A Comprehensive Guide to Valve Hydrostatic Testing

In the industrial sector, valves are indispensable components, acting as the "goalkeepers" of piping systems and controlling the flow of fluids. However, the quality of valves directly affects the safety and reliability of the entire system. To ensure that valves can withstand the designed pressure, hydrostatic testing has become a crucial inspection process in valve manufacturing. This article will provide a detailed introduction to the necessity, standards, procedures, and precautions of valve hydrostatic testing, helping readers gain a comprehensive understanding of this vital inspection process.

Although the manufacturing process of valves may seem simple, every step is crucial. From globe valves, ball valves to butterfly valves, the production cycle of these common valve types generally takes about three days. After production is completed, valves must undergo a series of rigorous performance inspections, with hydrostatic testing being the core part. The main purpose of hydrostatic testing is to verify whether the valve can withstand the designed pressure and ensure that there will be no leakage or rupture hazards during actual use.

After understanding the necessity of valve hydrostatic testing, let's delve into the specific standards and precautions. These standards and precautions are the keys to ensuring the accuracy and safety of the test and are also the important basis for whether the valve can pass the inspection.

Generally, newly manufactured valves usually do not need to undergo strength testing. However, repaired oil circuit boards and check valves, or those that have been damaged by corrosion, must undergo strength testing. For valves, the set pressure and reseating pressure tests should comply with the requirements of the user manual and relevant standards.

After valve assembly is completed, strength and seal tests are required. For low-pressure valves, sampling inspection is usually adopted, with a sampling ratio of 20%. If the sampling inspection is unqualified, then a 100% inspection of all valves is required. For medium and high-pressure valves, a 100% inspection is mandatory.

When conducting the test, the assembled parts of the valve should be in a position that is convenient for inspection. For example, for valves with welded connections, if it is inconvenient to perform a hydrostatic test using a blind plate, a conical seal or O-ring seal can be used for the hydrostatic test.

During hydrostatic testing, gases inside the valve should be expelled as much as possible. When testing, the pressure should be increased slowly, and it is strictly forbidden to increase the pressure significantly and suddenly. The duration of strength and seal tests is usually 2-3 minutes. For important and special valves, the duration should be 5 minutes. The test time for small-diameter valves can be relatively shorter, while for large-diameter valves, the test time can be relatively longer. If there are doubts during the test, the test time can be extended.

During the strength test, there should be no leakage or sweating of the oil circuit board and check valve. The seal test is usually conducted once for general valves. However, for important valves such as globe valves and high-pressure valves, the test should be conducted twice. During the test, for low-pressure, large-diameter, and unimportant valves, as well as valves with permissible leakage requirements, a small amount of leakage is allowed. However, since different types of valves such as general-purpose valves, power plant valves, and marine valves have different requirements, the leakage requirements should be implemented in accordance with relevant regulations.

Check throttle valves do not require a closure member seal test, but they must undergo strength testing as well as seal tests at the packing and gasket locations. During the hydrostatic test, the closing force of the valve should only be the normal force of one person and should not rely on levers or other tools (except for torque wrenches). When the diameter of the main shaft exceeds 320mm, two people are allowed to close it simultaneously. For valves with an upper seal, the packing should be removed for the seal test. During the seal test, the upper seal should not be in the sealing position. For valves with actuators, when testing their seal performance, the valve should be closed using the actuator for the seal test. If the valve is closed by power, a seal test for the power-closed valve should also be conducted.

After the hydrostatic test is completed, the accumulated water inside the valve should be immediately removed and dried, and the test records should be kept. This is crucial for ensuring the long-term stable operation of the valve.

After clarifying the standards and precautions for hydrostatic testing, let's take a detailed look at the specific methods and procedures of the test.

The upper seal test is the first step in valve hydrostatic testing. First, close the inlet and outlet of the valve and loosen the packing gland (if the valve is equipped with an upper seal inspection device and the upper seal performance can be reliably checked without loosening the packing gland, there is no need to loosen the packing gland). The valve is in the fully open position, the upper seal is closed, the body cavity is filled with the test medium, and the pressure is gradually increased to the specified test pressure, followed by checking the upper seal performance.

The shell test is the second step in hydrostatic testing. Close the inlet and outlet of the valve, tighten the packing gland to maintain the test pressure, and place the closure member in a partially open position. Fill the body cavity with the test medium and gradually increase the pressure to the test pressure (for check valves, pressure should be applied from the inlet end), and then inspect the shell (including the packing box and the connection between the valve body and valve cover).

The seal test is the final step in hydrostatic testing. The pressurization methods for the main valve types are as follows:

Gate valves, ball valves, and plug valves: Close both ends of the valve, place the closure member in a slightly open position, fill the body cavity with the test medium, and gradually increase the pressure to the test pressure. Close the closure member and release the pressure at one end of the valve. The other end of the valve is pressurized in the same manner. For valves with two independent sealing pairs, the medium can also be introduced into the body cavity between the two sealing pairs and pressure applied.

Globe valves, diaphragm valves: Pressurize the closure member in the direction that is most unfavorable for seat sealing. For example, for globe valves and angle diaphragm valves, the medium should be introduced and pressure applied in the direction that opens the valve disc.

Butterfly valves: Introduce and apply pressure in the direction that is most unfavorable for sealing. For butterfly valves with symmetrical seats, pressure can be applied in either direction.

Check valves: Introduce and apply pressure in the direction that closes the valve disc.

After mastering the testing methods and procedures, let's explore the common problems that may be encountered during hydrostatic testing and the corresponding solutions.

If valve leakage is detected during the test, the test should be immediately stopped and the leakage point checked. Common leakage points include the packing box and the connection between the valve body and valve cover. If packing aging or damage is found, the packing should be replaced promptly. For the connection between the valve body and valve cover, check whether the bolts are tightened, and if necessary, retighten the bolts.

During the test, if the clamping force of the valve flange on the valve is too great, it may cause valve deformation and affect the test results. Especially for cast iron valves, if pressed too tightly, the valve may be damaged. Therefore, during the test, ensure that the clamping force of the valve flange is moderate.

When conducting a hydrostatic test, clean water should be used as the test medium as much as possible. If other liquids are used, ensure that the chemical properties of the liquid will not corrode the valve material. After the test, the test medium inside the valve should be immediately removed and the valve dried.

Valve hydrostatic testing is a crucial step in ensuring valve quality and safety. Through strict testing standards and procedures, the strength and sealing performance of the valve can be effectively tested to ensure its reliability in actual use. When conducting hydrostatic testing, pay attention to every detail of the testing process to ensure the accuracy and safety of the test. Only by passing the rigorous hydrostatic test can valves operate stably in various complex industrial environments, ensuring the safety and efficient operation of the entire system.