Within the framework of an R&D program entitled "Long Distance Transport of Natural Gas by High Pressure Pipelines" various optimized configurations have been found which are able to satisfy the required task (i.e., transport of a fixed gas capacity along a fixed distance and for a fixed number of years). Some configurations are relevant to a traditional operating pressure (about 1087 psig (7.5 MPa (9))); others are relevant to very high operating pressures (about 2175 psig (15 MPa (9))). By comparing these optimized configurations we have found that they are characterized by the same total cost, i.e. different optimized configurations are equivalent on economic terms. Furthermore, the cost distribution (pipe cost, fuel cost, etc.) is the same for each optimized configuration. Finally, a mathematical model has been developed that justifies these findings.
The ENI Group is supporting since 1995 an R&D program, shared between Snam and Snamprogetti, about long distance transport of natural gas by high pressure pipelines. The available know-how within certain companies of the Group (Agip, Eniricerche, Saipem, Snam, Snamprogetti), supported by other Italian Companies (Nuovo Pignone, ILVA), forms the basis to develop this matter. The completion of program is expected at the end of June 1998.
The study of world natural gas reserves and gas demand has brought into focus a possible future scenario for the natural gas expioitation and transport, that is the exploitation of large deposits in the Middle East and the delivery of natural gas to Central Europe (Fig. 1). Based on the supposed scenario, we have carried out a technical-economic optimization of the transport system. In particular, we have considered two different transport alternatives, that are: hiah oressure oipelines; normal (i.e., commonly used) pressure oioelines (we will call them "low pressure pipelines" in the following chapters).
The transport system consists of a buried pipeline with several compressor stations. In order to simplify the analysis we have made the following assumptions: l the whole gas flow rate is transported by the pipeline from the production plant to destination; l the pipe diameter does not change along the line; l identical compressor stations are regularly spaced along the line; they are located at the same altitude. Furthermore, for the main items of the transport system, we have made the following technical choices:
gioeline nominal diameter: the diameters listed in the API 5L Spec. have been considered, up to 72 inch, although this large diameter has never been used before for gas pipelines.
pipe material: for the low pressure systems the grade X70 steel (API 5L Spec.) has been selected.
For the high pressure systems, a higher strength steel (X80) has been preferred to the X70, to limit the required wall thickness at a maximum value of 1.3 inch (33 mm), that is the maximum wall thickness of pipes supplied by the world's main producers, at present.