Influence of Shear Stress on the Pitting Corrosion Susceptibility of an Austenitic Stainless Steel in Brine Evaluated in the Rotating Cylinder Electrode

摘要

During drilling operations the drillstring might be subjected to downhole conditions leading to pitting corrosion. State-of-the-art directional drilling technologies are very demanding in terms of material requirements including corrosion resistance. Manganese-stabilized fully austenitic stainless steels in strain-hardened condition own a beneficial combination of high strength, high ductility and high toughness, by keeping their own non-magnetic character and . Therefore, CrMn-stainless steels have been extensively used in drilling equipment. Once in contact with high chloride bearing drilling fluids at elevated temperatures, however, their passivity is compromised leading to pit nucleation and propagation. In consequence, the pitting corrosion resistance of these materials becomes a significant limiting factor for their selection as well as for assessing the service life of drillstring components. To date the majority of the research work has been conducted to characterize the pitting susceptibility of CrMn-stainless steels under static conditions. Little attention, however, has been paid to the effect of shear stresses introduced by the flow of the drilling fluid on the pitting resistance and damage morphology produced on these materials when exposed to brines at elevated temperatures. To address this, electrochemical examinations were conducted using the rotating cylinder electrode. The present paper discusses the results from potentiodynamic polarization tests and their relation to the hydrodynamic conditions produced in the RCE at different temperatures.