Gripping Methodology: A New Approach Towards Enhanced Reliability for the Installation of Flexible Pipes

Abstract During offshore installation / retrieval with tensioners, the flexible pipe is submitted to an axial tension due to the suspended catenary weight. To sustain this downward axial force and avoid any slippage during installation, a suitable squeezing load must be radially applied to the flexible pipe by tensioner tracks to ensure a proper transmission of the tightening force, by friction, at every layer interface, to the core of the pipe without crushing the pipe inner structure. This paper presents a novel design methodology for the determination of the specific squeezing load during flexible pipe installation with tensioners. Various challenges are faced when determining the proper squeezing load to safely install flexible pipe, due to the diversity of interfaces above the tensile armour layers. Indeed, flexible pipe cross-sections may contain different sheath and tape materials (for mechanical, chemical, thermal, or manufacturing purposes). Every interface may behave differently depending on the environment (when exposed to water, temperature, etc.), and the level of contact pressure. Therefore, the design challenge was to build a comprehensive approach relying on the following main aspects: - Friction interaction between flexible pipe layers addressing influent parameters, thanks to an extensive small-scale test campaign, - Statistical treatment of these data and validation through testing with complete flexible pipes, - Development of Finite Element Analysis (FEA) Abaqus models to validate the load transmission mechanisms from the tensioner to the core of the flexible pipe, - Validation through a large full-scale test campaign including tensioner onboard an installation vessel, - Certification of the full methodology with an Independent Verification Agent (IVA). This novel methodology is a key enabler towards even safer offshore operations as it constructs clear installation domains which prevent slippage events considering multiple factors. The methodology was built in compliancy with DNV-ST-N001 that details how to derive the friction coefficients and select appropriate safety factors for flexible pipe industry.