coatings for offshore applicationcoatings for offshore application

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Subsea coating successes

Craig Thomas, COPON Pipelinings, E Wood Ltd, UK, discusses the benefits of using internal flow coatings for offshore gas pipelines, as seen recently on several important pipeline projects.

The concept of internally lining gas pipelines was developed in order to provide enhanced flow and therefore reduce operational costs. International oil and gas companies now recognise the many

benefits of internally coating pipelines in both an onshore and offshore environment. For this application, Copon EP2306 HF was developed by COPON Pipelinings, E Wood Ltd - a pioneer of internal flow coating technology.

In addition to enhanced flow, there are many other economical and technical benefits available to pipeline operators, in particular in an offshore environment.

Corrosion protection in storage and during commissioningStringent marine regulations now prohibit the disposal during commissioning of millscale and rust debris into the sea, which has wide ranging implications.

After the pipe has been blast cleaned, the application of an internal flow coating prevents rust from reforming, thus eliminating the need for additional pre-commissioning work, which can be very substantial in terms of time and cost, particularly for pipes stored in a marine environment and then used in the construction of a subsea pipeline.

It has been suggested in various reports that up to 150 000 kg of debris can be cleaned from a 250 km long, uncoated pipeline. Such debris would require removal in accordance with stringent guidelines.

Optimum commissioning

InspectionThe use of an internal flow coating provides for easier and faster commissioning of the pipeline after the pipeline has been laid and engenders more rapid drying after hydrostatic testing.

The avoidance of delays in the budgeted transmission date, which can be brought about by the removal of many tons of millscale and rust from uncoated pipe through pigging operations, means that the cost of the internal pipe coating can almost be reclaimed at this point in the pipeline’s operating life.

Testing and any robotic inspection procedures are greatly simplified by improved mobility of the equipment travelling down the internally coated pipe.

Pigging potentialWhen Statoil first started developing subsea pipelines to transport its gas from the North Sea to Europe in the 1990s, the pipeline lengths were too great to be commissioned by the pigging and testing technology of that time. Statoil stated in 2005 that pigging distances of up to 800 km could be feasible, when carefully designed pigs were used in combination with a smooth internal surface created by an internal flow coating.

Statoil also reported in 2005 that it made the decision to apply an internal epoxy coating (Copon EP2306 HF) to the pipe used for the Langeled gas pipeline project in order to increase transport capacity and reduce pig wear. It claimed that the amount of millscale and corrosion products was reduced and that extra pigging would have been required in the absence of an internal lining.

Drying the lineFurthermore, Statoil reported that examination of the existing methods of drying the pipeline after de-watering had created large scale uncertainty regarding the project schedule, which gave rise to further research into pipeline drying. Internal coating of the line was beneficial in this regard, leaving less free water in the pipeline due to the smooth swabbing action of the pigs.

Preventing corrosion after precommissioningWhen raw seawater enters an uncoated pipeline, the amount of corrosion can be substantial, resulting in tens of thousands of kg of corrosion debris that must be removed, along with internal corrosion up to 35% of the total pipe weight, resulting in a significant reduction in the effective life of the pipeline. It is reported that there are (uncoated) pipelines that have been cleaned during pre-commissioning to an exact specification, but have nevertheless produced up to 50 000 kg of

coatings for offshore application

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powder on start-up, causing damage to equipment and ultimately leading to the shutdown of the receiving facilities.

According to John Grover of BJ Process and Pipeline Services, "internal coating should be considered (for gas pipelines) not just on the merits of flow efficiency, but also on corrosion and ease of cleaning and drying". Andy Barden, of the same company, has also commented that many pipeline operators are so concerned about these issues that they have decided to internally coat the pipe just to mitigate against these problems.

Natural gas pipelines immersed in the North Sea, for example, may be filled with sea water for a year, and the internal flow coating is required to perform under these pre-service conditions. The corrosion protection characteristics of the internal flow coating are therefore extremely important in these circumstances.

Equally, line-fill water can be chemically treated to reduce the risk of internal corrosion in the pipeline during the commissioning process. Discharge of such water, again, has wide ranging environmental implications, which the application of an internal flow coating can help to reduce.

Internal flow coating benefitsIn addition to the previously mentioned economical and technical benefits, the following can also be achieved:lReduced energy costs in pumping and compressor

stations.lLow capital cost.lSealed surface – product purity.lDiverse pipeline use – easier product switch.lRapid payback.lReduced valve maintenance.lMinimal sidewall deposition.lImproved flow pattern.

During a period spanning almost half a century, COPON Pipelinings has supplied product for over 140 000 km of lined pipe worldwide for both onshore and offshore pipeline projects, including the Balgzand-Bacton line (North Sea); the Dolphin gas pipeline (Persian Gulf); as well as the Langeled gas pipeline (North Sea).

Offshore gas pipelines

BBLThe Balgzand- Bacton line (BBL) is a joint-venture of E.ON Ruhrgas, Fluxys and NV Nederlandse Gasunie. The 235 km long, 36 in. diameter pipeline, of which 230 km is offshore under the North Sea, will have a capacity of 15 billion m3/yr and was internally coated with Copon EP2306 Series. The BBL began commercial delivery of gas between The Netherlands and the UK in December 2006.

Dolphin gas pipelineThe Dolphin gas project is one of the largest trans-border energy projects ever undertaken in the Middle East. The second phase of project was the construction of a 370 km long, 48 in. diameter subsea pipeline to carry gas to the UAE. The pipeline, which was internally coated using Copon EP2306 HF, has the capacity to transport up to 91 million m3/d and came onstream in late 2006.

Langeled gas pipelineThe Langeled gas pipeline is the world’s longest subsea pipeline at 1200 km with diameters of 42 and 44 in. It comprises over 100 000 pipe joints that are internally coated with Copon EP2306 HF. The pipeline will deliver up to 70 million m3/d of gas to the UK and has a design life of 50 years according to Norsk Hydro.

The Langeled (Ormen Lange) project is a joint venture with partners such as Norsk Hydro (operator in the development phase); Statoil (responsible for designing and laying the pipeline); Royal Dutch Shell (operator in the production phase); and Gassco (operator of the pipeline after completion).

Delivery of gas to the UK through the 600 km, 44 in. southern leg of the pipeline began on 1st October 2006. The completion of the first stage of the project, the cost of which is reported to be NOK 17 billion, came in at NOK 3 billion under budget.

The 600 km x 42 in. northern leg is due to become operational in October 2007, which will coincide with deliveries from the Ormen Lange field in the Norwegian Sea. The Langeled system will have a total capacity of 20 billion m3/yr and will supply Great Britain with 20% of its gas.

Figure 1. 44 in. diameter steel pipe internally coated with Copon EP2306 HF for the 1200 km Langeled gas pipeline.

coatings for offshore application

Bibliography1. BARDEN, A., Preparation is Everything, World Pipelines (10/2006).2. BUCHANAN, R. AND HABERER, S., Coating the Long Connection, World

Pipelines (08/2006).3. Construction begins on the World’s Longest Subsea Pipeline, Pipeline-

News.com (Accessed on 20/06/2005).4. Dolphin Gas Project, Ras Laffan, Qatar, Hydrocarbons-technology.com

(Accessed on 27/03/2007).5. Dutch-UK Balgzand-Bacton Gas Line Starts, Oil & Gas Journal

(04/12/2006).6. FALK, C. and MARIBU, J., Extensive Sub-sea Commissioning, Pigging

pose Challenges, Oil & Gas Journal (21/11/2005).7. Gassco takes over Langeled Pipeline Operations, Oil & Gas Journal

Online (06/09/2006).8. Gas Deliveries to UK begin through New Pipeline, Oil & Gas Journal

Online (04/10/2006).9. Gas from Langeled reaches UK Market, PipeWire.net (04/10/2006).10. GROVER, J., Mitigating Threats: Strategies in Managing Offshore

Pipelines, Pipeline (Dubai) Magazine (10/2006).11. Dual Diameter Pigging reaches new Extremes; Langeled looms, Oil &

Gas Journal (28/11/2005).12. KUT, S., Liquid Internal and External Pipe Coatings for the Oil and Gas

Industry, Petrotech 2001 – 4th International Petroleum Conference, New Delhi, India (09/01/2001 - 12/01/2001).

13. London Inauguration marks Langeled start-up, Oil & Gas Journal (23/10/2006).

14. OTC: Ormen Lange Field Development continues apace, Oil & Gas Journal (17/05/2004).

15. The World’s Longest Subsea Pipeline is on Schedule, PipeWire.Net (17/05/2006).

16. THOMAS, C. The Inside Track, World Pipelines (08/2006).

Figure 2. 48 in. diameter, thick-walled steel pipe coated with Copon EP2306 HF awaiting onward shipment to the Middle East for the Dolphin gas pipeline project.

RepRinted FRom WoRld pipelines APRIL 2007 www.worldpipelines.com