Integrity management of unpiggable pipelines remains a significant challenge for operators. While some of these pipelines can be made piggable through customized in-line inspection (ILI) approaches, alternative assessment methods are needed when ILI is not feasible or when a preliminary screening is required before further inspection.

Non-Intrusive Pipeline Assessment (NIPA) is an above-ground integrity analysis methodology designed for unpiggable pipelines. It integrates and overlays data from construction and operational records, Large Stand-off Magnetometry (LSM), Cathodic Protection (CP), and Geographic Information Systems (GIS). Through combining multiple datasets, NIPA enhances confidence in anomaly detection, both internally and externally, allowing for Fitness for Purpose (FFP) assessments, repair scheduling, and Estimated Remaining Life (ERL) evaluations.

A key concern with any non-intrusive method is the reliability of indirect (above-ground) analysis. This paper presents a case study comparing the performance of NIPA to conventional ILI methods. The trial was conducted blindly, with NIPA analysis – comprising above-ground inspections, data overlay, and interpretation – completed before the ILI results were revealed.

Key performance metrics such as Probability of Detection (PoD), anomaly location, and severity were analysed. The results were highly favourable, with NIPA achieving an overall PoD of 88% and a 100% PoD for defects greater than 60% of wall thickness. While smaller anomalies may have been overlooked, the methodology demonstrated a high level of confidence in detecting large, critical defects, making NIPA a viable alternative for assessing unpiggable pipelines.