Contribution of Axial Soil Resistance in Buckle Initiation of the HPHT Pipelines on Sleepers

Abstract

The objective of this paper is to assess the impact of soil axial resistance on initiation of the buckles on sleepers. It also covers the effects of history of pressure and temperature increase on effective axial force as well as the incorporation of external pressure in the Finite Element (FE) models. This is carried out for 6″, 8″, 10″ and 12″ pipelines laying on sleepers with different heights for a range of axial soil frictions and mobilisations. Knowing the sensitivity of buckle initiation to soil parameters can help in simplifying engineering analysis by avoiding repetitive simulations for parameters with less importance. To carry out the above, a series of FE models including normal and bi-linear axial contacts between pipeline and sleeper / seabed were built in Abaqus FE package and at the point of initiation of the buckles, the effective axial force was extracted by a Python script. FE models were validated by comparison of the simulation results with analytical solutions and experimental results from published literature.

Response surface based reliability analysis of critical lateral buckling force of subsea pipelines

“…In addition, it should be noted that the CBF is not a function of the residual lay tension as pipeline buckles after reaching the CBF regardless of the loading path (history of pressure and temperature increase) or initial loading condition (residual lay tension). The effects of the loading path for buckling over a sleeper is outlined in [10].…”

“…𝐺(𝑅, 𝑆) = 𝑆𝑢𝑟𝑓(𝐼, W 𝑠𝑢𝑏 , 𝜅 𝑚𝑎𝑥 , 𝑀𝑜𝑏 𝑙𝑎𝑡 ) − 𝑆 𝑑𝑒𝑡 (10) An MCS with 50,000 trials was carried out to obtain the CDF of the CBF at nominally straight sections of the pipeline (𝑅) as shown in Figure 12. The selected number for trials is based on the sensitivity checks which showed that the results remain almost unchanged for trials equal to or greater than 50,000.…”

“…The CBF at sleeper was calculated for a range of sleeper heights based on the methodology outlined in [10]. A screenshot of the Abaqus model is presented in Figure 13.…”

Rogue lateral buckle initiation at subsea pipelines

“…the sequence of pressure and temperature increase, in a specific pipeline does not influence the CBF. This can be because of the buckling capacity being dependent on the pipeline stiffness, boundary conditions, and initial imperfections only [28]. In view of this, loading history is a non-contributing parameter.…”

“…During installation and in fully restrained sections of the pipeline, touchdown point can be considered as an axially fixed point. However, the adjacent point on catenary is free to move axially which results in release of the axial strain caused by hoop stress due to external pressure [28]. Consequently, external pressure/water depth is a non-contributing parameter.…”