation cotton and an optional third inner thermal insulation cotton are arranged on the inner wall of the unequal thickness structure heat exchanger, the second inner thermal insulation cotton is arranged opposite to the third outer thermal insulation cotton, and the third inner thermal insulation cotton is arranged opposite to the fourth outer thermal insulation cotton; After the temperature of the unequal thickness structure heat exchanger drops to the second set temperature, the first outer thermal insulation cotton, the second outer thermal insulation cotton and the first inner thermal insulation cotton are removed.

7. The method according to claim 6, characterized in that The layout width of the first outer thermal insulation cotton is calculated according to the following formula: L5 = L1 + (400-600) mm; The layout width of the second outer thermal insulation cotton is calculated according to the following formula: L6 = L2 + (300-500) mm; The layout width of the first inner thermal insulation cotton is calculated according to the following formula: L7=L5+L6; Among them, L5 is the layout width of the first outer thermal insulation cotton, L6 is the layout width of the second outer thermal insulation cotton, and L7 is the layout width of the first inner thermal insulation cotton.

8. The method according to claim 6, characterized in that The layout width of the third outer thermal insulation cotton is calculated according to the following formula: L8 = L3 + (400-600) mm; The layout width of the fourth outer thermal insulation cotton is calculated according to the following formula: L9 = L4 + (300-500) mm; The layout width of the second inner thermal insulation cotton is calculated according to the following formula: L 10 =L8; The layout width of the third inner thermal insulation cotton is calculated according to the following formula: <h2 style=";text-align:left;direction:ltr">L<h2 style=";text-align:left;direction:ltr"> 11 <h2 style=";text-align:left;direction:ltr"> =L9; Among them, L8 is the layout width of the third outer insulation cotton, L9 is the layout width of the fourth outer insulation cotton, L 10 L is the layout width of the second inner insulation cotton. 11 It is the layout width of the third inner insulation cotton.

9. The method according to claim 1, characterized in that: The plane where the annular weld is located is perpendicular to the axis of the heat exchanger with unequal thickness structure; The planes where the first auxiliary positioning loop line and the second auxiliary positioning loop line are located are both perpendicular to the axis of the heat exchanger with unequal thickness structure; The first set temperature is 600-705°C, the second set temperature is no more than 50°C, and the third set temperature is 250-450°C.

10. The method according to claim 6, characterized in that When the first heating element, the second heating element, the third heating element and the fourth heating element are all induction cables, the first outer thermal insulation cotton is arranged between the first heating element and the thick-walled cylinder, the second outer thermal insulation cotton is arranged between the second heating element and the thin-walled cylinder, the third outer thermal insulation cotton is arranged between the third heating element and the thick-walled cylinder, and the fourth outer thermal insulation cotton is arranged between the fourth heating element and the thin-walled cylinder; When the first heating element, the second heating element, the third heating element and the fourth heating element are not induction cables, the first outer thermal insulation cotton is arranged on the outer surface of the first heating element, the second outer thermal insulation cotton is arranged on the outer surface of the second heating element, the third outer thermal insulation cotton is arranged on the outer surface of the third heating element, and the fourth outer thermal insulation cotton is arranged on the outer surface of the fourth heating element.

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