This paper reports about the reverse-engineering of a five stage centrifugal compressor rotor by a Non-OEM turbo machinery service provider. In order to reach the aim of increasing the lifetime of the rotor, new enhanced material is used for some compressor rotor parts. The paper describes the method to manufacture a new rotor based on a used spare rotor. Furthermore, the results of the numerical calculations – stress analysis, rotor dynamics and flow analysis – are discussed to show how the required performance is achieved and a safe operation is given.
In the first step, the geometry of the complete rotor is captured with a highly precise and portable 3D-Scan device. The scan was performed on the assembled rotor and for all single parts after disassembly of the rotor. Since the scan is performed on a used rotor, a numerical flow analysis and stress analysis are executed to ensure that deviations or washouts of the used geometry have no effects on the performance and the safe operation of the rotor. In addition to that, a rotor dynamic calculation is executed for the rotor with original material as well as for the rotor with the new material. The comparison between these two configurations provides an indication for a safe operation.
The stress analysis shows a high stress level at the fillet radius to the cover plate of the first impeller stages. To decrease the stress level in these areas, the geometry is adjusted. The numerical flow analysis evaluates the flow field in the complete compressor. It is therefore also required to capture the geometry of the diaphragms. The results show that the performance of the compressor is assured. The rotor dynamics of the rotor with the new material show only insignificant differences to the rotor with the original material. After the numerical analysis the manufacturing, assembly and balancing of the rotor will be shortly described in the current paper.
The successful reverse engineering – which was executed without manufacturing drawings and only based on an old/used sample – of a centrifugal compressor including the use of enhanced material by a mid-size Non-OEM company is of substantial benefit to the state of knowledge in the petroleum industry. Commonly practiced in the European market, especially for industrial steam turbines, reverse engineering of turbo machinery equipment – without compromising on quality or performance – is to be considered a major cost saving opportunity for the petroleum industry.