Paper: Modulus of Elasticity and Fatigue Life Considerations in the Design and use of Fiberglass Sucker Rods

Fiberglass sucker rods have proven to be an economical solution to many sucker rod beam pumping problems. Two important parameters that contribute to the effectiveness of FRP sucker rods are effective modulus of elasticity and fatigue life. Using established computer predictive techniques, it has been shown that FRP sucker rod installations can benefit from using rod designs with a lower modulus of elasticity. Fatigue life of sucker rods is an important consideration for any sucker rod pumped oil well, for both steel and fiberglass rods. Fatigue life predicitons for steel sucker rods can be routinely determined from API publications and recommendations. Fiberglass sucker rod fatigue life predictions are determined from guidelines supplied by FRP sucker rod manufacturers. The fatigue life of fiberglass sucker rods cannot be reliably predicted using methods developed for predicting steel sucker rod fatigue life due to the difference in fatigue behavior of the two materials. Therefore, test programs have been developed to generate reliable fatigue life guidelines for field applications.