A common challenge for pipeline designers is the placement and safe operation of pipelines within unstable slopes. Consequently, special design and operation procedures must be created to maintain the integrity of the pipeline through its operating life. Nova Gas Transmission Limited (NGTL) has developed a methodology to monitor pipeline integrity in slow moving (creeping) unstable slopes.
This methodology uses Pipeline-Soil Interaction models to produce parameters that are in turn placed in Pipeline Integrity Assessment Techniques such as finite element analysis. For slope movements, pipeline integrity is based on pipeline strain criteria that are established from regulated codes or NGTL’s risk-based criteria. The result is that pipe strain can be estimated over time given a particular soil type and predicted ground movement.
The ability to predict when a pipeline is reaching a critical strain allows NGTL to effectively quantify the risk and associated cost for various remedial measures based on a given operating life (life-cycle cost). These remedial measures can take the form of strain relieving outages, re-routing of the pipeline, directional drilling, or conventional geotechnical remedial practices (dewatering, slope grading, buttressing, etc.). Two case studies are presented detailing this present state-of-practice methodology at NGTL.