Relatively thin walled moderate water depth pipelines prone to lateral buckling can have very limited bending capacity in terms of their through-life load, strain and fatigue limit states. For such pipelines effective force mitigation schemes are often impracticable and the use of intermittent rock dump constraint if available, expensive. An alternative option is to design the pipeline to be stable along its length under operational and external loading. However a multitude of uncertainties can impact on such an assessment among them the concrete weight coat properties (stiffness and weight), residual lay tension, field joint SCF, corrosion rate, seabed topography, pipe embedment with associated non-linear pipe soil interactions and the size and frequency of external impacts. This paper reports on a methodology for achieving quantitatively low risk designs meeting regulatory approval through in-place 3D finite element sensitivity studies coupled with structural risk assessments. A current design project utilizing this approach is described along with analytical equations governing excessive seabed and pipelay induced out-of-straightness and lateral buckling initiations. Ultimately this enabled specification of practical limits on pipelay imposed out-of-straightness to safeguard the heavy weight coated pipeline and its field joints during operation.

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