Abstract
ABSTRACT
Metal‐sealed bolted flange connections are critical in well‐control surface facilities, where cyclic loads may induce bolt loosening, leakage, and sealing failure. This study investigated the failure behavior of 6BX metal‐sealed flange connections under cyclic loading using field vibration measurement, finite element simulation, vibration loading tests, magnetic bolt‐stress monitoring, and microscopic surface characterization. Simulations showed that coupled axial and transverse vibration caused non‐uniform bolt stress redistribution and localized gasket contact‐stress concentration. Experiments under a 50 kN preload showed that loading amplitude had a stronger effect than frequency on bolt loosening and leakage‐rate increase. The leakage response lagged behind bolt loosening, indicating that interfacial wear accumulation controlled leakage‐path formation. SEM and surface‐profile analyses confirmed fretting wear, plastic deformation, spallation, and debris accumulation on the sealing surface. Critical bolt‐loosening rates and allowable cycle numbers were determined, providing guidance for reliability assessment and failure prevention in metal‐sealed flange connections.