Air tightness testing method for surface treatment layer of composite material cylinder inner wall

Abstract

The present invention discloses a method for detecting the air tightness of the surface treatment layer of the inner wall of a composite material cylinder. The method comprises the following steps: placing an inner support device on the inner wall of the composite material cylinder for close contact, assembling inner wall sealing devices at both ends of the composite material cylinder, performing initial leak detection by a helium mass spectrometer, thinning the side wall of the composite material cylinder by a milling machine after passing the test, and connecting the helium mass spectrometer again after thinning to determine whether the air tightness of the metal welding foil is qualified. If the metal welding foil is unqualified, a color flaw detection method is used to identify the leakage path. The testing method of the present invention can quantitatively test the air tightness of the metal welding foil on the inner wall of the composite material cylinder without regard to the air tightness of the cylinder in the early stage.

Description

Technical Field

[0001] The invention belongs to the field of vacuum technology, and in particular relates to a method for detecting the air tightness of a surface treatment layer on an inner wall of a composite material cylinder. Background Art

[0002] Composite materials are widely used in engineering due to their high specific modulus and specific strength, good designability and other advantages, including common composite pressure vessels and high-speed rotating cylinders. This type of composite cylinder must provide sufficient strength while also considering the special conditions and environment of its application. There are often special substances inside it, which requires the composite cylinder itself to have strict sealing performance to isolate it from the outside world. In order to increase the safety factor, it is also necessary to add a surface treatment layer on its inner wall, such as laying metal foil and welding. Therefore, in the early stage of the application of the composite cylinder, combined with the special substances to be stored, it is necessary to test the air tightness of the composite material, and also to test the air tightness of the welding foil applied to the inner surface of the composite material. The difficulty lies in how to test the air tightness of the welded metal foil alone when the air tightness of the composite material is intact. In summary, a set of air tightness detection methods suitable for the metal welding foil on the inner wall of the composite cylinder is designed, which can then detect the air tightness of the welding foil when the cylinder is in good air tightness. Summary of the invention

[0003] The present invention is proposed to overcome the shortcomings of the prior art and aims to provide a method for detecting the air tightness of the surface treatment layer of the inner wall of a composite material cylinder.

[0004] The present invention is achieved through the following technical solutions:

[0005] A method for detecting the air tightness of a surface treatment layer of an inner wall of a composite material cylinder comprises the following steps:

[0006] (i) assembling an internal support device inside the composite cylinder;

[0007] (ii) assembling an inner wall sealing device at the end of the composite cylinder;

[0008] (iii) connecting the entire composite material cylinder assembled in steps (i, ii) to a helium mass spectrometer to perform a helium leak rate test;

[0009] (iv) After the leak rate of step (iii) is qualified, the entire composite material cylinder is separated from the helium mass spectrometer, and the wall thickness of the outer wall position of the composite material cylinder corresponding to the weld is reduced by using a milling machine;

[0010] (v) After the wall thickness is reduced, the entire composite cylinder is reconnected to the helium mass spectrometer and the helium leak rate test is repeated to determine the sealing performance of the metal welding foil;

[0011] (vi) When the metal welding foil is judged to be leaking in step (v), the leakage path is identified by dye penetrating method.

[0012] In the above technical solution, the internal support device includes a left support member and a right support member, both of which are semi-circular structures, and a support rod arranged between the two; a threaded hole is formed in the middle of the left support member, and a limiting groove is formed on the inner bottom surface of the right support member; the support rod includes a threaded section that cooperates with the threaded hole and an insert section inserted into the limiting groove; a bearing is arranged between the insert section and the limiting groove.

[0013] In the above technical solution, the support rod also includes an adjustment section arranged between the threaded section and the plug-in section, and a limiting ring arranged adjacent to the plug-in section; the outer diameter of the limiting ring is larger than the inner diameter of the limiting groove.

[0014] In the above technical scheme, the inner wall sealing device includes an upper and a lower sealing mold arranged at both ends of the composite material cylinder, the upper sealing mold includes an upper outer flange in contact with the upper end surface of the composite material cylinder and an upper inner flange arranged in the composite material cylinder, and the two are connected by a plurality of bolts; a through hole is formed between the upper outer flange and the upper inner flange, and the top of the upper outer flange is connected to a vacuum mechanism; the lower sealing mold includes a lower outer flange in contact with the lower end surface of the composite material cylinder and a lower inner flange arranged in the composite material cylinder, and the two are connected by a plurality of bolts; an outer sealing ring is arranged between the upper inner and outer flanges, and between the lower inner and outer flanges; the vacuum mechanism includes a vacuum valve seat and two valves arranged thereon, one valve is connected to a vacuum acquisition system, and the other valve is connected to a vacuum detection device, and the vacuum valve seat is connected to the interior of the composite material cylinder through a through hole between the upper outer flange and the upper inner flange.

[0015] In the above technical solution, a convex ring is formed on the end face of the upper outer flange close to the upper inner flange; an annular groove is formed on the end face of the upper inner flange close to the upper outer flange, and the position of the annular groove corresponds to the position of the convex ring; an inner sealing ring is arranged in the annular groove.

[0016] In the above technical solution, the circumferential distance between the axial position of the threaded hole of the inner support device and the welding position of the metal foil is less than 5 mm.

[0017] In the above technical solution, the judgment standard of the helium leak rate test in step (iii) is: if the leak rate magnitude is ≤10 -10 Pa.m 3 .s -1 , it means that the composite material cylinder end seal is qualified and the composite material cylinder outer wall air tightness is good, and the subsequent steps are carried out; if the leakage rate is greater than 10 -10 Pa.m 3 .s -1, it can be directly determined that the metal foil is leaking without the need for subsequent steps.

[0018] In the above technical solution, in step (iv), the wall thickness is reduced to 0.2 mm to 0.5 mm.

[0019] In the above technical solution, the criterion for judging the sealing performance of the metal welding foil in step (v) is: the leakage rate is ≤10 -10 Pa.m 3 .s -1 , it is judged that the metal welding foil is sealed; the leakage rate is greater than 10 -10 Pa.m 3 .s -1 , it is judged that the metal welding foil is leaking.

[0020] In the above technical solution, the specific steps of using the color flaw detection method to identify the leakage path in step (vi) are: when the leakage level is greater than 10 -10 Pa.m 3 .s -1 Under the condition of maintaining the vacuum state of the inner cavity of the composite material cylinder, coloring inspection is carried out on the outer wall of the composite material cylinder, and coloring agent with nuclear grade particle size is selected for flaw detection and tracing; after spraying the coloring agent, the inner cavity is kept in vacuum for 12 hours and then the air is broken; spray the cleaning agent to complete the outer wall cleaning, unload the inner wall sealing mold and the inner support mold, observe the coloring agent penetration at the metal foil welding position, spray the developer, and complete the leakage path analysis.

[0021] The beneficial effects of the present invention are:

[0022] The invention provides a method for detecting the air tightness of a surface treatment layer of an inner wall of a composite material cylinder, which is used for detecting the air tightness of a welding foil when the cylinder has good air tightness. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic structural diagram of an inner support device used in the method for detecting air tightness of the surface treatment layer of the inner wall of a composite material cylinder of the present invention;

[0024] Figure 2 It is a cross-sectional view of the left support member in the inner support device used in the method for detecting the air tightness of the surface treatment layer of the inner wall of the composite material cylinder of the present invention;

[0025] Figure 3 It is a right view of the left support member in the inner support device used in the method for detecting the air tightness of the surface treatment layer of the inner wall of the composite material cylinder of the present invention;

[0026] Figure 4 It is a cross-sectional view of the right support member in the inner support device used in the method for detecting the air tightness of the surface treatment layer of the inner wall of the composite material cylinder of the present invention;

[0027] Figure 5 It is a left view of the right support member in the inner support device used in the method for detecting the air tightness of the surface treatment layer of the inner wall of the composite material cylinder of the present invention;

[0028] Figure 6 It is a schematic diagram of the assembly of the inner support device and the composite material cylinder used in the method for detecting the air tightness of the surface treatment layer of the inner wall of the composite material cylinder of the present invention;

[0029] Figure 7 It is a schematic structural diagram of the inner wall sealing device used in the method for detecting the air tightness of the inner wall surface treatment layer of the composite material cylinder of the present invention;

[0030] Figure 8 It is a schematic structural diagram of a composite material cylinder after milling in the method for detecting air tightness of the surface treatment layer of the inner wall of a composite material cylinder of the present invention.

[0031] in:

[0032] 1 Internal support device

[0033] 11 Left support 111 threaded hole

[0034] 12 Right support 121 groove

[0035] 13 Support rod 131 Threaded section

[0036] 132 plug-in section 133 adjustment section

[0037] 134 Limiting ring

[0038] 14 Bearings

[0039] 2 Inner wall sealing device

[0040] 201 Upper outer flange 202 Lower outer flange

[0041] 203 Upper inner flange 204 Lower inner flange

[0042] 205 Bolt 206 External sealing ring

[0043] 207 Vacuum valve seat 208 Valve

[0044] 209 convex ring 210 inner sealing ring

[0045] 3 Composite material cylinder.

[0046] For ordinary technicians in this field, other relevant drawings can be obtained based on the above drawings without any creative work. DETAILED DESCRIPTION

[0047] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the method for detecting air tightness of the inner wall surface treatment layer of a composite material cylinder of the present invention is further explained below in conjunction with the accompanying drawings and through specific implementation methods.

[0048] Example 1

[0049] A method for detecting the air tightness of a surface treatment layer of an inner wall of a composite material cylinder comprises the following steps:

[0050] (i) Assemble the internal support device inside the composite material cylinder to ensure that there is no relative displacement between the internal support device and the composite material cylinder, and the circumferential distance between the axial position of the hole (threaded hole) of the internal support device and the circumferential distance between the welding position of the metal foil material is less than 10 mm;

[0051] (ii) assembling an inner wall sealing device at the end of the composite material cylinder to form an inner sealing cavity;

[0052] (iii) Connect the entire composite material cylinder assembled in steps (i) and (ii) to a helium mass spectrometer for a helium leak rate test. If the leak rate reaches 10 -10 Pa.m 3 .s -1 , then proceed to the subsequent steps. If the leakage rate is greater than 10 -10 Pa.m 3 .s -1 , it can be directly determined that the metal foil is leaking without the need for subsequent steps;

[0053] If the result of the initial air tightness test is unqualified, it must be that the middle angle layer, the inner pure circumferential layer, and the inner lining layer are leaking at the same time, otherwise the result must be less than 10 -10 , no coloring inspection is required.

[0054] (iv) After the leak rate of step (iii) is qualified, the entire composite material cylinder is separated from the helium mass spectrometer and placed under a milling machine, where the wall thickness of the outer wall of the composite material cylinder corresponding to the weld is reduced to 0.2 mm to 0.5 mm by using the milling machine;

[0055] (v) After the wall thickness is reduced, the entire composite cylinder is as follows Figure 8 As shown, reconnect it to the helium mass spectrometer and repeat the helium leak rate test to determine the sealing of the metal welding foil. If the leak rate reaches 10 -10 Pa.m 3 .s -1 , the metal welding foil is considered to be sealed properly. If the leakage rate is greater than 10 -10 Pa.m 3 .s -1 , it is judged that the metal foil is leaking;

[0056] (vi) When the metal welding foil is judged to be leaking in step (v), the leakage path is determined by dye flaw detection. -10 Pa.m 3 .s -1 Under the condition of maintaining the vacuum state of the inner cavity, color flaw detection is carried out on the outer wall of the cylinder, and colorants with nuclear grade particle size are selected for flaw detection and tracing. After spraying the colorant, the inner cavity is kept in vacuum for about 12 hours, and then the air is broken; the cleaning agent is sprayed to complete the cleaning of the outer wall, the inner wall sealing mold and the inner support mold are unloaded, and the colorant penetration is observed at the welding position of the metal foil. If necessary, the developer is sprayed to complete the leakage path analysis.

[0057] like Figures 1 to 6 As shown, the inner support device includes a left support member 11, a right support member 12 and a support rod 13 arranged between the two; a threaded hole 111 is formed in the middle of the left support member 11, and a limiting groove 121 is formed on the inner bottom surface of the right support member 12; one end of the support rod 13 is connected to the threaded hole 111, and the other end is inserted into the limiting groove 121. The left support member 11 and the right support member 12 are both semi-circular ring-shaped, and a boss with a rectangular cross-section is formed in the middle of the inner side of the left support member 11 and the right support member 12. The threaded hole 111 and the limiting groove 121 are both formed at the corresponding boss position, and the boss with a flat bottom surface is convenient for assembly with the support rod 3. The support rod 13 includes a threaded section 131 threadedly matched with the threaded hole 111 and a plug-in section 132 inserted into the limiting groove 121.

[0058] The left support member 11 and the right support member 12 can form a complete cylinder, and the outer diameter of the cylinder is 1 mm smaller than the inner diameter of the composite material cylinder 3 .

[0059] In this embodiment, in order to facilitate manual rotation of the support rod, the support rod 13 further includes an adjustment section 133 disposed between the threaded section 131 and the plug section 132. The outer diameter of the adjustment section 133 is larger than that of the threaded section 131 and the plug section 132; the adjustment section 133 is a fastenable bolt, and the bolt is fastened by a wrench to complete the fastening.

[0060] In this embodiment, in order to prevent the plug-in section 132 from being over-inserted into the limiting groove 121 , the support rod 13 further includes a limiting ring 134 disposed adjacent to the plug-in section 132 . The outer diameter of the limiting ring 134 is greater than the inner diameter of the limiting groove 121 .

[0061] In this embodiment, in order to ensure smooth rotation of the support rod, a bearing 14 is provided between the plug-in section 132 of the support rod 13 and the limiting groove 121 .

[0062] In this embodiment, in order to ensure the balance of the supporting force of the device, the left support member 11, the right support member 12 and the support rod 13 are coaxial.

[0063] In this embodiment, in order to avoid affecting the air tightness test of the composite material cylinder, the left support 11 and the right support 12 are provided with a row of through holes with a diameter of 0.5 mm in any axial direction, with a hole spacing of 5 mm, and the through holes and the metal foil welding weld are in the same axial position. The purpose of this design is that when the outer wall of the inner support mold and the outer wall of the cylinder are in complete and tight contact, the gap between them is small, which may block the cracks on the surface, causing the test result that should have failed the air tightness test to become qualified, and the real air tightness of the weld position is restored through the through hole. When punching, it is only necessary to ensure that the axial direction is vertical. By rotating the position of the inner support, the through hole and the weld position can be ensured to be the same.

[0064] like Figure 7 As shown, the inner wall sealing device includes an upper and a lower sealing mold arranged at both ends of the composite material cylinder 3, the upper sealing mold includes an upper outer flange 201 in contact with the upper end surface of the composite material cylinder 3 and an upper inner flange 203 arranged inside the upper end of the composite material cylinder 3, and the two are fastened and connected by a plurality of bolts 205; an outer sealing ring 206 between the upper outer flange 201 and the upper inner flange 203;

[0065] Through holes are formed in the middle of the upper outer flange 201 and the upper inner flange 203. The top of the upper outer flange 201 is connected to a vacuum mechanism; the vacuum mechanism includes a vacuum valve seat 207 and two valves 208 arranged thereon, one valve 208 is connected to a vacuum acquisition system, and the other valve is connected to a vacuum detection device. The vacuum valve seat 207 is connected to the inside of the composite material cylinder 3 through the through hole in the middle of the upper outer flange 201 and the upper inner flange 203. The through hole in the middle of the upper outer flange 201 and the upper inner flange 203 is coaxial with the vacuum valve seat 207.

[0066] The lower sealing mold includes a lower outer flange 202 in contact with the lower end surface of the composite material cylinder 3 and a lower inner flange 204 disposed in the composite material cylinder 3, and the two are connected by a plurality of bolts 205;

[0067] An outer sealing ring 206 is disposed between the lower outer flange 202 and the lower inner flange 204 .

[0068] The diameters of the upper outer flange 201 and the lower outer flange 202 are larger than the outer diameter of the composite material cylinder 3 .

[0069] The diameters of the upper inner flange 203 and the lower inner flange 204 are smaller than the inner diameter of the composite material cylinder 3 .

[0070] The end surface of the upper inner flange 203 close to the upper outer flange 201 and the end surface of the lower inner flange 204 close to the lower outer flange 202 both form bosses, and the outer sealing ring 206 is placed between the outer wall of the boss and the inner wall of the composite material cylinder 3.

[0071] In this embodiment, in order to further ensure the sealing effect of the composite material cylinder, the upper sealing mold is provided with an internal sealing structure, and the internal sealing structure includes a convex ring 209 formed on the end face of the upper outer flange 201 close to the upper inner flange 203, and an annular groove formed on the end face of the upper inner flange 203 close to the upper outer flange 201. The convex ring 209 and the annular groove are relatively arranged, and an inner sealing ring 210 is arranged in the annular groove. When the bolt 205 tightens the upper outer flange 201 and the upper inner flange 203, the convex ring 209 squeezes the inner sealing ring 210 to achieve inner layer sealing and double-layer sealing protection.

[0072] Working principle of the present invention:

[0073] The threaded section 131 of the support rod 13 of the internal support device of the present invention is connected to the threaded hole 11 in the center of the left support member 11, the bearing 14 is placed in the limiting groove 121 in the center of the right support member 12, the plug-in section 132 of the support rod 13 is inserted into the bearing, and the entire device is placed in the inner cavity of the cylinder. By rotating the support rod 13, the depth of the threaded section 131 screwed into the threaded hole 111 is adjusted, so that the support rod is expanded axially from the threaded part, the distance between the left and right support members 11 / 12 is adjusted, and the two fastening semi-rings are stretched open to achieve the supporting effect.

[0074] The inner wall sealing device of the present invention realizes sealing of the two ends of the composite material cylinder through sealing molds at the upper and lower ends. The sealing mold is composed of an inner flange (i.e., an upper inner flange 203 and a lower inner flange 204) whose outer diameter is smaller than the inner diameter of the composite material cylinder and an outer flange (i.e., an upper outer flange 201 and a lower outer flange 202) whose outer diameter is larger than the outer diameter of the composite material cylinder. The two are fastened by bolts. When the bolts are tightened, the inner and outer flange structures approach each other, squeezing the rubber ring to deform, thereby generating pressure on the top of the inner wall of the cylinder to form a sealed cavity on the inner wall of the cylinder.

[0075] Before the experiment begins, one of the two vacuum valve seats and valves is connected to the vacuum acquisition system and the other to the vacuum detection device; the upper outer flange and the upper inner flange are squeezed by bolts, so that the upper outer sealing cavity ring is squeezed to produce inward and outward deformation, and contacts the inner wall of the composite cylinder to produce a sealing effect; similarly, the bolts squeeze the lower flange and the lower inner flange to deform the lower outer sealing cavity ring, producing a sealing effect at the lower end of the mold. Install the experimental device. After installation, turn on the vacuum acquisition system, pump to the limit pressure, close the valve connected to the vacuum acquisition system, and record the reading of the vacuum detection device after the system stabilizes for a certain period of time; use a helium mass spectrometer leak detector to detect the sealing condition at the sealing surface. After confirming that the sealing of the end face of the composite cylinder is qualified, start the subsequent test.

[0076] The purpose of introducing the milling machine is to locally cut and thin the side wall of the composite material cylinder to reduce the airtightness of the composite material cylinder, thereby realizing the detection of the sealing of the metal welding foil.

[0077] The application principle of the helium mass spectrometer is to evacuate the inside of the object to be tested and connect it to the helium mass spectrometer to form an internal vacuum environment, and spray helium gas on the outside of the object. If a leak occurs, helium atoms can leak from the leak to the inner cavity and be detected by the helium mass spectrometer.

[0078] The sealing test of the composite material cylinder using the method of Example 1 is as follows:

[0079] Example 1

[0080] (i) The inner diameter of the composite material cylinder tested is 200 mm, the outer diameter is 210 mm, the axial length of the cylinder is 300 mm, the inner wall metal welding foil material is Cu, and the thickness is 0.2 mm; the inner flange diameter of the inner wall sealing device is designed to be 199 mm, the outer flange diameter is 215 mm, and the diameter of the complete cylinder composed of the left support and the right support in the inner support device is 198 mm.

[0081] (ii) After the internal support device and the inner wall sealing device are assembled, the helium mass spectrometer is connected, and the initial leak rate is 10 - 10 Pa.m 3 .s -1 ;

[0082] (iii) Thinning the tube wall to 0.3 mm on a milling machine;

[0083] (iv) Connect the helium mass spectrometer and repeat the leak detection. The leak rate drops to 10 -5 Pa.m 3 .s -1 , it is judged that the leakage is caused by abnormal welding process of Cu foil;

[0084] (v) Using the color flaw detection method, it is determined that the leaking position of the Cu foil is a complete failure.

[0085] Example 2

[0086] (i) The inner diameter of the composite material cylinder tested is 100 mm, the outer diameter is 110 mm, the axial length of the cylinder is 300 mm, the inner wall metal welding foil material is Al, and the thickness is 0.2 mm; the inner flange diameter of the inner wall sealing device is designed to be 99 mm, the outer flange diameter is 115 mm, and the diameter of the complete cylinder composed of the left support and the right support in the inner support device is 98 mm;

[0087] (ii) After the inner support mold and the inner wall sealing mold are assembled, connect the helium mass spectrometer, and the initial leak rate is 10 - 10Pa.m 3 .s -1 ;

[0088] (iii) Thinning the tube wall to 0.5 mm on a milling machine;

[0089] (iv) Connect the helium mass spectrometer and repeat the leak detection. The leak rate is still 10 -10 Pa.m 3 .s -1 , it is judged that the Al foil welding process is qualified.

[0090] Example 3

[0091] (i) The inner diameter of the composite material cylinder tested is 100 mm, the outer diameter is 110 mm, the axial length of the cylinder is 300 mm, the inner wall metal welding foil material is Al, and the thickness is 0.2 mm; the inner flange diameter of the inner wall sealing device is designed to be 99 mm, the outer flange diameter is 115 mm, and the diameter of the complete cylinder composed of the left support and the right support in the inner support device is 98 mm;

[0092] (ii) After the inner support mold and the inner wall sealing mold are assembled, connect the helium mass spectrometer, and the initial leak rate is 10 - 10 Pa.m 3 .s -1 ;

[0093] (iii) Thinning the tube wall to 1.0 mm on a milling machine;

[0094] (iv) Connect the helium mass spectrometer and repeat the leak detection. The leak rate is still 10 -10 Pa.m 3 .s -1 , it is impossible to judge whether the Al foil process is qualified;

[0095] (v) Further thinning the tube wall to 0.5 mm on a milling machine;

[0096] (vi) Connect the helium mass spectrometer and repeat the leak detection. The leak rate drops to 10 -7 Pa.m 3 .s -1 , judge Al foil welding failure;

[0097] (ⅷ) Use the color flaw detection method to determine the leakage location of the Al foil and find that there is partial leakage at the weld.

[0098] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and the like are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", and the like may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0099] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0100] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for detecting the air tightness of the surface treatment layer of the inner wall of a composite material cylinder, characterized in that: The following steps are involved: (i) assembling an internal support device inside the composite cylinder; (ii) assembling an inner wall sealing device at the end of the composite cylinder; (iii) connecting the entire composite material cylinder assembled in steps (i, ii) to a helium mass spectrometer to perform a helium leak rate test; (iv) After the leak rate of step (iii) is qualified, the entire composite material cylinder is separated from the helium mass spectrometer, and the wall thickness of the outer wall position of the composite material cylinder corresponding to the weld is reduced by using a milling machine; (v) After the wall thickness is reduced, the entire composite cylinder is reconnected to the helium mass spectrometer and the helium leak rate test is repeated to determine the sealing performance of the metal welding foil; (vi) When the metal welding foil is judged to be leaking in step (v), the leakage path is determined by using the color flaw detection method; The inner support device (1) comprises a left support member (11) and a right support member (12) both of which are semi-circular structures, and a support rod (13) arranged between the two; a threaded hole (111) is formed in the middle of the left support member (11), and a limiting groove (121) is formed on the inner bottom surface of the right support member (12); the support rod (13) comprises a threaded section (131) threadably matched with the threaded hole (111) and an inserting section (132) inserted into the limiting groove (121); a bearing (14) is arranged between the inserting section (132) and the limiting groove (121); The left support member (11) and the right support member (12) of the inner support device are provided with a row of through holes arranged at intervals in any axial direction, and the circumferential distance between the axial position of the through hole and the welding position of the metal foil is less than 5 mm; In the step (iv), the wall thickness is reduced to 0.2 mm to 0.5 mm; The specific steps of using the color flaw detection method to identify the leakage path in step (vi) are as follows: when the leakage level is greater than 10-10Pa.m3.s-1, the inner cavity of the composite material cylinder is kept in a vacuum state, and the outer wall of the composite material cylinder is subjected to color flaw detection, and a colorant with a nuclear-grade particle size is selected for flaw detection tracing; after spraying the colorant, the inner cavity is kept in a vacuum state for 12 hours, and then the air is broken; a cleaning agent is sprayed to complete the cleaning of the outer wall, the inner wall sealing mold and the inner support mold are unloaded, the colorant penetration is observed at the welding position of the metal foil, and a developer is sprayed to complete the leakage path analysis.

2. The method for detecting air tightness of the surface treatment layer of the inner wall of a composite material cylinder according to claim 1, characterized in that: The support rod (13) further comprises an adjustment section (133) arranged between the threaded section (131) and the plug-in section (132), and a limiting ring (134) arranged adjacent to the plug-in section (132); the outer diameter of the limiting ring (134) is greater than the inner diameter of the limiting groove (121).

3. The method for detecting air tightness of the surface treatment layer of the inner wall of a composite material cylinder according to claim 1, characterized in that: The inner wall sealing device (2) comprises an upper and a lower sealing mold arranged at both ends of the composite material cylinder (3); the upper sealing mold comprises an upper outer flange (201) in contact with the upper end surface of the composite material cylinder (3) and an upper inner flange (203) arranged inside the composite material cylinder (3), and the two are connected by a plurality of bolts (205); through holes are formed in the middle of the upper outer flange (201) and the upper inner flange (203); the top of the upper outer flange (201) is connected to a vacuum mechanism; the lower sealing mold comprises a lower outer flange (202) in contact with the lower end surface of the composite material cylinder (3) and an upper inner flange (203) arranged inside the composite material cylinder (3); (3), and the two are connected by a plurality of bolts (205); an outer sealing ring (206) is arranged between the upper inner and outer flanges (203, 201), and between the lower inner and outer flanges (204, 202); the vacuum pumping mechanism comprises a vacuum valve seat (207) and two valves (208) arranged thereon, one valve (208) is connected to a vacuum obtaining system, and the other valve is connected to a vacuum detection device, and the vacuum valve seat (207) is connected to the interior of the composite material cylinder (3) through a through hole between the upper outer flange (201) and the upper inner flange (203).

4. The method for detecting air tightness of the surface treatment layer of the inner wall of a composite material cylinder according to claim 3, characterized in that: A convex ring (209) is formed on the end surface of the upper outer flange (201) close to the upper inner flange (203); an annular groove is formed on the end surface of the upper inner flange (203) close to the upper outer flange (201), and the position of the annular groove corresponds to the position of the convex ring (209); and an inner sealing ring (210) is arranged in the annular groove.

5. The method for detecting air tightness of the surface treatment layer of the inner wall of a composite material cylinder according to claim 1, characterized in that: The judgment standard of the helium leak rate test in step (iii) is: if the leak rate magnitude is ≤10 -10 Pa.m 3 .s -1 , it means that the composite material cylinder end is sealed properly and the composite material cylinder outer wall has good air tightness, and the subsequent steps are carried out; if the leak rate magnitude is greater than 10 - 10 Pa.m 3 .s -1 , it can be directly judged that the metal foil is leaking, and no subsequent steps are required.

6. The method for detecting air tightness of the surface treatment layer of the inner wall of a composite material cylinder according to claim 1, characterized in that: In step (v), the metal welding foil sealing criterion is: if the leakage rate is ≤10 -10 Pa.m 3 .s -1 , the metal welding foil sealing is considered intact; if the leakage rate is >10 -10 Pa.m 3 .s -1 , the metal welding foil is considered leaking.

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