As gas pipeline and industrial compressors become more powerful and more complex, it has become beneficial to conduct technical audits of these machines in the design stage. Detailed analysis of critical or advanced compressors by independent evaluators have identified operating limitations, resonant responses, potential vibrations, weak components, the onset of stall, and other instabilities, and have recommended ways to eliminate a variety of potential problems before the compressor is placed in operation. The suitability of a compressor and its driver for the planned service should be thoroughly evaluated, so that each component and the system not only satisfy the design conditions, but also extreme operating conditions. This paper presents a description of the tools available for design audits and gives examples of benefits that have resulted from recent audits. The rotordynamics of any large high-speed compressor should be carefully evaluated to identify potential instabilities, high vibration levels, and even destructive responses of the machine. Powerful rotordynamic analysis tools and specific knowledge exists to accurately predict bearing and seal stiffness and damping, lateral critical speeds, and damped forced responses. Some examples of significant results obtained from rotordynamic evaluations are presented, and typical problems that have been identified and eliminated are highlighted. Torsional vibration analyses for compressor trains are an essential aspect of a design audit that have identified vibration problems and weak components. Examples of torsional vibration responses and problems that can be identified and corrected are included in this paper. The aerodynamics of a compressor is a design audit topic to which attention should be paid. Thermophysical properties of the process gas, as it is compressed, are important quantities which can be accurately determined by modern equations of state. The internal velocity distribution and pressure rise per impeller and diffuser can be evaluated to identify areas of excess loss, poor work transfer, or restrictions within a compressor. Flow angles such as at the impeller and diffuser entrances can be predicted and evaluated. The diffuser inlet flow angle is a critical indicator of the onset of rotating stall. This type of aerodynamic analysis also provides important input for performance test planning and evaluation. This paper concludes with a summary of benefits of design audits for pipeline and industrial compressors.
An Investigation of Post Stall Transients and Recoverability of Axial Compression Systems: Part I — A Simplified Method