High resolution magnetic flux leakage (MFL) in-line inspection (ILI) technology has proven to be one of the most effective approaches to manage corrosion anomalies within the pipeline industry. However, due to the presence of extra metal, pipeline casings are suspected of impacting the detection and sizing accuracy of MFL systems for metal loss features when they are located under casings.

A research project was carried out by TC Energy (TCE) with ROSEN to better understand the effect of pipeline casings on the performance of axially-aligned MFL ILI (MFL-A) technology. The study involved full-scale pull through testing to investigate the effects of various casing conditions and the presence of different types of casing spacers on the inspection system’s sizing and detection performance for corrosion anomalies, including the casing eccentricity, the presence of metallic and electrolytic shorting, and the presence of different types of casing spacers. The testing for various eccentricity and shorting scenarios were compared to an uncased baseline scenario.

An important lesson learned by the project team through this research is the importance of identifying key factors that influence the system performance when analyzing the testing results. Failure in doing so can lead to less meaningful results: in this case, an overly conservative estimate of the sizing performance that does not discriminate appropriately where the system performed well and where the system performed worse than expected. The impact of such a broad-brushing and overly conservative estimate in the MFL system performance to pipeline integrity decisions is very significant and can result in a large number of unnecessary repairs in practice.

With comprehensive data analytics, it was identified that the key factors affecting the tool performance for cased pipes are the small annulus gaps between the casing and the carrier pipe at the feature location, and the presence of certain types of spacers. For the vast majority of cases, the ILI performance under casings is comparable to the performance for uncased pipes. The results from this research suggests that with appropriate consideration of the system performance, TCE’s probabilistic ILI based corrosion management program can effectively manage corrosion anomalies within cased pipes using ILI. Additional research and testing are underway to further support this conclusion.

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