Investigating the Relative Severity of Dents in Pipelines Based on Magnetic Flux Leakage Inspection Data

Dent damage in pipelines may result from either impact damage caused by third parties or construction damage. Third party damage generally occurs on the upper half of the pipe (between the 8 o’clock and 4 o’clock positions) and has historically contributed to the highest number of pipeline failures. Dents caused during construction generally occur on the bottom half of the pipe and tend to be constrained by the indenter causing the dent, i.e. a stone or rock in the pipeline bed/backfill. However, all dents have the potential to cause an increase in stress in the pipeline, and consequently increase the pipeline sensitivity to both static and fatigue loading. Although there are extensive recommendations for the ranking and repair of dents, recently, failures of dents that are acceptable to pipeline codes have been reported. Guidance is therefore needed in order that operators can identify dents for which excavation and inspection is uneconomic and could potentially be damaging to pipeline safety and dents for which further action is required. This paper provides a review of the published recommendations for the treatment of pipeline dents and goes on to present a method that is being developed to determine the relative severity of dents in a pipeline using magnetic flux leakage (MFL) signal data. The proposed method involves measuring MFL signal parameters related to the geometry of the dent and relating these to high resolution caliper inspection data. This analysis enables a relationship to be established between the MFL signal data and dent depth and shape measurements. Once the model is verified, this analysis can then be used to provide a severity ranking for dents on pipelines where only MFL data is available.