Stress Amplification Factor Analysis for Threaded Connector Fatigue
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Solution Overview
Problem
Existing methods for assessing the fatigue performance of threaded connectors in oil and gas recovery operations are inadequate as they primarily rely on finite element analysis under purely elastic conditions, failing to account for plastic deformations and cyclical loading, which are common in realistic operating scenarios.
Innovation Solution
A computer-implemented methodology that uses finite element analysis and other computer-assisted techniques to simulate plastic deformations and cyclical loading conditions, allowing for a comprehensive assessment of tubular connections by applying simulated forces to virtual models of tubular members connected by threaded pin and box connectors, and identifying peak stresses under these conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If finite element analysis is used under purely elastic conditions to calculate stress amplification factor, then the analysis is simple and provides a single value for characterization, but it fails to account for plastic deformations and cyclical loading that occur in realistic operating conditions
Solution Approach 1:
The patent changes the material behavior parameter from purely elastic to elastic-plastic, allowing the simulation to account for plastic deformations that occur during cyclical loading. This involves implementing material models that can transition between elastic and plastic states, thereby improving the accuracy of fatigue performance assessment while maintaining a systematic analysis approach
Solution Approach 2:
The patent introduces dynamic loading conditions by simulating cyclical loading sequences with varying magnitudes and directions. Instead of a static single-value SAF analysis, the methodology applies multiple load cycles that replicate realistic operating conditions, enabling the assessment of how stress amplification evolves throughout the loading history and accounting for cumulative damage effects
2Reliability
If tubular members are loaded to stress levels that induce plastic deformations, then the analysis reflects realistic operating conditions, but the geometry of the tubular members is altered and the initial FEA analysis and resulting SAF become less relevant
Solution Approach 1:
The patent performs preliminary elastic-plastic analysis cycles to establish the deformed geometry and stress distribution before conducting the final SAF calculation. By pre-loading the model to induce plastic deformations and then resetting or carrying forward the deformed state, the methodology ensures that subsequent SAF values are based on the actual geometric configuration that exists during operation, making the analysis more relevant to real-world performance
Solution Approach 2:
The patent applies periodic cyclical loading sequences that replicate the repeated connection and disconnection operations. By subjecting the model to multiple load-unload cycles, the analysis captures the evolution of stress distribution and geometric changes over time, allowing the SAF to reflect the cumulative effects of operational history rather than just a single loading event
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach provides a more accurate characterization of the operating performance of tubular connections under realistic conditions, accounting for stress redistribution due to plastic deformations and cyclical loading, thereby improving the assessment of their fatigue performance and reliability.
Implementation Method 1
applying by the computer at least one first simulated force to the virtual model, the at least one first simulated force sufficient to induce a simulated plastic deformation in at least one of the first and second tubular members of the virtual model
Implementation Method 2
identifying by the computer at least one peak stress in the virtual model induced by the at least one second simulated force
Data Source
AI summary
A computer-implemented method is disclosed for characterizing a threaded coupling such as between two tubular members, e.g., casing segments employed in the field of oil and gas recovery. In one embodiment, a virtual model of the coupling is generated, and the virtual model is re-arranged to simulate plastic deformation of at least part of the coupling. The re-arranged model is analyzed to derive a stress/strain distribution of the coupling subject to subsequent loading, and an SAF (stress amplification factor) is determined from the analysis that reflects the effect of cyclic loading of the coupling. The method facilitates a thorough assessment of the performance of the coupling in fatigue.