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Abstract: This paper mainly probes into the problem of valve inspection standards for LNG. The first part of the article is the introduction, which introduces the research background and research significance. The second part of the article introduces relevant domestic and foreign inspection standards. The third part of the article describes the methods specified in the inspection standards, including: external cooling and internal cooling. The fourth part of the article describes the requirements of the inspection standards, including: the choice of cooling medium; high pressure sealing requirements; pressure increment of high pressure sealing test.
Key words: valves for liquefied natural gas; inspection; temperature liquefied natural gas can be said to be one of the cleanest energy sources. The impact of liquefied natural gas on the environment after combustion is not very large, and it can basically meet the requirements of current enterprise green production, and has great advantages in practical application. At present, China's LNG storage and transportation system is continuously improving. Usually, special vessels or tank trucks are used to transport LNG, and gasification needs to be re-processed during use. In order to ensure the safety of LNG storage and transportation, it is necessary to scientifically and reasonably select and manage the valves, and strictly select and use them according to the relevant inspection standards to ensure that any node can meet the requirements of use and continuously improve storage. Safety factor for transportation and use.
1 Domestic and foreign relevant inspection standards 1.1 Domestic standards combined with the actual situation in China, the relevant departments of China have formulated the inspection standards for valves for LNG. At the end of the last century, China formulated the industry standard JB/T 7746-1995 for low temperature valves. Later, along with the continuous advancement and development of related technologies in China, China in August 2010 formulated the national standard GB/T24925-2010 for valves for liquefied natural gas. This standard refers to the terminology, technical requirements, structural types and inspection rules for cryogenic valves. And the test methods and other methods have been more detailed. This standard can be applied to many valve products for LNG, such as globe valves, cryogenic gate valves, ball valves, check valves and butterfly valves. The temperature range is from 196 degrees Celsius to minus 50 degrees Celsius. It should be said that The inspection and test temperatures for valves for LNG are covered.
1.2 Foreign Standards Today, there are two inspection standards for valves for LNG that are relatively popular abroad, one is the EU standard and the other is the British standard. Let me first talk about the EU standards. The European Union has developed a test standard specification EN 12567-2000 for valves for LNG. This standard mainly specifies the overall performance requirements of the isolation valves used in the production, storage and transportation of LNG. These isolation valves include both globe valves and gate valves, as well as butterfly valves and ball valves. The provisions include product testing. Product design, type testing and other aspects. This standard should be said to be the earliest in terms of the valve type test for liquefied natural gas. Second, let's talk about British standards. This standard mainly refers to BS 6364-1984. Since 1984, this standard has undergone four revisions, mainly to partially modify the ultra-low temperature test content of Appendix A. This standard has made provisions for the design, manufacture and test requirements of cryogenic valves, including both globe valves and gate valves, as well as ball valves, check valves and butterfly valves. This standard should be one of the earliest standards in the field of cryogenic valves. The current LNG valves are also referenced to the standard when designing, manufacturing and testing.
2 Methods specified in the inspection standard 2.1 External cooling method The BS 6364 standard specifies the external cooling test method. The method mainly relies on the method of immersing the valve body in the cooling medium to achieve the required test temperature. The method of detecting the performance of the valve. This method is mainly applied when the mass production valve is factory tested. This method is adopted when GB/T24925, ISO 28921-1 and EN 12567 are related to the inspection of valve products.
2.2 Internal Cooling Method The internal cooling method mainly refers to the method of injecting a cooling medium into the valve cavity to achieve the temperature required for the test. The EN 12567 standard makes such a provision that the valve life test should be carried out by internal cooling. Although the internal cooling method specified in the EN 12567 standard is more consistent with the actual situation of the LNG valve, the cooling medium specified in this standard can be liquefied natural gas. The outside of the valve and the pipeline during the test need to be wrapped with a layer of thermal insulation material. The thickness of the thermal insulating material is more than 160 mm, which increases the difficulty of practical operation to some extent.
3 Contents specified in the inspection standard 3.1 Selection of cooling medium In the process of testing the valve for liquefied natural gas by external cooling method, the cooling medium selected is generally liquid nitrogen. BS 6364 provides that the ultra-low temperature test should use liquid nitrogen to cool the test valve. The ISO 28921-1 standard specifies that liquid nitrogen should be used as the cooling medium if the test temperature reaches -196 degrees Celsius. If the test temperature is higher than -196 degrees Celsius, other cooling media can be used. The EN 12567 standard states that liquid nitrogen should be used as a cooling medium if the test temperature reaches -196 degrees Celsius. GB/T 24925 standard stipulates: According to the temperature requirements of low temperature valves, the cooling medium selected for the low temperature test can be either liquid nitrogen or a mixture of liquid nitrogen and alcohol.
3.2 High-pressure sealing requirements In order to be able to inspect the sealing performance of liquefied natural gas valves under ultra-low temperature conditions, the results obtained by high-pressure sealing tests are an important indicator. The requirements for high pressure seal test pressure at home and abroad are basically the same. The BS 6364 standard states that the maximum rated working pressure of the valve is the high pressure seal test pressure. ISO 28921-1 specifies that the high pressure seal test pressure is the maximum allowable working pressure. The EN 12567 standard states that the high pressure seal test pressure is the rated working pressure. China's standard GB/T 24925 stipulates that the high pressure seal test pressure of the valve for liquefied natural gas under low temperature conditions is the nominal pressure value. Because of the different operating conditions, this pressure value is generally lower than the high pressure seal test pressure value under normal temperature conditions.
references:
[1]Ni Kai, Chen Qinghua, Wu Zhenzhou, Deng Li.Characteristics and Application of Inner Leakage Sound Field of Natural Gas Pipeline Valves[J].Petrochemical Technology,2016(02).
Key words: valves for liquefied natural gas; inspection; temperature liquefied natural gas can be said to be one of the cleanest energy sources. The impact of liquefied natural gas on the environment after combustion is not very large, and it can basically meet the requirements of current enterprise green production, and has great advantages in practical application. At present, China's LNG storage and transportation system is continuously improving. Usually, special vessels or tank trucks are used to transport LNG, and gasification needs to be re-processed during use. In order to ensure the safety of LNG storage and transportation, it is necessary to scientifically and reasonably select and manage the valves, and strictly select and use them according to the relevant inspection standards to ensure that any node can meet the requirements of use and continuously improve storage. Safety factor for transportation and use.
1 Domestic and foreign relevant inspection standards 1.1 Domestic standards combined with the actual situation in China, the relevant departments of China have formulated the inspection standards for valves for LNG. At the end of the last century, China formulated the industry standard JB/T 7746-1995 for low temperature valves. Later, along with the continuous advancement and development of related technologies in China, China in August 2010 formulated the national standard GB/T24925-2010 for valves for liquefied natural gas. This standard refers to the terminology, technical requirements, structural types and inspection rules for cryogenic valves. And the test methods and other methods have been more detailed. This standard can be applied to many valve products for LNG, such as globe valves, cryogenic gate valves, ball valves, check valves and butterfly valves. The temperature range is from 196 degrees Celsius to minus 50 degrees Celsius. It should be said that The inspection and test temperatures for valves for LNG are covered.
1.2 Foreign Standards Today, there are two inspection standards for valves for LNG that are relatively popular abroad, one is the EU standard and the other is the British standard. Let me first talk about the EU standards. The European Union has developed a test standard specification EN 12567-2000 for valves for LNG. This standard mainly specifies the overall performance requirements of the isolation valves used in the production, storage and transportation of LNG. These isolation valves include both globe valves and gate valves, as well as butterfly valves and ball valves. The provisions include product testing. Product design, type testing and other aspects. This standard should be said to be the earliest in terms of the valve type test for liquefied natural gas. Second, let's talk about British standards. This standard mainly refers to BS 6364-1984. Since 1984, this standard has undergone four revisions, mainly to partially modify the ultra-low temperature test content of Appendix A. This standard has made provisions for the design, manufacture and test requirements of cryogenic valves, including both globe valves and gate valves, as well as ball valves, check valves and butterfly valves. This standard should be one of the earliest standards in the field of cryogenic valves. The current LNG valves are also referenced to the standard when designing, manufacturing and testing.
2 Methods specified in the inspection standard 2.1 External cooling method The BS 6364 standard specifies the external cooling test method. The method mainly relies on the method of immersing the valve body in the cooling medium to achieve the required test temperature. The method of detecting the performance of the valve. This method is mainly applied when the mass production valve is factory tested. This method is adopted when GB/T24925, ISO 28921-1 and EN 12567 are related to the inspection of valve products.
2.2 Internal Cooling Method The internal cooling method mainly refers to the method of injecting a cooling medium into the valve cavity to achieve the temperature required for the test. The EN 12567 standard makes such a provision that the valve life test should be carried out by internal cooling. Although the internal cooling method specified in the EN 12567 standard is more consistent with the actual situation of the LNG valve, the cooling medium specified in this standard can be liquefied natural gas. The outside of the valve and the pipeline during the test need to be wrapped with a layer of thermal insulation material. The thickness of the thermal insulating material is more than 160 mm, which increases the difficulty of practical operation to some extent.
3 Contents specified in the inspection standard 3.1 Selection of cooling medium In the process of testing the valve for liquefied natural gas by external cooling method, the cooling medium selected is generally liquid nitrogen. BS 6364 provides that the ultra-low temperature test should use liquid nitrogen to cool the test valve. The ISO 28921-1 standard specifies that liquid nitrogen should be used as the cooling medium if the test temperature reaches -196 degrees Celsius. If the test temperature is higher than -196 degrees Celsius, other cooling media can be used. The EN 12567 standard states that liquid nitrogen should be used as a cooling medium if the test temperature reaches -196 degrees Celsius. GB/T 24925 standard stipulates: According to the temperature requirements of low temperature valves, the cooling medium selected for the low temperature test can be either liquid nitrogen or a mixture of liquid nitrogen and alcohol.
3.2 High-pressure sealing requirements In order to be able to inspect the sealing performance of liquefied natural gas valves under ultra-low temperature conditions, the results obtained by high-pressure sealing tests are an important indicator. The requirements for high pressure seal test pressure at home and abroad are basically the same. The BS 6364 standard states that the maximum rated working pressure of the valve is the high pressure seal test pressure. ISO 28921-1 specifies that the high pressure seal test pressure is the maximum allowable working pressure. The EN 12567 standard states that the high pressure seal test pressure is the rated working pressure. China's standard GB/T 24925 stipulates that the high pressure seal test pressure of the valve for liquefied natural gas under low temperature conditions is the nominal pressure value. Because of the different operating conditions, this pressure value is generally lower than the high pressure seal test pressure value under normal temperature conditions.
references:
[1]Ni Kai, Chen Qinghua, Wu Zhenzhou, Deng Li.Characteristics and Application of Inner Leakage Sound Field of Natural Gas Pipeline Valves[J].Petrochemical Technology,2016(02).
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