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.

A Discussion of Practical Aspects of Reeled Flowline Installation

“…As discussed in [1], these equations are derived from consideration of the pure bending moment theory and cannot therefore take into account the beneficial effects of spooling-on (reeling-on) tension. Furthermore, the strain concentration due to presence of geometrical and material originated mismatches should be considered using a combination of reliability based techniques and FEA as described in detail in [8] and [9]. In the 2009 edition of API-RP-1111 [7], this has been recognized by stating that "bending strains are not simply nominal (global) bending strains and shall include an allowance for possible strain concentrations".…”

Optimising Reeled Pipe Design through Improved Knowledge of Reeling Mechanics

“…On the other hand, DNV-OS-F101 [5] provides more guidance on appropriate wall thickness sizing. However, despite their apparent simplicity of definition and application, such equation appears to be reliable for the assessment the minimum reelable wall thickness for a uniform, thin coated, pipeline [7,9]. For example, the beneficial effect of the spooling-on tension is not accounted for.…”

“…Technip have also developed a more refined calculation procedure, combining statistically based reliability work and a finite element based reeling model, to undertake more complex reeling assessments [7,8,9]. Typical applications include reelability analyses of thick coating pipeline [11], calculation of pipeline ovality [12,13], reelability of transition pieces between two pipe designs (variation in OD, wt, grade, etc…) and can extend to support to Level 3C ECAs [15].…”