Investigation of the Corrosion Performance of Stainless Steel and Low Alloy Steel Sucker Rod Materials in Aggressive Environments


Authors

Aleksey Shakhmatov (Weatherford) | Robert Badrak (Weatherford) | Rodrigo Barreto (Weatherford) | Oscar Martinez (Weatherford) | Sergey Kolesov (Weatherford) | William Howie (Weatherford)

Publisher

NACE - NACE International

Publication Date

June 14, 2020

Source

CORROSION 2020, 14-18 June

Paper ID

NACE-2020-14321


Abstract

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.

INTRODUCTION

Corrosion and fatigue are the most common sucker rod failure modes. There are no true fatigue endurance limits for low-alloy steels in corrosive environments due to the samples cross-section reduction by general corrosion or local corrosion damage and even at some point, cyclic stresses will ultimately result in fatigue damage by increasing the bulk/local tensile stress condition or building the crack initiation site.

Corrosion fatigue is usually the root cause of most sucker rods failures. Fatigue crack initiation begins at a corrosion pit, acting as a stress concentrator site. Crack initiation mechanisms including pitting corrosion, metal dissolution due to passive film disruption or active corrosion sites in persisted slip bands are presented and discussed in the paper in reference. It should be mentioned that the cycling operation nature and relative rods string movement usually increase the corrosion rate especially of low-alloy steels due to flow effect on corrosion.