Safety to the bottom of the sea

Louise Smyth

Specialist piping solutions designed for the oil and gas sector

All over the world, extraction of oil and gas on the high seas demands innovative and complex piping solutions using high-quality materials. It is no longer unusual for oil companies to be drilling for oil at more than 10,000m below the surface of the sea.

To ensure long-term profitability, any source needs to be exploitable for at least 25 years. Germany’s Schoeller Werk makes its own contribution to the necessary quality and planning assurance with its heavy-duty control-line & chemical-injection pipes for the offshore industry. Their technical design is such that they can withstand not only the extreme pressure conditions thatprevail in deep seas, but also extremely high temperatures and aggressive liquid media.

Worldwide, there are more than 2,000 offshore drilling rigs and many more individual wells with oil and gas being extracted on a continuous basis. The technical equipment for these installations sets extreme demands on the handpicked suppliers from the stainless steel industry. Schoeller Werk took up the offshore challenge 35 years ago and for many years has been among the kingpins of the industry. At its base in the Eifel, the company not only manufactures tubes for various sectors, it also creates technologically remarkable solutions for use on drilling rigs.

Oil and gas extraction in Norway

For one company alone, TCO Norway, service provider for Norway’s state-owned Statoil enterprise, Schoeller Werk has supplied over 500,000m of piping since winning its custom in spring 2014. At the core of this partnership is a plug-drawn annular pipe made of high-quality nickel-based alloys nos. 825 and 625. In addition there are austenitic pipes made of class 316 Ti stainless steel. The pipes being delivered impressed Statoil so much that it has defined them as standard for its own specifications. Apart from a variety of materials, it is necessary to manufacture the various diameters and wall thickness – plug-drawn Schoeller pipes cover all the possibilities. The pipe design and the corresponding quality testing make it possible for the finished solution to withstand internal pressure of up to 2,500 bars without difficulty. Moreover, the high-quality materials, in conjunction with improved surface quality deriving from the drawing process, are able to resist the effects of salt water and other aggressive media.

Plugs make things smooth

Among the features of the plug-drawn pipes are their geometrically precise curvature and high weld quality. In principle, the basic material is not a factor in this and it is possible to manufacture individual pipes of up to 2,000m in length. An internal mandrel (plug) acts to smooth the inside of the longitudinal weld. In conjunction with an external mandrel, the initial cross-section of the tube can thus be reduced by up to 50%. All in all, this is a longitudinally welded solution that gives the impression of being a seamless pipe. A look at the microstructure of the material reveals that the welded seam can hardly even be detected after the pipe has been drawn. Properties such as these have been key plus points for Schoeller Werk’s offshore customers.

Careful testing of control and injection pipes

The offshore industry uses such pipes as hydraulic control lines for safety valves as well as for pumping chemicals into an oil reservoir. In this way, they support the entire extraction process. The injection pipes make it possible for rig operators to use chemicals in targeted fashion to liquefy the oil and thus to improve its flow properties. During the complex manufacturing process, the pipes undergo various tests to ensure the special quality of the products before they are installed. Strips of metal are welded with a longitudinal seam using the tungsten inert gas (TIG) welding process and rolled into tubes. Apart from the obligatory eddy-current testing, the tubes subsequently undergo an air under water (AUW or ‘bubble’) test. The tubes are submerged in water and filled with air to a pressure of up to 210 bars. A visual inspection is made along the entire length of the tubes to check that they are airtight. So that Schoeller Werk can supply its customers with the required lengths of 15,000m and more, individual pipes are orbitally welded together and an X-ray is made to check that the orbital weld is airtight and free of any pores.

Before delivery to customers, Schoeller Werk also subjects the control and injection pipes to a hydraulic test. This involves filling the finished coils with hydraulic fluid and subjecting them to pressures of up to 2,500 bars to simulate the extreme conditions sometimes experienced in offshore work.

Apart from pure manufacture of pipes, Schoeller Werk also offers its customers from the offshore industry a comprehensive service package, which includes, for example, encapsulation of pipes with plastic sheathing in so-called flat packs. This means that bundles of pipes can be attached to the extraction tubes and protected from buckling and squashing. Other services include flushing and filling of pipes. Here the insides of the pipes are flushed with hydraulic fluid until the fluid reaches the specified ISO or SAE purity classification. The fluid filtered in this way can remain in the pipes if the customer so requires, meaning that users obtain a product that is ready to use. Furthermore, it is also possible to equip the pipe bundles with electrical wiring or stainless steel support cables. Also, thanks to the smooth internal surface, plug-drawn pipes are also ideal for use as ducting for optical fibre cables transmitting signals using light.

In its work with the offshore industry, Schoeller Werk has joined an international market. Apart from Norway and Great Britain around the North Sea in Europe, Russia, Saudi Arabia, UAE, Africa, Asia, Australia and South America all count among the key target regions for use of the Schoeller control-line & chemical-injection pipes.

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