The increasing needs of natural gas, foreseen for the next years, makes more and more important the type of transportation chosen, both from strategic and economic point of view. The most important gas markets will be Northern America, Europe, Asia and Russia but the demand shall be fulfilled also by emerging producers as Kazakhstan, Turkmenistan and Eastern Siberia that at the moment are developing their resources in order to be competitive on Gas market. In this way producers and customers will be placed at greater and greater distances implying realization of complex gas transportation pipeline network, when use of LNG tankers is impossible or uneconomic. On the base of these considerations in 1997 began a feasibility study on X100 steel, given that, comparing different design approaches, it has been observed that consistent savings could be obtained by means of using high grade steel and high pressure linepipes. In this multi-sponsored project (Eni group, European Community of steel and Carbon, CSM, Corus and Europipe) CSM and Corus group were involved in the laboratory and full-scale pipes testing, Europipe was the pipes producer and Snam Rete Gas was involved in field weldability and technical coordination. No technical breakthrough, but only improvements in the existing expertise were involved in the X100 production; consequently, the production window is very narrow. However optimized steelmaking practices and processes enabled the material to reach the desired properties: strength, toughness and weldability. This paper is intended to present the general results arising from this project, in terms of steel properties (chemical composition, mechanical properties), ductile and brittle fracture resistance (results of full scale burst tests, West Jefferson tests) and field weldability, but above all the know-how stored till now on high grade steel and its possible use from a Gas company and a Pipe maker point of view.

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