During this project the optimal wearplate thickness for pipe supports on the FPSO Maria Quiteria was investigated, aligning with the Yinson project specifications. The primary objective was to validate whether the prescribed wearplate thicknesses—6mm for pipes of 10” and smaller, 10mm for larger pipes, and 12.7mm for pipes with higher wall thickness—are structurally adequate under conservative loading scenarios. The evaluation was driven by the need to ensure structural integrity while adhering to project guidelines, focusing on how wearplate thickness influences stress distribution at the pipe support interface.
Problem Background
Wearplates serve as critical load-distributing elements welded between the pipe and its supporting shoe. Their function is to mitigate localized stress concentrations at the weld interface, which arise as the piping system transfers loads to the supports. Without a properly dimensioned wearplate, loads would be focused on a small area of the pipe, potentially resulting in localized overstressing and premature failure.
The Yinson specification references a tabulated system for wearplate thickness, supplemented by a discretionary note recommending thicker plates for pipes with higher wall thicknesses. The challenge was to determine if following this table was structurally sound or if the more conservative note should dictate wearplate selection.
Methodology
The study employed a finite element analysis (FEA) approach using FEPipe to model a representative pipe support configuration. The selected case was an 8” nominal diameter pipe with a substantial wall thickness of 27mm, subjected to internal pressure and maximum external support loads as identified in the pipe stress analysis for module M02. This configuration was chosen to represent a high-stress scenario, ensuring conservative results applicable across typical supports.
Three wearplate thicknesses were analyzed:
- 6mm, per the baseline table specification
- 12.7mm, reflecting the more conservative note for thicker-walled pipes
- 27mm, matching the pipe wall thickness, representing an upper-bound scenario
The FEA incorporated internal pressure and the highest anticipated support loads in all directions, even though such maxima rarely coincide in practice. This approach ensured a conservative assessment of wearplate performance.
Results and Analysis
The FEA output focused primarily on stress distributions in both the wearplate and the pipe wall under sustained and occasional (blast) loads. The results were analyzed against the allowable stress values defined in the project’s pipe stress analysis criteria.
For all three wearplate thicknesses, the maximum primary stress (considering only weight and pressure) varied by less than 1% between cases. While the stress in the wearplate itself was marginally higher in the thinner configurations, all values remained well within the allowable limits.
When evaluating maximum support loads, classified as occasional loads due to potential blast events, the 6mm wearplate experienced a maximum stress equivalent to 85% of the allowable value. It is important to note that this comparison did not apply the increased allowable stress typically sanctioned for blast conditions, adding a further layer of conservatism to the analysis. In contrast, the 12.7mm and 27mm wearplates resulted in lower maximum stresses—79% and 44% of the allowable, respectively. This trend demonstrated that increased wearplate thickness reduces peak stress in the support, though the reduction becomes less significant beyond the 12.7mm threshold.
Crucially, when examining the stress imparted to the pipe itself, the difference between the three wearplate thickness scenarios was negligible, with variations remaining under 1% of the allowable. The stress concentration was found primarily in the support component, not in the pipe wall. This indicates that the wearplate acts effectively as intended, distributing load and protecting the pipe regardless of the incremental increases in thickness beyond the baseline 6mm.
Discussion
The analysis confirms that the baseline specification—6mm wearplate for small-diameter pipes—is structurally sound for the most demanding loading conditions considered. Even under highly conservative assumptions, the resulting stress levels are safely below the allowable limits, and the pipe wall itself is not at risk of overstress due to support loads. Thicker wearplates, such as the 12.7mm recommended for high wall thickness pipes, do further reduce peak support stresses, but the benefit is marginal when compared with the baseline. The 27mm case, while academic, demonstrates diminishing returns in stress reduction and is likely unnecessary from a structural perspective.
The findings are significant in that they validate the project’s tabulated approach to wearplate sizing, offering assurance that the specified thicknesses provide adequate protection without incurring unnecessary material costs or fabrication complexity. The stress analysis, provides a high degree of confidence in the durability and safety of the pipe supports as designed.
Conclusion
The analysis confirms that the baseline specification—6mm wearplate for small-diameter pipes—is structurally sound for the most demanding loading conditions considered. Even under highly conservative assumptions, the resulting stress levels are safely below the allowable limits, and the pipe wall itself is not at risk of overstress due to support loads. Thicker wearplates, such as the 12.7mm recommended for high wall thickness pipes, do further reduce peak support stresses, but the benefit is marginal when compared with the baseline. The 27mm case, while academic, demonstrates diminishing returns in stress reduction and is likely unnecessary from a structural perspective.
The findings are significant in that they validate the project’s tabulated approach to wearplate sizing, offering assurance that the specified thicknesses provide adequate protection without incurring unnecessary material costs or fabrication complexity. The stress analysis, provides a high degree of confidence in the durability and safety of the pipe supports as designed.