Drying and storing process of heat exchanger for large-scale shielding motor

Abstract

The invention relates to a drying and storing process for a heat exchanger for a large-scale shielding motor, in particular to the field of heat exchanger drying, which comprises the following steps of: a, draining water after a water pressure test of the heat exchanger; b, vacuumizing and evaporating; c, drying the heat exchanger; d, performing a pressure rise test; e, backfilling nitrogen; and f, heat exchanger storage. Residual water existing in the inner cavity of the heat exchanger after a hydrostatic test is removed, water vapor is prevented from entering the inner cavity of the heat exchanger in the transportation or storage process, and the possibility that the inner cavity of the heat exchanger is corroded under the condition that the residual water or the water vapor exists in the inner cavity of the heat exchanger is avoided; therefore, possible corrosion is prevented from entering the shielding motor along with the cooling water, internal components of the shielding motor are prevented from being corroded, particularly, the risk of corrosion of the thrust disc is reduced, and the quality of the shielding motor is improved.

Description

Technical field:

[0001] The invention relates to a drying and storage process for a heat exchanger used for a large shielded motor, and in particular to the drying of a heat exchanger. Background technology:

[0002] As the country vigorously develops nuclear power generation, more and more nuclear power plants are using third-generation nuclear power technology, among which the main pumps for reactor cooling mostly use shielded motors. The heat exchanger is an important pressure boundary component for cooling the bearings and windings inside the shielded motor.

[0003] During the manufacturing process, there is residual water in the inner cavity of the heat exchanger after the water pressure test. In the presence of residual water, the inner cavity of the heat exchanger will easily rust, which will affect the performance of the shielded motor. Therefore, it is extremely important to dry and dry the heat exchanger to remove the residual water during the manufacturing process. At the same time, considering the transportation and long-term storage of the heat exchanger, it is also necessary to use a suitable method to store the heat exchanger to prevent water vapor from entering the inner cavity of the heat exchanger. In the past, for small, simple-structured, non-nuclear grade or non-shielded motor heat exchangers, after the water pressure test during the manufacturing process, the residual water in the inner cavity of the heat exchanger was only tilted and drained and dried naturally. Because the heat exchanger used in the shielded motor model of the third-generation nuclear technology is complex and cannot be disassembled, and in order to ensure its sealing, it cannot be directly heated to above 100°C for drying, so it is crucial to find a reliable drying method for drying and storage. Summary of the invention:

[0004] The purpose of the present invention is to provide a dry storage process for a heat exchanger for a large shielded motor, thereby avoiding the possibility of corrosion in the inner cavity of the heat exchanger when there is residual water or water vapor, thereby avoiding possible rust from entering the interior of the shielded motor with the cooling water, reducing the risk of corrosion of the thrust plate, and improving the quality of the shielded motor.

[0005] The technical solution of the present invention is: a dry storage process for a heat exchanger for a large shielded motor, comprising the following steps: a. Draining the heat exchanger (6) after the water pressure test: after the water pressure test is completed, the heat exchanger (6) is lifted at two points by a crane, and the heat exchanger (6) is tilted so that the primary side water outlet (7) is slightly downward so that the water in the inner cavity of the heat exchanger (6) can be drained, until no water flows out of the primary side water outlet (7) of the heat exchanger (6);

[0006] b. Vacuum evaporation: Place the heat exchanger (6) in a drying furnace (11), connect the primary water inlet (3) of the heat exchanger (6) to the first pressure gauge (9) with the second vacuum valve (2) and the dew point meter (10) with the first vacuum valve (1), connect the primary water outlet (7) of the heat exchanger (6) to the vacuum pump (24) with the cold trap (22), and similarly, connect the secondary water inlet (5) of the heat exchanger (6) to the third pressure gauge with the eighth vacuum valve (27). (26) and a dew point meter (25) with a ninth vacuum valve (28), the secondary water outlet (4) of the heat exchanger (6) is connected to the tenth vacuum valve (29), and then connected to a vacuum pump (24) with a cold trap (22), a vacuum gauge (19) with an eleventh vacuum valve (18) and a twelfth vacuum valve (20) is installed on the pipeline connected to the heat exchanger (6), and the inner cavity of the heat exchanger (6) is evacuated to a vacuum degree of less than 720 mTorr, and the evacuation is maintained for at least 6 hours;

[0007] c. Drying the heat exchanger (6): Start the heating furnace (11) switch, heat the heat exchanger (6) to 60°C at a heating rate not exceeding 28°C / h, and keep it warm and dry it, continue to evacuate the inner cavity of the heat exchanger (6) until the vacuum degree is less than 1 mTorr, and continue to keep it warm at 60°C and evacuate it for at least 12 hours;

[0008] d. Pressure rise test: After continuous insulation at 60°C and vacuuming for 12 hours, the sixth vacuum valve (21) and the seventh vacuum valve (23) are closed while continuous insulation at 60°C, and vacuuming is stopped. The pressure rise in the inner cavity of the heat exchanger (6) is monitored within 1 hour;

[0009] e. Nitrogen backfill: After the pressure rise test is qualified, the heating furnace (11) is closed, the fourth vacuum valve (12) and the fifth vacuum valve (14) are opened, the heat exchanger (6) and the second positive and negative pressure gauge (13), the filter (15) and the low-pressure regulating valve (16) are sequentially connected to the nitrogen source (17), the low-pressure regulating valve (16) is opened to introduce dry nitrogen with a controllable flow into the inner cavity of the heat exchanger (6), until the positive pressure of the inner cavity of the heat exchanger (6) reaches 0.02-0.05Mpa, the second vacuum valve (2) and the eighth vacuum valve (27) are opened, the low-pressure regulating valve (16) is closed, the fourth vacuum valve (12), the fifth vacuum valve (14) and the third vacuum valve (8) are closed, and the nitrogen source (17) is disconnected from the heat exchanger (6);

[0010] f. Storage of the heat exchanger (6): After the heat exchanger (6) is cooled to room temperature, for the primary side of the heat exchanger (6), the primary side refers to the connection with the high-temperature and high-pressure circulating water system inside the motor, the third vacuum valve (8) is kept in a closed state, and the first vacuum valve (1) and the second vacuum valve (2) are kept in an open state. Similarly, for the secondary side of the heat exchanger (6), the secondary side refers to the connection with the equipment cooling water system, which is used to cool the high-temperature and high-pressure circulating water on the primary side of the heat exchanger, the tenth vacuum valve (29) is kept in a closed state, the eighth vacuum valve (27) and the ninth vacuum valve (28) are kept in an open state, the connecting pipelines behind the third vacuum valve (8) and the tenth vacuum valve (29) are removed, and the heat exchanger (6) is stored in this state.

[0011] In step d, if the pressure increase in the inner cavity of the heat exchanger (6) after 1 hour is not greater than 320 mTorr, it is considered qualified. If the pressure increase is greater than 320 mTorr, the heat exchanger (6) needs to be dried again according to step c until the pressure increase within 1 hour is no greater than 320 mTorr.

[0012] In step e, after the nitrogen source (17) is disconnected from the heat exchanger (6), the first vacuum valve (1) of the dew point meter (10) is opened, and the ninth vacuum valve (28) of the dew point meter (25) is opened. The dew point temperature of the nitrogen should be less than -29°C. If the dew point temperature of the nitrogen is greater than -29°C, the nitrogen source (17) is replaced and the pressure increase test in step d is repeated until the dew point temperature of the nitrogen is less than -29°C.

[0013] In step f, 1. the pressure in the inner cavity of the primary side of the heat exchanger (6) is regularly checked by the first pressure gauge (9). The pressure displayed by the first pressure gauge (9) should not be lower than 0.02 MPa. If the pressure decreases by 0.02 MPa, step e needs to be repeated to fill the inner cavity of the primary side of the heat exchanger (6) with nitrogen to a pressure of 0.02-0.05 MPa; 2. the pressure in the inner cavity of the secondary side of the heat exchanger (6) is regularly checked by the third pressure gauge (26). The pressure displayed by the third pressure gauge (26) should not be lower than 0.02 MPa. If the pressure decreases by 0.02 MPa, step e needs to be repeated to fill the inner cavity of the secondary side of the heat exchanger (6) with nitrogen to a pressure of 0.02-0.05 MPa.

[0014] The technical effects of the present invention are:

[0015] 1. Use the hoisting method to tilt the heat exchanger to empty the residual water in the heat exchanger cavity after the water pressure test as much as possible, so as to reduce the vacuum time during the subsequent vacuum evaporation and drying of the heat exchanger; 2. The cooling water of the shielded motor enters from the primary water inlet of the heat exchanger and flows out from the primary water outlet of the heat exchanger, while the cooling water of the heat exchanger enters from the secondary water inlet of the heat exchanger and flows out from the secondary water outlet of the heat exchanger. When the heat exchanger is dried, the primary and secondary inner cavities of the heat exchanger can be dried at the same time; 3. At room temperature, vacuum the heat exchanger as a rough vacuum evaporation to prepare for the subsequent drying of the heat exchanger. When there is too much residual water in the heat exchanger cavity, it is difficult to directly vacuum the heat exchanger cavity to a vacuum degree of 1 mTorr or less in a short time; 4. At room temperature, due to vacuum During air evaporation, the temperature of the heat exchanger will drop due to the evaporation of residual water. When there is a lot of residual water in the heat exchanger cavity, the temperature drop of the heat exchanger will reduce the evaporation rate of the residual water in the heat exchanger cavity. The heat exchanger temperature is increased and the vacuum degree of the heat exchanger cavity is increased to dry and evacuate the heat exchanger, thereby increasing the drying efficiency of the heat exchanger; 5. By monitoring whether the pressure increase in the heat exchanger cavity is greater than 320 mTorr within 1 hour, if the pressure increase is greater than 320 mTorr, it is considered that there is still residual water in the heat exchanger cavity. A quantitative value is used to determine whether there is residual water in the heat exchanger cavity to avoid rust in the heat exchanger cavity due to the presence of residual water; 6. The dried heat exchanger cavity is filled with dry nitrogen until the positive pressure of the heat exchanger cavity reaches 0.02-0.05Mpa. Avoid water vapor entering the heat exchanger cavity during subsequent transportation and storage, which may cause corrosion due to water vapor liquefaction in the heat exchanger cavity; 7. After the heat exchanger is filled with nitrogen, the dew point temperature of the nitrogen in the heat exchanger cavity should be less than -29°C to ensure that the nitrogen filled into the heat exchanger cavity is dry. Regularly checking the pressure in the heat exchanger cavity and the dew point temperature of the nitrogen can ensure that no water vapor enters the heat exchanger cavity during storage. Description of the drawings:

[0016] Figure 1 It is the schematic diagram of the heat exchanger in the vacuum and drying state.

[0017] Figure 2 It is the schematic diagram of the heat exchanger in the nitrogen backfill state.

[0018] Figure 3 It is a schematic diagram of the heat exchanger in storage state. Specific implementation method:

[0019] like Figure 1A drying storage process for a large shielded motor heat exchanger is shown, a. Draining the heat exchanger 6 after the hydrostatic test: After the hydrostatic test is completed, the heat exchanger 6 is lifted by a crane at two points, and the heat exchanger 6 is tilted so that the primary side water outlet 7 is slightly downward so that the water in the inner cavity of the heat exchanger 6 can be drained, until no water flows out of the primary side water outlet 7 of the heat exchanger 6. The heat exchanger 6 is tilted by hoisting to drain as much residual water as possible from the inner cavity of the heat exchanger 6 after the hydrostatic test, so as to reduce the vacuum time during the subsequent vacuum evaporation and drying of the heat exchanger 6;

[0020] b. Vacuum evaporation: The cooling water of the shielded motor enters from the primary side water inlet 3 of the heat exchanger 6 and flows out from the primary side water outlet 7 of the heat exchanger 6, while the cooling water of the heat exchanger 6 enters from the secondary side water inlet 5 of the heat exchanger 6 and flows out from the secondary side water outlet 4 of the heat exchanger 6. The inner cavity of the heat exchanger 6 includes the primary side inner cavity of the heat exchanger 6 and the secondary side inner cavity of the heat exchanger 6. Figure 1 As shown, the heat exchanger 6 is placed in a drying furnace 11, or in a heat preservation cover where a heating fan is placed. The primary water inlet 3 of the heat exchanger 6 is connected to the first pressure gauge 9 with the second vacuum valve 2 and the dew point meter 10 with the first vacuum valve 1, and the primary water outlet 7 of the heat exchanger 6 is connected to the vacuum pump 24 with the cold trap 22. The cold trap 22 is used to evaporate the residual water by vacuum to form water vapor, which is liquefied in the cold trap and then the water vapor is removed. Similarly, the secondary water inlet 5 of the heat exchanger 6 is connected to the third pressure gauge 26 with the eighth vacuum valve 27 and the dew point meter 25 with the ninth vacuum valve 28, and the secondary water outlet 4 of the heat exchanger 6 is connected to the tenth vacuum valve 29, and then connected to the vacuum pump 24 with the cold trap 22. The primary inner cavity and the secondary inner cavity of the heat exchanger 6 can be dried at the same time. A vacuum gauge 19 with the eleventh vacuum valve 18 and the twelfth vacuum valve 20 is installed on the pipeline connected to the heat exchanger 6. Among them, the vacuum gauge 19 is used to measure the vacuum degree of the inner cavity of the heat exchanger 6, and the dew point meter 10 is used to measure the dew point of nitrogen. The inner cavity of the heat exchanger 6 is evacuated to a vacuum degree less than 720 mTorr, and the evacuation is maintained for at least 6 hours. At room temperature, the heat exchanger 6 is evacuated as a rough vacuum evaporation to prepare for the subsequent drying of the heat exchanger 6. When there is too much residual water in the inner cavity of the heat exchanger 6, it is difficult to directly evacuate the inner cavity of the heat exchanger 6 to a vacuum degree of 1 mTorr or less in a short time;

[0021] c. Drying heat exchanger (6): Figure 1As shown, start the switch of the heating furnace 11, heat the heat exchanger 6 to 60°C at a heating rate not exceeding 28°C / h, and keep it warm and dry it. Continue to evacuate the inner cavity of the heat exchanger 6 until the vacuum degree is less than 1 mTorr, and then keep it warm at 60°C and evacuate it for at least 12 hours. Under room temperature, the temperature of the heat exchanger 6 will drop due to the evaporation of residual water during vacuum evaporation. When there is a lot of residual water in the inner cavity of the heat exchanger 6, the temperature drop of the heat exchanger 6 will reduce the evaporation rate of the residual water in the inner cavity of the heat exchanger 6. By increasing the temperature of the heat exchanger 6 and then increasing the vacuum degree of the inner cavity of the heat exchanger 6 to dry the vacuum heat exchanger 6, the drying efficiency of the heat exchanger 6 is increased;

[0022] d. Pressure rise test: After continuously keeping the temperature at 60°C and evacuating for 12 hours, keep the temperature at 60°C, close the sixth vacuum valve 21 and the seventh vacuum valve 23, stop evacuating, and monitor the pressure increase in the inner cavity of the heat exchanger 6 within 1 hour. If the pressure increase in the inner cavity of the heat exchanger 6 after 1 hour is not greater than 320 mTorr, it is considered qualified. If the pressure increase is greater than 320 mTorr, the heat exchanger 6 needs to be dried again according to step c until the pressure increase is no greater than 320 mTorr within 1 hour. By monitoring whether the pressure increase in the inner cavity of the heat exchanger 6 is greater than 320 mTorr within 1 hour, if the pressure increase is greater than 320 mTorr, it is considered that there is still residual water in the inner cavity of the heat exchanger 6. A quantitative value is used to determine whether there is residual water in the inner cavity of the heat exchanger 6 to avoid rust in the inner cavity of the heat exchanger 6 due to the presence of residual water;

[0023] e. Nitrogen backfill: Figure 2 As shown, after the pressure rise test is passed, the heating furnace 11 is closed, the fourth vacuum valve 12 and the fifth vacuum valve 14 are opened, and the heat exchanger 6 is sequentially connected to the nitrogen source 17 with a positive and negative second pressure gauge 13, a filter 15 and a low-pressure regulating valve 16. The positive and negative second pressure gauge 13 is used to measure the pressure of the nitrogen in the inner cavity 6 of the heat exchanger during the backfilling of nitrogen, and the filter 15 is used to filter the oil and moisture that may exist in the nitrogen source 17 to ensure that the nitrogen entering the inner cavity of the heat exchanger 6 is dry. Open the low-pressure regulating valve 16 to introduce dry nitrogen with a controllable flow into the inner cavity of the heat exchanger 6 until the positive pressure of the inner cavity of the heat exchanger 6 reaches 0.02-0.05Mpa. Avoid water vapor entering the inner cavity of the heat exchanger 6 during subsequent transportation and storage, which may cause rust in the inner cavity of the heat exchanger 6 due to the liquefaction of water vapor. As shown Figure 3As shown, open the second vacuum valve 2 and the eighth vacuum valve 27, close the low-pressure regulating valve 16, close the fourth vacuum valve 12, the fifth vacuum valve 14 and the third vacuum valve 8, and disconnect the nitrogen source 17 from the heat exchanger 6. After disconnecting the nitrogen source 17 from the heat exchanger 6, open the first vacuum valve 1 of the dew point meter 10, open the ninth vacuum valve 28 of the dew point meter 25, and measure the dew point temperature of the nitrogen, which should be less than -29°C. If the dew point temperature of the nitrogen is greater than -29°C, replace the nitrogen source 17, and repeat the pressure increase test in step d until the measured dew point temperature of the nitrogen is less than -29°C. After the heat exchanger 6 is filled with nitrogen, measure the dew point temperature of the nitrogen in the inner cavity of the heat exchanger 6, which should be less than -29°C, to ensure that the nitrogen filled into the inner cavity of the heat exchanger 6 is dry;

[0024] f. Heat exchanger 6 storage: such as Figure 3 As shown, after the heat exchanger 6 is cooled to room temperature, for the primary side of the heat exchanger 6, the primary side refers to the connection with the high-temperature and high-pressure circulating water system inside the motor, keep the third vacuum valve 8 in a closed state, keep the first vacuum valve 1 and the second vacuum valve 2 in an open state, and regularly check the pressure in the inner cavity of the primary side of the heat exchanger 6 through the first pressure gauge 9. The pressure displayed by the first pressure gauge 9 should not be lower than 0.02Mpa. If the pressure decreases by 0.02Mpa, repeat step e to fill the primary side of the heat exchanger 6 with nitrogen to a pressure of 0.02-0.05Mpa, and check the dew point temperature of the nitrogen through the dew point meter 10 to be less than -29°C. Similarly, for the secondary side of the heat exchanger 6, the secondary side refers to the high-temperature and high-pressure circulating water connected to the equipment cooling water system and used to cool the primary side of the heat exchanger. Keep the tenth vacuum valve 29 in a closed state, keep the eighth vacuum valve 27 and the ninth vacuum valve 28 in an open state, and regularly check the pressure in the inner cavity of the secondary side of the heat exchanger 6 through the third pressure gauge 26. The pressure displayed by the third pressure gauge 26 should not be lower than 0.02Mpa. If the pressure decreases by 0.02Mpa, repeat step e to fill the secondary side of the heat exchanger 6 with nitrogen to a pressure of 0.02-0.05Mpa, and check the dew point temperature of nitrogen through the dew point meter 25 to be less than -29°C. Remove the connecting pipeline behind the third vacuum valve 8 and the tenth vacuum valve 29, and store the heat exchanger 6 in this state. Regularly checking the pressure in the inner cavity of the heat exchanger 6 and the dew point temperature of nitrogen can ensure that no water vapor enters the inner cavity of the heat exchanger 6 during storage.

Claims

1. A large shielded motor heat exchanger dry storage process, comprising the following steps: a. Draining the heat exchanger (6) after the hydraulic pressure test: After the hydraulic pressure test is completed, the heat exchanger (6) is lifted by a crane at two points, and the heat exchanger (6) is tilted so that the primary side water outlet (7) is slightly downward to allow the water in the inner cavity of the heat exchanger (6) to be drained, until no water flows out of the primary side water outlet (7) of the heat exchanger (6); b. Vacuum evaporation: Place the heat exchanger (6) in a drying furnace (11), connect the primary water inlet (3) of the heat exchanger (6) to the first pressure gauge (9) with the second vacuum valve (2) and the dew point meter (10) with the first vacuum valve (1), connect the primary water outlet (7) of the heat exchanger (6) to the vacuum pump (24) with the cold trap (22), and similarly, connect the secondary water inlet (5) of the heat exchanger (6) to the third pressure gauge with the eighth vacuum valve (27). (26) and a dew point meter (25) with a ninth vacuum valve (28), the secondary water outlet (4) of the heat exchanger (6) is connected to the tenth vacuum valve (29), and then connected to a vacuum pump (24) with a cold trap (22), a vacuum gauge (19) with an eleventh vacuum valve (18) and a twelfth vacuum valve (20) is installed on the pipeline connected to the heat exchanger (6), and the inner cavity of the heat exchanger (6) is evacuated to a vacuum degree of less than 720 mTorr, and the evacuation is maintained for at least 6 hours; c. Drying the heat exchanger (6): Start the heating furnace (11) switch, heat the heat exchanger (6) to 60°C at a heating rate not exceeding 28°C / h, and keep it warm and dry it, continue to evacuate the inner cavity of the heat exchanger (6) until the vacuum degree is less than 1 mTorr, and continue to keep it warm at 60°C and evacuate it for at least 12 hours; d. Pressure rise test: After continuous insulation at 60°C and vacuuming for 12 hours, the sixth vacuum valve (21) and the seventh vacuum valve (23) are closed while continuous insulation at 60°C, and vacuuming is stopped. The pressure rise in the inner cavity of the heat exchanger (6) is monitored within 1 hour; e. Nitrogen backfill: After the pressure rise test is qualified, the heating furnace (11) is closed, the fourth vacuum valve (12) and the fifth vacuum valve (14) are opened, the heat exchanger (6) and the second positive and negative pressure gauge (13), the filter (15) and the low-pressure regulating valve (16) are sequentially connected to the nitrogen source (17), the low-pressure regulating valve (16) is opened to introduce dry nitrogen with a controllable flow into the inner cavity of the heat exchanger (6), until the positive pressure of the inner cavity of the heat exchanger (6) reaches 0.02-0.05Mpa, the second vacuum valve (2) and the eighth vacuum valve (27) are opened, the low-pressure regulating valve (16) is closed, the fourth vacuum valve (12), the fifth vacuum valve (14) and the third vacuum valve (8) are closed, and the nitrogen source (17) is disconnected from the heat exchanger (6); f. Storage of the heat exchanger (6): After the heat exchanger (6) is cooled to room temperature, for the primary side of the heat exchanger (6), the primary side refers to the connection with the high-temperature and high-pressure circulating water system inside the motor, the third vacuum valve (8) is kept in a closed state, and the first vacuum valve (1) and the second vacuum valve (2) are kept in an open state. Similarly, for the secondary side of the heat exchanger (6), the secondary side refers to the connection with the equipment cooling water system, which is used to cool the high-temperature and high-pressure circulating water on the primary side of the heat exchanger, the tenth vacuum valve (29) is kept in a closed state, the eighth vacuum valve (27) and the ninth vacuum valve (28) are kept in an open state, the connecting pipelines behind the third vacuum valve (8) and the tenth vacuum valve (29) are removed, and the heat exchanger (6) is stored in this state.

2. The dry storage process of a heat exchanger for a large canned motor according to claim 1 is characterized by: In step d, if the pressure increase in the inner cavity of the heat exchanger (6) after 1 hour is not greater than 320 mTorr, it is considered qualified. If the pressure increase is greater than 320 mTorr, the heat exchanger (6) needs to be dried again according to step c until the pressure increase within 1 hour is no greater than 320 mTorr.

3. The dry storage process of a heat exchanger for a large canned motor according to claim 1 is characterized by: In step e, after the nitrogen source (17) is disconnected from the heat exchanger (6), the first vacuum valve (1) of the dew point meter (10) is opened, and the ninth vacuum valve (28) of the dew point meter (25) is opened. The dew point temperature of the nitrogen should be less than -29°C. If the dew point temperature of the nitrogen is greater than -29°C, the nitrogen source (17) is replaced and the pressure increase test in step d is repeated until the dew point temperature of the nitrogen is less than -29°C.

4. The dry storage process of a heat exchanger for a large canned motor according to claim 1 is characterized by: In step f, 1. the pressure in the inner cavity of the primary side of the heat exchanger (6) is regularly checked by the first pressure gauge (9). The pressure displayed by the first pressure gauge (9) should not be lower than 0.02 MPa. If the pressure decreases by 0.02 MPa, step e needs to be repeated to fill the inner cavity of the primary side of the heat exchanger (6) with nitrogen to a pressure of 0.02-0.05 MPa; 2. the pressure in the inner cavity of the secondary side of the heat exchanger (6) is regularly checked by the third pressure gauge (26). The pressure displayed by the third pressure gauge (26) should not be lower than 0.02 MPa. If the pressure decreases by 0.02 MPa, step e needs to be repeated to fill the inner cavity of the secondary side of the heat exchanger (6) with nitrogen to a pressure of 0.02-0.05 MPa.

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