Written by J. Stume, E. Likovskis, EMPIT GmbH, Berlin, Germany.
One of the major challenges the pipeline industry faces today is aging assets. Across the globe vast networks of buried steel pipelines continue to operate beyond their intended designed lifetime. It is safe to assume that nearly all are affected by corrosion to some extent. While cathodic protection (CP) systems generally keep corrosion under control, they can fail or lose effectiveness over time, often without visible signs until it’s too late. Thus, periodic inspections and integrity assessments are even more vital on aging pipelines.
However, these pipelines often lack launch and receive facilities or contain geometries too complex for in-line inspection (ILI) tools. Thus, they are considered “unpiggable”. Conventional over-the-line inspections such as CIPS or DCVG are used for ECDA, however, none of these methods provide any information on corrosion states (active corrosion vs. passivating conditions) at the pipeline surfaces. ILI does detect metal loss but can only give a momentous snapshot of the condition. CIPS or DCVG are used for coating defect localization and to confirm local CP efficiency but can only provide information on certain coating defect locations, while they can not draw any conclusion on others. This often leads to unnecessary excavations, cost, and uncertainty in corrosion management.
To overcome these limitations, EMPIT GmbH developed the Current Magnetometry Inspection (CMI) technology. The method enables over-the-line, contact-free assessment of buried pipelines — including unpiggable segments — by measuring and analyzing a self-applied magnetic field around the pipe from the earth’s surface. CMI combines advanced 3-dimensional mapping, including bending strain analysis, with precise defect localisation and direct evaluation of the corrosion state for all defect sizes and locations. As the analysed magnetic field is self-applied, CMI operates independently of existing CP systems and can even be applied on lines affected by strong stray currents — without shutdowns or operational interference.
Benchmarking CMI with conventional CIPS under controlled test conditions during the German research project “NEMEK” revealed that CMI surpasses conventional over-the-line techniques (CIPS) in both sensitivity and diagnostic value, with a higher Probability of Detection for 1 cm² defects (PoDCMI: 100 %, PoDCIPS: 20 %) and a more accurate determination of the , even for small defects with a low potential gradient (≈ 30 mV).
In addition, with the analysis of a surface layer presence on the pipeline, CMI provides a novel criterium to assess the local CP system effectiveness and resulting corrosion risk for every detected coating defect. Within the NEMEK research project, the reliability of the CMI results was verified on real pipelines with several excavations – all confirming the exact position and state of corrosion (active corrosion vs. passive conditions) on each excavated coating defect.
Thus, for the vast global inventory of unpiggable pipelines, CMI provides, for the first time, a reliable, non-intrusive integrity assessment method, without influence on CP systems or operational downtime. It drives the transformation of corrosion monitoring forward toward actionable, data-driven integrity management, enabling a safe pipeline operation, while reducing unnecessary excavations.
For more information, visit www.empit.com or meet us at the APGA conference (EMPIT | booth 35).
