DNV dives deep with X-Stream

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Norway’s DNV has unveiled a new pipeline concept, X-Stream, which it believes can significantly reduce the cost of deep- and ultra-deepwater gas pipelines.

DNV says X-Stream can achieve this by reducing both the pipeline wall thickness and time spent on welding and installation compared to deepwater gas pipelines currently in operation.

Dr. Henrik Madsen, DNV’s CEO, told a press briefing in London that many gas pipelines now being considered are in extreme water depths and at the very limits of current technology.

He said: “DNV has been instrumental in developing and upgrading the safety and integrity regime and standards for offshore pipelines over the past decades. Today, more than 65% of the world’s offshore pipelines are designed and installed to DNV’s offshore pipeline standard.

“As the deepwater gas transportation market will experience massive investments and considerable growth over the coming years, new, safe, and cost-efficient solutions are needed.”

He said DNV’s engineers had been tasked with finding a solution to get this gas to shore.

“One of the big challenges for the industry is the ultra-deepwater oil fields being developed. I’m thinking of the Brazilian pre-salt where we are at 3,000m and West Africa where we can also get down to those depths. We want to reduce gas flaring, so we need to find a gas solution to produce the oil.

“Because of the very deep water and the very high pressure on the pipe, if you just follow today’s tradition, you will get either very thick pipes or you will get very small diameter pipes.

“The distance to shore is increasing too. The X-Stream concept can for such fields represent an alternative to, for example, floating LNG plants combined with LNG shuttle tankers,” he said.

DNV says X-Stream, which has been developed by a team of mostly young engineers in Brazil, is based on established and field-proven technologies which have been innovatively arranged.

By controlling the pressure differential between the pipeline’s external and internal pressures at all times, the amount of steel and thickness of the pipe wall can be reduced by as much as 25-30%.

Asle Venås, DNV’s Global Pipeline Director, said: “The era of easy oil and gas is over and it is getting more and more difficult to produce. We are getting further and further away from shore to more harsh environments and deeper water.

“Long distance gas transportation in deepwater is very challenging and we are seeing bigger and bigger gas pipelines needed over longer and longer distances.

“We came up with the idea of controlling the difference between the internal and external pressure. The concept is based on a combination of already established technology put together in a very innovative way. It is not new. The concept meets today’s normal standards.”

He explained how the X-Stream pipeline system works. “By utilising an inverted High Pressure Protection System – i-HIPPS – and inverted Double Block and Bleed valves – i-DBB – the system immediately and effectively isolates the deepwater pipe if the pressure starts to fall. In this way, the internal pipeline pressure is maintained above a critical level for any length of time.”

He said the new concept is simple and reliable. During installation, it is necessary to fully or partially flood the pipeline to control its differential pressure. During operation, the i-HIPPS and i-DBB systems ensure that the pipeline’s internal pressure can never drop below the collapse pressure – plus a safety margin. A certain minimum pressure will be maintained in the pipeline at all times.

“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. This technology is not new to the industry. This method has already been initiated as standard practice by several oil companies,” said Venås.

Current deepwater gas pipelines have thick walls and, due to quality and safety requirements, the number of pipe mills capable of producing the pipe is limited.

Venås said the benefits of the new system are that expensive buckle arrestors would not be required, and that the thickness of the steel required for the pipeline could be reduced and more pipe mills would be capable of manufacturing it.

He said: “Pipes are coming to the limit of thickness of what can be built. They are very difficult to produce and only a very limited number of mills can produce them, so the price goes up. Handling and logistics of those big pipes is also very challenging.

“Another challenge is that you need buckle arrestors which are very costly. The pipelines need bigger and bigger vessels to install them.”

Venås said that one of the possible spin-offs would be that there would also be increased competition among pipelay vessels with more of them able to lay the lighter pipe. Welding times would also be reduced.

“When installing pipelines, the heavy weights are difficult to handle and the thick walls are challenging to weld. And finally, the number of pipe-laying vessels for deepwater pipelines is limited too,” he said.

Madsen highlighted a number of deepwater gas pipeline projects around the world that are currently being built or being considered, including South Stream, White Stream, Galsi, Poseiden, Sage, Medgaz 2, Liwan and Gendalo-Gehem.

Madsen added: “It’s essential for DNV that the new concept meets the strict requirements of the existing safety and integrity regime, and I’m pleased to confirm that this concept does.

“At DNV, we feel confident that, by further qualifying the X-Stream concept, huge financial savings can be made for long distance, deepwater gas pipelines without compromising pipeline safety and integrity.”

He stressed, however, that the DNV study is a concept study, and a basic and detailed design will need to be carried out before the X-Stream concept is realised on a real project. DNV intends to work further with the industry to refine and test the concept.

Date: 03/04/2012
Author: John Sheehan

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