An Investigation of Indicators for Determining Significant Changes in Dent Shapes Using Repeat ILI Data

Abstract The Pipeline and Hazardous Materials Safety Administration (PHMSA) has recently updated regulations for U.S. gas pipelines which went into effect in May 2023. As part of the new requirements for dent engineering critical assessments (ECA) detailed in 49 CFR § 192.712(c), a dent profile comparison shall be performed between the most recent and previous in-line inspections (ILIs) to identify significant changes in dent depth and shape. While the new initiative is essential to the integrity of the pipeline, either for new dent identification or ensuring the stability of the existing dents, a definition of “significant change” is not clarified in PHMSA regulations. In this paper, various indicators are investigated to help pipeline operators screen for an identify dents that may have undergone significant material changes in terms of depth or shape across multiple inspections. Limits are investigated to effectively differentiate dents exhibiting altered shapes from those merely experiencing variations within the expected depth during successive inspections utilizing high-resolution ILI. The approach involves a comprehensive examination of diverse indicators, including ILI listing dimensions, curvature-based strain calculations, and direct comparisons of profiles. Through the application of this methodology to a dataset comprising 650 dents, the efficacy in systematically screening for and identifying dents that are new or have undergone substantial changes is demonstrated, thereby providing a valuable tool for proactive integrity management. Discussion is also included on the factors that could lead to a change in dent shape and the importance of understanding the pipeline’s internal and external loading history.