Magnetic memory detection of oil casing threaded joints

In the process of oil and gas extraction, the failure of the casing connection could easily lead to accidents. Based on this, this article proposed a magnetic signal evaluation method for the integrity of casing joints. Due to the fact that the contact stress between the threads of the casing joint could be used as an important indicator to evaluate the sealing integrity quality of the casing joint, the author used magnetic memory detection method to test N80 short joint samples commonly used in casing under different makeup torques on a wellhead lifting testing machine. The detection signal, after filtering and gradient transformation, could visually display the stress concentration characteristics. By using the gradient peak value and gradient peak area of magnetic signals as parameters to evaluate the stress concentration of the casing thread section, it was possible to evaluate the quality of the casing thread connection. The experimental results showed that there was a positive linear correlation between the makeup torque value and the gradient peak value. After fitting the gradient peak area value and makeup torque using the Gauss function, there was a good fit, which provided a theoretical basis for evaluating the quality of casing thread connection.