Research On Evaluation Criteria Of Drill Thread Damage State Based On Magnetic Memory Testing

Failure drilling tool thread accidents caused by stress concentration happened occasionally in Tarim oilfield.Experimental results showed that magnetic memory signal could well reflect stress concentration situation of drilling tool thread.Formulating corresponding evaluation standard and managing drill in a better way have an important practice significance in oil production.The thesis carries out the serving drill,mainly analyzed the following aspects:(1)The mechanics condition of drilling screw engagement portion was simulated by finite element method.The distribution of stress in thread root portion under the defective state were obtained.The stress concentration factor of thread engagement portion was calculated and the distribution of the partial maximum stress in thread parts was presented by simplifying the tool joint model.(2)The magnetic memory test of different types and levels drilling thread was carried out in Tarim oilfield.Magnetic memory characteristic parameters of drilling thread which has the same type with different levels were analyzed and compared.Whether the existing evaluation standard of Tarim oilfield could be suitable to the result of magnetic memory test was discussed.(3)The critical feature values of crack initiation was counted based on the existing data of magnetic memory fatigue tests under the complex dynamic loading.The relationship between magnetic memory signal characteristic value and sample life under the complex dynamic loading was investigated.The different stages of the relationship curve which reflect the sample states were analyzed and the fatigue damage model was established.(4)Evaluation standards were established based on mathematical statistics method and fatigue test respectively.The more fit the actual method,mathematical statistics method,was selected by comparison.