This paper aims to discuss the behavior of different sucker rods steels in corrosive environments, the influence of manufacturing techniques and the development of a new Steel for Sucker Rod with enhanced properties for Corrosion-Fatigue.
Corrosion-fatigue is a major cause of premature failures in O&G industry and it is hard to predict its behavior. Besides the level of stresses, Corrosion Fatigue depends on many others factors, among which the most relevant are pressure, temperature, H2S and CO2 concentration, water, PH, chlorines and flow conditions.
Under harsh environment, steel performance is not only related to its mechanical properties. Parameters like alloying and residual elements, steel cleanliness, microstructure, toughness, among others play an important role.
Increased volumes of injection water/gas for mature fields, EOR and shale operations increase the risk of failures related to corrosion-fatigue mechanisms.
The performance of a steel material under the combined action of cycling loads and corrosive environments, depends on many factors, including the environment characteristics, the material properties, and the applied stresses. In corrosive environments, the fatigue life, both in terms of failure stresses or failure times, can be drastically reduced compared to the cycling stress in a non-corrosive environment.
A deep understanding of the behavior of standard steels and they failure mechanisms, allowed the development of a steel able to withstand harsh environments. Results of this research led to the development of new steel composition and processing routes, both for sucker rods and couplings, that notably increase the performance under corrosive environments.
Steel chemistry and manufacturing process were specially design to obtain a fine grain and ultraclean steel with increased hardenability and tempering resistance, and improved toughness. This features provides to the final product an outstanding Fatigue resistance in corrosive environment such us H2S and CO2.