Abstract
Fatigue and corrosion fatigue (CF) tests were carried out to investigate the behaviors of G105 and S135 low carbon high−strength drill pipe steels under different stress amplitudes in air as well as simulated H2S contained drilling environment. The regression analysis method was applied to obtain empirical equations governing the fatigue and CF lives of drill pipe steels in different environmental conditions. Results revealed that there exist fatigue limits for G105 and S135 drill pipe steels in air, and the fatigue life equations for G105 and S135 are Nf=3.28×108(Seqv−406.1)−2 and Nf=3.81×108(Seqv−472.5)−2 respectively. For both types of pipe steels, quasi−cleavage and cleavage fracture was identified as the main feature in the fatigue source zone of the two steels, while fatigue striations were the main feature in the stable crack growth zone. However, in H2S solution, no obvious fatigue limits were found for G105 and S135, and the corresponding CF life equations are Nf=3.58×108(Seqv−143.7)−2 and Nf=2.91×108(Seqv−119.6)−2. The CF sensitivity levels of G105 and S135 in H2S solution are high (64.6% and 74.7%, respectively), but S135 displays a higher sensitivity (74.7%) than G105 (64.6%). Further, no apparent plastic deformation appeared on the fracture surface in H2S solution, and the fatigue cracks sprout from the surface and expand into the specimen with radiation pattern.
Published Version
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