The Industry Challenge:
As the oil and gas industry pushes into more challenging environments such as thermal, ultra-deepwater and HPHT reservoirs, more complex equipment built from advanced materials are being used. These operating environments can impose complex loading conditions including combinations of sustained and cyclic loads that, in many cases, can result in permanent deformation of the equipment.
Additionally, the environment itself may alter the properties of the material including high temperature softening, low temperature embrittlement, chemical alteration causing embrittlement and cracking in metals and softening and swell in polymers.
To accurately evaluate the performance of structures, pipe and equipment deployed in these challenging environments require the application of advanced modeling techniques to accommodate large strains, displacements and complex material property models that account for changes in the strength and stiffness of the material over a broad range of operating conditions.
How we help:
C-FER works with our clients to develop effective models that provide insight into the stress/strain conditions in the equipment using Finite Element Analysis (FEA). This information is used to optimize the critical components by reducing the amount of material used, simplifying the manufacturing and extending the equipment run life. The results are also used to develop safe operating procedures, design inspection programs for critical components and evaluate the equipment performance will in new operating environments.
Custom structural models of the equipment or structure are developed from drawings provided by our clients or directly from measurements. Experienced FEA engineers optimize the model mesh to ensure that the analysis can be completed efficiently and that the stresses and strains in the critical components are considered correctly.
This mesh optimization is particularly important for complex structures where small mesh elements must be concentrated in areas where high stress/strain gradients are expected but larger mesh elements can be used where stress/strain gradients are smaller. C-FER primarily uses the FEA package ABAQUS from Simulia.
C-FER also develops custom material models to describe the performance of the material over the full range of operating conditions for the equipment. These material models often focus on defining the stress/strain behavior of the material beyond yield.
This allows the analysis to consider situations where permanent, large deformations and rupture of the material occurs. In some cases, cyclic loading must be considered, so that the models must consider the fatigue characteristics of the material.
This becomes especially challenging when the cyclic loads exceed the yield strength of the material, leading to plastic fatigue that can cause failure in only a few cycles. In other cases, the performance of the material is time-dependent, where a sustained, constant load causes the material to deform continuously. This can occur due to mechanisms such as stress relaxation at elevated temperature in metals or creep in geological materials like salt.
Material models are developed for the specific materials evaluated based on material tests conducted by third-party labs or C-FER. Through various projects, C-FER has developed a broad database of models for various materials including API steel grades, elastomers, cement and geological formations.
Example projects where FEA has been used include:
- Premium connections in thermal wells;
- Sand control systems in thermal wells;
- Ship collisions with offshore structures;
- Offshore ice resistant structures;
- Collapse of subsea pipelines; and
- Pipe-soil interaction.