Cause of leading to polish rod fracturing on screw pump wells and prevention measures

According to the analyses of the fracturing position of broken polish rod and the shape of fracturing surface, it is held that why the probability of polish rod fracture is greater than that of the upper part fracturing of pumping rod is that the polish rod above packing set is not coaxial to the polish rod below packing set. Because of the constraint of packing set to polish rod, bending moment is produced on the polish rod below packing set, and the polish rod produces fatigue failure under the effect of alternate stress in rotating process. The reason is also proven by the calculated result of stress. The authors hold that ensuring the incline of polish rod less than 0.5°is the effective measures for avoiding the fatigue failure of polish rod.