In-depth | DEEPWATER & ULTRA-DEEPWATER Piping up for a slimmer solution


Det Norske Veritas (DNV) has launched a new deepwater pipeline concept, X-Stream, intended to shave costs from future pipeline installations while maintaining safety standards.


T


he boom in international oil and gas exploration is leading operators into deeper and deeper waters,


necessitating reliable pipeline infrastructures to support the export of these products. Activities in India and China, for instance, have seen pipe-laying projects tackle depths of up to 3000m, while a number of exploration missions in South America and West Africa have taken place at distances such as 300km from the coast, and, as one would expect, the volume of steel required for such pipeline set-ups can prove to be extremely expensive. Of course, floating liquefied natural gas


(FLNG) hubs and LNG shuttle tankers could come to represent a cheaper option for deepwater projects over time, but, in the here and now, this solution is relatively new and nowhere near close to covering global energy demand single-handedly. In turn, Norwegian class society DNV


this January launched a new pipeline concept, named X-Stream, which seeks to reduce the amount of steel wall thickness in the typical pipeline arrangement, while controlling the pressure differential between the pipeline’s external and internal pressures, in order to maintain safety standards and pipeline integrity. Te concept itself relies on existing, long-established technological and engineering methods to achieve its aim. X-Stream’s genesis can be traced to a


brainstorming challenge hosted in Brazil in 2009, explains Asle Venås, global pipeline director at DNV. “We took a group of young engineers in Brazil, and set them the challenge of devising a way to bring gas from the pre-salt layer to shore in an economical manner,” he recounts, “but we wanted them to use existing technologies and to put them together in a new way.” He admits that the resultant X-Stream concept, which was developed by the group within a timeframe of two months, appeared so simplistic and almost obvious that DNV was pleasantly surprised to discover that it had not already been patented. DNV is now ready to roll out


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thickness by approximately 25-30% without compromising on ISO or the DNV-OS- F101 offshore pipeline standard.” Te latter DNV standard is reckoned to cover some 65% of all global offshore pipelines. Venås says: “By utilising an inverted high


Asle Venås, global pipeline director at DNV: the X-Stream concept could reduce pipeline steel thickness by 25-30%.


the concept to any interested parties who may wish to conduct joint studies with the class society.


Maintaining pressure “The time of ‘easy oil’ is over,” Venås continues. “Exploration is taking place in harsher environments and we’re seeing longer distances of pipeline, especially for gas exports. Deepwater operations carry the additional risk of very high external pressure, with internal pressure typically lower, to compensate, so thick pipeline walls have been the norm. However, there are problems associated


with relying on thick walls: they make the pipelines much heavier, which causes a handling and logistics nightmare; there is a limited number of pipe mills capable of meeting forthcoming oil and gas sector demand; the thickest steel pipes can be very difficult to weld; and the use of buckle arrestors, to prevent pipeline sections from buckling, can also be very expensive. X-Stream has been developed to reduce this


pressure protection system [i-HIPPS] and inverted double block and bleed valves [i-DBB] – both well-proven technologies, with more than 20 i-HIPPS being utilised in other applications around the world – the system immediately and effectively isolates the deepwater pipe if the internal pressure starts to fall.” In this way, the i-HIPPS and i-DBB ensure that, when in operation, the pipeline’s internal pressure never drops below the collapse pressure – as pressure drops below a certain point, the i-DBB valves automatically close. With a certain minimum pressure maintained within the pipeline at all times, the concept should prevent the likelihood of an implosion, even with the aforementioned reduction in steel thickness. According to Venås: “It will also be


important to maintain the minimum pressure in the pipeline during pre-commissioning. This can be done using produced gas separated from the water in the pipe by a set of separation pigs and gel. Tis method has already been initiated as standard practice by several oil companies.” With reductions of up to 30% in pipe


wall thickness on the cards, Venås sees a number of beneficial outcomes for the oil and gas industry. “For instance, Gazprom’s South Stream pipeline project has budgeted €15.5 billion [US$20.5 billion] so far,” he says. “Te X-Stream concept could result in savings of up to 5-10% in pipeline installation costs, thereby amounting to a cost saving of approximately €1 billion.” Other benefits of the concept could include increased pipe-lay rates and increased competitiveness between pipe-laying fleets, providing some potential stimulus to this sector. “We could also see elimination of the need for buckle arrestors altogether, saving more installation and transporation costs,” Venås adds. OMT


Offshore Marine Technology 1st Quarter 2012


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