Study on the axial force characteristics of the connecting bolts of the shale oil fracturing pump

The sudden fracture failure of connecting bolts often occurs at the shale oil fracturing construction site, and the main cause is the insufficient axial force of the bolts. At present, the bolts at the construction site are mainly inspected by the scribing method and visual inspection, which has a high labor intensity and cannot achieve the quantitative characterization of the bolt axial force. In this study, a finite element model of the bolt pre-tightening process was established, and the distribution characteristics of the bolt axial force under different working conditions were studied. The study found that the stress at the middle section of the bolt is the greatest, and it gradually decreases towards the two ends along the bolt axis; compared with the 1-8UNC bolt, the axial forces of the M36 and M52 bolts decrease by 14.8% and 36.6% respectively under the same torque working condition; when the friction coefficient increases from 0.07 to 0.14, the bolt axial force decreases by 20.6%. The quantitative relationships between different types of bolts in the oil field, the friction coefficients of each contact surface and the axial force are clarified, providing technical support for bolt selection, lubrication and the development of axial force detection devices.