Partial heat treatment method for heat exchanger with unequal thickness structure

Abstract

The application discloses a local heat treatment method for a heat exchanger with a non-uniform thickness structure, the heat exchanger with the non-uniform thickness structure comprising a thick-wall cylinder, a thin-wall cylinder and a girth weld connected with each other, and the method comprising the following steps: first heating the heat exchanger with the non-uniform thickness structure by using a first heating element and a second heating element respectively, and stopping heating when the temperature of the heat exchanger with the non-uniform thickness structure rises to a first set temperature; removing the first heating element and the second heating element after the temperature of the heat exchanger with the non-uniform thickness structure falls to a second set temperature; second heating the heat exchanger with the non-uniform thickness structure by using a third heating element and a fourth heating element, and stopping heating when the temperature of the heat exchanger with the non-uniform thickness structure rises to a third set temperature. The method improves the structure and mechanical properties of a girth weld on an inner wall of the heat exchanger with the non-uniform thickness structure and the stress distribution on an inner wall of a pipeline through first and second heating of the heat exchanger with the non-uniform thickness structure, so that the stress near the girth weld on the inner wall is reduced to compressive stress, and stress concentration is avoided.

Description

Technical Field

[0001] This invention relates to the field of local heat treatment and temperature uniformity control technology, specifically to a local heat treatment method for a heat exchanger with an unequal thickness structure. Background Technology

[0002] In the manufacturing process of high-pressure heat exchangers, uneven thickness joints are a common problem, especially between the shell and the head, creating structural discontinuities in the pressure vessel. These units operate under harsh conditions of high temperature (360–440°C) and high pressure, coupled with corrosive media such as hydrogen and hydrogen sulfide. The combined effect of these corrosive media and the high stress state of the reactor makes them highly susceptible to stress corrosion cracking, leading to significant economic losses and safety hazards. The high residual welding stress at the uneven thickness joints is a key factor in stress corrosion. While heat treatment is commonly used to relieve stress, localized heat treatment is less effective for unequal thickness structures in relieving internal surface stress. Furthermore, the inconsistent wall thickness can lead to unreasonable heat treatment temperature distribution, negatively impacting the performance and lifespan of the welded joint.

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

[0004] To address the shortcomings of existing technologies, this invention proposes a local heat treatment method for heat exchangers with unequal thickness structures. This method improves the microstructure and mechanical properties of the circumferential weld seam on the inner wall of the heat exchanger by first heating it, and improves the stress distribution on the inner wall of the pipe by second heating it, reducing the stress near the circumferential weld seam to compressive stress. This method is of great significance for the safe operation of high-pressure heat exchangers with unequal thickness structures.

[0005] To achieve the above objectives, the present invention provides a method for local heat treatment of a heat exchanger with unequal thickness structure. The heat exchanger with unequal thickness structure includes 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. The thick-walled cylinder and the thin-walled cylinder have the same inner diameter. The method includes the following steps:

[0006] Starting from the center of the circumferential weld, the first heating element is set on the outer wall of the thick-walled cylinder, and the second heating element is set on the outer wall of the thin-walled cylinder.

[0007] The first power supply is connected to the first heating element and the second power supply is connected to the second heating element to heat the heat exchanger with unequal thickness structure for the first time. Heating is stopped when the temperature of the heat exchanger with unequal thickness structure rises to the first set temperature.

[0008] Once the temperature of the heat exchanger with unequal thickness structure drops to the second set temperature, remove the first heating element and the second heating element.

[0009] With the first auxiliary positioning ring line on the thick-walled cylinder as the center line, the third heating element is set on the outer wall of the thick-walled cylinder; with the second auxiliary positioning ring line on the thin-walled cylinder as the center line, the fourth heating element is set on the outer wall of the thin-walled cylinder.

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

[0011] The effects of this invention are:

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

[0013] (2) The local heat treatment method for heat exchangers with unequal thickness structure proposed in this invention can significantly reduce the axial and circumferential stress of the circumferential weld seam on the inner wall of the heat exchanger with unequal thickness structure, and even make it into a compressive stress state. This solves the problem of excessive tensile stress after heat treatment of the inner wall of the heat exchanger with unequal thickness structure after welding, avoids stress concentration, and can fundamentally reduce the probability of stress corrosion cracking during service.

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

[0015] (4) The local heat treatment method for heat exchangers with unequal thickness structure proposed in this invention makes the stress distribution of the inner wall of the heat exchanger with unequal thickness structure precisely controllable by accurately 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 source and the fourth power source, and the third set temperature.

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

[0017] (6) The local heat treatment method for heat exchangers with unequal thickness structure proposed in this invention lays out 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 the first and second heating of 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 section. Attached Figure Description

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

[0020] Figure 1 This is a schematic flowchart of the local heat treatment method for heat exchangers with unequal thickness structures proposed in this invention.

[0021] Figure 2 This is a schematic diagram of the heat exchanger with unequal thickness structure proposed in this invention.

[0022] Figure 3 This is a schematic diagram of the axial stress curve of the circumferential weld seam on the inner wall of the heat exchanger with unequal thickness structure, which is a specific embodiment of the local heat treatment method for heat exchangers with unequal thickness structure proposed in this invention.

[0023] Figure 4 This is a schematic diagram of the radial stress curve of the circumferential weld seam on the inner wall of the heat exchanger with unequal thickness structure, as described in a specific embodiment of the local heat treatment method for heat exchangers with unequal thickness structure proposed in this invention.

[0024] Explanation of reference numerals in the attached figures:

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

[0026] 101-Thick-walled cylinder, 102-Thin-walled cylinder, 103-Circumferential weld, 104-First heating element or third heating element, 105-Second heating element or fourth heating element. Detailed Implementation

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

[0028] In this invention, unless otherwise stated, directional terms such as "upper" and "lower" generally refer to the upper and lower positions of the device in its normal operating state, for example, as shown in the reference. Figure 1 In the drawing orientation, "inner" and "outer" refer to those relative to the outline of the device. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first," "second," or "third" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

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

[0030] Starting from the center of the circumferential weld 103, the first heating element is set on the outer wall of the thick-walled cylinder 101, and the second heating element is set on the outer wall of the thin-walled cylinder 102.

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

[0032] After the temperature of the heat exchanger 1 with unequal thickness structure drops to the second set temperature, remove the first heating element and the second heating element.

[0033] With the first auxiliary positioning ring line on the thick-walled cylinder 101 as the center line, the third heating element is set on the outer wall of the thick-walled cylinder 101; with the second auxiliary positioning ring line on the thin-walled cylinder 102 as the center line, the fourth heating element is set on the outer wall of the thin-walled cylinder 102.

[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 to heat the heat exchanger 1 with unequal thickness structure for the second time. Heating is stopped when the temperature of the heat exchanger 1 with unequal thickness structure rises to the third set temperature.

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

[0036] In this invention, the axial and circumferential stresses of the circumferential weld 103 on the inner wall of the heat exchanger 1 with unequal thickness structure are significantly reduced, even to the point of being in a compressive stress state. This solves the problem of excessive tensile stress on the inner wall of the heat exchanger 1 with unequal thickness structure after welding heat treatment, avoids stress concentration, and can fundamentally and significantly reduce the probability of stress corrosion cracking during service.

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

[0038] L1 = (3-4)·δ1;

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

[0040] L2=(3-4)·δ2;

[0041] Wherein, L1 is the width of the first heating element, L2 is the 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 ring and the plane containing the circumferential weld 103 is used as the first auxiliary distance, which is calculated according to the following formula:

[0043]

[0044] The distance between the second auxiliary positioning ring and the plane containing the circumferential weld 103 is taken as the second auxiliary distance, which is calculated according to the following formula:

[0045]

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

[0047] L3 = (1.5-2)·δ1;

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

[0049] L4 = (1.5-2)·δ2;

[0050] Where L3 is the width of the third heating element, L4 is the 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 source 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] Where c is the specific heat capacity of the heat exchanger material with unequal thickness, ρ is the density of the heat exchanger material with unequal thickness, T0 is the initial temperature of the heat exchanger with unequal thickness, T1 is the first set temperature, T3 is the third set temperature, Q1 is the heat provided by the first power source, Q2 is the heat provided by the second power source, Q3 is the heat provided by the third power source, and Q4 is the heat provided by the fourth power source.

[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 and fourth heating elements are connected in series, the heat supplied 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 ceramic plates, induction cables, and heating ropes.

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

[0066] In this invention, 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 rated power of the third power supply (not shown) and the fourth power supply (not shown), and the third set temperature, the stress distribution of the inner wall of the heat exchanger 1 with unequal thickness structure can be precisely controlled.

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

[0068] Before the first heating of the heat exchanger 1 with unequal thickness structure, multiple inner wall thermocouples (not shown) are evenly distributed radially on the inner wall of the thick-walled cylinder 101, and multiple outer wall thermocouples (not shown) are evenly distributed radially on 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 heat exchanger 1 with unequal thickness structure.

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

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

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

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

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

[0074] In this invention, multiple inner wall thermocouples (not shown) and multiple outer wall thermocouples (not shown) are evenly distributed radially on the inner and outer walls of the thick-walled cylinder 101, thereby enabling 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 insulation cotton (not shown) is calculated according to the following formula:

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

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

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

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

[0080] L7 = L5 + L6;

[0081] Wherein, L5 is the width of the first outer insulation cotton, L6 is the width of the second outer insulation cotton, and L7 is the width of the first inner insulation cotton.

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

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

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

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

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

[0087] L 10 =L8;

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

[0089] L 11 =L9;

[0090] Where L8 is the width of the third outer insulation material, L9 is the width of the fourth outer insulation material, and L 10 L is the width of the second inner insulation layer. 11 This refers to the width of the third inner insulation layer.

[0091] According to the present invention, the plane containing the circumferential weld 103 is perpendicular to the axis of the heat exchanger 1 with unequal thickness structure;

[0092] The planes containing the first auxiliary positioning ring and the second auxiliary positioning ring are both perpendicular to the axis of the heat exchanger 1 with unequal thickness structure;

[0093] The first set temperature is 600-705℃, the second set temperature is no more than 50℃, and the third set temperature is 250-450℃.

[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 outer insulation cotton (not shown) is disposed between the first heating element and the thick-walled cylinder 101, the second outer insulation cotton (not shown) is disposed between the second heating element and the thin-walled cylinder 102, the third outer insulation cotton (not shown) is disposed between the third heating element and the thick-walled cylinder 101, and the fourth outer insulation cotton (not shown) is disposed between the fourth heating element and the thin-walled cylinder 102;

[0095] When none of the first heating element, second heating element, third heating element and fourth heating element are induction cables, the first outer insulation cotton (not shown) is disposed on the outer surface of the first heating element, the second outer insulation cotton (not shown) is disposed on the outer surface of the second heating element, the third outer insulation cotton (not shown) is disposed on the outer surface of the third heating element and the fourth outer insulation cotton (not shown) is disposed on the outer surface of the fourth heating element.

[0096] In this invention, before the first and second heating of the heat exchanger 1 with unequal thickness structure, 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 heat exchanger 1 with unequal thickness structure.

[0097] The present invention will now be described in more detail through a specific embodiment.

[0098] Example 1

[0099] This embodiment provides a method for localized heat treatment of a heat exchanger with an unequal thickness structure, such as... Figure 1 , Figure 2 As shown, in this embodiment, the unequal thickness 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, and the wall thickness δ2 of the thin-walled cylinder is 88 mm. A circumferential weld 103 is provided at the connection between the thick-walled cylinder 101 and the thin-walled cylinder 102. The thickness of the circumferential weld 103 is 6.5 mm, and the material is E309L+E316L stainless steel. The base material is SR626. The specific heat capacity c of the unequal thickness 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 includes the following steps:

[0100] Starting from the center of the circumferential weld 103, the first heating element is set on the outer wall of the thick-walled cylinder 101, and the second heating element is set on the outer wall of the thin-walled cylinder 102.

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

[0102] After the temperature of the heat exchanger 1 with unequal thickness structure drops to the second set temperature, remove the first heating element and the second heating element.

[0103] With the first auxiliary positioning ring line on the thick-walled cylinder 101 as the center line, the third heating element is set on the outer wall of the thick-walled cylinder 101; with the second auxiliary positioning ring line on the thin-walled cylinder 102 as the center line, the fourth heating element is set on the outer wall of the thin-walled cylinder 102.

[0104] 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 to heat the heat exchanger 1 with unequal thickness structure for the second time. Heating is stopped when the temperature of the heat exchanger 1 with unequal thickness structure rises to the third set temperature.

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

[0106] The planes containing the first auxiliary positioning ring and the second auxiliary positioning ring are both perpendicular to the axis of the heat exchanger 1 with unequal thickness structure;

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

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

[0109] L1=(3-4)·δ1=600-800mm, with a value of 800mm;

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

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

[0112] The distance between the first auxiliary positioning ring and the plane containing the circumferential weld 103 is taken as the first auxiliary distance, and the first auxiliary distance H1 is calculated according to the following formula:

[0113]

[0114] The distance between the second auxiliary positioning ring and the plane containing the circumferential weld 103 is taken as the second auxiliary distance, and the second auxiliary distance H2 is calculated according to the following formula:

[0115]

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

[0117] L3=(1.5-2)·δ1=300-400mm, with a value of 400mm;

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

[0119] L4 = (1.5-2)·δ2 = 132-176mm, with a value of 176mm;

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

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

[0124] The heat Q3 provided by the third power source is calculated using the following formula:

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

[0126] The heat Q4 provided by the fourth power source is calculated using the following formula:

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

[0128] The method also includes the following steps:

[0129] Before the first heating of the heat exchanger 1 with unequal thickness structure, four inner wall thermocouples (not shown) are evenly distributed radially on the inner wall of the thick-walled cylinder 101. Two of the four inner wall thermocouples (not shown) are located at the highest and lowest points of the inner wall of the thick-walled cylinder 101. Four outer wall thermocouples (not shown) are evenly distributed radially on the outer wall of the thick-walled cylinder 101. Two of the four outer wall thermocouples (not shown) are located at the highest and lowest points 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 heat exchanger 1 with unequal thickness structure.

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

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

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

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

[0134] Before the first and second heating of the heat exchanger 1 with unequal thickness structure, the opening of the heat exchanger 1 with unequal thickness structure is sealed with insulation cotton (not shown) to eliminate or reduce air flow in the pipe.

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

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

[0137] L5 = L1 + (400~600) mm, with a value of 1400 mm;

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

[0139] L6 = L2 + (300~500) mm, with a value of 750 mm;

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

[0141] L7 = L5 + L6 is 2150 mm;

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

[0143] L8 = L3 + (400~600) mm, with a value of 900 mm;

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

[0145] L9 = L4 + (300~500) mm, with a value of 600 mm;

[0146] The width L of the second inner insulation cotton (not shown) 10 Calculate using the following formula:

[0147] L 10 =L8 is 900mm;

[0148] The width L of the third inner insulation cotton (not shown) 11 Calculate using the following formula:

[0149] L 11 =L9 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 and circumferential stress of the inner wall circumferential weld 103 of the unequal thickness structure heat exchanger 1 compared with the traditional heat treatment method, and even make it into a compressive stress state. This solves the problem of excessive tensile stress after the heat treatment of the inner wall of the unequal thickness structure heat exchanger 1 after welding, avoids stress concentration, and fundamentally reduces the probability of stress corrosion cracking during service.

[0151] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations 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 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 thick-walled cylinder and the thin-walled cylinder have the same inner diameter, characterized in that... The method includes the following steps: Starting from the center of the circumferential weld, the first heating element is set on the outer wall of the thick-walled cylinder, and the second heating element is set on the outer wall of the thin-walled cylinder. The first power supply is connected to the first heating element and the second power supply is connected to the second heating element to heat the heat exchanger with unequal thickness structure for the first time. Heating is stopped when the temperature of the heat exchanger with unequal thickness structure rises to the first set temperature. Once the temperature of the heat exchanger with unequal thickness structure drops to the second set temperature, remove the first heating element and the second heating element. With the first auxiliary positioning ring line on the thick-walled cylinder as the center line, the third heating element is set on the outer wall of the thick-walled cylinder; with the second auxiliary positioning ring line on the thin-walled cylinder as the center line, the fourth heating element is set on the outer wall of the thin-walled cylinder. The third power supply is connected to the third heating element, and the fourth power supply is connected to the fourth heating element to heat the heat exchanger with unequal thickness structure for the second time. Heating is stopped when the temperature of the heat exchanger with unequal thickness structure rises to the third set temperature. The width of the first heating element is calculated according to the following formula: L1=(3-4)·δ1; The width of the second heating element is calculated according to the following formula: L2=(3-4)·δ2; Where L1 is the width of the first heating element, L2 is the 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. The width of the third heating element is calculated according to the following formula: L3 = (1.5 - 2)·δ1; The width of the fourth heating element is calculated according to the following formula: L4 = (1.5 - 2)·δ2; Where L3 is the width of the third heating element and L4 is the width of the fourth heating element.

2. The method according to claim 1, characterized in that, The distance between the first auxiliary positioning ring and the plane containing the circumferential weld is taken as the first auxiliary distance, which is calculated according to the following formula: ； The distance between the second auxiliary positioning ring and the plane containing the circumferential weld is taken as the second auxiliary distance, which is calculated according to the following formula: Where 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.

3. The method according to claim 2, characterized in that, The heat provided by the first power source is calculated according to the following formula: ； The heat provided by the second power source is calculated according to the following formula: ； The heat provided by the third power source is calculated according to the following formula: ； The heat provided by the fourth power source is calculated according to the following formula: ； Where c is the specific heat capacity of the heat exchanger material with unequal thickness, ρ is the density of the heat exchanger material with unequal thickness, T0 is the initial temperature of the heat exchanger with unequal thickness, T1 is the first set temperature, T3 is the third set temperature, Q1 is the heat provided by the first power source, Q2 is the heat provided by the second power source, Q3 is the heat provided by the third power source, and Q4 is the heat provided by the fourth power source.

4. The method according to claim 3, characterized in that, When the first heating element and the second heating element are connected in series, the heat provided by the second power source is calculated according to the following formula: ； When the third heating element and the fourth heating element are connected in series, the heat provided by the fourth power source is calculated according to the following formula: ； 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 ceramic plates, induction cables, and heating ropes.

5. The method according to claim 4, characterized in that, The method further includes the following steps: Before the first heating of the heat exchanger with unequal thickness structure, multiple inner wall thermocouples are evenly distributed radially on the inner wall of the thick-walled cylinder, and multiple 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 multiple inner wall thermocouples and the multiple outer wall thermocouples is used to monitor the real-time temperature of the heat exchanger with unequal thickness structure. Before the first heating of the heat exchanger with unequal thickness structure, a first external insulation cotton is laid on the outer surface of the first heating element, or a first external insulation cotton is laid between the first heating element and the thick-walled cylinder; a second external insulation cotton is laid on the outer surface of the second heating element, or a second external insulation cotton is laid between the second heating element and the thin-walled cylinder. Before the second heating of the heat exchanger with unequal thickness structure, a third external insulation cotton is laid on the outer surface of the third heating element, or a third external insulation cotton is laid between the third heating element and the thick-walled cylinder; a fourth external insulation cotton is laid on the outer surface of the fourth heating element, or a fourth external insulation cotton is laid between the fourth heating element and the thin-walled cylinder. Before the first heating of the heat exchanger with unequal thickness structure, an optional first inner insulation cotton is provided on the inner wall of the heat exchanger with unequal thickness structure, and the first inner insulation cotton is provided opposite to the first outer insulation cotton and the second outer insulation cotton. Before the second heating of the heat exchanger with unequal thickness structure, a second inner insulation cotton and an optional third inner insulation cotton are provided on the inner wall of the heat exchanger with unequal thickness structure. The second inner insulation cotton is arranged opposite to the third outer insulation cotton, and the third inner insulation cotton is arranged opposite to the fourth outer insulation cotton. After the temperature of the heat exchanger with unequal thickness structure drops to the second set temperature, the first outer insulation cotton, the second outer insulation cotton, and the first inner insulation cotton are removed.

6. The method according to claim 5, characterized in that, The width of the first external insulation cotton is calculated according to the following formula: L5 = L1 + (400~600) mm; The width of the second outer insulation cotton is calculated according to the following formula: L6 = L2 + (300~500) mm; The width of the first inner insulation cotton is calculated according to the following formula: L7 = L5 + L6; Wherein, L5 is the width of the first outer insulation cotton, L6 is the width of the second outer insulation cotton, and L7 is the width of the first inner insulation cotton.

7. The method according to claim 5, characterized in that, The width of the third outer insulation cotton is calculated according to the following formula: L8 = L3 + (400~600) mm; The width of the fourth outer insulation cotton is calculated according to the following formula: L9 = L4 + (300~500) mm; The width of the second inner insulation cotton is calculated according to the following formula: L 10 =L8; The width of the third inner insulation cotton is calculated according to the following formula: L 11 =L9; Where L8 is the width of the third outer insulation material, L9 is the width of the fourth outer insulation material, and L 10 L is the width of the second inner insulation layer. 11 This refers to the width of the third inner insulation layer.

8. The method according to claim 1, characterized in that, The plane containing the circumferential weld is perpendicular to the axis of the heat exchanger with unequal thickness structure. The planes containing the first auxiliary positioning ring and the second auxiliary positioning ring are both perpendicular to the axis of the heat exchanger with unequal thickness structure. The first set temperature is 600~705℃, the second set temperature is no more than 50℃, and the third set temperature is 250~450℃.

9. The method according to claim 5, 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 insulation cotton is disposed between the first heating element and the thick-walled cylinder, the second outer insulation cotton is disposed between the second heating element and the thin-walled cylinder, the third outer insulation cotton is disposed between the third heating element and the thick-walled cylinder, and the fourth outer insulation cotton is disposed between the fourth heating element and the thin-walled cylinder. When none of the first heating element, the second heating element, the third heating element, and the fourth heating element are induction cables, the first outer insulation cotton is disposed on the outer surface of the first heating element, the second outer insulation cotton is disposed on the outer surface of the second heating element, the third outer insulation cotton is disposed on the outer surface of the third heating element, and the fourth outer insulation cotton is disposed on the outer surface of the fourth heating element.

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