Fracture Analysis of Compressor Impellers in Olefin Units: Numerical and Metallurgical Approach

Abstract

This paper presents a failure analysis conducted in 7175 aluminum alloy compressor impellers used in olefin units which operate at 34500 rpm to compress gas in the process. Some characterizations such as chemical composition, microstructure, and hardness tests were conducted to obtain a detailed evaluation of the base alloy. Furthermore, a finite element method and a 3D point cloud data technique have used to determine critical stress points on the surface of impellers. The finite element result showed the root of blades has significant stress concentration. Moreover, the formed cyclic tension has led to a fatigue phenomenon in the root of the blade, so near this location, the local strain accumulation was visible in 3D points cloud data. The fractography results showed that the mode of crack progression and the fractured surface would change by changing the stress mode. In addition, CFD modeling for investigating the effect of flow hydrodynamics on the HP and LP compressor blades is analyzed. The results revealed that the maximum pressure of gas stream for the rotor speed of 34500 had taken place in the area of a blade that already breakdown took place, and the changes of pressure, stress, and temperature gradients of flow in the HP compressor were significantly higher than the LP compressor.