Metal bellows stress corrosion testing device and testing method

Abstract

The application provides a metal bellows stress corrosion test device and a test method, the test device comprises a heating container, a constant temperature oil bath, a liquid separation funnel, a thermometer and a bellows sample, heat conducting oil is arranged in the constant temperature oil bath, the heating container is arranged in the constant temperature oil bath, magnesium chloride solution is arranged in the heating container, the liquid separation funnel is used for dropping distilled water into the heating container, the thermometer is used for detecting the temperature of the magnesium chloride solution, the bellows sample is arranged in the heating container, at least part of a bellows section of the bellows sample is immersed into the magnesium chloride solution, and the metal bellows stress corrosion test is carried out on the bellows sample; the device is simple in structure, on one hand, can facilitate the development of the stress corrosion test of the bellows sample, on the other hand, can avoid the deviation caused by the stress state equivalence through a standard sample, and is favorable for guaranteeing the accuracy of the test result.

Description

Technical Field

[0001] This invention relates to the field of stress corrosion testing, and in particular to a stress corrosion testing apparatus and method for metal bellows. Background Technology

[0002] Although austenitic stainless steel has good corrosion resistance, it still has the risk of stress corrosion cracking under certain tensile stress and specific corrosive media conditions. The magnitude of stress is a key factor affecting stress corrosion.

[0003] Currently, research on stress corrosion of austenitic stainless steel is mainly based on YB / T5362 "Stress Corrosion Test Method for Stainless Steel in Boiling Magnesium Chloride Solution," with specimen shapes including rods, plates, and U-shaped specimens. However, for corrugated metal pipes, the stress state of the specimens in this standard differs significantly from that of the corrugated metal pipe itself. Corrugated metal pipes are thin-walled tube blanks that have achieved their geometric dimensions through a cold forming process. During cold forming, the tube blank undergoes plastic deformation, resulting in work hardening and significant residual stress. Furthermore, due to its corrugated cross-section, regardless of whether it is subjected to pressure load or displacement load, the corrugations experience both compressive and tensile stresses, as well as circumferential stress. The specimens specified in the standard cannot reflect the true magnitude and state of stress. Therefore, obtaining the stress corrosion performance of corrugated metal pipes under different stress states often results in significant deviations when using stress corrosion tests on conventional standard specimens. Summary of the Invention

[0004] In view of this, the present invention aims to provide a stress corrosion testing device and method for metal bellows, so as to solve the problem that it is often difficult to accurately measure the stress corrosion performance of metal bellows under different stress states in the prior art.

[0005] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0006] A stress corrosion testing apparatus for metal bellows includes a heating container, a constant temperature oil bath, a separating funnel, a thermometer, and a bellows sample. The constant temperature oil bath contains heat-conducting oil. The heating container is placed inside the constant temperature oil bath and contains a magnesium chloride solution. The separating funnel is used to add distilled water dropwise into the heating container. The thermometer is used to detect the temperature of the magnesium chloride solution. The bellows sample is placed inside the heating container, and at least a portion of the bellows section of the sample is immersed in the magnesium chloride solution for conducting a stress corrosion test on the bellows sample.

[0007] Furthermore, the corrugated pipe sample includes an inner core cylinder, an upper end pipe, a corrugated pipe, and a lower end pipe. One end of the corrugated pipe is connected to the upper end pipe, and the other end is connected to the lower end pipe. The inner core cylinder is disposed inside the corrugated pipe. One end of the inner core cylinder is connected to the upper end pipe, and the other end is connected to the lower end pipe. A sealed cavity is formed between the inner core cylinder and the corrugated pipe.

[0008] Furthermore, the corrugated pipe sample includes a monitoring tube, one end of which is connected to the cavity, and the other end is equipped with a pressure gauge.

[0009] Furthermore, a condenser cover is provided at the opening of the heating container, the thermometer penetrates the condenser cover, and the sensing end of the thermometer extends into the heating container; the dropper of the separating funnel penetrates the condenser cover and extends into the heating container.

[0010] A method for stress corrosion testing of metal bellows, using the aforementioned metal bellows stress corrosion testing device, the method comprising: S1, preparing a bellows sample under the designed stress state required for the test; S2, adding heat-conducting oil to a constant-temperature oil bath, placing a heating container in the heat-conducting oil, and adding magnesium chloride solution to the heating container; S3, installing a condenser cap, thermometer, and separatory funnel at the open end of the heating container; S4, turning on the constant-temperature oil bath to heat the magnesium chloride solution in the heating container; S5, monitoring the temperature T of the magnesium chloride solution in real time; S6, determining whether T has reached the preset temperature; if yes, using the preset temperature as the holding temperature, adjusting the constant-temperature oil bath to the holding state, and then proceeding to step S7; if no, returning to step S5; S7, placing the bellows sample from step S1 into the heating container, adjusting the dripping speed of distilled water into the heating container using the separatory funnel, and ensuring that the temperature of the magnesium chloride solution remains stable within the target temperature range;

[0011] S8. Detect and determine whether the corrugated pipe sample has cracks; if so, record the test duration at the current moment; if not, return to step S7; in step S7, start timing the test duration when the corrugated pipe sample is first placed in the heating container.

[0012] Furthermore, in step S1, the manufacturing process of the corrugated pipe sample is as follows: the corrugated pipe is hydroformed, one end of the corrugated pipe is welded to the upper pipe, and the other end is welded to the lower pipe to form a pre-assembled part. An inner core cylinder is assembled inside the pre-assembled part, one end of the inner core cylinder is welded to the lower pipe, and a tensile or compressive force is applied to the upper pipe so that the length of the pre-assembled part reaches the design size. Then, the other end of the inner core cylinder is welded to the upper pipe to obtain the corrugated pipe sample.

[0013] Furthermore, in step S1, the manufacturing process of the corrugated pipe sample is as follows: the corrugated pipe is hydroformed, one end of the corrugated pipe is welded to the upper pipe, and the other end is welded to the lower pipe to form a pre-assembled part. An inner core cylinder is assembled inside the pre-assembled part, one end of the inner core cylinder is welded to the lower pipe, and a tensile or compressive force is applied to the upper pipe to make the length of the pre-assembled part reach the design size. Then, the other end of the inner core cylinder is welded to the upper pipe. A monitoring tube is welded to the inner wall of the inner core cylinder and connected to the cavity to obtain a test piece. Then, an airtightness test is conducted on the test piece through the monitoring tube. After the airtightness test is qualified, the cavity is pressurized to the required test pressure through the monitoring tube. Then, a pressure gauge is installed at the end of the monitoring tube to obtain the corrugated pipe sample.

[0014] Further, step S8 includes: S81, determining whether bubbles emerge from the bellows sample in the magnesium chloride solution, or whether the pressure gauge reading begins to decrease; if yes, proceed to step S82; if no, return to step S7; S82, record the test duration and pressure gauge reading at the current moment, then remove the bellows sample for cleaning, perform colorimetric detection on the surface of the bellows, and record the location and size of the crack.

[0015] In step S1, the design stress state of the bellows sample is displacement stress, or the design stress state of the bellows sample includes displacement stress and pressure stress.

[0016] Compared with existing technologies, the stress corrosion testing device and method for metal bellows described in this invention have the following advantages:

[0017] The present invention discloses a stress corrosion testing device and method for metal bellows, which is used for stress corrosion testing of metal bellows. The device has a simple structure, which facilitates stress corrosion testing of bellows samples and eliminates the need for excessive restrictions on sample size. It breaks through the specific limitations on sample size of traditional stress corrosion testing devices, solves the problem that traditional standard samples cannot truly reflect the stress state of bellows, eliminates the need for equivalent testing using traditional standard samples, and avoids the deviation caused by stress state equivalence through standard samples, thus helping to ensure the accuracy of test results.

[0018] Meanwhile, this application can be used to study the stress corrosion performance comparison of bellows with different design fatigue lives, reflect the real stress state of bellows under pressure and displacement, conveniently characterize bellows under different displacement and pressure states, obtain the stress corrosion resistance performance of bellows under different design conditions, effectively and accurately carry out stress corrosion tests on metal bellows samples, and provide data reference for the corrosion safety evaluation of bellows. Attached Figure Description

[0019] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0020] Figure 1 This is a schematic diagram of the structure of a metal bellows stress corrosion testing device according to an embodiment of the present invention;

[0021] Figure 2 This is a schematic diagram of the structure of a corrugated pipe sample in a stress corrosion testing device for metal corrugated pipes according to an embodiment of the present invention.

[0022] Explanation of reference numerals in the attached figures:

[0023] 1. Iron stand; 2. Heat transfer oil; 3. Separating funnel; 4. Corrugated pipe sample; 41. Monitoring tube; 42. Inner core cylinder; 43. Upper end tube; 44. Corrugated pipe; 45. Lower end tube; 5. Thermometer; 6. Magnesium chloride solution; 7. Condensation cover; 8. Heating container; 9. Constant temperature oil bath. Detailed Implementation

[0024] The inventive concepts of this disclosure will be described below using terminology commonly used by those skilled in the art to communicate the essence of their work to others skilled in the art. However, these inventive concepts may be embodied in many different forms and should not be construed as limited to the embodiments described herein.

[0025] It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of this invention can be combined with each other. All concentration percentages in this application refer to mass concentration percentages, and all solutions refer to aqueous solutions.

[0026] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0027] Example 1

[0028] To address the difficulty in accurately assessing the stress corrosion performance of metal bellows under different stress states in existing technologies, this embodiment proposes a stress corrosion testing device and method for metal bellows, as shown in the attached figure. Figure 1-2As shown, the test apparatus includes a heating container 8, a constant temperature oil bath 9, a separating funnel 3, a thermometer 5, and a corrugated pipe sample 4. The constant temperature oil bath 9 contains heat-conducting oil 2. The heating container 8 is placed in the constant temperature oil bath 9, and a portion of the structure of the heating container 8 is immersed in the heat-conducting oil 2. A 42% magnesium chloride solution 6 is placed in the heating container 8. The separating funnel 3 is used to add distilled water dropwise into the heating container 8. The thermometer 5 is used to detect the temperature of the magnesium chloride solution 6. The corrugated pipe sample 4 is placed in the heating container 8, and at least a portion of the corrugated pipe section of the corrugated pipe sample 4 is immersed in the magnesium chloride solution 6 for conducting a metal corrugated pipe stress corrosion test on the corrugated pipe sample 4.

[0029] The test apparatus of this application is designed for stress corrosion testing of metal bellows. The apparatus has a simple structure, which facilitates stress corrosion testing of bellows samples and eliminates the need for excessive restrictions on sample size. It breaks through the specific limitations on sample size imposed by traditional stress corrosion testing apparatuses, solves the problem that traditional standard samples cannot truly reflect the stress state of bellows, eliminates the need for equivalent testing using traditional standard samples, and avoids the deviations caused by stress state equivalence using standard samples, thus ensuring the accuracy of the test results.

[0030] The corrugated pipe sample 4 includes an inner core cylinder 42, an upper end pipe 43, a corrugated pipe 44, and a lower end pipe 45. One end of the corrugated pipe 44 is connected to the upper end pipe 43, and the other end is connected to the lower end pipe 45. The inner core cylinder 42 is disposed inside the corrugated pipe 44, with one end connected to the upper end pipe 43 and the other end connected to the lower end pipe 45. Accordingly, due to the sealed connection at both ends, a closed cavity is formed between the inner core cylinder 42 and the corrugated pipe 44. Preferably, the connection between the corrugated pipe 44 and the upper end pipe 43 and the lower end pipe 45 can be welded, and the inner core cylinder 42 can also be connected in the same way. Thus, during the test, if bubbles are observed emerging from the corrugated pipe sample 4 in the magnesium chloride solution 6, or if cracks are detected in the corrugated pipe sample 4, the corrosion life of the corrugated pipe sample 4 under the corresponding test medium conditions can be determined.

[0031] Among them, all components of the corrugated pipe sample 4 (such as inner core cylinder 42, upper end pipe 43, corrugated pipe 44, lower end pipe 4, etc.) are austenitic stainless steel 316L, so that the material of each structural component is consistent with the material of the corrugated pipe, avoiding the influence of different structural component materials on the test results.

[0032] The heating container 8 is preferably an open container to facilitate the insertion and removal of the corrugated tube sample 4. A condenser cover 7 is provided at the open end of the heating container 8. The thermometer 5 penetrates the condenser cover 7, and the sensing end of the thermometer 5 extends into the heating container 8, preferably extending below the surface of the magnesium chloride solution 6, to accurately detect the temperature of the magnesium chloride solution 6. The dropper of the separating funnel 3 penetrates the condenser cover 7 and extends into the heating container 8, preferably extending above the surface of the magnesium chloride solution 6. The separating funnel 3 can be fixed by using an iron stand 1. The condenser cover 7 prevents excessive evaporation of the magnesium chloride solution 6, which could cause an excessive increase in concentration, while the separating funnel 3 allows for the appropriate addition of distilled water to the heating container 8.

[0033] Accordingly, this application proposes a stress corrosion testing method for metal bellows, wherein the testing method employs the aforementioned stress corrosion testing apparatus for metal bellows, and the testing method includes:

[0034] S1. Fabricate a bellows sample 4 under the design stress state required for the test;

[0035] Among them, corrugated pipe samples 4 with different design stress states can be made according to the test requirements. That is, multiple corrugated pipe samples 4 can be made, and stress corrosion test can be carried out on any one of the corrugated pipe samples 4 according to the test method of this application.

[0036] The manufacturing process of the corrugated pipe sample 4 is as follows: the corrugated pipe 44 is hydroformed, one end of the corrugated pipe 44 is welded to the upper pipe 43, and the other end is welded to the lower pipe 45 to form a pre-assembled part. At this time, the pre-assembled part is at its original length. The inner core cylinder 42 is assembled inside the pre-assembled part, one end of the inner core cylinder 42 is welded to the lower pipe 45, and a tensile or compressive force is applied to the upper pipe 43 so that the length of the pre-assembled part reaches the design size. Then, the other end of the inner core cylinder 42 is welded to the upper pipe 43 to obtain the corrugated pipe sample 4. Defect detection is performed on each weld in the corrugated pipe sample 4. After passing the inspection, the subsequent stress corrosion test can be carried out.

[0037] In this structure, the cavity between the inner core 42 and the bellows 44 of the bellows sample 4 has no pressure difference with the external environment. Furthermore, for a given bellows sample 4, by adjusting the length of the pre-assembled component to the design dimensions, the design stress state required for the experiment can be obtained. In this case, the design stress state of the bellows sample 4 is only displacement stress; correspondingly, the cavity is not pressurized, and the bellows is simply placed in a compressed or tensile state during fabrication.

[0038] For the design of the tensile or compressive displacement of the corrugated pipe sample 4, taking the heating industry as an example, since the corrugated pipes used in heating pipelines are generally large in diameter, it is necessary to transfer the stress state of the large-diameter corrugated pipe to the small-diameter corrugated pipe in order to facilitate the stress corrosion test. For the small-diameter corrugated pipe, the same design fatigue life number Nc as the large-diameter corrugated pipe can reflect the same comprehensive stress state.

[0039] The most critical design parameter for bellows design is the design fatigue life Nc. Nc is related to the overall stress state of the bellows. For austenitic stainless steel, the overall stress σ... t The relationship between the fatigue life Nc and the design fatigue life is as follows:

[0040] Nc=(12827 / σ t -372) 3.4 / 10

[0041] When designing the corrugated pipe, Nc=500 and Nc=1000 cycles, which are commonly used in the heating industry, are selected for design. Then, according to GB / T12777-2019, the displacement under the two design fatigue life cycles is calculated, which can be used as the tensile or compressive displacement of the corrugated pipe sample 4.

[0042] S2. Add an appropriate amount of heat transfer oil 2 to the constant temperature oil bath 9, place the heating container 8 in the heat transfer oil 2, and add an appropriate amount of magnesium chloride solution 6 with a concentration of 42% to the heating container 8.

[0043] It should be noted that the heating container 8 can be understood as having its opening facing upwards and floating in the heat transfer oil 2, rather than being completely submerged in the heat transfer oil 2. Correspondingly, the magnesium chloride solution 6 can be a pre-prepared solution, or magnesium chloride and distilled water can be added separately to the heating container 8, as long as the concentration of the magnesium chloride solution 6 is approximately 42%.

[0044] S3. Install a condenser cover 7, a thermometer 5, and a separatory funnel 3 at the open end of the heating container 8.

[0045] S4. Turn on the constant temperature oil bath 9 to heat the magnesium chloride solution 6 in the heating container 8;

[0046] S5. Real-time monitoring of the temperature T of magnesium chloride solution 6;

[0047] Among these measures, the temperature of magnesium chloride solution 6 can be monitored when the solution is nearing boiling.

[0048] S6. Determine whether T has reached the preset temperature; if yes, use the preset temperature as the heat preservation temperature, adjust the constant temperature oil bath 9 to the heat preservation working state, and then proceed to step S7; if no, return to step S5.

[0049] The preset temperature is 142℃~143℃, which ensures that the magnesium chloride solution 6 is in a state of slight boiling.

[0050] S7. Place the corrugated pipe sample 4 from step S1 into the heating container 8. Adjust the dripping speed of the distilled water from the separatory funnel 3 into the heating container 8 according to the water replenishment needs of the experiment, and ensure that the temperature of the magnesium chloride solution 6 is stable within the target temperature range.

[0051] The target temperature range is 143±1℃. Accordingly, the procedures for moving and reassembling the condenser cap 7, thermometer 5, and separatory funnel 3 during the placement of the corrugated pipe sample 4 into the heating container 8 are not detailed here. Furthermore, the test duration is started when the corrugated pipe sample 4 is first placed into the heating container 8.

[0052] S8. Every preset time interval, the corrugated pipe sample 4 is taken out from the heating container 8, and the corrugated pipe sample 4 is cleaned and colored in sequence to determine whether the corrugated pipe sample 4 has cracks; if so, the test duration at the current moment is recorded; if not, return to step S7.

[0053] The preset duration can be limited according to the requirements of each laboratory, such as 12 hours, 24 hours, etc.

[0054] The stress corrosion testing method for metal bellows disclosed in this application can be used to compare the stress corrosion performance of bellows with different design fatigue lives. It reflects the true stress state of the bellows under pressure and displacement conditions, avoiding the bias caused by using standard specimens for stress state equivalence testing. This method obtains the stress corrosion resistance of bellows under different design conditions, which not only improves the accuracy of the test but also provides data reference for evaluating the corrosion safety of bellows. Furthermore, this application overcomes the specific limitations of traditional stress corrosion testing equipment on specimen size, solving the problem that traditional standard specimens cannot accurately reflect the stress state of the bellows. It eliminates the need for equivalent tests using traditional standard specimens, conveniently characterizing bellows under different displacement and pressure conditions, and effectively and accurately conducting stress corrosion tests on metal bellows specimens.

[0055] Example 2

[0056] This embodiment is basically the same as Embodiment 1. This embodiment focuses on introducing the differences.

[0057] To further improve the accuracy of the test, the corrugated pipe sample 4 includes a monitoring tube 41. One end of the monitoring tube 41 is connected to the cavity, and the other end is equipped with a pressure gauge. This allows the cavity to be pressurized to the required test pressure during the processing of the corrugated pipe sample 4. During the test, the pressure gauge can accurately reflect the pressure within the cavity in real time. Once the pressure gauge reading drops, the corrosion life of the corrugated pipe sample 4 under the corresponding test medium conditions can be determined more precisely. Simultaneously, cracks and corrosion of the corrugated pipe sample 4 can be observed in a timely manner, avoiding excessive corrosion and greatly improving the accuracy, timeliness, and effectiveness of the test results. Regarding the placement of the monitoring tube 41, it is not recommended to damage the structure of the corrugated pipe 44. It can be placed in the inner core cylinder 42, the upper end pipe 43, or the lower end pipe 45, as long as the communication between the monitoring tube 41 and the cavity is maintained. The structure shown in the attached figure is preferred, where the monitoring tube 41 is connected to the inner wall of the inner core cylinder 42 and communicates with the cavity.

[0058] Accordingly, regarding the test method, based on the setting of the monitoring tube 41, the manufacturing process of the corrugated pipe sample 4 in this embodiment differs somewhat from that in embodiment 1 in step S1.

[0059] Specifically, the manufacturing process of the corrugated pipe sample 4 is as follows: The corrugated pipe 44 is hydroformed; one end of the corrugated pipe 44 is welded to the upper pipe 43, and the other end is welded to the lower pipe 45 to form a pre-assembled component. At this point, the pre-assembled component is at its original length. An inner core cylinder 42 is assembled inside the pre-assembled component, and one end of the inner core cylinder 42 is welded to the lower pipe 45. Tensile or compressive forces are applied to the upper pipe 43 to bring the length of the pre-assembled component to the designed size. Then, the other end of the inner core cylinder 42 is welded to the upper pipe 43. A monitoring tube 41 is welded to the inner wall of the inner core cylinder 42 and connected to the cavity to obtain a test piece. An airtightness test is then conducted on the test piece through the monitoring tube 41. After the airtightness test is passed, the cavity is pressurized to the required test pressure through the monitoring tube 41. A pressure gauge is then installed at the end of the monitoring tube 41 to obtain the corrugated pipe sample 4. Subsequent stress corrosion tests can then be performed.

[0060] At this point, the design stress state of the bellows sample 4 includes displacement stress and pressure stress. Accordingly, during manufacturing, the cavity needs to be filled to the pressure required for the test, and the bellows needs to be in a compressed or tensile state.

[0061] For steps S2-S7, the corresponding content of Example 1 is maintained.

[0062] In step S8, this embodiment proposes a test procedure different from that in embodiment 1, specifically as follows:

[0063] Step S8 includes:

[0064] S81. Determine whether bubbles emerge from the bellows sample 4 in the magnesium chloride solution 6, or whether the pressure gauge reading begins to decrease; if yes, proceed to step S82; if no, return to step S7.

[0065] S82. Record the test duration and pressure reading at the current moment. Then, take out the bellows sample 4 for cleaning, perform colorimetric testing on the surface of the bellows 44, and record the location and size of the crack.

[0066] Therefore, this embodiment, by setting up a monitoring tube 41 and further optimizing the test method, can, on the one hand, reflect the pressure in the cavity in real time and accurately. Once the pressure gauge reading drops, the corrosion life of the bellows sample 4 under the corresponding test medium conditions can be determined more precisely. At the same time, the cracks and corrosion of the bellows sample 4 can be observed in a timely manner, avoiding excessive corrosion and greatly improving the accuracy, timeliness and effectiveness of the test results. On the other hand, it also avoids the work of repeatedly taking out, cleaning, testing and putting back the sample during the test, reducing the workload of the test personnel and improving the test efficiency. Moreover, it also ensures that the bellows sample 4 can be continuously in a stable corrosive environment during the test, maintaining the continuity of the corrosion test and eliminating interference from external operations, which is conducive to further improving the accuracy of the test results.

[0067] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A stress corrosion testing apparatus for metal bellows, characterized in that, The test apparatus includes a heating container (8), a constant temperature oil bath (9), a separating funnel (3), a thermometer (5), and a corrugated pipe sample (4). The constant temperature oil bath (9) is filled with heat-conducting oil (2). The heating container (8) is placed in the constant temperature oil bath (9). The heating container (8) is filled with magnesium chloride solution (6). The separating funnel (3) is used to add distilled water to the heating container (8). The thermometer (5) is used to detect the temperature of the magnesium chloride solution (6). The corrugated pipe sample (4) is placed in the heating container (8). At least a portion of the corrugated pipe section of the corrugated pipe sample (4) is immersed in the magnesium chloride solution (6) for conducting a metal corrugated pipe stress corrosion test on the corrugated pipe sample (4). The corrugated pipe sample (4) includes an inner core cylinder (42), an upper end pipe (43), a corrugated pipe (44), and a lower end pipe (45). One end of the corrugated pipe (44) is connected to the upper end pipe (43), and the other end is connected to the lower end pipe (45). The inner core cylinder (42) is disposed inside the corrugated pipe (44). One end of the inner core cylinder (42) is connected to the upper end pipe (43), and the other end is connected to the lower end pipe (45). A sealed cavity is formed between the inner core cylinder (42) and the corrugated pipe (44). The corrugated pipe sample (4) includes a monitoring tube (41). One end of the monitoring tube (41) is connected to the inner wall of the inner core cylinder (42) and communicates with the cavity. A pressure gauge is installed at the other end. The cavity is filled to the required test pressure, while the corrugated pipe (44) is in a compressed or stretched state.

2. The stress corrosion testing apparatus for metal bellows according to claim 1, characterized in that, A condenser cover (7) is provided at the opening of the heating container (8), and the thermometer (5) passes through the condenser cover (7). The detection end of the thermometer (5) extends into the heating container (8). The dropper of the separating funnel (3) passes through the condenser cover (7) and extends into the heating container (8).

3. A method for stress corrosion testing of metal bellows, characterized in that, The test method employs the metal bellows stress corrosion testing apparatus according to any one of claims 1-2, and the test method includes: S1. Fabricate a bellows sample under the design stress state required for the test (4); S2. Add heat transfer oil (2) to the constant temperature oil bath (9), place the heating container (8) in the heat transfer oil (2), and add magnesium chloride solution (6) to the heating container (8); S3. Install a condenser cap (7), a thermometer (5), and a separatory funnel (3) at the opening of the heating container (8); S4. Turn on the constant temperature oil bath (9) to heat the magnesium chloride solution (6) in the heating container (8); S5. Real-time monitoring of the temperature T of the magnesium chloride solution (6); S6. Determine whether T has reached the preset temperature; if yes, use the preset temperature as the heat preservation temperature, adjust the constant temperature oil bath (9) to the heat preservation working state, and then proceed to step S7; if no, return to step S5. S7. Place the corrugated pipe sample (4) from step S1 into the heating container (8), adjust the dripping speed of the separatory funnel (3) into the heating container (8), and ensure that the temperature of the magnesium chloride solution (6) is stable within the target temperature range. S8. Detect and determine whether the corrugated pipe sample (4) has cracks; if yes, record the test duration at the current moment; if no, return to step S7. In step S7, when the bellows sample (4) is first placed into the heating container (8), the timer for the test duration is started.

4. The stress corrosion testing method for metal bellows according to claim 3, characterized in that, In step S1, the manufacturing process of the corrugated pipe sample (4) is as follows: the corrugated pipe (44) is hydroformed, one end of the corrugated pipe (44) is welded to the upper pipe (43), and the other end is welded to the lower pipe (45) to form a pre-assembled part. The inner core cylinder (42) is assembled inside the pre-assembled part, one end of the inner core cylinder (42) is welded to the lower pipe (45), and a tensile force or a compressive force is applied to the upper pipe (43) so that the length of the pre-assembled part reaches the design size. Then the other end of the inner core cylinder (42) is welded to the upper pipe (43) to obtain the corrugated pipe sample (4).

5. The stress corrosion testing method for metal bellows according to claim 3, characterized in that, In step S1, the manufacturing process of the corrugated pipe sample (4) is as follows: the corrugated pipe (44) is hydroformed, one end of the corrugated pipe (44) is welded to the upper pipe (43), and the other end is welded to the lower pipe (45) to form a pre-assembled part. An inner core cylinder (42) is assembled inside the pre-assembled part, one end of the inner core cylinder (42) is welded to the lower pipe (45), and a tensile or compressive force is applied to the upper pipe (43) so that the length of the pre-assembled part reaches the set value. Measure the dimensions, and then weld the other end of the inner core cylinder (42) to the upper tube (43); weld the monitoring tube (41) to the inner wall of the inner core cylinder (42) and connect the monitoring tube (41) to the cavity to obtain the test piece. Then, conduct an airtightness test on the test piece through the monitoring tube (41). After the airtightness test is qualified, pressurize the cavity to the required test pressure through the monitoring tube (41). Then, install a pressure gauge at the end of the monitoring tube (41) to obtain the corrugated pipe sample (4).

6. The stress corrosion testing method for metal bellows according to claim 5, characterized in that, Step S8 includes: S81. Determine whether bubbles emerge from the bellows sample (4) in the magnesium chloride solution (6), or whether the pressure gauge reading begins to decrease; if yes, proceed to step S82; if no, return to step S7. S82. Record the test duration and pressure reading at the current moment, then take out the bellows sample (4) for cleaning, perform colorimetric testing on the surface of the bellows (44), and record the location and size of the crack.

7. The stress corrosion testing method for metal bellows according to claim 3, characterized in that, In step S1, the design stress state of the bellows sample (4) is displacement stress, or the design stress state of the bellows sample (4) includes displacement stress and pressure stress.

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