Floating production systems are intended to remain on station throughout the field life, although fatigue and corrosion degradation modes are a major concern. Systems and components with limited access to inspection require innovative solutions with the deployment of alternate examination techniques and tools to verify the facility’s integrity. The Cascade and Chinook floating, production, storage and offloading vessel (FPSO) is located in the Walker Ridge area of the US Gulf of Mexico. Installed in 2010, it was the first FPSO in the Gulf of Mexico. The FPSO is provided with a disconnectable turret system moored at 8,200 feet water depth. Evaluation of the turret-buoy (TB) internal structure’s condition is not only important to confirm its integrity, but also to estimate the system’s overall remaining service life. Of particular interest within this structure are the ballast tanks, which do not have internal paint or anodes. To assess the condition of the TB’s bottom plate, the team chose to inspect using the phased array ultra-sonic testing (PAUT) method. The first inspection, performed in May 2018, covered a larger area and no significant uniform corrosion was found at the time, although three indications were identified and considered worth monitoring. In 2023 a new PAUT inspection was performed to monitor these indications and re-assess any further corrosion progress. The presentation describes the inspection tools and results, as well as how this sophisticated inspection method provided an assessment of probable origins of indication and the extent of the ballast tanks’ internal corrosion through external inspections. The use of such a technique, along with proper knowledge of the manufacturing process, can change the way inner tank surfaces in floating structures are inspected.