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Improvements in in-line inspection (ILI) and computing technology, coupled with the emergence of fitness-for-service standards, have created an opportunity to advance pipeline integrity assessment. This paper describes innovative approaches for assessing cracks, wall loss and dents in pipelines using data from ILI tools.
Crack detection ILI tools that rely on shear wave UT have improved significantly in both detection probability and sizing accuracy. Quest Integrity Group uses realistic fracture mechanics models that utilize 3D elastic-plastic finite element analysis. The combination of advanced modeling and reliable in-line inspection provides a superior alternative to hydrostatic testing for ensuring pipeline integrity.
Inline inspection tools that measure wall loss with compression wave UT provide superior results compared to other methodologies. The former outputs a digital map of individual thickness readings, which is ideally suited to effective area assessment methods such as RSTRENG and the API 579 Level 2 Remaining Strength Factor (RSF) calculation. Quest has developed software that can rapidly process large quantities of ILI wall loss data and evaluate the maximum allowable operation pressure (MAOP) at discrete locations. The ranking of these MAOP values serves as a rational and rapid means for prioritizing the severity of corrosion throughout the line.
Traditional dent assessments are based on a simplistic characterization of the dent (e.g. the ratio of the dent depth to the pipe diameter), combined with a simple empirical equation. Quest Integrity has developed an advanced dent assessment that combines a detailed mapping of the dent from ILI data (either UT or a caliper pig) with 3D elasticplastic finite element analysis. This advanced methodology can be applied to interacting anomalies such as dent/ gouge and dent/crack combinations, and can be used to demonstrate the fitness-for-service of difficult-to-repair pipelines.