3. Analysis of low-pressure sealing test standards for check valves
3.1 Requirements in the Chinese standard system
In the current national standard system, the main regulations related to check valves include GB/T 13932-2016 Iron Swing Check Valves and GBT 13927-2008 Pressure Tests for Industrial Valves. GB/T 13932-2016 section 5.2 Pressure Test stipulates that the shell's strength test and sealing performance test of the check valve shall be carried out in accordance with the method specified in GB/T 13927-2008. Table 3 in section 5.3.2 of GB/T 13927-2008 clearly indicates that fill the valve with test medium and gradually increase the pressure to the specified test pressure after block the outlet end of the check valve when the valve disc is at a close state; check for leakage at the inlet end. The so-called test pressure refers to 1.1 times the maximum allowable working pressure of the valve at a temperature of 20°C according to provisions in section 4.7.3.1 in the GB/T 13927-2008 standard. It can be seen that in the current national standard system, the sealing requirements for check valves only involve the high-pressure sealing test under normal pressure conditions, and there is no requirement for the sealing under low pressure conditions.
3.2 Requirements in the American Standardized System
In the current American standardized system, the main standards related to check valves include ASME B16.34-1996, MSS SP-61-2019, and API 598-2016. Taking section 7.2 of ASME B16.34-1996 used in the design document in the case as an example, the sealing test of the valve is required to be carried out at 1.1 times the rated pressure at a temperature of 37.8℃, but at the same time, the requirements for the sealing test changing with many different applications are pointed out. For guidance on this content, you can check MSS SP-61-2019 and API 598-2016.
In section 5.1.1 of MSS SP-61-201941, the sealing test of the valve is required to be carried out at 1.1 times the rated pressure at a temperature of 37.8℃ and at the pressure of 0.5bar, which is in line with ASME B16.34-1996. There is also no requirement for low-pressure differential sealing tests. However, in Table 1 of API 598-201651, the high-pressure sealing test, low-pressure sealing test, and upper sealing test are classified in detail, and it is clear that the check valve needs to be subjected to a high-pressure sealing test. For check valves, the low-pressure sealing test is optional but not necessary, and pressure requirements for the specific sealing test can be carried out between 0.4 and 0.7MPa according to Table 3. Check Table 4 for the duration of the sealing test, and Table 5 the maximum allowable leakage rate of the sealing test. It can be seen that the original designer's attention to Section 7.2 in ASME B16.34-1996 and API 598 was not enough in the treatment of the aforementioned problems.
3.3 Requirements in other standardized systems
After learning, European standards paid attention to this issue earlier. Regarding the relevant requirements for check valves, clause 5.2.2.2 of EN 1074-3:200061 stipulates that the test requirements for sealing tests of check valves' seats under low pressure difference shall be in accordance with section 5.2.2.2 of EN 1074-1:20007. Among them, the test time should be in accordance with the provisions of section 5.2.2.1 in EN 1074-1:2000. In EN 1074-1:2000 section 5.2.2, the sealing of seats clearly divided into high-pressure sealing (section 5.2.2.1) and low-pressure sealing (section 5.2.2.2). It is also pointed out that the low pressure differential sealing test pressure of the check valve should be below 0.05MPa, and the other test requirements are equivalent to the provisions in section 5.2.2.1.
4. Conclusion
From the comparison of the aforementioned problems and standards, it can be seen that the staff need long-term industrial practice and pay close attention to the needs of users in order to solve the problem of low-pressure sealing test of the check valve in time. Advanced industrial standards such as API 598-2016 and EN 1074 should be considered for the follow-up design for check valves on the basis of meeting national standards. However, it should be noted that these standards are quite different, and some contents even conflict with each other. The design standards should be selected selectively in the light of the actual situation. In addition, the relevant manufacturers should speed up the research and development of the required low-pressure sealing test device, so as to further improve the low-pressure sealing performance of the swing check valve.
3.1 Requirements in the Chinese standard system
In the current national standard system, the main regulations related to check valves include GB/T 13932-2016 Iron Swing Check Valves and GBT 13927-2008 Pressure Tests for Industrial Valves. GB/T 13932-2016 section 5.2 Pressure Test stipulates that the shell's strength test and sealing performance test of the check valve shall be carried out in accordance with the method specified in GB/T 13927-2008. Table 3 in section 5.3.2 of GB/T 13927-2008 clearly indicates that fill the valve with test medium and gradually increase the pressure to the specified test pressure after block the outlet end of the check valve when the valve disc is at a close state; check for leakage at the inlet end. The so-called test pressure refers to 1.1 times the maximum allowable working pressure of the valve at a temperature of 20°C according to provisions in section 4.7.3.1 in the GB/T 13927-2008 standard. It can be seen that in the current national standard system, the sealing requirements for check valves only involve the high-pressure sealing test under normal pressure conditions, and there is no requirement for the sealing under low pressure conditions.
3.2 Requirements in the American Standardized System
In the current American standardized system, the main standards related to check valves include ASME B16.34-1996, MSS SP-61-2019, and API 598-2016. Taking section 7.2 of ASME B16.34-1996 used in the design document in the case as an example, the sealing test of the valve is required to be carried out at 1.1 times the rated pressure at a temperature of 37.8℃, but at the same time, the requirements for the sealing test changing with many different applications are pointed out. For guidance on this content, you can check MSS SP-61-2019 and API 598-2016.
In section 5.1.1 of MSS SP-61-201941, the sealing test of the valve is required to be carried out at 1.1 times the rated pressure at a temperature of 37.8℃ and at the pressure of 0.5bar, which is in line with ASME B16.34-1996. There is also no requirement for low-pressure differential sealing tests. However, in Table 1 of API 598-201651, the high-pressure sealing test, low-pressure sealing test, and upper sealing test are classified in detail, and it is clear that the check valve needs to be subjected to a high-pressure sealing test. For check valves, the low-pressure sealing test is optional but not necessary, and pressure requirements for the specific sealing test can be carried out between 0.4 and 0.7MPa according to Table 3. Check Table 4 for the duration of the sealing test, and Table 5 the maximum allowable leakage rate of the sealing test. It can be seen that the original designer's attention to Section 7.2 in ASME B16.34-1996 and API 598 was not enough in the treatment of the aforementioned problems.
3.3 Requirements in other standardized systems
After learning, European standards paid attention to this issue earlier. Regarding the relevant requirements for check valves, clause 5.2.2.2 of EN 1074-3:200061 stipulates that the test requirements for sealing tests of check valves' seats under low pressure difference shall be in accordance with section 5.2.2.2 of EN 1074-1:20007. Among them, the test time should be in accordance with the provisions of section 5.2.2.1 in EN 1074-1:2000. In EN 1074-1:2000 section 5.2.2, the sealing of seats clearly divided into high-pressure sealing (section 5.2.2.1) and low-pressure sealing (section 5.2.2.2). It is also pointed out that the low pressure differential sealing test pressure of the check valve should be below 0.05MPa, and the other test requirements are equivalent to the provisions in section 5.2.2.1.
4. Conclusion
From the comparison of the aforementioned problems and standards, it can be seen that the staff need long-term industrial practice and pay close attention to the needs of users in order to solve the problem of low-pressure sealing test of the check valve in time. Advanced industrial standards such as API 598-2016 and EN 1074 should be considered for the follow-up design for check valves on the basis of meeting national standards. However, it should be noted that these standards are quite different, and some contents even conflict with each other. The design standards should be selected selectively in the light of the actual situation. In addition, the relevant manufacturers should speed up the research and development of the required low-pressure sealing test device, so as to further improve the low-pressure sealing performance of the swing check valve.
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