EuroWire March 2018

Technical Article

Umbilical cables and submarine cables are unlikely to see steel eliminated in the near future, though their replacement will be consistently under scrutiny with the improvements of composite materials. There will be a constant demand for manufacturers of steel wire, strip and tube to improve the performance and quality of their products if they are going to meet the demands for subsea cables in the future. n

In many recent deep water projects, steel tubes for control and injection lines have become the preferred solution over traditional thermoplastic hose-based designs. This is due to enhanced response time and prevention of permeation of fluids (particularly methanol) from the tube. In general, the preferred material for the steel tubes is super duplex stainless steel. The typical size for the steel tubes is between half an inch and one inch, though some designs are proposed which incorporate a large core tube (eg two to three inches), which is used for gas lift or methanol injection. Tubes are constructed as ‘seam-welded’ from strip or ‘seamless’ from hollows. Seamless is usually only available in relatively short lengths, necessitating welding to achieve the required production lengths. Seam-welded tube can be produced in lengths between 3,000m and 8,000m, depending on the tube size. Tubes are manufactured from carbon steel or stainless steel (duplex, super duplex, etc). The material chosen is dependent on corrosion resistance, pressure requirements and strength. Due to the product lengths, welding plays an important role in the production of seamless or seam-welded tube. This, in turn, necessitates high inspection standards for the tube, such as: Butt weld inspection : 100 per cent X-ray. Thick walled tubes require multiple welding passes (typically two to four depending on bore size/wall thickness, with 100 per cent X-ray after each weld pass. Seamwelds : Continuous eddy current inspection. This may also be combined with ultrasonic inspection. Stainless steel requires the tubes to be purged with inert gas to ensure the welds are to the correct specifications. Carbon and duplex steels (and super duplex where the surface temperature will exceed a critical limit) require the presence of external corrosion protection for service in marine environments. Generally, stainless steel materials of construction offer very high levels of corrosion resistance. However, care has to be taken as it is known that seawater containing sulphite– reducing bacteria can result in corrosion attack of welds.

Ceeco Bartell Machinery Systems LLC Ceeco Bartell Products 400 Applewood Crescent, Suite 100, Vaughan, Ontario, Canada Tel : +1 905 761 3000 Email : sales@bartellmachinery.com Website : www.bartellmachinery.com

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March 2018