Investigation on the failure of air compressor S. Sivaprasad a , N. Narasaiah a, * , S.K. Das a , G. Das a , S. Tarafder a , K.K. Gupta b , R.N. Ghosh a a Materials Science and Technology Division, National Metallurgical Laboratory (Council of Scientific and Industrial Research), Jamshedpur 831 007, India b Analytical Chemistry Centre, Jamshedpur 831 007, India article info Article history: Received 25 April 2009 Accepted 27 April 2009 Available online 5 May 2009 Keywords: Air compressor Impeller Fatigue abstract The cause for the failure of an air compressor has been investigated. It was found that a pre-existing fatigue crack was present at the root of the impeller blade. Transients and unsteady operation of the equipment prior to the accident are thought to have grown the fatigue crack to its critical size, thereby causing an imbalance in the impeller rotation and leading to failure. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Air compressor is one of the vital equipments in a plant that is used for the production of liquid air and other liquid gases. The first step in liquefying the air in a liquid gas plant is compression of air by the multistage highly efficient air compressor. Any failure in the compressor seriously jeopardises operation of the plant. One such air compressor catastrophically failed in a liquid gas producing plant and the industry wanted to know the reasons for the failure. The failed air compressor had a total of six compressor stages mounted on three shafts being driven by a bull gear and the major damage was restricted to stage 1 and stage 2 compressors. On discussion at site, it was noted that prior to the failure, the upstream turbine fed by the compressor tripped. On check- ing for obvious malfunctions, the turbine was re-loaded. The turbine tripped again twice in quick succession after about 2.5 h of operation. It was decided then to wait for a thorough instrumentation check on the turbine prior to commencement of operations. The compressor was therefore being idled under no-load, awaiting clearance from the turbine side. While the compressor was idling, it suddenly failed without any prior detectable signatures. At the time of failure, minor fires had engulfed the bearing areas because of oil leakage. 2. Visual inspection The extent of damage could be determined only after opening the casings. Visual inspection of the damaged components of the compressor parts was made and the following observations were noted:  the inlet contour vanes of the stage 1 were dented;  impellers of stages 1 and 2 had been sheared off their shaft and abraded along their periphery;  tie rods of both stage 1 and stage 2 were broken;  the nose cone of both stages 1 and 2 were dented, as would happen if they are displaced while in service, with their fastening bolts broken; 1350-6307/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.engfailanal.2009.04.016 * Corresponding author. Tel.: +91 657 2345187; fax: +91 657 2345213. E-mail address: narasaiahn@yahoo.co.in (N. Narasaiah). Engineering Failure Analysis 17 (2010) 150–157 Contents lists available at ScienceDirect Engineering Failure Analysis journal homepage: www.elsevier.com/locate/engfailanal