To determine whether a Double Flange Butterfly Valve is qualified, it is necessary to focus on four core dimensions: core performance, structural integrity, standard compliance, and installation adaptability, and verify it in the process of "appearance inspection - performance testing - standard verification". The details are as follows:

1. Basic Appearance and Structural Inspection

Valve Body and Flanges: The sealing surface of the flange shall be flat and free of damage; the valve body shall be free of casting defects; the coating shall be uniform and the marks shall be clear. The size and position of the flange bolt holes shall comply with standards, and the center distance error shall be within the allowable range to ensure alignment with the pipeline.

Internal Components: The surface of the valve disc shall be flat and fit evenly with the sealing surface; the valve stem shall be free of bending and rust, rotate flexibly, and be firmly connected to the valve disc with no damaged packing. The driving components shall operate without jamming or abnormal noise, and the full-open/full-close positioning shall be accurate.

2. Key Performance Testing

Sealing Performance: It is divided into valve seat sealing test and packing sealing test. Clean water is used for normal temperature conditions, and simulated medium or inert gas is used for high-temperature and high-pressure conditions. The test pressure is 1.1 times the nominal pressure (two-way sealing requires pressure application from both ends), and the pressure is maintained for 10-60 minutes (adjusted according to temperature). Qualification criteria: No visible leakage on the sealing surface and no seepage from the valve stem.

Strength Performance: Using clean water as the medium, the test pressure is 1.5 times the nominal pressure, and the pressure is maintained for 10-20 minutes. Qualification criteria: No cracks or leakage on the valve body and flanges, no permanent deformation, and no loose bolts.

Operational Performance: Use a torque wrench to measure the full-open/full-close torque, which shall be ≤ the value specified by the manufacturer and the torque curve shall be stable. Open and close continuously for 5-10 times without jamming; the rotation angle of the valve stem shall match the opening degree, and the limit positioning shall be accurate. For special working conditions, high and low temperature adaptability shall be tested, with a torque change rate of ≤ 20% and qualified sealing performance.

3. Standard Compliance Verification

Flange Standards: The connection size shall comply with corresponding standards such as ISO 7005-1 and ANSI B16.5 to avoid leakage caused by mixed use.

Material Compliance: The materials of the valve body (ductile iron, stainless steel, etc.) and sealing surface (soft/hard seal) shall meet the design requirements, with material certificates provided, and match the characteristics of the medium.

Certification and Marking: The valve shall have corresponding certifications such as ISO 9001 and API. The valve body shall be marked with nominal diameter, pressure, material and other information, which shall be consistent with the qualification certificate.

4. On-site Installation Adaptability

Size Adaptability: The length of the valve shall match the installation space; the flange bolt holes shall be aligned with the pipeline, and the bolts can be inserted smoothly.

Working Condition Adaptability: The rated parameters (pressure, temperature, etc.) shall cover the on-site working conditions.

Component Adaptability: For valves with actuators, the connection shall be firm and the signal transmission shall be normal.

Summary

A qualified double flange butterfly valve must meet the three requirements of "no obvious defects, up-to-standard performance, and compliance with adaptation". Through the above steps, a comprehensive judgment can be made to avoid failures of the pipeline system.