Subsea pipelines typically rely on In-Line Inspection (ILI) to monitor corrosion and support mechanical integrity programs. However, many subsea pipelines and risers are unpiggable due to design constraints, operational conditions such as deposits, or malfunctioning subsea valves. This leads to a heavy reliance on corrosion inhibitors and predictive corrosion models without the opportunity for direct inspection validation. In such cases, integrity programs are often reactive, initiated only in response to unplanned events rather than as a proactive strategy to identify and efficiently mitigate corrosion-related risks.

This paper presents a case study of an unpiggable deepwater riser that has never undergone inspection. Corrosion modelling and laboratory data indicated the potential for significant internal corrosion, prompting the need for inspection. Combined with corrosion and flow assurance analyses, statistical methods were used to plan an inspection campaign using advanced radiographic computed tomography (CT) technology. The CT system’s performance was validated in the shop prior to the completion of the subsea inspection. After inspection, the data was analyzed and extrapolated to assess the overall condition of the riser. The analysis from the CT campaign was also correlated with corrosion lab test results to add confidence to the integrity assessment. This study demonstrated an opportunity to enhance the safety and maintenance of unpiggable pipelines through a data-driven approach using advanced nondestructive evaluation.