Fatigue Fracture of a Cast Inconel 718 by Compression Loading and Its Verification by Finite Element Analysis (FEA)
Two out of three struts of a drilling tool’s 6.75″ Flow Diverter failed during operation. This failure resulted in invasion of mud into the electronic module of the tool. During drilling, high stick slip was observed. Measurement While Drilling (MWD) signal was good and Logging While Drilling (LWD) data was used to pick the oil/water contact point. At the end of the run, cracks were observed on the radii of the struts. Failure investigations were performed to identify the cause of the cracks. Material characterization, microstructural examinations, and fractography by SEM technique revealed that fatigue under compression forces was the cause of the cracking of the struts. Finite elemental analysis (FEA) was also used to determine the magnitude and the area of stress concentration. Failure mechanism has been explained. A few issues related to integrity of the material have also been raised.