The test pressure of the valve
Before leaving the factory, the valve will be pressure tested in accordance with relevant standards in the factory, including shell tests and sealing tests. The shell test is a pressure test of the entire valve shell formed by the connection of the valve body and the bonnet to test the sealing of the valve body and the bonnet and the pressure resistance of the entire shell including the connection between the valve body and the bonnet. The sealing test is used to check the sealing of the opening and closing parts and the sealing pair of the valve body. The medium of the valve pressure test can be liquid.
According to Article 4.7 of GB/T 13927-2008 " Pressure Tests for Industrial Valves", when the test medium is liquid, the test pressure of the valve shell is at least 1.5 times the maximum allowable working pressure of the valve at a temperature of 20°C. The test pressure of the valve sealing is at least 1.5 times that of the valve and 1.1 times the maximum working pressure is allowed at 20°C.
According to provisions 7.1 and 7.2 of GB/T 12224-2015 "General Requirements for Steel Valves", the test pressure of the valve shell shall not be lower than 1.5 times the pressure rating at 38°C, and the value shall be 0.1 MPa. The valve should be in a partially open state. After the shell test, the valve should be subjected to a sealing test, and the test pressure should be 1.1 times the pressure rating at 38°C. The valve should be in a closed state during the sealing test; water, kerosene or other suitable liquids with a viscosity not greater than water should be selected. The test medium is carried out at temperatures between 5 to 50°C. According to the above standards, when the valve is closed, the maximum pressure it can withstand is the sealing test pressure of the valve. Once this pressure value is exceeded, the valve sealing may be damaged and the valve may leak.
3. A comparison of test pressures between pipelines and valves
The test pressure of the first part of the strength test of the pipeline system hydrostatic test is 1.5 times the design pressure, which is consistent with the shell test pressure of 1.5 times the maximum working pressure in the valve factory before leaving the factory. The test pressure of the sealing test of the second part of the pipeline system hydrostatic test is 1.0 times the design pressure, which is slightly lower than the valve sealing test pressure which is 1.1 times the maximum working pressure.
When carrying out the hydraulic test of the piping system in the actual project, the first part of the strength test shall be carried out first, and the test pressure shall be 1.5 times the design pressure. The air release valve is in the open state, and the valve can withstand the hydraulic test pressure. However, the water discharge and air release valve is in a closed state at this time, and the test pressure of 1.5 times exceeds the valve sealing test pressure, which may cause damage to the sealing and leakage of valves.
Taking the condensate pipeline of a project as an example, the design parameter of the pipeline is 3.62MPa at a temperature of 50°C, and the hydraulic test pressure of the pipeline is 1.5 times the design pressure (5.43MPa). There is a Z41H-40 main shut-off valve on the condensate pipe, and a J41H-40 water discharge and air release valve. The main shut-off valve and water and air release valve have been subjected to shell tests and sealing tests according to the requirements in GB/T 12224-2015 before leaving the factory. During the shell test, the valve can withstand a test pressure of at least 6.12MPa, that is, 1.5 times of 4.08MPa. During the shell test, the valve is in a partially open state. During the sealing test, the valve can withstand a test pressure of at least 4.49MPa, that is, 1.1 times of 4.08MPa. During the sealing test, the valve is in a closed state.
During the hydrostatic test for the strength of the pipeline system, the main shut-off valve is in an open state. Since the test pressure of the valve shell (6.12MPa) is higher than the hydraulic test pressure (5.43MPa), the main shut-off valve can withstand the hydrostatic test. As for the water and air release valve, it is in a closed state at this time. Since the hydraulic test pressure (5.43MPa) exceeds the valve sealing test pressure (4.49MPa), the valve seal may be damaged and the valve may leak, resulting in failures of hydraulic tests. To avoid the above situation, when selecting the water and air release valve, the sealing test pressure of the water and air release valve should be considered. The selection parameter of the water discharge and air release valve is increased to 4.94 MPa at a temperature of 50°C. The model of the water discharge and air release valve is increased to J41H-63. The sealing test pressure of the water discharge and air release valve is greater than the strength water pressure test of the pipeline system, and the strength water pressure test of the pipeline system can be carried out.
Conclusion
When the hydrostatic test of the piping system is carried out after the installation of steam-water pipelines in thermal power plants, the water and air release valves in the piping system are in the closed state at this time, and the test pressure of 1.5 times exceeds the valve sealing test pressure, which may cause the valve seal to be damaged and the valve to leak, leading to the failure of the hydrostatic test. Therefore, the selection of the pressure level of the water discharge and air release valve for the hydraulic test of the thermal power plant should not only consider the design parameters, but also comprehensively consider the sealing test pressure of the water release and air release valve and the hydraulic test requirements of the piping system.
Before leaving the factory, the valve will be pressure tested in accordance with relevant standards in the factory, including shell tests and sealing tests. The shell test is a pressure test of the entire valve shell formed by the connection of the valve body and the bonnet to test the sealing of the valve body and the bonnet and the pressure resistance of the entire shell including the connection between the valve body and the bonnet. The sealing test is used to check the sealing of the opening and closing parts and the sealing pair of the valve body. The medium of the valve pressure test can be liquid.
According to Article 4.7 of GB/T 13927-2008 " Pressure Tests for Industrial Valves", when the test medium is liquid, the test pressure of the valve shell is at least 1.5 times the maximum allowable working pressure of the valve at a temperature of 20°C. The test pressure of the valve sealing is at least 1.5 times that of the valve and 1.1 times the maximum working pressure is allowed at 20°C.
According to provisions 7.1 and 7.2 of GB/T 12224-2015 "General Requirements for Steel Valves", the test pressure of the valve shell shall not be lower than 1.5 times the pressure rating at 38°C, and the value shall be 0.1 MPa. The valve should be in a partially open state. After the shell test, the valve should be subjected to a sealing test, and the test pressure should be 1.1 times the pressure rating at 38°C. The valve should be in a closed state during the sealing test; water, kerosene or other suitable liquids with a viscosity not greater than water should be selected. The test medium is carried out at temperatures between 5 to 50°C. According to the above standards, when the valve is closed, the maximum pressure it can withstand is the sealing test pressure of the valve. Once this pressure value is exceeded, the valve sealing may be damaged and the valve may leak.
3. A comparison of test pressures between pipelines and valves
The test pressure of the first part of the strength test of the pipeline system hydrostatic test is 1.5 times the design pressure, which is consistent with the shell test pressure of 1.5 times the maximum working pressure in the valve factory before leaving the factory. The test pressure of the sealing test of the second part of the pipeline system hydrostatic test is 1.0 times the design pressure, which is slightly lower than the valve sealing test pressure which is 1.1 times the maximum working pressure.
When carrying out the hydraulic test of the piping system in the actual project, the first part of the strength test shall be carried out first, and the test pressure shall be 1.5 times the design pressure. The air release valve is in the open state, and the valve can withstand the hydraulic test pressure. However, the water discharge and air release valve is in a closed state at this time, and the test pressure of 1.5 times exceeds the valve sealing test pressure, which may cause damage to the sealing and leakage of valves.
Taking the condensate pipeline of a project as an example, the design parameter of the pipeline is 3.62MPa at a temperature of 50°C, and the hydraulic test pressure of the pipeline is 1.5 times the design pressure (5.43MPa). There is a Z41H-40 main shut-off valve on the condensate pipe, and a J41H-40 water discharge and air release valve. The main shut-off valve and water and air release valve have been subjected to shell tests and sealing tests according to the requirements in GB/T 12224-2015 before leaving the factory. During the shell test, the valve can withstand a test pressure of at least 6.12MPa, that is, 1.5 times of 4.08MPa. During the shell test, the valve is in a partially open state. During the sealing test, the valve can withstand a test pressure of at least 4.49MPa, that is, 1.1 times of 4.08MPa. During the sealing test, the valve is in a closed state.
During the hydrostatic test for the strength of the pipeline system, the main shut-off valve is in an open state. Since the test pressure of the valve shell (6.12MPa) is higher than the hydraulic test pressure (5.43MPa), the main shut-off valve can withstand the hydrostatic test. As for the water and air release valve, it is in a closed state at this time. Since the hydraulic test pressure (5.43MPa) exceeds the valve sealing test pressure (4.49MPa), the valve seal may be damaged and the valve may leak, resulting in failures of hydraulic tests. To avoid the above situation, when selecting the water and air release valve, the sealing test pressure of the water and air release valve should be considered. The selection parameter of the water discharge and air release valve is increased to 4.94 MPa at a temperature of 50°C. The model of the water discharge and air release valve is increased to J41H-63. The sealing test pressure of the water discharge and air release valve is greater than the strength water pressure test of the pipeline system, and the strength water pressure test of the pipeline system can be carried out.
Conclusion
When the hydrostatic test of the piping system is carried out after the installation of steam-water pipelines in thermal power plants, the water and air release valves in the piping system are in the closed state at this time, and the test pressure of 1.5 times exceeds the valve sealing test pressure, which may cause the valve seal to be damaged and the valve to leak, leading to the failure of the hydrostatic test. Therefore, the selection of the pressure level of the water discharge and air release valve for the hydraulic test of the thermal power plant should not only consider the design parameters, but also comprehensively consider the sealing test pressure of the water release and air release valve and the hydraulic test requirements of the piping system.
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