A verification of commonly used approval in pipeline hydraulics is carried out that the work of friction forces performed at the movement of real gas on the gas pipeline completely turns into thermal energy. It is obvious that measurements of the actual temperature of the transported gas cannot confirm this hypothesis due to the inaccuracy of measurements of parameters affecting thermal processes in a real gas pipeline. The solution of the initial system of differential equations describing the 1-D process of stationary pipeline transportation of natural gas is considered as a serial set of values of thermobaric and rate flow parameters -pressure, temperature, velocity -of elementary volume of gas as it moves through the gas pipeline, that is, the Lagrangian approach is used in the study of the pipeline natural gas transport process. By means of integral definition of entropy by Clausius it is shown that the mentioned statement about the conversion of the work of the friction forces entirely into the thermal energy of the gas flow finds its confirmation with an accuracy acceptable for engineering applications in relation to the one-dimensional formulation of the problem of determining temperature of a gas along the length of pipeline.