Research of carbon fiber plastic rod connections with steel heads at the action of bending loads

Abstract

To increase the efficiency of the use of a sucker rod pumping unit (SRPU) today the columns of sucker rods of fiberglass and carbon fiber are used. Such polymer composites have a number of advantages over steel, but they have a significant drawback in the design of a sucker rod - a high concentration of stresses at the point where theyare connected to a steel head containing a thread. Many constructive solutions to this problem have been developed, but maintaining the connection of a fiberglass or carbon-plastic barrel with a metal head remains quite a challenge. As practice shows, the bending of the pump rods in the well are also subjected to bending loads, torque, friction to the column of tubing (tubing) and the like. Therefore, a comparative analysis of the parts of the pump rod structures: traditional steel and combined (metal tip with composite rod) should be carried out. In this work, such joints were subjected only to bending loads, which are particularly dangerous when passing through a rod of bent sections of a well and when running down the bar. It is established that at the time of bending the maximum normal stresses are distributed along the length of the pump rod unevenly and are concentrated in the transition between the head and the rod. The maximum normal stresses occurring in the transition between the steel tip and the carbon-plastic core, which are jointed without structural features (galtels, different transitions, etc.), have been determined to be greater than 1600 MPa. Such value of stress is undesirable when cycling the connection in well. For example, the design of a metal head was proposed, which allows reducing the stresses arising from bending and distribute them on the connection more evenly, compared to the traditional sucker rod.