ATS received a challenge from one of the largest companies in the field of oil exploration in Brazil, which referred to the solution of a serious problem of erosion that caused enormous damage and could cause severe structural damage to the oil exploration bases in the country. Following the guidelines of ASME VIII, the set of main regulations for the development of boilers, tubes and equipment for the transport and handling of fluids in general, ATS successfully conceived a study that demonstrated the importance of computational tools in erosion analysis, generating savings of approximately tens of millions of dollars to your client company dealing with oil extraction.
understanding the problem
The ATS study aimed to solve an engineering problem involving erosion in oil transport pipelines. This erosion is caused by the flow of the fluid which, moreover, is heterogeneous, with the solid parts contributing strongly to the process that could lead to rapid degradation of the pipe used. The central part of the erosion process studied takes place in the curves that the pipe makes; the diagram below shows how the fluid moves in that specific zone. We can see a deflection zone and a bifurcation zone that gives rise to the formation of a vortex.
Due to the impact of the fluid on the bifurcation and curvature zones within a pipe, so-called cushions are added. The addition of this part is essential to increase the durability of the part, being important to maintain it as soon as necessary, taking into account erosion rates as a function of time. The work of ATS was to analyze the longevity of the current pipelines used in the company, considering some specificities that will be discussed shortly.
The ATS Challenge
Given the heterogeneous nature of oil, it was necessary to carry out a computational analysis that took into account the behavior of this fluid in order to obtain a faithful reproduction of how the erosion process takes place. The fluid with solid particles, in this case, has a non-Newtonian behavior, which basically means that there is no directly proportional relationship between the shear stress and the deformation rate of the material. This simple fact brings a challenge regarding the physical modeling of the problem, since the interactions between the particles in the fluid occur in an unconventional way, with a distribution of particle sizes and modes of interaction that bring different results when compared to Newtonian fluids.
From these pre-defined geometries, the study is carried out with the CFD (Computational Fluid Dynamics) tool to predict the result of erosion. The modeling of a problem like this has several distinct steps, each one having a different approximation tool through CFD++. As a complete tool, it is possible to analyze the case and locate the areas with the highest erosion occurrence.
Other tools were also used to verify the results: Ennova Mesh Generator as a mesh generator, Tecplot 360 EX as a post processor, and Nastran as a structural solver.
Analysis of fluid behavior and erosion
To provide a complete picture of erosion evolution as a function of time, ATS performed an annual forecast of the impact of particles colliding with the pipeline walls. The CFD++ calculated the velocity and angle of impact of the particles on the walls and the Tecplot 360 EX post-processed the results to calculate an erosion rate at the site of each impact based on expressions from the open literature, which depend on the angle of impact, impact velocity and material.
Now, considering the erosion involved in the pieces, the results presented below were obtained, also for each of the pieces analyzed.
With the simulations, very relevant information was obtained for the consideration of the useful life of the pipelines. This is because it was possible to notice that most of the was on the walls of the tube after the curvature zones, precisely because it was a non-Newtonian fluid. In this way, a low-speed recirculation zone occurs in the cushion region, avoiding direct impact with its walls.
In this way, one of the biggest doubts of the company contracting the study could be resolved: they were thinking of increasing the thickness of the cushions because there was the notion that most of the erosion zones were concentrated there. The ATS studies thus show that replacement with thicker ones was not necessary at that time.
In addition, a calculation of annual average erosion on the walls of the pipe was made, and, using NASTRAN, an analysis program using finite elements, it was possible to calculate the tension in the pipes by the ASME Class VIII standard of Pressure Vessels . This structural analysis was repeated every 5 years to obtain a progression of the stress level in the pipes and to assess the average life of the pipes.
The stress analysis was carried out using the ASME VIII standard, until, due to the effects of erosion, the part presented a greater than that allowed by the safety standard, knowing, then, that it was the end of its useful life. .
With this success of structural analysis, ATS continues as one of the most reliable companies for the study using computational fluid dynamics, its area of expertise, establishing itself among one of the main in the country with action focused on this type of method of engineering analysis.
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