Optimal dimensioning of pipe networks: the new situation when the distribution and the transportation functions are disconnected

De Wolf and Smeers [9] consider the problem of the optimal dimensioning of a gas transmission network when the topology of the network is known. The pipe diameters must be chosen to minimize the sum of the investment and operating costs. This model does not reflect any more the current situation on the gas industry. Today, the transportation function and gas buying function are separated. This work considers the new situation for the transportation company. We present here first results obtained on the belgian gas network and on a part of the french network.