In-Line inspection (ILI) tools consisting of combined sensor technologies provide a unique opportunity for operators to understand the conditions of pipelines. While many threats including bending strain can be monitored by inline inspection, axial strain has required localized strain monitoring at known high-risk sites. Currently, (Inertial Measurement Unit) IMU inline inspections allow for the delimitation of areas of localized bending strains and run-to-run movement analysis, but do not detect either tensile or compressive loading. Operators now can use the inline axial strain inspection tool (AXISS™) to measure axial strain in pipelines without the need to expose the pipeline for the installation of surficial pipe monitoring systems (primarily strain gauges) or destructive testing. The key advantage of the new technology is that current methods of stress/strain measurement (including the installation of strain gauges) only detect strain changes going forward from the date of installation at a location of potential hazard. This in-line inspection technique measures total strain at the time of inspection.
AXISS delivers additional data that can be combined with the IMU inferred bending strain to have a fuller understanding of the total strain state of a pipeline.
This paper gives a brief introduction to the technique and the technology implementation and discusses the benefits of integrating the assessment of both the IMU bending strain and axial strain data streams. Axial strain inspection case studies are reviewed to present the framework for understanding the different strain measurement technologies and an investigation into the pipeline prior strain history (effects from fabrication, hydrostatic testing and external loads) and their corresponding impact on the material state at the time of inspection.