Analysis of the failure of an offshore compressor crankshaft

• Failure investigation of a failed compressor crankshaft.
• Large fracture surface with beach marks.
• Crankshaft probably failed by corrosion fatigue.

During the inspection of a North Sea oil and gas platform a crack was identified on the crankshaft of a compressor.Subsequently, the component was decommissioned and a failure examination undertaken to determine the mechanism of failure. The crankshaft was analysed using a range of inspection, measurement and fractographic techniques.Magnetic particle inspection (MPI) indicated that the crack extended for the majority of the shaft's length, rotating through approximately 225 degrees of the shaft's circumference. Laser scanning verified the dimensions and concentricity of the crankshaft were in accordance with the manufacturer's specifications. On sectioning the crack and forcing it open, complex fracture features were revealed. Optical and scanning electron microscopy were used to examine these features as well as the surface of the crankshaft.The investigation determined that the mechanism of failure of the crankshaft was probably corrosion fatigue, initiating from localised corrosive attack on the crankshaft's surface.