SimPipe, an explicit finite element solver was developed to power SAGE Profile 3D
The mandatory initial stage of any pipeline analysis consists of laying the pipeline on the seabed.
A realistic and computationally efficient approach was adopted to model this laying process onto a 3D seabed with the assistance of digital terrain modelling (DTM) techniques. Advanced tools (e.g. a customised graphical display) were developed to rapidly locate problem areas and re-route the pipeline.
Offshore pipelines laid on the seabed are exposed to hydrodynamic and cyclic operational loading. As a result, they may experience on-bottom instabilities, walking and lateral buckling. Finite element simulations are required at different stages of the pipeline design to check the different loading cases. Pipeline design is dependent on accurate modelling of axial and lateral soil resistances (Bruton, 2008). The pipe-soil interaction of surface laid pipelines is still too often modelled using single frictional factors in the axial and lateral directions. These assumptions are too simplistic, especially in soft deepwater clay. Improved modelling of the pipe-soil interaction can help significantly reduce costs through optimising pipeline design.
Based on recent research, these simple models were improved and implemented in a finite element software program for pipeline analysis, to better simulate the pipe-soil interaction of surface laid pipelines and to more accurately simulate full routes. In this paper, the main features of the soil models are explained. There are several improvements. A more recent pipe-soil vertical reaction law that models plastic unloading is built into the program. It considers lay and dynamic installation effects to compute a more representative pipeline embedment. Axial and lateral resistance is now linked to pipeline embedment. Finally, peak-residual axial and lateral reaction laws are implemented.
>> Read more – 2009
Daniel Cameiro and Adriano Castelo of Bureau Veritas explain how they use SAGE Profile 3D in their paper “Thermo-mechanical analyses of HP/HT pipelines with sliding foundation end structures”.
Non-buried subsea pipelines subjected to high internal pressures and high operational temperatures (HP/HT) might experience significant axial expansion. If this movement is restrained by an end structure, considerable loads can be imposed to the system. Sliding foundations have been used to minimize this effect, allowing free end displacement despite the equipment. However, thermo-mechanical behavior of HP/HT pipelines interacts with the end restrains in a complex manner. Axial displacements can accumulate over the operational cycles, in the phenomenon known as “pipeline walking”. If the sliding foundation design does not account for these accumulated displacements, axial loads (not considered in the pipeline design) might be imposed. As a result, the overall thermo-mechanical behavior in terms of lateral buckling and walking can change significantly.
This paper presents the results of finite element analyses performed to verify the importance of this interaction between the thermo-mechanical loads and the non-linear end restrain. The analyses were performed using highly non-linear tri-dimensional finite element models considering pipe-soil interaction with full 3D seabed bathymetry and load history maintained from pipe lay to operational cycles. The limited sliding range was imposed to the model ends. The results show that the pipeline global behavior after a few operational cycles is significantly different from the foreseen for the initial condition.
>> Read more – 2010