Pipeline Installation on Zero Radius Bending (ZRB) Sleepers for Large Diameter Concrete Coated Pipelines

Abstract Lateral buckling, predominantly induced by operational temperature and pressure expansion, remains a key design constraint for large-diameter subsea pipelines. The deployment of zero-radius bending (ZRB) sleepers presents an effective strategy for controlling lateral buckling by inducing a sharp, localized bend at a predetermined pipeline location. However, the installation of heavy, stiff, and concrete-coated pipelines onto ZRB sleepers introduces substantial technical challenges, particularly in maintaining structural integrity and precise geometrical control during critical phases of operation. This paper outlines a validated methodology for installing large-diameter concrete-coated pipelines onto ZRB buckle sleepers based on recent offshore project experience in Qatar. The developed procedure utilizes a Derrick lay barge (DB30) equipped with a truss stinger for the S-lay operations. Pre-lay analysis is used to optimize the vessel parameters and ensure persistent pipeline contact with the ZRB sleeper's bollard throughout the bend induction process. A critical process deviation from conventional practice involved achieving the required sharp bend radius through precise vessel heading adjustments directly at the ZRB post, thereby eliminating the need to drag the pipe along the seabed. The pipeline, featuring 38 inch & 28 inch diameter with 40 mm concrete weight coating over thick-walled pipe sections, was engineered to interface with the ZRB bollard at a predetermined elevation above the sleepers, thereby leveraging pipe stiffness and controlled vessel movement to maintain geometric conformity. Post-installation surveys and analytical verification confirmed the structural integrity of the pipeline within the ZRB region, with key parameters, such as sag bend stresses and DNV LCC Unity Check values, remaining within the specified design thresholds. The top tension and touchdown point tension were systematically optimized using tailored lay tables corresponding to varying water depths and pipeline configurations. Furthermore, the installed ZRB sleepers effectively resisted installation-induced vertical and lateral hydrodynamic loads, thereby confirming the robustness of the design. This field application substantiates a streamlined and robust methodology for installing large-diameter concrete-coated pipelines onto ZRB buckle sleepers using precise vessel positioning in place of pipe dragging for curve induction. This approach offers superior control and installation reliability, marking a notable advancement in lateral buckling mitigation for offshore pipeline construction. The resulting improvements in operational efficiency and risk reduction are expected to enhance project performance and long-term pipeline reliability.