What is the API 641 standard?
API 641-2016 details the essential requirements and acceptance criteria for type testing of volatile organic compound (VOC) emissions from valves at a 1/4 turn. This standard explicitly states that valve type testing must comply with the EPA Method 21 regulations regarding the detection and assessment of VOC emissions. Furthermore, the scope of API 641 is clearly defined: valves with a nominal size not exceeding NPS 24, a pressure rating not exceeding Class 1500, and a pressure and temperature rating of 6.89 bar or higher.
Main Contents of API 641 Valve Testing
The core objective of API 641 valve testing is to verify the valve's sealing performance and structural integrity under high-temperature conditions. The test typically includes the following key steps:
(1) Fire Resistance Test: The valve is continuously exposed to a high-temperature flame for a certain period to test its ability to maintain a sealed state.
(2) Leakage Rate Detection: After the test, the valve's leakage rate is measured to ensure it meets the standard requirements.
(3) Operational Performance Verification: The valve's opening and closing function is tested to ensure it functions normally after high-temperature exposure.
During the test, API 641 stipulates that methane with a purity of at least 97% must be used as the test medium, and the suction gun method must be used for detection. During the test, the valve sealing system must not be adjusted in any way, and the dynamic and static leakage rates at each measurement point must be controlled within 0.01%. Furthermore, the tested valve must undergo 610 mechanical cycles and 3 thermal cycles, and the cycling process should begin at ambient temperature.
API 641 standard groups valves in detail according to their maximum temperature rating, classifying them into six groups, A to F, with 260°C as the dividing line. The standard also specifies corresponding test parameters for each group of valves, including Te, Pe, and Pa, to ensure the accuracy and reliability of the tests.
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