Evaluation of the Inner Liner in Unbounded Flexible Pipelines in the Sealing System of End-Fitting

Abstract Unbonded flexible pipelines are widely used in the offshore oil and gas industry due to their numerous structural configurations and their adaptability to different environmental requirements. However, designing the end-fitting for connecting these pipes to the floating structure is one of the most challenging tasks. This connector has two main functions, ensuring sealing of the pipe fluid and transferring the loads from the pipe to the connecting system unit. The flexible pipes consist of many layers including carcass, inner liner, pressure armour, tensile armour, and outer sheath. The carcass prevents the collapse of the pipe against high hydrostatic pressure, and the inner liner plays the most significant part in the sealing system of the end-fitting. The current study assesses this role. The sealing method is based on dividing the termination of risers into two devices; barrier seal which is the mechanical restraint on the polymer barrier, and the seal system that is applied to seal the fluid of the riser. Therefore, two leak paths are observed; between the barrier seal and the polymer barrier, as well as, between the barrier seal and the body. Consequently, to improve the metal seal ring under high pressure, the compression on the polymer barrier must be enough. Besides, the contact pressure at the metal-to-the-metal interface has to be adequate.