Pushing limits on the line

John Bradbury

June 1, 2015

John Bradbury reports on new equipment designs for risers and umbilicals from DeepFlex and Technip, which the two top-tier players say can stretch the performance envelope.

Umbilical spools on Technip Umbilicals’ quayside in Newcastle. Photos from Technip.

Houston-based DeepFlex has been working for some time on a new design of hybrid reinforced pipe under the auspices of RPSEA (Research Partnership to Secure Energy for America) to develop an ultra deepwater composite pipeline.

This has been worked to a design brief for a pipeline with a 7in internal diameter, capable of operation in 10,000ft of sea water (3000m); suitable for sour service, and capable of withstanding up to 120°C.

Engineers have worked to produce what it claims is a unique structure with a fully unbonded layer construction. It features an outer jacket with a flooded outer annulus, and although composite material is exposed to sea water, it is not subjected to permeated gases, which can escape from the pipeline core, and it has low failure risk under bending and rapid pipe bore depressurization, as permeated gas is not absorbed by a composite.

An inner annulus provides a flow path to surface for permeated gas, and monitoring it allows early detection of fluid leakage, before any major containment loss.

Presenting at the MCE Deepwater Development conference in London in March, Eric Wilson, sales manager at DeepFlex claims the line pipe design is unique, comprising an outer jacket, anti-buckling tapes, tensile reinforcement, anti-wear tapes, a hoop layer, a membrane, a second hoop layer, a liner, a tape wrap layer, and a carcass.

The pipe features a composite tensile armor, which does not corrode in sea water, and an intermediate anti-collapse sheath with a membrane seal to prevent sea water ingress. Hybrid pressure armor has zero risk of corrosion: “We have a lot less risk of corrosion because it is a non-metallic material,” Wilson explained.

In air, the weight of the new pipeline is 170kg/m and in seawater it is 68.2kg/m.

During its development the new design has had to undergo a series of qualification tests. This has covered material qualification for the composite pressure and tensile armor reinforcement, gap spanning, wear and permeation tests, and then DeepFlex has moved on to prototype testing involving static, bending, dynamic and thermal cycling tests of the completed pipe, to meet the API 17B prototype qualification test standard. All of this is due to be completed by 2H 2015.

Phase 3a involves preparation of the pipe based on field specific data, incorporating findings from phase 2 as well as a dynamic fatigue tests, involving a service life simulation, and thermal cyclic testing to verify the integrity of pipe liner seals.

“It is easier produce, light, easier to get around,” Wilson said. Suitable for sour service, the new pipe has a 50% U value compared with a conventional flex riser, and so one continuous catenary riser is possible, Wilson said. ”We are pushing riser technology beyond today’s limitations, to enable deepwater solution,” he said.

During phase 2b, a prototype pipeline was constructed at DeepFlex’s Manitowoc, Wisconsin, facility. By the end of this year DeepFlex aims to complete all testing.

Afterwards the company will move into development phase 3a, pipe manufacturing, involving material procurement, manufacturing, procurement of end-fittings and verification of ancillary equipment qualification and procurement of bend-stiffeners. A sample has already been assembled and underwent factory acceptance tests.

Phase 3b is field deployment, which involves selection of an installation contractor and mobilization to the selected field. By 2Q 2016 DeepFlex aims to move to full manufacturing and field installation in 4Q 2016.

Deepwater umbilicals

Meanwhile Technip has been working to cut down the cost of design and deployment of deepwater umbilicals and earlier this year presented the fruits from its research.

Defining the characteristics of a subsea umbilical, Ian Probyn, research and development business manager for Technip, outlined the units as the critical connection to control subsea oil and gas equipment. Typically they comprise a protective outer sheath, polymer filler elements, fiber optic and electrical cables and fluid conduits within thermoplastic hoses, or steel tubes.

Deepwater umbilicals have to perform against a number of key factors including the basic design, component mix, capacity requirements and manufacturing assets.

And during their installation, Probyn explained how umbilicals have to contend with hold-back tensioners, manage the effects of inertia or DAF (dynamic amplification factor), as well as installation unit track length, and type, in addition to crush loads, heavier inner bundles, and offshore hold times. And they have to deal with in-service conditions of usage, fatigue, buoyancy, and the type of vessel to which they are attached.

In deepwater, the “install-ability” of an umbilical depends on the nature of the friction equipment – usually caterpillar tracks or grabbers on deployment vessels – and the top tension imposed on the umbilical, as well as its size, length, and its crush capacity. Installation is described by Probyn as the most critical phase in the service life of an umbilical.

In deeper water, there is greater top tension, greater weight, more components, necessitating larger installation equipment, which in turn imposes greater crush forces, and greater friction factors.

All of this has pushed up umbilical construction and installations costs, Probyn explained.

To combat this rising cost trend, Technip has developed a 3D finite element analysis modeling tool, FEMUS 3D, to analyze crush forces and top tension, to achieve umbilical designs which fulfill operational requirements but which also mitigate the higher cost trend.

Using FEMUS allows engineers to model installation methods. Umbilical crush capacity can be tailored for a specific installation scenario, allowing increased confidence in an umbilical design, while reducing conservatism and providing better behavioral insight and reducing cost.

“We can run the model for a range of crush forces....We can determine exactly what the limit is. We can learn exactly how the elements are inter-reacting with one another,” Probyn said at MCE Deepwater Development.

Outlining a typical approached to deep water umbilical installation, Probyn said this has involved use of a sufficient Factor of Safety (FoS), while physical tests have been used to confirm actual performance limits. This has resulted in larger, more expensive lay spreads and unnecessarily high crush loads, he argued.

Technip’s new tool can interrogate an installation process, and advice on the best setup, including pad size, type and spacing on an installation tractor unit.

Alternatives to the tool considered and rejected by Technip include physical testing, which although answering questions about crush force analysis, does not provide much insight, while being expensive and time consuming. “The information you get is either a go or a no go; it does not give you where the design limit is,” Probyn told conference attendees. “An FEA model gives you much more insight than a physical model.”

Empirical or mathematical modeling is deemed to be fast but provides less accuracy, and requires many assumptions to be made, while being built from test data only.

And 2D FEA analysis, while quick and inexpensive, Probyn said that with this approach 3D effects can be missed.

Turning to deepwater installation issues, Probyn said the typical industry approach has been to give an accepted friction co-efficient and apply a FoS, backed up by physical tests to confirm the friction factor. But this relies on a high FoS, leaving more unknowns and more risk.

Using this FEA analysis tool, Technip has devised a new, patent-pending high friction tape for umbilicals, which when crushed, doubles the friction or grip on an umbilical held in an installation tractor.

Probyn said once crush forces are removed from the tape, there is no effect on the umbilical fatigue life. With increased umbilical friction during deep water installation, there is less crush force imposed overall, reducing risk, and the cost on the unit.

Further work has been done to improve umbilical performance by using high strength aluminum, rather than copper in cables, to reduce weight, in high-density, low-strength components. This, Probyn suggests, can lead to less weight, higher strength, better fatigue performance, and greater water depth capability.

Another innovation is the introduction of high strength strain members to increase stiffness and to reduce umbilical strain while exposed to top tension force.

Also Technip has sought to “evolve” umbilical design down the water column; High tensile strands are used to stiffen the top section; an ‘evolving joint’ is used in a mid-section and a polymer filler is used in lower sections where strain is lower.