A mechanical model to determine upheaval buckling of buried submarine pipelines

Thermal loads in submarine pipelines generate an axial compressive load that can force the pipeline to buckle, leading to failure if these loads are not considered in the design. Buried pipes are constraint to displacements in all directions, which leads to a high compressive load in the longitudinal axis and makes the pipes more vulnerable to buckling. If buried pipes under thermal loads do not buckle, a high-stresses state takes place when it is combined with high-pressure conditions. In this work, a simple mechanical model to determine the axial buckling load of a buried pipeline is proposed. The model is based on a simply supported beam subjected to a distributed transverse load representing the soil uplift resistance obtained from a referenced model, and an axial compressive load that represents the effective axial force and is computed according to the DNV-RP-F110. Additionally, the pipe–soil system is analyzed through a non-linear finite element model to compare the results with the analytical solution. The proposed simple mechanical model can capture the upheaval buckling behavior and provides results that are consistent with the numerical analysis, specifically for the two main parameters evaluated, namely, the initial pipe curvature and the magnitude of the transverse load.

Integrity Monitoring of Offshore Arctic Pipelines

For safe and cost-efficient operations of new and existing offshore Arctic pipelines, monitoring of pipeline structural integrity is imperative. A well-founded pipeline integrity management program can optimize production output, extend the life of the pipeline, and serve as a tool for providing preventative maintenance information. Without the implementation of a routine integrity monitoring campaign, pipeline integrity degradation may go undetected until the point of failure. Arctic-specific offshore pipeline design and operational challenges, such as strudel scour, seabed ice gouge, pipeline upheaval buckling, permafrost thaw settlement, and remote location increase the risk and severity of a loss of pipeline integrity. These design cases can create abnormal conditions and ground deformations along sections of the pipeline which can be difficult to immediately detect through standard integrity monitoring systems and schedules. Many of the existing offshore pipelines in the Arctic are buried in remote locations under seasonal ice cover and the failure to detect pipeline damage in a timely manner could have severe safety, environmental, and economic consequences. An Arctic pipeline integrity monitoring philosophy can be implemented to provide further mitigation against loss of pipeline structural integrity by means of regular bathymetry surveys, In-Line Inspection (ILI) campaigns and Fiber Optic Cable (FOC) monitoring. This paper provides a guideline for buried offshore Arctic pipeline integrity monitoring. The guideline covers pipeline integrity assurance incorporated into the pipeline design, the surveys to be completed during installation, as-built assessment of the pipeline profile, the warm-up assessment/implementation needed before start-up, and the integrity inspections to be completed during operations.