ETCE 2002/OT-29152 ENHANCEMENT OF COMPOSITE SUCKER RODS FOR USE IN THE OIL INDUSTRY

ABSTRACT Analysis of polymer-matrix composite sucker rod systems using finite element methods is performed. Composite sucker rods fail mainly due to fatigue loading. In majority of cases, the failure is in the region of the joint where the composite rod and the steel endfitting meet. 2D and 3D Finite Element Analysis and experimental tests are carried out in order to observe the stress distribution and to find the regions of stress concentrations inside the endfitting. The causes of fatigue failure of the composite sucker rods are identified. These are overloading of the rod causing high transverse compressive stress that results crushing of the rod, and high stress concentrations present at the grooves of the endfitting that initiate premature fatigue cracks. Based on the result of this study, enhanced design of the composite sucker rod system can be accomplished. INTRODUCTION Composite sucker rods are usually made of polymer matrix composite manufactured by pultrusion process. Polymer matrix composites offer excellent mechanical properties over other types of composites and are finding many applications in marine and oil industries. Inherent advantages of polymer matrix composite include lightweight and low cost. The main advantage of using composite sucker rods over steel rods is less weight, and thus eliminating the purchasing of large expensive pumping units. In addition, corrosion resistance is considered an important advantage. Composite sucker rod systems have steel rods at the lower portion of the rod strings to act as weighing mechanism for the whole system. Corrosion fatigue is of less concern in steel portion of the fiberglass sucker rod strings because the most highly stressed rods (in the upper portion of the rod strings) are nonmetallic. Concerning corrosion of the steel endfittings, the cross section of steel endfittings is larger than the rod bodies, so minor pitting on the endfittings or couplings does not lead to fatigue failure rapidl