Keywords: threaded pipe joint, contact pressure, connectivity criterion, leakage channel, low temperature, finite element analysis.

To address the gas leakage problem of threaded pipe joints in a train brake pipeline under low-temperature service conditions, a three-dimensional finite element contact model of a conventional threaded pipe joint was established in this study. Since the gap value directly obtained from finite element analysis is insufficient to accurately characterize the actual leakage opening and the risk of through-leakage paths, a leakage channel identification method based on a contact-pressure connectivity criterion was proposed. The results show that, with increasing tightening torque, the high-pressure regions on the threaded contact surface gradually expand and form locally continuous compressed zones, which effectively weaken the connectivity of low-pressure regions. Under low-torque conditions, the low-pressure regions are more likely to form continuous leakage paths in both the circumferential and axial directions. Compared with the room-temperature condition, low temperature causes redistribution of the contact state, enlarges the candidate leakage regions, and significantly increases the number of leakage elements, the equivalent leakage area, and the equivalent flow index. The proposed criterion overcomes the limitations of a single gap-based criterion, which is sensitive to local numerical values and cannot effectively determine the connectivity of leakage paths. The method provides a reference for leakage risk assessment and assembly parameter optimization of conventional threaded pipe joints under low-temperature conditions.

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