In Indonesia, corrosion-induced structural degradation, especially in the splash zone, is posing a growing threat to aging offshore jacket platforms, many of which have been in operation for more than 20 years. This deterioration significantly compromises the structural integrity of the platforms and reduces their capacity to sustain heavy environmental loads. The Reserve Strength Ratio (RSR) was examined under simulated corrosion conditions (10–50% thickness loss in 1–4 members) in the important environmental load directions (90°, 180°, 270°, and 315°). With RSR falling to 1.002 during severe corrosion (25% thickness loss in four members), the results showed that 180° was the most vulnerable direction, exceeding the API RP 2A safety standard (RSR < 1.6). Without intervention, temporal projections predict structural breakdown in 17 years, based on a corrosion rate of 0.127 mm/year.