Evaluation of the “nickel effect” in sulfide stress cracking of low alloy steels using thiosulfate as an alternative to H2S-containing environments

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Effect of nickel in solid solution on hydrogen transport kinetics in low alloy steels

The use of low alloy steels (LAS) in H2S-containing environments in the oil and gas industry is governed by the ISO standard 15156-2 (NACE MR0175-2). One requirement, which has been disputed over the years, is that the nickel (Ni) content shall not exceed 1 wt%. This work investigated the effect of Ni in solid solution on hydrogen diffusion, solubility, and trapping in ferritic/pearlitic research-grade LAS with nominal Ni contents from 0 to 3 wt%. Hydrogen permeability experiments were carried out in a Devanathan-Stachurski setup at 15, 45 and 70 °C. The effective diffusion coefficients, calculated by the tlag method, decreased with increasing Ni content. The sub-surface hydrogen concentration in lattice and trap sites increased with increasing Ni content. There was no difference between the first and subsequent hydrogen permeation transients, suggesting that Ni in solid solution forms reversible traps. The effect of Ni in refining the microstructure may be superimposed on the effect of Ni in solid solution, and should be investigated in future work

The Role of Nickel in Low Alloy Steels exposed to H2S-containing environments. Part I: Trench Formation at the Open Circuit Potential

The nickel content in low alloy steels (LAS) for oil and gas exploration and production is limited to a maximum of 1 wt.% according to ANSI/NACE MR 0175/ISO 15156. This restriction is imposed to avoid sulfide stress cracking (SSC) in sour (H2S-containing) environments. In this work, the effect of Ni on SSC of LAS was studied independently of other alloying elements. For this purpose, quenched and tempered steels heat treated to a yield strength of 610 MPa with a Ni content below and above the 1 wt.% threshold were evaluated at the open circuit potential (OCP) in unstressed specimens, and in slow strain rate tests (SSRT) at room temperature. Thiosulfate was used as a surrogate of H2S, according to the Tsujikawa method. It is concluded that Ni contributes to the stabilization of the sulfide films that form on the steel´s surface at OCP. The rupture of this film due to tensile stress promotes the nucleation of elongated deep pits, referred to as trenches, which can act as sulfide stress crack initiators. Trenches were observed exclusively in stressed, Ni-containing specimens. Moreover, trenches´ morphology, dimensions, and distribution varied with the Ni content in the steels. For the steels studied in this work, the Ni effect on trenching persisted below the 1 wt.% threshold.Fil: Chalfoun, Dannisa Romina. Universidad Nacional de San Martín. Instituto Sabato; Argentina. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Kappes, Mariano Alberto. Universidad Nacional de San Martín. Instituto Sabato; Argentina. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Perez, Teresa E.. Universidad Nacional de San Martín. Instituto Sabato; ArgentinaFil: Otegui, José L.. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Iannuzzi, Mariano. Curtin University; Australi

Use of an Electrochemical Split Cell Technique to Evaluate the Influence of Shewanella oneidensis Activities on Corrosion of Carbon Steel

Microbially induced corrosion (MIC) is a complex problem that affects various industries. Several techniques have been developed to monitor corrosion and elucidate corrosion mechanisms, including microbiological processes that induce metal deterioration. We used zero resistance ammetry (ZRA) in a split chamber configuration to evaluate the effects of the facultatively anaerobic Fe(III) reducing bacterium Shewanella oneidensis MR-1 on the corrosion of UNS G10180 carbon steel. We show that activities of S. oneidensis inhibit corrosion of steel with which that organism has direct contact. However, when a carbon steel coupon in contact with S. oneidensis was electrically connected to a second coupon that was free of biofilm (in separate chambers of the split chamber assembly), ZRA-based measurements indicated that current moved from the S. oneidensis-containing chamber to the cell-free chamber. This electron transfer enhanced the O2 reduction reaction on the coupon deployed in the cell free chamber, and consequently, enhanced oxidation and corrosion of that electrode. Our results illustrate a novel mechanism for MIC in cases where metal surfaces are heterogeneously covered by biofilms

Unusual Correlation between SKPFM and Corrosion of Nickel Aluminum Bronzes

Scanning Kelvin probe force microscopy was used to investigate the influence of microstructure on the corrosion behavior of nickel aluminum bronzes in ammoniacal and NaCl solutions as well as under potential control in Na2SO4. The results showed an inverse correlation between the measured Volta potential difference and the observed corrosion behavior. In other words, the phase with initially higher Volta potential was preferentially attacked whereas those with the lowest Volta potential difference values remained intact. This behavior suggests that Volta potential difference maps in air cannot be universally correlated with practical nobility or reactivity in solution, as proposed by other investigators. The implications of these findings are discussed

Aluminium AA2024 T351 aeronautical alloy: Part 1. Microbial influenced corrosion analysis

The aim of this paper was to correlate the elemental distribution of alloying elements with the MIC attack morphology of the AA2024 T351 alloy by the fungus Hormoconis resinae. Anodic polarisation was applied up to the Ep of the AA22024 alloy after different thermal treatments, especially T351, and to Al 99.999% as reference. The aqueous solutions were sterile Bushnell–Haas culture medium employed both as mineral nutrient for fungal growth and as support electrolyte. The variation in aggressiveness of cultures with time was also electrochemically analysed. The attack after different tests was evaluated using ESEM, SEM, EDX and optical microscopy. It was demonstrated the MIC susceptibility of the AA2024 T351 alloy to fungal cultures and the dangerous tunnelling morphology of the respective attack through grain boundaries.Fil: Rosales, Blanca Margarita. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones en Tecnología de Pinturas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones en Tecnología de Pinturas; ArgentinaFil: Iannuzzi, Mariano. Ohio State University; Estados Unido

Hydrogen Embrittlement of Magnesium and Magnesium Alloys: A Review

Magnesium and magnesium alloys are susceptible to stress corrosion cracking in various environments, including distilled water. There is compelling evidence to conclude that SCC is assisted, at least in part, by hydrogen embrittlement. This paper reviews the thermodynamics of the Mg-H system and the kinetics of hydrogen transport. Aspects of magnesium corrosion relevant to hydrogen absorption are also discussed. Crack growth mechanisms based on delayed hydride cracking, hydrogen adsorption dislocation emission, hydrogen enhanced decohesion, and hydrogen enhanced localized plasticity have been proposed and evidence for each of them is reviewed herein

Use of electrochemical techniques to determine the effect of Sigma (σ)-phase precipitation on a 25 wt% Cr Super Duplex Stainless Steel.

Corrosion resistant alloys (CRA) for subsea pressure-retaining components must be compatible with production fluids and resistant to pitting and crevice corrosion in seawater. Whereas materials selection for production environments is governed by well-established standards such as ISO1 15156, debate still exists as of how to determine the seawater corrosion resistance of CRA. While most industry specifications rely on the ASTM2 G48 standard to determine localized corrosion resistance, for duplex and super duplex stainless steels there is no consensus on surface finish prior to testing and test temperature. Moreover, it is unclear whether existing procedures are sensitive enough to determine the onset of deleterious phases such as σ-phase and chromium nitrides. The objective of this investigation was to quantify the seawater pitting corrosion resistance of a 25 wt% Cr super duplex stainless steel and its correlation with: i) alloy’s microstructure and ii) surface finish before testing. Cyclic potentiodynamic polarization (CPP) testing was used to determine the effect of different σ-phase volume fractions on corrosion response. CPP tests were conducted at various temperatures, ranging from 20 to 900C, to determine the effect of deleterious phases on critical pitting and crevice temperatures (CPT and CCT, respectively). CPP results were compared with reported values based on ASTM G48 method D, ASTM G150, and zero resistance amperometr

Hydrogen uptake and diffusivity in steel armor wires with different chemical composition, carbide distribution, grain size, and degree of deformation

In this study, six flexible pipe steel armor wires used in oil and gas transportation are characterized, and their hydrogen diffusion coefficients and hydrogen uptakes are measured using an electrochemical hydrogen permeation technique. The wires have ferritic–pearlitic microstructures with round, lamellar, or partially lamellar carbides and the shape and orientation of the grains indicate that the microstructures were plastically deformed to different degrees. It was assumed that hydrogen was transported through the ferrite, so the presence of cementite in the steel armor wires leads to longer hydrogen diffusion paths through the ferrite, which was quantified with a tortuosity factor. After compensating for tortuosity, the normalized steady-state flux shows a tendency to increase as the grain size decreases. The effective diffusion coefficients increase with a decrease of the ferrite–cementite interface area, suggesting trapping on the ferrite–cementite interfaces. The uptake of diffusible hydrogen was lowest for the least plastically deformed materials and about twice as high for the more plastically deformed materials