Above and Below

Managing geohazards has largely been the realm of engineers and geologists, all of whom identify threats by observation, typically conducting a high-level review from data such as topographical maps and aerial imagery followed by boots-on-the-ground assessments and physical measurements in areas perceived as affected. While this approach has merit, it is a process that retains a significant level of subjectivity. It is also the case that changing weather patterns and the localized severity of weather events mean areas not previously considered prone to geohazards now are. This new level of susceptibility has now found prevalence in the U.S. Code of Federal Regulation, with both gas transmission and hazardous liquid pipeline regulations containing new provisions compelling inspection following extreme weather events.

Many pipeline operators include inertial measurement units (IMUs) in their suite of inline inspection technology for periodic assessments. The IMU process utilizes a series of gyroscopes and accelerometers that measure the differential attitude of the host platform, which allows for the calculation of pipeline curvature. Through detailed analysis, the characteristics of these curvatures can indicate whether they are related to construction activities – which is the case for field bends – or indicative of movement, with the degree of curvature being directly proportionate to the level of strain induced. This technology allows operators to identify areas of bending strain and areas where active geohazards potentially exist.

In the U.S., to comply with regulatory requirements, these periodic inspections are typically conducted in intervals of 5 to 7 years. This interval is logical when monitoring time-dependent threats such as corrosion, but it is likely insufficient for monitoring time-independent threats like geohazards. In the past, IMU was deployed in combination with other inline technologies, such as a corrosion or geometry tools. This meant the IMU was limited by the operational parameters of the host platform, which had significant implications for operators, including reduced pressure and flow. This meant that more regular internal inspections that evaluated the entire pipeline were prohibitive. ROSEN now has a dedicated IMU platform, RoGeo PD, which overcomes many of those limitations. This technology was introduced for the first time at the 2022 Pipeline Pigging and Integrity Management (PPIM) conference in Houston.

IMU and bending strain analysis now forms a significant portion of the geohazards programs of many operators. As well as being utilized during periodic inspections, the new technology allows for more frequent assessments, with some operators running the technology once every 3 months. These technological developments have been accompanied by improvements in alignment and processing techniques, reducing the timescale associated with analysis from weeks to days. It is the advancement of technology and process that has facilitated the change in practice, making the previously infeasible now feasible.

While these developments are exciting and provide a more regular and robust solution, it must also be recognized that IMU does not complete the geohazard picture. IMU cannot tell you what has caused the displacement of the pipeline to occur below ground. Furthermore, active geohazards do not necessarily affect the pipeline. To complete the picture, what is going on at the surface of the right of way must also be appreciated. Light detection and ranging (LiDAR) has long been recognized as a valuable tool in the management of geohazards, with data being collected routinely for pipelines and areas deemed susceptible.

LiDAR works by targeting the surface with a laser and measuring the time it takes for the emitted light to return. By collecting many of these measurements, a high-resolution surface map can be created, and by further post processing, the surface map can exclude noise due to vegetation and other artifacts in order to form a true topographical map. Active landslides, erosion, subsidence and other instances of land movement can be identified accurately. Again, technological advances mean that processing that data is now a matter of days rather than weeks or even months.

The contention is that the combination of LiDAR and IMU (i.e., above and below) now represents a potential paradigm shift in the management of geohazards. LiDAR now has the capacity and availability to identify active and potential geohazards on the surface, and IMU can determine if those have manifested on the pipeline. This combination of technologies is now providing a feasible alternative for identifying and quantifying the nature and magnitude of geohazard threats on a more regular, robust and objective basis. Two example applications are provided hereafter. In each case, a copy of aerial imagery, the bending strain profile from IMU and the LiDAR data are provided.

In Example 1, the aerial image shows evidence of erosion and scarping; an active landslide area was identified by LiDAR, and large vertical and horizontal bending strains were recorded by IMU. This is a clear correlation between the data sets.

SO, WHICH METHOD TO USE?

Example 2 is less clear: the aerial imagery shows only the tree canopy and no apparent threat. The IMU data shows clear and significant vertical bending strain. The LiDAR data did not identify a specific geohazard, but the removal of the tree canopy revealed a forest track coincident with the bending strain anomaly. The bending was considered most likely resultant of construction activities or repeated passage of motor vehicles.

No single dataset will provide all of the information, but these examples show the complementary and complete nature of IMU and LiDAR in conjunction. This data is shared as a prelude to a forthcoming paper, which will be presented at the 2023 PPIM conference in Houston. ROSEN will be appearing with partners to discuss this subject, and we hope to see you there.

As stated initially, it is insufficient to identify a need for change without presenting a credible alternative. While relatively few failures due to geohazards occur, occur they do. Additionally, regulatory changes recognize increasingly volatile weather patterns and the threat to pipelines. In conjunction, there is a clear need to develop more robust and objective geohazard management practices. The combination of LiDAR and IMU technologies represents a potential paradigm shift in the way geohazards are characterized, inspected for and monitored. The availability and processing times of these data sets now means they represent a technically and commercially feasible option for pipeline operators to the extent of underpinning and informing the entire geohazard program.