Hot and Cold Performance Tests of Valves (Part One)

Hot and Cold Performance Tests of Valves (Part One)


Abstract: valves usually need to work under high temperature and high pressure in many industrial fields such as petroleum, chemical industry, and nuclear power. Testing the performance of valves by simulating the actual working conditions of the valves is of great significance to ensure the quality of valves. A test system and its working principle for testing cold and hot working conditions of valves are introduced in this article. The testing methods and evaluation indicators of the basic performance of valves under cold and hot working conditions are explained, aiming to provide valuable information for valves and provide references for the development of testing equipment and testing technology under cold and hot conditions.
 
1. Overview
A valve is a common device used for opening and closing, flow control and safety protection of pipelines. It plays a very important role in industrial production, process control and other fields. Its function, effect and reliability are directly related to the reliability of unit operation. In recent years, with the continuous improvement of technology in process industries such as petroleum, chemical industry, electric power and metallurgy, the use conditions of valves have become more and more complex, and the requirements for the valve’s performance have become more and more stringent. Therefore, it is very necessary to study the safety and reliability of valves. Among them, in the fields of nuclear power and the petrochemical industry, valves usually work under high temperatures and high pressure. To ensure that the valve can work normally during actual operation and that the various performances of the valve can meet the requirements of standard specifications, preliminary debugging and testing of valves have become extremely important. The test of the valve can be divided into two test conditions: the hot state and the cold state according to the test temperature. Generally, the valve test condition with a temperature greater than 120°C is called a hot test, while the test performed at normal temperature is called a cold test. To verify the reliability of the nuclear ball valve developed by Dalian University of Technology, Jianbo Chen conducted cold and hot tests on the valve to confirm that the valve design meets nuclear standards. To verify whether the main steam safety valve ACP1000 of the nuclear island can meet the requirements, Minghai Fu and others from the Shanghai Special Equipment Supervision and Inspection Technology Research Institute conducted cold and hot tests.
 
In summary, in many fields such as nuclear power and chemical industry, cold and hot testing of valves is very important to ensure the reliability of valves and is an important means to reflect the performance of valves under actual working conditions. However, there is currently relatively little research on the cold and hot testing methods of valves in China. Therefore, the cold and hot testing test benches and the testing methods of valves in cold and hot states are explained in this article.
 
2. Hot and cold cycle test systems
2.1 Test devices
The valve thermal test system can meet the cold cycle function test and hot cycle function test of the valve at the same time (Figure 1). It adopts a closed cycle structure as a whole, which mainly consists of high-temperature water tanks, circulating water pumps, booster pumps, components to be tested, temperature and pressure sensors and electrical control systems. Among them, the high-temperature water tank is mainly used to store and heat the test medium, usually deionized water, and is equipped with electric adding devices and sensor devices such as temperature, pressure and liquid level; circulating water pumps and booster pumps are mainly used to pressurize and deliver the test medium that has been heated to the temperature and pressure required by the test conditions to the valve under test to simulate the actual operating conditions of the valve. The temperature and pressure sensor and electrical control system are used to test the temperature and pressure sensors of the test system, and the operation of water pumps and other electrical appliances in the system.
 
The main working process and principle of the test system are that before the test, install the valve to be tested in the system pipeline; keep the valve at a certain opening angle; inject the test medium into the system and raise the system pressure to the test working pressure to detect leaks, ensuring that the installation connection of the valve will not leak under the test pressure; the electric heating wire in the high-temperature and high-pressure water tank is used to heat the test medium, so that the temperature of the water in the water tank increases, and the circulating water pump is turned on at the same time. At the same time, turn on the circulating water pump to circulate the heated water to the valve to be tested and preheat the valve.
 
until the sub-temperature in the high-temperature and high-pressure water storage tank rises to the test working condition, continue to circulate until the valve temperature rises to the test working condition; wait until the valve surface temperature rises to the test temperature, the booster pump in the pipeline is turned on to pressurize the water in the pipeline. The pressurized high-temperature and high-pressure water flows to the valve to be tested, and the hot state test of the valve is started.
 
After the valve test is completed, turn off all electric heaters, maintain the operation of the medium circulation pump, and use the cooler to cool down and depressurize the loop system. By controlling the cooling system, the temperature reduction rate of the pipeline and the measured valve body is adjusted to reduce the thermal stress generated in the cooling process. When the temperature and pressure of the medium in the pipeline are close to normal temperature and pressure, turn off the medium circulation pump, remove the valve under test and clean the pipeline to prepare for the next valve test.

Thermal test systems of valves 
1. High-temperature and high-pressure water tanks 2. Electric heating wire 3. Liquid level controllers 4. Temperature and pressure sensors 5. Globe valves 6. Circulating water pumps 7. Flow meters 8. Booster water pumps 9. Globe valves 10. Temperature and pressure sensors 11. Tested valves 12. Temperature and pressure sensors 13. Globe valves 14. Check valves
Figure 1 Thermal test systems of valves

2.2 Arrangement of measuring points
In this test system, the layout and selection of measuring points are more important. The main measuring points are temperature, pressure, liquid level and flow measuring points. Among them, temperature, pressure and liquid level measuring points are arranged in the water storage tank. Temperature and pressure measuring points real-time monitoring and feedback of the temperature and pressure in the water storage tank ensures that the temperature and pressure in the water storage tank reach the test conditions; the liquid level measuring point is used to feedback the water level in the water storage tank to prevent safety hazards caused by too high or too low water levels; flow measuring points are arranged in the pipe to provide feedback on the flow rate of the pipeline in the test system; temperature and pressure measuring points are arranged before and after the pipeline in the valve to be tested to determine that the temperature and pressure before and after the valve meet the test conditions in the test process. The layout of the main measuring points is shown in Figure 1.
 
3. Test trials
3.1 Cold cycle tests
Before conducting hot cycle testing, the valve usually needs to be cold cycle tested. The cold cycle test is mainly a type of test of the valve under normal temperature to ensure the reliability of the valve operation. The cold cycle test can identify whether the valve meets the basic design requirements and whether the valve and its components perform well under normal temperatures. At the same time, the cold cycle test also prepares the valve for testing under a hot state. Shortens the test time, and improves the test efficiency of the valve. The cold cycle function test mainly includes valve pressure performance tests, action performance tests, sealing performance tests, service life tests and other tests.
 
3. 1. 1 Pressure resistance performance test in a cold state
The pressure resistance performance test of the valve is also called the valve body (shell) pressure resistance strength test. It is a performance test to detect the pressure resistance of the valve. When conducting a pressure performance test on a valve, the opening and closing parts of the valve should first be opened; the air in the valve cavity should be removed, and the test medium with a temperature not higher than 58°C should be introduced into the valve body in the direction of the valve inlet, while close the other end of the valve body and increase the test medium pressure to 1.5 times the maximum allowable working pressure of the valve at 38°C, so that the valve cavity and internal components of the valve body can withstand pressure for no less than 3 minutes. During the pressure holding period of the test, no visible liquid or surface moisture is allowed on the surface of the valve body and the sealing joints. After the test is completed, slowly unload the pressure inside the valve body and check whether there is any permanent deformation in the appearance of the inside and outside of the valve and the joints.