Screw compressors used to produce compressed air in refineries have two rotors. One of the main causes of failure of these compressors is rotor fracture. In this research, the fracture causes of the female rotor of a screw compressor after only 603 working hours was studied. Experiments showed that the main cause of the failure was fatigue due to a defect in the cooling system of the compressor that caused thermal expansion, touching of rotors and finally fracture after only 25-43 min. (c) 2005 Elsevier Ltd. All rights reserved.