Perpustakaan Digital ITB

Fatigue integrity is a critical design factor in piping systems exposed to internal unsteady multiphase flow, as interfacial dynamics generate cyclic pressure loads that can accelerate structural damage. This study evaluates the fatigue response of a thin-walled L-shaped pipe carrying a gas-liquid internal flow by means of one-way CFD-to-FEA coupling. The flow field is computed using a transient pressure-based RANS solver in ANSYS Fluent, employing the VOF model for interface capturing and the standard ???? ? ???? model for turbulence closure without solving energy equation. Wall pressure time histories are then extracted from CFD and imparted onto the pipe walls using ANSYS Mechanical where the pipe structure is modeled using a linear-elastic shell formulation. The stress response is then processed using rainflow counting algorithm before the fatigue damage and life is computed using S-N approach while incorporating Basquin approximation, Modified Goodman mean stress correction and Palmgren-Miner linear damage accumulation. The analysis shows that the multiphase flow case generates higher stress amplitudes (up to approximately 5 MPa) compared to the singlephase equivalent (approximately 0.25 MPa mean fluctuation). Such loading results in no fatigue damage accumulation since the peak stress value on both cases falls under the steel’s endurance limit.