Growing competitiveness in the launcher market is driving metallic propellant tanks toward tighter mass limits, increasing the need for reliable buckling prediction under combined axial compression and internal pressurization. Thin-walled cylinders are imperfection-sensitive, and current practice relies on conservative knockdown factors derived mainly from unpressurized tests. This work evaluates alternative nonlinear imperfection modeling approaches for pressurized launcher tank segments, with an emphasis on reliability and welding-induced imperfection signatures.

Five imperfection-sensitive strategies were assessed using NASA Shell Buckling Knockdown Factor Project cylinders at 0, 2, and 4 bar, including SPLA, MPLA, EIA, MGI, and a distributed-force perturbation approach (DFPA). Reliability was quantified using the coefficient of variation, Kendall’s W, and the intraclass correlation coefficient.

Results show that pressurization reduces imperfection sensitivity by increasing geometric stiffness. Distributed and multiple-perturbation methods were the most stable across pressures, whereas localized approaches exhibited strong pressure sensitivity. Accurate pressurized buckling prediction, therefore, requires pressure-aware imperfection mechanisms.
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