Numerical Investigation of the Collapse Pressure of Concentric Tubes with Frictionless and Tied Interface
The code presented in Appendix A (paper) can be run with an .exe file. Additionally, a matlab file and online python version can be used to implement the collapse evaluation. The corresponding author would like to know the people interested in this work. Below, provide your data for us to map the interest.
The understanding and study of the mechanical behavior of submarine pipes have significant relevance in ocean exploration, allowing the application of these structures in adverse conditions. In this sense, protecting the tube's internal surface is vital for the transportation of corrosive materials, threatening structural integrity. Usually, the external surface is at constant hydrostatic pressure, leading to possible structural failure if the project does not consider all failure modes. Within the framework of Metallurgically Cladded Pipes (MCP) and Mechanically Lined Pipes (MLP), Corrosion-Resistant Alloys (CRAs) are inserted in the internal surface of pipelines. However, they are not typically deemed in the structural analysis as an integrant part of the mechanical resistance for the external load. This work presents an initial analytical proposal to calculate the collapse pressure of concentric tubes incorporating the rigidity provided by the CRA. Tied or frictionless numerical models are assumed to describe the interaction between the two bodies at the interface region. These two scenarios establish the upper and lower boundaries for cases where friction is part of the problem. The methodology applies a least-square minimization function based on nonlinear finite element simulations to extract analytical expressions that estimate the collapse pressure. An effort is made to reduce the number of sensitive parameters involved in the analytical proposals and minimize the complexity of the formulation. This process allows the analyst to visualize which parameters are more relevant in various scenarios. Nevertheless, the main goal is to evaluate how the variables are coupled and develop a methodology that can be adapted to reproduce the analyst's necessities.
Propagation Pressure Collapse in Conventional Pipelines and MLPs: Numerical investigation
The collapse of submarine pipelines can have immense economic and environmental impacts, and understanding the mechanical behavior of such structures under extreme external pressure is vital for the design, fabrication, installation, and operation. The pipe's outer surface is susceptible to damage/impacts due to uncontrolled circumstances, possibly leading to structural changes.This work applies numerical tools to evaluate the collapse and buckle propagation in steel pipes, considering the effects of an initial known deformation caused by different puncher's shapes. Therefore, the structure assumes a new geometry leading to modification in the capacity to withstand external pressure. The analysis applies and compares two numerical methods: the arc-length (Riks) and dynamic-explicit approaches. This comparison allows establishing a direct association between the observed features of the two methodologies. In a general manner, the observation indicates that an increasing indentation causes a reduction in the collapse pressure but also significant changes in the propagation pressure. The similar results between the two methods applied in steel pipes permitted extending this concept to estimate the propagation pressure in Mechanically Lined Pipes (MLPs), where the Riks method is unstable, and the dynamic approach is suitable. In this scenario, the possibility of the internal liner buckling before the external backing steel and the appearance of new failure modes is part of a new complex scenario where the number of variables grows significantly, and the collapse circumstances must be reassessed. The boundary conditions, interface state, and other structural parameters increase the difficulty in this type of analysis, showing that in MLPs the number of variables associated with propagation pressure is much higher than in steel pipes.