Principles and Considerations for Valve Pressure Testing

The production process for industrial valves combines both complexity and systemization, generally involving multiple stages from raw material preparation to final product testing. Common types of valves typically take about three days to manufacture. However, to ensure reliability and safety in real-world applications, finished valves must undergo rigorous performance testing, with pressure testing being among the most critical. Pressure testing is designed to verify whether an industrial valve can withstand its specified design pressure, ensuring its stability and safety. This article delves into four main areas: pressure testing principles, testing methods, operational guidelines, and key considerations.

Pressure Testing Principles and Preparation

The primary purpose of pressure testing is to confirm the valve's structural strength and sealing integrity. Specific requirements include the following aspects.

1. Strength Testing Requirements

Generally, finished valves do not require further strength tests. However, if the valve body or bonnet has undergone repairs or shows signs of corrosion damage, re-testing for strength is mandatory to ensure structural safety.

2. Special Valve Requirements

For special valves like safety valves, testing parameters such as set pressure and reseating pressure should strictly follow the product manual and relevant guidelines.

3. Pre-Installation Testing

Before installation, valves must be tested for strength and sealing. Low-pressure valves undergo sampling tests (20% sampled); if any fail, then 100% must be tested. Medium and high-pressure valves require 100% testing. During testing, the valve should be positioned to allow easy inspection for accuracy and convenience.

Testing Methods and Conditions

Various testing methods are used depending on the valve's connection type and pressure conditions.

1. Seal Testing for Welded Valves

For welded valves, if blind flange testing is impractical, alternative sealing options such as conical seals or O-rings can be used.

2. Hydraulic Testing

During hydraulic testing, ensure that all air is removed from the valve body. Pressure should be increased gradually to avoid damage or inaccurate results.

3. Test Duration

For strength and sealing tests, the standard duration is generally 2 to 3 minutes; for critical valves, it may be extended to 5 minutes for stability assurance. Small-diameter valves may have shorter test times, while larger valves require longer. If any uncertainty arises during testing, the duration can be extended for further validation.

Testing Requirements

Pressure testing consists primarily of strength and sealing tests, with specific requirements.

1. Strength Testing

During the test, there should be no leaks or "sweating" from the valve body or bonnet. If leaks occur, it indicates that the valve cannot withstand the expected pressure.

2. Sealing Testing

Standard valves typically require a single sealing test, but critical valves like safety and high-pressure valves may require two rounds to confirm sealing reliability. For low-pressure, large-diameter, and non-critical valves, slight leakage may be allowed within industry standards.

3. Throttle Valve Requirements

Throttle valves do not require sealing tests on the closure component but must be tested for strength and sealing of the packing and gaskets to ensure overall sealing performance.

Operational Guidelines and Special Considerations

During pressure testing, the following points should be observed.

1. Operating Standards

Only one person should close the valve during pressure testing using normal force, without extra leverage (torque wrenches are exceptions). If the handwheel diameter exceeds 320mm, two people may close it together.

2. Upper Seal Structure

If a valve has an upper seal structure, remove the packing before testing to check for leaks when the upper seal is closed. For gas tests, water can be added to the packing gland for easier observation.

3. Testing with Actuators

For valves with actuators, seal tests should be conducted using the actuator to close the valve, followed by a manual seal test if applicable.

4. Cast Iron Valve Inspection

During strength testing for cast iron valves, tapping the valve body and bonnet with a copper hammer can help detect leaks. If any leaks are found, further inspection is required.

Important Considerations

Attention to the following details during pressure testing ensures accuracy and protects the valve from potential damage.

Seal Surface Preparation: Apart from plug valves, other valves should not have oil applied to the sealing surfaces during testing, as this may affect results.
Blind Flange Pressure: The clamping force of the blind flange should not be excessive to avoid deformation or damage to the valve, especially for cast iron valves, which may crack under too much pressure.
Post-Test Cleaning: After testing, promptly drain and dry the valve body, ensuring cleanliness. Thoroughly document test results for traceability.

Conclusion

Valve manufacturing involves a complex series of steps, with pressure testing as a critical stage to confirm reliability and safety. Through strength and sealing tests, the structural integrity of the valve body and bonnet is verified, preventing potential issues caused by material weaknesses or seal failures. Strict testing requirements, standardized operational protocols, and specialized measures for certain valve types enhance durability and adaptability. Detailed records post-testing facilitate quality management and future maintenance traceability. Overall, standardized pressure testing procedures and careful operation are not only essential to ensuring valve quality but also foundational to achieving safe, long-lasting performance.