This study presents the structural reliability of rolled steel beams on offshore platforms exposed to corrosion during their design service period and beyond. The rate of corrosion of the rolled steel beam was determined using a standard expression for extreme marine environment. Limit equations were used to evaluate the shear performance, deflection, and resistance moment of the rolled steel beams during their design and service life. The exposure to corrosion was evaluated using the First Order Reliability Method (FORM) in MATLAB with FERUM Version 4.1 (Finite Element Reliability Using Matlab). An increasing decline in the shear, resistance moment and deflection was observed as the cross sectional area decreased due to corrosion, which is consistent with experimental data obtained from literature. However, it is also noted that the design formulation is very robust and sufficient to exceed the design life prediction in the relevant deign code. It is no wonder that oil companies involved in exploration while using steel offshore platforms and other structures in sub-sea and upland marine environments do exceed the design lie recommended for the structures.