What are the practical implications of pipeline ovality on the accuracy of in-line inspection (ILI) tools?

Pipeline ovality, which is the deviation of a pipeline's cross-section from a perfect circle, has several practical implications for the accuracy of in-line inspection (ILI) tools. ILI tools are used to detect and characterize defects in pipelines. Ovality can affect the tool's ability to accurately measure the size and shape of these defects. Firstly, ovality can cause errors in wall thickness measurements. ILI tools often rely on sensors that measure the distance to the pipe wall. If the pipe is oval, the distance measured by the sensor may not accurately reflect the true wall thickness, leading to underestimation or overestimation of the severity of corrosion or other metal loss defects. Secondly, ovality can affect the tool's ability to accurately locate and size dents and buckles. Dents and buckles are often associated with ovality, and the combination of these features can make it difficult for the tool to distinguish between them. This can lead to inaccurate assessments of the structural integrity of the pipeline. Thirdly, ovality can affect the tool's speed and stability. Significant ovality can cause the ILI tool to slow down or become unstable, reducing the quality of the data collected. Extreme ovality can even prevent the tool from passing through the pipeline altogether. Fourthly, it can impact the mapping and positioning accuracy of the ILI tool. The tool's odometer, which measures the distance traveled, may be affected by ovality, leading to errors in the location of defects. Furthermore, ovality can complicate the interpretation of ILI data. Analysts must account for the effects of ovality when assessing the severity of defects. To mitigate these effects, it's important to calibrate ILI tools for ovality, use tools that are specifically designed to handle ovality, and perform pre-ILI surveys to assess the extent of ovality in the pipeline.