Research on Airtightness Test Device for CO2 Fracturing Device Filling Valve

Background and Technical Challenge

The filling valve of the CO2 fracturing device is a critical component that must maintain airtightness under high pressure conditions. Any leakage in the valve can result in underfilling of the device, leading to insufficient fracturing energy and potential operational failure. The airtightness of the valve is therefore a critical quality control parameter that must be verified before the device is deployed in the field. However, the airtightness testing of the filling valve is technically challenging due to the high operating pressure, the small size of the valve, and the need for precise pressure measurement and leakage detection. The development of a dedicated airtightness test device is therefore essential to ensure the reliability and safety of the CO2 fracturing operation.

Design Principles and Technical Specifications

The airtightness test device for the CO2 fracturing device filling valve is designed based on the principle of pressure decay testing. The valve is mounted on the test device, and the test chamber is pressurized to the maximum operating pressure of the valve, typically 16 to 20 MPa. The pressure is held constant for a specified duration, and the pressure decay is monitored by a high-precision pressure transducer. If the pressure decay exceeds a predefined threshold, the valve is considered to have failed the airtightness test. The test device must be capable of withstanding the maximum test pressure with a safety factor of at least 2.5, and the test chamber must be manufactured from high-strength steel with full-penetration welds inspected by ultrasonic testing.

Valve Structure and Failure Analysis

The filling valve of the CO2 fracturing device typically consists of a valve body, a valve seat, a valve stem, and a sealing element such as a PTFE or metal seal ring. The common failure modes include seal ring deformation, valve seat wear, thread leakage, and stem seal failure. A systematic FMEA (Failure Mode and Effects Analysis) of the valve assembly identifies the critical failure modes and their potential consequences. Seal ring deformation is the most common failure mode, typically caused by excessive pressure cycling or thermal cycling. Valve seat wear is caused by repeated opening and closing of the valve, and can be mitigated by using hardened valve seat materials. Thread leakage is caused by improper thread engagement or thread damage, and can be prevented by using thread sealant and proper assembly torque.

Test Procedure and Quality Control

The airtightness test procedure for the filling valve includes the following steps. First, the valve is cleaned and inspected for any visible damage. The valve is then mounted on the test device, and the test chamber is pressurized to the maximum operating pressure at a controlled rate of 1 to 2 MPa per second. The pressure is held constant for the specified duration, and the pressure decay is monitored by the pressure transducer. If the pressure decay exceeds the leakage threshold, the valve is removed and inspected for the source of the leakage. The valve is then repaired or replaced, and the test is repeated until the valve passes the airtightness requirement. The test results are recorded and archived for traceability, and the test device is calibrated at regular intervals to ensure measurement accuracy.

Study Insights and Recommendations

The development of a dedicated airtightness test device for the CO2 fracturing device filling valve is a critical step in ensuring the reliability and safety of the CO2 phase-change fracturing operation. The test device must be designed and fabricated with the same rigor as the fracturing device itself, with attention to material selection, welding quality, and pressure testing. The test procedure must be standardized and documented, with clear acceptance criteria and traceability requirements. Future improvements should focus on developing automated test systems that can perform the airtightness test quickly and accurately, reducing the testing time and improving the throughput of the production line. The integration of the test device with a data management system for real-time monitoring and quality tracking is also recommended to enhance the overall quality control of the fracturing device manufacturing process.