Anchors to mitigate pipeline walking often involve very large piles, requiring large crane installation vessels, which bring cost, schedule and HSE risk implications. Optimizing such piles traditionally require substantial FEA effort, and frequently, project decisions are made, and purchase orders are placed based on conservative assumptions.
The choice of anchor-to-pipeline connection can significantly influence the anchor sizing. In some cases, allowing some free slide-back displacement when the anchor is being unloaded can substantially reduce the maximum load levels.
This paper presents simple analytical calculations that can be used to determine whether this artifice is effective or not for any given condition; how much load reduction can be achieved; and how much slide-back length is required for that. Results for typical, hypothetical pipeline properties are presented. These show that while some cases will see no benefit, in others cases the load can be reduced by over 1 MN by allowing no more than a few centimeters slide-back tolerance.
Having the ability to assess multiple options with minimum effort, then use FEA for detailed confirmation (rather than using expensive FEA on a trial and error basis) will allow certain projects to realize significant savings.