Long Seam Characterization by Means of a Phased Array Based Inline Inspection

Pipelines can show imperfections at the longitudinal weld. These imperfections are often introduced by the welding process in the pipe mill and can differ from mill to mill and welding technology. Some of those imperfections are acceptable variations within the manufacturing specifications of the longitudinal seam, either on the internal or external weld trim or cap. Others may exceed acceptable tolerances and introduce a risk for safe operation. In addition, sometimes radial offsets, misalignment, peaking and flat spots can occur. All those variations can lead to signals wrongly classified as crack-like defects, leading to unnecessary repair activities or shading of real flaws. A phased array based ILI tool can map and accurately measure localized wall thicknesses and surface variations. Phased array elements typically have a width of 0.4 mm (16 mils) to 0.8 mm (32 mils), which enables high circumferential resolution compared to the latest generation of traditional single sensor ultrasonic tools of 2 mm (79 mils), while the ILI industry standard has a circumferential resolution around 4 mm (158 mils). This increase in resolution can be used to reconstruct the inner surface, the wall thickness and outer surface of the long seam itself and the vicinity. This includes misalignment, the weld cap height and width, potential trim issues, and similar effects. The authors will show and explain the robustness of the measurement methodology based on laboratory/test data and real-world pipeline inspection. Furthermore, the benefit of knowing accurately the local seam wall thickness will be discussed, as a higher wall thickness reduces the severity of defects. For a selected set of anomalies, it can be shown that a significant number that may exceed acceptable limits (actionable anomalies) can be treated as non-critical considering the ILI measured local WT. Finally, the authors show how the gathered data can be used to build 3D models and perform simulations with different flaws to further optimize the inspection tool and utilize the phased array tool to its maximum benefit.