The Development of a Refined Assessment Procedure for the Pipeline Reeling Process Using Reliability and Finite Element Techniques

Abstract

The reel-lay method is a fast and efficient rigid pipeline installation method for infield flowlines and smaller export lines (up to 20″). However, reeling operations induce significant bending strain in the pipeline. To avoid pipe buckling during reeling, it is a common practice to limit pipe yield strength and wall thickness variations in addition to ensuring an adequate wall thickness. Simple formulas in design standards, based on the assumption of pure bending, are often used to determine the minimum reelable wall thickness. It is, however, known that the mechanics of reeling process differs from pure moment bending. Therefore, the likelihood of pipe buckling during reeling may depend on factors that are not captured by these simple formulae. A more refined procedure for establishing the minimum reelable wall thickness and the associated probability of failure has been developed. This procedure involves the combination of finite-element and statistical analyses. It is aligned with the methodology which is regularly used by Technip to demonstrate the on-reel integrity of non-standard pipeline configurations such as thick coated pipelines with soft field joint coating or transitions between pipelines with different nominal sizes or material grades. This paper outlines the procedure, which can be used to determine the level of safety associated with the simple formulae for the minimum wall thickness in the design standards. The reeling parameter studies carried out in this work have shown that it is not only the maximum bending strain, pipe outer diameter and the statistical variations of wall thickness and yield strength that affect the reliability of the reeling process, but also the arrangement of the reeling equipment.