Type testing of cryogenic valves in pressure piping components

Cryogenic valves, including gate valves, globe valves, ball valves, check valves, and butterfly valves, are crucial in industries dealing with extremely low temperatures. The type testing of these valves involves a series of technical reviews and stringent inspection procedures to ensure their reliability and safety under such conditions.

Cryogenic gate valve

1.Technical Document Review

The review of technical documents covers several key areas:

（1）Design Conditions: This includes the operating conditions, product standards, and any special technical requirements for specific applications.

（2）Material Selection: The suitability of materials used for the valve body, closure elements, and other parts, as well as their compliance with design conditions, is thoroughly evaluated.

（3）Sealing Structure: The design and material selection for the sealing components must align with the specified design conditions.

（4）Strength Verification: This includes checking the strength of the valve body, connections, closure elements, and operating components. When standards do not specify values, calculations are made to verify strength and operating forces or torques.

（5）Forming and Technical Requirements: The manufacturing methods for the valve body materials, such as casting and forging, and their defect acceptance levels, are critically assessed.

（6）Welding, Heat Treatment, and Nondestructive Testing: The correctness of technical requirements related to these processes is verified.

（7）Inspection and Testing Procedures: The accuracy of the procedures for inspecting and testing the valves is reviewed.

（8）Material Compatibility: The selection of materials for the valve body, bonnet, stem, and sealing elements is assessed for compatibility with cryogenic media.

（9）Mechanical Properties at Design Temperature: The mechanical properties of metal materials at the design temperature are evaluated.

（10）Overpressure Protection: The structure to prevent overpressure and leakage upon a temperature rise in the cryogenic media is examined.

2.Inspection and Testing Items

The type testing of cryogenic valves includes the following inspections and tests:

（1）Visual and Marking Inspection: Ensuring the valve’s appearance and markings meet standards.

（2）Mechanical Properties: For iron bodies, the mechanical properties are tested, while the chemical composition is checked for other materials.

（3）Dimensional Checks: Minimum wall thickness of the valve body, stem diameter, thread dimensions of connection studs, and the dimensions of closure assembly connections are measured.

（4）Strength and Sealing Tests: These tests verify the valve’s ability to withstand pressure and maintain a proper seal.

（5）Operation Tests at Room Temperature: Valves are operated under pressure for a specified number of cycles to ensure functionality. For instance, solenoid valves are operated 100 times under pressure, while check valves are operated 20 times unloaded.

（6）Tensile Test for Steel Gate Valves: A tensile test is conducted on closure assemblies of nominal diameter DN ≤ 200mm and nominal pressure PN ≤ 16.0MPa.

（7）Hardness of Sealing Surfaces: After alloy welding, the hardness of the sealing surfaces on gate valves, globe valves, check valves, butterfly valves, and metal-sealed ball valves is tested.

（8）Antistatic Performance Test: If applicable, this test is conducted to ensure the valve’s safety.

（9）Vibration Resistance Test: This test is performed when required.

（10）Fugitive Emissions Test: This test is conducted if the valve stem uses a bellows sealing structure.

（11）Cryogenic Testing: Valves undergo testing in cryogenic environments, including operation and sealing tests at the design temperature.

（12）Post-Test Sealing and Leak Test: After returning to room temperature, the valve undergoes a final sealing and leak test.

3.Sampling Rules

Sampling for type testing follows these guidelines:

Sample Selection: Two different specifications are selected from products with similar structures, with a minimum sampling base of five units. If only one specification is produced, one unit is selected for testing.

High-Pressure and Large Diameter Valves: For valves with PN ≥ 10MPa and PN × DN ≥ 5000 MPa·mm or DN ≥ 1000mm, at least two units are sampled.

4.Coverage

The coverage of the type test must meet the following conditions:

（1）Specification and Pressure Rating Coverage: When PN ≤ 4.0MPa, PN* ≤ 4.0MPa, DN* ≤ 2DN. For PN > 4.0MPa, PN* ≤ PN, DN* ≤ 2DN.

（2）Temperature Rating Coverage: The lowest covered temperature corresponds to the lowest design temperature of the type test sample.