基于可靠性的S135钻杆疲劳裂纹萌生寿命预测

Life prediction of S135 drilling pipe due to fatigue crack initiation based on reliability theory

基于可靠性理论对S135钻杆疲劳裂纹萌生寿命预测进行系统研究,计算得到50%、90%、99%和99.9%可靠度条件下S135钻杆的疲劳裂纹萌生寿命预测方程。结果表明,服役过程中S135钻杆管体部位承受的附加应力载荷明显大于接头螺纹连接部位。在应力比为-1条件下,S135钻杆的疲劳强度约为500 MPa;在置信度为95%,误差为5%条件下,应力水平分别为660、620、580和540 MPa时的疲劳裂纹萌生寿命对数值分布符合正态分布规律,随着应力水平下降,疲劳裂纹萌生寿命对数值分布概率密度函数峰值逐渐降低,离散性逐渐增强。

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.