Perpustakaan Digital ITB

The second-stage regeneration gas heater (RGH) in liquefied natural gas processing facilities experiences severe cyclic thermal and pressure loading. This cyclic operation with an U-bend support construction introduces a structural restraints at tube bundle, restricting thermal expansion and causing low-cycle thermal fatigue. Removing these restraints elevates the susceptibility to destructive vibration. This research aims to evaluate the thermomechanical integrity and vibration susceptibilities of the RGH and formulate structural improvements that mitigate both failure risks without penalizing the design rating. The research utilized a stepwise empirical baseline model to extract steady-state temperatures. These loads were applied to a structural finite element method incorporating a multilinear kinematic hardening material model to resolve cyclic plastic strains. Fatigue life was quantified using the Coffin-Manson relationship and Americal Society of Mechanical Engineers criteria. A three-dimensional finite volume method then resolved localized crossflow velocities. Dynamic stability was assessed by integrating these hydrodynamic loads with values extracted from the structural modal analysis. The restrained baseline design exhibits an insufficient allowable life of 289 to 773 cycles due to severe plastic deformation at the tube intrados. Removing the U-bend support safely reduced localized stresses but left the structure vulnerable to vortex shedding resonance. An improved design was proposed to resolve these competing failures by eliminating the U-bend constraints and installing an intermediate support at the outlet midspan. This improvement reduced the vibration susceptibility, indicated by the vortex shedding ratio from 1.32 to 0.38, ensuring the component satisfies its operational design life.