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Abstract

In this study, we investigated the causes for the failure of the propeller no.10 of the 4-th stage of the carbondioxide compressor belonging to the southern company for fertilizers, which had failures many times. A detailed study of the propeller was carried out which consisted of a series of investigations including mechanical and structural properties, as well as microscopic and scanning electron microscope tests. It was observed from this study failure symptoms due to fatigue besides the existence of old internal cracks in the metal of the propeller which originated from the manufacturing process that played a great rool in the metal's failure. An investigation of the holes region of the rivet, showed nodes which act as sources of stress concentration which then enhanced the failure process. Microhardness and impact tests showed a large scatter in the results, which was attributed to metal's nonuniformity. The characteristic curves indicated clearly that although the ordinary operating conditions of the propeller were outside the surge region but they were close enough to this region that a slight decrease in flow leaded to a close approach to the surge condition which resulted in accelerating the failure process.

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