Subsea Pipe Joint Wall Thickness Using Collapse Tail Modeling
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Solution Overview
Problem
Current methods for determining the minimum wall thickness of subsea pipelines overestimate the required thickness to prevent external pressure collapse, leading to increased manufacturing and installation costs without adequately addressing the risk of collapse.
Innovation Solution
A method involving determining the internal diameter and minimum allowable hydrostatic pressure, manufacturing preliminary pipe joints, conducting external pressure collapse tests, and using a statistical tail model from Extreme Value Theory to calculate a reduced wall thickness corresponding to a low probability of collapse, thereby reducing the wall thickness while maintaining safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If standard industrial design guidance is used to calculate pipeline dimensions, then the minimum wall thickness is overestimated to ensure avoidance of external pressure collapse, but this conservative approach significantly increases the cost of manufacturing and installing pipelines
Solution Approach 1:
The patent changes the statistical parameters used in design guidance from conservative estimates to empirically-derived distributions based on actual test data. By using measured collapse pressure data fitted to statistical models (such as Weibull or log-normal distributions), the design can determine wall thickness corresponding to a specific reliability level (e.g., 99.999% survival probability) rather than applying excessive safety factors, thereby optimizing the balance between reliability and manufacturing cost
Solution Approach 2:
The patent replaces the conventional mechanical/engineering judgment-based design approach with a statistically-based methodology. Instead of relying on conservative engineering estimates and safety factors, the invention uses statistical analysis of test data to determine the actual collapse pressure distribution, allowing for more accurate and less conservative wall thickness calculations that maintain reliability while reducing manufacturing costs
2Reliability
If the wall thickness of the pipeline is increased to prevent external pressure collapse, then the reliability against collapse is improved, but the internal diameter control and operational cost are adversely affected
Solution Approach 1:
The patent applies statistical parameter analysis to determine the optimal wall thickness that achieves the required reliability level without excessive conservatism. By using collapse pressure data and fitting statistical distributions, the method identifies the minimum wall thickness needed to achieve a specified reliability (e.g., 1 in 100,000 probability of collapse), preventing unnecessary increases in wall thickness that would reduce internal diameter and transport capacity
3Ease of manufacture
If the wall thickness of the pipeline is reduced to lower manufacturing and installation costs, then the cost is decreased, but the possibility of external pressure collapse increases
Solution Approach 1:
The patent replaces conservative engineering estimation with statistical analysis of actual test data to determine the true relationship between wall thickness and collapse resistance. By analyzing the distribution of collapse pressures from tested pipelines and using statistical models to predict the probability of collapse at different wall thicknesses, the method identifies the optimal thickness that achieves acceptable reliability (e.g., 99.999% survival probability) without excessive conservatism, thereby reducing manufacturing and installation costs while maintaining adequate safety
Solution Approach 2:
The patent changes from using fixed safety factors and conservative estimates to using statistically-derived parameters based on empirical test data. This allows for determination of wall thickness corresponding to a specific reliability level rather than applying uniform conservative margins, enabling cost optimization while maintaining the required level of safety against external pressure collapse
Data Source
AI summary
A method of determining a minimum wall thickness for a pipe joint for use in a subsea pipeline comprises the steps of: i) determining an internal diameter of the pipe joint; ii) determining a minimum allowable hydrostatic pressure at the depth at which the pipe joint is to be used; iii) determining a target wall thickness for the pipe joint, the target wall thickness corresponding to the internal diameter and the minimum allowable hydrostatic pressure; iv) manufacturing a plurality of preliminary pipe joints having the internal diameter and the target wall thickness; v) carrying out external pressure collapse tests resulting in data representative of the hydrostatic collapse pressures at which the plurality of preliminary pipe joints collapse; vi) determining a probability distribution corresponding to the data based on a statistical tail model derived from Extreme Value Theory; vii) determining from the probability distribution a hydrostatic collapse pressure occurring with a probability of 10−5 or lower; and, viii) determining a wall thickness of the pipe joint corresponding to the internal diameter and the hydrostatic collapse pressure.