TPi July 2010

developments products &

Tungum tube pipe work for offshore construction

MGI-Imhäuser GmbH, a specialist in tube production and manipulation, manufactures tubes using Tungum – an aluminium-nickel-silicon-brass alloy – for offshore applications. Highly resistant to seawater and its atmosphere, Tungum resists both stress and crevice corrosion to offer serviceability even at intermittent duty in the highly corrosive ‘splash’ zone. Tungum tube was launched in the early 1920s as a decorative alloy. It was soon realised to be an excellent copper- based engineering alloy, and prior to World War II was a favoured material for many applications, such as military aircraft, ships, ferries and dredgers. Its non-magnetic and non-sparking properties make Tungum suitable for use in piping high pressure gases, particularly oxygen, where its thermal

conductivity/diffusivity characteristics virtually eliminate the potential dangers present when lesser materials are employed. Tungumalloy is also a cryogenicmaterial, suitable for chemical engineering and low temperature processes. Its corrosion resistance often enables its use in conveying fluids and gasses containing corrosive elements. In salt-laden marine atmospheres, 316 stainless steel is susceptible to crevice corrosion and chloride pitting. After just a few years of salt spray exposure it may still look bright from a distance, but closer inspection can reveal signs of imminent failure to hold pressure. However, according to the manufacturer, Tungum alloy possesses a natural protection mechanism whereby, on exposure to salt spray, a very thin oxide coating is generated over the exposed surface, no more than two thousandths of an inch thick, when complete. The tube becomes discoloured, and may even have a verdigris coating, but under the oxide layer the tube material is perfect and will remain so for a long time. In one example, Tungum alloy tube remained unscathed despite more than ten years’ marine exposure on a

semi-submersible support vessel. The stainless steel section, from a southern North Sea gas platform, shows both crevice corrosion and chloride pitting after barely five years in the same environment, in lines under pipe clamps. The strength to weight ratio of Tungum alloy compares favourably with other materials. In tubes, this can provide the opportunity to employ smaller, lighter sections, reducing the size and cost of fittings. As would be expected of a material originally developed for use in the hydraulic control systems of aircraft, Tungum alloy is said to have excellent fatigue resisting properties. Fields of application for offshore platforms and associated specialised vessels include hydraulic and pneumatic control; instrumentation and impulse lines; fire fighting (deluge) control and instrumentation lines; life support systems; and marine auxiliary systems (pedestal cranes and other mechanical handling systems). The tubes are also of use in offshore dive systems (life support circuits, hyperbaric weld habitats and hydraulic control systems), and marine repair work (replacement of corroded carbon steel deck machinery lines, renewal of cargo valve control lines, and tank wash-down system pipe-work). MGI-Imhäuser GmbH – Germany info@mgi-olpe.de www.mgi-olpe.de

Photographs courtesy of Subsea 7 Ltd

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Tube Products International July 2010

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