Bending Over Backwards

Successful pipeline life extension within active landslide

In a Nutshell:

Pipelines have a remarkable capacity to navigate the bend-or-break enigma. While pipelines do contain intentional bends formed during manufacturing (fabricated bends) and construction (field bends), the stresses and strains associated with these bends are generally carefully considered during the pipeline's design phase. However, unforeseen loads experienced during construction or while in service can induce undesirable bending, resulting in stresses or strains that may surpass safe limits.

When excessive compressive stresses occur on the inside of a bend, localized buckling and wrinkling can transpire. On the other hand, tensile stresses on the outside of a bend can lead to fractures, particularly if there is an anomaly in the pipe wall, such as circumferential cracking. Numerous factors can cause bending loads, including landslides. In this case, an operator experienced pipe movement on one of their assets due to a landslide. This particular pipeline had the added risk due to its vicinity to a river crossing. This would result in a far higher consequence in the event of a leak.

The pipeline industry worldwide has witnessed an increasing emphasis on pipeline integrity management programs, particularly concerning pipelines traversing geotechnical and hydrotechnical hazards. This heightened attention stems from several notable incidents involving pipeline failures. Recognizing the importance of mitigating the risks associated with geohazard-related pipeline failures, several pipeline operators have engaged ROSEN as their integrity partner.

ROSEN was contracted to assess three landslide sites impacting a total of six operational pipelines. For the purpose of this case, our focus will be on one specific landslide, namely Landslide B, which is actively affecting three operational pipelines: Line A, Line B, and Line C.

Reaching performance limits – reduce the load

In the case of Landslide B, the landslide is occurring near perpendicular to the pipelines, resulting in horizontal pipeline movement in the creep range (less than 5 mm a year). The movement on the slope is believed to be primarily seasonal, and a distinct boundary for the landslide has been identified. To gain a better understanding of the slope, multiple slope inclinometers and survey monuments have been installed.

Up to this point, pipeline integrity has been managed through recurring caliper and Inertial Measurement Unit (IMU) in-line inspections, as well as remote sensing systems. Additionally, slope instrumentation, including LiDAR change detection, slope inclinometers, and survey monuments, has been employed. The slope instrumentation indicates ongoing land sliding within the creep range. Furthermore, assessments using IMU bending strain and Finite Element Analysis (FEA)-based pipeline structural analysis reveal that strains (including bending and axial) in Line A are approaching performance limits, based on a tensile strain limit of 0.5% at the girth weld. It is predicted that Line B will also reach strain performance limits in the near future.

To mitigate the potential risk of containment failure, the operator requested that ROSEN develop a strategy to alleviate stress on the pipelines. Additionally, they asked for an examination of options to reduce future loading on the lines considering the continuing ground movement.

Figure 1: Results of FEA showing strain development within the pipeline relative to continued ground movement and the predicted stress relief achieve by the excavation and air bag lift.

Stress mitigation and continued monitoring

As a conclusion, it was determined that excavating a section of each pipeline at the boundary of the landslide and implementing a stress relief project would be the most suitable course of action. This project involves lifting the pipelines using airbags, which allows the elastic strains to be released. The stress relief process effectively reduces the loading exerted on the pipelines by the ground movement. It is anticipated that this approach will enable the operator to maintain the lines in service and ensure their safe operation for an extended period, securing their functionality for many years to come.

Figure 2: Photograph excavation site during stress relief.

To accurately measure and quantify the amount of stress relief achieved, strain gauges were installed at specific locations where the structural analysis had indicated the highest anticipated strains in the event of further ground movement. These strain gauges provide measurements of tension and compression as a percentage of elongation relative to the original length. For instance, if a 10 cm bar stretches by 0.1 cm, it has undergone a strain of 1%.

By utilizing strain gauges, we can precisely determine the extent of strain relief achieved and also establish a means for remote monitoring of strain introduced in the future as the landslide continues to shift. In-field measurements of the backfill were also collected, enabling ROSEN to update the structural model calculations. This updated information will facilitate the assessment of the relationship between ongoing ground movement and pipe strain. Furthermore, it will enable continuous monitoring of strain development within the pipeline utilizing the newly installed strain gauges.

Extended pipeline lifespan

Over the course of four years, through the collaborative efforts of multiple teams at ROSEN Canada, supported by our global experts, comprehensive mitigation measures have been successfully implemented to prolong the lifespan of the three pipelines affected by the active landslide. These efforts encompassed a range of activities, including repeated surveys, site-specific analysis, strain monitoring, and on-site engineering support. By adopting a proactive and all-encompassing approach to pipeline integrity, ROSEN played a crucial role in ensuring the continued safety and reliability of the affected pipelines.

The combination of innovative backfilling solutions and advanced monitoring techniques formed the cornerstone of effective risk mitigation strategies. These measures not only address the immediate challenges posed by landslides but also lay the groundwork for ongoing protection and maintenance of pipeline infrastructure in areas prone to such geohazards. ROSEN's dedication to comprehensive solutions underscores our commitment to safeguarding critical infrastructure and maintaining the highest standards of pipeline integrity.