The corrosion resistance of sucker rod materials can be a significant concern, especially in aggressive service environments with high acid gas concentrations. Corrosion-related failures have been associated with increased levels of produced hydrogen sulfide (H2S) and carbon dioxide (CO2). The presence of corrosion damage, which is characterized by local material dissolution and pitting formation under the influence of CO2 and/or H2S, provides the initiation sites in a fatigue cracking mechanism. The fatigue crack propagation in corrosion aggressive environments is associated with the following factors: (1) local tensile stress concentration at crack tip, and (2) local corrosion dissolution. Therefore, using a material that tends to re-passivate as it interacts with the environment would be the optimum solution in order to mitigate the likelihood of field failures and reduce overall operating costs. Regarding passive film disruption processes abrasion and high temperature influences were not considered at this stage of the present study and repassivation kinetics were not measured. Conventional sucker rod production processes include normalize and temper (N&T) or quench and temper (Q&T) heat treatments to meet desired strength levels of low alloy steels. In order to enhance the corrosion properties and provide a resistant sucker rod solution, 13Cr martensitic stainless steel may provide a viable alternative to low alloys steels. This paper focuses on the characterization of 13Cr sucker rod material by comparing the general corrosion and corrosion fatigue performance with low-alloy steels.
Sweet (CO2) and sour (H2S) corrosion have continuously been a challenge in oil and gas production and transportation. Yet, some key issues are still not well understood, especially at high temperature production conditions. A CO2/H2S ratio of 500, which has been used (often inaccurately) to determine which corrosion mechanism is dominant, is probably even less valid at high temperature. The nature of the corrosion products forming at high temperature in CO2/H2S environments and their effects on the corrosion rate are not known. Finally, the impact on pipeline integrity of environmental changes between sweet and sour production conditions (simulating reservoir souring) has not been well documented. CO2, H2S, and CO2/H2S corrosion experiments were conducted at 120oC to investigate corrosion mechanisms and corrosion product layer formation at high temperature. The results show that the corrosion products were still clearly dominated by H2S under the pCO2/pH2S ratio of 550. Formation of Fe3O4, FeCO3, and FeS corrosion product layers had a direct impact on the measured corrosion rates and was dependent on the gas composition and on the sequence of exposure (CO2 then H2S and vice versa). Compared with H2S corrosion alone, the presence of CO2 could retard Fe3O4 formation in CO2/H2S mixture environment. No obvious change in steady state corrosion rate was observed when the corrosion environment was switched from CO2 to H2S and vice versa.