Recently, there have been several cracking failures of type HL carbon steel sucker rods with evidence of fatigue striation. In order to find out the reason for the fracture failure, the fracture morphology, material properties, loading and corrosion product of the failed type HL 35CrMoA sucker rod were analyzed, combined with the corrosion environment. The results show that the material properties of the failed 35CrMoA sucker rod meet the GB/T 26075-2010 standard requirements. Also the result of loading analysis shows that the loading is far from the fatigue limit stress. The type HL sucker rod’s yield strength is almost 1049 MPa and hardness is 35.2 HRC. In addition, the low in-situ pH and high H2S-CO2 partial pressure places the sucker rods in the Region 3 of sulfide stress corrosion cracking, which means the quenched and tempered sucker rod’s yield strength should not exceed 863 MPa and hardness should not exceed 30 HRC, according to the ISO 15156-2:2015 standard. It is concluded that the high hardness level of the type HL sucker rod led to sulfide stress corrosion cracking in the high H2S-CO2 partial pressure and low in-situ pH condition.
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.