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Strain-hardened austenitic stainless steels are commonly used as structural materials in drilling equipment because they meet the demanding requirements in terms of mechanical, magnetic, and chemical properties necessary for drilling technologies in subterranean energy resources exploration. Drilling operational conditions might become a challenge for the integrity of these materials due to the cyclic loading the drillstring is subjected to, in combination with the downhole temperature, and the corrosivity of the drilling fluid. In this research work, the relationship among the pitting corrosion resistance of one Mn-stabilized austenitic stainless steel and its corrosion fatigue behavior has been determined by means of electrochemical methods, advanced surface characterization, and corrosion fatigue testing in brines of near-neutral pH with different chloride contents at room temperature (RT) and 150°C. It has been determined that the corrosion fatigue behavior of the investigated CrMn stainless steel is strongly affected by its susceptibility to pitting corrosion. The synergistic effect between the corrosive environment and the mechanical load depends upon the applied stress amplitude and the pitting resistance of the material. The corrosion fatigue behavior of the austenitic stainless steel at RT was synergistically affected by the environmental and loading conditions at low stress amplitudes. In contrast, the large susceptibility to pitting of the material at 150°C has a significant detrimental effect on its corrosion fatigue behavior when subjected to high stress amplitudes. The observed damage mechanism at 150°C can be described as pitting-induced corrosion fatigue because pit propagation controlled the corrosion fatigue behavior of the CrMn stainless steel. The obtained experimental results have shown that the pitting resistance, assessed for instance by multiple electrochemical methods, could in cases where pitting susceptibility has a large influence on the environmentally sustained cracking mechanism, be used as an indicator of the expected corrosion fatigue behavior of the material. As demonstrated in this study, however, results from accelerated electrochemical testing solely might have a limited prediction capability of long-term corrosion behavior.

Nickel alloys are broadly used in upstream oil and gas applications as a result of an advantageous set of properties including high mechanical strength accompanied by good ductility and toughness, ...

There are a great variety of commercial nickel alloys mainly because nickel is able to dissolve a large amount of alloying elements while maintaining a single ductile austenitic phase. Nickel alloys are generally designed for and used in highly aggressive environments, for example, those where stainless steels may experience pitting corrosion or environmentally assisted cracking. While nickel alloys are generally resistant to pitting corrosion in chloride-containing environments, they may be prone to crevice corrosion attack. Addition of chromium, molybdenum and tungsten increases the localized corrosion resistance of nickel alloys. This review on the resistance to localized corrosion of nickel alloys includes specific environments such as those present in oil and gas upstream operations, in the chemical process industry and in seawater service Fil: Klapper, Helmuth S. Center For Materials Research, Baker Hughes; Alemania Fil: Zadorozne, Natalia Silvina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Materiales de Misiones. Universidad Nacional de Misiones. Facultad de Ciencias Exactas Químicas y Naturales. Instituto de Materiales de Misiones; Argentina Fil: Rebak, Raul Basilio. General Electric Global Research; Estados Unidos

As a result of their appropriate mechanical and non-magnetic properties, Alloy 718 (UNS N07718) has been used in directional drilling tools, particularly in applications where superior corrosion re...

Electrochemical noise measurements on anodically polarised type 304 stainless steel surfaces in contact with buffer solutions of neutral pH were performed to study the effect of chloride ions in the nucleation of pitting corrosion. Passive layer stability and susceptibility to pitting corrosion after pickling and passivation at different environmental conditions were also investigated by means of electrochemical current noise measurements under cathodic and anodic polarisation. According to the obtained experimental results pits nucleate independently on the presence of chloride ions. It has been also shown that protectiveness of stainless steel surfaces after pickling strongly depends on the relative humidity of the environment in which the surface is subsequently passivated.

The use of electrochemical noise (EN) measurements for the investigation and monitoring of corrosion has allowed many interesting advances in the corrosion science in recent years. A special advantage of EN measurements includes the possibility to detect and study the early stages of localized corrosion. Nevertheless, the understanding of the electrochemical information included in the EN signal is actually very limited. The role of the cathodic process on the EN signals remains uncertain and has not been sufficiently investigated to date. Thus, an accurate understanding of the influence of the cathodic process on the EN signal is still lacking. On the basis of different kinetics of the oxygen reduction it was established that the anodic amplitude of transients arising from pitting corrosion on stainless steel can be decreased by the corresponding electron consumption of the cathodic process. Therefore, the stronger the electron consumption, the weaker the anodic amplitude of the EN signal becomes. EN signals arising from pitting corrosion on stainless steel can be measured because the cathodic process is inhibited by the passive layer. This was confirmed by means of EN measurements under cathodic polarisation. Since the cathodic process plays a decisive role on the form of transients arising from pitting corrosion, its influence must be considered in the evaluation and interpretation of the EN signals.

Oxygen reduction occurring at the passive layer is probably the most important cathodic reaction involved in corrosion processes on stainless steel. Furthermore, the influence of the surface state on the oxygen reduction reaction is a key point for the understanding of the mechanism of localized corrosion on stainless steel. In this study, electrochemical noise measurements under cathodic polarization were carried out to obtain new information about this influence. It has been confirmed that the surface state of stainless steel plays a very important role in the kinetic of this cathodic reaction. Oxygen reduction kinetics was significantly reduced on passivated surfaces and improved on pre-reduced and ground surfaces. In addition, electrochemical current noise measurements allowed to differentiate between the electrochemical activity produced by the oxygen reduction reaction and that due to the reduction of the passive layer, in direct dependence on the characteristics of the different surface states investigated.

The influence of the flow velocity and the temperature on the corrosion of UNS G10200 in aerated brines had been evaluated by means of electrochemical techniques at the RCE. Increasing the flow velocity and the temperature enhances the corrosion kinetic of the system and changes the corrosion mechanism. This behaviour was adduced to the presence of a mixed control on the corrosion process related with the formation and stabilization of corrosion product layers on the electrode surface. The correlations of Wranglen and Silverman for the mass transfer and the wall shear stresses respectively were validated at the RCE for this system.

In order to provide basic information on corrosion resistance to the designers and users of geothermal plants different metallic materials including duplex and austenitic stainless steels as well as a nickel alloy have been evaluated in artificial geothermal fluids simulating the conditions in some locations with geothermal potential in Germany as well as two sites in Indonesia. By electrochemical and long-term exposure tests at 100 °C and 150 °C the suitability of low alloyed steel UNS G41300, stainless steels UNS S31603 UNS S31803, UNS S32760, super austenitic steel UNS N08031 and nickel based alloy UNS N06059 was investigated in these geothermal fluids, using critical potentials and corrosion rates. In high-saline environments the crevice corrosion turned out to be the determining mechanism. The nickel based alloy shows excellent corrosion resistance against pitting corrosion. Excluding its high cost, it is very good to be used in the construction of geothermal facilities having highly saline brines. Stainless and duplex steels exhibit a limited corrosion resistance concerning pitting and crevice corrosion. Therefore they are not suitable for highly saline brines. The super austenite UNS N08031 showed a temperature depending behavior. In non-saline environments the low-alloyed steel UNS G41300 (beside of the higher alloyed materials) could be employed as a constructional material for the geothermal power plant, as long as a sufficient wall thickness of the material is considered.

Precipitation hardenable (PH) nickel (Ni) alloys are often the most reliable engineering materials for demanding oilfield upstream and subsea applications especially in deep sour wells. Despite their superior corrosion resistance and mechanical properties over a broad range of temperatures, the applicability of PH Ni alloys has been questioned due to their susceptibility to hydrogen embrittlement (HE), as confirmed in documented failures of components in upstream applications. While extensive work has been done in recent years to develop testing methodologies for benchmarking PH Ni alloys in terms of their HE susceptibility, limited scientific research has been conducted to achieve improved foundational knowledge about the role of microstructural particularities in these alloys on their mechanical behaviour in environments promoting hydrogen uptake. Precipitates such as theγ′,γ′′ and δ-phase are well known for defining the mechanical and chemical properties of these alloys. To elucidate the effect of precipitates in the microstructure of the oil-patch PH Ni alloy 718 on its HE susceptibility, slow strain rate tests under continuous hydrogen charging were conducted on material after several different age-hardening treatments. By correlating the obtained results with those from the microstructural and fractographic characterization, it was concluded that HE susceptibility of oil-patch alloy 718 is strongly influenced by the amount and size of precipitates such as theγ′ andγ′′ as well as the δ-phase rather than by the strength level only. In addition, several HE mechanisms including hydrogen-enhanced decohesion and hydrogen-enhanced local plasticity were observed taking place on oil-patch alloy 718, depending upon the characteristics of these phases when present in the microstructure.This article is part of the themed issue ‘The challenges of hydrogen and metals’.