Pipelines that cross mountainous areas are susceptible to ground movement loading from landslides. In-line inspection using inertial mapping tools provides an excellent method of evaluating the current pipeline integrity. A single inspection only gives an indication of the pipeline integrity at a single point in time. Multiple inspections over a period of time can be used to estimate positional change and the nature of the loading process. An essential element of pipeline integrity management in geohazard areas is the ability to determine future performance so that intervention methods are correctly designed and scheduled and resources are efficiently administered. This requires the reliable prediction of the future development of pipeline integrity based on trends in the mapping data from multiple inspections. The approach developed by the authors to predict the future integrity of pipelines affected by ground movements is set out in this paper. It involves inertial mapping data from multiple inspections and calculates future strains in the pipeline using finite element analysis. Unlike methods based on interpreting inspection data alone, the finite element model includes the effects of soil-pipe interaction and axial pipeline stress together with the operational loads to provide a more complete assessment of pipeline integrity. The method is illustrated through the use of a case study.

In-line inspection by inertial mapping techniques is an essential tool for pipeline operators in areas susceptible to geohazards. The detection of previously unknown movements can provide early warning of the presence of a hazard. Positional change and the nature of the loading process can be monitored using the results of multiple inspections over time. Structural modelling is required to fully evaluate the integrity of the pipeline and whether a failure condition is being approached. Finite element techniques can be used, including the effects of soil-pipe interaction, axial forces and operational loads. This enables the prediction of future performance, based on trends from multiple inspections, so that mitigation or intervention methods are efficiently designed and scheduled. This paper considers some key aspects of the analysis process. The use of ILI mapping data to detect small movements below the tool measurement tolerance is examined. The importance of structural analysis is demonstrated by consideration of the axial force component. The inherent variability of the soil surrounding the pipe and its influence on the load transfer effects is illustrated, together with the issues of significant interaction within the transition zones of landslides or faults.

Following a loss of containment incident in July 2016 on a 16-inch diameter pipeline on the south slope of the North Saskatchewan River located in Saskatchewan, Canada, Husky completed extensive studies to understand and learn from the failure. The cause of the incident was ground movement resulting from a landslide complex on the slope involving two deep-seated compound basal shear slides as well as a near surface translational slide in heavily over consolidated marine clays of the Upper Cretaceous Lea Park Formation. One aspect of the studies has been to undertake structural analysis of the pipeline response to the loading imposed from the ground movement to minimize the potential for a similar occurrence from happening in the future and determine the integrity of the pipeline at the time of the assessment. Given the scale and complexity of the landslide, slope stabilization measures were not practical to implement, so repeat ILI using caliper and inertial measurement technology (IMU), in addition to a robust monitoring program was implemented. Realtime monitoring of ground movements, pipe strain and precipitation levels provided a monitoring and early-warning system combined with documented risk thresholds that identified when to proactively shut-in the pipeline. The methodology and findings of the slope monitoring and structural analysis that was undertaken to examine the robustness of the pipeline to withstand future landslide movement are presented herein. The work involved modelling of the pipeline history on the slope including loads that had accumulated in the original pipeline sections based on historical ILI results and slope monitoring. The pipeline orientation was parallel with the ground movement in the landslide complex, so the development of axial strain in the pipeline was the dominant load component, which are particularly damaging in the compression zone. The work provided recommendations and technical basis to continue safe operation of the pipeline with consideration of continuing ground movement and assisted the operator with decisions over the long-term strategy for the pipeline.

Pipelines crossing mountainous areas are susceptible to ground movement loading from landslides. Structural analysis of pipeline performance from landslide loads is critical for making decisions on the requirement and timing of intervention activities. Current analytical assessment methodologies for pipelines affected by ground movement tend to assume the landslide as an abrupt boundary from the stable region to moving ground, causing an over conservative estimation of the condition of the pipeline. In-line inspection using inertial mapping tools provides invaluable information to assist in the determination of the current pipeline integrity but does not provide a complete picture because axial loads are not defined. Interpretation of in-line inspection data allows the estimation of a transition zone width between stable and unstable ground, where there is a progressive increase in ground movement. Due allowance for the transition zone can remove conservatisms in the assessment methodology and allow a pipeline integrity plan to be created. This paper investigates the influence of landslide transition zone dimensions on the pipeline response and a methodology is developed for the prediction of the transition zone width. The interaction between the ground and the pipe movement is modelled using finite element analysis techniques. The definition of the transition zone properties provides a more reliable prediction of the pipeline performance and enables the current and future pipe integrity to be established with greater confidence.

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