Unpiggable and pipelines account for thousands of kilometres around Europe alone. The integrity management of these pipelines requires nondestructive evaluation techniques, which can be applied without introducing inspection tools into pipelines. Pipeline diagnostics shall therefore be executed from above ground. Indirect approaches like DC Voltage Gradient (DCVG) survey or External Corrosion Direct Assessment (ECDA) can be used for this purpose. However, such approaches are characterized through distinct limitations, i.e., properties of soil (DCVG), or necessity of reference excavations (ECDA). Consequently, the latterly mentioned techniques can only be used for external corrosion and coating damage detection and not for information about a metal loss in the pipe wall.
The presented Above Ground Inspection Technique (AGIT) has been developed to overcome limitations of DCVG, ECDA and In-Line Inspection (ILI). Thus, AGIT is capable of detecting and categorizing external and internal metal losses of unpiggable pipelines and coating damages in one inspection run. The EMPIT GmbH holds all exclusive rights and assets of AGIT.
First, the physical basics will be explained as the technique is based on measurements of the magnetic field around a buried pipeline under test. The inducted AC magnetic field is measured by a sensor array and the field data are processed and stored in a data collection module. Metal loss defects in the pipeline wall result in measurable changes of the magnetic field at different frequencies.
Secondly, a review of performed inspection runs including a comparison of detected features and their validation through excavations is presented. It is evidenced that AGIT demonstrates a high level of reliability in detection of pipeline defects corresponding with its technical specifications.
Lastly, the goals, approaches and first test results of improvements achieved by a new development of the AGIT including the method itself, the field inspection unit and the evaluation procedure are discussed.