Resumen del autor, extraído del trabajo. High pressure (HP) pipelining is considered the most economic and safe technology for long-distance transportation of large volumes of natural gas. Since 1995, several Eni companies have been involved in a research project for the development of high pressure (10-15 MPa) technology. The project outcome at the end of 1998 was the definition of a new technology, using high strength steel API 5L X-80 line pipe. At present time a group of Eni companies (Snamprogetti, Snam, Saipem, Eni Div. Agip, EniTecnologie, Aquater) are engaged in new developments of the HP technology, mainly focusing on higher strength steel pipe (X100), aiming at obtaining further investment cost reduction. Thermodynamics as well as fluid dynamics of natural gas at high pressure have to be addressed, in order to correctly describe the flow behaviour. The designer should be able to predict the pressure of shock waves travelling in the pipeline and evaluate the effect on the devices installed in the pipe. Besides, very low temperatures can be reached downstream valves and orifices, due to gas expansion, and pipe wall material can overcome the brittle-fracture point. Three-dimensional CFD codes integrating Navier-Stokes equations, simulate such flow problems, but require large computation times to handle piping systems. Thus the need for a one-dimensional (1-D) code becomes evident; nevertheless information relevant to multidimensional flow configurations must be added to this simpler calculation scheme. According to this concept, an innovative approach has been developed based on the use of a 3-D commercial CFD code ("FLUENT") in order to supply complex flow and pressure patterns in fittings and boundary areas. Starting from these calculations, a more simplified description is derived and implemented within a new 1-D computer code ("MACHNET").