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Subsea pipelines composed primarily of carbon steel are susceptible to upheaval buckling in the presence of elevated temperatures and pressures. The thermal performance of submarine pipelines is a crucial factor that controls the buckling behaviour, and the carbon content of carbon steel pipelines significantly influences their thermal properties. This paper establishes a theoretical model for subsea pipeline upheaval buckling that takes carbon content and temperature into account, and a comparison with the classic solutions is used to validate the parsing solutions. The influence of temperature-dependent thermal properties under different carbon contents on the buckling configuration and post-buckling behaviour of submarine carbon steel pipelines is analysed. The findings indicate that, when taking into account how carbon content affects material qualities, the temperature dependence significantly affects the upheaval buckling of carbon steel pipelines. Furthermore, at the same temperature, subsea pipelines with higher carbon content have a lower coefficient of thermal expansion and thus experience less thermal-induced axial compression. Subsea pipelines' critical buckling temperature rises in a linear fashion as the amount of carbon in the pipeline increases. For higher carbon content, both the maximum stress and the buckling displacement amplitude decrease in the post-buckling stage. • A theoretical model is proposed for upheaval buckling of subsea pipelines with the effect of carbon content. • The influence of temperature-dependent thermal properties on the buckling behaviour is analysed. • The critical buckling temperature increases with increasing carbon content. [ABSTRACT FROM AUTHOR]

Unburied subsea pipelines are vulnerable to lateral buckling due to high temperature and high pressure, which can be mitigated by inducing controlled lateral buckling through introducing residual curvatures at designable positions. The axial soil resistance is crucial in controlling buckling. Thus, a tri-linear pipe-soil resistance model is incorporated into the numerical model through springs in ABAQUS to study the influence of nonlinear axial soil resistance on lateral buckling. The effect of various factors on pipeline buckling is investigated, including the model length of pipeline, axial peak soil resistance, axial peak mobilization distance, axial residual soil resistance, and axial residual mobilization distance. Results demonstrate that insufficient pipe length inhibits buckling deformation at higher temperatures, which could reduce displacement amplitude and maximum stress. Pipeline buckling is significantly affected by axial resistance. The axial peak resistance and peak mobilization distance affect both pre-buckling and post-buckling states, while axial residual resistance and residual mobilization distance mainly affect post-buckling state. Therefore, in the engineering design of pipeline buckling, it is recommended to minimize the distance between adjacent residual curvatures that trigger buckling and to carefully select an appropriate axial soil resistance model that considers the actual field conditions. [ABSTRACT FROM AUTHOR]

Under thermal loading, upheaval buckling of subsea pipelines occurs when the axial compressive force exceeds the critical buckling load. In order to accurately predict the upheaval buckling behaviour of subsea pipelines, the axial pipe-soil resistance should be considered more precisely, rather than traditionally treated as rigid-plastic in prior analytical researches on pipeline upheaval buckling. Consequently, this study integrates a bi-linear axial pipe-soil resistance model into the mathematical framework of upheaval buckling. This mathematical model incorporates the von-Kármán type of geometrical nonlinearity and the Euler-Bernoulli beam theory. The research examines typical upheaval buckling behaviour and investigates the influence of axial mobilization distance and ultimate resistance on pipeline upheaval buckling behaviour. The results reveal that incorporating bi-linear axial pipe-soil resistance, in contrast to rigid-plastic resistance, leads the pipeline more susceptible to buckling. Displacement amplitudes increase with the axial mobilization distance during the post-buckling stage. Notably, a larger axial mobilization distance exerts a stronger influence on pipeline buckling. Moreover, the critical buckling temperature exhibits an almost linear negative correlation with axial mobilization distance and a positive correlation with axial ultimate resistance. Additionally, greater axial ultimate resistance magnifies the impact of axial mobilization distance. Therefore, in pipeline buckling design, it is advisable to consider a more sophisticated axial pipe-soil model to accurately account for these complexities. • The mathematical model for pipeline upheaval buckling with bi-linear axial pipe-soil interaction is proposed. • The behaviors of upheaval buckling with bi-linear and rigid-plastic axial pipe-soil interaction are compared. • The pipeline is more susceptible to upheaval buckling when bi-linear axial pipe-soil interaction is considered. [ABSTRACT FROM AUTHOR]

In practice, pipelines are inevitably buried in sloping ground, however, previous studies and guidelines of pipe-soil interaction mainly focus on level ground. In this study, the upward resistance-displacement curve for slopes with angles up to 20° was numerically investigated. To reflect the state-dependence, pre-peak hardening, and post-peak softening properties for dense sand, a modified Mohr-Coulomb model was implemented and validated by available physical tests. Numerical studies were carried out to explore the resistance-displacement curve, considering the coupling effects of slope angle, pipe-soil interface roughness, burial depth ratio. It is found that the pipeline in slopes is subjected to unbalanced lateral contact stress around its periphery. The pipeline and surrounding soil tend to move towards the slope toe during the uplift, especially for the perfectly smooth pipeline. As the slope angle increases, the peak resistance decreases for the perfectly smooth pipeline while increases for the perfectly rough one. Besides, the generally rough pipeline shows a quick post-peak reduction in the resistance. Possible mechanisms behind these phenomena were explored. Finally, considering the coupling effects of slope angle, interface roughness, burial depth ratio, a simplified method for the resistance-displacement curve based on the limit equilibrium method was proposed. [ABSTRACT FROM AUTHOR]

• A mathematical model to simulate the lateral buckling of a two-layer lined pipe is proposed. • The influences of different buckling modes on the buckled configurations and post-buckling behaviour of two-layer lined pipe are discussed. • Different types of lateral buckling modes only affect the behaviour of lateral buckled deflection, however, it has little effect on the axial deformation behaviour of the lined pipe. The use of lined or clad pipes, which have a highly corrosion-resistant material inner layer, is common in subsea pipelines. Unburied lined pipes may experience lateral buckling under high-temperature and high-pressure conditions. In this study, closed-form analytical solutions for different lateral buckling modes have been developed with the Euler-Bernoulli beam theory. The study also discusses the impact of different buckling modes on the buckled configurations and post-buckling behaviour. In addition, the buckling behaviour of the outer pipe and liner in the post-buckling process is compared. The research indicates that the length of the buckled lined pipe can't be assumed to be a fixed value in lateral buckling analysis. While different types of lateral buckling modes only affect the behaviour of lateral buckled deflection, they have little effect on the axial deformation behaviour of the lined pipe. In the post-buckling process, the axial compressive force in the wall of the liner may be higher than that of the outer pipe when the temperature is sufficiently high. [ABSTRACT FROM AUTHOR]

Offshore platforms in deep seas require extremely long large diameter pipe piles (LDPPs) to support the loads generated from the structure itself, wind and waves. One of the construction issues related to the installation of a LDPP into a seabed is pile running. Unexpected pile running during the LDPP driving process may break the steel wires connected to the heavy hammer or may cause the loss of the hammer into the sea. An analytical method to predict the occurrence of pile running is proposed in this paper. The framework for determining the calculation parameters from a laboratory or field test are established. The dynamic resistance of the surrounding soil during the pile driving process is considered through analysis of the soil sensitivity and the induced excess pore water pressure. Three case studies were conducted to verify the accuracy of the proposed method. Good agreement indicated that the proposed method is capable of predicting pile running during the driving process of LDPPs in layered soil deposits. [ABSTRACT FROM AUTHOR]

An analytical method is proposed in this paper to calculate the maximum embedded depth of a dragged Hall anchor when passing through rock berm and to thus define a minimum buried depth of pipelines in rock berm to prevent pipelines from being damaged by dragging anchors. The movement of a Hall anchor in rock berm is interpreted based on the equilibrium conditions for resisting and driving moments acting on the anchor. To verify the accuracy of the proposed analytical method, model tests were carried out by using three scaled Hall anchor models and dragging them through rock berm. The comparisons between the two studies show that the average value of their differences for the stable embedded depth of a Hall anchor in sand and in rock berm are only 1.7% and 2.7%, respectively. The good agreements indicate that the proposed method is accurate enough to calculate the minimum buried depth of pipeline in rock berm during pipeline design. [ABSTRACT FROM AUTHOR]