DeepFlex’s dynamic riser connects to a calm buoy off the Cape of Good Hope. (Image courtesy of DeepFlex)

Flexible pipes are often used as dynamic risers that connect seabed flowlines to floating production facilities. They are used as seabed flowlines where they are more cost-effective to install than rigid steel pipe and in projects where the flowline may be recovered for reuse after a short field life. Flexible pipes also are used as static and dynamic jumpers at the sea floor, on hybrid risers, or as surface jumpers on deck.

DeepFlex has developed a new option for unbonded flexible pipe that does not use metallic reinforcement. Unlike metal pipe, the DeepFlex Flexible Fiber Reinforced Pipe (FFRP) is highly resistant to the corrosive properties of saltwater and other more aggressive chemicals such as the high H2S and CO2 concentrations being encountered more frequently in harsh offshore environments.

The FFRP connects wellheads, risers, flowlines, export pipelines, and well testing and intervention vessels to enable offshore oil and gas production in the most challenging environments.

Benefitting from innovation

The FFRP is constructed from extruded polymeric layers that are reinforced with unbonded laminated glass-fiber tape stacks. The pipe layers are unbonded to enable independent movement and provide greater flexibility. Laminating the tape stacks improves structural integrity.

This new generation of lightweight, flexible, non-metallic, unbonded pipes has been developed for use in both shallow and deepwater subsea applications. The pipes are the first of their kind, offering large savings in weight, as much as 60%less than traditional steel flexible pipe. This lighter weight pipe enables the use of a larger spectrum of installation vessels, which results in total installed costs that are often significantly less when compared to traditional steel flexible pipe.Additionally, the FFRP delivers a higher strength-to-weight ratio and a higher tensile strength per kilogram than steel, resulting in lower top tension requirements during installation for any water depth.

The construction of this new flexible pipe eliminates metallic reinforcements, removing the associated corrosion concerns with seawater. The FFRP composite construction also improves the U-value of the pipe (the rate of heat loss or gain through a material). Thermal performance of FFRP is significantly better than that of the traditional metal-reinforced unbonded flexible pipes designed for the same internal and external pressure requirements.

Construction

The patented construction process for the FFRP produces continuous long lengths. It involves two basic processes: extruding thermoplastic sheaths and winding unbonded composite reinforcements. API 17 type thermoplastic materials (HDPE, PA-11 or PA-12, PVDF) are used in the extruded sheaths. The type of material is dependent on the operating temperatures and fluids running through the pipe.

The FFRP has an internal polymer liner that serves as the smooth chemically resistant conduit for the hydrocarbons. It is surrounded by several layers of composite reinforcements made of E glass/epoxy composites. Depending upon the design pressure, there are often two layers of pressure reinforcement that are torque-balanced and separated from each other by anti-wear tapes for dynamic service.

Each layer of composite reinforcement is made of multistart stacks of custom-engineered, pre-cured unidirectional composite tapes that are bonded together in what the company refers to as a “stack.”

Fit for purpose

DeepFlex’s internal testing and qualification program is designed to meet all applicable API 17J and 17B standards for metallic flexible pipe. The FFRP has consistently exceeded the current industry operating parameters in crush and collapse testing, meaning the product is ideal for operating in deepwater installations and operations. Industry-recognized independent verification agents (IVAs) monitor both customer-specific testing and qualification requirements as well as DeepFlex’s new technology qualification program. These programs result in type approval for the FFRP.

Application

FFRP is a critical part of an engineered solution designed to meet requirements specific to the project, client, and installation. In a recent project undertaken by DeepFlex, the company designed, delivered, and replaced 1,608 ft (490 m) of traditional steel flexible pipe being used as an oil export riser for South Africa’s PetroSA.

The flexible steel line, installed 10 years prior, was connected to an offloading buoy in 394 ft (120 m) of water in the Oribi field near the coast of the Cape of Good Hope. Routine diver inspection and subsequent detailed examination discovered that the existing traditional steel flexible pipe was in a “failure stage” due to advanced abrasion of the pipe jacket and subsequent corrosion of the metal armoring.

The riser needed to be replaced quickly and efficiently to avoid a costly field shutdown. PetroSA requested completion within a very short time period, and contractor J. Ray McDermott S.A. contacted DeepFlex for a solution. The FFRP was selected because it met the needs and timeline of both PetroSA and J. Ray McDermott.

FFRP was an ideal product for replacing the existing steel flexible pipe because of its non-corrosive properties, higher fatigue resistance, and lower weight. Installing the FFRP allowed production to be maintained with minimal shut-in time.

DeepFlex was able to deliver this pipe in less than three months from the time of order, allowing PetroSA to replace the riser system in a fraction of the time that would have been required if another riser solution had been selected.