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The power of polymer pipelines

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Oilfield Technology,

Ross McSkimming, Swagelining, and Dr Chris O’Connor, DNV GL, share their insights into working together to create the next generation of pipeline material and encourage confidence in its uptake.

How would you describe the uptake of polymer lining solutions so far, particularly as their use has been limited by corrosion resistant alloy (CRA) connectors since the 1990s?

Ross: The value of polymer lining solutions for subsea applications has remained largely untapped due to historical reliance on less cost-effective and complex-to-weld CRA connectors to join sections of polymer lined pipeline together and terminate the pipeline. This has resulted in the true cost benefit of a polymer lining solution not being realised. Swagelining’s development of the first all-polymer connector, LinerBridge®, represents a viable alternative to CRA connectors.

We anticipate that the development of this connector technology is likely to accelerate the adoption of polymer lining. Not only does it simplify construction of pipelines, it also opens up the opportunity for the installation of steel catenary risers (SCRs) and pipelines installed via the S-Lay method. As operators seek more cost-efficient pipeline materials for long-term operations, the uptake has steadily increased. Upwards of 300 km of polymer-lined subsea pipeline has already been protected from corrosion using Swagelining’s integrated lining system. Of this total meterage, around 70% has been installed in the past ten years. This year, we will begin working on over 50 km-plus of water injection pipeline.

Connectors manufactured from CRA material have traditionally been used to join lengths of polymer-lined pipeline. What are the drawbacks to this, both technically and economically? And based on this – where does the new technology offer an improvement?

Ross: There are several drawbacks ranging from complex girth welding procedures to the cost and schedule of connector procurement. As CRA weld procedures require additional working measures to ensure quality and compliance to stringent specification and acceptance criteria, this can often hinder pipeline fabrication and installation offshore. CRA materials are also inherently expensive and involve long-lead times. The all-polymer connector facilitates the use of conventional carbon steel welding procedures, which therefore removes the need for complex bureaucracy and significantly cuts cost and schedule time.

The use of CRA connectors typically facilitates a requirement for CRA clad cut-to-length pipes as a measure of adjusting pipeline lengths at laydown points - driving up the cost of installation. Polymer connector technology removes the need for clad cut-tolength joints and enables structures and terminations to be tied into the pipeline offshore during the pipeline lay-down campaign.

Recent studies have proven the pipeline hydraulic performance is unaffected by polymer connectors as it offers a smooth bore with minimal restriction to the pipeline ID. In CRA connections, ID restrictions can lead to increase pumping costs, the potential for residue to build up within the pipeline as well as the potential to prohibit pigging operations.

How does the fully integrated polymer barrier work within the pipeline?

Ross: The connector (Figure 1) expands upon the robust and proven concept of electrofusion welding, which is commonly used in the utilities sector when installing buried gas and water pipelines. By machining a profile into the polymer-lined pipe ends, the connector is seated in accordance with engineered tolerances allowing two pipe ends to be brought together using standard fit-up methods. Specifically engineered insulation materials facilitate carbon steel girth welding whilst ensuring damage to the polymer material within the connector body is prohibited.

Figure 1. LinerBridge connector cross-section.

The electrofusion welding process allows the tight-fitting polyethylene (PE) liner pipe to be joined to the connector body to form a homogenous seal. When in service, access for the transported medium to the internal surface of the carbon steel host pipe is prohibited, therefore providing end-to-end corrosion protection.

Equinor has granted approval for the technology to be used in their water injection applications worldwide. What was involved in this programme of works?

Ross: The scope of the Equinor Technology Qualification Programme (TQP) was twofold; firstly to qualify the LinerBridge through a series of simulated reeling and hydrostatic pressure testing, and secondly to qualify the Swagelining integrated polymer-lining system through accelerated age testing. The programme ran for some 15 months at end of life conditions, subjecting both the LinerBridge connector and Swagelining’s tight fitting liner to installation and in-service conditions likely to be seen in the most onerous water injection pipelines projects. A rigorous post mortem inspection and testing regime confirmed the integrity and suitability of the integrated lining system and global approval was granted.

As 80% of the required testing had been completed through Equinor’s Technical Qualification Programme, the qualification process with DNV GL took just five months. What is involved in this process?

Chris: The DNV-RP-A203 qualification framework provides a systematic approach to qualification and document technology, managing qualification at any stage of the development life cycle. The risk-based approach means it is scalable and can be tuned to different scenarios. Other investigations are often shown to be unnecessary and otherwise unidentified risks are solved before deployment, where failure would have significant reputational and financial cost.

The first stage is to define what the technology is, what it has to do and what parameters are important when considering success. Armed with this information, the process can continue to the risk assessment and mitigation phase. The process is a structured sequence of steps, with feedback loops to capture and adapt to change.

Equinor’s Snorre Expansion Project will see the inaugural use the new connector technology for water injection line tie-ins. What does the work scope involve and how is the fabrication and tie-in work progressing?

Ross: In just seven months, the qualification and implementation of this technology was fast tracked on four commercial projects. The first of these to be fabricated was the Equinor Snorre Expansion Project (Figure 2) with first oil forecast for 2021 – thus reinforcing Equinor’s investment in the technology. The Snorre project utilises Subsea 7’s Pipeline Bundle technology encompassing multiple pipelines and control systems within a single carrier pipe, which is then transported to location offshore using the controlled depth tow method. The overall 20.8 km length of bundle system is made up of three discrete bundles, all of which are to be fabricated in Subsea 7’sfabrication facility in Wick and include a 12 in. water injection pipeline.

Figure 2. Equinor Snorre polymer liner insertion. 

To date, ten LinerBridge tie-ins (Figure 3) have been executed to complete the water injection pipeline within the first bundle. To fabricate the water injection pipeline within the remaining two bundles, a further twenty tie-ins will be completed towards the end of Q3 2019.

Figure 3. Equinor Snorre LinerBridge tie-in. 

Four projects have selected this technology as their preferred pipeline connection methodology. Are these all bundle projects or do they involve other subsea pipeline installation methods?

Ross: One project will install the LinerBridge connectors as part of an integrated lining system for a Pipeline Bundle. The other three projects will install the connectors using the reel-lay method. Fabrication for the Wintershall Nova project is now underway at Subsea 7’s Vigra spoolbase in Norway. This pipeline will be installed in the North Sea later this year (Figure 4). Following qualification with operators and DNV GL, the technology is continually being adopted for commercial use for offshore as well as onshore reel-lay tie-ins. This enables installation of PLETs (pipeline end terminations) and flanged connections to be built into the pipeline without the need for complex CRA welding procedures and clad cut-to-length joints.

Figure 4. The LinerBridge connector is qualified for installation via reel-lay and onshore tie-ins.

To address the growing demand for extreme high-pressure water injection systems, hydrostatic testing has been completed to raise the qualified pressure rating of the technology above 380 bar(g). What progress is being made to qualify this enhancement?

Ross: A hydrostatic pressure test was recently completed on a 12 in. test string incorporating a LinerBridge connector (Figure 5). DNV GL has reviewed the test reports and quantified acceptance of the results against failure modes and corresponding acceptance criteria, which was proven in the qualification last year. Subsequently, an updated version of the Technology Qualification Certificate been issued to supersede the previous version – thus increasing the pressure ceiling to 445 bar(g).

Figure 5. Test string fabrication. 

Chris: This involves a comprehensive review of pre-existing qualification data, design failure mode, effects and criticality analysis (DFMECA), further DFMECA and manufacture survey. The process is essentially focussed on identifying and closing out all failure modes from materials supply, component manufacture, installation, pipeline deployment and operation.

Ross: The next step in the qualification process was aimed at providing evidence of the suitability to install connectors offshore in the 6G (45°) and 2G (90°) orientation (Figure 6). This work is now completed and has been qualified by DNV GL. This represents a huge step forward as it sees the boundaries of the technology expanded allowing new markets to open for its application.

Figure 6. 6G LinerBridge installation.

Chris: There is a lot of value in being involved from as early a stage as possible. At the concept stage, we can help assess for feasibility and benchmarking against alternative technology concepts. During development of the technology, we can help ensure that all critical issues are dealt with, so nothing is found to have been forgotten when the entire budget has been spent. Uncertainty can be forced out without disrupting the innovation process.

How will the technology be further developed and supported in the future?

Ross: With the financial impact of corrosion on the oil and gas industry thought to cause billions of dollars in losses each year, it is important that the boundaries of technology continue to be pushed in order to protect the industry’s pipelines. We believe in making subsea fluid transport systems more sustainable by offering a cost-efficient corrosion resistant pipeline solution for all types of rigid pipeline systems – globally. To realise this vision, Swagelining are actively developing new technologies to bring the corrosion resistant benefits of polymer lining to dynamic steel catenary risers and multi-phase hydrocarbon pipelines. Also in development is a modified version of the LinerBridge connector to accommodate automatic welding processes opening up the potential for polymer lining for S-Lay and J-Lay installation methods. Following in the footsteps of this technology, we will continue to work together with DNV GL to ensure new technologies are appropriately qualified for use in commercial projects.

Chris: The technology qualification process helps to bridge ‘uncertainty’ and improve the uptake of great ideas by encouraging confidence in new technology. Few organisations are prepared to be the first to invest or use a new technology that could have significant downsides as well as upsides – they want to see evidence and track record. Often, that takes time. We aim to address their concerns about using new solutions with a systematic, targeted process enabling technology and delivering to market.

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