Bart Steuten, Airborne Oil & Gas, the Netherlands, details how

thermoplastic composite pipe is changing the face of the

SURF market during the recent downturn.

A low oil price is the new reality that everyone in the offshore oil and gas industry has to live with. Operators today

face the challenge of maintaining production and developing projects at an acceptable cost. Large field developments struggle to reduce costs and marginal field developments become even more marginal. At the same time, in some regions the decommissioning has started in earnest, leading to the hard requirement of considering decommissioning costs right from the start. In this setting, existing practices are being challenged and all those involved are required to come up with cost saving ideas.

SURFING THE TCP

Figure 1. Thermoplastic composite pipe flowline (6 in. ID) with end-fittings on transportation reel.

As a result of the relentless focus on minimising upfront cash, project and pipeline engineers must first come up with solutions that bring down the flowline and riser as-installed cost. This includes reduction in material cost, installation spread cost and smarter project execution. At the same time, there is also a continuing realisation that in the long run, it is the lifecycle cost that should drive investment decisions, including future cost for inspection, maintenance and decommissioning. One solution for the reduction in as-installed cost and lifecylce cost is thermoplastic composite pipe (TCP).

As outlined in this article, TCP is changing the face of the subsea, umbilical, riser and flowline (SURF) market today, offering the opportunity to reduce installation and operational cost. Its intrinsic properties, reeling in long lengths and the absence of corrosion, allow for new business models such as leasing, rental and reuse. This reduces the costs in the conventional arena of SURF and opens up new avenues for sustained low cost production.

TCPTCP is a spoolable, fully bonded, thermoplastic pipe with glass or carbon fibre reinforcements. The pipe uses a one material design concept, in which an internal liner, composite layers and an outer coating are all of the same polymer material. The pipe is made with an in situ consolidation manufacturing process that melts/fuses all layers together in order to form a strong and stiff

solid wall. The result is a pipe that is insusceptible to corrosion, collapse resistant, spoolable in long lengths and light weight.

The solid wall TCP is predictable and does not have the numerous failure mechanisms and modes of the multilayer structure and annulus of a conventional unbonded flexible pipe. In the bonded TCP, any issues associated with relative movement and friction between layers or with the annulus are avoided. The pipe manufacturing process allows an infinite length that, in practice, is bound only by the storage volume of the production carrousels. The current Airborne Oil & Gas manufacturing plant allows for line lengths of 3000 m for the largest size flowlines, up to 7.5 in. ID.

ApplicationsWithin the oil and gas market, TCP is applied within the market segments of SURF, well intervention and pipeline precommissioning. Well intervention includes operations such as acid stimulation, chemical injection and plug and abandonment.

The following products are applied in intervention and precommissioning:

) Downline: free-hanging pipe, deployed from surface vessel to the seabed to pump fluids down.

) Jumper: the dynamic, flexible and collapse resistant pipe between static and dynamic subsea equipment, e.g. from downline to injection skid or Xmas tree.

In SURF, typical TCP applications are:

) Flowlines: for corrosion free static flowlines and risers for hydrocarbons and water injection.

) Jumper spools: providing flexibility to cope with large deflection envelopes.

) Flexible (dynamic) riser: for deepwater production operations providing low weight seabed to surface fluid conduit.

Material selectionEach TCP design and selection of materials is adapted to the specific requirements of each project, ensuring the best fit-for-purpose and most cost-effective solution. The Airborne Oil & Gas manufacturing process is suitable for a variety of polymers and fibre materials, including high density polyethylene (PE100), polyamide (PA12), polyvinylidene fluoride (PVDF) and polyetheretherketone (PEEK) polymers, as well as glass and carbon

reinforcement fibres. Which material is selected depends on temperature requirements, chemical resistance and loading conditions. The ability to select the best material for each application has a significant impact on pipe material cost, and ensures that the lowest cost solution is selected for each project.

Today, Airborne Oil & Gas delivers pipe with pressure ratings up to 15 000 psi at 2 in. ID, 10 000 psi at 6 in. ID and 5000 psi at 7.5 in. ID. It should be noted that the limitations of diameter versus pressure are related to the diameter capability of the current manufacturing equipment, not by technology limitations.

Figure 2. Deployment of high pressure methanol injection TCP jumper. Image courtesy of Chevron North Sea Limited.

Table 1. TCP material selection

Material Applications Maximum continuous operating temperatures

Service

E-glass/PE TPC jumper, TCP jumper

spool, TCP flowline

60˚C (140˚F) Water, methanol,

hydrocarbons,

acids

E-glass/polypropylene TCP downline 60˚C (140˚F) Water, nitrogen,

methanol, acids

Carbon/PA12 TCP flowline 80˚C (176˚F) Hydrocarbons,

seawater

Carbon/PVDF TCP flowline, TCP riser 130˚C (266˚F) Hydrocarbons

World Pipelines / REPRINTED FROM MARCH 2017

End-fittings As part of a piping system, end-fittings are indispensable when connecting the composite pipe to other parts of the system. They are metallic, allowing flanged or welded connections. The TCP end-fittings also rely on a proven and simple clamping method.

The extensively tested and proven clamping method avoids having to terminate individual reinforcement layers, can be applied at any point in a pipe and can be assembled at any offshore location in the world. The end-fitting is fully piggable, with a typical diameter of 95% of the flowline’s internal diameter and fitted with a client specified connecting flange. In case of inline fittings – connecting two lengths of TCP flowline – no flange connection is required. Instead, the inner stem extends from one end to the other, using the same clamping mechanism twice.

Materials and corrosion The fully bonded composite wall of TCP is impervious to corrosion, including the most aggressive and most unpredictable types such as microbiologically induced corrosion (MIC), caused by sulfur reducing bacteria (SRB).

Contrary to steel corrosion, which is often difficult to predict, the long term effects (such as polymer ageing that slowly reduce the strength of composite flowlines) are accurately characterised and implemented in the design. To do this and as part of the generic qualification, material coupons of the liner, laminate and coating materials are exposed to relevant environments (seawater, hydrocarbons etc.), temperatures (minimum and maximum design and operating temperatures) and loadings (static and dynamic loadings) in order to establish material properties of the design for both the short and long term. Typical operational fluids that are tested with the pipe materials are sour crude (as per the Norsok M710 specification), methanol and common oilfield chemicals including corrosion inhibitor, solvents and biocides. Rapid gas decompression testing has been perfomed at a 70 bar/min. depressurisation rate with methane and carbon dioxide.

In comparison with carbon steel pipeline systems, significant operational benefits are obtained by designing out the possibility of flowline corrosion.

) Corrosion and biocide inhibition can be omitted. Equipment such as pumps, storage tanks, tubings, umbilicals etc. and logistical operations for the chemicals supplies are not required.

) Wall thickness measurement by intelligent pigging is not required. Instead of this, ageing of the polymer materials can be monitored with coupon monitoring and can be compared to design values.

Monitoring and inspectionIn-service monitoring and inspection relies on standard available and proven methods, including:

) Internal pressure, temperature and fluid composition monitoring.

) Visual inspection – internal and external.

) Calliper pigging – detecting liner damage and geometric anomalies.

) Coupon monitoring.

As a result of the solid wall, any mechanical damage that is critical to the pressure or tension capabilities of the pipe is reflected in deformation of liner. Such liner deformation can be detected by means of a calliper pig, which can register anomalies to an accuracy of 2 mm and detect buckling, crushing or overpull of the pipe. Visual inspection, both internal and external, is used to confirm the location and extent of the damage. Airborne Oil & Gas has experience with in-service monitoring and inspection, and has build its inspection plan based on this field experience and in close co-operation with its clients and regulators.

Coupon monitoring is used to compare the potential material degration under operating conditions to the design assumptions. Dogbone coupons are exposed to the actual production fluid in a coupon holder. From time to time, coupons are removed, analysed and tested. Based on the mechanical properties of the retrieved coupons, the structural condition of the pipe can be confirmed and the remaining service life established.

Low cost installationThe spoolability of TCP and the possibility to manufacture long lengths, allows for efficient and cost-effective reel lay installation methods. This can be done with dedicated reel lay vessels, cable lay or multipurpose vessels, fitted with the required pipelaying equipment. This results in low installation vessel costs. As the flexible TCP flowline will follow the seabed profile, no seabed preparation or free span corrections are required. A further cost saving is by omitting subsea pipeline end terminations (PLETs) and spools, as the TCP can connect directly to the Xmas tree, manifold or can be pulled in and hung off directly to the topsides. For relatively short flowlines the cost saving is most significant, with the biggest benefit being in well jumper applications. Here, the

Figure 3. TCP jumpers for intervention, which are ready for subsea deployment.

Figure 4. TCP downline for intervention on a deployment reel at the back deck of Subsea 7’s vessel, Seven Viking.

REPRINTED FROM MARCH 2017 / World Pipelines

cost savings are typically 60% on the jumper as-installed cost on a project basis, compared to steel jumpers.

Pipeline reuseThe ability to reel the pipe, quickly re-terminate with mechanical end-fittings and to establish the remaining life through the coupon monitoring and full scale testing of a cut off pipe section, make the TCP particularly suitable to be reused after a first deployment. This is of great value for marginal field developments, where only a short field life is expected.

After recovery of the TCP flowline by a reversed installation procedure, the pipe will be visually externally and internally inspected, as well as the end-fittings removed. A short section of pipe will be cut off and mechanically full scale tested. Small coupon samples of liner and laminate will be tested to confirm the material mechanical properties and remaining lifetime. This way, a complete assessment of the fitness for purpose for the new assignment can be made, before being certified for reuse. Airborne Oil & Gas has completed such exercises for the TCP downline used by Saipem on the Guara and Lula project in Brazil.

Design and qualificationAirborne Oil & Gas’ TCP is designed and qualified to fit the DNV GL RP-F119 recommended practice, specifically designed for

TPCs. This document is the result of a large joint industry project initiated by Airborne Oil & Gas and with the participation of 19 companies, including operators, installation contractors, pipe manufacturers and material suppliers. The recommended practice specifies requirements for design, qualification and manufacturing QA/QC of TCP. Airborne Oil & Gas is the first manufacturer to have implemented this standard fully in its manufacturing and design methodology, and is the first to supply pipe qualified to this standard.

Alternatively, TCP can be supplied under the API15S specification. This specification, which is primarily intended for onshore use, sets requirements for manufacturing, materials and pipe performance, but does not address pipe design. Therefore, for offshore engineered applications, the DNV recommended practice is preferred.

Track recordHaving supplied spoolable pipe to the intervention industry for many years, Airborne Oil & Gas now moves into the SURF arena with the first permanent methanol injection jumper installed in summer 2016. This high pressure jumper was supplied to Chevron North Sea for the Alder field development. Airborne Oil & Gas has qualified its products for major operators for both intervention and SURF applications, and continues to expand on its qualification envelope and customer base.

World Pipelines / REPRINTED FROM MARCH 2017