What is the standard test for cryogenic valves?
The standard test of cryogenic valve mainly focuses on material performance, sealing, pressure resistance and low temperature stability, the core basis is MSS SP-134 and other specifications, the specific test content is as follows:
1. Core test items
Air tightness test:
Seat sealing test is carried out in low temperature environment (e.g. -196℃), and helium gas is required as the medium, applying ≥1.1 times the nominal pressure to ensure no leakage.
Valves need to be pre-cooled to the target temperature in liquid nitrogen to verify the accuracy of the sealing surface fit (e.g. roundness error ≤ 0.01mm).
Material low temperature impact test:
Charpy V-notch impact test on the valve body, valve seat and other key components, requiring impact work ≥ 27J, to ensure that the material is not brittle fracture at low temperatures.
Pressure strength test:
Shell strength test at room temperature, pressure ≥ 1.5 times the nominal pressure for 1 minute without deformation or leakage.
Temperature cycling test:
Simulate extreme working conditions through liquid nitrogen rapid cooling and rewarming to verify the stability of valve structure and sealing durability.
2. Standard basis and scope of application
MSS SP-134:
MSS SP-134: Define the definition of low-temperature valves (applicable temperature -100℃~-195℃), standardise the design of valve body / bonnet extension, sealing structure and test medium (e.g. liquid nitrogen, helium).
MIL-STD-810F:
MIL-STD-810F is a U.S. military standard for environmental testing of cryogenic valves in the military field, including temperature shock, vibration and other composite conditions.
ASTM D7437-07:
Low-temperature performance test for non-metallic sealing materials (e.g. PTFE, flexible graphite) to evaluate their resistance to shrinkage and wear.
3. Test procedure and conditions
Test medium:
Liquid nitrogen (-196°C) or liquid argon (-186°C) is used to simulate extreme low temperature environment.
Structural requirements:
The valve cover should be designed as a long neck structure to ensure that the temperature at the bottom of the stuffing box is ≥0℃ to avoid freezing of the seals.
Metal+non-metal composite seal should be adopted between valve seat and ball/gate to enhance the reliability of low-temperature sealing.
Operation verification:
Test the opening and closing torque of the valve under low-temperature working conditions, requiring flexible operation and no jamming.
4. Special requirements and judgement criteria
Material selection:
Valve body commonly used LCB, LC3 and other low-temperature carbon steel, ball selection of 304/316 stainless steel, modified PTFE or graphite sealing surface to enhance low-temperature performance.
Test report:
Need to record the pre-cooling time, temperature uniformity, leakage and other key data, and based on MSS SP-134 to determine compliance.
Summary: The U.S. cryogenic valve standard test is based on MSS SP-134 as the core, covering material impact toughness, helium sealing, compressive strength and temperature cycling verification, which is suitable for LNG, chemical and other harsh working conditions.
