This thesis investigates the structural and sealing performance of large-diameter, preload-dominated flange joints used in low-pressure vessel applications. In conventional design, standardized flange dimensions are often applied even when operating pressures are low. However, for such applications, the structural response is primarily governed by the bolt preload required for gasket seating rather than internal pressure. This study aims to evaluate the feasibility of reducing flange thickness to minimize material consumption and manufacturing costs while maintaining structural integrity and sealing reliability. The research was conducted using a parametric finite element study. A baseline configuration, based on an existing industrial design with a flange thickness of 40 mm, was first analysed. Subsequently, four additional configurations were evaluated with thickness reductions in 5 mm increments down to 20 mm. The evaluation criteria were based on allowable von Mises stress in the flange hub transition region (≤ 140 MPa) and a target gasket contact pressure range (10–40 MPa) across the inner and outer gasket diameters. The results show that flange thickness significantly influences stress distribution and flange rotation. For the baseline case (40 mm), the evaluation criteria were satisfied within a bolt preload interval of 20–25 kN. As thickness was reduced, the structural stresses in the hub region increased, and the contact pressure distribution became increasingly sensitive to flange rotation. Specifically, thinner configurations reached the allowable stress limit at lower preload levels, narrowing the window for acceptable operation. The results indicate that the flange thickness could be reduced to 30 mm while still maintaining an operational window, whereas further reduction significantly compromised the structural integrity. The study concludes that while standardized dimensions provide a high level of conservatism, significant thickness reductions are limited by the requirement to maintain uniform gasket compression without exceeding material yield limits. The findings suggest that acceptable preload intervals can serve as an effective metric for evaluating the feasibility of slimmer flange designs in preload-dominated applications.