Most failures in sucker rod strings in service are fatigue failures, the rods being subjected to maximum tensile stress on the upstroke and minimum tensile stress (sometimes compression) on downstroke. Since the fatigue limit of full size sucker rods is not known, the design of sucker rod string, at present day, is based on API Modified Goodman diagram, used to calculate the permissible variable stress.
An innovative technique for fatigue limit or endurance limit estimation is based on the measurement of the mean temperature variation of the sample, closely related to the plastic deformation and fatigue behavior during cyclic loading (thermoplastic effect).
This paper presents a method for sucker rod fatigue limit estimation using infrared thermography. The temperature evaluation of the sample during fatigue testing was performed by using high sensitive FLIR E50 thermographic infrared imaging system. The method has been validated by comparing the experimental data with the predicted fatigue limit, as presented within the final discussion of the results.