New Approaches in Utilizing Eddy Current Testing to Address Pipeline Inline Inspection Requirement

Eddy current testing is one of the most widely used NDT inspection techniques for both ferrous and non-ferrous materials. This may explain why it was one of the very early techniques implemented on an inline inspection tool (ILI) back in the 1970s, following the first implementation of Magnetic Flux Leakage (MFL) tools. Eddy current testing is primarily developed to accurately detect and size surface breaking defects. The technology is now mature and has been deployed in various applications, most notably for pipeline in-ditch inspection. As of today, the technology as a crack detection technique is not deployed commercially on ILI tools as it can only detect cracks on the inner pipe wall. The most common use of the eddy current technology in ILI tools is the simple configuration for lift-off measurement. This offers a way to discriminate between internal and external corrosion on a volumetric tool (MFL) or enhance caliper-based geometry measurements. The most advanced applications of eddy current testing are targeting measurement of electromagnetic properties of the pipe wall to either measure material properties (pipe grade) or pipe stress due to external loading. Both pipe grade or pipe stress eddy current technologies can only operate successfully in combination with a magnetically saturated pipe wall, either prior to or during the measurement. The first objective of this development is to remove the requirement for magnetic saturation, thus removing the need for MFL magnets or large electromagnets. The second objective is to progress the established Eddy current development to allow for the measurement of an additional parameter. Current commercial stress measurement method is uniaxial and aligned in the axial/longitudinal direction with limited coverage around the pipe circumference. The new development will make measurements in 2-D, longitudinal and hoop directions, and will include a full array of sensors to provide a full coverage 2-D stress map of the pipe wall. The latest development will address accurate detection and sizing of defects on the internal wall of the pipeline. Most crack detection tools are focused on the outer wall, e.g. Stress Corrosion Cracking. However, the growing interest in hydrogen transportation and the potential for Hydrogen Induced Cracking (HIC) on the internal surface of pipelines, has focused the industry on developing tools for internal crack detection. Detection and sizing of surface breaking defects are at the core of eddy current technologies.