<p>A persistent challenge in the oil industry is internal corrosion in pipelines that convey oil, water, and gas. In offshore operations, a cost-effective strategy to reduce maintenance and limit the replacement of saltwater-carrying pipe sections employs carbon steel pipes lined internally with high-density polyethylene (HDPE), hereafter referred to as a liner. However, dissolved gases in the flow, such as CO₂, H₂S, and O₂, can permeate through the coating, leading to interfacial detachment and eventual displacement. This study introduces a novel methodology based on ultrasonic A-Scan signal analysis for the direct, non-destructive evaluation of HDPE liner integrity stages in carbon steel pipelines. Departing from current practices that rely on liner service-life estimation, the proposed technique demonstrates the feasibility of distinguishing between regions of integrity, detachment, and displacement based on characteristic variations in ultrasonic signal behavior. Using this diagnostic criterion, a multichannel inspection tool was developed, comprising a circumferential collar of ultrasonic transducers that enables a full-circumference assessment of liner condition within a targeted section. Implementing this tool can reduce unplanned production shutdowns on FPSO platforms, lower corrective maintenance costs, and enable the scheduled replacement of compromised pipeline segments before corrosion-induced clogging or leakage occurs.</p>