Compressors of various purposes and types play an important role in the gas and oil industry. In the gas industry, the installed capacity of centrifugal compressors is about 55 million kW. The role of turboexpander aggregates is quantitatively secondary in comparison with pipeline compressors(about 1 million kW of installed capacity), but without turboexpander aggregates, it is impossible to transport and process natural and petroleum gas. It is important that turboexpander aggregate compressors operate with high efficiency and provide all the variety of possible operating flow rates. The main domestic manufacturer of turboexpander aggregates, JSC Turboholod, has been subcontracting the St. Petersburg Polytechnic University for compressor design since mid-2000. Prof. Y. Galerkin’s Universal Modeling Method has been well proven and widely applied in design practice. SPbPU and JSC Turboholod constantly cooperate since then. By 2021, 22 types of centrifugal compressors have been designed for more than 120 turboexpander aggregates operating in the industry. The unit capacity of the compressor is up to 6500 kW, the outlet pressure is up to 12 MPa, the total capacity of the turboexpanders is more than 400 MW. Although computational fluid dynamic methods still cannot correctly calculate the gas dynamic characteristics of a centrifugal compressor, the calculation of the flow in the stationary elements of the flow path provides correct information. The analysis of the inlet tract, consisting of a supply pipe, a connecting pipe and the compressor inlet nozzle, gave information about the flow structure, showed the problem areas of the inlet tract, made it possible to estimate the loss of efficiency in the tract, and outline the directions for improving this element of the flow path in perspective designs.