Four North American pipeline operators and a pipeline inspection company have been working together on a research project assessing the feasibility of using an electromagnetic non-contacting strain measurement tool capable of being deployed during ILI inspection to measure axial strain in pipelines. The axial strain sensor is the TSC StressProbe. It is an electromagnetic technique which makes use of the fact that when a steel structure is loaded, its electromagnetic properties change. Monitoring the changes in magnetic properties allows one to measure changes in strain.
The use of in-line inspection high resolution inertial survey tool data in the determination of bending strain in operating pipelines is well developed and understood. The missing component in determining the total strain in the pipeline is to understand the component of axial strain that the pipeline is experiencing without the need to expose the pipeline for the installation of surficial pipe monitoring (primarily strain gauges) or destructive testing (such as cut-outs). Many current methods of stress/strain measurement including the installation of strain gauges only allows for the determination of change in strain going forward from the date of install; whereas, the StressProbe responds to total strain at the time of inspection.
This paper will present the technology implementation, inspection feasibility and discuss preliminary results from case studies in determining the ability of the in-line inspection axial strain measurement to correlate with known changes in strain in pipelines being influenced by ground movements.