Hot and Cold Performance Tests of Valves (Part Two)

Hot and Cold Performance Tests of Valves (Part Two)


3.1.2 Cold sealing performance tests
The sealing performance test of the valve is generally divided into high-pressure sealing and low-pressure sealing performance tests. The test pressure of the high-pressure sealing test is 1.1 times the maximum allowable working pressure of the valve at 38°C or the maximum allowable working pressure difference. The test media can be water, air or low-viscosity non-corrosive liquid. It should be noted that when the actual medium used is gas, nitrogen and other inert media. The pressure strength test using water as the medium should be completed first, and then the valve body sealing test using gas should be performed; low-pressure sealing test pressure is usually between 0.4MPa to 0.7MPa, and the test medium is inert gases such as air and nitrogen. The low-pressure sealing test items can be carried out according to the regulations in TSG D7002, Table 1. In the actual test process, after the valve is installed in the test system, the test should be carried out in the order of high-pressure sealing test first and then low-pressure sealing test. At the same time, valves with an upper sealing structure should also be subjected to an upper sealing test.
 
Table 1 Sealing test items of valves and cryogenic valves at normal temperatures
Projects  Types of valves
Gate valves Globe valves Plug valves Floating ball valves Butterfly valves and trunnion ball valves Check valves Diaphragm valves and plug valves
Low-pressure sealing Must Must Must Must Must \\ \\
High-pressure sealing Must Must Must Must Must Must Must
DN less than and equal to 100mm, PN greater than 25MPa or DN greater than and equal to 125mm, PN greater than 10MPa
Projects  Types of valves
Gate valves Globe valves Plug valves Floating ball valves
 
 
 
 
Must
Trunnion ball valves Check valves
Low-pressure sealing \\ \\ \\ Must \\
High-pressure sealing Must Must Must Must Must
 
3.1.3 Cold action tests and opening and closing response time tests
The cold action performance test is to verify whether the opening and closing operations of the valve meet the specified requirements when the valve is under pressure. For pneumatic or electric valves, the valve's opening and closing action time should also be tested. During the test, the valve is first installed in the test system, so that the test medium circulates inside the valve and is pressurized. When the pressure increases to the test pressure, close the valve and start timing. When the valve is fully opened, the time for the half cycle stroke is recorded as the valve's closing time. Then relieve the pressure on one side of the valve closing member, establish the rated pressure difference of the valve according to the specified fluid direction of the valve, and then open the valve and time it. It is not necessary to maintain the pressure difference after the closing member leaves the valve seat. Record each time when the valve is completely closed. The measured value of the stroke time of half a cycle is the opening time of the valve. During each test, you should carefully observe whether the valve operates smoothly, there is any jamming, the movement time meets the design requirements, and whether there is obvious wear on the valve stem and other movable parts. In addition, after completing the action test of the valve, the sealing performance test of the valve should be carried out again as required.
 
3.1.4 Cold action life tests
The cold action life test is to verify the safety and reliability of the valve throughout its life cycle. The valve is installed in the test pipeline so that the medium flows in a certain direction, and at the same time, the valve is opened, closed and opened at a certain frequency. The action cycles a certain number of times, and each half cycle should be at least 80% of the rated stroke. When the valve is operated, check whether the valve moves smoothly and there is any jamming. After the test, the wear of the valve stem and other movable parts should be checked and perform sealing performance test.
 
3.2 Thermal cycle tests
After passing the cold test, in order to verify the performance of the valve when it is operated under high temperature and high pressure, it is necessary to conduct a hot performance test on the valve. Thermal performance testing refers to the corresponding performance testing of the valve under the working condition where the medium temperature is greater than 120°C. The thermal testing is to identify whether the valve meets the requirements during actual use by simulating the working conditions of high temperature and high pressure. Before the test, first, clean the valve and testing pipeline to remove possible impurities, and then place the valve on the testing pipeline to keep the valve at a certain opening position; turn on the electric heating device and the testing pipeline circulation pump to allow the testing medium to flow in the pipeline, and at the same time slowly increase the temperature of the testing pipeline and the valve to be tested, ensuring that the temperature distribution in the testing pipeline is relatively uniform to reduce thermal stress. When the temperature of the testing medium reaches the requirements for the test and the valve body's surface temperature is stable, the thermal cycle function test can be started.
 
3.2.1 Hot sealing performance tests
The thermal sealing performance test is to verify whether the sealing performance of the valve meets the specified requirements under high temperature and high pressure. During the test, the test medium is circulated inside the valve and the valve is opened and closed several times to determine whether the valve operates normally under high temperature. After the valve is opened and closed normally, slowly close the valve and open the booster system. The valve pressure is raised to the test pressure, and the pressure is relieved on the closed side of the valve. After the pressure is relieved to 0MPa, the globe valve of the pipeline at the rear end of the valve is closed and maintained for some time. Record and observe the changes in the pressure on the closed side of the valve during the pressure holding period to initially judge the sealing condition of the valve under hot conditions. If the pressure behind the valve does not change within the specified time, it means that the sealing performance is good. If it does not meet the specified requirements, the test should be repeated and recorded as the basis for evaluating the sealing performance. After the test is completed, open the globe valve in the pipeline at the rear end of the valve; open the valve to a certain opening and slowly release the pressure.
 
3.2.2 Thermal action tests and opening and closing response time tests
The thermal action performance test is to test the valve's ability to operate under unfavorable conditions such as temperature and pressure. The thermal action test of the valve should be carried out after passing the thermal sealing performance test. The thermal action performance test should be carried out after the specified temperature in the hot state. Let the valve close under the specified pressure, and open under the specified pressure difference. After each action, carefully observe whether the movement of the valve stem is smooth, the wear and tear of the valve stem and other moving parts, and record the pressure values before and after opening and closing, as well as the opening and closing time of the valve every time, which are used to determine whether the basic operating performance of the valve meets the requirements.
 
3.2.3 Thermal operating life tests
The thermal operating life test is to detect the operability and sealing performance of the aging of the valve after long-term action under actual use conditions, as well as the mechanical action aging performance of each component of the valve body. In the thermal operating life test, the temperature and pressure specified in the test should always be maintained, so that the valve performs cyclic actions at a certain frequency, and after the valve operates to a certain number of times, the cycle can be suspended and the valve's intermediate sealing performance can be tested. If the sealing is good, continue the test, and retest the sealing performance of the valve again after the cycle reaches the specified number of times. If an abnormal situation occurs or the sealing performance does not meet the requirements, the test should be stopped and the situation recorded during the test.
 
3.3 Cold tests after hot tests
After the valve's thermal test is completed, turn off the electric heating device in the system to maintain a certain opening of the valve body and maintain the operation of the circulation pump to allow the medium to flow in the pipeline. At the same time, use the cooling device of the system to cool down the system pipeline. When the temperature of the system returns to normal temperature, the operating performance and sealing performance of the valve should be tested again according to the requirements specified in the cold state to eliminate the impact of cold shrinkage of various components in the valve body caused by the reduction from high temperature to low temperature.