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| Life prediction of S135 drilling pipe due to fatigue crack initiation based on reliability theory |
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LI Fangpo, WANG Yong, WANG Jianjun, HAN Lihong1,2,3
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1. CNPC Tubular Goods Research Institute, Xi'an 710077, China;2. State Key Laboratory for Performance and Structure Safety of Petroleum Tubular Goods and Equipment Materials, Xi'an 710077, China;3. College of Electromechanical Engineering in China University of Petroleum, Qingdao 266580, China
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| Abstract: |
| The fatigue life of the S135 drilling pipe is studied systematically based on the reliability analysis, and the drilling pipe's fatigue life prediction equations whose reliability are 50%, 90%, 99% and 99.9% are solved. The calculation results show that the stress in the drill pipe body is significantly greater than that in the tool joints during the drilling process. The drilling pipe body's fatigue strength is about 500 MPa under the conditions that the stress ratio is -1. Under the condition that the confidence level is 95% and deviation is 5%, the data on the drilling pipe's logarithmic fatigue life satisfy the normal distribution while the stress amplitudes are 660、620、580 and 540 MPa, respectively. With the decrease of the stress amplitude, the peak of the logarithmic fatigue life' probability density distribution curve decreases gradually, and its dispersion gradually increases. |
| Key words: S135 drilling pipe fatigue life life due to fatigue crack initiation life prediction reliability |
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