New Deep-water Pipeline Concept, Reduces Cost but not Safety

By , DNV

DNV has developed a new pipeline concept, called X-Stream, that can significantly reduce the cost of a deep- and ultra-deepwater gas pipeline while still complying with the strictest safety and integrity regime. X-Stream is based on established and field-proven technologies which have been innovatively arranged.

X-Stream can reduce both the pipeline wall thickness and time spent on welding and installation compared to deep-water gas pipelines currently in operation. The exact reduction in the wall thickness depends on the water depth, pipe diameter and actual pipeline profile. Typically, for a gas pipeline in water depths of 2,500 m, the wall thickness reduction can be 25 to 30 % compared to traditional designs.

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

New offshore oil and gas fields are being developed in deeper and deeper waters and export solutions for the gas are critical. New exploration activities are also heading for ultra-deepwaters. The distance to shore is increasing too. The X-Stream concept can for such fields represent an alternative to e.g. floating LNG plants combined with LNG shuttle tankers.

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 % - or even more compared to today’s practice and depending on the actual project and its parameters. This will of course make it easier and cheaper to manufacture and install the pipeline.

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 inverted High Pressure Protection System  (i-HIPPS) and inverted Double Block and Bleed valves (i-DBB) systems ensure that the pipeline’s internal pressure can never drop below the collapse pressure – plus a safety margin. In sum – a certain minimum pressure will be maintained in the pipeline at all times.

Source:

http://www.dnvusa.com/press_area/press_releases/2012/newdeepwaterpipelineconceptreducescostbutnotsafety.asp. Accessed by 20-1-2014