Stress- and strain-based reliability assessment of pipelines subjected to internal pressure and permanent ground movement
Creators: Zheng, Qian
Publisher: name: University of Alberta Library
Year: 2023

<p>As a critical member of infrastructural lifeline, pipelines fulfill a vital role in energy delivery across long distances from source to market. Pipelines at service can be exposed to a wide variety of loads depending on the environment and the area of application. Internal pressure and ground movements, which are two typical loads respectively controlled by force and displacement, are of great concern in pipeline integrity. Internal pressure is the primary load exerted on the pipe wall for the duration of operation; ground movements induced by geohazards are significant threats to long-distance transmission pipelines. This research carries on the reliability-based analysis of pipes subjected to internal pressure and ground movements regarding the respective industry concerns. <br>
For pipes subjected to internal pressure, a comprehensive reliability assessment is performed towards intact and defected pipes based on the CSA Z662:19. Various limit states related to the pipe design, pre-commission hydrostatic testing, and operation are studied. Specifically, both corrosion and crack defects are considered for pipeline integrity assessment based on different defect scenarios. The probabilities of failure (PoFs), are reported with respect to design factors, hydrostatic test pressure factors, and safety factors, which can be used in designing new pipes, determining the applied pressure in hydrostatic tests, and operation pressure control of defected pipes, respectively. The effects of pipe grade, pipe dimensions (i.e., diameter and wall thickness), corrosion or crack defect sizes (e.g., length and depth), and internal pressure on PoFs for different limit states are also investigated. <br>
In light of the limitations that existing models are not applicable for reliability calculation, a novel model is developed to predict the pipe response to ground movements based on the finite difference method (FDM-based model). The pipe is modeled as an Euler-Bernoulli beam with large deformations, and the governing differential equations are formulated as functions of displacements of the deformed pipe in the axial and lateral directions at each grid node. The nonlinearities arising from the pipe material and the pipe-soil interaction are accommodated within the finite difference formulation. The initial thermal axial strains and biaxial state of stress due to internal pressure can be appropriately incorporated into the stress-strain relationship of the material based on the flow rule of plasticity. Results of the FDM-based model are in good agreement with those derived from the finite element method (FEM).<br>
The strain-based limit state function is established where the FDM-based model is used to calculate the results of strain demands. The PoFs of pipes at a given magnitude of ground movements are calculated using the Monte Carlo Simulation (MCS). The calculation code is equipped with computational optimization functions to enhance computational efficiency. At last, calculator-like tools are established respectively for assessment of the integrity of pipelines subjected to ground movements, using the developed codes of the FDM-based model and the related reliability calculation. Furthermore, considering the probability of ground movement initiation, the formula of calculating the cumulative PoFs of pipes is developed for decision-making on the maintenance plan for pipes buried across landslide-prone zones.</p>