Non-metallic Unbonded Flexible Pipes for Deepwater

Abstract

Abstract A new generation of lightweight, flexible, non-metallic, un-bonded pipes has been developed for use in subsea and deepwater floating system applications. These pipes are the first of their kind offering large savings in weight and cost to operators. In addition, the elimination of metallic reinforcements removes the associated corrosion concerns in sea water and the U-value of the pipe is improved. The Flexible Fiber Reinforced Pipe (FFRP) is constructed from extruded polymeric layers reinforced with unbonded laminated glass-fiber tape stacks. The unique design allows the construction of lightweight flexible pipes with attractive features such as capability for high internal and external pressures, in a wide range of sizes varying from 2 inch to 16 inch. It is intended to be used in deepwater. An overview of FFRP technology is presented in this paper. Typical designs of the pipe are described. A brief overview of qualification tests is provided along with a description of initial applications. This technology has the potential to be a 'game changer', enabling new, lower cost field development solutions in offshore areas around the world. Introduction Unbonded flexible pipe technology has enabled floating production systems of various types to produce oil and gas from offshore fields in shallow and deepwater. Flexible pipes are used as dynamic risers connecting seabed flowlines to floating production facilities, and as static sea bed flowlines where it is more cost effective to install than rigid steel pipe, or when it is desired to recover the flowline for reuse after a short field life. Flexible pipes are also used as static and dynamic jumpers at the sea floor, on a hybrid riser, or on the floating platform deck. Until now, flexible pipes have been available with helical metallic reinforcements made of steel. Use of reinforcement steel results in higher weight and several other disadvantages including corrosion, corrosion fatigue, and sensitivity to H2S and C02. In this paper, we present a new option for unbonded flexible pipes without the use of any metallic reinforcement. The Flexible Fiber Reinforced Pipe (FFRP) presented in this paper is constructed from extruded polymeric layers reinforced with unbonded laminated glass-fiber tape stacks. This new generation of lightwight, non-metallic, unbonded flexible pipes have the potential to enable new field development scenarios in deep and ultra-deepwater fields around the world. Description of Pipe Structure FFRP is custom designed and built to meet project specific design requirements. There are two main types of patented pipe structures which are currently being offered for use in field development projects: 'Standard FFRP' and 'Free-venting FFRP'. Several variations and design options exist within each general type of pipe structure. We begin with a description of the first type. A typical view of the standard pipe is shown in Figure 1. The pipe has an internal polymer liner which serves as the smooth chemically resistant conduit for fluids. It is surrounded by burst reinforcements made of glass-epoxy composities. There are two layers of burst (or pressure) reinforcements that are torque balanced, and are separated from each other by anti-wear tapes for dynamic service. Each layer of composite reinforcement is made of multi-start stacks of specially made pre-cured unidirectional composite tapes which are bonded together. The manufacturing process is designed to allow continuous production of the pipe with the required curing of the bond between tapes within stacks, with each reinforcement stack remaining unbonded from other stacks. Figure 1 indicates the relative positions of all layers including the collapse reinforcement, the membrane (which serves as a barrier against external sea water), tensile reinforcements, and the external jacket. Not shown are anti-birdcaging tapes which can be used on the outside of tensile reinforcements for ultra-deepwater applications.