Method for testing pressure vessel and test assembly for pressure vessel

Abstract

The present disclosure relates to a method (100) for testing a pressure vessel, comprising: providing (110) at least one electrode in a media storage space of the pressure vessel, the pressure vessel comprising a metal hollow body and an inner wall of the metal hollow body being coated with an insulating material in order to insulate the media storage space from the metal hollow body; filling (120) the media storage space with a test liquid in order to generate a test pressure in the media storage space; carrying out (130) a current and / or resistance measurement between the at least one electrode and the metal hollow body while applying a test pressure to the medium storage space; and determining (140) an insulation characteristic of the insulation material based on a result of the current and / or resistance measurement.

Description

Technical Field

[0001] The present disclosure relates to methods for testing pressure vessels and test assemblies for pressure vessels. The present disclosure relates in particular to testing permeation barriers, such as plastic coatings, steel vessels during pressure testing. Background Art

[0002] For historical reasons, a considerable number of motor vehicles are still currently operated by internal combustion engines. Due to the limited availability of fossil fuels and the environmental pollution caused by the harmful emissions of such internal combustion engines, there is a trend towards alternative drive technologies, in particular electric drives. Electric vehicles can be equipped with lithium batteries or fuel cells, for example, which serve as energy sources for the electric drive.

[0003] Fuel cells convert the chemical energy of hydrogen into electrical current, with only water vapor being produced without nitrogen oxides and carbon dioxide. Fuel cells are therefore generally environmentally friendly. A challenge in vehicles operated with fuel cells is the storage of hydrogen in the vehicle. For this purpose, hydrogen tanks are used, which are subject to high safety requirements, since hydrogen tanks are often filled up to 875 bar. In addition, hydrogen is a corrosive medium, so that only very few steels are suitable for producing hydrogen tanks.

[0004] Typically, hydrogen containers are made of carbon fiber reinforced plastic (CFK). CFK is a strong material and does not become brittle due to hydrogen. However, the production of hydrogen containers made of CFK is complex and expensive, so the production costs of such hydrogen containers are high.

[0005] Document JP 2009-133767 A relates to a container for supplying medical liquids. The container comprises a container body, the inside of which is lined with a corrosion-resistant material. A resistance measuring device is connected in one example to the outside of the container body and to electrodes of a leak detection device in order to determine the state of the insulation layer.

[0006] JP 2000-081362 A relates to a leakage detection device for a liquid container. An inner electrode is arranged in the liquid of the liquid container, and the inner wall surface of the liquid container is covered with a lining layer. Summary of the invention

[0007] The object of the present disclosure is to provide a method for testing a pressure vessel and a test assembly for a pressure vessel, which can realize effective quality testing of the pressure vessel. In particular, the object of the present disclosure is to realize rapid and reliable testing of the insulation layer of a steel vessel.

[0008] This object is achieved by the subject matter of the independent claim. Advantageous embodiments are specified in the dependent claims.

[0009] According to an independent aspect of the present disclosure, a method for testing a pressure vessel, in particular a steel vessel, is provided. The method comprises: arranging at least one electrode in a medium storage space of the pressure vessel, wherein the pressure vessel comprises a metal hollow body and the inner wall of the metal hollow body is coated with an insulating material so as to insulate the medium storage space from the metal hollow body; filling the medium storage space with a test liquid so as to generate a test pressure for a pressure test in the medium storage space; performing a current and / or resistance measurement between the at least one electrode and the metal hollow body for a coating quality test while applying the test pressure to the medium storage space; and determining the insulating properties of the insulating material based on the results of the current and / or resistance measurement.

[0010] According to the invention, both a pressure test and a coating quality test are carried out in a single process step. For this purpose, a test liquid is filled into the medium storage space of the pressure vessel in order to generate a test pressure for the pressure test. In addition, electrodes are arranged in the medium storage space and are therefore surrounded by the test liquid. In order to test the coating quality, the current passing between the electrode and the metal hollow body or the corresponding resistance is measured. In particular, the test liquid conducts electric current, so that in the case of a defective coating, electric current flows between the electrode and the metal hollow body. In contrast, in the case of a non-defective coating, basically no current flows. Therefore, the quality of the coating can be inferred from the current and / or resistance measurement. As a result, effective quality testing of the pressure vessel can be achieved.

[0011] For current and / or resistance measurement, a defined voltage is applied to at least one electrode and the metal hollow body, so that the current or the corresponding resistance between the at least one electrode and the metal hollow body can be measured. For example, the current can be measured with an ammeter and the resistance can be measured with an ohmmeter.

[0012] Preferably, the test pressure is 1000 bar or more. The test pressure may be, for example, 1050 bar or more.

[0013] Preferably, the test liquid is water. The present disclosure is however not limited thereto, and the test liquid may be another electrically conductive liquid, which enables current and / or resistance measurements.

[0014] Preferably, determining the insulation property of the insulation material based on the results of the current and / or resistance measurement comprises comparing a current flowing between at least one electrode and the metal hollow body or a corresponding resistance value with a threshold value.

[0015] In some implementation forms, if the through current is (equal to or) less than the threshold value, then the pressure vessel can be determined to be a qualified part, and if the through current is (equal to or) greater than the threshold value, then the pressure vessel is a non-qualified part. Similarly, if the resistance value is (equal to or) greater than the threshold value, then the pressure vessel can be determined to be a qualified part, and if the resistance value is (equal to or) less than the threshold value, then the pressure vessel is a non-qualified part. In particular, the through current or the corresponding resistance value can indicate the presence of a defect in the insulating material. The defect can be a hole, which exposes the metal hollow body to the medium storage space and thus enables the through current.

[0016] Components that meet certain quality requirements are generally called qualified parts. Correspondingly, components that do not meet the quality requirements can be called unqualified parts.

[0017] The threshold value can be determined by means of suitable tests. For example, the threshold value can be determined based on a quality standard, which can be legally stipulated, in order to distinguish between good and bad parts. In some embodiments, holes can be introduced purposefully into the coating of the pressure vessel, so that it can be determined at which current or corresponding resistance value the presence of the hole can be inferred. This current or corresponding resistance value can then be used, for example, to determine the above-mentioned threshold value for distinguishing between good and bad parts.

[0018] Preferably, the at least one electrode comprises a first electrode and a second electrode.

[0019] Preferably, the method further comprises: performing a first current and / or resistance measurement between the first electrode and the metal hollow body and performing a second current and / or resistance measurement between the second electrode and the metal hollow body, and determining the insulation property of the insulation material based on the result of the first current and / or resistance measurement and the result of the second current and / or resistance measurement. Redundancy can be achieved thereby to improve the reliability of the test result of the pressure vessel.

[0020] In addition or alternatively, the method may also include: performing a current and / or resistance measurement between the first electrode and the second electrode, and determining the state of the test liquid based on the result of the current and / or resistance measurement between the first electrode and the second electrode. Thus, the method according to the invention can provide another function without changing the hardware, namely a quality test of the test liquid. For example, the conductivity of the test liquid may increase with increasing age due to contamination, which can be identified by current and / or resistance measurement.

[0021] In some embodiments, the method according to the invention can be carried out at least partially automatically and preferably fully automatically with the aid of suitable software.

[0022] Accordingly, according to a further independent aspect of the disclosure, a software (SW) program is proposed. The software (SW) program can be designed to be executed on one or more processors and thus to execute the method for testing a pressure vessel described herein.

[0023] According to another independent aspect of the present disclosure, a storage medium is provided. The storage medium may include a SW program which is configured to be executed on one or more processors and thereby execute the method for testing a pressure vessel described herein.

[0024] According to another independent aspect of the disclosure, software with a program code is provided. The software is designed to carry out a method for testing a pressure vessel when the software runs on one or more software-controlled devices.

[0025] According to another independent aspect of the present disclosure, a system for testing a pressure vessel is provided, wherein the system comprises one or more processors and at least one memory connected to the one or more processors and containing instructions, wherein the instructions can be executed by the one or more processors to perform the method for testing a pressure vessel described herein.

[0026] A processor or a processor module is a programmable computing unit, ie a machine or an electronic circuit, which controls other components according to given instructions and thereby carries out algorithms (processes).

[0027] Preferably, the pressure vessel is designed for use or installation in a vehicle. The term vehicle includes cars, trucks, buses, motorhomes, motorcycles, etc., which are used to transport people, objects, etc. In particular, the term includes motor vehicles for the transportation of people.

[0028] Preferably, the metal hollow body is made of steel. The steel may be high-strength steel, which may have a tensile strength of 500 MPa or more, 1000 MPa or more, or 2000 MPa or more, for example. In some embodiments, the steel may be 300M steel or V132 steel.

[0029] Coating the inner wall of the metal hollow body with an insulating material protects the metal material from corrosion by the stored medium, so that the metal pressure vessel can also be used to store corrosive media. This can reduce the cost for storing corrosive media because the metal pressure vessel can be manufactured more cost-effectively than, for example, a CFK container. In addition, metal can be recycled better than, for example, CFK. In addition, the metal pressure vessel can have a thinner wall than, for example, a CFK container under the same compressive strength, so that more medium can be filled into the pressure vessel and maintained there under the same size.

[0030] Preferably, the pressure vessel is set up for storing gaseous and / or liquid media. In other words, the medium stored in the pressure vessel can be gas and / or liquid. In some embodiments, the medium stored in the pressure vessel can be only gas or only liquid. In other embodiments, the medium stored in the pressure vessel can have a gaseous part and a liquid part. For example, a gaseous medium can also be present above a liquid.

[0031] Preferably, the pressure vessel is a hydrogen container. Coating the inner wall of the metal hollow body with an insulating material protects the metal material from corrosion by hydrogen, so that, for example, steel containers can also be used to store hydrogen. This can reduce the costs for storing hydrogen, for example in vehicles, especially because steel containers can be manufactured more cost-effectively than, for example, CFRP containers. In addition, the pressure vessel according to the invention can have thinner walls than, for example, CFRP containers at the same compressive strength, so that more hydrogen can be stored in the same installation space in the vehicle, which can increase the vehicle's range.

[0032] Preferably, the insulating material forms a permeation barrier. The term "permeation" generally refers to a process in which a substance or a permeate passes through or penetrates a solid. Accordingly, the insulating material prevents the medium in the medium storage space from reaching the metal hollow body and corroding it. The insulating material can be selected depending on which medium the pressure vessel is intended for. If the medium stored in the pressure vessel has a gaseous part and a liquid part, the insulating material can form a permeation barrier for the medium in both physical states.

[0033] In some implementations, the insulating material may form a hydrogen permeation barrier.

[0034] Preferably, the insulating material is a plastic. The insulating material can be selected appropriately in order to prevent penetration of the medium to be stored in the pressure vessel.

[0035] Preferably, the insulating material is selected from the group consisting of ethylene vinyl alcohol (EVOH), epoxide, silicon dioxide, polytetrafluoroethylene (PTFE), Teflon, liquid crystal polymer (LCP) and combinations thereof or consisting thereof.

[0036] Preferably, the inner wall of the metal hollow body is coated with the insulating material in a single layer. However, the present disclosure is not limited thereto and the insulating material may be formed in multiple layers, for example, from different materials.

[0037] Preferably, the layer thickness of the insulating material on the inner wall of the metal hollow body is in the range between 10 μm and 500 μm, in particular between 50 μm and 200 μm.

[0038] According to another independent aspect of the present disclosure, a test assembly for a pressure vessel is provided.

[0039] The test assembly may be configured to implement aspects of the method for testing a pressure vessel described herein.

[0040] The test component includes: at least one electrode, which can be arranged in the medium storage space of the pressure vessel, wherein the pressure vessel includes a metal hollow body and the inner wall of the metal hollow body is coated with an insulating material to insulate the medium storage space from the metal hollow body; a pressure generating device, which is configured to introduce a test liquid into the medium storage space and generate a test pressure for a pressure test in the medium storage space; and a current and / or resistance measuring device, which can be connected to the at least one electrode and the metal hollow body, so as to implement current and / or resistance measurement between the at least one electrode and the metal hollow body in a coating quality test in order to determine the insulating properties of the insulating material.

[0041] Preferably, the at least one electrode comprises a first electrode and a second electrode. Optionally, one or more further electrodes may be provided.

[0042] Preferably, the current and / or resistance measuring device is configured to perform a first current and / or resistance measurement between the first electrode and the metal hollow body and a second current and / or resistance measurement between the second electrode and the metal hollow body. This allows redundancy to be achieved in order to improve the reliability of the test results of the pressure vessel.

[0043] Additionally or alternatively, the current and / or resistance measuring device can be configured to carry out a current and / or resistance measurement between the first electrode and the second electrode in order to determine the state of the test liquid. For example, the conductivity of the test liquid can increase with increasing age due to contamination, which can be detected by measuring the current or resistance passing between the first electrode and the second electrode, both of which are surrounded by the test liquid or immersed in the test liquid.

[0044] Preferably, the test assembly further comprises at least one adapter, which is configured to be connected to at least one inlet and / or outlet of the medium storage space. For example, the at least one adapter can be at least partially inserted into the inlet and / or outlet of the medium storage space. The at least one adapter can usually be connected to the inlet and / or outlet in a substantially waterproof manner. This can prevent the test liquid from flowing out of the at least one inlet and / or outlet.

[0045] Preferably, at least one adapter is made of plastic, ceramic or plastic-coated metal. The at least one adapter can electrically insulate the at least one electrode from the metal hollow body, so that reliable current and / or resistance measurement between the at least one electrode and the metal hollow body is possible.

[0046] Preferably, the at least one adapter is designed to conduct the test liquid into the medium storage space and / or to discharge the test liquid from the medium storage space.

[0047] In some embodiments, the at least one adapter may include a first adapter that can be connected to an inlet of the medium storage space. For example, the first adapter can be connected to the pressure generating device via a test liquid input line to introduce the test liquid provided by the pressure generating device into the medium storage space.

[0048] Additionally or alternatively, the at least one adapter may include a second adapter that can be connected to an outlet of the medium storage space, such as the second adapter can be connected to a test liquid outlet line, so that the test liquid can be discharged from the medium storage space after the test process is completed.

[0049] The inlet of the medium storage space is here an opening through which the test liquid is introduced into the medium storage space. The outlet of the medium storage space can be an opening through which the test liquid is discharged from the medium storage space.

[0050] Preferably, the inlet and outlet are arranged on opposite ends or sides of the media storage space.

[0051] In other embodiments, a single opening can serve as both inlet and outlet.

[0052] Preferably, at least one electrode extends through the at least one adapter. Thus, if the adapter is connected to the inlet and / or outlet, the at least one electrode projects into the medium storage space, so that the at least one electrode is surrounded by the test liquid or immersed in the test liquid during the test process.

[0053] Preferably, at least one electrode is designed in the form of a rod. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Embodiments of the present disclosure are shown in the accompanying drawings and are further described below. The accompanying drawings show:

[0055] Figure 1 A flow chart showing a method for testing a pressure vessel according to an embodiment of the present disclosure;

[0056] Figure 2 schematically illustrates a test assembly and a pressure vessel according to an embodiment of the present disclosure; and

[0057] Figure 3 A test assembly and a pressure vessel according to a further embodiment of the present disclosure are schematically shown. DETAILED DESCRIPTION

[0058] In the following, the same reference numerals are used for identical and identically acting elements unless otherwise indicated.

[0059] Figure 1 A flow chart of a method 100 for testing a pressure vessel according to an embodiment of the present disclosure is schematically shown.

[0060] Method 100 includes: in box 110, at least one electrode is set in the medium storage space of the pressure vessel, wherein the pressure vessel includes a metal hollow body and the inner wall of the metal hollow body is coated with an insulating material so as to insulate the medium storage space from the metal hollow body; in box 120, the medium storage space is filled with a test liquid so as to generate a test pressure in the medium storage space; in box 130, a current and / or resistance measurement is performed between the at least one electrode and the metal hollow body while applying the test pressure to the medium storage space; and in box 140, the insulating properties of the insulating material are determined based on the results of the current and / or resistance measurement.

[0061] Method 100 combines a hydraulic pressure test with the determination of the coating quality in a single step. In a hydraulic pressure test, a pressure vessel can be filled with a test liquid, for example water, ensuring that no air is located in the pressure vessel. The water can then be compressed to approximately 150% NWP (for example 1.5×700 bar=1050 bar) and the pressure maintained for a certain time.

[0062] During this holding phase, the coating quality is measured simultaneously by applying a voltage to the electrodes and the metal hollow body located in the test liquid. In the case of a good coating without defects, no (almost no) current flows. In the case of defects, the test liquid comes into contact with the metal hollow body and thus forms an electrically conductive connection between the electrode and the container wall, so that a relatively large electrical current flows. By means of the boundary sample, a threshold value for the electrical through-current or the corresponding electrical resistance can be defined, so that a distinction can be made between good and bad parts.

[0063] After the holding phase, the test pressure can be reduced, the test liquid removed from the container, and a drying process carried out. The pressure vessel is then completed or reaches the next process step of the end-of-line test.

[0064] Figure 2 A test arrangement 100 and a pressure vessel 10 according to an embodiment of the present disclosure are schematically shown.

[0065] The test assembly 100 includes: at least one electrode 110, which is arranged in the medium storage space 16 of the pressure vessel 10, wherein the pressure vessel 10 includes a metal hollow body 12 and the inner wall of the metal hollow body 12 is coated with an insulating material 14 so as to insulate the medium storage space 16 from the metal hollow body 12; a pressure generating device 120, which is configured to introduce a test liquid into the medium storage space 16 and generate a test pressure in the medium storage space 16; and a current and / or resistance measuring device 130, which is connected to the at least one electrode 110 and the metal hollow body 12 so as to implement current and / or resistance measurement between the at least one electrode 110 and the metal hollow body 12 in order to determine the insulating properties of the insulating material 14.

[0066] For current and / or resistance measurement, a defined voltage is applied to at least one electrode 110 and the metal hollow body 12, so that the current flowing between the at least one electrode 110 and the metal hollow body 12 or the corresponding resistance can be measured. For example, the current can be measured with an ammeter and the resistance can be measured with an ohmmeter. Figure 2 An ammeter is shown in the example.

[0067] The quality of the coating or insulating material 14 can be determined by comparing the current flowing between the at least one electrode 110 and the metal hollow body 12 or the corresponding resistance value with a threshold value. If, for example, there are holes in the coating, the current flowing between the at least one electrode 110 and the metal hollow body 12 increases or the resistance between the at least one electrode 110 and the metal hollow body 12 decreases.

[0068] If the threshold value of the current flow is exceeded or the threshold value of the resistance is exceeded, the pressure vessel 10 can be determined as a defective part and, for example, sorted out. If, by contrast, the threshold value of the current flow is exceeded or the threshold value of the resistance is exceeded, the pressure vessel 10 can be determined as a good part.

[0069] The test assembly 100 can be calibrated by means of suitable tests. For example, holes can be introduced purposefully into the coating of the pressure vessel so that it can be determined at which current or corresponding resistance value the presence of holes in the coating can be inferred. This current or corresponding resistance value can then be used, for example, to define a threshold value for distinguishing between good and bad parts.

[0070] In some embodiments, the metal hollow body 12 can be made of steel. The steel can be high-strength steel, which can have a tensile strength of 500 MPa or more, 1000 MPa or more, or 2000 MPa or more, for example. The steel can be, for example, 300M steel or V132 steel.

[0071] In some embodiments, the pressure vessel 10 is a hydrogen container, which is used, for example, in a fuel cell-driven vehicle. The inner wall of the metal hollow body 12 is coated with an insulating material 14 to protect the metal material from corrosion by hydrogen, so that, for example, a steel container can be used to store hydrogen. This can reduce the costs for hydrogen storage in the vehicle, especially because steel containers can be manufactured more cost-effectively than, for example, CFRP containers. In addition, the pressure vessel according to the invention can have thinner walls than, for example, CFRP containers at the same compressive strength, so that more hydrogen can be stored in the same structural space in the vehicle, which can increase the vehicle's range.

[0072] Typically, the insulating material 14 forms a permeation barrier, such as a hydrogen permeation barrier. In some embodiments, the insulating material may be selected from the group consisting of ethylene vinyl alcohol (EVOH), epoxide, silicon dioxide, polytetrafluoroethylene (PTFE), Teflon, liquid crystal polymer (LCP), and combinations thereof or consisting thereof.

[0073] The layer thickness of the insulating material 14 on the inner wall of the hollow metal body 12 can be in the range between 10 μm and 500 μm, in particular between 50 μm and 200 μm.

[0074] Figure 3 A test arrangement and a pressure vessel 10 according to a further embodiment of the present disclosure are schematically shown. Figure 3 The test component is similar to Figure 2 and see the description of the same or similar aspects, for which see Figure 2 Together with the description.

[0075] The test assembly comprises a first electrode 110 and a second electrode 112. Optionally, one or more further electrodes may be provided. Typically, the first electrode 110 and the second electrode 112 are each designed in the form of a rod.

[0076] The test assembly further comprises a first adapter 140, which is connected to the inlet 20 of the medium storage space 16, in particular inserted therein. For example, the first adapter 140 can be connected to the pressure generating device via a test liquid input line (not shown), and the test liquid provided by the pressure generating device is introduced into the medium storage space (indicated by arrow 1).

[0077] Furthermore, the test assembly comprises a second adapter 142, which is connected to, in particular inserted into, the outlet 22 of the medium storage space 16. For example, the second adapter 142 can be connected to a test liquid outlet line (not shown), so that after the test process has been concluded, the test liquid can be discharged from the medium storage space 16 (indicated by arrow 2).

[0078] The inlet 20 and the outlet 22 may be disposed on opposing ends or sides of the media storage space 16 .

[0079] The first electrode 110 can extend through the first adapter 140. Thus, if the first adapter 140 is inserted into the inlet 20, the first electrode 110 protrudes into the medium storage space 16, so that the first electrode 110 is surrounded by the test liquid or immersed in the test liquid during the test process. The first adapter 140 can electrically insulate the first electrode 110 from the metal hollow body 12, so that reliable current and / or resistance measurement between the first electrode 110 and the metal hollow body 12 is possible.

[0080] The second electrode 112 can extend through the second adapter 142. Thus, if the second adapter 142 is inserted into the outlet 22, the second electrode 112 protrudes into the medium storage space 16, so that the second electrode 112 is surrounded by the test liquid or immersed in the test liquid during the test process. The second adapter 142 can electrically insulate the second electrode 112 from the metal hollow body 12, so that reliable current and / or resistance measurement between the second electrode 112 and the metal hollow body 12 is possible.

[0081] The current and / or resistance measuring device of the test assembly can be configured to perform a first current and / or resistance measurement between the first electrode 110 and the metal hollow body 12 and a second current and / or resistance measurement between the second electrode 112 and the metal hollow body 12. This allows redundancy to be achieved in order to improve the reliability of the coating test.

[0082] Additionally or alternatively, the current and / or resistance measuring device can be configured to carry out current and / or resistance measurement between the first electrode 110 and the second electrode 120 in order to determine the state of the test liquid. For example, the conductivity of the test liquid may increase with age due to contamination, which can be detected by measuring the current or resistance between the first electrode 110 and the second electrode 112, both of which are surrounded by the test liquid or immersed in the test liquid.

[0083] According to the invention, both a pressure test and a coating quality test are performed in a single process step. For this purpose, a test liquid is filled into the medium storage space of the pressure vessel in order to generate a test pressure for the pressure test. In addition, electrodes are arranged in the medium storage space and are therefore surrounded by the test liquid. In order to test the coating quality, the current passing between the electrode and the metal hollow body or the corresponding resistance is measured. In particular, the test liquid conducts current, so that in the case of a defective coating, current flows between the electrode and the metal hollow body. In contrast, in the case of a flawless coating, essentially no current flows. Therefore, the quality of the coating can be inferred from the current and / or resistance measurement. As a result, an effective quality test of the pressure vessel can be achieved.

[0084] Although the present invention has been further illustrated and explained in detail by preferred embodiments, the present invention is not limited by the disclosed examples and other variations can be derived therefrom by those skilled in the art without departing from the scope of protection of the present invention. It is therefore clear that multiple variations are possible. It is also clear that the exemplary embodiments described are actually only examples, which should not be understood as limiting the scope of protection, application possibilities or configuration of the present invention in any way. Moreover, the above description and the accompanying drawings enable those skilled in the art to specifically implement the exemplary embodiments, wherein, in the case of knowing the disclosed inventive concept, those skilled in the art can, for example, make various changes with respect to the functions or arrangement structures of the elements described in the exemplary embodiments without departing from the scope of protection, which is defined by the claims and their legal equivalents, for example, further explained in the specification.

Claims

1. A method (100) for testing a pressure vessel, comprising: - arranging (110) at least one electrode in a medium storage space of a pressure vessel, wherein the pressure vessel comprises a metal hollow body and an inner wall of the metal hollow body is coated with an insulating material so as to insulate the medium storage space from the metal hollow body; - filling (120) the medium storage space with a test liquid so as to generate a test pressure for a pressure test in the medium storage space; - carrying out (130) a current and / or resistance measurement between the at least one electrode and the metal hollow body for a coating quality test, while applying a test pressure to the medium storage space; and - Determining ( 140 ) insulation properties of the insulation material based on the results of the current and / or resistance measurements.

2. The method (100) according to claim 1, wherein: The test pressure is at least 1000 bar; and / or the test liquid is water.

3. The method (100) according to claim 1 or 2, wherein: Determining the insulation characteristics of the insulation material based on the results of the current and / or resistance measurement includes: Comparing the current passing between the at least one electrode and the metal hollow body with a threshold value, and determining that the pressure vessel is a qualified part if the current passing is less than the threshold value, and determining that the pressure vessel is a failed part if the current passing is greater than the threshold value; and / or The resistance value between the at least one electrode and the metal hollow body is compared with a threshold value, and if the resistance value is greater than the threshold value, the pressure vessel is determined to be a good part, and if the resistance value is less than the threshold value, the pressure vessel is determined to be a bad part.

4. The method (100) according to claim 3, wherein: The passage of the current or the resistance value indicates the presence of a defect in the insulating material, in particular a hole which exposes the hollow metal body to the dielectric storage space.

5. The method (100) according to any one of claims 1 to 4, wherein: The at least one electrode comprises a first electrode and a second electrode, and the method further comprises: Performing a first current and / or resistance measurement between the first electrode and the metal hollow body and a second current and / or resistance measurement between the second electrode and the metal hollow body, and determining the insulation properties of the insulation material based on the results of the first current and / or resistance measurement and the results of the second current and / or resistance measurement; and / or A current and / or resistance measurement is performed between the first electrode and the second electrode, and the state of the test liquid is determined based on the result of the current and / or resistance measurement between the first electrode and the second electrode.

6. The method (100) according to any one of claims 1 to 5, wherein: The metal hollow body is made of steel; and / or The pressure vessel is designed to store gaseous and / or liquid media; and / or the pressure vessel is a hydrogen container; and / or The insulating material forms a permeation barrier, in particular a hydrogen permeation barrier; and / or The insulating material is plastic; and / or The insulating material is selected from the group consisting of ethylene vinyl alcohol, epoxide, silicon dioxide, polytetrafluoroethylene, Teflon, liquid crystal polymer and combinations thereof; and / or The inner wall of the metal hollow body is coated with a single layer of insulating material; and / or The layer thickness of the insulating material on the inner wall of the metal hollow body is in the range between 10 μm and 500 μm, in particular between 50 μm and 200 μm.

7. A test assembly (100) for a pressure vessel (10), the test assembly comprising: At least one electrode (110, 112) which can be arranged in a medium storage space (16) of a pressure vessel (10), wherein the pressure vessel (10) comprises a metal hollow body (12) and the inner wall of the metal hollow body (12) is coated with an insulating material (14) so ​​as to insulate the medium storage space (16) from the metal hollow body (12); a pressure generating device (120) configured to introduce a test liquid into the medium storage space (16) and generate a test pressure for a pressure test in the medium storage space (16); and A current and / or resistance measuring device (130) is connectable to the at least one electrode (110, 112) and the metal hollow body (12) so as to carry out a current and / or resistance measurement between the at least one electrode (110, 112) and the metal hollow body (12) in order to determine the insulating properties of the insulating material (14) in a coating quality test.

8. The test assembly (100) according to claim 7, wherein: The at least one electrode (110, 112) comprises a first electrode (110) and a second electrode (112), and the current and / or resistance measuring device is configured as follows: Performing a first current and / or resistance measurement between the first electrode (110) and the metal hollow body (12) and performing a second current and / or resistance measurement between the second electrode (112) and the metal hollow body (12); and / or A current and / or resistance measurement is performed between the first electrode (110) and the second electrode (112) in order to determine the state of the test liquid.

9. The test assembly (100) according to claim 7 or 8, further comprising at least one adapter (140, 142), which is configured to be connected to at least one inlet and / or outlet (20, 22) of the medium storage space (16), wherein: The at least one electrode (110, 112) extends through the at least one adapter (140, 142), and in particular the at least one adapter (140, 142) is designed to electrically insulate the at least one electrode (110, 112) from the metal hollow body (12).

10. The test assembly (100) according to claim 9, wherein: The at least one adapter (140, 142) is designed to introduce a test liquid into the medium storage space (16) and / or to discharge the test liquid from the medium storage space (16).

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