A comprehensive corrosion assessment has been done to ensure the integrity of 24 inch outside diameter (OD) and 70 km length of transmission pipeline against production figure changes during and beyond of the initial design life. By design, the pipeline was intended to transport the wet gas for 20years design life with medium level of top of line and bottom of line corrosion likelihood. During operation, the pipeline was operated to sustain gas rate more than the designed capacity. Which commonly known as de-bottlenecking. In consequence, the corrosion likelihood increased as obtained from the inspection result. When the initial design life is almost over, the new reserves combining oil and wet gas is found thus the life extension assessment shall be accommodated. This paper summarizes the engineering study methodology and the results, thus the pipeline integrity able to synchronize the fit for purpose and production operation excellence.