Offshore oil & gas construction pipes for deep water are exposed to high collapse pressure, to high axial loads and partly to fatigue in the girth welds. Pipes suitable for this application are characterized by heavy wall thickness, higher strength material, by tighter tolerances and high fracture toughness properties. Looking into water depths of 10,000 ft (3,000 m) and above these properties are becoming increasingly more crucial.
Today the UOE pipe making process is best suited to produce longitudinal welded pipes of the same dimension in large amounts with short deliveries and low costs. Additionally to the UOE forming process generally the DSAW welding is applied in order to accommodate the high productivity requested to take full benefit from the high efficiency of the UOE process. Both fabrication methods have been limited to a wall thickness up to ca. 1.50?? (38.1 mm) wall thickness and the grade API 5 L X-70 to deliver the requested high fracture toughness and tight tolerances.
State of the art plate production, integrated R&D activities between plate supplier and pipe manufacturer create a position where the delivered pipes fulfil the extreme requirement for the ultra deep water business. Tendon pipes with 1.70?? (38.1 mm) wall thickness in X-75 were delivered with the fracture toughness requested, a wall thickness up to 2.0?? (50.8 mm) is possible and material grades higher than X-80 can reach into deeper water without changing the standard design for pipe based tools. This article takes reference to the above mentioned products and provides an outlook what will be available in the near future.
New larger offshore oil & gas fields justifying bigger scale investments and being able to serve larger markets are moving further out into the open sea. Most of the important oil & gas offshore areas are reaching water depths of 6,500 ft (2,000 m) and more. Areas like the Brazilian East Coast, the West Coast of Africa, the eastern part of the Mediterranean Sea, the Atlantic Margin and others are to be named. In these projects pipes are used not only for pipe lines in order to transport the fluids but also as structural components, partly in combination with the use as a liquid transportation tool. The challenges pipes have to withstand in this environment are becoming progressively more severe. Growing collapse pressures, high axial loads and increasingly fatigue loads are some of the most important challenges designers and pipe producers have to create solutions for. Over all beside the technical solution to be created the safe and long term operation is driving very much the economics for these projects which finally is the basis for a positive final investment decision.
