Wenzhou Unique Valve Co., Ltd.
High Temperature and High-pressure Wear Resistant Ball Valves (Part Two)
Apr 12, 2021
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3. Finite element analyses
Before the design of valves is finalized, the stress field and temperature field of the valve must be comprehensively analyzed by the finite element.
3.1 Stress analyses of valve bodies and spheres
Through simulation calculation, the equivalent stress distribution diagram of the inner wall of the valve body is obtained, as shown in Figure 6. The maximum equivalent stress of the inner wall of the valve is distributed at the inlet and outlet flow passages, and the maximum equivalent stress is about 185MPa. The equivalent stress of the remaining parts of the inner wall of the valve is relatively small, which is less than the stress specified by the standard.
Figure 6 Stress distribution on the inner wall of the valve
(1) Analysis results of the stress of the valve body
It can be seen from Figure 6 that the maximum stress of the valve body is distributed at the inlet end of the flow passage and the valve stem's hole; the maximum equivalent stress is about 153MPa; the equivalent stress of the rest of the valve body wall is relatively small, which is less than the stress specified by the standard.
(2) The analysis results of the sphere are shown in Figure 6. The maximum stress of the sphere is distributed in the flow channel, and the maximum equivalent stress is about 109MPa. The equivalent stress of the rest of the valve body wall is relatively small, which is less than the stress specified by the standard.
3.2 Stress analyses of valve stems
(1) Equivalent stress analyses of valve stems
Through simulation calculation, the cloud diagram of the equivalent stress distribution of the valve stem is obtained, as shown in Figure 7. The maximum equivalent stress of the valve stem is distributed at the upper end; the maximum equivalent stress is about 275.09MPa, and the equivalent stress of the remaining parts is small, which is lower than the allowable stress.
Figure 7 Stress distribution diagrams of valve stems
(2) A cloud diagram of the shear stress distribution of the stem is obtained after simulation calculation. The maximum shear stress of the valve stem is 66.366MPa, which is lower than the allowable shear stress of the material.
3.3 Analyses of the temperature field
The valve is in contact with the medium in the closed state, and the heat exchange reaches the equilibrium state. The maximum temperature of the wall surface of the valve body in contact with the medium is 550℃ in the middle cavity of the valve body, and the lowest temperature is 190℃ at the outlet flange. The distribution of the temperature field on the inner wall of the valve is shown in Figure 8.
Figure 8 The temperature field of the inner wall of the valve
4. Inspecting and testing
The wear resistant ball valve is installed on the key device of residual oil hydrogenation catalysis; working conditions of media are harsh, and it is a substitute for imported wear resistant ball valves. Therefore, the following three types of tests should be carried out before the ball valve leaves the factory:
(1) Perform pressure test according to API598 standard before the ball valve leaves the factory.
(2) Conduct cold and hot alternating cycle tests.
(3) Carry out static pressure life tests.
4.1 Performing pressure test before the ball valve leaving the factory
According to the API 598 standard, perform the shell hydraulic strength test, high pressure liquid sealing test, low pressure gas sealing test at room temperature, and also carry out opening and closing tests with media and without media for 5 times respectively to observe whether there is jamming. Use the torque wrench with digital display to test opening and closing torque, and records the maximum values for opening and closing torque respectively. At room temperature, a helium mass-spectrometer leak detector should be used in accordance with the ISO 15848-2 standard. Check the helium leakage values at connecting parts of valve bodies, bonnets and stuffing boxes of valve stems, which should meet the standard requirements of Level B.
4.2 The cold and hot alternating cycle test for ball valves
The fluidized bed residue hydrogenation unit is mainly divided into two parts: the first is the reaction part, and the second is the catalyst online addition and discharge part. The temperature between 150°C and 453°C and pressure from 0MPa to 19.94MPa alternate for the second part, so the wear resistant ball valve should be subjected to a cold and hot alternating cycle test. The content and method of the cold state test (at room temperature) are the same as those of the pressure test of valves before leaving the factory, and the hot state test is more complicated. The devices for the hot state test consist of a valve heating system, a pressure system, and a measurement and control system (Figure 9). The valve heating system is composed of a high temperature box heated by resistance wire and a valve pushing mechanism. The pressure system consists of gas cylinders, bus bars, pressure regulating devices, booster pumps, high-pressure pipelines, etc. The measurement and control system is comprised of a sensing unit, an acquisition control unit, a control loop, and a human computer interface.
1. Heating boxes 2. Tested valves 3. Pressure boost mechanisms 4. Power supply cabinets 5. Control cabinets
Figure 9 Devices for the hot state test for valves
When the valve is subjected to a hot state test, first install a blind plate for pressure testing of the valve, and then place a temperature sensor in the valve cavity, stuffing box and box. Connect the other end to the control cabinet. When the temperature in the valve body rises to the set temperature, keep the temperature and conduct an opening and closing test to test the opening and closing torque for valves without media. Then fill the valve with nitrogen or air at a rated pressure to conduct an opening and closing test to test the opening and closing torque for valves with media. Conduct a pressure sealing test at the inlet and outlet ends. Measure the leakage amount of the valve seat at the inlet and outlet ends by a flowmeter. After the test, take out the valve and make it cool to room temperature, and perform various tests according to the API 598 standard, including the opening and closing test, torque test with media and without media as well as low leakage test. The ball valve should be tested in such a cold and hot alternating cycle 3 times to complete the tests.
4.3 Static pressure life tests for valves
The high-frequency ball valve used for the reaction filter of the S-zorb device has an opening and closing of 25,000 to 30,000 times/a. Therefore, when valves with a DN smaller than or equal to 50, it is best to perform the static pressure lifetime according to the JB/T 8861 standard. Many manufacturers have static pressure life testing equipment, and professional inspection and test systems can also be used to make reasonable judgments on the product structure, material selection, and hardening effect of the sealing surface.
5. Conclusion
With the improvement of petrochemical technology, the application fields of wear resistant ball valves have gradually expanded. The ball valve with medium pressure is widely used in catalytic cracking, continuous reforming, and S-zorb catalytic desulfurization units, while the ball valve with high pressure is mainly used in fluidized bed hydrogenation and slurry bed hydrogenation, suspended bed hydrogenation, fixed bed hydrogenation and coal gasification, coal liquefaction and coal tar hydrogenation. Moreover, it is also much applied to industries such as polysilicon, mineral and paper industry.
Before the design of valves is finalized, the stress field and temperature field of the valve must be comprehensively analyzed by the finite element.
3.1 Stress analyses of valve bodies and spheres
Through simulation calculation, the equivalent stress distribution diagram of the inner wall of the valve body is obtained, as shown in Figure 6. The maximum equivalent stress of the inner wall of the valve is distributed at the inlet and outlet flow passages, and the maximum equivalent stress is about 185MPa. The equivalent stress of the remaining parts of the inner wall of the valve is relatively small, which is less than the stress specified by the standard.
Figure 6 Stress distribution on the inner wall of the valve
(1) Analysis results of the stress of the valve body
It can be seen from Figure 6 that the maximum stress of the valve body is distributed at the inlet end of the flow passage and the valve stem's hole; the maximum equivalent stress is about 153MPa; the equivalent stress of the rest of the valve body wall is relatively small, which is less than the stress specified by the standard.
(2) The analysis results of the sphere are shown in Figure 6. The maximum stress of the sphere is distributed in the flow channel, and the maximum equivalent stress is about 109MPa. The equivalent stress of the rest of the valve body wall is relatively small, which is less than the stress specified by the standard.
3.2 Stress analyses of valve stems
(1) Equivalent stress analyses of valve stems
Through simulation calculation, the cloud diagram of the equivalent stress distribution of the valve stem is obtained, as shown in Figure 7. The maximum equivalent stress of the valve stem is distributed at the upper end; the maximum equivalent stress is about 275.09MPa, and the equivalent stress of the remaining parts is small, which is lower than the allowable stress.
Figure 7 Stress distribution diagrams of valve stems
(2) A cloud diagram of the shear stress distribution of the stem is obtained after simulation calculation. The maximum shear stress of the valve stem is 66.366MPa, which is lower than the allowable shear stress of the material.
3.3 Analyses of the temperature field
The valve is in contact with the medium in the closed state, and the heat exchange reaches the equilibrium state. The maximum temperature of the wall surface of the valve body in contact with the medium is 550℃ in the middle cavity of the valve body, and the lowest temperature is 190℃ at the outlet flange. The distribution of the temperature field on the inner wall of the valve is shown in Figure 8.
Figure 8 The temperature field of the inner wall of the valve
4. Inspecting and testing
The wear resistant ball valve is installed on the key device of residual oil hydrogenation catalysis; working conditions of media are harsh, and it is a substitute for imported wear resistant ball valves. Therefore, the following three types of tests should be carried out before the ball valve leaves the factory:
(1) Perform pressure test according to API598 standard before the ball valve leaves the factory.
(2) Conduct cold and hot alternating cycle tests.
(3) Carry out static pressure life tests.
4.1 Performing pressure test before the ball valve leaving the factory
According to the API 598 standard, perform the shell hydraulic strength test, high pressure liquid sealing test, low pressure gas sealing test at room temperature, and also carry out opening and closing tests with media and without media for 5 times respectively to observe whether there is jamming. Use the torque wrench with digital display to test opening and closing torque, and records the maximum values for opening and closing torque respectively. At room temperature, a helium mass-spectrometer leak detector should be used in accordance with the ISO 15848-2 standard. Check the helium leakage values at connecting parts of valve bodies, bonnets and stuffing boxes of valve stems, which should meet the standard requirements of Level B.
4.2 The cold and hot alternating cycle test for ball valves
The fluidized bed residue hydrogenation unit is mainly divided into two parts: the first is the reaction part, and the second is the catalyst online addition and discharge part. The temperature between 150°C and 453°C and pressure from 0MPa to 19.94MPa alternate for the second part, so the wear resistant ball valve should be subjected to a cold and hot alternating cycle test. The content and method of the cold state test (at room temperature) are the same as those of the pressure test of valves before leaving the factory, and the hot state test is more complicated. The devices for the hot state test consist of a valve heating system, a pressure system, and a measurement and control system (Figure 9). The valve heating system is composed of a high temperature box heated by resistance wire and a valve pushing mechanism. The pressure system consists of gas cylinders, bus bars, pressure regulating devices, booster pumps, high-pressure pipelines, etc. The measurement and control system is comprised of a sensing unit, an acquisition control unit, a control loop, and a human computer interface.
1. Heating boxes 2. Tested valves 3. Pressure boost mechanisms 4. Power supply cabinets 5. Control cabinets
Figure 9 Devices for the hot state test for valves
When the valve is subjected to a hot state test, first install a blind plate for pressure testing of the valve, and then place a temperature sensor in the valve cavity, stuffing box and box. Connect the other end to the control cabinet. When the temperature in the valve body rises to the set temperature, keep the temperature and conduct an opening and closing test to test the opening and closing torque for valves without media. Then fill the valve with nitrogen or air at a rated pressure to conduct an opening and closing test to test the opening and closing torque for valves with media. Conduct a pressure sealing test at the inlet and outlet ends. Measure the leakage amount of the valve seat at the inlet and outlet ends by a flowmeter. After the test, take out the valve and make it cool to room temperature, and perform various tests according to the API 598 standard, including the opening and closing test, torque test with media and without media as well as low leakage test. The ball valve should be tested in such a cold and hot alternating cycle 3 times to complete the tests.
4.3 Static pressure life tests for valves
The high-frequency ball valve used for the reaction filter of the S-zorb device has an opening and closing of 25,000 to 30,000 times/a. Therefore, when valves with a DN smaller than or equal to 50, it is best to perform the static pressure lifetime according to the JB/T 8861 standard. Many manufacturers have static pressure life testing equipment, and professional inspection and test systems can also be used to make reasonable judgments on the product structure, material selection, and hardening effect of the sealing surface.
5. Conclusion
With the improvement of petrochemical technology, the application fields of wear resistant ball valves have gradually expanded. The ball valve with medium pressure is widely used in catalytic cracking, continuous reforming, and S-zorb catalytic desulfurization units, while the ball valve with high pressure is mainly used in fluidized bed hydrogenation and slurry bed hydrogenation, suspended bed hydrogenation, fixed bed hydrogenation and coal gasification, coal liquefaction and coal tar hydrogenation. Moreover, it is also much applied to industries such as polysilicon, mineral and paper industry.
