FAILURE ANALYSIS IN HEAVY-WEIGHT DRILLPIPES DURINGDRILLING OPERATION OF OFF-SHORE OIL WELL

摘要

The main purpose of this study was the failure analysis of a Heavy-Weight Drill Pipe 5"rn(HWDP5) that showed radial cracks in the threaded connection sections. Metallographic resultsrnwere obtained using stereoscopic microscopy, image analysis and scanning electronrnmicrocopy (SEM), with Energy Dispersive Spectroscopy (EDS). Hardness tests and chemicalrnanalysis of the HWDP5 sample and semi-micro inorganic qualitative analysis of the mud werernalso carried out. It could be seen by visual inspection that the male member of the threadedrnconnection (pin member) was not able to reach the last two threads of the female screw (boxrnmember), promoting in this area a high stress concentration. It was also observed that cracksrnwere formed from corrosion pitting at the screw base. The chemical analysis gave a positivernresult confirming the presence of H2 S in the mud. Sulfide stress cracking (SSC) could bernobserved due to three main factors: 1. Changing in the manganese sulfides size, 2. Highrnvalues of hardness and 3. Existence of HzS showed by the EDS spectra of the samples andrnchemical analysis of the drilling mud. It could be concluded that sulfide stress crackingrnresulting from the presence of the HzS in the mud in addition to the existence of high stressedrnareas were responsible for the premature failure of the HWDP5 device.