Subsea Pipe Joint Wall Thickness from Test Ring Collapse Data
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current methods for determining the wall thickness of subsea pipelines are overly conservative, leading to increased manufacturing and installation costs due to excessive safety factors, and existing testing methods for external pressure collapse are expensive and inefficient, particularly for ultra-deep water projects.
Innovation Solution
A method involving the use of a test ring cut from a pipe joint, machined to uniform length, is subjected to controlled hydrostatic pressure to determine the hydrostatic collapse pressure, allowing for a reduced safety factor and more accurate calculation of wall thickness using a Generalised Pareto Distribution (GPD) model instead of a Normal distribution, reducing the need for full-scale pipe testing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If standard industrial design guidance with high safety factors is used to determine wall thickness, then the pipeline's resistance to external pressure collapse is improved, but the manufacturing and installation cost increases significantly
Solution Approach 1:
The patent changes the statistical distribution parameter from Normal distribution to Generalised Pareto Distribution (GPD) for modeling hydrostatic collapse pressure. This parameter change allows for more accurate prediction of collapse pressure at extreme low probabilities (10^-7), enabling reduced safety factors while maintaining the same reliability level, thus reducing manufacturing costs.
Solution Approach 2:
The patent uses a scaled-down test ring (copy) cut from the actual pipe joint to perform collapse pressure testing. This test ring is machined to uniform length and tested under controlled conditions. The results from this simplified copy are then used to determine the hydrostatic collapse pressure for the full-scale pipe joint, avoiding the need for expensive full-scale testing and enabling more accurate determination of minimum wall thickness.
2Measurement precision
If full-scale pipe joint collapse testing is performed to accurately determine hydrostatic collapse pressure, then the measurement precision is improved, but the testing cost and time increase
Solution Approach 1:
The patent creates a scaled-down test ring by cutting a section from the actual pipe joint and machining it to a uniform, reduced length. This test ring serves as a representative copy that captures the essential structural characteristics of the full-scale pipe joint. Testing this smaller copy requires significantly less time and resources while providing accurate predictive data for the full-scale component through statistical scaling relationships.
Solution Approach 2:
The patent performs preliminary testing on the reduced-scale test ring before full-scale implementation. The test ring is subjected to controlled hydrostatic pressure to determine collapse pressure characteristics. These preliminary results are then used to calculate the hydrostatic collapse pressure for the actual pipe joint using the GPD model, avoiding the need for time-consuming full-scale testing while maintaining measurement precision.
3Device complexity
If conventional Normal distribution is used for statistical analysis of collapse pressure, then the analysis simplicity is maintained, but the accuracy of wall thickness determination at extreme low probabilities deteriorates
Solution Approach 1:
The patent transitions from using Normal distribution parameters to Generalised Pareto Distribution (GPD) parameters for statistical analysis. The GPD model with its shape parameter ξ and scale parameter σ provides superior accuracy for modeling extreme low probability events (10^-7) compared to the Normal distribution. This parameter change, while slightly increasing analytical complexity, dramatically improves the precision of collapse pressure prediction and subsequent wall thickness determination.
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 significantly reduces the wall thickness of pipe joints, resulting in substantial cost savings while ensuring the pipeline's ability to resist external pressure collapse, with potential savings of up to £204 million for a 500km pipeline.
Implementation Method 1
A method involving the use of a test ring cut from a pipe joint, machined to uniform length, is subjected to controlled hydrostatic pressure to determine the hydrostatic collapse pressure
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
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.