1. Appearance inspection
Valve body and sealing surface inspection
Directly observe whether there are sand holes, cracks or corrosion defects on the surface of the valve body, check the flatness of the sealing surface (carbide/stainless steel material), and confirm that there are no scratches, wear or deformation;
Use an endoscope or microscope to assist in checking the microscopic damage in the contact area of the sealing surface to avoid potential leakage risks that are invisible to the naked eye.
2. Static inspection
Hydraulic pressure test
After closing the valve, connect it to the test pipeline, fill it with water and pressurize it to 1.5 times the rated pressure (such as PN40 valve pressurized to 60Bar), maintain the pressure for 10-15 minutes, and observe whether the pressure gauge is stable and leak-free;
Focus on checking the leakage of the flange connection, valve stem stuffing box and valve body welding parts.
Air pressure test
Use compressed air or nitrogen as the medium, pressurize it to 1.1 times the rated pressure, and detect the leakage point of the sealing surface by applying soapy water or using a helium mass spectrometer, with a sensitivity of up to 10^-6 mbar·L/s;
Applicable to working conditions that avoid water media or need to detect small leaks.
3. Dynamic detection
Switch operation and flow detection
Open and close the valve repeatedly (≥100 times), measure the leakage flow in the fully closed state, and require the leakage rate to be ≤0.01% of the rated flow;
Use a flow meter to monitor the residual amount of medium in the closed state to verify whether the sealing surface fits the standard.
Pressure fluctuation test
Perform 5-10 rapid pressure increase/depressurization cycles within the rated pressure range (such as PN16~PN64) to observe whether the sealing performance decreases due to pressure shock.
4. Material performance verification
Hardness and chemical composition analysis
Perform Rockwell hardness test on the sealing surface (hard alloy should be ≥HRC60) to ensure that the wear resistance meets the working conditions;
Use a spectrometer to detect the composition of the sealing material (such as tungsten carbide, 316 stainless steel) to eliminate the sealing failure caused by substandard materials.
Corrosion resistance test
For acidic or high-salt media, immerse the valve in the simulated medium for 72 hours to observe whether the corrosion rate of the sealing surface exceeds 0.1mm/year.
V. Other auxiliary tests
Low temperature/high temperature adaptability test
Perform a sealing test at extreme temperatures of -40℃ or 425℃ to verify the compatibility of the thermal expansion coefficient of the sealing material with the valve body;
High temperature conditions require additional inspection of the oxidation and decarburization of the sealing surface.
Torque and operating force detection
Use a torque wrench to measure the opening and closing torque. If it exceeds the design value (such as DN50 valve ≤50N·m), it may indicate excessive wear or assembly deviation of the sealing surface.
Qualification standards and judgment basis
Conventional leakage rate: The pressure drop during the water pressure/air pressure test is ≤5%, and there is no visible leakage;
Extreme working condition requirements: Nuclear power plants and other scenes need to pass helium mass spectrometry leak detection (leakage rate ≤1×10^-9 mbar·L/s);
Material properties: The hardness error of the sealing surface is ≤±2HRC, and the deviation of the chemical composition from the standard value is ≤0.5%.
Selection suggestion: It is preferred to use a combination of water pressure + helium mass spectrometry to take into account both cost and accuracy; dynamic cycle testing is required for strong corrosion or high temperature scenes.