Fatigue breakdowns of drill stems
UDC: 620.16
DOI: -
Authors:
ELAGINA O.YU.
1,
BURYAKIN A.V.1,
POCHES N.S.1
1 National University of Oil and Gas "Gubkin University", Moscow, Russia
Keywords: drill stem, drill pipe, fatigue failures, cyclic load, fatigue crack, washout of a pipe string, heavy-weight drill pipe (HWDP), stress state
Annotation:
Washouts of a drill pipe body are one of the most frequent causes of drill stems failures. The authors of the article consider the mechanism of fatigue cracks initiation and development. The results of studying the stress state effect on the reduction of drill pipes fatigue strength are presented using the example of pipes of S-135 strength group. It is shown that when alternating cyclic loads are applied to the wall of drill pipes of S-135 strength group, reduction of their mechanical properties is observed, while the yield strength shows greater sensitivity to the accumulation of fatigue damage than the temporary resistance to destruction. Operation of drill pipes of S-135 strength group under cyclic loading with an equivalent maximum stress of no more than 276 MPa ensures the absence of initiation of fatigue cracks on the basis of at least 1,0 million cycles. The obtained results can be used to assess the durability of the material when stress values exceed the standard ones during drilling.
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